Aboveground herbivory increases soil nematode abundance of an invasive plant

Abstract

Abstract Aims Plant invasions have the potential to affect the community structure of soil nematodes, but little is known about whether such effects are mediated by aboveground herbivores since invasive plants are not completely released from herbivores in the introduced range. In this study, we explored how aboveground insect herbivores mediated the effect of invasive plant Alternanthera philoxeroides on soil nematodes and examined the temporal variations of such an herbivory-elicited effect. Methods We conducted a greenhouse experiment by applying different herbivory treatments (no insect herbivores, specialist Agasicles hygrophila and generalist Cassida piperata) to potted A. philoxeroides, and then measured the community compositions of soil nematodes in corresponding pots on the 1st, 10th and 20th day after removal of all herbivores. In addition, the carbon content of roots and root exudate of A. philoxeroides were also measured. Important Findings Our results showed that aboveground herbivory significantly increased the abundance of soil nematodes of A. philoxeroides, likely plant feeder nematodes, after insect herbivores were removed immediately (1st day). However, such impacts waned with time and there was no significant difference at later stages (10th and 20th days). Furthermore, the effects of specialist A. hygrophila and generalist C. piperata herbivory were consistent on the abundance of soil nematodes. Overall, our results suggest that aboveground insect herbivores have the potential to alter the effects of plant invasions on soil nematodes, but such impacts are transient. Furthermore, our study highlighted the importance of integrating the effects of above- and belowground organisms when evaluating the impacts of plant invasions.