Effects of elevated CO₂ and cutting frequency on plant community structure in a temperate grassland

Abstract

Abstract Monoliths of a fertile, N limited, C3 grassland community were subjected (or not) to an atmospheric CO 2 enrichment (600 µmol mol ‐‐1 ) using a Mini‐FACE system, from August 1998 to June 2001 and were subjected to two contrasting cutting frequencies (3 and 6 cuts per year). We report here the effects of the CO 2 and cutting frequency factors on the plant community structure and its diversity. Species‐specific responses to elevated CO 2 and cutting frequency were observed, which resulted in significant changes in the botanical composition of the grassland monoliths. Elevated CO 2 significantly increased the proportion of dicotyledones (forbs + legumes) and reduced that of the monocotyledones (grasses). Management differentiated this response as elevated CO 2 increased the proportion of forbs when infrequently and of legumes when frequently defoliated. However, among the two dominant forbs species only one was significantly enhanced by elevated CO 2 . Moreover, not all grass species responded negatively to high CO 2 . At a low cutting frequency, the observed decline under ambient CO 2 in species diversity (Shannon‐Weaver index) and in forb species number was partly alleviated by elevated CO 2 . This experiment shows that the botanical composition of temperate grasslands is likely to be affected by the current rise (+ 0.5% per year) in the atmospheric CO 2 concentration, and that grassland management guidelines may need to be adapted to a future high CO 2 world.