Temperate grasslands and global atmospheric change: a review

Recent reviews confirm and extend previous observations that elevated carbon dioxide (CO₂) concentrations stimulate photosynthesis, leading to increased plant productivity. Elevated CO₂ concentrations tend to reduce the sensitivity of grassland ecosystems to low levels of precipitation but induce progressive nitrogen (N) limitations on plant growth which can be alleviated by supplying a significant external input of N in the form of mineral fertilizer or through the increased use of N-fixing legumes. Other nutrients, such as phosphorus, can act as the main limiting factor restricting the growth response in legumes to atmospheric CO₂ concentration. The botanical composition of temperate grasslands is affected by the rise in atmospheric CO₂ concentration, possibly through a decline in the relative abundance of grasses. Elevated CO₂ concentration will also alter the feeding value of herbage to grazers both in terms of fine-scale (for example, crude protein concentration and C:N ratio) and coarse-scale (legumes vs. grasses and C₃- vs. C₄-species) changes. The management guidelines of grasslands will need to be adapted to global atmospheric and climatic changes and to increased variability in climate.