Temperature controls of leaf respiration in a marsh-mangrove ecotone and the role of temperature acclimation

Matthew Sturchio1, Jeff Chieppa2, Gabriela Canas1, Samantha Chapman3, Michael Aspinwall21Department of Biology, University of North Florida, 1 UNF Drive, Jacksonville, FL 32224 USA; 2School of Forestry and Wildlife Sciences, Auburn University, 602 Duncan Drive, Auburn, AL 36849 USA;

3Department of Biology, Villanova University, 800 Lancaster Avenue Villanova, PA 19085

Background and Rationale

Figure 1. Northern and southern sites designated by yellow and orange stars respectively. Below the map of Florida are the experimental species x treatment combinations (Avicenniaambient, Avicennia warmed, Spartina ambient, Spartina warmed).

Location & ApproachDespite covering a small proportion of earth’s surface, vegetated coastal ecosystems (saltmarshes and mangrove forests) play a major role in the global carbon (C) cycle. Climate warming might impact important processes (photosynthesis and respiration) that regulate plant C uptake and use.

Thermal acclimation might modify photosynthetic and respiratory responses to climate warming, which could affect C flux modelling and how we understand coastal C cycling locally.

Overall, the aim of this project was to utilize a climate warming experiment replicated at two sites within the Guana Tolomato Matanzas National Estuarine Research Reserve (GTMNERR) on the Atlantic coast of Florida to improve our understanding of temperature controls of respiratory CO2 fluxes in marsh and mangrove species.

1. Examine changes in the short-term temperature response of leaf respiration (CO2efflux) over space (two sites) and time (seasons) in a dominant C4 marsh grass species(Spartina alterniflora) and C3 mangrove species (Avicennia germinans) (Figure 1).

2. Determine whether leaf respiration ‘acclimates’ to seasonal temperature changes across sites, and whether respiratory responses to temperature across seasons and sites differs between S. alterniflora and A. germinans.

3. Use passive warming chambers at each site to determine whether experimental warming alters respiratory responses to temporal and spatial changes in temperature in both species.

4. Test whether variation in leaf N (proxy for enzyme concentrations) explains temperature acclimation patterns over space and time in both species.

Objectives

Leaf Physiology Results

Takeaways

Leaf N Results

Leaf samples were collected in situ (Figure 1) ~ bi-monthly over a 10-month period at two sites. Sampling was done pre-dawn to avoid photosynthetic activation.

High resolution, short-term temperature response curves (20°- 40°C) of leaf respiration were generated.

Leaf dry mass per unit area ( LMA, g cm-2) was calculated Using measurements of surface area and dry mass of the leaves. Homogenized leaf material was processed using an Elementar rapid max N combustion analyzer to determine leaf N concentrations.

Methodology

Although temperature acclimation of R differed between species, air temperature and leaf N were strong predictors of leaf R in both species.

These results improve our quantitative and predictive understanding of temperature controls of leaf respiration in coastal plant species.

Figure 3. Relationships of leaf N concentration and leaf Rfor A. germinans (panels a and c) and S. alterniflora(panels b and d) at both sites, with and without warming. Leaf R per unit area at 25°C (Rarea25) relationship to leaf N per unit area (Narea) (panels a and b). Leaf R per unit mass at 25°C (Rmass25) relationship to leaf N per unit mass (Nmass) (panels c and d). *Please see note for clarification of regression symbols*

Figure 2. Relationships of 7 day daily mean temperature and leaf phys. traits for A. germinans (c, e, g) and S. alterniflora (d, f, h) at two sites, with and without warming. Leaf R per unit mass at 25°C (Rmass25) (panels c and d); Temperature sensitivity (Q10) of Rmass25(panels e and f); Leaf mass per unit area (LMA) (panels g and h). *Please see note for clarification of regression symbols*

In Spartina, Rm25 and the temperature sensitivity (Q10) of R declined as temperatures increased across treatments and sites (Figure 2, panel d and f).

In Avicennia, Rm25 increased as temperatures increased at the southern site only (Figure 2, panel c). The Q10 of R decreased as temperatures increased across sites and treatments (Figure 2, panel e). In both species, leaf respiration scaled positively with leaf N (Figure 3).

** NOTE: Red and blue lines = significant effect of warming across

sites.**