Different Drought-adaptation Strategies as Characterized by Hydraulic and Water-relations Traits of Evergreen and Deciduous Figs in a Tropical Karst Forest

To investigate drought adaptation of evergreen and deciduous fig species occurring in dry karst forests, we compared anatomical traits, stem hydraulic conductivity, leaf water relation traits, photosynthesis, drought-resistance, and seasonal changes in physiology in evergreen Ficus orthoneura and deciduous F.pisocarpa, both of which belong to F.subgen. urostigma. Results showed that the two fig species have adapted to drought in different ways. Both have typical xeromorphic leaf structures, as shown by their two-layered palisade cells, highly-defused sponge cells and cystolith in leaves. They have a low cuticular evaporation (g_min) and stomatal conductance (g_s) to alleviate water loss. However, F.orthoneura possesses a xylem structure more resistant to cavitation and lower g_min and adopts conserved water use to adapt to drought stress and maintains its leaves all year. In contrast, F.pisocarpa escapes from extreme drought stress by shedding leaves at the beginning of the dry season. To compensate the loss of carbon gain in the leafless period, F.pisocarpa has a particularly high rate in hydraulic and photosynthesis during the rainy season.The diversification of drought adaptation and water use reduces their competition for water and makes it possible for these fig species to coexist in the karst topography.