Photosynthetic thermal tolerance and recovery to short duration temperature stress in desert and montane plants: A comparative study

Background/Question/Methods

Climate change models predict an increase in frequency and amplitude of extreme events, including heat waves. The rate of climate change could potentially change the distribution and diversity of plant species, resulting in fundamental shifts in the composition of plant communities at the biome level. To better predict how the composition and distribution of plant assemblages might respond to extreme temperature events, it is important to understand how plant species currently respond to these extremes. In this study, we asked (1) do desert plants have higher temperature thresholds for photosynthetic thermal tolerance (T₂₅) and photosynthetic recovery (RT₂₅) than plants in a montane environment (2) do leaf temperatures approach or exceed these tolerances,  (3) is leaf mass area (LMA) correlated to photosynthetic thermal tolerance and photosynthetic recovery, and (4) is there correlated evolution between T₂₅, RT₂₅, LMA, and environment. T₂₅ and RT₂₅ were measured using a chlorophyll fluorescence protocol incorporating sub-saturating light and short duration heat stress in 16 desert and 11 montane species. We monitored leaf temperature in the field for select desert and montane species. We measured LMA for all 27 species.

Results/Conclusions

T₂₅ was significantly different between desert and montane species (48.3^oC and 44.6^oC, respectively). RT₂₅ was not significantly different between desert and montane species (98% and 88.2%, respectively). LMA was significantly different between desert and montane species (250 g/m² and 140 g/m², respectively).  There was a relationship between T₂₅ and LMA in both desert and montane environments. Also, we found evidence for correlated evolution between T₂₅ and LMA. Leaf temperatures exceeded T₂₅ thresholds for several desert species. Results highlight that the ability to recover from heat stress does not differ between two biomes that experience vastly different mean maximum temperatures during the summer months. Additionally, LMA is a predictive leaf trait for thermal tolerance. We suggest that desert plants may be more at risk from climate change than those in milder biomes.