Altered microbial P cycling genes drive P availability in soil after afforestation.

Soil Phosphorous (P) availability is a limiting factor for plant growth and regulates biological metabolism in plantation ecosystems. The effect of variations in soil microbial P cycling potential on the availability of soil P during succession in plantation ecosystems is unclear. In this study, a metagenomics approach was used to explore variations in the composition and diversity of microbial P genes along a 45-year recovery sequence of Robinia pseudoacacia on the Loess Plateau, as well soil properties were measured. Our results showed that the diversity of P cycling genes (inorganic P solubilization and organic P mineralization genes) increased significantly after afforestation, and the community composition showed clear differences. The gcd and ppx genes were dominant in inorganic P transformation, whereas phnM gene dominated the transformation of organic P. The abundance of genes involved in inorganic P solubilization and organic P mineralization was significantly positively correlated with P availability, particularly for phnM, gcd, ppx, and phnI genes, corresponding to the phyla Gemmatimonadetes, Acidobacteria, Bacteroidetes, and Planctomycetes. The critical drivers of the microbial main genes of soil P cycling were available P (AP) and total N (TN) in soil. Overall, these findings highlight afforestation-induced increases in microbial P cycling genes enhanced soil P availability. and help to better understand how microbial growth metabolism caused by vegetation restoration in ecologically fragile areas affects the soil P cycling.

Changes in Soil Organic C Fractions and C Pool Stability Are Mediated by C-Degrading Enzymes in Litter Decomposition of Robinia pseudoacacia Plantations.

Litter decomposition is the main source of soil organic carbon (SOC) pool, regarding as an important part of terrestrial ecosystem C dynamics. The turnover of SOC is mainly regulated by extracellular enzymes secreted by microorganisms. However, the response mechanism of soil C-degrading enzymes and SOC in litter decomposition remains unclear. To clarify how SOC fraction dynamics respond to C-degrading enzymes in litter decomposition, we used field experiments to collect leaf litter and SOC fractions from the underlying layer in Robinia pseudoacacia plantations on the Loess Plateau. Our results showed that SOC, easily oxidizable organic C, dissolved organic C, and microbial biomass C increased significantly during the decomposition process. Litter decomposition significantly decreased soil hydrolase activity, but slightly increased oxidase activity. Correlation analysis results showed that SOC fractions were significantly positively correlated with the litter mass, lignin, soil moisture, and oxidase activity, but significantly negatively correlated with cellulose content and soil pH. Partial least squares path models revealed that soil C-degrading enzymes can directly or indirectly affect the changes of soil C fractions. The most direct factors affecting the SOC fractions of topsoil during litter decomposition were litter lignin and cellulose degradation, soil pH, and C-degrading enzymes. Furthermore, regression analysis showed that the decrease of SOC stability in litter decomposition was closely related to the decrease of soil hydrolase to oxidase ratio. These results highlighted that litter degradation-induced changes in C-degrading enzyme activity significantly affected SOC fractions. Furthermore, the distribution of soil hydrolases and oxidases affected the stability of SOC during litter decomposition. These findings provided a theoretical framework for a more comprehensive understanding of C turnover and stabilization mechanisms between plant and soil.

Soil ecoenzymatic stoichiometry reveals microbial phosphorus limitation after vegetation restoration on the Loess Plateau, China.

Exploring the limitations of soil microbial nutrient metabolism would help to understand the adaptability and response mechanisms of soil microbes in semi-arid ecosystems. Soil ecoenzymatic stoichiometry is conducive to quantifying the nutrient limitations of microorganisms. To quantify microbial nutrient limitation during plant restoration, we measured soil physicochemical properties, microbial biomass, and the activities of four enzymes (ꞵ-1,4-glucosidase, leucine aminopeptidase, ꞵ-1,4-N-acetylglucosaminidase, and alkaline phosphatase) in the soils of the northern Loess Plateau. Vegetation restoration patterns significantly affected soil properties, microbial biomass, enzymatic activity, and associated stoichiometry. Soil enzymatic activity increased significantly after vegetation restoration, especially in Robinia pseudoacacia plantations (RP). Correlation analysis showed that soil nutrients (C and N), moisture and pH were significantly correlated with ecoenzymatic activities and their stoichiometries. Vector-threshold element ratio (VT) model analysis revealed that microbial nutrient metabolism was limited by P, and soil microbial C limitation was significantly weakened after vegetation restoration, particularly in RP. Correlation analysis indicated that microbial nutrient limitations represented by the VT model were significantly correlated with soil moisture, nutrients, and associated stoichiometry. Therefore, the soil microbial community was mainly limited by P rather than N in vegetation restoration on the Loess Plateau via the VT model, and this limitation was primarily associated with the variation in soil properties. In addition, the soil microbial C limitation was significantly negatively correlated with microbial nutrient (P or N) limitation, which illustrated that soil microbial nutrient metabolism has strong stoichiometric homeostasis.

[Changes in Soil Microbial Carbon-Degrading Enzymes and Their Relationships with Carbon Pool Components During the Restoration Process of Robinia pseudoacacia].

To reveal the change in the characteristics of soil microbial C-degrading enzyme activities and the response to the components of C during the restoration process of Robinia pseudoacacia forests in the Loess Plateau, the components of the soil C pool, C-degrading enzyme activities, and microbial metabolic entropy of R. pseudoacacia in different restoration stages were studied, and the response relationship between C-degrading enzymes and soil C components was explored. The results showed that the microbial respiration (MR) first increased and then decreased with the restored years. We found that the microbial metabolic entropy (qCO2) decreased significantly with the restored years, but the microbial entropy (qMB) increased. Soil C-degrading enzymes increased significantly in the early-stage restoration of R. pseudoacacia; however, oxidizing enzymes (PO and PER) and cellobiohydrolase (CBH) decreased in the late stage of restoration. The soil organic C and recalcitrant organic C increased significantly with the restored years; however, there was no significant difference for the labile organic C. Correlation analysis and the partial least squares-path model (PLS-PM) showed that soil C-degrading enzymes and C components were significantly correlated with microbial respiration and entropy (qCO2 and qMB), respectively. The hydrolytic enzyme (BG+CBH) was significantly positively correlated with SOC, microbial biomass C, qMB, and recalcitrant and labile organic C. The oxidizing enzyme (PO+PER) was significantly positively correlated with the soil clay and qCO2. In addition, the recalcitrant organic C was the key driver of soil microbial metabolism affected by vegetation restoration. Overall, the ecosystem of R. pseudoacacia plantations would gradually stabilize with the increase in restored years and significantly increase the sequestration effect of soil C. These results will be helpful to understand the transformation rule and regulation mechanism of the soil C pool in vulnerable habitats and provide scientific basis for the restoration and management of vegetation in the Loess Plateau.

Plant Biomass and Soil Nutrients Mainly Explain the Variation of Soil Microbial Communities During Secondary Succession on the Loess Plateau.

Soil microorganisms play an important role in the circulation of materials and nutrients between plants and soil ecosystems, but the drivers of microbial community composition and diversity remain uncertain in different vegetation restoration patterns. We studied soil physicochemical properties (i.e., soil moisture, bulk density, pH, soil nutrients, available nutrients), plant characteristics (i.e., Shannon index [HPlant] and Richness index [SPlant], litter biomass [LB], and fine root biomass [FRB]), and microbial variables (biomass, enzyme activity, diversity, and composition of bacterial and fungal communities) in different plant succession patterns (Robinia pseudoacacia [MF], Caragana korshinskii [SF], and grassland [GL]) on the Loess Plateau. The herb communities, soil microbial biomass, and enzyme activities were strongly affected by vegetation restoration, and soil bacterial and fungal communities were significantly different from each other at the sites. Correlation analysis showed that LB and FRB were significantly positively correlated with the Chao index of soil bacteria, soil microbial biomass, enzyme activities, Proteobacteria, Zygomycota, and Cercozoa, while negatively correlated with Actinobacteria and Basidiomycota. In addition, soil water content (SW), pH, and nutrients have important effects on the bacterial and fungal diversities, as well as Acidobacteria, Proteobacteria, Actinobacteria, Nitrospirae, Zygomycota, and microbial biomass. Furthermore, plant characteristics and soil properties modulated the composition and diversity of soil microorganisms, respectively. Overall, the relative contribution of vegetation and soil to the diversity and composition of soil bacterial and fungal communities illustrated that plant characteristics and soil properties may synergistically modulate soil microbial communities, and the composition and diversity of soil bacterial and fungal communities mainly depend on plant biomass and soil nutrients.

Global scaling the leaf nitrogen and phosphorus resorption of woody species: Revisiting some commonly held views.

Leaf nutrient resorption is one of the important mechanisms for nutrient conservation in plants. Element stoichiometry is crucial to characterizing nutrient limitations and terrestrial ecosystem function. Here, we use nitrogen (N) and phosphorus (P) resorption efficiencies (NRE and PRE) and their stoichiometry to evaluate the response patterns of leaf nutrient resorption efficiency (NuRE) to plant functional groups, species traits, climate, and soil nutrients on the global scale. In light of the findings from the global data set of published literature on N and P resorption by woody plants, we revisit the commonly held views that: The strong N fixation ability of N-fixers weakened the NRE, which was consistent with the general views. The NuRE was linearly negatively correlated with plant growth rate. The higher NuRE of evergreen species than deciduous plants revealed how leaf life span constrains nutrient conservation. From the perspective of NRE, PRE and their ratios, woody plants were limited by P in the tropical zone and the limiting nutrient gradually transformed into N in the temperate zone (23.43-66.57°). The NuRE of woody plants in the frigid zone was the largest than that of others implied that low temperature may limit the nutrient absorption by plant roots, thereby enhancing the retranslocation of nutrients by senesced leaves. Furthermore, Akaike weights analysis found that mean annual precipitation (MAP) and temperature (MAT), N-fixers, soil nutrients, and leaf life span have significant effects on nutrient resorption patterns, sequentially. Overall, these results showed that the plasticity of plant nutrient resorption patterns was strongly sensitive to plant functional groups and soil nutrients, but the regularity of NuRE on a global scale was controlled by temperature and precipitation. And the resorption stoichiometry pattern better interprets plant nutrient limitation and the synergy effect of N and P in plant and soil on multiple scales.

[Leaf nutrient resorption characteristics of Robinia pseudoacacia at different ages and their response to soil nutrient availability]. / ä¸åŒæž—é¾„åˆºæ§å¶ç‰‡å »åˆ†é‡å¸æ”¶ç‰¹å¾åŠå ¶å¯¹åœŸå£¤å »åˆ†æœ‰æ•ˆæ€§çš„å“åº”.

To reveal nutrient resorption characteristics of Robinia pseudoacacia and their driving factors in hilly and gully regions, we measured the concentration of total nitrogen and total phosphorus in leaves and the concentrations and stoichiometry of organic carbon, total nitrogen, total phospho-rus, ammonium, nitrate and available phosphorus in soils of R. pseudoacacia plantations with different stand ages. We analyzed the relationship between leaf nitrogen and phosphorus resorption efficiencies and soil nutrient characteristics. The nutrients in plants and soil changed significantly with stand ages. The total and available phosphorus concentrations were low in the soil. Nitrogen resorption efficiency first increased and then decreased with the increases of stand age, with a range of 48.2%-54.0% and a mean value of 48.5%. Phosphorus resorption efficiency increased significantly with stand age, with a range of 45.2%-49.4% and a mean value of 46.9%. Nitrogen resorption efficiency showed negative response to soil nitrogen and N:P. Phosphorus resorption efficiency was significantly positively correlated to soil N:P and negatively correlated to soil available phosphorus. Our results indicated that soil nutrient availability negatively drove nutrient resorption efficiency. The strategies of leaf nutrient resorption responded strongly to soil N:P due to the N2-fixing effect and P-limitation of R. pseudoacacia.

Dynamics of bacterial community in litter and soil along a chronosequence of Robinia pseudoacacia plantations.

As the driver of plantation ecosystem function, microorganisms can decompose plant residues and soil organic matter. To identify dynamics of microbial communities in litter and soil and its influence by vegetation and soil at regional scales, the plantations of Robinia pseudoacacia at different successional stages (13, 19, 29, and 44 y) was selected on the Loess Plateau. High-throughput sequencing of the 16S rRNA gene was used to examine bacterial communities in litter and soil, and changes in vegetation, litter, and soil characteristics were analyzed. With increase of stand age, coverage and biomass of understory vegetation increased significantly and peaked at 44-y. Concentrations of carbon (C), nitrogen (N), and phosphorus (P) in litter and soil increased significantly, whereas pH values decreased significantly. Composition and diversity of bacterial communities in litter and soil were significantly different. Diversity and richness of litter bacterial communities were higher than that of soils. Relative abundances of Actinobacteria and Proteobacteria in litter were higher than that in soil; relative abundance of Acidobacteria exhibited the reverse trend. The diversity and richness index of vegetation significantly affected that of litter bacterial communities. Soil C/P significantly affected the Simpson and Shannon index of soil bacterial communities. The C/P and pH of litter and soil were significantly correlated with bacterial composition, primarily including Actinobacteria, Acidobacteria, and Gemmatimonadetes. Diversity of litter bacterial communities was more sensitive to the diversity and richness of vegetation flora than that of soil in the succession of R. pseudoacacia. Canopy density, vegetation, and litter and soil nutrients might directly or indirectly affect bacterial communities. Carbon, phosphorus, and pH may be critical factors influencing the composition of bacterial communities in litter and soil.