不同浓度和形态磷处理下内生真菌感染对高羊茅的影响

以感染内生真菌(endophyte-infected,EI)和不感染内生真菌(endophyte-free,EF)的高羊茅(Festuca arundinacea Schreb.)为材料,在温室沙培条件下研究内生真菌对高羊茅适应缺磷及利用不同形态磷肥的影响。结果表明,1)缺磷条件下,高羊茅EI和EF植株生长差异不显著;正常供磷条件下,高羊茅EI植株拥有更多分蘖数和绿叶数。说明正常供磷条件下内生真菌改善了宿主高羊茅的生长。2)与水溶性磷相比,高羊茅根有机酸和酸性磷酸酶(acid phosphatase,APase)活性在难溶性磷条件下显著增加,而根总酚含量无显著变化。在水溶性磷条件下,高羊茅EI植株根总酚含量显著高于EF植株,此时EI植株比EF植株拥有更多分蘖数和绿叶数,说明在水溶性磷条件下内生真菌对宿主地上部生长具有一定贡献。在难溶性磷条件下,虽然高羊茅EI植株根总酚含量仍然高于EF植株,但同时EI植株根有机酸含量显著低于EF植株,因此内生真菌感染只是增大了宿主植物的根冠比,而对分蘖数和绿叶数等无显著影响,说明内生真菌对宿主利用难溶性磷贡献不大。可见,内生真菌对宿主植物的生长在水溶性磷条件下更有利。

Effects of endophyte infection on tall fescue in different phosphorus levels and forms

Phosphorus (P) is one of the essential nutrient elements for plant growth and development, but the effective phosphorus in the soil is often low. Many studies showed that mycorrhizal fungi could improve the ability of the host plants in using sparingly soluble phosphate fertilizer. Similar to mycorrhizal fungi, endophytes are symbiotic with plants to some extent. Cool-season grasses and fungal endophyte Neotyphodium coenophialum are reported to be mutualistic symbions. But reports on endophyte-related responses of grasses to P nutrition, particularly to P forms are limited. In this paper, endophyte-infected (EI) and endophyte-free (EF) tall fescue were used as materials and their ecophysiological response to different P levels and P forms were compared.The experiment was carried out in the greenhouse on the campus of Nankai University. There were three phosphate fertilizer treatments, i.e. application of sparingly soluble phosphorus fertilizer, water-soluble phosphorus fertilizer and no addition of phosphorus fertilizer. Each treatment consisted of 5 pots of EI and 5 pots of EF tall fescue plants. In addition, N, P, and K fertilizer were applied with 300, 100, and 150mg/kg, respectively. At the end of the experiment, we noted the number of tillers and leaves, and measured the dry weight of the shoot and the root. Besides, we detected the content of total phenol and organic acid as well as the activity of acid phosphatase (Apase).When no P fertilizer was added, there was no significant difference in growth between EI and EF plants, and EI plants tended to perform worse than EF plants. When normal P fertilizer was supplied, EI plants had more tillers and leaves than EF plants, which may partly prove the viewpoint that the beneficial effect of endophyte infections usually occurs in high soil nutrients conditions.As for the responses to different phosphorus forms, we found that the root organic acid content and the acid phosphatase activity were significantly higher in the sparingly-soluble P conditions than in the water-soluble P conditions, while total phenol content of the root was similar between the two treatments. In the water-soluble P conditions, EI plants had both higher content of total phenol and more tillers, and leaves than EF plants, which indicated that the endophyte had certain contributions to shoot growth of the host plants. In the sparingly-soluble P conditions, EI roots had higher content of total phenol but lower content of organic acids than EF plants; meanwhile, endophyte infection just increased the root-shoot ratio of the host plants. This indicated that endophyte infection contributed little to the host plants in using sparingly-soluble P. Since we did not determine the root morphology of the experimental tall fescue, we could not rule out the possibility of endophyte infection changing the root morphology of tall fescue without changing the root biomass, which needs further study. Besides, whether endophyte infection is beneficial to the host plant in the P-deficient condition depends on the host plant species or varieties. In a word, our experiment indicated that endophyte infection was more beneficial to host growth when water-soluble P was supplied.