Phosphorus deficiency is the main limiting factor for re-vegetation and soil microorganisms in Mu Us Sandy Land, Northwest China

Forest management impacts on soil phosphorus cycling: Insights from metagenomics in Moso bamboo plantations

Bamboo forests are crucial ecosystems and provide essential ecological and economic services in both tropical and subtropical regions. Soil phosphorus (P), a vital nutrient for plant growth, is fundamental to the productivity and health of bamboo forests. However, the microbial mechanisms through which management practices affect soil P processes in bamboo forests remain poorly understood. This study employed metagenomics to examine alterations in microbial P cycling in Moso bamboo plantations under three distinct management conditions. The results revealed that intensive management (M2, annual fertilization, selective harvesting, and understory vegetation removal) significantly increased soil inorganic P (Pi) by 61.76% and 87.39% compared to extensive management (M1, selective bamboo trunk and shoot harvesting every two years) and non-management (M0), respectively, while decreasing soil organic P (Po) by 50.41% and 41.05%. Forest management significantly altered the bacterial communities: Firmicutes, WPS-2, and Acidobacteriales were represented in M2, Xanthobacteraceae in M1, and Chloroflexi AD3, Acidothermus, and Subgroup_2 in M0. M2 significantly increased the community-level habitat niche breadth and weakened the deterministic process of bacterial community assembly relative to M1 and M0 (p ≤ 0.05). Furthermore, functional metagenomics showed that the total abundance of genes related to Po mineralization, P transportation, and P regulation was significantly lower (p ≤ 0.05) in M2 than in M0 and M1. pstA, pstB, and pstC were more abundant in M2 (p ≤ 0.05), whereas phnN, phnI, phnG, phoA, phoD, phnC, phnD, and phnE were more abundant in M1 (p ≤ 0.05), and phnF was significantly abundant in M0 (p ≤ 0.05). A partial least squares path model indicated that soil bacterial community and P cycling genes had direct effects on Pi and Po, respectively. These findings enhance our understanding of the links between forest management practices and P cycling, providing insights for improving soil functionality and nutrient balance.

Effects of nitrogen addition on rhizosphere priming: The role of stoichiometric imbalance

Nitrogen (N) input has a significant impact on the availability of carbon (C), nitrogen (N), and phosphorus (P) in the rhizosphere, leading to an imbalanced stoichiometry in microbial demands. This imbalance can result in energy or nutrient limitations, which, in turn, affect C dynamics during plant growth. However, the precise influence of N addition on the C:N:P imbalance ratio and its subsequent effects on rhizosphere priming effects (RPEs) remain unclear. To address this gap, we conducted a 75-day microcosm experiment, varying N addition rates (0, 150, 300 kg N ha-1), to examine how microbes regulate RPE by adapting to stoichiometry and maintaining homeostasis in response to N addition, using the 13C natural method. Our result showed that N input induced a stoichiometric imbalance in C:N:P, leading to P or C limitation for microbes during plant growth. Microbes responded by adjusting enzymatic stoichiometry and functional taxa to preserve homeostasis, thereby modifying the threshold element ratios (TERs) to cope with the C:N:P imbalance. Microbes adapted to the stoichiometric imbalance by reducing TER, which was attributed to a reduction in carbon use efficiency. Consequently, we observed higher RPE under P limitation, whereas the opposite trend was observed under C or N limitation. These results offer novel insights into the microbial regulation of RPE variation under different soil nutrient conditions and contribute to a better understanding of soil C dynamics.