Effects Of Fungal Endophyte On Intraspecific Competition Of Elymus Nutans Under Water Stress

Elymus nutans, belonging to Elymus of Gramineae, is a kind of high-quality grazing grass in the Qinghai-Tibetan Plateau of China. In order to discover effects of fungal endophyte on intraspecific competition of E. nutans, greenhouse and field experiments under different water stresses were carried out. The main results were as follows:1. In lab experiment, E-seeds were obtained through water treatment. It was shown that the temperature of60℃for20min was very effective in killing endophyte fungi, while not significantly affecting the germination rate and germination potential.2. The experimental design was based on a De Wit-type replacement series, we used three levels of water stresses, that is, soil water capacity of70%(unlimited water treatment as control (CK),50%(moderate drought stress, M) and30%(severe drought stress, S) as well as five treatments, referring five different ratios of E-to E+:1:0,3:1,1:1,1:3, and0:1, with5replicates for each treatment, to study the effects of endophyte infection on plant growth and competitive ability of E. nutans in intraspecific competition. In monocultures, the results show that stomatic conductance, transpiration rate and net photosynthetic rate for both endophyte-infected (E+) and endophyte-free (E-) E. nutans decreased with the increase of water-stress intensity. Under severe drought stress, stomatal conductance and transpiration rate of E+plants were significantly lower than that of E-plants, but the net photosynthetic rate of E+plants were significantly greater than that of E-plants. The content of proline, activities of catalase and peroxidase of E+plants were greater than that of E-plants through the whole treatment. At the beginning of severe drought stress the malondialdehyde of E+plants was greater than E-plants, but at the end, the content in E+plants was lower than that E-ones. This study showed that endophytic fungi could largely increase the resistance of its host to stresses. Through measuring nitrogen and phosphorus contents in E+and E-plants, it was found that under different conditions of drought stresses the nitrogen content in E+plants and E-plants were not significant; phosphorus content was higher in E+plants than E-plants and the difference under severe drought stress reached significant level (P<0.05).3. In monocultures, the above-ground dry biomass (DMY) of endophyte-infected (E+) and endophyte-free (E-) plants declined as water stress increased, and the DMY of infected pants were greater than E-Plants. E+plants produced more DMY than E-plants under the treatments of CK, M and S, with relative increases of40%,41%and27%, respectively. The DMY of E+and E-plants were significant under conditions of CK and M (P<0.05). When mixing E+and E-plants, under conditions of different water stresses, the values of Relative Yield (RY) increased with increasing proportion of E+plants, while RY values of E-plants decreased. In the mixture of1:1, RY values of E+plant were significantly greater than1.0, showing that its competitiveness was greater than E-plants. Under conditions of different water stresses and planting rates, Relative Yield Total (RYT) had no significant difference from1.0, showing that E+and E-plants needed the same resources and E+plants could exclude E-plants in a long time growing period. Through comparing Aggressivity index (A), it was found that the competitiveness of E+plants was greater than E-plants. Therefore, endophytic fungi infection could partly improve the competitive ability of E. nutans.4. In the field experiment, we used three levels of water stresses and three treatments including different ratios of E+to E-:1:0,1:1,0:1. Split block design was utilized with three replicates to examine the effects of endophyte infection on plant growth and competitive ability of E. nutans in intraspecific competition. The results indicated the above-ground biomass of endophyte infected (E+) and endophyte free (E-) plants declined with the increase of water stresses. E+was observed to be of no difference (P>0.05) vs. E-under CK, but significantly greater for E+than E-plants under M and S. with relative increases of27%and32%, respectively. In mixture, the above-ground biomass of E+was significantly greater than E-plants under the three water stresses.This study showed that endophyte fungi infection could improve the growth and competitiveness of E. nutans. The research provided technology support for future study on plant competition, community succession and improvement of grassland productivity with the help of endophyte fungi.