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).