热带喀斯特森林常绿和落叶榕树的水力特征和水分关系与抗旱策略

以热带喀斯特地区的直脉榕(Ficus orthoneura)和豆果榕(F.pisocarpa)为实验材料,研究了常绿和落叶树木枝条和叶片的解剖结构特征、光合水分特征和耐旱性的差异,目的在于探讨不同生活型榕树适应干旱生境的策略.直脉榕和豆果榕的叶片都有两层栅栏组织、游离状的海绵组织和钟乳体等旱生结构,同时叶片角质层蒸腾速率(gmin)和气孔导度(gs)相对较低.但与落叶的豆果榕相比,常绿的直脉榕的枝条木质部失去50％传导率的水势(P50)和gmin更低,表现出更保守的水分利用策略.总体上,两种榕树都表现出了对喀斯特干旱生境的良好适应,但是它们的适应策略表现出一定的差别.豆果榕通过落叶度过旱期,而直脉榕在结构和功能上比豆果榕更耐旱.抗旱策略和水分利用策略的不同导致两种榕树的生态位分异,减少了彼此间的水分竞争,有利于它们在喀斯特生境中共存.

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 （gm~n） and stomatal conductance （gs） to alleviate water loss. However, F. orthoneura posses- ses a xylem structure more resistant to cavitation and lower gm~n 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 thesefig species to coexist in the karst topography.