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International audience• Context A large area of abandoned land in the semiarid temperate region of China has been converted into plantations over the past decades. However, little information is available about the ecosystem C storage in different plantations. • Aim and methods Our objective was to estimate the C storage in biomass, litter, and soil of four different plantations (monospecific stands of Larix gmelinii, Pinus tabuliformis, Picea crassifolia, and Populus simonii). Tree component bio-mass was estimated using allometric equations. The bio-masses of understory vegetation and litter were determined by harvesting all the components. C fractions of plant, litter, and soil were measured. • Results The ecosystem C storage were as follows: Picea crassifolia (469 t C/ha)>Larix gmelinii (375 t C/ha), Populus simonii (330 t C/ha) > Pinus tabuliformis (281 t C/ha) (P<0.05), 59.5–91.1 % of which was in the soil. The highest tree and understory C storage were found in the plantation of Pinus tabuliformis (247 t/ha) and Larix gmelinii (1.2 t/ha) respectively. The difference in tree C fraction was significant among tree components (P<0.05), following the order: leaf> branch>trunk>root. The highest soil C (SC) was stored in Picea crassifolia plantation (411 t C/ha), while Populus simonii plantation had a higher SC sequestration rate than others. • Conclusion C storage and distribution varied among differ-ent plantation ecosystems. Coniferous forests had a higher live biomass and litter C storage. Broadleaf forests had consider-able SC sequestration potential after 40 years establishment

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1. Temporal stability of primary productivity is the key to stable provisioning of ecosystem services to human beings. Yet, the effects of various global changes on grassland stability remain ambiguous.2. Here, we conducted a comprehensive meta-analysis based on 1070 multi-year paired observations from 173 studies, to examine the impacts of various global changes on productivity, community stability and plant diversity of grasslands on a global scale. The global change drivers include nitrogen (N) addition, phosphorus (P) addition, N and P addition, precipitation increase, precipitation decrease, elevated CO 2 and warming.3. Global change drivers generally had stronger impacts on grassland productivity than on temporal stability, except for precipitation changes. Community temporal stability was reduced by N addition, N and P addition and precipitation decrease, but was increased by precipitation increase and remained unchanged under P addition, elevated CO 2 and warming. In addition, species richness decreased under N addition, N and P addition and precipitation decrease. At the plant functional group level, N and P addition reduced grasses' stability and precipitation increase enhanced forbs' stability.4. Nutrient additions decreased community stability via increasing the inter-annual variation more than the mean of primary productivity, while precipitation changes mainly affected community temporal stability via changing mean productivity. The negative impacts of global change drivers (i.e. N and P addition, warming) on community temporal stability increased with the degree of species loss but decreased with increasing stability of grasses. Moreover, the negative impacts of nutrient addition and precipitation decrease on community stability was lessened while the positive effect of precipitation increase on community stability was enhanced in grasslands with higher historical precipitation variability, greater soil fertility and longer experimental duration. 5. Synthesis. Our findings demonstrate that N-based nutrient additions and drought destabilise grassland productivity, while precipitation increase enhances community stability. Impacts of global changes on community productivity and stability are mediated by species richness, plant functional group, site-specific | 2851

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Grazing exclusion is a common management strategy for improving grasslands degraded due to overgrazing. Although previous meta‐analyses proved that grazing exclusion improved soil carbon (C) storage of grasslands in China, we know little about its effect on grassland ecosystems elsewhere and whether litter accumulation induced by grazing exclusion regulates soil C storage. Using meta‐analysis, we integrated 91 publications to examine the effects of grazing exclusion on community litter and soil C storage, accompanied by analysis of the regulating roles of body size of herbivore, climatic conditions, and grazing exclusion duration. We found that grazing exclusion enhanced litter biomass and decomposition rate but did not change litter chemical quality. Generally, grazing exclusion enhanced plant production and soil C storage across grassland worldwide. Exclusion of medium and small herbivores had stronger effects on aboveground litter production and soil C storage than exclusion of large herbivores, and grazing exclusion's enhancement on litter production and soil C storage tended to increase as grazing exclusion proceeded. Notably, grazing exclusion‐induced increase in aboveground litter biomass was attributed to the increase in biomass of graminoids, while root biomass, not aboveground litter biomass, primarily regulated the increase in soil C storage. The stimulating effect of grazing exclusion on soil C storage was enhanced possibly due to enhanced root biomass response along a precipitation gradient. Generally, our study provided new insights that management practice under grazing exclusion should take plant community dynamics, grazing exclusion duration, preceding grazer type, and climate conditions into account simultaneously.