Effects of ploidy level and haplotype on variation of photosynthetic traits: Novel evidence from two Fragaria species

To reveal the effects of ploidy level and haplotype on photosynthetic traits, we chose 175 genotypes of wild strawberries belonging to two haplotypes at two types of ploidy levels (diploidy and tetraploidy) and measured photosynthetic traits. Our results revealed that ploidy significantly affected the characteristics of light-response curves, CO2-response curves, and leaf gas exchange parameters, except intercellular CO2 concentration (Ci). Tetraploid species had a lower light saturation point (LSP) and CO2 saturation point (CSP), higher light compensation point (LCP), dark respiration (Rd), and CO2 compensation point (CCP) than diploid species. Furthermore, tetraploid species have lower photosynthetic capacity than diploid species, including net photosynthetic rate (Pn), stomatal conductivity (Gs), and transpiration rate (Tr). In addition, haplotype had a significant effect on LSP, CSP, Tr, and Ci as well as a significant interactive effect between ploidy and haplotype on the maximal photosynethic rate of the light-response curve and Rd. Most of the variance existed within haplotypes among individuals. These results suggest that polyploidization was the main driver for the evolution of photosynthesis with increasing ploidy level (i.e. from diploidy to tetraploidy in Fragaria species), while the origin of a chromosome could also affect the photosynthetic traits and the polyploidization effect on photosynthetic traits.为揭示倍性水平（ploidy level）与单倍型（haplotype）对光合性状（photosynthetic traits）的影响，本研究选取了隶属于两种单倍型、两类倍性水平（二倍体与四倍体）的175份野生草莓基因型，并对其光合性状进行了测定。研究结果显示，除胞间二氧化碳浓度（intercellular CO2 concentration, Ci）外，倍性水平显著影响光响应曲线、二氧化碳响应曲线的特征以及叶片气体交换参数。与二倍体材料相比，四倍体草莓的光饱和点（light saturation point, LSP）与二氧化碳饱和点（CO2 saturation point, CSP）更低，但其光补偿点（light compensation point, LCP）、暗呼吸速率（dark respiration, Rd）与二氧化碳补偿点（CO2 compensation point, CCP）更高。此外，四倍体的光合能力低于二倍体，包括净光合速率（net photosynthetic rate, Pn）、气孔导度（stomatal conductivity, Gs）与蒸腾速率（transpiration rate, Tr）。进一步分析发现，单倍型对LSP、CSP、Tr与Ci具有显著影响；同时，倍性水平与单倍型的交互作用对光响应曲线最大光合速率及Rd存在显著调控效应。绝大多数变异存在于单倍型内的个体间。上述结果表明，多倍化（polyploidization）是草莓属（Fragaria）物种光合性状随倍性水平提升（即从二倍体向四倍体演化）的主要驱动因素，而染色体组的起源也可对光合性状及多倍化对光合性状的调控效应产生显著影响。