Do tropical and desert plant leaves trade carbon gain against non-lethal temperature maintenance?
Abstract
Global warming may increase plant temperatures and alter plant performance. Non-lethal, high leaf temperatures (Tleaf) can reduce net photosynthetic rates and growth. However, alternate physiological strategies that might maintain functioning and carbon balance during hot conditions (Tleaf>35 °C) are not well understood. We investigated whether tropical and desert plant species exhibit alternate water-use strategies to preserve carbon-costly tissues via evaporative cooling, instead of optimizing carbon gain per unit water loss. To assess whether warming leaves by ~2 °C would induce a shift in water-use strategies in order to cool sun-exposed leaves, we installed passive heating treatments. We measured diurnal leaf net photosynthesis (An), transpiration (Et), and stomatal conductance (gs) and Tleaf (thermal infrared camera) of 11 common Sonoran desert plant species and 15 Panamanian wet tropical forest tree species during their dry seasons. Predawn and midday leaf water potentials (ψl; MPa) and leaf mass per area (LMA; g/m2) served as proxies for drought tolerance and leaf carbon investment, respectively. All three physiological parameters (An, Et and gs) declined between 29-37% (P<0.001) when tropical leaves were heated, while for desert plants An declined by 40% (P<0.05), but Et and gs were sustained (-3% and -13%, respectively; ns). In tropical species, there was no difference in diurnal trends between control and heated leaves, and no evaporative cooling. In contrast, 6 desert species showed evaporative cooling capacities when Tleaf was high. Water loss from tropical canopies was highly influenced (P<0.001) by leaf-to-air vapor pressure deficit (VPDl) while desert canopies kept stomata open even when VPDl was above 3 kPa (ns). Most desert plants with high LMA adopted a heat avoidance strategy, while tropical plants with high drought tolerance (ie., leaves with large difference of midday and predawn ψl (Δψl)) had low An and Et when heated (r2=0.62 and 0.52, respectively; P<0.05). In other words, when under heat stress, desert plants spend available water for leaf cooling, thus preserving photosynthetic tissue, while tropical plants suppress gas exchange to avoid hydraulic failure.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B31D..07A
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0426 Biosphere/atmosphere interactions;
- BIOGEOSCIENCES;
- 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCES;
- 0476 Plant ecology;
- BIOGEOSCIENCES