Effect of human reclamation and Spartina alterniflora invasion on C-N-P stoichiometry in plant organs across coastal wetlands over China

Background and aims Coastal wetland types have been severely altered by human reclamation activities and Spartina alterniflora invasion. However, how these changes impact C-N-P stoichiometry and nutrient allocation of coastal plants remain unclear. Methods We investigated C, N, and P contents and ratios in leaf, stem, and root from 30 sites with adjacent natural wetlands (as control, dominated by native Phragmites australis ), reclaimed wetlands (dominated by native P. australis ), and invasive wetlands (dominated by exotic S. alterniflora ) across eastern coast of China. Results C content and N:P ratio remained constant, N and P contents decreased significantly, but C:N and C:P ratios increased with increasing latitude in natural wetlands. While the direction or magnitude of these latitudinal patterns in reclaimed and invasive wetlands were extremely changed at both individual and organ level. Interestingly, leaf had significant higher C, N, and P contents but lower C:N and C:P ratios than stem and root in each wetland. Compared with natural wetlands, both reclaimed and invasive wetlands had significant lower C and N contents and N:P ratio but higher C:N ratio, invasive wetlands also had significant higher leaf P content. P. australis enhanced the homeostasis for N:P, strength allometric relationship of N and P in leaf, but exhibited a isometric relationship of N and P at individual level after reclamation. S. alterniflora had strict homeostasis for N, P and N:P in most organs and strong ability to decouple the allometric relationship of N and P in leaf, and N changed faster than P at individual level. Conclusions Importantly, large-scale observations showed that reclamation and especially S. alterniflora invasion significantly decreased N:P ratio in each organ, which might highly affect below- and above-ground trophic chains in the future. Our study provides practical insights in understanding species-specific and multiorgan biogeochemical process and the nutrient allocation strategies of plants under reclaimed and invasive pressures in coastal salt marshes.