黑麦草-内生真菌共生体对磷缺乏的生理生态反应

Effects of endophyte infection on ecophysiological response of perennial ryegrass under phosphorus deficiency

选取感染和未感染的黑麦草为材料,在田间盆栽条件下研究内生真菌感染对宿主植物抵抗磷胁迫方面的贡献。结果表明,土壤中缺磷或内生真菌感染对黑麦草地上部生长的影响不显著,但内生真菌感染对植株地下部生长和生理指标有明显影响。缺磷条件下,内生真菌感染有助于黑麦草地下部分的生长,表现在根系总长度更长,生物量更大;同时根中酚类物质和有机酸的含量也显著高于未感染植株,但因酚类物质和有机酸总量增加的同时并未伴随着二者浓度的增加,由此推测,内生真菌在改变宿主黑麦草根系代谢活动方面的贡献有限。此外,内生真菌感染显著提高了宿主植物的磷利用效率,这可能和缺磷条件下内生真菌感染植株具有更高的酸性磷酸酶活性有关。

Neotyphodium endophytes and cool-season grasses are mutualistic symbionts. The host grasses provide necessary photosynthates for the fungi. The endophytes often enhance the hosts＇ growth and protect them from biotic and abiotic stresses, contributing to their widespread adaptability. Abiotic attributes affected by Neotyphodium endophytes include drought resistance, light, temperature and mineral stresses. Studies on endophyte-related responses of grasses to nutrient acquisition have focused upon the influence of soil nitrogen （N） availability, since this element is a constituent of alkaloids in infected plants. Similar to N nutrition, phosphorus （P） availability influences ergot alkaloid production in EI （endophyte-infected） grasses. But reports of endophyte-related responses of grasses to P nutrition are relatively limited. In this paper, Lolium perenne L. cv. SR4000 infected by Neotyphodium lolii （originally from Beijing Clover Seed Company, China） was employed to establish EF （endophyte-free） and EI populations. EI and EF ryegrasses were grown in the field and tested for their ecophysiological response to P deficiency. The experiment was carried out at the campus experiment site of Nankai University, Tianjin. There were two separate 2-month periods of P stress treatment. The first began in mid July. The second began in late Sept. Two-factor randomizedblock design was used. The first factor was P treatment and two levels of P treatments were imposed, i.e. P supply （ P ＋ ） and P deficiency （ P - ） ; the other factor was endophyte status, i.e. EI and EF. Each treatment was replicated five times. P ＋ treatment was achieved by addition of P to the soil in the form of Hoagland nutrient solution. For P - treatment, 2000μM KCl was added instead of KH2PO4. Two liters nutrient solution per pot was added once a month, and four times in total. The results showed that endophyte infection did not have significant effect on leaf growth but did improve root development of perennial ryegrass under P deficiency. In response to P deficiency, EI roots were longer and had higher mass than EF roots. The root ： shoot ratio was also greater in EI individuals. The content of total phenolics and organic acids was greater in EI roots than in EF roots at low P supply. However, the concentration of both did not increase with endophyte infection. The results suggest that higher root dry weight contributes to higher content of total phenolics and organic acids for EI plants, and endophyte infection might have negligible effects on chemical modification of perennial ryegrass. Endophyte infection did not increase the rate of P uptake bat did improve P use efficiency when P was limited. Higher P use efficiency of EI ryegrass might result from higher acid phosphatase activity （APA） for EI ryegrass. Higher APA may contribute to ryegrass ability to reuse a limited P source, which is further beneficial to the development of ryegrass roots.