5. Conclusions
Overall, our results verified our primary hypothesis that marsh degradation significantly influenced the accumulation and transformation of soil P owing to the desiccation accompanied with plant community and overgrazing, further altering soil P availability. Lightly and moderately degraded marsh soils had significantly higher total P and P availability than relatively pristine marsh soils. However, soil P availability in the heavily degraded marsh was lower than that in the relatively pristine marsh. Marsh degradation primarily induced the transformation from soil slowing P to organic and labile P via litter return or livestock excreta combined with marsh desiccation. For alpine wetland ecosystem, soil available P was mainly related to organic and non-occluded P that might also be non-negligible direct source of available P. Marsh degradation regulated soil P availability via the transformation of apatite P to organic P. Our work illustrates that the risk of P limitation occurred in heavily degraded marsh soils with low available P. Future research should focus on measures to improve P availability for the ecological restoration of desertified meadows, such as grazing exclusion and the application of organic fertiliser. In addition, the variations of organic P fractions in differently degraded marsh soils also should be investigated to understand the transformation of organic P fractions and their effects on soil P supply, which has great significance for the ecological restoration of alpine degraded marshes.
Acknowledgements
This research was financially supported by the grant from Applied Basic Research Programs of Science & Technology Department of Sichuan Province, China [ grant number 2021YJ0341], the National Natural Science Foundation of China [grant number 41401328] and the Key Research and Development Program of Sichuan Province, China (2019YFN0020).