Litter-Mediated Soil Alterations by Guinea Grass (Megathyrsus maximus) in Semiarid Rangelands

Abstract

Invasive plants are regarded as both drivers and passengers of change in the ecosystems they invade. In both conditions, these plants are reported to cause significant changes in soil biological, physical, and chemical characteristics, which have a long-lasting impact in the invaded soils compared with the surrounding uninvaded soils. One of the mechanisms of such change is the addition of both aboveground and belowground plant organic material. The goal of this study was to explore the plant-soil feedback in a non-native invasive grass, Guinea grass (Megathyrsus maximus) that invades rangelands, agricultural fields, and natural areas in the tropics and warm temperate regions. We hypothesized that the soil under Guinea grass is significantly different from natives. We also hypothesized that high tissue nitrogen leads to a higher litter nutrient status, driving this change. To test these hypotheses, we selected five different sites with significant Guinea grass invasion history and analyzed the soils under Guinea grass and coexisting native grasses. Our results show there was no significant difference between Guinea grass and natives in the amount of organic matter in the soil, but the nitrogen (N) content in both soil and leaf tissue in Guinea grass and natives was significantly different. The higher N content in the leaves was strongly correlated with soil N, moisture, and organic matter salinity, and negatively correlated with soil pH. Therefore, our results show that due to its nitrogen-rich leaf tissues, Guinea grass adds higher-quality litter back into the soil, resulting in a higher nutrient pool in its rhizosphere compared with the native grasses, thereby further aiding in the invasion success of Guinea grass.