Loss of fungal symbionts at the arid limit of the distribution range in a native Patagonian grass – resource ecophysiological relations

1. Crucial to our understanding of plant ecology is the consideration of the eco-physiological responses and constraints of plant-fungal symbioses throughout the native distribution range of their host.

2. We examined key eco-physiological roles of two co-occurring fungal symbionts [Epichloë endophytes and arbuscular mycorrhizal fungi (AMF)] in the endemic grass Hordeum comosum across a wide bioclimatic gradient and contrasting grazing severity. We sampled H. comosum plants along four humid-to-arid transects in Patagonia, Argentina, covering its entire distribution range and determined Epichloë presence, AMF root colonization, nitrogen and phosphorus concentration, intrinsic water use-efficiency (iWUE, the ratio of photosynthesis to stomatal conductance) and 18O-enrichment of cellulose in shoots.

3. Root colonization by AMF increased with Epichloë-presence. All plants hosted Epichloë in the humid range of the gradient, but symbioses occurrence decreased towards arid sites which al...