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Switchgrass (SG) is considered a model bioenergy crop and a warm‐season perennial grass (WSPG) that traditionally served as forage feedstock in the United States. To avoid the sole dependence on SG for bioenergy production, evaluation of other crops to diversify the pool of feedstock is needed. We conducted a 3‐year field experiment evaluating eastern gamagrass (GG), another WSPG, as complementary feedstock to SG in one‐ and two‐cut systems, with or without intercropping with crimson clover or hairy vetch, and under different nitrogen (N) application rates. Our results showed that GG generally produced lower biomass (by 29.5%), theoretical ethanol potential (TEP, by 2.8%), and theoretical ethanol yield (TEY, by 32.9%) than corresponding SG under the same conditions. However, forage quality measures, namely acid detergent fiber (ADF), crude protein (CP), and elements P, K, Ca, and Mg were significantly higher in GG than those in SG. Nitrogen fertilizer significantly enhanced biomass (by 1.54 Mg ha−1), lignin content (by 2.10 g kg−1), and TEY (787.12 L ha−1) in the WSPGs compared to unfertilized treatments. Intercropping with crimson clover or hairy vetch did not significantly increase biomass of the WSPGs, or TEP and TEY in unfertilized plots. This study demonstrated that GG can serve as a complementary crop to SG and could be used as a dual‐purpose crop for bioenergy and forage feedstock in farmers' rotations. [ABSTRACT FROM AUTHOR]

Summary: Introducing N2‐fixing tree species into Eucalyptus plantations could replace nitrogen (N) fertilization to maintain high levels of N consumption and productivity. However, N enrichment may exacerbate phosphorus (P) limitation as Eucalyptus robusta Smith is extensively planted in P‐poor tropical and subtropical soils.We conducted a field experiment in a pure plantation of Eucalyptus urophylla × grandis to investigate the impacts of N fertilization and introduced an N2‐fixing tree of Dalbergia odorifera T. Chen on soil P transformation.Nitrogen fertilization significantly enhanced soil occluded P pool and reduced the other P pools due to acidification‐induced pH‐sensitive geochemical processes, lowering Eucalyptus leaf P concentration with higher N : P ratio. By contrast, introduced N2‐fixing tree species did not change soil pH, labile inorganic P pool, and Eucalyptus leaf N : P ratio, even enhanced organic P pools and reduced occluded P pool probably due to altering microbial community composition particularly stimulating arbuscular mycorrhiza fungal abundance.Our results revealed differential responses and mechanistic controls of soil P transformation in Eucalyptus plantations with N fertilization and introduced N2‐fixing tree species. The dissolution of occluded P pool along with organic P accumulation observed in the mixed plantations may represent a promising future to better manage soil P availability. [ABSTRACT FROM AUTHOR]

Background and aims: Understanding how altered precipitation patterns affect the dynamics of phosphorus (P) fractions in both soil and foliage is crucial for predicting climate-induced changes in plant growth and community structure, especially within tropical forests with P-impoverished soils.We conducted a nine-year precipitation experiment in a secondary tropical forest, simulating delayed (DW) and wetter wet season (WW) to reflect potential precipitation changes. We analyzed P fractions in soil (0–10 cm and 10–20 cm) and foliage of four dominant trees, and investigated the correlations among these P fractions and photosynthesis.DW treatment reduced soil P bioavailability and induced foliar P redistribution, while WW treatment increased soil pH and NH4+-N content but had little influence on soil P form. DW treatment generally reduced foliar total P levels and diminished various P fractions with notable species-specific disparities. Moreover, DW treatment variably reduced area-based photosynthetic carbon assimilation rates (Aarea), exhibiting species-specific effects, while WW treatment inconsistently elevated Aarea across species. The structural equation model revealed that Aarea was directly influenced by foliar P fractions and photosynthetic nutrient efficiency, and indirectly by precipitation treatment on soil properties and P fractions.Altered seasonal precipitation patterns affect soil bioavailable P forms and/or soil chemical properties, and thereby influence foliar P fractions allocation and photosynthesis of dominant trees. Soil and foliar P fractions responses to precipitation treatments varied across different sampling months, underscoring the complexity of P cycle and suggesting tree acclimation and resilience. These insights improve our understanding of climate effects on nutrient cycles and resilience.Methods: Understanding how altered precipitation patterns affect the dynamics of phosphorus (P) fractions in both soil and foliage is crucial for predicting climate-induced changes in plant growth and community structure, especially within tropical forests with P-impoverished soils.We conducted a nine-year precipitation experiment in a secondary tropical forest, simulating delayed (DW) and wetter wet season (WW) to reflect potential precipitation changes. We analyzed P fractions in soil (0–10 cm and 10–20 cm) and foliage of four dominant trees, and investigated the correlations among these P fractions and photosynthesis.DW treatment reduced soil P bioavailability and induced foliar P redistribution, while WW treatment increased soil pH and NH4+-N content but had little influence on soil P form. DW treatment generally reduced foliar total P levels and diminished various P fractions with notable species-specific disparities. Moreover, DW treatment variably reduced area-based photosynthetic carbon assimilation rates (Aarea), exhibiting species-specific effects, while WW treatment inconsistently elevated Aarea across species. The structural equation model revealed that Aarea was directly influenced by foliar P fractions and photosynthetic nutrient efficiency, and indirectly by precipitation treatment on soil properties and P fractions.Altered seasonal precipitation patterns affect soil bioavailable P forms and/or soil chemical properties, and thereby influence foliar P fractions allocation and photosynthesis of dominant trees. Soil and foliar P fractions responses to precipitation treatments varied across different sampling months, underscoring the complexity of P cycle and suggesting tree acclimation and resilience. These insights improve our understanding of climate effects on nutrient cycles and resilience.Results: Understanding how altered precipitation patterns affect the dynamics of phosphorus (P) fractions in both soil and foliage is crucial for predicting climate-induced changes in plant growth and community structure, especially within tropical forests with P-impoverished soils.We conducted a nine-year precipitation experiment in a secondary tropical forest, simulating delayed (DW) and wetter wet season (WW) to reflect potential precipitation changes. We analyzed P fractions in soil (0–10 cm and 10–20 cm) and foliage of four dominant trees, and investigated the correlations among these P fractions and photosynthesis.DW treatment reduced soil P bioavailability and induced foliar P redistribution, while WW treatment increased soil pH and NH4+-N content but had little influence on soil P form. DW treatment generally reduced foliar total P levels and diminished various P fractions with notable species-specific disparities. Moreover, DW treatment variably reduced area-based photosynthetic carbon assimilation rates (Aarea), exhibiting species-specific effects, while WW treatment inconsistently elevated Aarea across species. The structural equation model revealed that Aarea was directly influenced by foliar P fractions and photosynthetic nutrient efficiency, and indirectly by precipitation treatment on soil properties and P fractions.Altered seasonal precipitation patterns affect soil bioavailable P forms and/or soil chemical properties, and thereby influence foliar P fractions allocation and photosynthesis of dominant trees. Soil and foliar P fractions responses to precipitation treatments varied across different sampling months, underscoring the complexity of P cycle and suggesting tree acclimation and resilience. These insights improve our understanding of climate effects on nutrient cycles and resilience.Conclusion: Understanding how altered precipitation patterns affect the dynamics of phosphorus (P) fractions in both soil and foliage is crucial for predicting climate-induced changes in plant growth and community structure, especially within tropical forests with P-impoverished soils.We conducted a nine-year precipitation experiment in a secondary tropical forest, simulating delayed (DW) and wetter wet season (WW) to reflect potential precipitation changes. We analyzed P fractions in soil (0–10 cm and 10–20 cm) and foliage of four dominant trees, and investigated the correlations among these P fractions and photosynthesis.DW treatment reduced soil P bioavailability and induced foliar P redistribution, while WW treatment increased soil pH and NH4+-N content but had little influence on soil P form. DW treatment generally reduced foliar total P levels and diminished various P fractions with notable species-specific disparities. Moreover, DW treatment variably reduced area-based photosynthetic carbon assimilation rates (Aarea), exhibiting species-specific effects, while WW treatment inconsistently elevated Aarea across species. The structural equation model revealed that Aarea was directly influenced by foliar P fractions and photosynthetic nutrient efficiency, and indirectly by precipitation treatment on soil properties and P fractions.Altered seasonal precipitation patterns affect soil bioavailable P forms and/or soil chemical properties, and thereby influence foliar P fractions allocation and photosynthesis of dominant trees. Soil and foliar P fractions responses to precipitation treatments varied across different sampling months, underscoring the complexity of P cycle and suggesting tree acclimation and resilience. These insights improve our understanding of climate effects on nutrient cycles and resilience. [ABSTRACT FROM AUTHOR]

Light condition and neighbor effects are important environmental factors that need to be considered for restoration of mangroves, especially when introduced species are mixed with native species. To evaluate different mangrove species performance under various light intensities and different planting systems, we selected three native mangrove species (Avicennia marina, Aegiceras corniculatum, and Kandelia obovata) and grew them with Sonneratia apetala in multispecies plots and in monospecies plots without S. apetala under three light conditions in Futian Nature Reserve, south China. After 10 months of the experiment, plant functional traits were measured. The results showed that S. apetala was a light‐demanding species and A. corniculatum and A. marina were suitable for growth under the medium light condition. The native species were inhibited by S. apetala. Specifically, the height and basal diameter of the native species were lower in the multispecies plots than in the monospecies plots. In the multispecies plots, native species changed their functional growth traits, with higher‐specific leaf area and chlorophyll content, and reduced leaf thickness, leaf dry‐mass content, and carotenoid content compared to those in the monospecies plots. These results indicated trade‐offs between traits that enhance light interception and traits that stimulate plant growth in native species. Our findings revealed that S. apetala is an adequate species with good invasion capability for restoration in open‐degraded areas, but its ecological impact on the inhibited growth of native species should be carefully considered in mangrove restoration. [ABSTRACT FROM AUTHOR]

Plant mixtures can enhance soil quality and optimize ecosystem carbon (C), nitrogen (N), and phosphorus (P) (C:N:P) stoichiometry to support sustainable production; yet this hypothesis has not been thoroughly examined in mixed plantations containing N-fixing tree species (N-fixers). Introduced N-fixers are often used as alternatives to N fertilization in forest plantations but may potentially disrupt the ecosystem C:N:P stoichiometric balance. Here, we compared the effects of N fertilization (100 kg N ha−1 year−1) and the introduction of an N-fixer (Dalbergia odorifera) into Eucalyptus plantations on the C:N:P stoichiometry across soil, microorganisms, enzymes, and leaves and roots. The experiment was organized into a randomized complete block design (n = 5) and lasted five years. N fertilization generally caused an imbalance in ecosystem C:N:P stoichiometry except for the microbial biomass C:N ratio. Introduced the N-fixers decreased the soil C:N ratio and increased the C:P and N:P ratios, whereas the other pools of C:N:P stoichiometry remained unchanged. Two meta-analyses further verified these findings, reinforcing the idea that mixed plantations with N-fixers, as a substitute for N fertilization, can help maintain ecosystem C:N:P stoichiometry to support sustainable production. Comparing the effects of N fertilization and introduced N-fixers using structural equation modeling approach underscored the importance of plant-microbial interactions in maintaining the balance of ecosystem C:N:P stoichiometry. This, in turn, can provide government and policymakers with compelling evidence for a nature-based solution for sustainable plantation management. • N fertilization caused an imbalance C:N:P stoichiometry across plants, soil, microbes, and enzymes. • N-fixers Maintained C:N:P stoichiometry in plants, microbes, and enzymes, but not in soil. • N-fixers Enhanced the sustainable development of the plantation. [ABSTRACT FROM AUTHOR]

As the carbon (C) credit market evolves, incorporating organic matter into soils has emerged as a key strategy in C farming. Soil heterotrophic respiration (RH) plays a pivotal role in maintaining the C balance in terrestrial ecosystems, yet the contrasting impacts of fresh and pyrogenic organic matter applications on soil RH, and associated underlying mechanisms, have not been fully investigated. Through a 2-year field experiment, we investigated how applying maize straw and its derived biochar affect the physical, chemical, and microbial properties of soil in a subtropical Moso bamboo forest. Results showed that straw application increased soil RH, while biochar application suppressed it. Soil RH was correlated positively with β-glucosidase and cellobiohydrolase activities but negatively with RubisCO enzyme activity. Increased soil RH under straw application was linked to the increased β-glucosidase/cellobiohydrolase activities driven by elevated water-soluble organic C and O-alkyl C levels as well as GH48 and cbhI gene abundances, and the decreased RubisCO enzyme activity caused by reduced cbbL gene abundance. Conversely, reduced soil RH under biochar application was linked to reductions in β-glucosidase and cellobiohydrolase activities induced by increased aromatic C and decreased GH48 and cbhI gene levels, and increases in RubisCO enzyme activity driven by higher cbbL gene abundance. More importantly, changes in soil RH were clearly linked to microbial dynamics. Specifically, increases in the relative abundances of Alphaproteobacteria and Sordariomycetes and decreases in AD3 and Tremellomycetes contributed to the enhanced soil RH under straw application. With biochar application, the reverse effect occurred, ultimately contributing to the reduced soil RH. Our study demonstrates that maize straw application increases while biochar application decreases soil RH in the subtropical forest. These findings reveal that biochar reduced soil RH through changing microbial activity in subtropical forests, providing insight into complex dynamics of soil C cycling in response to diverse interventions. [ABSTRACT FROM AUTHOR]

Ecosystem functional responses such as soil CO2 emissions are constrained by microclimate, available carbon (C) substrates and their effects upon microbial activity. In tropical forests, phosphorus (P) is often considered as a limiting factor for plant growth, but it is still not clear whether P constrains microbial CO2 emissions from soils. In this study, we incubated seven tropical forest soils from Brazil and Puerto Rico with different nutrient addition treatments (no addition, Control; C, nitrogen (N) or P addition only; and combined C, N and P addition (CNP)). Cumulative soil CO2 emissions were fit with a Gompertz model to estimate potential maximum cumulative soil CO2 emission (Cm) and the rate of change of soil C decomposition (k). Quantitative polymerase chain reaction (qPCR) was conducted to quantify microbial biomass as bacteria and fungi. Results showed that P addition alone or in combination with C and N enhanced Cm, whereas N addition usually reduced Cm, and neither N nor P affected microbial biomass. Additions of CNP enhanced k, increased microbial abundances and altered fungal to bacterial ratios towards higher fungal abundance. Additions of CNP, however, tended to reduce Cm for most soils when compared to C additions alone, suggesting that microbial growth associated with nutrient additions may have occurred at the expense of C decomposition. Overall, this study demonstrates that soil CO2 emission is more limited by P than N in tropical forest soils and those effects were stronger in soils low in P. Highlights: A laboratory incubation study was conducted with nitrogen, phosphorus or carbon addition to tropical forest soils. Soil CO2 emission was fitted with a Gompertz model and soil microbial abundance was quantified using qPCR. Phosphorus addition increased model parameters Cm and soil CO2 emission, particularly in the Puerto Rico soils. Soil CO2 emission was more limited by phosphorus than nitrogen in tropical forest soils. [ABSTRACT FROM AUTHOR]

Aims: Invasive plants often modify soil biota to benefit their own fitness over native species, and create a positive plant-soil feedback (PSF). Rhizosphere effect (RE), the alterations of decomposition processes by living roots and associated rhizodeposits, may act as a mechanism that contributes to the positive PSF via accelerating litter decomposition and subsequent soil nutrient turnover. However, the relative effects attributable to litter quality versus plant composition and edaphic conditions on RE remain unclear. Methods: A reciprocal translocation decomposition experiment was conducted in a screenhouse with root litter from an invasive (Flaveria bidentis) and a native species (Bidens maximowicziana) in two types of soils (one dominated by the invasive species and another by the native species) with four plantings (two monocultures, one mixture with both species, and one without living plants). We examined the performance of invasive and native species responses to different soils (PSF) and quantified the RE on litter decomposition. Results: PSF and RE were dependent on whether focal species grew in the monocultures or mixture, and interspecific competition ameliorated negative PSF of F. bidentis when it competed with a weaker competitor. All RE values associated with B. maximowicziana litter under the monocultures were positive, whereas F. bidentis litter exhibited neutral to negative REs, mainly depending on the soil type examined. The RE values in the invaded soil were significantly greater than those in the native soil under the monocultures. However, mixture planting tended to decrease REs on decomposition, which in turn feedback to host plant by affecting soil N availability and microbial composition. Conclusions: Our study showed that innate differences between the two litters in terms of their decomposability and edaphic conditions are likely to exert a much greater impact in controlling litter decomposition. Importantly, rhizosphere-mediate belowground process has the potential to be an important contributor to plant-interaction outcomes. [ABSTRACT FROM AUTHOR]

Climate changes, including chronic changes in precipitation amounts, will influence plant physiology and growth. However, such precipitation effects on switchgrass, a major bioenergy crop, have not been well investigated. We conducted a two-year precipitation simulation experiment using large pots (95 L) in an environmentally controlled greenhouse in Nashville, TN. Five precipitation treatments (ambient precipitation, and -50%, -33%, +33%, and +50% of ambient) were applied in a randomized complete block design with lowland "Alamo" switchgrass plants one year after they were established from tillers. The growing season progression of leaf physiology, tiller number, height, and aboveground biomass were determined each growing season. Precipitation treatments significantly affected leaf physiology, growth, and aboveground biomass. The photosynthetic rates in the wet (+50% and +33%) treatments were significantly enhanced by 15.9% and 8.1%, respectively, than the ambient treatment. Both leaf biomass and plant height were largely increased, resulting in dramatically increases in aboveground biomass by 56.5% and 49.6% in the +50% and +33% treatments, respectively. Compared to the ambient treatment, the drought (-33% and -50%) treatments did not influence leaf physiology, but the -50% treatment significantly reduced leaf biomass by 37.8%, plant height by 16.3%, and aboveground biomass by 38.9%. This study demonstrated that while switchgrass in general is a drought tolerant grass, severe drought significantly reduces Alamo’s growth and biomass, and that high precipitation stimulates its photosynthesis and growth. [ABSTRACT FROM AUTHOR]

Aims: The objective of this study was to investigate the effects of the precipitation changes on soil, microbial and root respirations of switchgrass soils, and the relationships between soil respiration and plant growth, soil moisture and temperature. Methods: A mesocosm experiment was conducted with five precipitation treatments over two years in a greenhouse in Nashville, Tennessee. The treatments included ambient precipitation, −50%, −33%, +33% and +50% of ambient precipitation. Soil, microbial, and root respirations were quantified during the growing seasons. Results: Mean soil and root respirations in the +50% treatment were the highest (2.48 and 0.93 μmol CO m s, respectively) among all treatments. Soil microbial respiration contributed more to soil respiration, and had higher precipitation sensitivity mostly than root respiration. Increases in precipitation mostly enhanced microbial respiration while decreases in precipitation reduced both microbial and root respirations. Across precipitation treatments, soil respiration was significantly influenced by soil moisture, soil temperature, and aboveground biomass. Conclusions: Our results showed that microbial respiration was more sensitive to precipitation changes, and precipitation regulated the response of soil respiration to soil temperature. The information generated in this study will be useful for model simulation of soil respiration in switchgrass fields under precipitation changes. [ABSTRACT FROM AUTHOR]

Aim Anthropogenic additions of nitrogen (N) are expected to drive terrestrial ecosystems toward greater phosphorus (P) limitation. However, a comprehensive understanding of how an ecosystem's P cycle responds to external N inputs remains elusive, making model predictions of the anthropogenic P limitation and its impacts largely uncertain. Location Global. Time period 1986-2015. Major taxa studied Terrestrial ecosystems. Methods We conducted a meta-analysis including 288 independent study sites from 192 articles to evaluate global patterns and controls of 10 variables associated with ecosystem P cycling under N addition. Results Overall, N addition increased biomass in plants (+34%) and litter (+15%) as well as plant P content (+17%), while decreasing P concentrations in plants and litter (−8% and −11%, respectively). N addition did not change soil labile P or microbial P, but enhanced phosphatase activity (+24%). The effects of N addition on the litter P pool and soil total P remained unclear due to significant publication biases. The response of P cycling to N addition in tropical forests was different from that in other ecosystem types. N addition did not change plant biomass or phosphatase activity in tropical forests but significantly reduced plant P and soil labile P concentrations. The shift in plant P concentration under N addition was negatively correlated with the N application rate or total N load. N-induced change in soil labile P was strongly regulated by soil pH value at the control sites, with a significant decrease of 14% only in acidic soils (pH < 5.5). Main conclusions Our results suggest that as anthropogenic N enhancement continues in the future it could induce P limitation in terrestrial ecosystems while accelerating P cycling, particularly in tropical forests. A quantitative framework generated on the basis of this meta-analysis is useful for our understanding of ecosystem P cycling with N addition, and for incorporating the anthropogenic P limitation into ecosystem models used to analyse effects of future climate change. [ABSTRACT FROM AUTHOR]

Increasing atmospheric CO2 concentrations generally alter element stoichiometry in plants. However, a comprehensive evaluation of the elevated CO2 impact on plant nitrogen : phosphorus (N:P) ratios and the underlying mechanism has not been conducted. We synthesized the results from 112 previously published studies using meta-analysis to evaluate the effects of elevated CO2 on the N:P ratio of terrestrial plants and to explore the underlying mechanism based on plant growth and soil P dynamics. Our results show that terrestrial plants grown under elevated CO2 had lower N:P ratios in both above-and below-ground biomass across different ecosystem types. The response ratio for plant N:P was negatively correlated with the response ratio for plant growth in croplands and grasslands, and showed a stronger relationship for P than for N. In addition, the CO2-induced down-regulation of plant N:P was accompanied by 19.3% and 4.2% increases in soil phosphatase activity and labile P, respectively, and a 10.1% decrease in total soil P. Our results show that down-regulation of plant N:P under elevated CO2 corresponds with accelerated soil P cycling. These findings should be useful for better understanding of terrestrial plant stoichiometry in response to elevated CO2 and of the underlying mechanisms affecting nutrient dynamics under climate change. [ABSTRACT FROM AUTHOR]

Aims: Drivers of soil respiration ( R) in rock outcrop ecosystems remain poorly understood. We investigated these drivers in limestone cedar glades, known for their concentrations of endemic plant species and for seasonal hydrologic extremes (xeric and saturated conditions), and compared our findings to those in temperate grasslands and semi-arid ecosystems. Methods: We measured R, soil temperature ( T), volumetric soil water content (SWC), soil organic matter (SOM), soil depth, and vegetation cover monthly over 16 mo and analyzed effects of these variables on R. Results: Seasonally, R primarily tracked T (r = 0.77; P < 0.01), however R was depressed during a summer drought. SOM was highly variable spatially, and incorporating SOM effects into the R model dramatically improved model performance. Both shallow soil and sparse vegetation cover were also associated with lower R. Conclusions: Soil depth, SOM, and vegetation cover were important drivers of R in limestone cedar glades. Seasonal R patterns reflected those for mesic temperate grasslands more than for semi-arid ecosystems, in that R primarily tracked temperature for most of the year. [ABSTRACT FROM AUTHOR]

Background: A three-year field experiment was conducted to examine the responses of corn yield and soil nitrous oxide (N2O) emission to various management practices in middle Tennessee. Methodology/Principal Findings: The management practices include no-tillage + regular applications of urea ammonium nitrate (NT-URAN); no-tillage + regular applications of URAN + denitrification inhibitor (NT-inhibitor); no-tillage + regular applications of URAN + biochar (NT-biochar); no-tillage + 20% applications of URAN + chicken litter (NT-litter), no-tillage + split applications of URAN (NT-split); and conventional tillage + regular applications of URAN as a control (CT-URAN). Fertilizer equivalent to 217 kg N ha-1 was applied to each of the experimental plots. Results showed that no-tillage (NT-URAN) significantly increased corn yield by 28% over the conventional tillage (CT-URAN) due to soil water conservation. The management practices significantly altered soil N2O emission, with the highest in the CT-URAN (0.48 mg N2O m-2 h-1) and the lowest in the NT-inhibitor (0.20 mg N2O m-2 h-1) and NT-biochar (0.16 mg N2O m-2 h-1) treatments. Significant exponential relationships between soil N2O emission and water filled pore space were revealed in all treatments. However, variations in soil N2O emission among the treatments were positively correlated with the moisture sensitivity of soil N2O emission that likely reflects an interactive effect between soil properties and WFPS. Conclusion/Significance: Our results indicated that improved fertilizer and soil management have the potential to maintain highly productive corn yield while reducing greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

Drought events are projected to be more extreme and frequent in the future and have profound influences on the structure and functions of terrestrial ecosystems. Thus, better understanding the mechanisms of recovery is critical for predicting the future dynamics of terrestrial ecosystems. We performed a 7‐year field precipitation experiment to examine recovery of a grassland ecosystem from different magnitudes of sustained drought, from slight to extreme. The ecosystem was exposed to precipitation treatments in the first 3 years (2010–2012) and recovered during the last 4 years (2013–2016) without precipitation treatments. Overall, large reductions of aboveground net primary productivity (ANPP, −43.3%) and perennial forb biomass (−83.1%) were observed in the third year (2012) of extreme drought only. Nevertheless, ANPP fully recovered within 1 year after the drought treatments were terminated, and the rapid recovery was mainly due to increased soil total nitrogen and root biomass allocation after drought. Surprisingly, large increases of ANPP under the extreme drought treatment occurred during the recovery periods from 2013 to 2015 (+74.1, +88.5, and +119.8 g m−2 year−1) compared to the control. The overcompensation offset the extreme drought‐induced reduction of ANPP in the treatment years and was primarily ascribed to the enhanced biomass of perennial grasses (PG). Higher resistance to drought and fast resource acquisition strategy might drive the rapid recovery and expansion of PG. Our findings revealed the rapid recovery of grasslands and the critical role of community overcompensation in maintaining grassland ecosystem function and stability under future climate change scenarios. [ABSTRACT FROM AUTHOR]

The temperature sensitivity (Q10) of soil heterotrophic respiration (Rh) is an important ecological model parameter and may vary with temperature and moisture. While Q10 generally decreases with increasing temperature, the moisture effects on Q10 have been controversial. To address this, we conducted a 90-day laboratory incubation experiment using a subtropical forest soil with a full factorial combination of five moisture levels (20%, 40%, 60%, 80%, and 100% water holding capacity - WHC) and five temperature levels (10, 17, 24, 31, and 38°C). Under each moisture treatment, Rh was measured several times for each temperature treatment to derive Q10 based on the exponential relationships between Rh and temperature. Microbial biomass carbon (MBC), microbial community structure and soil nutrients were also measured several times to detect their potential contributions to the moisture-induced Q10 variation. We found that Q10 was significantly lower at lower moisture levels (60%, 40% and 20% WHC) than at higher moisture level (80% WHC) during the early stage of the incubation, but became significantly higher at 20%WHC than at 60% WHC and not significantly different from the other three moisture levels during the late stage of incubation. In contrast, soil Rh had the highest value at 60% WHC and the lowest at 20% WHC throughout the whole incubation period. Variations of Q10 were significantly associated with MBC during the early stages of incubation, but with the fungi-to-bacteria ratio during the later stages, suggesting that changes in microbial biomass and community structure are related to the moisture-induced Q10 changes. This study implies that global warming’s impacts on soil CO2 emission may depend upon soil moisture conditions. With the same temperature rise, wetter soils may emit more CO2 into the atmosphere via heterotrophic respiration. [ABSTRACT FROM AUTHOR]

Based on the isometric hypothesis, belowground plant biomass (MB) should scale isometrically with aboveground biomass (MA) and the scaling exponent should not vary with environmental factors. We tested this hypothesis using a large forest biomass database collected in China. Allometric scaling functions relating MB and MA were developed for the entire database and for different groups based on tree age, diameter at breast height, height, latitude, longitude or elevation. To investigate whether the scaling exponent is independent of these biotic and abiotic factors, we analyzed the relationship between the scaling exponent and these factors. Overall MB was significantly related to MA with a scaling exponent of 0.964. The scaling exponent of the allometric function did not vary with tree age, density, latitude, or longitude, but varied with diameter at breast height, height, and elevation. The mean of the scaling exponent over all groups was 0.986. Among 57 scaling relationships developed, 26 of the scaling exponents were not significantly different from 1. Our results generally support the isometric hypothesis. MB scaled near isometrically with MA and the scaling exponent did not vary with tree age, density, latitude, or longitude, but increased with tree size and elevation. While fitting a single allometric scaling relationship may be adequate, the estimation of MB from MA could be improved with size-specific scaling relationships. [ABSTRACT FROM AUTHOR]

Establishing seedlings in subtropical plantations is very important for forest health, succession and management. Information on seedling nutrient concentrations is essential for both the selection of suitable indigenous tree species to accelerate succession of the established plantation and sustainable forest management. In this study, we investigated the concentrations of nitrogen ([N]), phosphorus ([P]), and N∶P ratio in leaves, stems and roots of seedlings of three indigenous tree species (Castanopsis chinensis, Michelia chapensis and Psychotria rubra) transplanted with removing or retaining understory vegetation and litter at two typical subtropical forest plantations (Eucalyptus plantation and native species plantation). We also measured the relative growth rate (RGR) of seedling height, and developed the relationships between RGR and leaf [N], [P] and N∶P ratio. Results showed that treatments of understory vegetation and associated litter (i.e. removal or retained) generally had no significant effects on leaf [N], [P], N∶P ratio and RGR of the transplanted tree seedlings for the experimental period. But among different species, there were significant differences in nutrient concentrations. M. chapensis and P. rubra had higher [N] and [P] compared to C. chinensis. [N] and [P] also varied among different plant tissues with much higher values in leaves than in roots for all indigenous species. RGR of indigenous tree seedlings was mostly positively correlated with leaf [N] and [P], but negatively correlated with leaf N∶P ratio. Considering the low [P] and high N∶P ratio observed in the introduced indigenous tree seedlings, we propose that the current experimental plantations might be P limited for plant growth. [ABSTRACT FROM AUTHOR]

Abstract: Phosphatases play an important role in mineralization of organic phosphorus, soil phosphorus availability and global phosphorus cycling. Release of phosphorus in different ecosystems is important for plant growth and microbial function, and may be simulated by modeling organic phosphate mineralization. The half-saturation constant (K m ) and the maximum enzyme activity (V max) in the Michaelis–Menten equation are the two important kinetic parameters in these models, but their values have not been systematically investigated. In this study, we compiled a database of kinetic parameters of phosphatase from 139 publications, estimated the means, variations and distributions of the kinetic parameters, and tested the differences in kinetic parameters of phosphatases of different types, origins and under different incubation conditions. We also analyzed the activation energy (E a ), temperature sensitivity (Q 10 ), optimum pH (pH opt ) and sensitivity of pH (pH sen ) of phosphatase activity. Our results indicated that: 1) Both V max and K m were log-normal distributed with large variations; 2) There was no significant difference in K m between the acid or alkaline phosphatases, but a significantly higher V max for acid phosphatases was found compared with alkaline phosphatases; 3) K m and V max varied with the origins of enzymes and under different incubation conditions. Plant originated enzymes had the highest V max while soil originated enzymes had the lowest V max. Larger variation in V max was found among the incubation times than among the incubation temperatures; 4) The mean values of E a for acid and alkaline phosphatases were 36.30 and 23.61 kJ mol−1, respectively, with an overall mean of 34.40 kJ mol−1. The mean value of estimated pH opt for acid phosphatase was 5.2 while that for alkaline phosphatase was 9.5. The information generated in this study will be useful for phosphorus mineralization modeling and uncertainty analysis. [Copyright &y& Elsevier]

The aim of this research is to propose an improved method to partition single species contributions to decomposition in mixed species litters and to detect additive or non-additive responses in litter decomposition. Using simulated data, we demonstrate that additive responses can arise from multiple conditions, including no changes in litter decomposition rates of both species in the mixtures, or an enhanced decomposition of one species and a reduced decomposition of another. Antagonistic responses can be caused by reduced decomposition of only one species, or of both species. Without partitioning of the contributions of single species proposed here, it is difficult to distinguish the different causes of the overall responses. Our analyses provide a better understanding of litter decomposition in mixtures and have significant implications for modeling litter decomposition. [ABSTRACT FROM AUTHOR]

Developing adequate indicators of biodiversity change is an urgent task for biodiversity studies and policy. An important component of any indicator is a measure of the uncertainty in the estimates it produces. In this paper, we derive the biodiversity intactness variance (BIV) as a formal measure of uncertainty to accompany the recently developed biodiversity intactness index (BII) (Scholes and Biggs [Scholes, R.J., Biggs, R., 2005. A biodiversity intactness index. Nature 434, 45–49]). The BII is based on estimates of baseline species richness, the area of different land-uses, and the abundance of different species under different land uses. The BIV quantifies uncertainty in the abundance estimates, which are the main source of uncertainty in BII. The BII for southern Africa in the year 2000 has been estimated at 84.4%. We calculate the accompanying BIV at 50.4, providing a 95% confidence interval of 76.6–92.2% for BII. By applying the BIV, we can quantify the major sources of uncertainty in the BII for southern Africa: they stem from the abundance estimates for mammals and birds, and for savanna regions and degraded areas. The BIV therefore provides a means for better assessing the state of biodiversity loss and for highlighting research priorities. [Copyright &y& Elsevier]

Abstract: Many factors could influence the allometric scaling exponent β estimation, but have not been explored systematically. We investigated the influences of three factors on the estimate of β based on a data set of 626 species of basal metabolic rate and mass in mammals. The influence of sampling error was tested by re-sampling with different sample sizes using a Monte Carlo method. Small random errors were introduced to measured data to examine their influence on parameter estimations. The influence of analysis method was also evaluated by applying nonlinear and linear regressions to the original data. Results showed that a relative large sample size was required to lower statistical inference errors. When sample size n was 10% of the base population size (n=63), 35% of the samples supported β=2/3, 39% supported β=3/4, and 15% rejected β=0.711, even though the base population had a β=0.711. The controversy surrounding the estimation of β in the literature could be partially attributable to such small sample sizes in many studies. Measurement errors in body mass and base metabolic rate, especially in body mass, could largely increase alpha and beta errors. Analysis methods also affected parameter estimations. Nonlinear regressions provided better estimates of the scaling exponent that were significantly higher than these commonly estimated by linear regressions. This study demonstrated the importance of the quantity and quality of data as well as analysis method in power law analysis, raising caution in interpreting power law results. Meta-data synthesis using data from independent studies seems to be a proper approach in the future, but caution should be taken to make sure that such measurements are made using similar protocols. [Copyright &y& Elsevier]

Missing data is a ubiquitous problem in evaluating long-term experimental measurements, such as those associated with the FluxNet project, due to the equipment failures, system maintenance, power-failure, and lightning strikes among other things. To estimate annual values of net ecosystem carbon exchange (NEE), latent heat flux (LE) and sensible heat flux (H), such gaps in the measured data must be filled or imputed. So far, no standardized method has been accepted and the imputation methods used are largely dependent on the researchers’ choice. Here, we used multiple imputation (MI) to gap-fill the missing data for annual estimations of NEE, LE and H at three flux sites associated with the FluxNet effort. MI is a Monte Carlo technique in which the missing values are replaced by several simulated values. Each data set imputed is a complete one where the observed values are the same as those in the original data set; only the missing values are different. Thus, the normal statistical analysis (e.g. annual total calculation) can be applied to each data set separately. The results of each analysis can be recombined into one summary. We applied the MI method to eddy covariance measurements collected from Walker Branch Watershed (WBW) site (a deciduous forest), Duke site (a coniferous forest) and Niwot site (a subalpine forest). Results showed that annual estimations of NEE, LE and H by MI were comparable to other imputation methods but MI was much easier to apply because of readily available software and standard algorithms. Besides the normal statistical analyses, MI also provided confidence intervals for each estimated parameter. This confidence interval is most useful when assessing energy, water, and carbon balance closures at a given tower site. Significant differences in annual NEE, LE and H were found among years at the three AmeriFlux sites. NEE at the Niwot Ridge site was lower and LE and H were higher than at the other two sites. With the available software and realistic gap-filling capability, MI has the potential to become a standardized method to gap-fill eddy covariance flux data for annual estimations and to improve the analysis of uncertainties associated with annual estimations of NEE, LE and H from regional and global flux networks. [Copyright &y& Elsevier]

Summary This study used an environmentally controlled plant growth facility, EcoCELLs, to measure canopy gas exchanges directly and to examine the effects of elevated [CO2] on canopy radiation- and water-use efficiencies. Sunflowers (Helianthus annus var. Mammoth) were grown at ambient (399 μmol mol-1) and elevated [CO2] (746 μmol mol-1) for 53 days in EcoCELLs. Whole canopy carbon- and water-fluxes were measured continuously during the period of the experiment. The results indicated that elevated [CO2] enhanced daily total canopy carbon- and water-fluxes by 53% and 11%, respectively, on a ground-area basis, resulting in a 54% increase in radiation-use efficiency (RUE) based on intercepted photosynthetic active radiation and a 26% increase in water-use efficiency (WUE) by the end of the experiment. Canopy carbon- and water-fluxes at both CO2 treatments varied with canopy development. They were small at 22 days after planting (DAP) and gradually increased to the maxima at 46 DAP. When canopy carbon- and water-fluxes were expressed on a leaf-area basis, no effect of CO2 was found for canopy water-flux while elevated [CO2] still enhanced canopy carbon-flux by 29%, on average. Night-time canopy carbon-flux was 32% higher at elevated than at ambient [CO2]. In addition, RUE and WUE displayed strong diurnal variations, high at noon and low in the morning or afternoon for WUE but opposite for RUE. This study provided direct evidence that plant canopy may consume more, instead of less, water but utilize both water and radiation more efficiently at elevated than at ambient [CO2], at least during the exponential growth period as illustrated in this experiment. [ABSTRACT FROM AUTHOR]

• Soil C, N, and P were examined in tropical forests on Hainan Island, China. • Soil nutrient concentrations varied among depths. • Large spatial variations of C, N, P and their ratios were found on the Island. • Soil C, N and P were mostly influenced by habitat variables. • The findings are useful for ecosystem modeling and forest management. Soil carbon (C), nitrogen (N), and phosphorus (P) are three important elements. The study of stoichiometric relationships of soil C, N, and P in tropical forests on Hainan Island, China could improve our understanding of nutrient cycling and provide valuable information for forest management. Soil samples were collected at five different depths from 0 to 100 cm at 100 sites among four different forest types on Hainan Island, and total C, N, and P concentrations were measured. Soil C and N concentrations and soil C:P and N:P ratios declined from the surface soil layer to the deeper soil layers and soil P and C:N ratio had relatively small variations among different depths, due to that soil C and N were mostly controlled by biological processes such as photosynthesis and N 2 -fixation, while P was more influenced by bedrock. Large spatial variations were found for soil C, N, P concentrations and their ratios. Soil C and N concentrations were significantly influenced by longitude and vegetation cover, while soil P concentration and C:P and N:P ratios were significantly controlled by latitude. This study produced a comprehensive data set of soil C, N, and P stoichiometry, and their variation patterns and controls in the tropical forests. The information generated here could help improve ecosystem models for better understanding of forest element stoichiometry, ecosystem productivity, and plant-environment relationships. [ABSTRACT FROM AUTHOR]

South China has been experiencing very high rate of acid deposition and severe soil acidification in recent decades, which has been proposed to exacerbate the regional ecosystem phosphorus (P) limitation. We conducted a 10‐year field experiment of simulated acid deposition to examine how acidification impacts seasonal changes of different soil P fractions in a tropical forest with highly acidic soils in south China. As expected, acid addition significantly increased occluded P pool but reduced the other more labile P pools in the dry season. In the wet season, however, acid addition did not change microbial P, soluble P and labile organic P pools. Acid addition significantly increased exchangeable Al3+ and Fe3+ and the activation of Fe oxides in both seasons. Different from the decline of microbial abundance in the dry season, acid addition increased ectomycorrhizal fungi and its ratio to arbuscular mycorrhiza fungi in the wet season, which significantly stimulated phosphomonoesterase activities and likely promoted the dissolution of occluded P. Our results suggest that, even in already highly acidic soils, the acidification‐induced P limitation could be alleviated by stimulating ectomycorrhizal fungi and phosphomonoesterase activities. The differential responses and microbial controls of seasonal soil P transformation revealed here should be implemented into ecosystem biogeochemical model for predicting plant productivity under future acid deposition scenarios. [ABSTRACT FROM AUTHOR]

The home-field advantage (HFA) hypothesis predicts that plant litter would decompose more quickly beneath its own plant species in the soil than beneath other plant species. Theoretically, HFA can be induced by the rhizosphere of growing plants, due to so-called rhizosphere effect (RE). Despite growing evidence for the site condition-dependence of both effects, few work has be conducted to explore how site climate, vegetation type and soil properties interact to affect RE and HFA, and especially limited in situ representation from subtropical wetland systems. In a field experiment, we reciprocally incubated three root litter species (Rumex dentatus L., Carex thunbergii Steud., and Polygonum cripolitanum Hance) along a hydroperiod gradient in a subtropical wetland, which differed mainly with respect to vegetation and soil microclimate, with and without growing plants. The occurrence and magnitude of HFA and RE were mainly determined by litter quality and were stage-specific. Collectively, we detected significant HFA with chemically-recalcitrant litter from C. thunbergii and P. cripolitanum , but only at the first stage of decomposition. The presence of growing plants generally reduced litter decomposition, but the magnitude of the response was species-specific, with the positive effects detected only for root litters from C. thunbergii at the first stage of decomposition. In addition, we did not find a significant relationship between HFA and RE, indicating that plant species that produce litters exhibiting HFA may not accelerate litter decomposition via RE at same time. Structural equation models (SEM) revealed that site microclimate factors were conducive with soil properties in regulating C dynamics. Overall, soil microclimate in this wetland ecosystem was likely important in driving C cycling, either directly by changing environmental conditions, litter quality, and plant trait spectra, or indirectly by interrupting the interactions between litter and decomposers. Unlabelled Image • Both HFA and RE were mainly determined by litter quality and stage-specific. • The presence of growing plants generally depressed root litter decomposition. • Microclimate factors were conducive with soil properties in regulating C dynamics. [ABSTRACT FROM AUTHOR]

Ecological stoichiometry is the study of the balance of ecosystem energy and nutrient cycling, especially carbon (C), nitrogen (N), and phosphorus (P). C, N, and P are the key elements for plant growth and metabolism. Systematic research on leaf stoichiometry in mangrove forest ecosystems is still lacking. To understand the leaf stoichiometry of introduced species and native species in mangrove forests, we selected four species (one introduced species, Sonneratia apetala , and three native species, Avicennia marina , Aegiceras corniculatum , and Kandelia obovate) and measured leaf C, N, and P contents under different light conditions. The results showed that there were significant negative scaling relationships of leaf C versus N and C versus P but positive scaling relationships of leaf N versus P in the four mangrove species. Light and competition had significant effects on leaf stoichiometry, especially under the full light condition. S. apetala influenced leaf elements in a mixture with native species. Interspecific competition reduced leaf N and P contents in A. corniculatum and K. obovate but increased leaf N and P contents in A. marina. Leaf N and P contents of the four species showed similar responses to both intraspecific and interspecific competition. The ratio of leaf C:N:P (108:11:1) in the mangrove forests was lower than that in other ecosystems, and species with a higher growth rate had a higher leaf P content and lower N:P ratio, supporting the growth rate hypothesis. Leaf N:P was 11.04, indicating that there was N limitation in the mangrove forests. This systematic research of leaf stoichiometry of mangrove forests improves our understanding of mangrove growth and nutrient use strategies in response to different environmental stresses. Unlabelled Image • Leaf C, N, and P concentrations and their ratios had scaling relationships in the mangrove forests. • Light and competition significantly influenced the leaf stoichiometry of mangrove plants. • There was N limitation in the mangrove forests. • Leaf stoichiometry of the mangrove forests supported the growth rate hypothesis. [ABSTRACT FROM AUTHOR]

The amplifying interannual precipitation variability has been observed globally and is projected to intensify under climate change scenarios. However, its impacts on terrestrial vegetation and carbon (C) sink have not been well investigated.As part of a field manipulative experiment with three precipitation variabilities (20%, 40% and 60%) in a semi‐arid grassland, this study was conducted to examine the responses of ecosystem C cycling to increased precipitation variability.Across the 3 experimental years from 2010 to 2012, amplified precipitation variability enhances gross primary productivity (GPP) and ecosystem respiration (ER), as both GPP and ER were more sensitive to above‐ than below‐average precipitation. In addition, the larger responses of GPP than ER to precipitation variability resulted in an enhancement of net ecosystem productivity (NEP), such that NEP increased with the increasing precipitation variability. More species with higher sensitivity to increased precipitation under wet conditions and the insensitivity of root growth to decreased precipitation could largely be responsible for the above observations, which suggest that the semi‐arid grassland was more sensitive to wet treatment yet strongly resistant to drought.Our results provide empirical evidence that intensified precipitation variability could stimulate grassland C sink. The findings revealed in this study could facilitate the mechanistic understanding and imply the potential positive feedback of climate variability‐terrestrial C sink. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

How climate warming interacts with atmospheric nitrogen (N) deposition to affect carbon (C) release from soils remains largely elusive, posing a major challenge in projecting climate change‒terrestrial C feedback.As part of a 5‐year (2006–2010) field manipulative experiment, this study was designed to examine the effects of 24‐hr continuous warming and N addition on soil respiration and explore the underlying mechanisms in a semi‐arid grassland on the Mongolian Plateau, China.Across the 5 years and all plots, soil respiration was not changed under the continuous warming, but was decreased by 3.7% under the N addition. The suppression of soil respiration by N addition in the third year and later could be mainly due to the reductions in the forb‐to‐grass biomass ratios. Moreover, there were interactive effects between continuous warming and N addition on soil respiration. Continuous warming increased soil respiration by 5.8% in the ambient N plots, but reduced it by 6.3% in the enriched N plots. Soil respiration was unaffected by N addition in the ambient temperature plots yet decreased by 9.4% in the elevated temperature plots. Changes of soil moisture and the proportion of legume biomass in the community might be primarily responsible for the non‐additive effects of continuous warming and N addition on soil respiration.This study provides empirical evidence for the positive climate warming‒soil C feedback in the ambient N condition. However, N deposition reverses the positive warming‒soil C feedback into a negative feedback, leading to decreased C loss from soils under a warming climate. Incorporating our findings into C‐cycling models could reduce the uncertainties of model projections for land C sink and global C cycling under multifactorial global change scenarios. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Obtaining a holistic understanding of the impacts of atmospheric nitrogen deposition on multiple ecosystem services of forest is essential for developing comprehensive and sustainable strategies, particularly in heavy N deposition regions such as subtropical China. However, such impacts remain incompletely understood, with most previous studies focus on individual ecosystem function or service via understory N addition experiments. To address this knowledge gap, we quantified the effects of over‐canopy and understory N additions on multiple ecosystem services based on a 7‐year large‐scale field experiment in a typical subtropical forest. Our results showed continued over‐canopy N addition with 50 kg ha−1 year−1 over a period of 4–7 years significantly increased plant nutrient retention, but did not affect the services of soil nutrient accumulation, water yield, C sequestration (in plants and soil), or oxygen release. There were trade‐offs between the soil and plant on providing the services of nutrient accumulation/retention and C sequestration under over‐canopy N addition. However, without uptake and retention of tree canopy, the trade‐off between soil and plant were more weaken under the understory N addition with 50 kg ha−1 year−1, and their relationships were even synergetic under the understory N addition with 25 kg ha−1 year−1. The results suggest that understory N addition cannot accurately simulate the effects of atmospheric N deposition on multiple services, along with mutual relationships. Interestingly, the services of plant N, P retention, and C sequestration exhibited a synergetic increase under the over‐canopy N addition but a decrease under the understory N addition. Our results also found tree layer plays a primary role in providing plant nutrient retention service and is sensitive to atmospheric N deposition. Further studies are needed to investigate the generalized effects of forest canopy processes on alleviating the threaten of global change factors in different forest ecosystems. [ABSTRACT FROM AUTHOR]

Agricultural soils play a dual role in regulating the Earth's climate by releasing or sequestering carbon dioxide (CO2) in soil organic carbon (SOC) and emitting non‐CO2 greenhouse gases (GHGs) such as nitrous oxide (N2O) and methane (CH4). To understand how agricultural soils can play a role in climate solutions requires a comprehensive assessment of net soil GHG balance (i.e., sum of SOC‐sequestered CO2 and non‐CO2 GHG emissions) and the underlying controls. Herein, we used a model‐data integration approach to understand and quantify how natural and anthropogenic factors have affected the magnitude and spatiotemporal variations of the net soil GHG balance in U.S. croplands during 1960–2018. Specifically, we used the dynamic land ecosystem model for regional simulations and used field observations of SOC sequestration rates and N2O and CH4 emissions to calibrate, validate, and corroborate model simulations. Results show that U.S. agricultural soils sequestered 13.2±1.16$$ 13.2\pm 1.16 $$ Tg CO2‐C year−1 in SOC (at a depth of 3.5 m) during 1960–2018 and emitted 0.39±0.02$$ 0.39\pm 0.02 $$ Tg N2O‐N year−1 and 0.21±0.01$$ 0.21\pm 0.01 $$ Tg CH4‐C year−1, respectively. Based on the GWP100 metric (global warming potential on a 100‐year time horizon), the estimated national net GHG emission rate from agricultural soils was 122.3±11.46$$ 122.3\pm 11.46 $$ Tg CO2‐eq year−1, with the largest contribution from N2O emissions. The sequestered SOC offset ~28% of the climate‐warming effects resulting from non‐CO2 GHG emissions, and this offsetting effect increased over time. Increased nitrogen fertilizer use was the dominant factor contributing to the increase in net GHG emissions during 1960–2018, explaining ~47% of total changes. In contrast, reduced cropland area, the adoption of agricultural conservation practices (e.g., reduced tillage), and rising atmospheric CO2 levels attenuated net GHG emissions from U.S. croplands. Improving management practices to mitigate N2O emissions represents the biggest opportunity for achieving net‐zero emissions in U.S. croplands. Our study highlights the importance of concurrently quantifying SOC‐sequestered CO2 and non‐CO2 GHG emissions for developing effective agricultural climate change mitigation measures. [ABSTRACT FROM AUTHOR]

Invasive plant species are often able to alter soils in a way that benefits their own fitness over that of native species. While interspecific competitions may drive species to acquire different forms of nitrogen (N) to avoid intensive competition, plant-mycorrhizal interactions can also influence plant nutrient acquisition. Yet, it is unclear whether a variation in N acquisition by an invasive species is driven by interspecific resource partitioning due to competition with native species or by its symbiosis with arbuscular mycorrhizal (AM) fungi. We conducted a pot experiment to examine the effects of competition and fungicide on the uptake of different N forms by Flaveria bidentis, an invasive plant having symbiotic relationships with AM fungi, and two coexisting native species, mycotrophic Bidens maximowicziana and non-mycotrophic Amaranthus retroflexus (referred to by genus hereafter), by growing them either in two-species mixtures or in monocultures. We found that the growth of Flaveria was suppressed by its association with AM fungi regardless of the presence of competing native species, but the degree of suppression was related to the native species with which Flaveria competed. When growing in monocultures, all three species showed a strong preference for NO3−-N over NH4+-N and glycine-N regardless of mycorrhizal status. However, under competition conditions, Flaveria increased 15N recovery in any form of N available (in particular NH4+-15N), depending on neighboring plant identity and AM fungi association, whereas Amaranthus specially tended to decrease NH4+-15N uptake when competing with Flaveria, suggesting a niche complementarity in the utilization of N between two species. Our findings suggested that AM fungi may have the potential to limit the invasion of Flaveria, in the short term, and that interspecific competition plays an important role in partitioning soil N acquisition between plant species. [ABSTRACT FROM AUTHOR]

Mangrove afforestation is considered an important measure in the "natural-based solution" for mitigating climate warming through sequestering massive carbon (C) into vegetation biomass, yet how the planted mangrove species facilitate soil C sequestration remains unclear. Here, we investigated the stock, source, and fraction of soil organic carbon (SOC) over 1 m depth after 20-year afforestation of five mangrove pure plantations (Acrostichum aureum, Acanthus ilicifolius, Aegiceras corniculatum, Kandelia obovate, and Excoecaria agallocha) on Qi'ao Island, South China. The results showed that SOC stocks did not significantly differ among the five plantations, with an average value of 16.7 kg C m−2. Based on the two-end-member mixing model with plant–soil C stable isotope signatures, the autochthonous (mangrove-derived) C source accounted for 20.2–34.1% of SOC but varied significantly among the plantations. The SOC stock in particulate fraction (1.2–2.0 g C kg−1) and mineral-associated fraction (14.3–16.0 g C kg−1) also significantly differed among the plantations. The similar SOC stock but different source contributions and C fractions among the plantations observed here may have important implications for mangrove afforestation to optimize stand structure and maximize C sequestration. [ABSTRACT FROM AUTHOR]

How soil microbes assimilate carbon-C, nitrogen-N, phosphorus-P, and sulfur-S is fundamental for understanding nutrient cycling in terrestrial ecosystems. We compiled a global database of C, N, P, and S concentrations in soils and microbes and developed relationships between them by using a power function model. The C:N:P:S was estimated to be 287:17:1:0.8 for soils, and 42:6:1:0.4 for microbes. We found a convergence of the relationships between elements in soils and in soil microbial biomass across C, N, P, and S. The element concentrations in soil microbial biomass follow a homeostatic regulation curve with soil element concentrations across C, N, P and S, implying a unifying mechanism of microbial assimilating soil elements. This correlation explains the well-constrained C:N:P:S stoichiometry with a slightly larger variation in soils than in microbial biomass. Meanwhile, it is estimated that the minimum requirements of soil elements for soil microbes are 0.8 mmol C Kg−1 dry soil, 0.1 mmol N Kg−1 dry soil, 0.1 mmol P Kg−1 dry soil, and 0.1 mmol S Kg−1 dry soil, respectively. These findings provide a mathematical explanation of element imbalance in soils and soil microbial biomass, and offer insights for incorporating microbial contribution to nutrient cycling into Earth system models. [ABSTRACT FROM AUTHOR]

Abstract: Changing precipitation regimes could have profound influences on carbon (C) cycle in the biosphere. However, how soil C release from terrestrial ecosystems responds to changing seasonal distribution of precipitation remains unclear. A field experiment was conducted for 4 years (2013–2016) to examine the effects of altered precipitation distributions in the growing season on soil respiration in a temperate steppe in the Mongolian Plateau. Over the 4 years, both advanced and delayed precipitation peaks suppressed soil respiration, and the reductions mainly occurred in August. The decreased soil respiration could be primarily attributable to water stress and subsequently limited plant growth (community cover and belowground net primary productivity) and soil microbial activities in the middle growing season, suggesting that precipitation amount in the middle growing season is more important than that in the early, late, or whole growing seasons in regulating soil C release in grasslands. The observations of the additive effects of advanced and delayed precipitation peaks indicate semiarid grasslands will release less C through soil respiratory processes under the projected seasonal redistribution of precipitation in the future. Our findings highlight the potential role of intra‐annual redistribution of precipitation in regulating ecosystem C cycling in arid and semiarid regions. [ABSTRACT FROM AUTHOR]

Changes in water and nitrogen (N) availability due to climate change and atmospheric N deposition could have significant effects on soil respiration, a major pathway of carbon (C) loss from terrestrial ecosystems. A manipulative experiment simulating increased precipitation and atmospheric N deposition has been conducted for 9 years (2005-2013) in a semiarid grassland in Mongolian Plateau, China. Increased precipitation and N addition interactively affect soil respiration through the 9 years. The interactions demonstrated that N addition weakened the precipitation-induced stimulation of soil respiration, whereas increased precipitation exacerbated the negative impacts of N addition. The main effects of increased precipitation and N addition treatment on soil respiration were 15.8% stimulated and 14.2% suppressed, respectively. Moreover, a declining pattern and 2-year oscillation were observed for soil respiration response to N addition under increased precipitation. The dependence of soil respiration upon gross primary productivity and soil moisture, but not soil temperature, suggests that resources C substrate supply and water availability are more important than temperature in regulating interannual variations of soil C release in semiarid grassland ecosystems. The findings indicate that atmospheric N deposition may have the potential to mitigate soil C loss induced by increased precipitation, and highlight that long-term and multi-factor global change studies are critical for predicting the general patterns of terrestrial C cycling in response to global change in the future. [ABSTRACT FROM AUTHOR]

There is little published information on sensory attributes and quality indices of organically grown sweetpotato (Ipomea batatas L.) even though there is a growing demand for this product. A study was conducted to identify the best cultivars based on sensory characteristics and organoleptic acceptability of sweetpotato grown under an organic management production system. Baked samples of 14 sweetpotato cultivars were evaluated by taste panelists on a 4-point hedonic scale for color, taste, texture, and overall acceptability. The cvs. All Purple (purple fleshed), Carolina Ruby (orange fleshed), and Ginseng (orange fleshed) had the highest taste, texture, and aroma scores; the white fleshed cv. Japanese Purple was least accepted overall. The most preferred sweetpotato cultivar was associated with the descriptors pasty, umami (monosodium glutamate like), sodium, and adhesive. The purple flesh color was well liked by all panelists and rated as the top color of all cultivars. Panelist preference was toward nontraditional cultivars. [ABSTRACT FROM AUTHOR]

• Phylogeny and functional trait analyses were used to test community assembly. • The relative importance of dominant ecological processes changed during succession. • Soil P content has a important impact on community assembly during succession. • Both environmental filtering and competitive exclusion played a role during succession. • The test of ecological processes could be biased if used one functional strategy. Understanding community assembly process could enhance forest conservation and restoration, while which dominant ecological process drives the community assembly during forest succession is still controversial. In this study, the phylogeny-based and functional trait-based indicators were used to investigate the community assembly processes during forest succession in southern China. 30 dominant species and 33 functional trait indicators related to plant competition, reproduction, and defense strategies, 7 environmental factors related to light availability and soil nutrients, and species richness were selected to explore the dominant ecological processes during succession via Monte Carlo method, structural equation model, multiple linear regression, and one-way ANOVA analysis. Results showed that both the community phylogenetic and functional trait structures changed during succession. Phylogenetic structure clustering and functional trait clustering were evident in early succession. In middle succession, the phylogenetic structure and functional trait structure were randomly dispersed. In middle and later succession, the phylogenetic structure clustering, functional trait clustering, and functional trait evenly dispersed were found. The environmental factors, especially the soil P content, and species richness were found to have significant effects on the community assembly processes during succession. Dominant species in early succession always occupied acquisitive strategies and had high light-use ability and low investment in defense, but dominant species in later succession showed more conservative strategies and exhibited diverse defense strategy, reproductive strategy, and light and nutrient resource-use strategy, apparently in order to adapt changing and more complex environments. The results demonstrate that the relative importance of ecological processes changed during succession. Environmental filtering mainly dominated in early succession, and its strength gradually decreased as succession progressed. Both environmental filtering and competitive exclusion had important effects on community assembly in later succession. The assessment of the relative importance of ecological processes during succession could be biased if only based on one plant functional strategy. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) is the third important long‐lived greenhouse gas next to carbon dioxide and methane and croplands are considered biogeochemical hotspots of soil N2O emissions. To reduce soil N2O and other greenhouse emissions, climate‐smart agricultural practices including biochar application have been applied. Many studies have been conducted with biochar application but results from these studies are not conclusive. To address this issue, meta‐analysis, a quantitative review that synthesizes results from multiple independent studies, has been widely used. The results from different meta‐analyses also differ but are seldomly evaluated. In this study, we evaluated meta‐analyses on the effects of biochar application on soil N2O emissions. A grand mean response ratio (RR) was further proposed to estimate an overall effect and the impacts of experiment setting, properties of biochar and soil, and agricultural practices. We found 18 meta‐analysis papers were published between 2014 and 2022. Sample size (publications or experiments) varied from less than 30 to more than 1000, with a mean sample size of 275. RR was calculated in all studies except one. While four meta‐analyses did not find a significant effect of biochar application on soil N2O emissions, all others reported reductions of soil N2O emissions, but the magnitude ranged from −10.5% to −54.8%. Synthesizing all results from these meta‐analyses, we found that biochar application overall significantly reduced the soil N2O emissions by 38.8%. The impacts increased with experimental duration till one and half years and reduced after that. Biochar application rate and C:N ratio had large influence on the effects of biochar application on soil N2O emissions. This study demonstrated that while meta‐analysis provides a more comprehensive and better estimation, the inconsistence among these studies may need to be further evaluated. A grand mean RR based on meta‐analyses could be more accurate and representative than single meta‐analysis. [ABSTRACT FROM AUTHOR]

Aims: Soil warming significantly influences soil organic carbon (SOC) pools in terrestrial ecosystems through its impact on the processes of carbon (C) input and decomposition as well as the stabilization of SOC pools. Most studies demonstrated that soil warming reduces SOC pools, but the magnitude is highly variable, and the underlying mechanisms are poorly understood. Methods: The concentration, stability (dissolved, particulate, and mineral-associated SOC) and source (plant-derived vs. microbial-derived) of SOC, soil microbial community composition, and enzymatic activities were studied in a 10-year soil warming field experiment in an East Asian monsoon forest. Results: 10-year soil warming significantly enhanced SOC in the top 0–10 cm soil. The increased SOC induced by warming was mainly derived from plants, with lignin and phenol markers increasing by 60% on average, accompanied by a 27% decrease in microbial-derived SOC. However, the overall effect of warming on SOC stability was not statistically significant. Conclusions: The results suggest that the moist monsoon forest soil could sequester SOC upon long-term warming. The discrepancy between our findings and those from other regions highlights an urgent need for a better understanding of how the contrasting effects of plant- and microbial-derived C mediate the response of the SOC pool to warming across biomes. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to the article "Asia on the rise" published in the previous issue.

With the continuing increase in anthropogenic activities, acid rain remains a serious environmental threat, especially in the fast developing areas such as southern China. To detect how prolonged deposition of acid rain would influence soil organic carbon accumulation in mature subtropical forests, we conducted a field experiment with simulated acid rain (SAR) treatments in a monsoon evergreen broadleaf forest at Dinghushan National Nature Reserve in southern China. Four levels of SAR treatments were set by irrigating plants with water of different pH values: CK (the control, local lake water, pH ≈ 4.5), T1 (water pH = 4.0), T2 (water pH = 3.5), and T3 (water pH = 3.0). Results showed reduced pH measurements in the topsoil exposed to simulated acid rains due to soil acidification. Soil respiration, soil microbial biomass and litter decomposition rates were significantly decreased by the SAR treatments. As a result, T3 treatment significantly increased the total organic carbon by 24.5% in the topsoil compared to the control. Furthermore, surface soil became more stable as more recalcitrant organic matter was generated under the SAR treatments. Our results suggest that prolonged acid rain exposure may have the potential to facilitate soil organic carbon accumulation in the subtropical forest in southern China. [ABSTRACT FROM AUTHOR]

Afforestation may alter soil microbial community structure and function, and further affect soil carbon (C) and nitrogen (N) dynamics. Here we investigated soil microbial carbon and nitrogen (MBC and MBN) and microbial community [e.g. bacteria (B), fungi (F)] derived from phospholipid fatty acids (PLFAs) analysis in afforested (implementing woodland and shrubland plantations) and adjacent croplands in central China. Relationships of microbial properties with biotic factors [litter, fine root, soil organic carbon (SOC), total nitrogen (TN) and inorganic N], abiotic factors (soil temperature, moisture and pH), and major biological processes [basal microbial respiration, microbial metabolic quotient ( q CO 2 ), net N mineralization and nitrification] were developed. Afforested soils had higher mean MBC, MBN and MBN:TN ratios than the croplands due to an increase in litter input, but had lower MBC:SOC ratio resulting from low-quality (higher C:N ratio) litter. Afforested soils also had higher F:B ratio, which was probably attributed to higher C:N ratios in litter and soil, and shifts of soil inorganic N forms, water, pH and disturbance. Alterations in soil microbial biomass and community structure following afforestation were associated with declines in basal microbial respiration, q CO 2 , net N mineralization and nitrification, which likely maintained higher soil carbon and nitrogen storage and stability. [ABSTRACT FROM AUTHOR]

The phyllosphere, particularly the leaf surface of plants, harbors a diverse range of microbiomes that play a vital role in the functioning of terrestrial ecosystems. However, our understanding of microbial successions and their impact on functional genes during plant community development is limited. In this study, considering core and satellite microbial taxa, we characterized the phyllosphere microbiome and functional genes in various microhabitats (i.e., leaf litter, moss and plant leaves) across the succession of a plant community in a low-altitude glacier foreland. Our findings indicate that phyllosphere microbiomes and associated ecosystem stability increase during the succession of the plant community. The abundance of core taxa increased with plant community succession and was primarily governed by deterministic processes. In contrast, satellite taxa abundance decreased during plant community succession and was mainly governed by stochastic processes. The abundance of microbial functional genes (such as C, N, and P hydrolysis and fixation) in plant leaves generally increased during the plant community succession. However, in leaf litter and moss leaves, only a subset of functional genes (e.g., C fixation and degradation, and P mineralization) showed a tendency to increase with plant community succession. Ultimately, the community of both core and satellite taxa collaboratively influenced the characteristics of phyllosphere nutrient-cycling genes, leading to the diverse profiles and fluctuating abundance of various functional genes during plant community succession. These findings offer valuable insights into the phyllosphere microbiome and plant–microbe interactions during plant community development, advancing our understanding of the succession and functional significance of the phyllosphere microbial community. [ABSTRACT FROM AUTHOR]

Atmospheric acid deposition remains a widespread problem that may influence the protection of carbon (C) in soil by altering organo-mineral interactions. However, the impacts of additional acidity on organo-mineral interactions and soil C sequestration in naturally acidic tropical soils with a high content of reactive iron (Fe) phases have not been well studied. Here we conducted a long-term (9.5-year) field experiment with a gradient of acidity treatments (3, 9.6, 32, 96 mol H+ ha−1 year−1 as nitric + sulfuric acid, added to ambient deposition) to examine how acidification alters organo-mineral interactions and soil organic carbon (SOC) pools in a tropical forest of China where soils are already highly acidic (pH ≈ 4). As expected, soil acidification significantly enhanced the leaching of base cations (e.g., Ca2+), and it also altered the solubility and composition of Fe and Al phases. The acidity treatments decreased total Fe and converted more crystalline Fe (oxyhydr) oxides to short-range-ordered phases, evidenced by an increase in Fe extracted by citrate-ascorbate solution and 0.5 M hydrochloric acid, and a decrease in the difference in Fe extracted by citrate-dithionite and citrate-ascorbate. Together, these changes led to a large increase in Fe-bound C versus a relatively small decrease in Ca-bound C. Overall, the acidity treatments increased the mineral-associated C stock to 32.5–36.4 Mg C ha−1 versus 28.8 Mg C ha−1 in the control, accounting for 71–83% of the observed increase in total SOC stock. These findings highlight the importance of pH-sensitive geochemical changes and the key roles of Fe in regulating the response of SOC to further inputs of acid deposition even in highly weathered and naturally acidic soils. The magnitude of SOC changes observed here further reveals the necessity of including pH-sensitive geochemistry in Earth system models to better predict ecosystem C budgets under future acid deposition scenarios. [ABSTRACT FROM AUTHOR]

Unprecedented nitrogen (N) inputs into terrestrial ecosystems have profoundly altered soil N cycling. Ammonia oxidizers and denitrifiers are the main producers of nitrous oxide (N2O), but it remains unclear how ammonia oxidizer and denitrifier abundances will respond to N loading and whether their responses can predict N‐induced changes in soil N2O emission. By synthesizing 101 field studies worldwide, we showed that N loading significantly increased ammonia oxidizer abundance by 107% and denitrifier abundance by 45%. The increases in both ammonia oxidizer and denitrifier abundances were primarily explained by N loading form, and more specifically, organic N loading had stronger effects on their abundances than mineral N loading. Nitrogen loading increased soil N2O emission by 261%, whereas there was no clear relationship between changes in soil N2O emission and shifts in ammonia oxidizer and denitrifier abundances. Our field‐based results challenge the laboratory‐based hypothesis that increased ammonia oxidizer and denitrifier abundances by N loading would directly cause higher soil N2O emission. Instead, key abiotic factors (mean annual precipitation, soil pH, soil C:N ratio, and ecosystem type) explained N‐induced changes in soil N2O emission. Altogether, these findings highlight the need for considering the roles of key abiotic factors in regulating soil N transformations under N loading to better understand the microbially mediated soil N2O emission. [ABSTRACT FROM AUTHOR]