Plant functional traits can guide the regeneration of soil fertility in Kenyan grasslands

Abstract

Background and aims In mesic areas of Sub-Saharan Africa, grassland and soil degradation is widespread and accelerating through overgrazing, alien plant encroachment, and climate change. Selection of native plant species that help to regenerate soil fertility is needed. Here we used a plant functional traitbased approach to species selection aiming to identify traits of native grassland plants that may regenerate soil fertility in degraded grasslands. Methods We set up a mesocosm experiment with degraded and undegraded grassland soils from two contrasting locations in western Kenya. Mesocosms were planted with 18 local plant species. After six months, we harvested the plants and measured survival, plant functional traits, and a range of soil chemical and biological properties related to soil health. Results Seedling mortality was widespread, with eleven out of eighteen species not surviving after six months when planted in the degraded soils. Carbon and nitrogen concentrations of degraded soils from both sites were lower than for undegraded soils, as was microbial biomass carbon and nitrogen. In soil of the surviving plant species, we found greater carbon and nitrogen, and enhanced enzyme activity for carbon, nitrogen and phosphorus cycling. This was linked to plant traits, including lower leaf dry matter content, high tissue nutrient content, and deep roots. Conclusion Overall, our findings provide evidence that sowing native plant species with dense and nutrient rich tissues, such as high yielding forage grasses and slow-growing legumes, can help regenerate the fertility of degraded grassland soils in mesic tropical regions.