Soil inoculum identity and rate jointly steer microbiomes and plant communities in the field

Altitudinal decline of vegetation restoration effects on soil microbial communities on high-altitude roadside slops: Environmental drivers and management implications

Construction activities in high-altitude regions have left many bare roadside slopes vulnerable to degradation, complicating restoration efforts. Soil microorganisms are vital for plant growth and nutrient cycling, yet their responses to restoration efforts at various altitudes remains uncertain. This study investigates soil microbial composition, network properties, ecological functions, keystone taxa, and environmental drivers across three restored vegetation types: herbaceous plants (H), shrubs + herbaceous plants (SH), and trees + shrubs + herbaceous plants (TSH) at elevations from 3100 to 3800 m. Our structural equation model identifies elevation and vegetation type as key factors influencing microbial communities, directly or indirectly, through their effects on plant and soil properties. We also found that bacterial α-diversity decreased with elevation, while fungal α-diversity increased, resulting in more complex but less stable microbial networks. R-strategists predominated in the herbaceous type (H) and at lower altitudes, whereas K-strategists dominated in the SH and TSH types, and at higher altitudes. Keystone species of type H, associated with pathotrophs and plant pathogens, showed a negative correlation with plant properties, which weakened at higher altitudes. Both bacterial and fungal communities were driven more by abiotic factors, especially ammonium (NH4+-N) and dissolved organic nitrogen (DON) for bacteria and soil water content (SWC) for fungi. This study proposes managing restoration-sensitive microbes and keystone taxa associated with specific vegetation types for effective restoration at appropriate altitudes, especially those shared by SH and TSH. Furthermore, integrating suitable legume or nitrogen-fixing woody vegetation into restoration efforts at lower altitudes and herbaceous vegetation into higher altitudes has the potential to significantly enhance plant growth and health at high altitudes. This study offers valuable guidance for optimizing restoration strategies by effectively addressing key environmental factors and nurturing essential microbial species crucial for successful restoration efforts and global warming mitigation.

Fungal communities are passengers in community development of dune ecosystems, while bacteria are not

An increasing number of studies of above-belowground interactions provide a fundamental basis for our understanding of the coexistence between plant and soil communities. However, we lack empirical evidence to understand the directionality of drivers of plant and soil communities under natural conditions: 'Are soil microorganisms driving plant community functioning or do they adapt to the plant community?' In a field experiment in an early successional dune ecosystem, we manipulated soil communities by adding living (i.e., natural microbial communities) and sterile soil inocula, originating from natural ecosystems, and examined the annual responses of soil and plant communities. The experimental manipulations had a persistent effect on the soil microbial community with divergent impacts for living and sterile soil inocula. The plant community was also affected by soil inoculation, but there was no difference between the impacts of living and sterile inocula. We also observed an increasing convergence of plant and soil microbial composition over time. Our results show that alterations in soil abiotic and biotic conditions have long-term effects on the composition of both plant and soil microbial communities. Importantly, our study provides direct evidence that soil microorganisms are not "drivers" of plant community dynamics. We found that soil fungi and bacteria manifest different community assemblies in response to treatments. Soil fungi act as "passengers," that is, soil microorganisms reflect plant community dynamics but do not alter it, whereas soil bacteria are neither "drivers" nor "passengers" of plant community dynamics in early successional ecosystems. These results are critical for understanding the community assembly of plant and soil microbial communities under natural conditions and are directly relevant for ecosystem management and restoration.

The effect of ectomycorrhizal fungal exposure on nursery-raised Pinus sylvestris seedlings: plant transpiration under short-term drought, root morphology and plant biomass

Drought is a major environmental stressor that limits seedling growth. Several studies have found that some ectomycorrhizal fungi may increase the drought tolerance of nursery-raised seedlings. However, the precise role that different ectomycorrhizal fungi species play in drought tolerance remains unclear. We evaluated the transpiration rate of Pinus sylvestris seedlings under drought stress in greenhouse conditions by exposing seedlings to 10 ectomycorrhizal fungi species, with different functional traits (exploration type and hydrophobicity), and to 3 natural soil inoculums. We measured the transpiration and water potential of the seedlings during a 10-day drought period and a 14-day recovery period. We then analyzed their root morphology, stem, needle, root biomass and needle chlorophyll fluorescence. We showed that exposing seedlings to ectomycorrhizal fungi or soil inoculum had a positive effect on their transpiration rate during the driest period and through the recovery phase, leading to 2- to 3-fold higher transpiration rates compared with the nonexposed control seedlings. Seedlings exposed to medium-distance ectomycorrhizal fungi performed better than other exploration types under drought conditions, but ectomycorrhizal fungi hydrophobicity did not seem to affect the seedlings response to drought. No significant differences were observed in biomass accumulation and root morphology between the seedlings exposed to different ectomycorrhizal fungi species and the control. Our results highlight the positive and species-specific effect of ectomycorrhizal fungi exposure on drought tolerance in nursery-raised Scots pine seedlings. The studied ectomycorrhizal fungi functional traits may not be sufficient to predict the seedling response to drought stress, thus physiological studies across multiple species are needed to draw the correct conclusion. Our findings have potential practical implications for enhancing seedling drought tolerance in nursery plant production.