Simulated grazing and nitrogen addition facilitate spatial expansion of Leymus chinensis clones into saline-alkali soil patches: Implications for Songnen grassland restoration in northeast China

The spatial expansion characteristic of most clonal plant species makes them produce large networks by elongating rhizomes/stolons, and occupy more physical space; thus it could contribute to restoring patchy degraded grasslands. Grazing and fertilization may affect the expansion of clonal plants, and thus can affect the vegetation recovery of degraded grassland. However, these have never been tested under field conditions. A field study was conducted from 2014 to 2019 to evaluate the effects of simulated moderate grazing (SG) and nitrogen (N) addition on spatial expansion of Leymus chinensis, a widespread clonal plant species in the eastern part of the Eurasian steppe. Results showed that SG and N addition increased the number of L. chinensis ramets (small but intact modules units of this plants and with its own roots) growing in saline-alkali soil patches; moreover, SG increased the total rhizome length and bud density of these ramets across the years by 59% and 52%, and N addition increased them by 88% and 98%, respectively. SG and N addition also increased the community biomass of the saline-alkali soil patches by 27% and 74%, respectively. Under SG conditions, more biomass of L. chinensis was allocated to belowground organs, and to ramets growing in saline-alkali soil patches. The findings demonstrated that both SG and N addition improved the spatial expansion of L. chinensis from favourable patches into saline-alkali soil patches, thereby potential ramet recruitment and vegetation reconstruction. Moderate grazing management or fertilization could improve the restoration of patchy degraded grasslands by affecting the spatial expansion of clonal plants.