甘肃马先蒿寄生对禾草内生真菌共生体光合特性的影响

Effects of Pedicularis kansuensis parasitism on the photosynthetic characteristics of host grass-Epichloë symbionts

摘要:

[目的]甘肃马先蒿与感染内生真菌的禾草（紫花针茅和麦宾草）建立根寄生关系，有关内生真菌对根寄生危害禾草光合作用调控方面的研究较少。[方法]本研究以紫花针茅和麦宾草带菌（E+）、不带菌（E-）植株为研究对象，研究甘肃马先蒿寄生和未寄生处理对紫花针茅和麦宾草E+、E-植株不同生长阶段光合特性影响的动态变化。[结果]甘肃马先蒿寄生显著降低紫花针茅和麦宾草的净光合速率、蒸腾速率和气孔导度，而胞间二氧化碳浓度和水分利用率却显著增加，这与禾草是否感染内生真菌无关。甘肃马先蒿寄生后E+紫花针茅的净光合速率、气孔导度和蒸腾速率高于E-植株，而麦宾草E+植株的净光合速率、气孔导度和蒸腾速率却低于E-植株；同时，根寄生条件下E+紫花针茅的胞间二氧化碳浓度和水分利用率低于E-植株；而E-麦宾草植株的胞间二氧化碳浓度和水分利用率却低于E+植株。[结论]内生真菌侵染影响甘肃马先蒿根寄生危害禾草的光合作用；甘肃马先蒿和内生真菌同时成为禾草营养消耗库时，内生真菌与禾草的共生关系处于一种互惠共生和相互拮抗的动态变化。

Abstract:

[Objective] Pedidcularis kansuensis forms parasitic relationship with Epichloë-infected host grasses through root haustoria connections. However, only few studies have paid attention to the effects of Epichloë endophyte on host grass photosynthetic characteristics while the host grasses were parasitized by root hemiparasitic plants. [Methods] Thus, in this study, we evaluated effects of endophyte infection on net photosynthesis rate (P_n), transpiration rate (T_r), stomatal conductance (G_s), concentration of CO₂ intercellular (C_i) and water use efficiency (WUE) of two host grasses (Stipa purpurea and Elymus tangutorum) in the presence (or absence) of P. kansuensis.[Results] Irrespective of endophyte status, P_n, T_r and G_s of host plants decreased in the presence of P. kansuensis; however, C_i and WUE of host plants increased in the presence of P. kansuensis. P_n, T_r and G_s of endophyte-infected (E+) S. purpurea were higher than endophyte-free (E-) counterpart, while C_i and WUE of E+ S. purpurea were lower than E- ones. By contrast, P_n, T_r and G_s of E+ E. tangutorum was lower than E- counterpart, while C_i and WUE of E+ E. tangutorum higher than E- ones. [Conclusion] Consequently, these results suggest that interactions between endophyte and host grasses are context-dependent, and the relationships between host grass and Epichloë endophyte range from mutualism to parasitism when grasses become common hosts to root hemiparasitic plant and Epichloë endophyte.