Departamento de Botânica, Universidade Federal de Minas Gerais, Av. Antônio Carlos 6627, E-31270-901, Belo Horizonte, Minas Gerais, Brazil.
Departamento de Botânica, Universidade Federal de Minas Gerais, Av. Antônio Carlos 6627, E-31270-901, Belo Horizonte, Minas Gerais, Brazil.
Plant Physiol Biochem. 2019 Nov;144:283-291. doi: 10.1016/j.plaphy.2019.10.004. Epub 2019 Oct 3.
Flowers require high amounts of water, which ultimately may compromise pollinator attractiveness under water limitation. Water-use and -conservation strategies in leaves from hot and dry ecosystems are well documented, yet little is known about mechanisms of water allocation in flowers, particularly in tropical savanna ecosystems. We evaluated traits related to corolla water status in two Kielmeyera species that differ in flowering phenology and flower size: larger-flowered K. regalis blooms during the rainy summer and smaller-flowered K. coriacea blooms during the dry winter. To test the hypothesis that water demand in corollas increases with increasing vapor pressure deficit (VPD), we analyzed interspecific differences in corolla stomatal conductance and density, water content, and fresh and dry mass per unit area. We also performed hand-pollination and pollinator-exclusion experiments to determine variation in floral longevity. Corolla transpiration rates were higher in K. coriacea (157 vs 95 g·HO·m·h for K. coriacea and K. regalis, respectively), and increased with VPD in both species. Stomatal density was 25-fold higher in K. coriacea, and corolla fresh and dry mass per unit of area were 47% and 21% higher, respectively, in K. coriacea, due to thick pectin-rich cell walls. The high pectin content increases water content in corollas of K. coriacea. Regardless of pollination, flowers lasted one day in K. coriacea and three in K. regalis. Our study suggests structure-function relationships of floral traits with flowering season, and that K. coriacea displays small and short-lived corollas with high water content to buffer the high evaporative demand during the dry period.
花朵需要大量的水，但在水资源有限的情况下，这最终可能会影响传粉者的吸引力。在炎热干旱的生态系统中，叶片的水分利用和节水策略已有详细记录，但人们对花朵水分分配的机制知之甚少，尤其是在热带稀树草原生态系统中。我们评估了两个 Kielmeyera 物种的与花瓣水分状态相关的特征，这两个物种在开花物候和花朵大小上存在差异：花较大的 Kielmeyera regalis 在雨季开花，花较小的 Kielmeyera coriacea 在旱季开花。为了检验花瓣水分需求随蒸气压亏缺（VPD）增加而增加的假设，我们分析了种间花瓣气孔导度和密度、水分含量以及单位面积鲜重和干重的差异。我们还进行了人工授粉和传粉者排除实验，以确定花的寿命的变化。Kielmeyera coriacea 的花瓣蒸腾速率较高（K. coriacea 为 157 g·HO·m·h，而 K. regalis 为 95 g·HO·m·h），并且在两种物种中均随 VPD 增加而增加。Kielmeyera coriacea 的气孔密度高 25 倍，而单位面积的花瓣鲜重和干重分别高 47%和 21%，这是由于果胶丰富的细胞壁较厚。高果胶含量增加了 Kielmeyera coriacea 花瓣的水分含量。无论授粉与否，Kielmeyera coriacea 的花持续一天，而 Kielmeyera regalis 的花持续三天。我们的研究表明，开花季节与花朵特征的结构-功能关系，并且 Kielmeyera coriacea 具有小而短命的花瓣，水分含量高，以缓冲旱季高蒸发需求。
