Climate warming increases the invasiveness of the exotic Spartina alterniflora in a coastal salt marsh: Implications for invasion management.

Spartina alterniflora is a major invasive C grass in coastal wetlands worldwide. It spreads rapidly through both clonal growth and sexual reproduction, causing significant negative impacts on the ecological functions of coastal wetland ecosystems. A key question is whether climate warming will affect its invasiveness and how adaptive management strategies can be developed to address the anticipated climate warming. In this study, open-top chambers (OTCs) were used to elevate temperature (+1.5 °C) throughout the entire growing season for two years (2019-2020), we measured the leaf gas exchange, leaf and plant growth functional traits, as well as clonal and sexual reproduction traits of S. alterniflora under the warming and ambient (control) conditions. The results showed that (1) Compared to the control, warming significantly increased shoot biomass of S. alterniflora through both physiological and phenotypic changes in the middle and later periods of the growing season (p<0.05); (2) Warming did not affect clonal shoots (p>0.05), but it increased the shoot biomass allocation to spikes, resulting in higher spike biomass and seed production (both number and weight) compared to the control (p<0.05); (3) Warming induced alterations in seed morphology and mass distribution, leading to an increase in seed floating time (p<0.05), while the weight of the endosperm and embryo remained unaffected, and no differences in seed germination were observed (p>0.05). We concluded that climate warming affected shoot biomass through both physiological and phenotypic modifications and influenced reproductive traits by altering resource allocation to organs and seed composition. The invasiveness of S. alterniflora should increase due to increased shoot biomass, higher seed production, and longer seed floating times. Implementing cutting measures at the early flowering stage is recommended to mitigate the effects of anticipated climate warming.