云杉矮槲寄生的侵染对青杄光合与蒸腾作用的影响

 云杉矮槲寄生(Arceuthobium sichuanense)属半寄生性多年生种子植物,是青海省云杉天然林毁灭性生物灾害之一。本研究首次报道了云杉矮槲寄生在自然条件下可以侵染青杄,并对健康与染病青杄(Picea wilsonii)针叶形态及其光合日变化进行了测定。结果表明:1)染病青杄的针叶长度和宽度显著小于健康青杄(P＜0.001),而染病青杄的针叶比叶面积(SLA)显著大于健康青杄(P＜0.001);2)云杉矮槲寄生的侵染显著降低了青杄叶片的净光合速率、蒸腾速率以及气孔导度(P＜0.05),但不影响其胞间CO₂浓度(P =0.32);3)冗余分析(RDA)表明,云杉矮槲寄生的侵染导致青杄对不同环境因子的依赖程度发生变化,健康青杄表现为环境CO₂浓度(CO₂)＞空气温度(T_air)＞叶片温度(T_l)＞蒸汽压亏缺(Vpd)＞空气相对湿度(RH)＞光合有效辐射(PAR),而染病青杄则出现T_l＞RH＞T_air＞PAR＞Vpd＞CO₂,且T_l成为影响染病青杄叶片光合与蒸腾作用(P_n、T_r)的主要环境因子,且染病青杄对RH和PAR变化的响应更加敏感。此外,染病青杄叶片的水分利用率(WUE)显著低于健康寄主(P＜0.05)。因此,云杉矮槲寄生的侵染可降低青杄对环境的适应能力,从而加速寄主的衰老死亡。

Effects of Arceuthobium sichuanense infection on photosynthesis and transpiration of Picea wilsonii

Arceuthobium sichuanense, a hemiparasitic plant, is the most destructive pathogen of natural and man-made spruce forest in China. First report of A. sichuanense infection in Picea wilsonii trees in Qinghai province, China was released in this study, and the morphological characters of needles, diurnal changes of photosynthesis and transpiration in healthy and infected P. wilsonii trees were investigated. It was shown that the length and width of needles from the infected P. wilsonii were significantly smaller than those from control trees (P＜0.001), but the specific leaf area (SLA) of diseased P. wilsonii was significantly bigger than that of control trees (P＜0.001). Furthermore, infection by A. sichuanense significantly reduced net photosynthesis rate (P_n), transpiration rate (T_r) and stomatal conductance (G_s) of P. wilsonii trees (P＜0.05). However, substomatal CO₂ concentration (C_i) was not influenced by A. sichuanense infection (P=0.32). Relationship analysis between environmental factors and photosynthesis-transpiration of P. wilsonii trees based on redundancy analysis (RDA) revealed that the importance of the tested environmental factors were changed by A. sichuanense infection, from ambient CO₂ concentration (CO₂)＞air temperature (T_air)＞leaf temperature (T_l)＞vapor pressure deficit (Vpd)＞air relative humidity (RH)＞photosynthetic active radiation (PAR) for control trees to T_l＞RH＞T_air＞PAR＞Vpd＞CO₂ for diseased trees. T_l became the key factor affecting P_n and T_r of diseased P. wilsonii trees. The P_n and T_r of diseased P. wilsonii trees also became more sensitive to RH and PAR. Moreover, water use efficiency (WUE) of diseased trees was significantly lower than that of control trees (P＜0.05). Therefore, infection by A. sichuanense would weaken the adaptive capacity of P. wilsonii to environment and accelerate the death of the trees.