Dynamics of photosynthetic responses in 10 rubber tree (<i>Hevea brasiliensis</i>) clones in Colombian Amazon: Implications for breeding strategies

The rubber tree [Hevea brasiliensis (Willd. Ex Adr. de Juss.) Muell.-Arg] is the main source of natural rubber in the world. However, in the Amazon region, its production is reduced by biotic and abiotic limitations, which have prompted breeding programs in order to identify desirable agronomic and physiological indicators. The objective of this study was to analyze the temporal dynamics of photosynthetic responses based on the parameters of leaf gas exchange and chlorophyll a fluorescence in 10 rubber tree clones during the immature phase (pre-tapping) in three large-scale clone trials, during daily cycles and under two climatic periods (dry and rainy) in the Caquetá region (Colombian Amazon). The variables A, LT, ΦPSII, ETR and qP were significantly higher in the dry period, where the highest values of PAR, AT and VPD were seen. In San Vicente del Caguán and Florencia, the highest averages were estimated for A, E and gs, as compared with Belén de los Andaquíes. In Florencia, the highest fluorescence parameters of chlorophyll a were recorded. At 9:00 h and 12:00 h, the highest means of A, E, ΦPSII and ETR were observed. The majority of the clones displayed the highest Fv/Fm mean (0.82–0.84) in the dry period. The clones FX 4098, FDR 4575, MDF 180, GU198 and FDR 5788 represent genotypes with the best photosynthetic performance (greater photosynthetic rates and better ability of the photosynthetic apparatus to capture, use and dissipate light energy). These desirable genotypes constitute a promising gene pool for expanding the genetic resource of rubber trees in the Colombian Amazon.巴西橡胶树[Hevea brasiliensis (Willd. Ex Adr. de Juss.) Muell.-Arg]是全球天然橡胶的核心来源。然而在亚马逊区域，其产量受生物与非生物胁迫制约，为此科研人员已启动多项育种计划，以筛选优良农艺与生理性状指标。本研究的目标为：针对哥伦比亚亚马逊河卡克塔（Caquetá）地区的3个大型橡胶树无性系试验，分析10个处于幼龄未开割阶段的橡胶树无性系，基于叶片气体交换与叶绿素a荧光（chlorophyll a fluorescence）参数的光合响应时间动态，试验覆盖日周期与两个气候期（旱季与雨季）。试验测得的净光合速率（A, Net Photosynthetic Rate）、叶温（LT, Leaf Temperature）、PSII实际光化学效率（ΦPSII, Actual Photochemical Efficiency of PSII）、电子传递速率（ETR, Electron Transport Rate）与光化学淬灭系数（qP, Photochemical Quenching Coefficient）在旱季显著更高，而旱季同时对应光合有效辐射（PAR, Photosynthetically Active Radiation）、大气温度（AT, Air Temperature）与水汽压亏缺（VPD, Vapor Pressure Deficit）的最高水平。相较于贝伦德洛斯安达基耶斯（Belén de los Andaquíes）试验点，圣维森特德卡瓜（San Vicente del Caguán）与弗洛伦西亚（Florencia）试验点的净光合速率（A）、蒸腾速率（E, Transpiration Rate）与气孔导度（gs, Stomatal Conductance）的平均水平更高。弗洛伦西亚试验点的叶绿素a荧光参数表现最优。在当日9:00与12:00时段，净光合速率（A）、蒸腾速率（E）、PSII实际光化学效率（ΦPSII）与电子传递速率（ETR）均达到最高均值。多数无性系在旱季的最大光化学效率（Fv/Fm, Maximum Photochemical Efficiency of PSII）均值最高，区间为0.82~0.84。无性系FX 4098、FDR 4575、MDF 180、GU198与FDR 5788展现出最优光合性能：具备更高的光合速率，且光合机构捕获、利用与耗散光能的能力更强。上述优良种质可为哥伦比亚亚马逊地区橡胶树遗传资源的扩增提供极具潜力的基因库。