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Identifying the thresholds for the positive responses of total net primary productivity (NPP) to nitrogen (N) enrichment is an essential prerequisite for predicting the benefits of N deposition on ecosystem carbon sequestration. However, the responses of below-ground NPP (BNPP) to N enrichment are unknown in many ecosystems, which limits our ability to understand the carbon cycling under the scenario of increasing N availability. We examined the changes in above-ground NPP (ANPP), BNPP, and NPP of a temperate meadow steppe across a wide-ranging N addition gradient (0, 2, 5, 10, 20, and 50 g N m -2  year -1 ) during 5 years. Both ANPP and NPP increased nonlinearly with N addition rates. The N saturation threshold for ANPP (T A ) and NPP (T N ) was at the rate of 13.11 and 6.70 g N m -2  year -1 , respectively. BNPP decreased with increasing N addition when N addition rates ˃5 g N m -2  year -1 , resulting in much lower T N than T A . Soil N enrichment played a key role in driving the negative impacts of high N addition rates on BNPP, and consequently on the earlier occurrence of N saturation threshold for NPP. Our results highlight the negative effects of soil N enrichment on NPP in natural grasslands super-saturated with N. Furthermore, by considering ANPP and BNPP simultaneously, our results indicate that previous findings from above-ground might have over-estimated the positive effects of N deposition on primary productivity., (© 2023 John Wiley & Sons Ltd.)

Elucidating mechanisms underlying community assembly and biodiversity patterns is central to ecology and evolution. Genome size (GS) has long been hypothesized to potentially affect species' capacity to tolerate environmental stress and might therefore help drive community assembly. However, its role in driving β-diversity (i.e., spatial variability in species composition) remains unclear. We measured GS for 161 plant species and community composition across 52 sites spanning a 3200-km transect in the temperate grasslands of China. By correlating the turnover of species composition with environmental dissimilarity, we found that resource filtering (i.e., environmental dissimilarity that includes precipitation, and soil nitrogen and phosphorus concentrations) affected β-diversity patterns of large-GS species more than small-GS species. By contrast, geographical distance explained more variation of β-diversity for small-GS than for large-GS species. In a 10-year experiment manipulating levels of water, nitrogen, and phosphorus, adding resources increased plant biomass in species with large GS, suggesting that large-GS species are more sensitive to the changes in resource availability. These findings highlight the role of GS in driving community assembly and predicting species responses to global change., (© 2022 The Authors. Ecology published by Wiley Periodicals LLC on behalf of The Ecological Society of America.)

Temporal stability of net primary productivity (NPP) is important for predicting the reliable provisioning of ecosystem services under global changes. Although nitrogen (N) addition is known to affect the temporal stability of aboveground net primary productivity (ANPP), it is unclear how it impacts that of belowground net primary productivity (BNPP) and NPP, and whether such effects are scale dependent. Here, using experimental N addition in a grassland, we found different responses of ANPP and BNPP stability to N addition at the local scale and that these responses propagated to the larger spatial scale. That is, N addition significantly decreased the stability of ANPP but did not affect the stability of BNPP and NPP at the two scales investigated. Additionally, spatial asynchrony of both ANPP and BNPP among communities provided greater stability at the larger scale and was not affected by N addition. Our findings challenge the traditional view that N addition would reduce ecosystem stability based on results from aboveground dynamics, thus highlighting the importance of viewing ecosystem stability from a whole system perspective., (© 2022 John Wiley & Sons Ltd.)

Plant genome size (GS) varies greatly over 2400-fold in angiosperms. Genome sizes are closely related to plant traits from cellular to individual level, which would have far-reaching ecolo-gical implications. Genome size may shape the interspecific responses of plants to changes of resource availability in Inner Mongolia grassland which is co-limited by water and nitrogen availabi-lity. We tested the role of genome size in structuring plant community composition after single and combined water (W) amd nitrogen (N) addition in a typical grassland of Inner Mongolia. Plant genome sizes were estimated by flow cytometry. We found that the response of plant aboveground net primary production (ANPP) to change in water availability was significantly affected by genome size. Water and NW addition significantly increased ANPP of small GS plants, instead of large GS species. Nitrogen addition had no effects on ANPP of both small and large GS plants. We found no effects of all the treatments on plant species richness. Results showed that GS modulated the response of grassland plant species to changes in water rather than nitrogen availability in Inner Mongolia. Since GS is a relatively constant trait with substantial interspecific variation, the application of GS in ecological studies would be of great significance to better understanding of ecosystem structure and function under global change.

Aims: The stoichiometric characteristics of plant communities are important controller for several fundamental ecological processes. The effects of environmental changes on community stoichiometric characteristics are driven by intra- and inter-specific variation. However, the relative importance of both pathways has seldom been empirically examined., Methods: We quantified the relative contribution of intra- and inter-specific variation to the changes of community nitrogen (N) and phosphorus (P) concentrations after seven-year factorial N addition and mowing treatments in a semi-arid grassland of northern China., Results: Nitrogen addition significantly increased community N and P concentrations and N:P ratio. Mowing significantly increased community N concentration and N:P. Intra-specific variation contributed more than inter-specific variation to the total variability of all the nutritional and stoichiometric characteristics, with intra-specific variation accounting for 68%, 70%, and 75% of the total variation in community-level N, P, and N:P, respectively. Negative covariations between the contribution of intra- and inter-specific variation occurred for community N and P concentrations. Further, N addition and mowing interacted to affect the impacts of intra- and inter-specific variation on community N concentration and N:P stoichiometry., Conclusions: Our results highlight different ways of trait selection for N addition and mowing treatments. Interactions between those two factors make it more difficult to accurately predict the responses of plant-mediated biogeochemical cycles under co-occurrence of environmental changes., (Copyright © 2019 Elsevier B.V. All rights reserved.)

There is considerable debate regarding how the taxonomic diversity of microbial communities relates to the functional diversity across space while similar questions have been explored in macro-organism communities. Here, we investigated the taxonomic and functional diversity patterns of soil microbial communities by coupling the data obtained from marker genes sequencing and functional gene surveys. Meanwhile, we evaluated the relative effects of environment and geographic distance on shaping these patterns in alpine grasslands of northern China. Although the taxonomic diversity and composition of microbial communities varied across sites, we found no consistent changes in the functional structure. Both the environmental factors and geographic distance concurrently affected the taxonomic diversity patterns but they had no effects on the spatial variations in functional genes. The functional alpha diversity was weakly correlated to the taxonomic alpha diversity across sites. Moreover, we found no significant relationship between the taxonomic and functional composition similarity among microbial communities. Together, our results provide evidence that spatial variation in microbial functions could be independent of their variations in taxonomic diversity. Even the drivers of spatial variations in the functional structure could be totally different from those of taxonomic variations such as environmental differences and dispersal limitation. Our findings suggest that spatial variations of microbial function structure within a community would not follow the variations of taxonomic structures due to different drivers between both of them over space., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Nitrogen (N) enrichment has great consequences on several fundamental ecological processes through its impacts on plant nutrition traits (i.e. nutrient concentration and stoichiometric ratios); however, the extent to which the effects of N enrichment depend on phosphorus (P) availability are less well understood. While there is mounting evidence for the species-specific responses of plant nutrition traits to nutrient enrichment, we know little about the changes at the community-level. Here, we measured community-level biomass weighted (CWM) and non-weighted (CM) plant N and P concentrations and N:P ratio in a temperate meadow steppe after four years factorial N and P addition, with biomass and nutrition traits of each species in each plot being recorded. Nitrogen addition significantly increased community-level N concentration, decreased P concentration, and enhanced community N:P ratio. Phosphorus addition had no impacts on community-level N concentration, significantly increased P concentration, and reduced community N:P ratio. The impacts of N addition on community nutrition traits were not dependent on P addition and the community-level nutrition trait responses to N and P additions were primarily driven by intraspecific trait variation (ITV) rather than by species turnover. Community-level nutrition traits in the temperate meadow steppe were sensitive to the projected N and P enrichment. While nutrient enrichment had substantially changed community composition, its impacts on community nutrition traits were driven by ITV. Nitrogen deposition would result in imbalance of N and P in plant community, as indicated by the substantial increase in community-level N:P, which was not affected by increased P availability., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The existence of biogeographic patterns among most free-living microbial taxa has been well established, yet little is known about the underlying mechanisms that shape these patterns. Here, we examined soil bacterial β-diversity across different habitats in the drylands of northern China. We evaluated the relative importance of environmental factors versus geographic distance to a distance-decay relationship, which would be explained by the relative effect of basic ecological processes recognized as drivers of diversity patterns in macrobial theoretical models such as selection and dispersal. Although the similarity of bacterial communities significantly declined with increasing geographic distance, the distance-decay slope and the relative importance of factors driving distance-decay patterns varied across different habitats. A strong distance-decay relationship was observed in the alpine grassland, where the community similarity was influenced only by the environmental factors. In contrast, geographic distance was solely responsible for community similarity in the desert. Even the average compositional similarity among locations in the desert was distinctly lower compared with those in other habitats. We found no evidence that dispersal limitation strongly influenced the β-diversity of bacterial communities in the desert grassland and typical grassland. Together, our results provide robust evidence of habitat specificity for microbial diversity patterns and their underlying drivers. Our findings suggest that microorganisms also have multiple drivers of diversity patterns and some of which may be parallel to some fundamental processes for explaining biodiversity patterns in macroorganisms.

Increased atmospheric nitrogen (N) deposition and altered precipitation regimes have profound impacts on ecosystem functioning in semiarid grasslands. The interactions between those two factors remain largely unknown. A field experiment with N and water additions was conducted in a semiarid grassland in northern China. We examined the responses of aboveground net primary production (ANPP) and plant N use during two contrasting hydrological growing seasons. Nitrogen addition had no impact on ANPP, which may be accounted for by the offset between enhanced plant N uptake and decreased plant nitrogen use efficiency (NUE). Water addition significantly enhanced ANPP, which was largely due to enhanced plant aboveground N uptake. Nitrogen and water additions significantly interacted to affect ANPP, plant N uptake and N concentrations at the community level. Our observations highlight the important role of plant N uptake and use in mediating the effects of N and water addition on ANPP.

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• Effects of fencing facility on plant species and soil organic carbon were investigated. • Plant biomass and soil organic carbon increased with approaching fencing facility. • Edge effect is used to explain the variations of plant species and soil organic carbon. Fencing facility has been widely employed in steppes. However, the effects of fencing facility on plant species and soil organic carbon (SOC) have been rarely understood in steppes. Using soil sampling and plant quadrat clipping methods, in this study, we investigated the effects of fencing facility on the distributions of plant species and SOC in the temperate steppes of the Inner Mongolia. Plant biomass significantly increased with approaching fencing facility and was obviously higher in the leeward (south) than windward (north) sides. Perennial grasses accounted for approximately 68%–76% of the total aboveground biomass in both sides of fencing facility. SOC content also significantly increased with approaching fencing facility in the 0–10 soil layer but slightly increased in the 10–30 cm soil layer. Wind erosion and dust storm did markedly neither change the fractions of soil texture nor cause the difference in SOC content between the windward and leeward sides. Fencing facility increased SOC storage by 16.5% and 9.1% at 0.1 and 0.5 m locations relative to at 3 m location in the 0–10 cm soil layer, respectively. Edge effect is suggested as a potential mechanism driving the variations of plant species and SOC in both sides of fencing facility. [ABSTRACT FROM AUTHOR]