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Mowing and P-fertilization enhance legume seedling establishment, assisting in successful restoration of degraded grasslands. Legume establishment may influence soil chemical compounds and soil microbial assemblage to facilitate legume productivity. We aim to better understand these complex plant-soil-microbial interactions to improve grassland productivity following overgrazing. We conducted a 3-years Medicago falcata reseeding experiment was in semi-arid meadows, assessing responses of aboveground plant biomass, soil chemical compounds, and soil microbial community composition. Reseeded plots were mowed and/or P-fertilized. Application of both management practices increased grassland biomass compared with all other combinations. Soil chemical diversity predicted fungal alpha diversity, and fungal alpha diversity positively correlated with aboveground biomass. Our results indicate reseeded alfalfa directly altered bulk soil chemical compounds with subsequent alterations in grassland microbial communities. Soils contained chemical compounds with antifungal properties that indirectly improved grassland productivity via antagonism to pathogenic fungi. Furthermore, we found three specific compounds (5-methyltridecane, pentatriacontane, and N-tridecane) reduced microbial diversity. Here we demonstrate soil chemical compounds play an important role in shaping beneficial microbial communities to improve grassland biomass. These results may help direct beneficial soil microbial community composition through improved grassland management practices.

Arbuscular mycorrhizal (AM) fungi are abundant in grassland ecosystem. We assessed AM hyphal contributions to soil CO2 efflux across plant functional groups to better quantify AM fungal influences on soil carbon dynamics. We conducted a field experiment using in-growth mesocosms to partition soil CO2 efflux from roots, AM hyphae, and free-living soil microbes associated with C3 grasses, C4 grasses, forbs, and diverse plant communities from May to August in 2017. AM hyphae contributed

The semi-arid Inner Mongolia grassland ecosystem is experiencing dramatic decreases in plant diversity as global N deposition increases. However, a comprehensive understanding of the mechanisms for this loss in diversity is lacking. We collected biotic and abiotic properties on plant community and soils in a 6-year field study with six levels (ranging between 0 to 25.14 g N m−2 yr.−1) of N addition rate in this ecosystem. The decrease in plant diversity was primarily driven by the loss of forb species. We developed a comprehensive assessment of the mechanisms contributing to this forb loss, and demonstrated the pivotal role of soil-mediated effects of acidification in reducing forbs richness. Soil acidification was associated with altered status of soil exchangeable cations and reduced soil arbuscular mycorrhizal fungi (AMF) biomass. This led to reduced nutrient cations uptake, the accumulation of phytotoxic metals, and reduced P acquisition by plants. The acidification effects notably overwhelmed other operating mechanisms, such as light limitation, and increased N availability. Our results provide a comprehensive mechanistic understanding of diversity loss under N enrichment in this semi-arid ecosystem, and suggest that soil acidification is a major threat to biodiversity under future scenarios of N deposition.

Global nitrogen enrichment has been identified as a major environmental problem that poses a threat to ecosystem functioning. However, there is no consensus on the impact of enriched nitrogen on ecosystem stability or the underlying mechanisms driving that impact. We conducted a 5-year multi-level nitrogen addition experiment in Inner Mongolia grassland. We determined plant diversity, species asynchrony, population stability, functional group stability and dominant stability, focusing on investigating the impact of nitrogen enrichment on stability and the driving mechanisms. Community stability responded negatively to nitrogen enrichment. Added nitrogen decreased plant diversity, and had a direct negative effect on species asynchrony, graminoid functional group stability, population stability, and dominant stability; all of these showed tight associations with reduced community stability. In addition, community stability showed no significant response at nitrogen addition rate ≤ 1.01 g N m−2 year−1, and saturated at ≥9.17 g N m−2 year−1. Nitrogen-induced reduction in diversity, together with alterations in species asynchrony, graminoid functional group stability, population stability and dominant stability, worked concurrently leading to deceased stability in the Inner Mongolia grassland. In addition, an effect threshold and saturation rate for added nitrogen was observed.

Soil salinity varies greatly in the plant rhizosphere. The effect of nonuniform salinity on the growth and physiology response of alfalfa plants was determined to improve understanding of salt stress tolerance mechanisms of alfalfa. Plant growth, predawn leaf water potential, water uptake, and tissue ionic content were studied in alfalfa plants grown hydroponically for 9 days using a split-root system, with uniform salinity or horizontally nonuniform salinity treatments (0/S, 75/S, and 150/S corresponding to 0, 75, and 150 mM NaCl on the low salt side, respectively). Compared with uniform high salinity, 0/S and 75/S treatments significantly increased the alfalfa shoot dry mass and stem extension rate. Compensatory water uptake by low salt roots of 0/S and 75/S treatments was observed. However, decreased leaf Na+ concentration, increased leaf K+/Na+, and compensatory growth of roots on the low salt side were observed only following the 0/S treatment. Nonuniform salinity dose not enhance plant growth once a threshold NaCl concentration in low salinity growth medium has been reached. Compensation of water uptake from the low-salt root zone and regulation of K+/Na+ homeostasis in low salt root play more important role than regulation of leaf ions in enhancing alfalfa growth under nonuniform salinity.

Background and aims Nitrogen (N) deposition usually alters plant community structure and reduces plant biodiversity in grasslands. Seedling recruitment is essential for maintaining species richness and determines plant community composition. Arbuscular mycorrhizal fungi (AMF) are widespread symbiotic fungi and could facilitate seedling establishment. Here we conducted an experiment to address whether the influence of AMF on seedling recruitment depends on N addition and plant species.