Mixing litter effects of exotic invasive plant Mikania micrantha H.B.K. with native plants

Background/Question/Methods

Successful plant invaders have the potential to influence nutrient cycling in the invaded ecosystem, which in turn can affect native plant community function. Invasive plants alter the N cycling process through litter. Much research has reported both synergistic and antagonistic effects for decomposition and nutrient release due to the mixing of litter from different species, but few have investigated the effects of non-native litter to date. The exotic plant Mikania micrantha H.B.K. (M. micrantha) has invaded many forests in south China and has altered ecosystem processes. Our previous studies showed that M. micrantha invasion impact the litter decomposition rate and nutrient release greatly through allelopathy, but the effects of mixing M. micrantha litter with native litter are unclear. To quantify litter decomposition rate, a litterbag technique was used. Litter of the invasive plant M. micrantha was mixed with the litter of 7 native plants, respectively, as 3 ratios: M₁ (1: 4), M₂ (1: 1) and M₃ (4: 1). After 60-days decay, the litter decomposition rate and nutrient (C, N) release were determined.

Results/Conclusions

We found that the mono-species litter decomposition rate of M. micrantha was higher than 3 natives, while lower than other 4 natives. It is interesting that both the higher decomposition rate of 3 natives’ mono litter and the lower 4 natives showed similar mixing effects. The results showed that under M₁, the observed litter decomposition rate (OLD) were lower than the predicted litter decomposition rate (PLD), while, under M₂ and M₃, OLD were much higher than PLD. During harvesting, more earthworms were found surrounding the litterbags when native litter was mixed with the litter of M. micrantha. The increased OLDs may be due to soil changes rather than litter quality. The C and N release from litter showed changes similar to those observed in decomposition rate: the observed C and N release were lower than predicted under M₁, while the observed were much higher than predicted under M₃. These results imply that with the degree of M. micrantha invasion, more litter will mix with the litter of native plants, accordingly, which will enhance C and N release from litter. This increase in nutrient release might represent positive feedback to M. micrantha invasion. However, it remains unclear as to why all the different quality litter of 7 native species showed similar mixing effects when mixed with litter of exotic plant M. micrantha, which merits further study.