PS 57-116
Adaptation to freezing-induced photoinhibition in blackbrush along the warm/cold desert boundary, from the Mojave to Colorado Plateau
The extreme temperature variation and sunlight exposure that accompany aridity are important but relatively unstudied factors affecting plant adaptation and species’ distributions in deserts. We evaluated the hypothesis that interactions of low-temperature and sunlight stress are a key factor in climate adaptation of blackbrush (Coleogyne ramosissima), a dominant shrub whose geographic distribution spans a wide range of minimum temperature across the boundary between the warm and cold deserts of Western N America. Changes in chlorophyll fluorescence (dark-adapted Fv/Fm) and foliar morphology were used to assess resistance or avoidance of photosynthesis to chilling or freezing, with or without subsequent exposure to sunlight, among 16 populations of blackbrush. These populations span the Mojave to Colorado Plateau deserts and were planted together in common gardens.
Results/Conclusions
Preliminary findings suggest Fv/Fm was resistant to chilling and decreased only marginally with deep freezing alone, but had marked decreases from > 0.7 to < 0.35 when frozen and then subjected to bright sunlight, indicating vulnerability to low-temperature photoinhibition of photosynthesis (LTP). Furthermore, populations from the cooler Colorado Plateau ecoregion exhibited only half of the depression in Fv/Fm than plants of the Mojave Desert, suggesting ecotypic variation in resistance to LTP. Populations whose home climates had greater cold exposure and aridity exhibited substantially greater resistance to LTP. Populations with greater resistance to LTP grew taller and had greater survival, and they exhibited greater photosynthetic water-use efficiency as indicated by carbon-isotope discrimination. The Colorado Plateau ecotype had thicker leaves, and the sunlight interception efficiency of shoots (sunlit-to-total leaf area, STAR) was greater in populations from colder and more arid climates. The combination of resistance to LTP (indicated by Fv/Fm) and avoidance of LTP (indicated by both leaf thickness and STAR) was highly correlated with cold exposure and aridity of the population’s home climates (r2 = 0.94). Development of both structural avoidance and physiological resistance to LTP are key to the ecoregional patterns of growth and survivorship observed at the common gardens and contributed to blackbrush’s capacity to colonize the cold, arid, and sunny basins of the Colorado Plateau during the Holocene.