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 T95 metrics 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
T95 heat 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.