Changes in plant-soil-microbe C-N-P contents and stoichiometry during poplar shelterbelt degradation

Abstract

<p>Extensive poplar shelterbelts are experiencing degradation, yet the consequences of this deterioration on plant-soil-microbe stoichiometry remain poorly understood. In this study, we selected three distinct types of pure poplar shelterbelts and examined the dynamics of tree leaf, soil, and microbial biomass carbon (C), nitrogen (N), and phosphorus (P) contents, as well as their stoichiometric relationships, at different stages of shelterbelt degradation, in order to explore the balance and limitation of nutrients in these rapidly degrading ecosystems. Our results show a consistent reduction in foliar N:P ratio throughout the degradation process for all shelterbelts, indicating an amplified N limitation on tree growth as degradation ensued. However, the underlying mechanisms varied among tree species. For Populus alba shelterbelts, the diminished soil organic carbon and total nitrogen (TN) contents during degradation suggest a reduction in the availability of substrates and energy sources for N mineralization, which combines with higher microbial N assimilation reflected by elevated soil microbial biomass carbon (SMBC) content, contributing to lower N absorption by trees. In Lombardy poplar shelterbelts, the inconsistent trends among reduced foliar N, stable soil TN, and unaltered SMBC and SMBC: SMBN ratio suggest either a decrease in microbial activity as degradation advanced or a reallocation of N by trees into tissues like roots, leaving the leaves N-deficient. Within Populus popular's shelterbelts, the diminished foliar N content, accompanied by an augmented foliar C:N ratio and reduced soil N:P ratio, indicates potentially deteriorated litter quality. This deterioration contributes to knock-on effects involving N-deficit soil organic matter, limited soil N availability, decreased N absorption by trees, and subsequently reduced foliar N content. Our study highlights the distinctive responses of plant-soil-microbe C-N-P stoichiometry to shelterbelt degradation, contingent on tree species, underscoring the diverse strategies that poplar shelterbelts employ when confronted with harsh internal and external conditions.</p>