TRADE-OFFS UNDERLYING THE VARIABILITY IN LEAF MINIMUM CONDUCTANCE ACROSS CERRADO SPECIES: CAUSES, CONSEQUENCES, AND IMPLICATIONS FOR CARBON ASSIMILATION AND WATER USE AND CONSERVATION

Abstract

Even after complete stomatal closure, plants keep losing water from their leaves to the atmosphere. This minimum transpiration rate, also known as minimum conductance (gmin), represents an inevitable water leak, which has a great impact on the strategies of water use and conservation across species. However, despite the importance of gmin to overall water balance, especially under drought conditions, few is known about how differences in leaf functional properties are related to the high variability of this trait across species of the same site, and also across biomes. The main objective of the present study was to make a deep characterization of the gmin variability among species from Brazilian Cerrado, and to better elucidate which are the main morphoanatomical characteristics that may drive the presumably high variability of water leaks among species and functional groups from this important Brazilian domain. Although both leaf sides had significantly explained the high gmin variability across species, their relative contribution differed substantially, with peristomatal transpiration representing 67% of the total minimum transpiration. The high variability in gmin rates was tightly associated with the growth strategies of the studied species, suggesting the existence of a trade-off between carbon assimilation and water loss thought minimum conductance. This tradeoff, by its turn, seemed to be linked to the differential stomata allocation in the epidermis. In order to allow high CO2 diffusion, fast-growing species (deciduous) invested in small and numerous stomata, which resulted in higher CO2 diffusion capacity. However, although this strategy maximizes the CO2 assimilation rate, it also led to higher water loss thought stomata leaks. On the other hand, the more conservative strategy of evergreen species involved the construction of leaves with fewer and larger stomata, a strategy that led to a lower CO2 assimilation capacity (A), but also prevented excessive water leaks (gmin) thought the leaves. The variability in gmin rates between functional groups had a substantial impact on the time to hydraulic failure (mortality) under our modeled severe drought conditions, with evergreen species surviving 28 days longer than the deciduous species. However, besides the high impact of stomata morphoanatomy to the overall gmin variability across species and functional groups, significative contributions of cuticle properties were not found.