Drying-rewetting changes soil phosphorus status and enzymatically hydrolysable organic phosphorus fractions in the water-level fluctuation zone of Three Gorges reservoir

Transformation of phosphorus forms and its regulation on phosphorus availability across differently degraded marsh soils

“…Thus, soil P availability was significantly higher in the LDM than in the NDM (Figure 5a, b), although the released soluble P might have been slightly lost because of inundation (Kröger et al, 2012;Zhou et al, 2019) in the wet season. This was similar to the results previously observed in the water-level fluctuation zones of the Three Gorges Reservoir area, China (Wang, Guo, et al, 2021), estuarine wetlands with different vegetation in the Yellow River Delta, China (Qu et al, 2021(Qu et al, , 2018Xu et al, 2012), and managed wetland cells of Mississippi, USA (Kröger et al, 2012).…”

“…Our result was closely associated with water status, combined with changes in the plant community or overgrazing. When alpine marshes experienced light or moderate degradation, dense plant communities of hygrophytes and mesophytes, such as Carex , Blysmus sinocompressus , and Kobresia tibetica (Table 2), increased plant coverage, aboveground biomass (Table 2), biodiversity and richness owing to the drying‐rewetting of seasonal flooding (Wang, Guo, et al, 2021) and water table drawdown to the soil subsurface (Zeng et al, 2021). Consequently, plant roots might take up more bioavailable inorganic P and then return more organic P (Huang et al, 2015) via a high litter input compared to NDM, particularly in surface soil (Table 2).…”

“…Theoretical and experimental studies have demonstrated that soluble P (available P) is regulated by the direct and indirect effects of various P forms (Gama‐Rodrigues et al, 2014; Hou et al, 2016), and changes in soil environments (e.g., plant community and hydrography) also influence the transformation of P forms to available P (Wang, Guo, et al, 2021). Thus, a priori structural equation model of the direct and indirect effects of soil P forms on available P under marsh degradation is constructed in Figure 2 based on the following hypothesis: (1) marsh degradation has an indirect effect on available P by the mobilization of stable and moderately labile inorganic P and organic P; (2) the mobilization of soil P in alpine wetlands mainly follows a process from organic P to inorganic P and from stable P to moderately labile P and labile P in turn (Hou et al, 2016).…”

“…This can be ascribed to the differences in hydrography, vegetation, and grazing between NDM and degraded marshes. Some studies have confirmed that frequent drying-rewetting and organic acids from litter and/or organic fertilizer (e.g., livestock excreta) might induce direct and indirect transformation from apatite and organic P to labile and moderately labile inorganic P (Hallama et al, 2019;Schelfhout et al, 2021;Wang, Guo, et al, 2021). Organic acids can dissolve occluded P into non-occluded P (Gatiboni et al, 2021;Touhami et al, 2020), and organic and occluded P might be potential sources of available P in P-deficient soils (Turner et al, 2014).…”

“…Changes in P accumulation and forms further alter P availability in wetland soils (Wang, Guo, et al, 2021). For example, Huang et al, 2015 observed that the exotic invasive plant Spartina alterniflora significantly increased the concentrations of P extracted by 1.0 mol L −1 NH 4 Cl, bicarbonate/dithionite‐extracted P, and P extracted by 0.5 mol L −1 NaOH in the Yancheng wetland of eastern China, leading to an increase in available P. Similarly, Hu et al (2021) observed that an increase in wetland salinity might significantly enhance labile P release owing to iron (Fe)‐bound P reduction in the Min River estuary wetland, China.…”