Understanding the impact of a complex environmental matrix associated with climate change on the European marshes engineer species Spartina maritime

Abstract A challenge exists in the need to understand plant responses in complex environmental matrixes, such as those predicted by climate change models, being this information essential for species that support important ecosystem functions. A factorial climatic chamber experiment was designed to evaluate the impact of atmospheric CO2 concentration (400 ppm and 700 ppm CO2) in combination with two maximum and minimum temperature ranges (28/13 °C and 32/17 °C) and salinity concentrations (0 and 171 mM NaCl) on the growth and photosynthetic responses of the ecosystem engineer species Spartina maritima. Plants grown at 32/17 °C showed a reduction ∼39% on relative growth rate (RGR) and this was more drastic (i.e. 64%) in those exposed to 700 ppm CO2, which also showed an increment in the percentage of dead tillers regardless of salinity. These reductions were explained by the negative impact on net photosynthetic rate (AN), which decreased with temperature increment, being this reduction more acute at 700 ppm CO2. This response was associated with an augmentation in CO2 diffusion limitations, as indicated the lower stomatal conductance (gs), together with a down-regulation photochemical apparatus efficiency, as indicated the lower electron transport rate (ETR) and energy fluxes derived from Kautsky curves. In addition, the greatest gs drop at 700 ppm CO2, would limit plant ability to cope with temperature excess through evapotranspiration, a fact that could have boosted temperature-triggered damage and, consequently, leaf senescence. Therefore, we can conclude that temperature and atmospheric CO2 increments would compromise the development of S. maritima and consequently the maintaining of its ecosystem functions.