Drought, thermal response and climate-patterning in cuticular conductance of the widespread C4 grass, Themeda triandra

Grasslands are vital ecosystems for biodiversity, carbon cycling and climate resilience, yet their persistence is increasingly challenged by rising temperatures and water scarcity. This study examined intraspecific variation in leaf cuticular traits−minimum cuticular conductance following stomatal closure (g _min ), and its temperature dependency−across six Australian accessions of Themeda triandra from contrasting climates. Plants were grown under well-watered conditions and exposed to experimental drought. Trait variation and drought responses were quantified in relation to climate-at-origin. For well-watered plants there was no relationship between g _min and accession climate-at-origin. However, under drought, g _min showed clear climate signals, being lower in plants from wetter and cooler regions−in the opposite direction to that predicted. g _min also varied clearly (positively) with leaf mass per area, LMA. The six accessions varied substantially in g _min responses to drought, from negative to positive. Thermal responses in g _min also varied among accessions although, in common, none showed a clear threshold (phase transition) at which g _min increased rapidly. That is, g _min was more thermally stable than expected. Taken together, these findings highlight substantial intraspecific variation in cuticular traits related to water loss, providing initial steps towards a pathway for selecting climate-resilient genotypes for use in grassland restoration and conservation.