Effects of water and nutrient availability on morphological, physiological, and biochemical traits of one invasive and one native grass of a Neotropical savanna

Abstract

The cerrado is a Neotropical savanna characterized by a soil and vegetation mosaic where plants endure dystrophic soils and seasonal drought. Dry spells or flooding are the main environmental stress native species face in their growth period. African grasses are common invasive species, jeopardizing the biodiversity by displacing native species and outgrowing them. Invasive species may benefit from human interventions that increase nutrient availability in natural areas and may respond differently than natives to environmental conditions. Therefore, we compared the performance of one native (Schizachyrium microstachyum) and one invasive (Melinis minutiflora) grass in different conditions of water and nutrient availability simulating possible cerrado scenarios. Five-week-old seedlings were submitted to different irrigation treatments (simulating dry spells, normal rainfall, and flooding) and fertilization treatments (high or low nutrient availability) for four weeks, and were analyzed for morphological (leaf area, length of the shoot, number of tillers, seedling dry weight, and root:shoot ratio) and physiological parameters (chlorophyll fluorescence, pigment concentration, nutrient content, and biochemical assays). There was a trend for the invasive species to show better responses to water stress by growing more profusely, showing an even higher effect when the soil was richer in nutrients. The invasive species may outcompete the native species by using nutrients and water more efficiently, showing a weaker oxidative response to drought and fertilization. The native species would perform at a similar pace to the invasive species in conditions of less water and nutrient availability, whereas unnatural fertilization inputs and high-water availability would benefit the invasive species.