Abstract:
The heat tolerance of photosystem II (PSII) may promote carbon
assimilation at higher temperatures and may help explain plant responses
to climate change. PSII heat tolerance could lead to 1) increases in the
high temperature compensation point (Tmax); 2) increases
in the thermal breadth of photosynthesis (i.e. the photosynthetic Ω
parameter) to promote a thermal generalist strategy of carbon
assimilation; 3) increases in the optimum rate of carbon assimilation
Popt and promote faster carbon assimilation; and/or 4)
increases in the optimum temperature for photosynthesis
(Topt). To address these hypotheses, we tested if the
Tcrit, T50 and T95metrics of PSII heat tolerance were correlated with each carbon
assimilation parameter for 21 species. Hypothesis 1 was not supported,
but we observed that T50 may estimate the upper thermal
limit for Tmax at the species-level, and that community
mean Tcrit may be useful for approximating
Tmax. The T50 and T95heat tolerance metrics were positively correlated with Ω in support of
hypothesis 2. We found no support for hypotheses 3 or 4. Our study shows
that high PSII heat tolerance is unlikely to improve carbon assimilation
at higher temperatures, but may characterize thermal generalists with
slow resource acquisition strategies.
Key Words: (need 5-10) leaf economics spectrum, climate change,
photosynthetic temperature response, thermoregulation, mountain passes
hypothesis