Vegetation recovery reshapes the composition and enhances the network connectivity of phoD-harboring microorganisms to promote P availability in a karst ecosystem

The type and degree of salinized soils together shape the composition of phoD-harboring bacterial communities, thereby altering the effectiveness of soil phosphorus cycling

Limitations in soil nutrient content, particularly phosphorus (P), are key factors constraining saline soil ecosystems. Soil phosphorus-cycling functional microorganisms contribute to the conversion of insoluble phosphorus and increase available phosphorus (AP) levels in phosphorus-deficient soils. However, there is limited knowledge on how soil phoD-harboring bacterial communities regulate AP availability across varying salinization types and degrees. This work evaluated the diversity, composition, assembly, and co-occurrence network properties of phoD-harboring bacteria, and explored their relationship with AP in salinized soils of Ningxia. First, TP, APi, and Ca10P levels were high in all salinized soils, whereas bioavailable fractions (AP, MBP, Ca2P, and Ca8P) were significantly low, limiting plant phosphorus uptake. Notably, the phoD gene, which is the most abundant functional gene involved in phosphorus cycling in saline soils, exhibits a pronounced salt-stress attenuation pattern along with the Shannon and Chao1 indices of the phoD-harboring bacterial community. Consistent with this pattern, the network complexity and stability of these bacteria were overall negatively affected by saline stress pressure when compared to non-saline soils. Furthermore, as evidenced by the distribution variations among bacteria such as Bradyrhizobium, Skermanella, Pseudomonas, Streptomyces, and Mesorhizobium, the type and degree of salinization jointly shape the composition of soil phoD-harboring bacterial communities. Importantly, the composition of these bacteria communities significantly regulates alkaline phosphatase ALP activity, thereby increasing soil AP levels. Consequently, the type and degree of salinized soil can indirectly regulate AP levels by influencing the composition of the phoD-harboring bacterial community. The research findings highlight that the composition of the phoD-harboring bacteria community is critical for the regulation of phosphorus efficiency in saline-affected soils, which holds significant theoretical and practical implications for the management of phosphorus in salinized soils and sustainable agricultural practices.

Epiphytic bacterial consortia drive growth regulation in potato under methyl jasmonate elicitation: A leaf surface multi-omics perspective

Methyl jasmonate (MeJA), a lipid-derived signaling molecule widely reported as a plant growth regulator, was revealed in this study to coordinate oxidative stress adaptation and delay senescence in potato through metabolite-microbe interactions, ultimately improving yield. MeJA triggered leaf oxidative stress while integrating rapid enzymatic scavenging, sustained osmoprotectant accumulation, and membrane stabilization, effectively delaying senescence initiation. Metabolic reprogramming under MeJA suppressed endogenous jasmonic acid synthesis while promoting saturated fatty acid biosynthesis, altering leaf surface lipid composition. These lipid changes, combined with MeJA-induced alkaloids, drove functional restructuring of phyllosphere epiphytic bacteria through fatty acid-mediated niche specialization, enhancing bacterial metabolism and enriching stress-resistant Proteobacteria. Notably, the enrichment of saturated fatty acids correlated with microbial taxa exhibiting specialized lipid metabolism. Field trials demonstrated that 200 μmol/L MeJA optimized redox homeostasis and photosynthetic longevity in early-maturing cultivar 'Favorita', translating delayed senescence into significant yield increases. This study proposes a "metabolite-guided microbial niche construction" model, where host lipid metabolism and secondary metabolites jointly shape stress-adapted microbial communities, providing new strategies for precision agrochemical design targeting phyllosphere microbiome engineering.

Plants Drive Microbial Biomass and Composition but Not Diversity to Promote Ecosystem Multifunctionality in Karst Vegetation Restoration

Natural restoration has emerged as a prominent approach in recent decades for the rehabilitation of degraded ecosystems globally. However, the specific changes and underlying mechanisms by natural restoration that influence the multifunctionality of karst ecosystems remain poorly understood. In this study, soil, litter, and fine root samples were collected from four chronosequence stages of vegetation restoration-grassland (G), shrubland (SH), shrub-tree land (ST), and forest (F)-within a karst ecosystem in Southwestern China. The aim was to evaluate the impacts of vegetation restoration on ecosystem multifunctionality using an averaging approach. The results demonstrated that the indices of C-cycling functionality, N-cycling functionality, P-cycling functionality, and total ecosystem multifunctionality increased as vegetation restoration progressed, along with plant diversity. The structure of plant, bacterial, and fungal communities varied across different stages of vegetation restoration, exhibiting the highest microbial diversity indices in the SH stage. Additionally, the tightness and complexity of co-occurrence networks of bacteria and fungi increased with advancing vegetation restoration, and higher positive links were observed in fungi than bacteria. The four functional indices were significantly and positively correlated with increasing plant diversity, fine root and litter nutrient contents, fine root biomass, microbial biomass, fungal community, enzyme activities, and soil nutrient contents but not with bacterial and fungal diversities. Furthermore, Random Forest model results revealed that plants exerted a significantly greater influence on ecosystem multifunctionality compared to other factors. It is plausible that plants influence soil microbial biomass, fungal community and co-occurrence networks, enzyme activities, and nutrient levels through the input of root and litter nutrients rather than by altering microbial diversity to enhance karst ecosystem multifunctionality. Therefore, initiatives to increase plant diversity are beneficial for sustainable ecological restoration management in the karst regions of Southwestern China.

Root and mycorrhizal nutrient acquisition strategies in the succession of subtropical forests under N and P limitation

BACKGROUND

Nutrient limitation is a universal phenomenon in terrestrial ecosystems. Root and mycorrhizal are critical to plant nutrient absorption in nutrient-limited ecosystems. However, how they are modified by N and P limitations with advancing vegetation successions in karst forests remains poorly understood. The present study compared the diversity indices, composition, and co-occurrence network of arbuscular mycorrhizal fungi (AMF) between grassland, shrubland, shrub-tree forest, and tree forest in subtropical karst forests, as well as soil nutrients and fine root functional traits (e.g., specific root length (SRL), specific root area (SRA), diameter, biomass, and N and P contents).

RESULTS

The fine roots diameter, biomass, and N and P contents increased with advancing succession, whereas SRL and SRA decreased. Network complexity and Richness and Chao1 indices of AMF increased from grassland to shrub-tree forest but decreased in tree forest. The fine roots N and P contents were positively related to their diameter and biomass, soil nutrients, and AMF composition but were negatively correlated with SRL and SRA. Moreover, these two parameters increased with the increase of soil nutrients. The variations in fine roots N and P contents were mainly explained by soil nutrients and fine root functional traits in grassland and by the interactions of soil nutrients, fine root functional traits, and AMF in the other three stages. Additionally, the interactive explanation with AMF increased from shrubland to shrub-tree forest but decreased in tree forest.

CONCLUSIONS

Our results indicated that mycorrhizal strategy might be the main nutrient acquisition strategy under N and P co-limitation. In contrast, the root strategy is the main one when an individual is subject to limitations in N or P in karst ecosystems. Root and mycorrhizal nutrient acquisition strategies are generally mutualistic, mycorrhizal strategy enhances plant nutrient acquisition under N and P co-limitation.

Planted Citrus Regulates the Community and Networks of phoD-Harboring Bacteria to Drive Phosphorus Availability Between Karst and Non-Karst Soils

The phosphorus (P) availability in soils is influenced by microbes, particularly those containing the gene responsible for phosphate solubilization. The present study investigated the community structure, diversity, and co-occurrence networks of phoD-harboring bacteria in karst and non-karst citrus orchard soils across a planting duration gradient, natural forests, and abandoned land, as well as the soil total P (TP) and available P (AP) contents and enzyme activities. The soil AP contents were lower in the karst regions than in the non-karst regions, while the soil organic carbon (C; SOC), exchangeable calcium, and microbial biomass nitrogen (N) contents; alkaline phosphatase (ALP) and β-Glucuronidase activities; and pH had the opposite trends. In addition, the soil AP and SOC contents and the ALP and acid phosphatase (ACP) activities in the karst regions decreased with an increase in the planting years, whereas the AP, TP, and microbial biomass P contents and ACP activities in the non-karst regions increased. The diversity indices and network complexity of phoD-harboring bacteria were higher in the karst regions than in the non-karst regions, with marked community differences between different planting years in the non-karst regions. The soil AP was significantly and positively correlated with the rare genera Pelagicola, Methylobacter, Streptomyces, and Micromonospora in the karst regions and Roseivivax, Collimonas, Methylobacterium, Ralstonia, and Phyllobacterium in the non-karst regions. Structural Equation Modeling showed that citrus cultivation altered the soil pH, SOC, and total N, and, in turn, the phoD-harboring bacterial community structure and diversity, which led to changes in the ALP activity and P availability. Thus, the rare genera of the phoD-harboring bacteria, influenced by the pH and SOC, highly regulated the availability of P in the karst and non-karst citrus orchard soils.

Lithology and elevated temperature impact phoD-harboring bacteria on soil available P enhancing in subtropical forests

Plants are generally limited by soil phosphorus (P) deficiency in forest ecosystems. Soil available P is influenced by lithology, temperature, and soil microbes. However, the interactive effects of these factors on soil P availability in subtropical forests remain unclear. To assess their impacts, we measured soil inorganic and available P fractions and the diversity, composition, and co-occurrence network of phoD-harboring bacteria in two contrasting forest soils (lithosols in karst forests and ferralsols in non-karst forests) in the subtropical regions of southwestern China across six temperature gradients. The present results showed that the complexities in composition and network and the diversity indices of phoD-harboring bacteria were higher in the karst forest soils than those in the non-karst forest soils, with marked differences in composition. In both types of forest soils, the complexities of composition and networks and the diversity indices were higher in the high-temperature regions (mean annual temperature (MAT) > 16 °C) compared to the low-temperature regions (MAT <16 °C). Soil total inorganic and available P contents were lower in the karst forest soils compared to the non-karst forest soils. Soil total available P contents were lower in the high temperature regions than those in the low temperature regions in both forest soils, whereas soil total inorganic P contents were contrary. Variance partitioning analysis showed that soil inorganic and available P fractions were predominantly explained by lithology and its interaction with soil microbes and climate. The present findings demonstrate that soil P availability in subtropical forests of southwestern China is influenced by lithology and temperature, which regulate the diversity, composition, and network connectivity of phoD-harboring bacteria. Furthermore, this study highlights the significance of controlling the composition of phoD-harboring bacteria for mitigating plant P deficiency in karst ecosystems.