Patterns of Thermal Acclimation of Leaf Respiration in a Marsh-Mangrove Ecotone

Abstract:

Vegetated coastal ecosystems (saltmarsh, mangroves) make a large contribution to global net primary productivity and carbon (C) cycling despite covering a small proportion of the earth’s surface. Yet, our understanding of coastal C cycling processes over space, time, and in response to temperature, remain limited. Leaf respiration (R) is key component of local and global-scale carbon cycling and is a key parameter in global models that predict climate carbon cycle interactions. However, respiratory responses to temperature remain uncertain in marsh and mangrove species.

We measured short-term temperature responses of leaf respiration on a monthly basis for one year in a dominant C4 marsh grass species (Spartina alterniflora) and C3 mangrove species (Avicennia germinans) grown in situ under ambient temperatures and experimental warming at two sites in Florida. We tested whether marsh grasses and mangroves show similar acclimation of leaf R to seasonal temperature changes, and whether acclimation is consistent across sites and between plants grown under ambient and warmed conditions.

Across sites, Spartina showed convergent thermal acclimation of leaf R in response to both seasonal temperature changes and experimental warming. Specifically, R at 25 °C declined as seasonal temperatures increased and did so similarly across temperature treatments. Avicennia, however, showed no evidence of thermal acclimation of leaf R at either site. In fact, R at 25 °C tended to increase as seasonal temperatures increased and with warming. These results indicate that thermal acclimation of leaf R in marsh grasses could dampen the positive feedback between warming and rising atmospheric CO₂. However, no acclimation in Avicennia indicates that respiratory C fluxes from mangroves might increase substantially with climate warming. These data may be useful for advancing the representation of temperature controls of C cycling processes in coastal wetlands in earth system models.