Near‐term impacts of elevated CO2, nitrogen and fungal endophyte‐infection on Lolium perenne L. growth, chemical composition and alkaloid production

Abstract

ABSTRACTCarbon dioxide has been rapidly accumulating in the atmosphere and is expected to continue to do so. This accumulation is presumed to have important direct effects on plant growth. The interacting affects of a small increase in CO2 concentration (466 p.p.m., approximately 30% increase from current ambient conditions), nitrogen fertilization and fungal endophyte (Neotyphodium lolii) infection on the growth and chemical composition of perennial ryegrass (Lolium perenne) were investigated. It was found that dry mass production was approximately 50% greater under elevated CO2 than under ambient CO2, but only in conditions of high soil N. High molecular weight carbohydrates and total carbohydrates (LMW + HMW CHO) depended on an interaction between CO2 and endophyte infection. Infected plants contained significantly more carbohydrate than endophyte‐free plants, and the difference was greatest in ambient CO2 conditions. Protein concentrations were also influenced by the interaction between CO2 and endophyte‐infection. Endophyte‐free plants had 40% lower concentrations of soluble protein under elevated CO2 than under ambient CO2, but this CO2 effect on soluble protein was largely absent in endophyte‐infected plants. CO2, endophyte‐infection and nitrogen interacted to influence the total chlorophyll concentration of the grass such that chlorophyll concentration was always lower in elevated CO2 but this decline was much greater in endophyte‐free plants, particularly in conditions of high soil N. In the endophyte‐infected plants, the concentrations of the pyrrolopyrazine alkaloid peramine depended on the interaction between CO2 and N fertilization such that peramine concentrations declined with increasing N at ambient CO2 but remained roughly constant across N levels at elevated CO2. A similar pattern was seen for the ergot alkaloid ergovaline. The biochemical responses of perennial ryegrass to elevated CO2 are clearly modified by the presence of endophytic fungi.