Drought represents a paramount abiotic stressor constraining global agroforestry productivity. Plants have evolved multifaceted adaptive strategies involving active modulation of symbiotic microbial communities to mitigate drought stress. These plant-associated microbes enhance plant drought adaptation via five principal mechanisms: (i) extracellular polymeric substance-mediated biofilm formation on plant surface enhances hydroregulation and edaphic structural stability; (ii) osmoprotectant biosynthesis (e.g., proline) maintains cellular osmotic equilibrium; (iii) synthesizing antioxidants to reduce damage from reactive oxygen species and oxidative stress; (iv) regulating plant phytohormone metabolism by secreting hormones (e.g. indole-3-acetic acid) and 1-aminocyclopropane-1-carboxylic deaminase; (v) emitting signaling molecules (e.g. volatile organic compounds, hormones and enzymes) to activate plant drought adaptation. Future researches should focus on the development of host-specific drought-adaptive microbial consortia while elucidating phyllosphere–rhizosphere microbiome crosstalk, ultimately harnessing translational microbiome engineering to evaluate their efficacy in multi-environment agricultural systems.

The mechanisms of plant adaptation to environmental gradients have been the focus of ecological research, with environmental stresses driving coordinated or differentiated regulation of plant functional traits. Plant resource acquisition involves root trait plasticity and mycorrhizal symbiosis. However, root trait plasticity along precipitation gradients and root-mycorrhizal trade-offs remain unclear. We conducted community surveys along a west-east precipitation gradient in four natural grassland communities (alpine desert steppe, alpine steppe, alpine meadow steppe and alpine meadow) on the plateau in northern Xizang Plateau. Six key root traits (root diameter, RD; root dry matter content, RDMC; root tissue density, RTD; specific root length, SRL; root branching intensity, RBI; and root length colonization percentage, RLC) were measured in 18 alpine plant species to investigate the coordination and trade-offs between root traits and mycorrhizal fungi along the precipitation gradient. Our results showed community-level declines in RDMC, RD, RTD and RLC with increasing precipitation, contrasting with elevated RBI and SRL. Functional groups exhibited distinct patterns: grasses and legumes demonstrated root-mycorrhizal trade-offs, sedges displayed synergy and forbs showed inconsistent responses. Divergent trends in plant root traits and mycorrhizal fungi were observed at the species level. Alpine plants in humid eastern meadows favored root elongation, while those in arid western desert steppe relied on radial growth and mycorrhizal fungal cooperation for resource acquisition. These findings highlight varied root absorption strategies among alpine plants along environmental gradients, supporting the importance of ecological niche diversification in maintaining alpine ecosystem diversity and stability.

Arbuscular mycorrhizal fungi (AMF) and Bacillus play a crucial role in promoting the growth and defense of exotic plants, and their interaction may further enhance plant invasions. Soil nitrogen level is an important factor that affects the interaction. However, the effect of the interaction on the growth and defensive ability of exotic plants under different nitrogen levels remains unclear. In this study, a pot experiment was conducted using Rhizoglomus intraradices (RI) and Bacillus megaterium (BM), one of the dominant AMF and Bacillus in the rhizosphere of Flaveria bidentis, with three soil nitrogen levels (0, 3.75 and 7.5 g m⁻²) and four inoculation treatments (uninoculated, inoculation with RI, inoculation with BM and co-inoculated with RI and BM). Significant correlations were observed between microbial inoculations and indicators of plant growth and defense across varying soil nitrogen levels. Co-inoculation notably enhanced both plant growth and defense compared to single inoculations, especially under the nitrogen concentration of 3.75 g m⁻². Specifically, compared to single inoculation, co-inoculation increased the biomass of F. bidentis by 8.27% and 16.4%, as well as the flavonoids concentration by 21.89%–30.95% and phenolic acids concentration by 54.22%–60.93%, respectively. These enhancements in growth and defensive compound production likely promote the competitive ability of F. bidentis and its resistance to biotic and abiotic stresses, thereby contributing to its successful invasion.

Trait-based functional diversity (FD) is an important predictor of tree species ecological multifunctionality (TS-EMF), but its relationship may be mediated by environmental factors. Currently, the study of threshold-dependent relationship between FD and TS-EMF along urban and suburban gradients and their environmental regulatory mechanisms is still quite limited. In this study, 12 typical tree species from urban and suburban forests in Shenyang were used to calculate TS-EMF by combining the multithreshold and averaging method, and to assess community FD, aiming to reveal the role of FD on TS-EMF and how environmental factors regulate TS-EMF through FD and community-weighted mean (CWM) traits. The results showed that urban TS-EMF was generally higher than suburban (P < 0.05). There were differences in the driving mechanisms of TS-EMF at different threshold levels, with air humidity (total effect: 0.435) and CWM P_n (net photosynthetic rate, relative importance: 24.42%) being the key drivers at high threshold levels. At low threshold levels, functional evenness (FEve) played a dominant role, but the extent to which influenced TS-EMF depended on the type and number of tree species within the TS-EMF threshold range. Notably, the effects of CWM P_n and FEve on TS-EMF showed threshold dependence, with thresholds of 61.18% and 64.47%, respectively. Additionally, the urban–suburban gradient could significantly influence the driving mechanism: the direct effect of environmental factors and CWM traits prevailed in urban forests, while suburban forests showed a multifactorial cascade effect. The study showed that the formation of TS-EMF in urban forests is the result of multifactorial coupling of traits, FD and environmental factors, and this finding provides a new theoretical perspective for understanding the ecosystem service drivers of urban forests.