Distribution, abundances, and associations of the endophytic fungal community of Arizona fescue (Festuca arizonica)

Abstract

We documented patterns of species diversity, relative abundances, and associations of the fungal endophyte community inhabiting Arizona fescue (Festuca arizonica), a dominant perennial bunchgrass in ponderosa pine-grassland communities of the Southwestern USA. We also determined spatial variation in frequency of a vertically-transmitted and asexual fungus, Neotyphodium starrii, a dominant endophyte in Arizona fescue. To determine if Neotyphodium frequency is affected by grazing, we compared frequency of infected grasses inside and outside long-term grazing exclosures in four Arizona fescue populations. Likewise, we correlated soil nitrogen levels within and among these four, and an additional, population to determine if the frequency of Neotyphodium-infected plants is related to available soil nutrients. More than 400 different fungi were isolated from Arizona fescue. However, most of these were extremely rare and isolated only once. Neotyphodium starrii and 13 other morphospecies comprised the majority of fungal taxa. These results suggest that the fungal endophyte communities of perennial grasses may be as diverse as fungal endophyte communities of woody shrubs and trees, despite high infection levels of the asexual and vertically-transmitted Neotyphodium. The diversity and dominance of non-Neotyphodium endophytes were highly variable among Arizona fescue populations and varied seasonally and yearly within and among populations. Most of these fungal species are probably opportunistic colonizers that increase in abundance in late summer with seasonal rains that promote spore transmission and germination and hyphal growth. Neotyphodium starrii also varied spatially within and among Arizona fescue populations, although always occurring at higher levels than other endophytic fungi. However, Neotyphodium frequencies were not greater outside grazing exclosures as expected if the endophyte confers increased resistance to vertebrate herbivores. Likewise, Neotyphodium frequencies were not related to soil nitrogen levels, either within or among grass populations. Non-Neotyphodium endophytes tended to be negatively associated with the presence of Neotyphodium both among and within host plants. Thus, Neotyphodium may inhibit colonization or growth of other endophytes. The endophytic fungal communities of natural grass populations that harbor Neotyphodium endophytes may be very diverse and variable. Consequently, the interactions among fungal species within a common grass host plant are also probably complex.

Key Words:

• endophyte
• mutualism
• Neotyphodium
• population
• species diversity
• relative abundances