Endophytic fungi facilitate the coexistence of host grasses and neighboring legumes by changing rhizobial abundance

Purpose: Grass-endophyte and legume-rhizobium symbionts coexist in grasslands. However, the effects of endophyte infection on legume-rhizobium symbionts remain poorly understood, especially in natural grasslands. Methods: In this study, Achnatherum sibiricum - Epichloë endophytes and Medicago ruthenica -rhizobia were selected as materials to investigate whether and how endophyte infection affected the growth of legume-rhizobia symbionts. It was hypothesized that endophytes can facilitate the coexistence of grass-legume systems. Results: The results demonstrated that endophyte infection affected the growth of both rhizobia and M. ruthenica -rhizobia symbionts, and the results depended on rhizobial identity. Endophyte infection inhibited the growth of Mesorhizobium ciceri , which significantly promoted the growth of M. ruthenica , and promoted Sinorhizobium meliloti , which had no significant effect on the growth of M. ruthenica . Endophyte infection also changed the interaction between A. sibiricum and M. ruthenica . When inoculated with M. ciceri , endophyte infection weakened the promoting effect of A. sibiricum on M. ruthenica , while when inoculated with S. meliloti , endophyte infection enhanced the promoting effect. Endophyte infection affected the growth of M. ruthenica -rhizobia symbionts by affecting rhizobia abundance in roots and nitrogen content in plant leaves. Conclusion: In conclusion, endophyte infection was beneficial to biomass accumulation and species coexistence in grass-legume mixed planting systems. In this study, it was proposed that endophyte infection may change the growth of legume-rhizobia symbionts by affecting the growth and nitrogen fixation of rhizobia.

Effects of Epichloë Endophytes on The Litter Decomposition of Three Host Grass Species in The Qinghai-Tibetan Plateau

Aims Grass fungal endophyte symbioses are widespread in the Qinghai-Tibetan plateau grasslands. It is not clear whether endophytes will influence litter decomposition in alpine grassland. It is important to understand the role of fungal endophytes in the litter decomposition of host grasses in the grasslands of Qinghai-Tibetan Plateau. Method s This study utilized Festuca sinensis, Stipa purpurea and Achnatherum inebrians as objects and compared their litter with endophyte (E+) infection and without (E-) during the change in litter weight, total nitrogen, lignin and cellulose contents and their residual rate during the decomposition process. The microbial biomass carbon and nitrogen of soil under litters were also compared. Results The litter from E + F. sinensis and S. purpurea decomposed more quickly along with the cellulose compared with E-. The contents and residual rates of nitrogen and lignin in the F. sinensis and S. purpurea litters had no apparent trend of change. The microbial biomass nitrogen of soil under the E + F. sinensis and S. purpurea litters was higher than that of the E- litters. Alternatively, the rates of decomposition and degradation of lignin were lower in the E + A. inebrians litter than those of the E- litter. The endophyte decreased the microbial biomass carbon of soil under A. inebrians litter. Conclusions Endophytes played an important role in the nutrient cycling of alpine grassland ecosystems by promoting or decreasing the decomposition of host plants. The results will provide basic data to apply to grass endophyte symbioses in alpine grassland.

Drivers of grass endophyte communities in prairies of the Pacific Northwest, USA

Prairies of the Pacific Northwest are highly threatened, with only ∼2% of historic land area remaining. The combined risk of global climate change and land use change make these prairies a high conservation priority. However, little attention has been paid to the microbiota of these systems, including the hyper diverse fungi that live asymptomatically in their leaves, the endophytes. Using culture-free, full-community DNA sequencing, we investigated the diversity, composition, and structure of full fungal foliar endophyte and ecological guild communities in two native, cool-season bunchgrasses along a climate gradient. We quantified the relative importance of host, host fitness, environment, and spatial structuring in microbial community structure. We found markedly different communities between the southern and central-northern sites, suggesting a potential dispersal limitation in the Klamath Mountains. We also found that each host species was home to distinct fungal communities. Climate was the strongest predictor of endophyte community, while fitness (e.g., plant size, reproductive status, density) was less important for community structure. For both host species, seasonality contributed strongly to the variation we observed. At the ecological guild level, saprotrophs tended to decline with latitude, whereas symbiotrophs and pathotrophs both tended to increase with latitude. Our results suggest that climate change will have large consequences for these diverse fungal communities.

Effect of Epichloë gansuensis endophyte on rhizosphere bacterial communities and nutrient concentrations and ratios in the perennial grass species Achnatherum inebrians during three growth seasons

Achnatherum inebrians is an invasive perennial grass widespread in natural grasslands of north-west China and plays an important role in grassland ecological restoration. The presence of the seed-borne endophytic fungus Epichloë gansuensis in A. inebrians promotes grass growth, increases resistance to abiotic stress, and affects the rhizosphere microbial community of host plants. However, the relationships among E. gansuensis, rhizosphere bacteria and plant contents of carbon (C), nitrogen (N), phosphorus (P) and potassium (K) during different growing seasons are not clear. We examined changes in the rhizosphere bacterial community and in nutrient contents and ratios in A. inebrians with (E+) and without (E−) E. gansuensis in May, August and December. The Shannon diversity index was higher for rhizosphere bacteria of E+ than E− plants in the three different seasons. Leaf C, N and P contents and root P and K contents were higher in E+ than E− plants in May, and leaf K and root C were higher in E+ than E− plants in August. Leaf C:N ratios were lower in E+ than E− plants in December, and leaf C:K ratios were lower in E+ than E− plants in August and December. In addition, our results indicate significant interactions among rhizosphere bacteria, C, N, P and K contents, and endophyte treatment in three different seasons. In conclusion, E. gansuensis enhanced the C, N, P and K contents of host plants, and affected nutrient ratios of A. inebrians probably by increasing rhizosphere bacterial diversity and altering rhizosphere bacterial community structure. This study provides new findings on the ecological function of the endophyte E. gansuensis, including its potential role in enhancing soil fertility. The improvements in soil fertility were utilised in extrapolating to forage grass–endophyte associations.

Using novel-grass endophyte associations as an avian deterrent

Birds can be major pests in agricultural and horticultural crops as well as being serious hazards to operating aircraft. Cultivars of perennial ryegrass, a hybrid ryegrass and tall fescue, associated with selected Epichloë fungal endophytes were evaluated in aviary and field experiments for their management potential of three nuisance bird species selected as model systems representative of major bird classifications based on their diet. Granivores, namely European green finches, ate more endophyte-free perennial ryegrass seed than endophyte- infected seed, while the representative omnivores, black-backed gulls, avoided endophyte- enhanced feed pellets. The selected herbivore, Canada geese, showed an aversion to field trial plots sown with endophyte-infected grass containing ergovaline compared with the existing ground cover. Therefore habitat modification using selected grass-endophyte associations offers an effective wildlife management option aimed at reducing birds in problematic areas.

Phylogenetic analysis suggests joint control of transmission mode in a grass-endophyte symbiosis

How symbionts are transmitted between hosts is key to determining whether symbioses evolve to be harmful or beneficial. Vertical transmission favors mutualistic symbionts, and horizontal transmission more virulent ones. Transmission mode evolution itself depends on whether the host or symbiont can respond to selection on transmission mode. When hosts control the transmission mode, vertical transmission should evolve under more restrictive circumstances than when symbionts are in control. We take a phylogenetic approach to determine whether the host, symbiont, or both control transmission mode using the pooid grass-epichloid endophyte symbiosis as a model system. This study is the first to investigate control of transmission mode evolution in a phylogenetic context. We find a signal of host phylogeny but only in conjunction with symbiont identity. This pattern suggests joint control of transmission mode by the host and symbiont. It also suggests that non-genetic or non-conserved symbiont traits may determine whether host traits lead to vertical or horizontal transmission.