Depth matters: The impact of vegetation clipping on phosphorus fractions across peatland depth profiles

Abstract

The stability of carbon (C) stocks in peatlands is closely linked to phosphorus (P) bioavailability. Plant plays a crucial role in modulating P bioavailability. However, the mechanisms by which different plant functional types (PFTs; mainly Sphagnum moss, shrub, and graminoid) modulate P bioavailability in peatlands remain unknown, especially the vertical stratification related to plant belowground biomass distributions. In this study, we investigated the effects of PFT clipping on soil P bioavailability through a vegetation clipping manipulation, followed by the application of low molecular weight organic acids (LMWOAs) (azelaic, malonic, and muconic acids) and phosphatase enzymes (acid phosphatase, phosphodiesterase, and phytase). The results showed that LMWOAs are the key factors in promoting the concentration of soluble P in the soil, especially for organic P (P_o). Following PFT clipping, P bioavailability significantly decreased, except for graminoids, where clipping increased it. The relative abundance of P-solubilizing bacteria Acinetobacter and Rhodanobacter increased while soil pH decreased after graminoid clipping, which enhanced the desorption and dissolution of inorganic P and increased water-soluble orthophosphate concentration. Acid phosphatase activity decreased by ∼40 % after PFT clipping, indicating the reduction in the mineralization of P_o and the accumulation of potentially bioavailable P (i.e., enzyme-labile P_o), especially acid phosphatase and phosphodiesterase labile P_o. Furthermore, Sphagnum mosses, shrubs, and graminoids were the primary regulators of P bioavailability at depths of 0–10, 0–20, and 20–30 cm, respectively. Shift in vegetation composition driven by climate change and human activity may significantly influence P dynamics and the stability of C stock in peatlands, offering critical insights for balancing peatland conservation and agricultural utilization.