Search

Biocrusts are special components of dryland ecosystems and play important roles in ecosystem carbon cycles. Vegetation restoration not only affects carbon storage but also changes the characteristics of biocrusts. However, how vegetation restoration influences the contribution of biocrusts to soil carbon cycling in dryland ecosystems is poorly understood.Using continuous field measurements combined with metagenomic shotgun sequencing, we explored the effect and regulatory mechanisms of Caragana korshinskii vegetation restoration on the contribution of biocrusts to total soil respiration.We found that vegetation restoration increased the contribution of biocrusts to total soil respiration, with the biocrust contribution increasing from −5.6% for mixed biocrusts in a typical steppe to 17.1%, 18.1% and 19.6% for cyanobacteria–algae, lichen and moss biocrusts, respectively, in a Caragana korshinskii vegetation restoration area. The driving factors for total soil respiration changed from solely soil temperature to soil temperature and moisture after vegetation restoration. In contrast, the driving factors for soil respiration estimated for biocrust layers changed from precipitation alone to soil temperature and precipitation after vegetation restoration. We reveal that changes in microbial functional structure play important roles in regulating the effect of vegetation restoration and biocrusts on soil respiration. In addition, vegetation restoration also increases the microbial activity in biocrusted soils.This calls for an improved understanding of the effects of biocrusts on soil respiration under vegetation restoration scenarios to advance our ability to evaluate soil carbon releases from dryland ecosystems. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) in shrublands is an important component of global carbon cycling. However, there is a dearth of large-scale systematic observations of SOC stocks at different soil depths, and it remains uncertain whether and how the relative importance of biotic and abiotic variables in regulating SOC stocks changes with soil depth. Here, we quantified large-scale patterns and controlling factors of SOC storage per area (SOCD, kg m−2) for both topsoils (0–30 cm) and subsoils (30–100 cm) by taking full advantage of a consistent stratified random sampling study of one-meter soil profiles across 1211 sites in Chinese shrublands. We found that subsoils stored about 53.30% of total SOCD, falling into the range of previously reported values for terrestrial ecosystems. SoilGrids250m model-derived assessments overestimated SOCD by 13.72 and 65.49% for topsoils and subsoils, respectively. The effects of climate means and seasonality on SOCD were equally strong in both topsoils and subsoils. The predominant effects of edaphic properties on SOCD were more robust in subsoils than in topsoils. Belowground biomass of shrublands was the only significant predictor of topsoil SOCD, but it did not predict subsoil SOCD accurately. These findings have refined our understanding of the pivotal role of shrublands in SOC storage and sequestration potential and could serve as an ecologically valuable baseline for large-scale improvement and validation of depth-dependent SOC dynamics for multilayer SOC modules in Earth Systems Models. [ABSTRACT FROM AUTHOR]

Purpose: To assess the direction and strength of climate and leaf litter trait effects on decomposition dynamics throughout the litter decomposition process. Methods: We performed a three-year-long litterbag translocation experiment along an elevational gradient in a transitional mixed forest in China. We explored temporal shifts in the relative contribution of microclimate and litter traits of seven dominant species to mass loss throughout the decomposition process. Results: Air temperature and soil moisture imparted no significant effects on mass loss in the initial decomposition stage (0–6 months) but exerted positive effects after 6 months' incubation (p < 0.05). Initial specific leaf area (SLA) was positively associated with mass loss only during the early decomposition stages (0–12 months). Litter P concentration was positively while N concentration was negatively associated with mass loss for almost all decomposition stages. Both litter Mg and Ca concentrations were negatively associated with mass loss throughout the whole decomposition process (p < 0.05). The relative contribution of microclimate was weaker than that of litter traits during the early stages but increased in the late decomposition stage (after 36 months). SLA and Mg were the most important traits during the early stages (0-12 months), whereas N and Mg were relatively stronger during the later stages (30–36 months). Conclusion: Our results have highlighted that microclimate (particularly temperature) exerted dominant control over later-stage litter decomposition. Often-overlooked litter traits such as Mg, are key potential drivers of litter decomposition dynamics and should be more explicitly incorporated into current biogeochemical models to better understand litter-driven nutrient and carbon cycling. [ABSTRACT FROM AUTHOR]

Carbon sinks in terrestrial ecosystems can be significantly increased by afforestation, which will slow global warming. However, it is still unclear how different plantations influence the carbon sink and how they respond to environmental factors, especially in drylands. In this study, eddy correlation method (EC) was used to measure carbon and water fluxes and environmental factors of two artificial forests (Larix principis-rupprechtii and Pinus tabulaeformis) in the dryland of Northwest China, and the responses of evapotranspiration (ET), net ecosystem exchange (NEE), gross primary productivity (GPP), and ecosystem respiration (RECO) to environmental factors were also assessed. Results showed that the L. principis-rupprechtii forest ecosystem had higher water use efficiency (WUE), light use efficiency (LUE), GPP, and RECO than the P. tabulaeformis forest ecosystem. However, the proportion of net ecosystem production (NEP) to GPP in the P. tabulaeformis forest ecosystem (62.89%) was higher than that in the L. principis-rupprechtii forest ecosystem (47.49%), indicating that the P. tabulaeformis forest ecosystem had the higher carbon sequestration efficiency. In addition, the CO2 and H2O fluxes in the L. principis-rupprechtii forest ecosystem were more sensitive to environmental factors, compared with the P. tabulaeformis forest ecosystem. Further, the RECO of the L. principis-rupprechtii forest ecosystem was more sensitive to temperature changes, which implies that the L. principis-rupprechtii forest ecosystem will release more CO2 than the P. tabulaeformis forest ecosystem with a warming climate. Therefore, the P. tabulaeformis forest ecosystem may have better carbon sequestration potential. These results are important for understanding the effects of climate change on the CO2 and H2O cycles in coniferous plantation ecosystems in drylands. [ABSTRACT FROM AUTHOR]

Plants often adjust their leaf mitochondrial ("dark") respiration (Rd) measured at a standardized temperature such as 20°C (R20) downward after experiencing warmer temperatures and upward after experiencing cooler temperatures. These responses may help leaves maintain advantageous photosynthetic capacity and/or be a response to recent photosynthate accumulation, and can occur within days after a change in thermal regime. It is not clear, however, how the sensitivity and magnitude of this response change over time, or which time period prior to a given measurement best predicts R20. Nor is it known whether nighttime, daytime, or 24‐hour temperatures should be most influential. To address these issues, we used data from 1620 Rd temperature response curves of 10 temperate and boreal tree species in a long–term field experiment in Minnesota, USA to assess how the observed nearly complete acclimation of R20 was related to past temperatures during periods of differing lengths. We hypothesized that R20 would be best related to prior midday temperatures associated with both photosynthetic biochemistry and peak carbon uptake rates that drive carbohydrate accumulation. Inconsistent with this hypothesis, prior night temperatures were the best predictors of R20 for all species. We had also hypothesized that recent (prior 3–10 days) temperatures should best predict R20 because they likely have stronger residual impacts on leaf‐level physiology than periods extending further back in time, whereas a prior 1‐ to 2‐day period might be a span shorter than one to which photosynthetic capacity and Rd adjust. There was little to no support for this idea, as for angiosperms, long time windows (prior 30–60 nights) were the best predictors, while for gymnosperms both near‐term (prior 3–8 nights for pines, prior 10–14 nights for spruce/fir) and longer‐term periods (prior 45 nights) were the best predictors. The importance of nighttime temperatures, the relatively long "time‐averaging" that best explained acclimation, and dual peaks of temporal acclimation responsiveness in some species were all results that were unanticipated. [ABSTRACT FROM AUTHOR]

Background and aims: Despite the important role of biological soil crusts in the soil carbon cycles of desert ecosystems, the responses of soil respiration in biological soil crust-dominated areas to warming are not well understood. The goal of this study was to investigate the expected increases in temperature on soil respiration both diurnally and seasonally in biological soil crust-dominated areas. Methods: We used open-top chambers to simulate warming in the Shapotou region in the Tengger Desert, northern China. An automated soil respiration system was used to measure the soil respiration rates in moss-dominated crusts. The measured environmental variables included the precipitation, volumetric soil water content, air temperature and soil temperature at depths of 0, 5, 10, 20, and 50 cm. Results: The response of soil respiration to warming is a function of soil moisture following rainfall in desert ecosystems. Our results showed that 1.5 °C of simulated warming significantly decreased soil respiration, indicating that the inhibition of soil respiration was likely due to the reduction in soil water content at a relatively high temperature. Over daily cycles, hourly soil respiration rates have commonly been related to hourly temperatures. The observed diel hysteresis between hourly soil respiration and temperature resulted in semielliptical hysteresis loops, and the temperature often lagged behind soil respiration for several hours. The lag times between soil respiration and temperature were significantly and positively related to the depth of the soil temperature measurements. The proximate reason for the diel hysteresis between soil respiration and temperature was likely a mismatch between the depth of CO2 production and the depth of the temperature measurements. Conclusions: Our results indicate that warming increases the response of soil respiration to soil water availability in biological soil crust-dominated desert ecosystems. Therefore, the accelerated drying effect of warming on soil respiration and diel soil respiration patterns between soil respiration and temperature at different depths should be considered in future soil carbon cycle models for biological soil crust-dominated desert ecosystems. [ABSTRACT FROM AUTHOR]

Aims: Our understanding of the determinants of leaf litter decomposition is lacking for mixed evergreen and deciduous broad-leaved forests compared with tropical and temperate forests. This study aimed to assess the relative importance of litter properties, climate and soil on decomposition in a mixed above-mentioned forest in a transitional zone, central China. Methods: We utilized leaf litter from seven canopy tree species in conjunction with a transplant litterbag experiment along an elevational gradient over three years by measuring decomposition rate. Results: Initial leaf litter nitrogen (N), phosphorus (P) and magnesium (Mg) as well as C:P were robust predictors of leaf litter decomposition. Mg was the single best predictor of leaf litter decomposition across all species. Soil moisture and air temperature could predict leaf litter decomposition very well across the elevational gradient. The explanatory power of elevation-related variables (27.75 %) was much lower than that of species-related variables (38.97 %). Conclusions: More nutrients such as Mg than N and P commonly used in proposed indices should be taken into account when evaluating the decomposability of leaf litter. Tree species identity is the most important determinant of leaf litter decomposition in this target transitional mixed forest. Therefore, shifts in tree species composition may influence leaf litter decomposition rates more than changes in site conditions under the context of future climate change. [ABSTRACT FROM AUTHOR]

• Soil respiration in BSC-dominated areas was suppressed under warmer conditions. • The inhibited soil respiration by warming was greater on the moss than lichen crust. • Soil respiration in BSC-dominated areas was significantly induced by rainfall pulses. • Diel hysteresis between soil respiration and temperature was modified by rainfall. Biological soil crusts (BSCs) across desert ecosystems play an important role in modulating terrestrial carbon cycles. Global warming and changes in precipitation patterns are expected to be important triggers for biological activity in BSC-dominated desert ecosystems. Therefore, it is crucial to study the effects of warming and rainfall pulses on soil respiration dynamics at BSC-dominated microsites to predict terrestrial carbon cycling under climate change. In this study, soil respiration rates were monitored continuously during three types of natural precipitation events in lichen-dominated and moss-dominated crusts in both control and warming treatments. Our results revealed that soil respiration was inhibited in BSC-dominated microsites in the warming treatment because of reduced soil water content induced by the warmer conditions, and that the extent of inhibition was lower in the lichen-dominated crusts than in the moss-dominated crusts. During all the precipitation events, soil respiration rates were significantly increased by rainfall pulses and gradually declined thereafter. Over the daily cycle, the clockwise diel hysteresis loop between soil respiration and soil temperature was modified by soil water availability, which was affected by the magnitude of rainfall pulses. Moreover, the effect of photosynthetically active radiation and the mismatch between the depth of carbon dioxide (CO 2) production and soil temperature measurement may have contributed to the diel hysteresis pattern. Our results indicated that warming and different types of precipitation events in BSC-dominated desert ecosystems impact soil carbon release through changes in the magnitude of soil respiration. [ABSTRACT FROM AUTHOR]

Rainfall pulses are one of the most important factors affecting soil respiration, especially in drylands where water is limited. Biocrusts are also crucial in dryland ecosystems and play important roles in regulating soil carbon cycling. However, it is unclear how biocrusts mediate the effects of rainfall pulses on soil respiration. Using continuous field monitoring, we explored whether and how different types of biocrusts (including cyanobacteria-, lichen- and moss-dominated biocrusts) modulate the effects of precipitation on soil respiration under drying-rewetting cycles at event and seasonal scales. We found that soil respiration was induced after rainfall pulses, especially at different types of biocrusted microsites. The increments of soil respiration during drying-rewetting cycles were greater in the moss-dominated biocrusts than in the bare soil, which suggested that the response of soil respiration to drying-rewetting cycles was increased by moss-dominated biocrusts. The length of the dry period, number of cycles, intensity of the dry period and frequency of rewetting affected the magnitude of soil respiration at event scales. However, when we analysed all of the drying-rewetting cycles together, that is, at the seasonal scale, the soil temperature was the driving factor affecting the maximum soil respiration after rainfall pulses. Therefore, soil temperature, rather than soil moisture, is the key factor regulating the response of soil respiration to drying-rewetting cycles at the seasonal scale. This study highlights the importance of temperature in regulating soil respiration under drying-rewetting cycles, and the regulatory factors of soil respiration vary at different temporal scales. • Biocrusts augment the effect of precipitation on soil respiration. • The effects of rainfall on soil respiration vary with drying-rewetting events. • Rainfall itself affects the magnitude of soil respiration at the event scale. • Soil temperature drives the effect of rainfall on soil respiration at the seasonal scale. • The driving factors of soil respiration vary at different temporal scales. [ABSTRACT FROM AUTHOR]

Biological soil crusts (biocrusts), specialized communities of cyanobacteria, lichens, mosses, fungi and bacteria occurring on the ground surface, are key drivers of soil carbon (C) cycles in drylands, yet our understanding of how biocrusts directly and indirectly (through soil temperature or moisture) affect soil respiration and the contributions of biocrusts to soil C efflux is very limited. Using continuous field measurements in bare and biocrusted soils, we assessed the influence of biocrusts on soil respiration and the biocrust contribution to soil respiration over a one-year period and explained the mechanisms by which biocrusts directly and indirectly regulate soil respiration. Although the overall effect of biocrusts on soil respiration was positive, contrasting effects of biocrusts on soil respiration were also found. Unfortunately, the indirect effect of biocrusts on soil respiration through soil temperature or moisture was nonsignificant. The driving factor of total soil respiration was soil temperature, but soil moisture, photosynthetically active radiation and precipitation were driving factors for soil respiration in the biocrust layer. We proposed conceptual frameworks to explain the contrasting mechanisms by which biocrusts modulate soil respiration. In addition, biocrusts decreased the temperature sensitivity of soil respiration. Our findings indicate that biocrusts may alter the driving factors, forming contrasting mechanisms to regulate soil respiration in the biocrust layer, and emphasize the important roles of biocrusts as modulators of C cycles in dryland soils. Incorporating biocrusts into terrestrial C process models may improve predictions of climate change impacts on dryland ecosystems. • The direct effect of biocrusts on soil respiration was either negative or positive. • The indirect effect of biocrusts via soil temperature or moisture was nonsignificant. • Contrasting mechanisms may regulate soil respiration in the biocrust layer. • Biocrusts decreased the temperature sensitivity of soil respiration. • Biocrusts are important modulators of carbon cycles in dryland soils. [ABSTRACT FROM AUTHOR]

• The diel cycles of soil respiration peaked earlier than did the soil temperature. • Similar clockwise hysteresis loops were found at both bare and biocrusted microsites. • Biocrusts slightly affected the diel hysteresis pattern. • Photosynthesis may be the key driver of diel hysteresis pattern regulation. Soil respiration is an important ecosystem process in drylands and is closely related to soil temperature but often occurs out of phase with soil temperature. As ecosystem engineers in dryland ecosystems, biological soil crusts (biocrusts) greatly affect soil carbon cycle processes, such as soil respiration. However, the diel hysteresis pattern between soil respiration and soil temperature at biocrusted microsites and its influencing factors are not well understood. Here, we performed continuous field measurements of in situ soil respiration to evaluate the effect of biocrusts on the diurnal cycles of soil respiration and the influencing factors of the diel hysteresis pattern between soil respiration and soil temperature at biocrusted microsites. Over daily cycles, soil respiration peaked earlier than soil temperature, and their relationship exhibited similar clockwise hysteresis loops at both bare and biocrusted microsites. Unexpectedly, the effect of biocrusts on the diel hysteresis pattern between soil respiration and soil temperature was negligible. However, photosynthesis may be the key driver regulating the diel hysteresis pattern between soil respiration and soil temperature, because little or even no hysteresis was observed between soil respiration and photosynthetically active radiation. Our results highlight the important role of photosynthate transportation in plants or biocrusts in diel hysteresis pattern regulation between soil respiration and soil temperature. [ABSTRACT FROM AUTHOR]