Disruption of Traditional Grazing and Fire Regimes Shape the Fungal Endophyte Assemblages of the Tall-Grass Brachypodium rupestre

Abstract

The plant microbiome is likely to play a key role in the resilience of communities to the global climate change. This research analyses the culturable fungal mycobiota of Brachypodium rupestre across a sharp gradient of disturbance caused by an intense, anthropogenic fire regime. This factor has dramatic consequences for the community composition and diversity of high-altitude grasslands in the Pyrenees. Plants were sampled at six sites, and the fungal assemblages of shoots, rhizomes, and roots were characterized by culture-dependent techniques. Compared to other co-occurring grasses, B. rupestre hosted a poorer mycobiome which consisted of many rare species and a few core species that differed between aerial and belowground tissues. Recurrent burnings did not affect the diversity of the endophyte assemblages, but the percentages of infection of two core species -Omnidemptus graminis and Lachnum sp. -increased significantly. The patterns observed might be explained by (1) the capacity to survive in belowground tissues during winter and rapidly spread to the shoots when the grass starts its spring growth (O. graminis), and (2) the location in belowground tissues and its resistance to stress (Lachnum sp.). Future work should address whether the enhanced taxa have a role in the expansive success of B. rupestre in these anthropized environments.

Keywords: Brachypodium rupestre; Epichloë typhina; Lachnum sp.; Omnidemptus graminis; culturable endophytes; disturbances; fire recurrence.

FIGURE 1

Locations selected for collecting plants. Red points represent low-diversity grasslands and green points high-diversity grasslands (C). Pictures of the Brachypodium rupestre invaded (A) and non-invaded (B) areas.

FIGURE 2

Venn’s diagrams indicating the number of shared fungal species across grassland types (A) and tissues (B).

FIGURE 3

Species-accumulation curves of the mycobiota isolated from Brachypodium rupestre according to plant tissue and grassland type. Black line, based estimator of the total number of species; shaded zone, standard deviation; dark blue, all species included; orange, excluding singleton species. (A) All tissues, (B) Shoots, (C) Rhizomes, (D) Roots, (E) Low-diversity grasslands, (F) High-diversity grasslands.

FIGURE 4

Species richness and diversity indexes (Shannon and Simpson) of the mycobiome of shoots, rhizomes, and roots of Brachypodium rupestre in low and high-diversity grasslands.

FIGURE 5

Non-metric multidimensional scaling (NMDS) of the fungal endophyte community composition of tissues of Brachypodium rupestre from low and high-diversity grasslands.

FIGURE 6

Probability of incidence of fungal indicator species of Brachypodium rupestre calculated with GLMM.

FIGURE 7

Venn’s diagrams indicating the number of shared fungal endophyte species among grass species.

FIGURE 8

Species-accumulation curves of fungal endophytes from Brachypodium rupestre, Festuca rubra and Agrostis capillaris shoots from high-diversity grasslands. Black line, based estimator of the total number of species; shaded zone, standard deviation; dark blue, all species included; orange, excluding singleton species.

FIGURE 9

Species richness and diversity indexes (Shannon, Simpson) of the mycobiome of shoots from three representative grasses of high-diversity grasslands from three locations.

FIGURE 10

Probability of incidence of Epichloë spp. and Omnidemptus graminis in the aboveground tissues of the most common grasses of high-diversity grasslands.