N enrichment affects the arbuscular mycorrhizal fungi-mediated relationship between a C4 grass and a legume

Arbuscular mycorrhizal fungi regulate the diversity-invasion resistance relationship by influencing the role of complementarity and selection effects

Arbuscular mycorrhizal fungi (AMF) play a crucial role in influencing plant community dynamics, yet their impact on the relationship between plant diversity and resistance, especially resistance to plant invasion, remains largely unclear. We conducted an experiment using plant communities with varying species richness (one, three and six species) and subjected them to invasion by Solidago canadensis and AMF inoculation. We measured community resistance by comparing the biomass of invaded communities to uninvaded communities and investigated the effect of AMF inoculation on the diversity-resistance relationship. Our results indicate that communities with higher plant species richness displayed greater resistance to invasion, and this effect was stronger in the presence of AMF than in its absence. AMF inoculation weakened the positive complementarity effect-resistance relationship (i.e. a decreasing species asynchrony) due to AMF-induced alterations in community composition, but shifted the negative selection effect-resistance relationship to neutral (i.e. a negative-to-neutral sampling effect) due to the enhanced role of the dominant species Mosla scabra. Furthermore, the AMF-induced changes in plant species resistance were positively correlated with their relative growth rate and specific root surface area. These findings suggest that AMF inoculation alters the mechanisms underlying diversity-resistance relationships, with implications for how plant communities respond to disturbances such as invasion.

Xizang meadow degradation alters resource exchange ratio, network complexity, and biomass allocation tradeoff of arbuscular mycorrhizal symbiosis

The response of arbuscular mycorrhizal (AM) symbiosis to environmental fluctuations involves resource exchange between host plants and fungal partners, associations between different AM fungal taxa, and biomass allocation between AM fungal spore and hyphal structures; yet a systematic understanding of these responses to meadow degradation remains relatively unknown, particularly in Xizang alpine meadow. Here, we approached this knowledge gap by labeling dual isotopes of air 13CO2 and soil 15NH4Cl, computing ecological networks of AM fungal communities, and quantifying AM fungal biomass allocation among spores, intra- and extraradical hyphae. We found that the exchange ratio of photosynthate and nitrogen between plants and AM fungi increased with the increasing severity of meadow degradation, indicating greater dependence of host plants on this symbiosis for resource acquisition. Additionally, using 18S rRNA gene metabarcoding, we found that AM fungal co-occurrence networks were more complex in more degraded meadows, supporting the stress gradient hypothesis. Meadow degradation also increased AM fungal biomass allocation toward traits associated with intra- and extraradical hyphae at the expense of spores. Our findings suggest that an integrated consideration of resource exchange, ecological networks, and biomass allocation may be important for the restoration of degraded ecosystems.

Bacillus cereus CGMCC 1.60196: a promising bacterial inoculant isolated from biological soil crusts for maize growth enhancement

Soil microbial inoculants are widely recognized as an environmentally friendly strategy for promoting crop growth and increasing productivity. However, research on utilizing the microbial resources from desert biological soil crusts to enhance crop growth remains relatively unexplored. In the present work, a bacterial strain designated AC1-8 with high levels of amylase, protease, and cellulase activity was isolated from cyanobacterial crusts of the Tengger Desert and identified as Bacillus cereus (CGMCC 1.60196). The refinement of the fermentation parameters of B. cereus CGMCC 1.60196 determined that the most effective medium for biomass production was composed of 5 g/L glucose, 22 g/L yeast extract and 15 g/L MgSO4, and the optimal culture conditions were pH 6.0, temperature 37°C, inoculation quantity 3% and agitation speed 240 rpm. Furthermore, the utilization of B. cereus CGMCC 1.60196 has resulted in substantial improvements in various growth parameters of maize seedlings, including shoot length, shoot fresh and dry weights, root fresh and dry weights, and the contents of chlorophyll a, chlorophyll b, and total chlorophyll. The most pronounced growth promotion was observed at an application concentration of 1 × 109 CFU/m2. These results suggest that the novel B. cereus strain, isolated from cyanobacterial crusts, can be regarded as an exemplary biological agent for soil improvement, capable of enhancing soil conditions, promoting crop cultivation and supporting food production.

Belowground bud banks and land use change: roles of vegetation and soil properties in mediating the composition of bud banks in different ecosystems

Introduction

Belowground bud banks play integral roles in vegetation regeneration and ecological succession of plant communities; however, human-caused changes in land use severely threaten their resilience and regrowth. Although vegetation attributes and soil properties mediate such anthropogenic effects, their influence on bud bank size and composition and its regulatory mechanisms under land use change have not been explored.

Methods

We conducted a field investigation to examine impacts of land use change on bud bank size and composition, vegetation attributes, and soil properties in wetlands (WL), farmlands (FL), and alpine meadow (AM) ecosystems in Zhejiang Province, China.

Results

Overall, 63 soil samples in close proximity to the vegetation quadrats were excavated using a shovel, and samples of the excavated soil were placed in plastic bags for onward laboratory soil analysis. The total bud density (1514.727 ± 296.666) and tiller bud density (1229.090 ± 279.002) in wetland ecosystems were significantly higher than in farmland and alpine meadow ecosystems [i.e., total (149.333 ± 21.490 and 573.647 ± 91.518) and tiller bud density (24.666 ± 8.504 and 204.235 ± 50.550), respectively]. While vegetation attributes critically affected bud banks in WL ecosystems, soil properties strongly influenced bud banks in farmland and alpine meadow ecosystems. In wetland ecosystems, total and tiller buds were predominantly dependent on soil properties, but vegetation density played a significant role in farmlands and alpine meadow ecosystems. Root sprouting and rhizome buds significantly correlated with total C in the top 0 - 10 cm layer of farmland and alpine meadow ecosystems, respectively, and depended mainly on soil properties.

Discussion

Our results demonstrate that land use change alters bud bank size and composition; however, such responses differed among bud types in wetland, farmland, and alpine meadow ecosystems.

Nitrogen Addition Does Not Change AMF Colonization but Alters AMF Composition in a Chinese Fir (Cunninghamia lanceolata) Plantation

Aims: Our aim was to investigate how N addition affects arbuscular mycorrhizal fungal (AMF) growth in Chinese fir plantations. Methods: A Chinese fir plantation was treated with four different N addition treatments for one and half years starting in April 2019. AMF colonization, hyphal length density, community composition, and soil properties were under measurement. Results: N addition caused inapparent effects on AMF colonization, hyphal length density, and functional guilds (rhizophilic, edaphophilic, and ancestral). The predominant AMF species in the soil was Septoglomus viscosum. N addition altered AMF community and some rare species (e.g., Entrophospora infrequens) disappeared with N addition. Conclusion: AMF community structure was more sensitive to short-time N deposition than the symbiotic relationship between AMF and host plants.

Mycorrhizal and rhizobial interactions influence model grassland plant community structure and productivity

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 C₄ grass (Andropogon gerardii) and C₃ forb (Ratibida pinnata). This may be due to rhizobial symbiosis as well as the relatively greater mycorrhizal growth response of M. sativa, compared to the other model plants. Clipping and N-fertilization altered relative costs and benefits of both symbioses, presumably by altering host-plant nitrogen and carbon dynamics, leading to a relative decrease in mycorrhizal responsiveness and proportional biomass of M. sativa relative to the total biomass of the entire plant community, with a concomitant relative increase in A. gerardii and R. pinnata proportional biomass. Our results demonstrate a strong influence of both microbial symbioses on host-plant competitiveness and community dynamics across clipping and N-fertilization treatments, suggesting the symbiotic rhizosphere community is critical for legume establishment in grasslands.