Mowing and phosphorus affect plant diversity and soil carbon and nitrogen storage under nitrogen enrichment in the semi-arid alpine steppe

Plant diversity strongly affected the grassland productivity and soil C and N storage. Nitrogen enrichment weakens the stability of the ecosystem through decreased biodiversity. Mowing is a viable management tool for the maintenance of diversity in grasslands. However, it is unclear how plant diversity affects soil C and N storage in mowing (or phosphorus) under N enrichment in the semi-arid alpine steppe. In the present study, a 3-year trial has investigated the effects of nitrogen, mowing (or phosphorus), and their interactions on plant diversity and soil C and N storage in a semi-arid alpine steppe in Qilian mountains, northern China. We found that aboveground biomass (AGB) was significantly increased in N (nitrogen added alone) and NP (both nitrogen and phosphorus added), significantly decreased in M (mowing) across the three years (2019-2021) (P < 0.05), and significantly increased by 21.4% in the third year in MN (nitrogen added at the time of mowing). Plant diversity was significantly decreased in N and NP, but had no significant effect under M, MN, and P across the three years. We found that SOC stock was significantly decreased by 13% in the 0-10 cm soil layer in N, while increased by 6% at the 10-20 cm soil layer in MN. In contrast, NP had no significant effect on SOC stock and TN stock, while both NO3-N and AP significantly increased. M increased the relative biomass of sedge and forb, while N increased the relative biomass of grass and decreased the relative biomass of forb. Forb is positively correlated with C storage and negatively correlated with N storage, while the grass is the opposite. Therefore, the results indicated that mowing modulated the effects of N addition on diversity loss and carbon stock loss. In contrast, phosphorus is ineffective for the negative effect of nitrogen on grassland species diversity.

Automated summary

Plant diversity has a strong impact on grassland productivity and soil C and N storage. Nitrogen enrichment decreases biodiversity and weakens ecosystem stability. Mowing is an effective management tool for maintaining diversity in grasslands. This study investigated the effects of nitrogen, mowing (or phosphorus), and their interactions on plant diversity and soil C and N storage in a semi-arid alpine steppe. The results showed that mowing can modulate the effects of nitrogen addition on diversity loss and carbon stock loss, while phosphorus has no effect on the negative impact of nitrogen on grassland species diversity.