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Aims Plant species mixtures with different functional traits or microbial associations can more fully utilize soil nutrient pools. However, there is a gap in our understanding of the synergistic influences of arbuscular mycorrhizal (AM) fungi in nutrient capture and resource partitioning across different soil depths in mixed plant communities, as well as their possible effects on plant coexistence. To address these knowledge gaps, we assessed the effect of AM fungi on nutrient uptake and competition between shallow- and deep-rooted pairs of grass and legume species. Methods To quantify the mycorrhizal mediation of N uptake at different rooting depths, 15N tracer was injected into soil at 3- and 25-cm depths of monoculture or bi-species mixtures, with or without AM fungi. Results AM symbioses reduced plant competition by equalizing access to N and subsequently increasing shoot N and P concentrations of co-cultivated plant species. Niche differentiation, based on rooting depth, had minimal effects on grass and legume competitive interactions. Both deep-rooted plant species, i.e., Medicago sativa and Dactylis glomerata, and shallow-rooted species, i.e., Lolium perenne and Trifolium repens, primarily acquired nutrients from shallow soil layers. However, AM fungi significantly increased the rooting depth of both shallow- and deep-rooted plant species, enhancing nutrient uptake and N2 fixation from depths of both 3 and 25 cm. Conclusion Our results suggest a strong influence of AM fungi on host-plant competitiveness and vertical nutrient capture in mixed plant communities, underscoring that microbial mutualist-mediated nutrient acquisition is a key driver of gains in productivity of grass–legume mixtures.

Interspecific competition and plant-soil feedbacks are powerful drivers of plant community structure. However, across a range of edaphic conditions the interactive effects of these drivers on complex plant communities remain unclear. For example, plant-soil feedback studies focus on soil trained by a single plant species. We developed a method to assess effects of plant-microbial interactions (PMI) on a complex plant community. We established mesocosms with 13 grassland species, grown individually or together, in overgrazed or restored soil, with or without soil microbial inoculum collected from a productive and diverse native grassland. We assessed biomass production as influenced by edaphic conditions, interspecific competition and PMI. Furthermore, we assessed potential influences of interspecific competition and edaphic conditions on strength and direction of PMI. Our results indicate PMI drives negative growth responses for graminoids while forbs experience positive growth responses. Generally, interspecific competition did not alter the magnitude or direction of PMI-mediated growth responses. Edaphic conditions altered the influence of soil microbial communities on individual plant growth while PMI facilitated plant evenness. In plant community mesocosms, PMI-associated benefits were observed in overgrazed soil. However, interspecific competition overwhelmed plant growth benefits associated with soil microbial communities when plant communities were grown in restored soil. In mesocosms containing dominant grass species, interspecific competition had negative effects on species coexistence, but both positive and negative PMI partially counterbalanced this influence on plant species evenness. Understanding these mechanisms may improve our capacity to manage diverse and productive grasslands by enabling prediction of plant community composition following disturbance and subsequent restoration.

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 and rhizobium are likely important drivers of plant coexistence and grassland productivity due to complementary roles in supplying limiting nutrients. However, the interactive effects of mycorrhizal and rhizobial associations on plant community productivity and competitive dynamics remain unclear. To address this, we conducted a greenhouse experiment to determine the influences of these key microbial functional groups on communities comprising three plant species by comparing plant communities grown with or without each symbiont. We also utilized N-fertilization and clipping treatments to explore potential shifts in mycorrhizal and rhizobial benefits across abiotic and biotic conditions. Our research suggests AM fungi and rhizobium co-inoculation was strongly facilitative for plant community productivity and legume (Medicago sativa) growth and nodulation. Plant competitiveness shifted in the presence of AM fungi and rhizobium, favoring M. sativa over a neighboring C

Seeding legumes into degraded grasslands may effectively replace nitrogen fertilization and restore ecosystem stability by retaining or increasing native plant species diversity while increasing forage production. However, previous research indicated limited legume persistence and potential plant community diversity loss following seeding of legumes into grasslands, constraining successful restoration of degraded grasslands. Our research defined optimal management thresholds for successful legume establishment, reconciling both environmental conservation and production priorities. Large areas of degraded steppe in Inner Mongolia, northeast China, were seeded to either native alfalfa (yellow‐flowered alfalfa: Medicago falcata L.), cultivated alfalfa (purple‐flowered alfalfa: Medicago sativa L.), or left nonseeded (control). Within each seeded area, management treatments (P fertilization or mowing) were assigned to plots in the second year of alfalfa establishment. Our results indicated P amendments and mowing improve native alfalfa establishment, increasing plant productivity while maintaining diverse plant communities, thereby successfully rehabilitating degraded meadow steppe grasslands. However, cultivated alfalfa was not persistent under any management treatment. Alfalfa shoot N and P concentration was linearly related to plant‐available P, indicating P fertilization differentially benefits alfalfa compared with the dominate C₃ grass, Leymus chinensis (Trin.) Tzvel. Mowing successfully increased plant species diversity and plant species asynchrony; however, mowing did not alter the temporal stability of plant community productivity, potentially maintaining or enhancing ecosystem stability. Our research showed promise that native alfalfa seeding combined with P fertilization and mowing can restore degraded grasslands to support both forage production and diverse plant communities.

Author(s): Ren, H; Eviner, VT; Gui, W; Wilson, GWT; Cobb, AB; Yang, G; Zhang, Y; Hu, S; Bai, Y | Abstract: Livestock grazing has been shown to alter the structure and functions of grassland ecosystems. It is well acknowledged that grazing pressure is one of the strongest drivers of ecosystem-level effects of grazing, but few studies have assessed how grazing pressure impacts grassland biodiversity and ecosystem multifunctionality (EMF). Here, we assessed how different metrics of biodiversity (i.e., plants and soil microbes) and EMF responded to seven different grazing treatments based on an 11-year field experiment in semi-arid Inner Mongolian steppe. We found that soil organic carbon, plant-available nitrogen and plant functional diversity all decreased even at low grazing pressure, while above-ground primary production and bacterial abundance decreased only at high levels of grazing pressure. Structural equation models revealed that EMF was driven by direct effects of grazing, rather than the effects of grazing on plant or microbial community composition. Grazing effects on plant functional diversity and soil microbial abundance did have moderate effects on EMF, while plant richness did not. Synthesis. Our results showed ecosystem functions differ in their sensitivity to grazing pressure, requiring a low grazing threshold to achieve multiple goals in the Eurasian steppe. A plain language summary is available for this article.

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

While the effects of row crop agriculture on arbuscular mycorrhizal (AM) fungi have been studied in temperate climates, much less is known about the consequences of methods employed by smallholder farmers in Africa. We compared soils from 12 small farms in rural eastern Zambia with soil from nearby grasslands (control) to assess microbial abundances, including AM fungi, using phospholipid and neutral lipid fatty acid (PLFA/NLFA) analyses. We also measured soil pH, soil organic matter, and key nutrients, and categorized farms to link microbial abundances with agricultural practices including: low and high input cultivation, conservation farming, and agroforestry. Soil organic matter was significantly greater in grassland (control) soils, compared to any of the farms. Concentrations of N, P, and K were greater in farm soils compared to grassland soil. Extra-radical AM fungal biomass was significantly greater in grassland soils compared to farms, and grasslands contained more than double the total microbial biomass compared to any farm. Our results indicate agricultural practices in Zambia are negatively affecting AM fungi as well as other soil microbes. However, conservation farming shows promise in facilitating AM fungal recovery, with potential long-term benefits for soil stability via hyphal exudates and physical entanglement.

Reseeding yellow-flowered alfalfa (YFA) in degraded grasslands may require a vegetation-free microsite for germination and subsequent establishment. This study aimed to examine the role of microclimates of different-sized vegetation gaps on seedling performance and adult plant production of YFA. Field microsites were established in the meadow steppe of Hulunber, Inner Mongolia, China. Seedling performance, plant production, the microclimate within vegetation gaps, and soil nutrients (plant-available N, P, and K, total N concentration) were assessed at the end of each growing season from 2013 to 2015. Our results indicate light availability, and topsoil temperature of each gap were significantly increased as gap size increased, while topsoil moisture and air relative moisture were decreased in larger gaps. Small gaps (diameter ≤10 cm) improved seedling emergence, survival, biomass, and root nodulation, as compared with seedling performance associated with the larger gaps, presumably in response to increased shade and moisture. Additionally, large gaps (>20 or >40 cm) were characterized by significantly lower plant-available P, total N concentrations, plant-available K, and soil pH. However, root exclusion treatments did not improve overall seedling performance, plant production, or soil properties, as compared to corresponding microsites with root presence, regardless of gap size. Our results suggest that reseeding YFA into grasslands where disturbance, such as light grazing, has resulted in small gaps will be more effective than in highly degraded grasslands.

It is imperative for sorghum breeders to focus on enhancing plant-microbial partnerships to help deliver efficient genotypes for sustainable agricultural systems. Alternative farm fertility amendments and field management practices may also improve sorghum yields and grain quality, especially in combination with appropriately bred genotypes. Therefore, we assessed four genotypes of grain sorghum (two commercial hybrids and two landrace open-pollinated cultivars) for their influence on soil microbial communities, particularly arbuscular mycorrhizal fungi, at two field sites. All genotypes were grown as sole crops, while one commercial hybrid and one open-pollinated cultivar were also intercropped with cowpea to compare the two farm management practices. We established three treatments: non-amended control, commercial fertilizers (N and P), and worm compost (alternative fertility amendment). Grain production and nutritional quality were assessed to link belowground influences from genotypes and management on aboveground outcomes. Soil microbial communities were influenced by genotype, and higher fungal to bacterial biomass ratio was observed following worm compost amendment. Grain production was not significantly different between genotypes or treatments; however, percentage mycorrhizal root colonization was significantly greater for plants grown in soil amended with worm compost, as compared to commercial fertilizers. Genotype also had a significant effect on grain nutritional quality, while intercropping and/or amendment with worm compost generally resulted in similar or improved grain quality as compared to sole cropping and/or amendment with commercial fertilizers. Selective breeding of sorghum for agricultural systems designed around these alternative practices may further benefit grain nutrition and soil microbial communities.

Syntheses of large datasets have allowed increased clarity of distribution patterns and variation in soil major and trace elements. However, the drivers of variation in topsoil elements across biogeographical scales are not well understood. Our aim was to (1) identify how landscape-scale climate, geographical features, and edaphic factors influence soil elements, and (2) determine key environmental thresholds for shifts in soil element concentration. We analyzed patterns of variation in topsoil elements using 9830 samples collected across 39,000km2 in subtropical land in southeast China. Canonical correlations and multiple linear regressions were used to model variations of each element across mean annual temperature (MAT), mean annual precipitation (MAP), land use, spatial topography, and soil pH. Element concentrations show significant latitudinal and longitudinal trends, and are significantly influenced by climate, land use, spatial topography, and soil pH. Longitude, pH, MAT, and MAP were the environmental factors most tightly correlated with element concentrations. Climate and soil pH drove positive or negative alterations in soil elements, with threshold indicators of MAP=1000mm/1500mm, MAT=17.8°C/18.0°C, and pH=5.8/5.0, respectively. Our results indicate topsoil elements have structural and functional thresholds of climate and soil pH in relatively wet and acidic environments. Our findings can facilitate holistic soil element concentration predictions and help elucidate the specific influences of climate and soil pH, enabling development of more complete biogeochemical models.

In grasslands, forage and livestock production results in soil nutrient deficits as grasslands typically receive no nutrient inputs, leading to a loss of grassland biomass. The application of mature compost has been shown to effectively increase grassland nutrient availability. However, research on fertilization regime influence and potential microbial ecological regulation mechanisms are rarely conducted in grassland soil. We conducted a two-year experiment in meadow steppe grasslands, focusing on above- and belowground consequences of organic or Trichoderma biofertilizer applications and potential soil microbial ecological mechanisms underlying soil chemistry and microbial community responses. Grassland biomass significantly (p = 0.019) increased following amendment with 9,000 kg ha−1 of Trichoderma biofertilizer (composted cattle manure + inoculum) compared with other assessed organic or biofertilizer rates, except for BOF3000 (fertilized with 3,000 kg ha−1 biofertilizer). This rate of Trichoderma biofertilizer treatment increased soil antifungal compounds that may suppress pathogenic fungi, potentially partially responsible for improved grassland biomass. Nonmetric multidimensional scaling (NMDS) revealed soil chemistry and fungal communities were all separated by different fertilization regime. Trichoderma biofertilizer (9,000 kg ha−1) increased relative abundances of Archaeorhizomyces and Trichoderma while decreasing Ophiosphaerella. Trichoderma can improve grassland biomass, while Ophiosphaerella has the opposite effect as it may secrete metabolites causing grass necrosis. Correlations between soil properties and microbial genera showed plant-available phosphorus may influence grassland biomass by increasing Archaeorhizomyces and Trichoderma while reducing Ophiosphaerella. According to our structural equation modeling (SEM), Trichoderma abundance was the primary contributor to aboveground grassland biomass. Our results suggest Trichoderma biofertilizer could be an important tool for management of soils and ultimately grassland plant biomass.

Overgrazing substantially contributes to global grassland degradation by decreasing plant community productivity and diversity through trampling, defoliation, and removal of nutrients. Arbuscular mycorrhizal (AM) fungi also play a critical role in plant community diversity, composition, and primary productivity, maintaining ecosystem functions. However, interactions between grazing disturbances, such as trampling and defoliation, and AM fungi in grassland communities are not well known. We examined influences of trampling, defoliation, and AM fungi on semiarid grassland plant community composition for 3 yr, by comparing all combinations of these factors. Benomyl fungicide was applied to reduce AM fungal abundance. Overgrazing typically resulted in reduced dominance of Stipa Krylovii, contributing to degradation of typical steppe grasslands. Our results indicated trampling generally had little effect on plant community composition, unless combined with defoliation or AM fungal suppression. Defoliation was the main component of grazing that promoted dominance of Potentilla acaulis over Stipa krylovii and Artemisia frigida, presumably by alleviating light limitation. In non-defoliated plots, AM fungi promoted A. frigida, with a concomitant reduction in S. krylovii growth compared to corresponding AM suppressed plots. Our results indicate AM fungi and defoliation jointly suppress S. krylovii biomass; however, prolonged defoliation weakens mycorrhizal influence on plant community composition. These findings give new insight into dominant plant species shifts in degraded semiarid grasslands.

Grazing and topography have drastic effects on plant communities and soil properties. These effects are thought to influence arbuscular mycorrhizal (AM) fungi. However, the simultaneous impacts of grazing pressure (sheep ha-1) and topography on plant and soil factors and their relationship to the production of extra-radical AM hyphae are not well understood. Our 10-year study assessed relationships between grazing, plant species richness, aboveground plant productivity, soil nutrients, edaphic properties, and AM hyphal length density (HLD) in different topographic areas (flat or sloped). We found HLD linearly declined with increasing grazing pressure (1.5-9.0 sheep ha-1) in sloped areas, but HLD was greatest at moderate grazing pressure (4.5 sheep ha-1) in flat areas. Structural equation modeling indicates grazing reduces HLD by altering soil nutrient dynamics in sloped areas, but non-linearly influences HLD through plant community and edaphic changes in flat areas. Our findings highlight how topography influences key plant and soil factors, thus regulating the effects of grazing pressure on extra-radical hyphal production of AM fungi in grasslands. Understanding how grazing and topography influence AM fungi in semi-arid grasslands is vital, as globally, severe human population pressure and increasing demand for food aggravate the grazing intensity in grasslands.

Rhizobia-legume symbiosis is the most well researched biological nitrogen fixation system. Coating legume seeds with rhizobia is now a recognized practical measure for improving the production of legume corp. However, the efficacy of some commercial rhizobia inoculants cannot be guaranteed in China due to the low rate of live rhizobia in these products. A greenhouse experiment was conducted to assess the effects of different rhizobial inoculant formulations on alfalfa productivity and nitrogen fixation. Two rhizobia strains, (ACCC17631 and ACCC17676), that are effective partners with alfalfa variety Zhongmu No. 1 were assessed with different concentrations of ammonium molybdate in seed-coat formulations with two different coating adhesives. Our study showed that the growth, nodulation, and nitrogen fixation ability of the plants inoculated with the ACCC17631 rhizobial strain were greatest when the ammonium molybdate application was0.2% of the formulation. An ammonium molybdate concentration of 0.1% was most beneficial to the growth of the plants inoculated with the ACCC17676 rhizobial strain. The sodium carboxymethyl cellulose and sodium alginate, used as coating adhesives, did not have a significant effect on alfalfa biomass and nitrogen fixation. However, the addition of skimmed milk to the adhesive improved nitrogenase activity. These results demonstrate that a new rhizobial seed-coat formulation benefitted alfalfa nodulation and yield.