Effects of increased temperature on growth and nutritional value of mesic grasslands, with or without woody legume seedling competition.

Abstract

Mesic grasslands are complex ecosystems covered in grasses and other graminoid vegetation. The species composition varies due to variation in rainfall and temperature; these grasslands are climatically supported. They also vary in nutritive value and grasslands with high species richness have low nutritive value because grasses differ genetically. Grasses’ response to high temperature and competition is species dependent. Grasslands are ideal for ecological experiments because grasses grow fast and their response to environmental changes is noticeable. Therefore, an experiment of induced warming with legume seedlings interaction was conducted at the University of KwaZulu-Natal, using open top chambers and Vachellia sieberiana var. woodii. This was done to determine the effect of increased temperature on the biomass, growth, morphology and nutritive value of Themeda triandra and Aristida junciformis. These species were chosen because they occur naturally and dominate in the Ukulinga farm, where the experiment was conducted. They also have contrasting palatability, T. triandra is highly palatable and A. junciformis is less palatable. Vachellia sieberiana seedlings were grown from seed and transplanted after two months to the field to interact with grasses for four months. The results suggest that the interaction of warming and woody seedlings reduces the biomass of the investigated species. This implies that warming reduces grass biomass. Plant traits such as grass height, leaf area, tiller width and tuft diameter responded differently to the treatments. The fibre (neutral detergent fibre) of T. triandra was increased by warming. The interaction of warming and woody seedlings had no effect on the regrowth fibre content. The interaction of warming and woody seedlings increased the protein content of A. junciformis. Warming and woody seedlings independently increased the protein content of T. triandra. The response of plants to increased warming will help ecologists understand the effects of global warming. To provide more insight into these findings, further research on specific species with longer experimental duration and high woody seedling neighbour density is of importance.