干旱胁迫下内生真菌感染对羽茅的生理生态影响

Physiological ecological effect of endophyte infection on Achnatherum sibiricum under drought stress

在田间环境下对感染和未感染内生真菌的天然宿主羽茅(Achnatherum sibiricum (L.) Keng)进行了干旱胁迫实验,结果发现在干旱胁迫下,内生真菌感染对宿主植物的营养生长、生物量累积和叶绿素含量都没有显著影响,但对宿主植株光系统Ⅱ光化学效率(Fv/Fm)的维持产生了有利效应。同时,内生真菌感染缓解了宿主植物细胞膜的旱害程度,表现在与未感染植株相比,感染植株的丙二醛(MDA)含量显著降低,但内生真菌的感染并未促使宿主植物体内保护酶如超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性的增加,只是显著增加了类胡萝卜素的含量。由此推测在羽茅中,内生真菌对宿主植物的保护作用可能更多的体现在非酶系统上。

Endophytes and their host grasses are mutually symbiotic.On one hand,the host grasses provide necessary photosynthates for the fungi;on the other hand,endophyte-infected grasses express a range of adaptations to biotic and abiotic stresses,including drought,mineral imbalance,and soil acidity.Cool-season grasses infected with Neotyphodium endophytes have an extraordinary impact on the ecology and economy of pasture and turf.In this paper,Achnatherum sibiricum infected by Neotyphodium lolii was employed to establish endophyte-free（EF） and endophyte-infected（EI） populations.EI and EF Achnatherum sibiricum were grown in the field and tested for their ecophysiolocal response to water deficiency.Relative water content（RWC）,chlorophyll,soluble sugar and protective enzymes of EI and EF populations under normal and drought stress conditions were calculated. The experiment was carried out on the campus of Nankai University,Tianjin.The stress treatment began in mid-June and ended in mid-July,over a time span of 35 days.All experimental plants were watered to saturation before the experiment.During the treatment,half of the plants were served as the control group,they were watered once or twice a day.The remaining plants were subjected to drought-stress treatment.Every morning,a soil moisture probe（ECH2O Check,Decagon Devices,Pullman,WA） was inserted to a 5 cm depth into each pot to record the volumetric water content percentage,i.e.,the amount of total soil volume consisting of water.Control plants were watered to maintain field capacity,i.e.,soil moisture readings at 35%.For plants in the drought treatment,sufficient water was added to keep the soil moisture readings between 5% and 10%. The results showed that endophyte infection had no significant effect on the host′s vegetative growth,total biomass,chlorophyll content.On the other hand,it has a favorable effect on the host′s maintenance of photochemical efficiency（Fv/Fm）,and made a contribution to keep the stability of photosystem Ⅱ.Endophyte infection had no significant effect on Fv/Fm in the control treatment,but enhanced the Fv/Fm of the host plant significantly under drought stress.At the same time,endophyte infection alleviated the drought injury on the cell membrane of the host grass,i.e.endophyte infection reduced the production of malondialdehyde（MDA）.Endophyte infection did not improve the activity of protective enzymes such as superoxide dismutase（SOD） and catalase（CAT）,while the carotenoid content of the EI plants was significantly higher than that of the EF plants under drought stress.Therefore,we suggested that under drought stress,endophyte infection may alleviate the adverse effect mainly through non-enzyme systems instead of protective enzymes.Others studies have showed that the endophyte promotes host natural grass tolerance of drought mainly by two mechanisms：（1） by changing the morphological and physiological characteristic of the host plants to help them maintain a reasonable growth rate under drought stress;（2） the endophyte enables plant tissues to withstand water deficits,but as a trade-off,the endophyte reduces the host plant′s growth.In our study,the endophyte infection did not have a significant effect on the host plant′s vegetative growth and biomass accumulation under drought stress,but did remit the drought damage to some extent.We suggest that endophyte may enable plants invest more in structural carbohydrates such as lignin and fiber to help host plant overcome the resource-limited environment.Thus,it will be interesting to determine whether endophyte infection contributes to greater investment in structural carbohydrates in plants.