Broad‐scale variation of fungal‐endophyte incidence in temperate grasses

Abstract

Summary1. The strength of many interactions between plants and other organisms changes across regional gradients. For example, the relevance of plant-herbivore interactions increases with primary production. Likewise, biotic interactions collectively become more intense from the poles to the equator. Yet, the regional variation of the interaction between grasses and systemic fungal endophytes, which provide resistance to biotic and abiotic environmental factors (i.e. herbivory and drought), is poorly understood. 2. We compiled 1008 records of the incidence level of fungal endophytes (Epichlo€ e, Ascomycetes: Clavicipitaceae) on wild populations of 48 cool season grasses, encompassing 10 biomes across a broad latitudinal expanse and primary production gradient. Symbiosis incidence was analysed as a function of mean primary production, precipitation, temperature and latitude of each site, which in turn were obtained from climatic and satellital sources. 3. Across a 30-fold variation of mean primary production, average symbiosis incidence increased from 20% to 70%. The pattern became stronger when the analysis was restricted to the single grass genus Festuca, which accounted for half of the total data. 4. The number of grass populations showing no symbiosis incidence (0%) decreased as primary production increased, whereas those with 100% of incidence increased. 5. Primary production at the regional scale was negatively correlated with latitude but positively with mean annual temperature and precipitation. Symbiosis incidence was similarly correlated with latitude and temperature, and it was not with mean annual precipitation. 6. Synthesis. Different descriptors of this grass-fungus symbiosis show that average incidence in wild populations world-wide increases with mean primary production. As at large spatial scales herbivory and temperature increase and aridity decreases with primary production, our results suggest that, at broad-scales, these biotic and abiotic factors may be important drivers of the symbiosis success.

Fungal endophyte diversity in tundra grasses increases by grazing

“…Both Jensen et al (2011) and the present study found grass species of tundra to hold a range of fungal endophyte taxonomic units (also by the culture method), suggesting that latitudinal patterns are dependent on the type of species of the host plant. Still, even among grass host species, low colonization frequency of Epichlo€ e endophytes at higher latitudes have been found (Semmartin et al 2015), indicating latitudinal patterns are likely also dependent on type of endophytic species. As demonstrated in the present study, fungal endophytes are both common at high latitude and are affected by tundra ecosystem processes.…”

Occurrence of Epichloë fungal endophytes in the sheep-preferred grass Hordeum comosum from Patagonia

“…For example, the incidence of fungal endophytes was positively correlated with mean annual precipitation in populations of Bromus setifolius, another palatable grass occurring in southernmost Patagonia (Novas et al, 2007). A very recent global review showed that sites with low aboveground net primary productivity (ANPP), likely as a result of water shortage, presented higher probability of populations with no-endophyte or low incidence of endophytes compared with sites with high ANPP (Semmartin et al, 2014). In addition, is worth mentioning that studies that experimentally addressed the hypothesis of improved tolerance to drought mediated by endophytes have been carried out with the mesophytic species tall fescue and perennial ryegrass exposed to water shortage for short periods of time (Saikkonen et al, 2006).…”

Inferring field performance from drought experiments can be misleading: The case of symbiosis between grasses and Epichloë fungal endophytes

“…The idea of positive effects of endophytes on plant tolerance to drought has been used to explain ecological patterns in which high symbiosis incidence is associated with low levels of precipitation (Lewis et al, 1997;Malinowski and Belesky, 2006;Afkhami et al, 2014). However, a recent global survey of endophyte incidence including a larger number of grass and fungal endophyte species in a wider environmental gradient revealed a different pattern (Semmartin et al, 2015). By reviewing the literature and adding information to the drier extreme of the gradient, they found a positive relationship between endophyte incidence and mean aboveground net primary productivity (ANPP), a variable closely associated with mean precipitation (Sala et al, 1988).…”

“…Mean annual precipitation of the distributional range for B. setifolius and H. comosum is 259 and 471 mm, respectively, while for L. perenne and S. phoenix is 592 and 685 mm (data took from Semmartin et al, 2014, andCasas et al, 2015). Thus, it seems that the negative relationship between endophyte incidence and parameters of environmental quality (e.g., precipitation or ANPP) would be not valid in arid ecosystems (see Semmartin et al, 2015) or, at least, would be specific to species and/or ecosystems.…”

“…Concerning the third issue, we put forward a mechanistic hypothesis that would account for the observed regional patterns of incidence showing an overall growing trend with ANPP (Semmartin et al, 2015), but also for the apparent larger variance of incidence towards low-precipitation locations (see Novas et al, 2007;Iannone et al, 2015;Casas et al, 2015). Local population endophyte incidence depends mainly on three processes: (1) the relative fitness of symbiotic vs. non-symbiotic plants, (2) same for net migration rates, and (3) the efficiency with which the endophyte is vertically transmitted (Saikkonen et al, 2002;Gundel et al, 2008Gundel et al, , 2011a.…”