Influence of invasive plants on nematode communities under simulated CO2 enrichment

Abstract

Relationships between exotic plant invasion and environmental change including CO2 increase have been studied, but little is known about effects of invasive plants and global change on belowground faunal communities. Nematodes are abundant and trophically diverse soil biota, and are susceptible to environmental changes. Alteration of their community composition can illustrate changes in belowground ecosystems. In this study, we examined responses of nematode communities to exotic invasive plants and native plants under current and increased CO2. We grew individual plants of two invasive and two native species under ambient and elevated CO2 under controlled conditions. Soil nematode abundance, the proportion of nematode trophic groups and their ecological indices were measured to determine their responses to invasive and native plants under different CO2 conditions. Canonical correspondence analysis (CCA) showed that elevated CO2 and invasiveness significantly affected nematode communities. Elevated CO2 significantly increased bacteria-feeding nematode proportions under two invasive plants, and decreased their proportion under the native Eupatorium heterophyllum. Elevated CO2 decreased the proportion of plant-feeding nematodes under the invasive plant Chromolaena odorata, and increased the proportion of plant-feeding nematodes under E. heterophyllum, indicating that elevated CO2 could benefit C. odorata by reduced belowground herbivory compared to this native plant species. Ecological indices showed that invasives had higher nematode diversity than natives. Under elevated CO2, the value of structural index (SI) was greater than 50, while the value of enrichment index (EI) was <50 with two invasive plants. SI and EI were <50 under two native plants, indicating that these invasive plants developed more stable belowground ecosystems than native species, and that this could promote their colonization under CO2 increase. Overall, our results suggested that elevated CO2 can favor particular invasive plants over native species, and increase successful invasion by these plant species.