Native Phragmites australis promotes greater carbon sequestration and stocks than Spartina alterniflora with future warming

Abstract

Climate model projections suggest a significant increase in global mean temperature by the end of the 21st century. Elevated temperature affects plant physiology within coastal wetlands, thereby affecting carbon sequestration processes. There is, however, limited knowledge about how native and invasive coastal wetland plants differ in their physiological responses to climate warming; warming may further promote invasive plant expansion at the expense of carbon sequestration. Here, we simulated future projected temperature increases using in‐situ open top chambers (OTCs) to understand photosynthetic and growth responses of a C3 native grass, Phragmites australis, and a C4 non‐native grass, Spartina alterniflora, in Yancheng, China. Warming slightly reduced the leaf net photosynthetic rate (Pn), specific leaf area, and chlorophyll content of P. australis, potentially due to an earlier termination of its growing season within the OTCs. In contrast, warming significantly enhanced Pn and chlorophyll content in S. alterniflora. For both species, shoot height increased, whereas shoot density decreased. Warming decreased the overall aboveground biomass of S. alterniflora by 24.5%, but only slightly reduced that of P. australis (by 5.9%). The P. australis wetland maintained a greater carbon stock and sequestration rate than S. alterniflora under elevated temperatures (~ 1.5°C), despite an apparent enhancement of leaf‐level ecophysiological function in S. alterniflora. As S. alterniflora invades Chinese marshes to the detriment of native plants, this implies potentially reduced carbon sequestration and biomass storage under future warming.