Stoichiometric ratios in soil are relevant to the abundance of constructive species in reed-dominated saline-alkaline marshes

Ecological stoichiometry is an important mediator of the feedback between plant and soil systems, which greatly affects ecosystem processes and functions. However, how carbon (C), nitrogen (N) and phosphorus (P) stoichiometry in plants and soils influence helophytes' performance to environmental changes remain unclear. In this study, the saline-alkaline marsh dominated by Phragmites australis in the Western Songnen Plain of China was investigated, and soil and plant samples along a saline-alkaline and flooding gradient were collected in 22 marsh sites. The results showed that C, N and P contents of leaf and soil and soil C:N:P stoichiometric ratios decreased significantly with increasing soil salt content (p < 0.05), but increased significantly with increasing flooding depth (p < 0.05). Soil C:N:P ratios decreased by 24.6 %-47.1 % in severely salinised sites (>5 g kg(-1)) than in unsalinised sites (<1 g kg(-1)), and they increased by 11.0 %-99.0 % in deeply flooded sites (>5 cm) than in shallowly flooded sites (<5 cm). Changes rates of foliar C:N:P ratios were remarkedly smaller than those of soil C: N:P ratios. Foliar N and P contents increased with increasing soil N and P contents, but foliar C:P and N:P ratios had negative associations with soil C:P and N:P ratios. The abundance of P. australis was explained by soil C:N:P stoichiometric ratios more than individual contents of C, N and P, in which soil N:P ratio played the largest role. These results suggest that maintaining the balances amongst C, N and P in soil is critical when restoring degraded marsh ecosystems.