Explore the vast range of titles available.

The continuing nitrogen (N) deposition observed worldwide alters ecosystem nutrient cycling and ecosystem functioning. Litter decomposition is a key process contributing to these changes, but the numerous mechanisms for altered decomposition remain poorly identified. We assessed these different mechanisms with a decomposition experiment using litter from four abundant species ( Achnatherum sibiricum , Agropyron cristatum , Leymus chinensis and Stipa grandis ) and litter mixtures representing treatment-specific community composition in a semi-arid grassland under long-term simulation of six different rates of N deposition. Decomposition increased consistently with increasing rates of N addition in all litter types. Higher soil manganese (Mn) availability, which apparently was a consequence of N addition-induced lower soil pH, was the most important factor for faster decomposition. Soil C : N ratios were lower with N addition that subsequently led to markedly higher bacterial to fungal ratios, which also stimulated litter decomposition. Several factors contributed jointly to higher rates of litter decomposition in response to N deposition. Shifts in plant species composition and litter quality played a minor role compared to N-driven reductions in soil pH and C : N, which increased soil Mn availability and altered microbial community structure. The soil-driven effect on decomposition reported here may have long-lasting impacts on nutrient cycling, soil organic matter dynamics and ecosystem functioning.

1. Between-species variation in nutrient resorption is one of the mechanisms explaining the positive relationship between biodiversity and primary productivity. Yet, the role of within-species variations in nutrient resorption in mediating the relationship between biodiversity and productivity remains unclear. 2. We examined how within-species nutrient resorption, and ultimately productivity, respond to changes in species richness by using four traits related to nitrogen and phosphorus use in four dominant species from different plant functional groups in a biodiversity removal experiment in the temperate steppe. 3. Nitrogen and phosphorus concentrations in both green and senesced leaves in all species significantly decreased with increasing plant species richness, suggesting that plants used those limiting nutrients more efficiently with increasing biodiversity. Plants in higher diversity communities resorbed more nutrients during senescence, which may facilitate reproduction and vegetative regrowth in the next year. 4. Synthesis. Our results highlight the importance of considering within-species variation in nutrient resorption as an important underlying mechanism explaining the positive effects of biodiversity on primary productivity and ecosystem carbon accumulation.

Background and aims Primary productivity in the temperate steppe is assumed to be co-limited by nitrogen (N) and water availability, but empirical evidence is scarce. We examined the N and water limitation status of primary productivity from the species scale to community scale under the framework of resource colimitation. Methods We compared the responses of aboveground net primary productivity (ANPP) at different ecological levels to factorial N and water addition in two years in a temperate steppe of northern China. Results Water addition significantly enhanced total ANPP by 46%, with stronger effects in the dry year. Total ANPP was sub-additively co-limited by N and water availability, being more sensitive to water addition than to N addition in the dry year and equally sensitive to both resources in the year with normal precipitation. The responses of total ANPP to resource additions were largely driven by the changes of grasses rather than the forbs. Species level ANPP showed conservative responses to resource additions. Conclusions Our results highlight the hierarchical patterns of limitation status in primary productivity at different biological organization levels in this temperate steppe. The sub-additive limitation by N and water in this ecosystem deserves more attention in modelling the dynamics of ecosystem carbon cycle under global change scenarios.

Background and aims Nitrogen use efficiency (NUE), defined as plant biomass production per unit N assimilated, is an important component of plant resource use strategies as well as a component of ecosystem function. Clarifying the mechanisms underlying the variations of species level NUE is an essential prerequisite for predicting the alterations of ecosystem level N cycling under global change scenarios. While plant NUE is usually examined under the leaf economic spectrum framework, we know little about their associations with broader ecological strategies and evolutionary history. Methods Using a comparative method, we evaluated the links between NUE and functional traits, Grime’s CSR ecological strategies, and phylogeny for 73 species in a temperate steppe of northern China. Results Plant NUE was strongly constrained by phylogeny, showing a unimodal relationship with taxa divergence times. Under the CSR framework, species with greater R-selection (ruderality) typically had lower NUE. Both phylogeny and R-selection were more important than single functional traits in predicting the species level variations of NUE. Conclusions Our results highlight the role of phylogeny in structuring the species level variations of plant NUE and established a link between species CSR strategies and NUE, which sheds light on understanding the divergence and convergence in plants in response to the most growth-limiting nutrient.

Purpose Soil nematodes play a fundamental role in regulating ecosystem carbon and nutrient cycling. It is widely recognized that soil nematode community composition is sensitive to nutrient enrichment, but the linkage between community assembly processes and functional changes under nutrient enrichment condition remains poorly understood. Methods We examined the compositional and functional responses and quantified the role of main community assembly processes (genus losses, genus gains, and context-dependent variations of abundance) in driving the carbon budget of soil nematode communities in response to nitrogen (N) and phosphorus (P) addition in a temperate grassland. Results Nitrogen and P addition significantly interacted to affect nematodes abundance, biomass, and functional variables of C cycling, in that P addition increased all the variables under ambient N condition but not under N enriched condition. Soil pH, ammonium concentration, and total phosphorus concentration played important roles in driving the variations of nematode C budgets, indicating the minor role of plant community characteristics. The enhancement of all variables following P addition was caused by the increases in the abundance of common genera (e.g. Acrobeles , Scutylenchus , and Tylencholaimus ). The variation of genus richness contributed to the P-induced increases of nematode abundance but not to the increases of carbon budgets. Conclusions Our results uncover the linkages between community assembly processes and the abundance and C cycling function of soil nematode community under nutrient enrichment conditions. The significant interactive effects between N and P addition highlight the complexity in predicting the compositional and functional changes in soil nematode community under a scenario of multiple-nutrient enrichment.

Anthropogenic nitrogen (N) deposition has affected plant community composition and nutrient cycling in terrestrial ecosystems worldwide. This includes changes to the way plants use and recycle nutrients, including effects on nutrient resorption, which is a key process through which plants recover nutrients from tissue during senescence. Nutrient resorption has considerable adaptive and functional significance for plants and helps regulate core ecosystem processes such as decomposition. However, our understanding of how N deposition affects nutrient resorption and, in particular, of how N inputs alter ecosystem resorption via changes to existing species’resorption compared with changes to community composition remains poor. To disentangle the role of species versus community composition controls driving variation in nutrient resorption responses to N inputs, we carried out an experiment with six different N addition rates in a temperate steppe. We found that species-scale nutrient resorption responses to N enrichment were variable; for example, only half of the measured species reduced both N and P resorption efficiency in response to increased N inputs. In contrast, community-scale responses consistently resulted in reduced N and P resorption. Still, N-induced changes in community composition were a weaker control on overall resorption responses than were the effects on individual species; however, it was the synergistic interaction between the two that resulted in the large total reductions of nutrient resorption in the face of increased N. Taken together, our results highlight that understanding and predicting nutrient resorption responses will be most accurately scaled by accounting not only for species’ reductions in resorption but also for changes in community composition.

Aims Nutrient addition is a widely-used strategy to restore degraded grasslands. It remains unknown whether and how the number of added nutrients affects the soil nematode community in degraded grasslands. Methods We examined the immediate responses of taxonomic and functional composition of the soil nematode community to different numbers of added nutrients using factorial combinations of nitrogen (N), phosphorus (P), and potassium (K + micronutrients) in a degraded grassland of northern China. Results The taxonomic and functional composition of the soil nematode community generally formed a unimodal relationship with the number of added nutrients. Changes of soil pH after fertilization affected the structural stability and complexity of the soil nematode community. The magnitude of nematode functional responses to nutrient supply was driven by changes of plant aboveground biomass and soil pH. Conclusions Soil nematode community showed non-linear responses to the variations of the number of added nutrients in a degraded grassland, which contrasts previous findings from plant community. The number of added nutrients should be given full consideration in formulating effective restoration strategies for degraded grasslands.

Aims The responses of functional structures in plant communities to global change drivers is predicted to be driven by both species turnover and intraspecific trait variability (ITV). However, the relative importance of those two drivers is not well-known, which retards our ability to predict the functional changes of plant community under global change scenarios. We hypothesized that ITV rather than species turnover would drive the nutritional responses of plant community at the initial stage after nitrogen and water enrichment. Methods We measured community weighted means (CWM) and non-weighted means (CM) of foliar N and P concentrations and N:P ratio in a temperate steppe after two years factorial N and water addition. Species composition and nutrition traits of each species were recorded in each plot. Results The impacts of N addition on community level nutrition traits were highly dependent on water conditions, as indicated by significant interactive effects between N and water addition. Nitrogen addition significantly increased CWM of foliar N, but only under ambient water condition. Water addition decreased CWM of foliar P and increased that of N:P. Consistent with our hypothesis, communities responded to both N and water addition after two years treatments mainly through ITV. Conclusions Our results highlight the importance of ITV in driving short-term responses of community functional composition to the increases of nitrogen and water availability in the temperate steppe. The existence of interactive effects of N and water addition would make it more difficult to predict the impacts of N deposition on plant-mediated biogeochemical cycling under the scenarios of precipitation regime changes than previously assumed.

Aims The stoichiometric traits of litter play an important role in driving litter decomposition and ecosystem nutrient cycling. While the impacts of nitrogen (N) deposition on the species-level litter stoichiometric traits have been well addressed, we know little about that at community-level, which is supposed to be driven by both intra-specific variation and changes in community composition. Methods We examined the effects of N deposition on litter phosphorus (P) concentration and N:P ratio at both species- and community-level in a semi-arid grassland of northern China. We further decomposed the community-level variations of litter nutritional traits into intra- and inter-specific variation. Results Nitrogen addition, especially at high rates, substantially changed community composition. Litter P concentrations and N:P ratios significantly varied among different species. Litter P concentrations and N:P ratios at both species- and community-level were positively correlated with N addition rates. Biomass-weighted community-level N:P ratios were more sensitive to N addition than the non-weighted ones, indicating that community composition strengthened the positive impacts of N addition on litter N:P ratios. There was positive co-variation between intra- and inter-specific variation for litter N:P ratio, indicating the consistency of community composition and intra-specific variation in their effects on litter N:P ratio. Conclusions Our results indicated that the imbalance of N and P following N enrichment would be much larger than the expectation based on the findings from species-level, and thus highlight the importance of changes in community composition in driving the responses of community-level litter N:P stoichiometry to N deposition in the semi-arid grassland.

Calcium is a vital trace element for the human body, and its deficiency can result in a range of pathological conditions, including rickets and osteoporosis. Despite the numerous types of calcium supplements currently available on the market, these products are afflicted with a number of inherent deficiencies, such as low calcium content, poor aqueous solubility, and low human absorption rate. Many microorganisms, particularly beneficial microorganisms, including edible fungi, lactic acid bacteria, and yeast, are capable of absorbing and enriching calcium, a phenomenon that has been widely documented. This opens the door to the potential utilization of microorganisms as novel calcium enrichment carriers. However, the investigation of calcium-rich foods from microorganisms still faces many obstacles, including a poor understanding of calcium metabolic pathways in microorganisms, a relatively low calcium enrichment rate, and the slow growth of strains. Therefore, in order to promote the development of calcium-rich products from microorganisms, this paper provides an overview of the impacts of calcium addition on strain growth, calcium enrichment rate, antioxidant system, and secondary metabolite production. Additionally, it highlights calcium transport and enrichment mechanisms in microorganism cells and offers a detailed account of the progress made on calcium-binding proteins, calcium transport pathways, and calcium storage and release. This paper offers insights for further research on the relevant calcium enrichment in microorganism cells.