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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]

The vulnerability of plant xylem to embolism can be described as the water potential at which xylem conductivity is lost by 50% (P50). According to the traditional hypothesis of hydraulic vulnerability segmentation, the difference in vulnerability to embolism between branches and roots is positive (P50 root−branch > 0). It is not clear whether this occurs broadly across species or how segmentation might vary across aridity gradients. We compiled hydraulic and anatomical datasets from branches and roots across 104 woody species (including new measurements from 10 species) in four biomes to investigate the relationships between P50 root–branch and environmental factors associated with aridity. We found a positive P50 root–branch relationship across species, and evidence that P50 root–branch increases with aridity. Branch xylem hydraulic conductivity transitioned from more efficient (e.g., wider conduit, higher hydraulic conductivity) to safer (e.g., narrower conduit, more negative P50) in response to the increase of aridity, while root xylem hydraulic conductivity remained unchanged across aridity gradients. Our results demonstrate that the hydraulic vulnerability difference between branches and roots is more positive in species from arid regions, largely driven by modifications to branch traits. [ABSTRACT FROM AUTHOR]

• Soil fungal community shifted from symbiotroph and saprotroph species towards pathotroph species with increased soil nutrients after two decades along a shrub plantation chronosequence. • Changes in microbial community composition and more fragmented network structure preceded the degradation of shrub physiology and biomass after 40 years. • A breakdown in soil microbial community structure can be an early warning sign of declines in shrub productivity and land degradation. Large-scale restoration is intended to promote ecological recovery. Improvements in plant and microbial conditions, however, may slow or even reverse in late succession. To better understand long-term restoration outcomes and underlying drivers of successional pathways, we tracked plant, bacterial and fungal, and soil conditions across a 40-year shrub plantation that was intended to stabilize desertified land in northern China. We found that planted Haloxylon ammodendron shrubs developed and then subsequently became degraded after 30–40 years. Bacterial abundance and α-diversity were much higher than those of fungi, but no significant differences in composition and structure were found in different plantation ages. In contrast, the dominant taxa of fungal communities shifted from symbiotroph and saprotroph species towards pathotroph species with increased soil nutrients in the plantation chronosequence after two decades. The changes in fungal dominant species led to a transition in microbial network structure and function, with an increase in negative linkages among taxa that began in the middle stages of succession. Changes in fungal community structure had direct and indirect negative effects on shrub leaf physiology, root activity, and biomass. Our results highlight the preceding role of a breakdown in soil microbial community composition and network structure on the degradation of shrub performance in long-term desert succession. Our study emphasizes the importance of understanding soil-microbial-plant linkages on restoration outcomes, and mechanisms that can slow or reverse the recovery of ecosystems. [ABSTRACT FROM AUTHOR]

Straw return has been widely used to increase SOC storage globally, but such C accrual is frequently constrained by other nutrients which are needed to maintain soil ecological stoichiometry balance. However, the impact of fertilization on SOC stocks under straw return remains unexplored at broad spatial scales. We constructed a national-scale dataset to explore the fertilization effect on SOC stocks (0–20 cm) under straw return and identified the dominant drivers and pathways in upland and paddy systems across China. On average, straw return enhanced SOC stocks and sequestration rate by 1.74 Mg C ha−1 and 0.27 Mg C ha−1 y−1 relative to straw removal (CK). Yet, straw co-applied with nutrient enrichment further increased SOC stock and sequestration rate by 0.81 Mg C ha−1 and 0.12 Mg C ha−1 y−1, compared to straw return only. These results indicated a general nutrient limitation on SOC sequestration under straw return. The fertilization effect on SOC stocks varied greatly across nutrient enrichment types and cropping systems, with greater soil C gain occurring under balanced fertilization (i.e., NPK) and more in uplands than in paddy fields. In the uplands, SOC sequestration with fertilization was positively correlated with increased belowground biomass. In paddy fields, however, improved biomass with fertilization did not translate into increased SOC accumulation, owing to the co-limitations of soil acidification and initial SOC. We further clarified the differential pathways by which chemical fertilization altered SOC stocks, i.e., productivity pathway in uplands but decomposition pathway in paddy fields. These mechanistic insights on the fertilization control over SOC can help us optimize the context-specific integrated straw and fertilization management strategies for greater SOC sequestration, and also inform the development of soil C projections by incorporating fertilization management into biogeochemical models in agroecosystems. [Display omitted] • Nutrient limitation of SOC stocks under straw return was assessed across China. • Balanced fertilization promoted SOC sequestration under straw return. • SOC gain due to fertilization was much higher in uplands than in paddy fields. • Improved productivity with fertilization did not translate into increased SOC in paddies. • Fertilization modified SOC stocks via differential pathways across cropping systems. [ABSTRACT FROM AUTHOR]