Fungal endophyte (Epichloë festucae) alters the nutrient content of Festuca rubra regardless of water availability

Abstract

Festuca rubra plants maintain associations with the vertically transmitted fungal endophyte Epichloë festucae. A high prevalence of infected host plants in semiarid grasslands suggests that this association could be mutualistic. We investigated if the Epichloë-endophyte affects the growth and nutrient content of F. rubra plants subjected to drought. Endophyte-infected (E+) and non-infected (E-) plants of two half-sib lines (PEN and RAB) were subjected to three water availability treatments. Shoot and root biomass, nutrient content, proline, phenolic compounds and fungal alkaloids were measured after the treatments. The effect of the endophyte on shoot and root biomass and dead leaves depended on the plant line. In the PEN line, E+ plants had a greater S:R ratio than E-, but the opposite occurred in RAB. In both plant lines and all water treatments, endophyte-infected plants had greater concentrations of N, P and Zn in shoots and Ca, Mg and Zn in roots than E- plants. On average, E+ plants contained in their shoots more P (62%), Zn (58%) and N (19%) than E- plants. While the proline in shoots increased in response to water stress, the endophyte did not affect this response. A multivariate analysis showed that endophyte status and plant line impose stronger differences in the performance of the plants than the water stress treatments. Furthermore, differences between PEN and RAB lines seemed to be greater in E- than in E+ plants, suggesting that E+ plants of both lines are more similar than those of their non-infected version. This is probably due to the endophyte producing a similar effect in both plant lines, such as the increase in N, P and Zn in shoots. The remarkable effect of the endophyte in the nutrient balance of the plants could help to explain the high prevalence of infected plants in natural grasslands.

Figure 1. Biomass production and water content of Festuca rubra plants.

Effect of fungal endophyte status (• = E+, infected; ο = E-, non-infected) of two lines (PEN and RAB) of plants, growing at different water treatments (C= control; W1= moderate stress; W2= severe stress). Values, expressed as g of dry weight (DW) per pot, are means ± 2 SE (n=6).

Figure 2. Nutrient concentration of Festuca rubra plants.

Effect of fungal endophyte status (• = E+, infected; ο = E-, non-infected) of two lines (PEN and RAB) of plants, growing at different water treatments (C= control; W1= moderate stress; W2= severe stress). Values are means ± 2 SE (n=6).

Figure 3. Proline and total phenolic compounds (TPhC) of Festuca rubra plants.

Effect of fungal endophyte status (• = E+, infected; ο = E-, non-infected) of two lines (PEN and RAB) of plants, growing at different water availability levels (C= control; W1= moderate stress; W2= severe stress). Values are means ± 2 SE (n=6).

Figure 4. Ergovaline concentration in endophyte infected (E+) plants.

Two lines (☐= PEN; ■= RAB) of plants, growing at different water treatments (C= control; W1= moderate stress; W2= severe stress). Values are means ± 2 SE (n=6).

Figure 5. Hierarchical cluster with the Euclidean distance using the biplot scores.

Each sample was labelled with a first letter for plant line (P= PEN; R= RAB), a second letter for endophyte status (E+= endophyte infected; E-= non-infected), and a third letter for water treatment (C= control; W1= moderate stress; W2= severe stress). The cophenetic correlation coefficient was 0.679.

Figure 6. H-J biplot representation of samples and variables on the factorial plane I-II.

Each sample was labelled with a first letter for plant line (P= PEN; R= RAB), a second letter for endophyte status (E+= endophyte infected; E-= non-infected), and a third letter for water treatment (C= control; W1= moderate stress; W2= severe stress). Variable labels: DW_shoot = shoot biomass; DW_root=root biomass; TPhC_shoot= total phenolic compounds in shoots; TPhC_root= total phenolic compounds in roots; Proline_shoot= proline in shoots; Proline_root= proline in roots; and nutrient concentration in shoot and roots: N_shoot, N_root, P_shoot, P_root, K_shoot, K_root, Ca_shoot, Ca_root, Mg_shoot, Mg_root, Zn_shoot, Zn_root.