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Biocrusts are critical biological components of drylands and play an important role in soil carbon (C) cycling. However, the effect of biocrusts on soil CO 2 exchange across global gradients of temperature and moisture is poorly understood. Moreover, their response to climate change remains highly uncertain. Bayesian hierarchical meta-analyses were performed on 47 published studies to quantify the impact of biocrusts on net soil exchange (NSE) of carbon- the difference between respiration and photosynthesis. Meta-analyses were also used on 23 studies to examine the effects of experimental warming on NSE in biocrusts. Meta-regressions further explored the thermal and wetness sensitivities of biocrust NSE and potential adaptation of biocrust responses to climate change. The development of biocrusts in dryland soils significantly increased NSE by 66.5 [22.2, 112.2] g C m−2yr−1, despite seasonal fluctuations, indicating a net loss of carbon to the atmosphere. Experimental warming, on average, increased biocrust NSE by 22.9 [-0.1, 40.8] g C m−2yr−1 per °C. However, across the spatial climate gradient, aridity limited the effects of warming, while high temperature decreased the thermal sensitivity of biocrust NSE, thus supporting the thermal adaptation of biocrusts. These results emphasize the critical role of biocrusts in modulating soil carbon exchange in response to climate warming across drylands, with particularly high thermal sensitivity in cool and moist regions. This highlights the need to incorporate biocrusts into global carbon budgets and models for a comprehensive understanding of their impact on the carbon cycle. • Biocrusts increase soil CO2 efflux by 66.5 g C m-2yr-1 in drylands worldwide. • Climate warming increases CO2 efflux in biocrust soil by 22.9 g C m-2yr-1 per °C. • Thermal adaptation reduces thermal sensitivity of biocrust carbon efflux. [ABSTRACT FROM AUTHOR]

Abstract: This study used a 40‐year chronosequence of Haloxylon ammodendron plantations to evaluate its impacts on soil and vegetation conditions in a desert–oasis ecotone with extremely low annual precipitation (≈100 mm). We found that the fraction of silt and clay contents significantly increased from 6.4% and 5.1% in Year 0 to 22–23.3% and 15.8–18% in the 40‐year‐old plantation in the soil depths of 0–10 and 10–20 cm, respectively. Soil nutrients (i.e., soil organic matter, total nitrogen, and total phosphorus) were significantly improved after H. ammodendron plantations. However, there was a significant increase in soil salinity, which may negatively affect sustainability of ecosystem restorations in future (drier and warmer) climate. Planted H. ammodendron established and thrived in the first 25 years, but the percent vegetation cover started to decrease afterwards because of reduction in deep soil moisture and less access to groundwater. By comparison, herbaceous plants gradually developed after H. ammodendron plantations and finally dominated the ecosystems with high density (300–400 herbs·m−1), cover (25–30%), and biomass (50–60 × 10−3 kg·m−2) after 30–40 years. These results suggest that although introduced shrubs can act as nurse plants to improve vegetation and soil conditions, their dominance could be a transient state. Thus, evaluation of ecosystem restoration through plantations should use long‐term data, and the stable plant restorations for years or even decades could be a transient state and does not necessarily suggest a successful revegetation effort in the long run. Further, its environmental consequences (i.e., soil salinity) of shrub plantations need to be evaluated in ecosystem restorations especially in a changing and harsh environment. [ABSTRACT FROM AUTHOR]

Intensified anthropogenic activities have drastically altered many ecosystems, motivating the use of restoration to regain key ecosystem functions and services and to stem biodiversity losses. Restoration is particularly difficult when human activities have pushed an area into a new state with self‐reinforcing feedbacks. This study investigated a long‐term restoration project in a dryland ecosystem of the Tengger Desert in northwestern China, initiated in 1956. We analyzed shrub and grass cover for 49 yr after the installation of restoration infrastructure that altered external conditions (i.e., using packed straw to reduce wind erosion) and system state (by planting shrubs). After 37–40 yr, the re‐vegetation project was successful in restoring the system to a state similar to native vegetation, with high grass cover (30–50%), low shrub cover (8–10%), and a thick biological soil crust (biocrust). However, the shift to high grass cover did not begin until year 37, before which shrub cover was high (15–20%) and grasses were subdominant (usually <10%). The shift from shrub to grass dominance was abrupt, registering significant nonlinear changes over time and relative to a key driver of vegetation dynamics, estimated biocrust thickness. Biocrust thickness increased gradually over time, which reduced rainfall infiltration into deep soil and thus increased soil moisture available for the shallow‐rooted grasses. The shift from the bare soil state to the steppe state exhibited a long time lag, suggesting that it can take decades to determine whether dryland restoration efforts succeed. The results indicate that persistence might be critical to forcing desired state transitions and that dryland restoration can proceed as a series of time lags, punctuated by abrupt changes in ecosystem state. [ABSTRACT FROM AUTHOR]

When restoring dryland ecosystems, growing biological soil crust (biocrust) may greatly change the redistribution of rainfall in layered soils. However, ecohydrological modelling studies generally ignore biocrust and thus, the ecohydrological effects of biocrust on restorations remain largely unexplored. Using a long-term restoration case (located in the southeast edge of the Tengger Desert, northern China), we developed an ecohydrological model with explicit consideration of the infiltration in three layered soils (biocrust, shallow and deep sand layers) to investigate influences of biocrust on restoration dynamics in drylands. The proportion of infiltration that reaches ‘annual grass’ (including biocrust and shallow sand layers, 0–30 cm) and ‘shrub’ layers (30–150 cm) with biocrust significantly increased and decreased relative to the values without biocrust, respectively. Meanwhile, biocrust significantly decreased soil water content in deep sand layer, but not in shallow sand layer. As more water was used by transpiration than evaporation, the ecosystem with biocrust reached a final grass-dominated state (high grass cover of 40%, low shrub cover of 4%) rather than a shrub-dominated state (grass cover of 3%, shrub cover of 20%). This study suggests that we need to account for the roles of biocrust on rainfall infiltration to better understand vegetation and restoration dynamics in dryland ecosystems. [ABSTRACT FROM AUTHOR]