High and diverse plastic responses to water availability in four desert woody species of South America

Key message Desert woody species demonstrated a high morphological plasticity to water. This would allow them to use increased rainfall predicted by climate change, but might challenge the drought resistance of irrigated nursery-produced plants for revegetation. Abstract Phenotypic plasticity is the ability of a given genotype to produce different phenotypes in response to changing environmental conditions. Despite its high adaptive value, it may have a high cost in resource-poor ecosystems, restricting the ability of plants to take advantage of surplus resources, e.g., increased levels of precipitation. We aimed to determine the phenotypic plasticity to water availability of four woody species from a hot desert of South America. We carried out a pot experiment with two levels of irrigation in a glasshouse, where performance (biomass production, stem growth, survival) and functional traits (biomass allocation, total leaf area, leaf size, specific leaf area; stomata size, density and index; photoprotective and antioxidant compounds) were measured. The plasticity patterns differed between species, with the highest plasticity in leaf traits (around 80% change between treatments), and the lowest in biochemical traits (no significant variation between treatments). All four species increased their performance under high-water supply, with different magnitudes (the two phreatophytes > the two xerophytes). However, some of them showed increased allocation to stem biomass, increased total leaf area and leaf size, increased stomata size, and reduced root growth, potentially allowing them to use water for growth when it is available, although hampering their drought resistance, based on classic interpretation of traits’ adaptive value. These changes promoted in irrigated nursery-produced seedlings should be considered in dryland revegetation plans. Moreover, our results suggest that the patterns of phenotypic plasticity would not be associated with the functional group of the species in relation to access of the water table in the field, but this issue needs to be explored further.