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Applying biochar amendment and manure in tea plantation ecosystems can diminish soil acidification and degradation. However, the impact of these practices on soil respiration and associated mechanisms remains unclear. In this study, we combined a two-year field experiment and laboratory analyses based on soil properties, functional genes, and microbial co-occurrence networks to explore the determinants of soil respiration intensity in a subtropical tea plantation with biochar amendment and manure application. The results showed that the effect of biochar amendment on soil respiration was unconspicuous. Although biochar amendment increased bacterial richness and Shannon index, biochar amendment did not alter the abundance of species associated with C-cycling functional genes. Besides directly adding recalcitrant C to the soil, biochar also indirectly enhanced C sequestration by weakly increasing soil carbon dioxide (CO2) emissions. However, replacing mineral fertilizer with manure significantly stimulated soil respiration in the tea plantation, resulting in a 36% increase in CO2 emissions over two years. The increase in CO2 emissions under the manure treatment was mainly attributed to the increased soil labile C pool, the activity of hydrolytic enzymes (e.g., cellobiohydrolase and acetylglucosaminidase), and the relative abundance of functional genes associated with the C-cycle. This may also be related to the application of manure that increased the abundance of Gemmatimonadetes and altered ecological clusters in bacterial co-occurrence networks. Our correlation network analysis suggested that Gemmatimonadetes might be the potential hosts for C-cycling genes due to their strong positive correlation with the abundance of C-cycling genes. Overall, these findings provide new insights into soil respiration under biochar amendment and manure application in tea plantations and broaden the options for carbon sequestration in soils. Highlights: Manure application rather than biochar amendment increased acidic soil respiration. Biochar application promoted soil C sequestration in the tea plantation. Manure application stimulated CO2 emissions by altering ecological clusters' abundance. Gemmatimonadetes might be the dominant hosts for C-cycling genes. [ABSTRACT FROM AUTHOR]

Despite the increasing impact of atmospheric nitrogen (N) deposition on terrestrial greenhouse gas (GHG) budget, through driving both the net atmospheric CO2 exchange and the emission or uptake of non‐CO2 GHGs (CH4 and N2O), few studies have assessed the climatic impact of forests and grasslands under N deposition globally based on different bottom‐up approaches. Here, we quantify the effects of N deposition on biomass C increment, soil organic C (SOC), CH4 and N2O fluxes and, ultimately, the net ecosystem GHG balance of forests and grasslands using a global comprehensive dataset. We showed that N addition significantly increased plant C uptake (net primary production) in forests and grasslands, to a larger extent for the aboveground C (aboveground net primary production), whereas it only caused a small or insignificant enhancement of SOC pool in both upland systems. Nitrogen addition had no significant effect on soil heterotrophic respiration (RH) in both forests and grasslands, while a significant N‐induced increase in soil CO2 fluxes (RS, soil respiration) was observed in grasslands. Nitrogen addition significantly stimulated soil N2O fluxes in forests (76%), to a larger extent in grasslands (87%), but showed a consistent trend to decrease soil uptake of CH4, suggesting a declined sink capacity of forests and grasslands for atmospheric CH4 under N enrichment. Overall, the net GHG balance estimated by the net ecosystem production‐based method (forest, 1.28 Pg CO2‐eq year−1 vs. grassland, 0.58 Pg CO2‐eq year−1) was greater than those estimated using the SOC‐based method (forest, 0.32 Pg CO2‐eq year−1 vs. grassland, 0.18 Pg CO2‐eq year−1) caused by N addition. Our findings revealed that the enhanced soil C sequestration by N addition in global forests and grasslands could be only marginally offset (1.5%–4.8%) by the combined effects of its stimulation of N2O emissions together with the reduced soil uptake of CH4. [ABSTRACT FROM AUTHOR]

Purpose: The purposes of this study are to characterize the relationship between basal soil respiration at 0 °C (R0) and the temperature sensitivity (Q10) of soil respiration and climate, soil, and vegetation factors and to establish R0 and Q10 models. Materials and methods: We compiled R0 and Q10 and variables (i.e., climate factors, soil properties, and vegetation characteristics) that were measured in various terrestrial ecosystems. Results and discussion: The results showed that both R0 and Q10 could generally be fitted by a normal distribution curve across various ecosystems, but they varied greatly among the different ecosystems. The lowest median R0 and Q10 appeared in the desert, while the highest median R0 and Q10 appeared in the deciduous broad-leaf forest and deciduous needle-leaf forest ecosystems, respectively. The relationship between R0 and Q10 across different soil depths varied among the different ecosystems, with the highest and lowest R2 occurring in the cropland (R2 = 0.701) and evergreen needle-leaf forest (R2 = 0.095), respectively. A model that included Q10, fine root production and the ratio of soil organic carbon to total nitrogen (TN) explained 75.0% (R2 = 0.750) of the variation in R0, with a P value less than 0.001. Q10 was further expressed as a model (R2 = 0.663, P < 0.001) including annual precipitation, mean air temperature, TN, bulk density, and leaf area index. Conclusions: Our R0 models can potentially be used to improve terrestrial carbon cycle models by considering the comprehensive effects of Q10 and soil and vegetation factors. [ABSTRACT FROM AUTHOR]

Aim: Drought has been shown to alter terrestrial ecosystem carbon (C) and nitrogen (N) dynamics, and thus feedback to future climate. However, drought‐induced changes in terrestrial upland C and N pools and the drought response of soil carbon dioxide (CO2) and nitrous oxide (N2O) fluxes are yet to be quantified. Location: Global upland ecosystems. Time period: 2000–2018. Major taxa studied: Terrestrial C and N fluxes. Methods: A meta‐analysis was conducted that compiled 1,344 measurements from 128 manipulative studies worldwide to obtain a general picture of terrestrial C and N cycling responses to soil drought stress and identify the primary driving factors. Results: We showed that drought significantly decreased plant C pools, with stronger negative responses of aboveground than belowground C components. Drought significantly decreased soil respiration (RS) and N2O fluxes by 19% and 29%, respectively. There were non‐significant changes in soil organic C and N pools in response to drought; in contrast to a considerable decrease in soil dissolved organic C (−22%), there was a robust increase in soil nitrate‐N (26%) following short‐term drought impact. By relating net ecosystem productivity (NEP) to the difference between net primary production (NPP) and soil heterotrophic respiration (RH), drought was found to drive a decrease up to −37% in NEP, being equivalent to a reduction in terrestrial net C uptake of 2.91 t C/ha. Main conclusions: Our study provides insights into soil release of CO2 and N2O with a linkage to the changes in terrestrial C and N pools in response to drought across upland biomes. Our findings highlight that, despite the lowered soil C release rate, the capacity of upland biomes as a C sink to slow climate change would still be weakened due to a robust decline of plant‐derived C input to soil in a future drier climate. [ABSTRACT FROM AUTHOR]

Warming can accelerate the decomposition of soil organic matter and stimulate the release of soil greenhouse gases (GHGs), but to what extent soil release of methane (CH4) and nitrous oxide (N2O) may contribute to soil C loss for driving climate change under warming remains unresolved. By synthesizing 1,845 measurements from 164 peer‐reviewed publications, we show that around 1.5°C (1.16–2.01°C) of experimental warming significantly stimulates soil respiration by 12.9%, N2O emissions by 35.2%, CH4 emissions by 23.4% from rice paddies, and by 37.5% from natural wetlands. Rising temperature increases CH4 uptake of upland soils by 13.8%. Warming‐enhanced emission of soil CH4 and N2O corresponds to an overall source strength of 1.19, 1.84, and 3.12 Pg CO2‐equivalent/year under 1°C, 1.5°C, and 2°C warming scenarios, respectively, interacting with soil C loss of 1.60 Pg CO2/year in terms of contribution to climate change. The warming‐induced rise in soil CH4 and N2O emissions (1.84 Pg CO2‐equivalent/year) could reduce mitigation potential of terrestrial net ecosystem production by 8.3% (NEP, 22.25 Pg CO2/year) under warming. Soil respiration and CH4 release are intensified following the mean warming threshold of 1.5°C scenario, as compared to soil CH4 uptake and N2O release with a reduced and less positive response, respectively. Soil C loss increases to a larger extent under soil warming than under canopy air warming. Warming‐raised emission of soil GHG increases with the intensity of temperature rise but decreases with the extension of experimental duration. This synthesis takes the lead to quantify the ecosystem C and N cycling in response to warming and advances our capacity to predict terrestrial feedback to climate change under projected warming scenarios. [ABSTRACT FROM AUTHOR]

• The soil respiration model used temperature, moisture, LAI, and soil properties as key variables. • The measured soil respiration in twenty-six agroecosystems in China well validated the model. • The modeled soil respiration varied greatly across regions and months in agroecosystems in China. Characterizing the seasonal patterns of soil respiration using a biophysical model is crucial for understanding the mechanisms of the terrestrial carbon (C) cycle. We developed a biophysical soil respiration model including four submodels that were associated with the functions of soil temperature, moisture, leaf area index (LAI), and soil organic C, and the model parameters were determined and calibrated. The modeling reproducibility was examined in various crop fields at our study site, and the modeling performance was also validated in twenty-five other agroecosystems in China. The monthly and annual soil respiration was estimated using the model, and the modeling uncertainty was evaluated. The results showed that the soil respiration model had good modeling reproducibility in various crop fields at our site. The measured soil respiration in the different agroecosystems in China validated our model well. The R 2, root mean squared error (RMSE), model efficiency (ME), and mean absolute error (MAE) were within the ranges of 0.449‒0.932, 0.526‒1.465 μmol m−2 s−1, 0.176‒0.796, and 0.312‒1.377 μmol m−2 s−1, respectively, across the twelve agroecosystem sites for validation. The measured soil respiration was significantly (P < 0.001) correlated with the modeled soil respiration across all twenty-six validation sites. Adding LAI significantly improved the modeling of soil respiration when the performance of the model (with LAI) vs. that without LAI was compared. The modeled monthly soil respiration was within the range of 0.016 ± 0.001‒0.117 ± 0.006 Pg C mo−1 in 2010 in agroecosystems in China. The black soils in Northeast China are fertile, which resulted in high temperature sensitivity and a clear increasing tendency of soil respiration from winter to summer in 2010 in agroecosystems in Northeast China. The established biophysical soil respiration model was proven to be effective for characterizing the temporal variations of soil respiration in various agroecosystems in China. [Display omitted] [ABSTRACT FROM AUTHOR]

Soil respiration ( R s ) is a key process in the terrestrial carbon cycle. Measurement and simulation of R s has received much attention recently. We collected annual R s field datasets to examine key controls of temporal and spatial variability in annual R s at the global scale. Published studies that reported annual field R s , mean annual temperature (MAT), annual precipitation (AP), soil (0–20 cm) properties and vegetation characteristics were compiled. MAT, AP and soil organic carbon (SOC) were the three most important variables in these datasets, together being responsible for 50% of the variance in annual R s in a global model (MAT&AP&SOC-model). Combining other site soil properties (e.g. pH) and vegetation variables, such as tree age (TA), tree height (TH), litter fall biomass (LF) and leaf area index (LAI), into the MAT&AP&SOC-model improved model performance. The site characteristic that explained the most variation in R s was AP followed by MAT, SOC, net primary productivity (NPP), pH, TA, TH, LF, LAI, elevation (EL) and diameter at breast height (DBH). Among the simulated models, the model based on MAT, AP, SOC and pH had the best fit for annual R s variance. There was a highly significant logarithmic relationship between R r / R s (the contribution of root respiration to R s ) and AP. The AP value of 0.4 m was a threshold for R r / R s , corresponding to R r / R s of 0.4 which reflects water limitation of root growth and plant productivity. [ABSTRACT FROM AUTHOR]

Litter decomposition is a fundamental ecosystem process in which breakdown and decay of plant detritus releases carbon and nutrients. Invasive exotic plants may produce litter that differs from native plant litter in quality and quantity. Such differences may impact litter decomposition and soil respiration in ways that depend on whether exotic and native plant litters decompose in mixtures. However, few field experiments have examined how exotic plants affect soil respiration via litter decomposition. Here, we conducted an in situ study of litter decomposition of an annual native grass (Eragrostis pilosa), a perennial exotic forb (Alternanthera philoxeroides), and their mixtures in an annual grassland in China to examine potential invasion effects on soil respiration. Alternanthera litter decomposed faster than Eragrostis litter when each was incubated separately. Mass loss in litter mixes was more rapid than predicted from rates in single species bags (only 35% of predicted mass remained at 8 months) showing synergistic effects. Notably, exotic plant litter decomposition rate was unchanged but native plant litter decomposition rate was accelerated in mixtures (decay constant k = 0.20 month−1) compared to in isolation (k = 0.10 month−1). On average, every litter type increased soil respiration compared to bare soil from which litter was removed. However, the increases were larger for mixed litter (1.82 times) than for Alternanthera litter (1.58 times) or Eragrostis litter (1.30 times). Carbon released as CO2 relative to litter carbon input was also higher for mixed litter (3.34) than for Alternathera litter (2.29) or Eragrostis litter (1.19). Our results indicated that exotic Alternanthera produces rapidly decomposing litter which also accelerates the decomposition of native plant litter in litter mixtures and enhances soil respiration rates. Thus, this exotic invasive plant species will likely accelerate carbon cycling and increase soil respiration even at intermediate stages of invasion in these annual grasslands. [ABSTRACT FROM AUTHOR]

Abstract: To develop a model describing the dependence of annual soil respiration on climate and soil properties, we compiled 657 published annual soil respiration (R s ) measurements that were assembled from 147 sites globally, representing croplands, grasslands, forests and tundra ecosystems. Each of these annual soil respiration data was then aggregated with the appropriate mean air temperature (T) and annual precipitation (P) data derived from geographically referenced datasets and with soil properties gathered from the original literature. Partial correlation analyses showed that global annual R s significantly related to annual mean temperature, annual precipitation, and topsoil (0–20cm) organic carbon (SOC) storage, while topsoil total nitrogen (SN) and pH did not show a direct and clear relationship with R s across ecosystems. While we employed the T&P-model that used temperature and annual precipitation to globally predict annual soil respiration, it was able to explain 41%, 57%, and 31% of the variability of soil respiration for croplands, grasslands and forests, respectively. However, the residuals were significantly related to SOC for croplands and grasslands. Thus, we developed a T&P&C-model that includes SOC as an additional predictor of annual R s . This extended but still simple model performed better than the T&P-model and explained 69%, 89%, and 47% of the interannual and intersite variability of R s with a mean absolute error of 0.11, 0.18 and 0.28kgCm−2 yr−1 for croplands, grasslands and forests, respectively. Overall, the modeling efficiency of the T&P&C-model was nearly 60% across ecosystems. Globally, the mean turnover time of topsoil carbon (SOC/R s ) was highly comparable among croplands, grasslands and forests, equivalent to 6.1–6.3 years. Therefore, better estimates of global annual soil respiration would be obtained with the new model driven by climate and soil properties together. We expect significant improvements of global annual soil respiration predictions given that measurements of soil respiration coupling with soil properties and site productivities are widely taken across ecosystems over the world. [Copyright &y& Elsevier]

Grassland ecosystems are sensitive to invasions by plants from other functional groups which can alter soil greenhouse gas (GHG) fluxes. However, the effects of plant invasion on net GHG exchanges between soils and the atmosphere, plant production, and global warming potential (GWP) of annual grasslands is poorly understood. To evaluate the impacts of perennial forb invasions on GHG budgets of an annual grassland in China, we measured soil carbon dioxide (CO 2 ), methane (CH 4 ), and nitrous oxide (N 2 O) fluxes over two years in replicated invaded (dominated by Alternanthera philoxeroides or Solidago canadensis ) and non-invaded (dominated by the annual grass Eragrostis pilosa or the annual forb Sesbania cannabina ) field sites. On average, soil CO 2 and N 2 O emissions from invaded sites were 30% and 76% higher, respectively, relative to sites dominated by native species. Emissions of N 2 O and CO 2 were especially high in Solidago and Alternanthera dominated sites, respectively. Soil CH 4 emissions did not vary with plant species. On average, total biomass C of invaded sites was higher than that of the native dominated sites but this reflected the high C in Solidago dominated sites. Global warming potential (GWP) was increased by Alternanthera invasions and decreased by Solidago invasions. Plant invasions affected GWP of these annual grasslands through higher emissions of some GHGs but also sometimes higher biomass C. Together, this suggests that perennial forb invasions could change the net source or sink role of annual grasslands for GHG budgets, but the effects on GWP vary among species depending on GHG responses and C storage. [ABSTRACT FROM AUTHOR]