Heavy drought reduces the decomposition rate of the mixed litters of two composite invasive alien plants

Compositae family comprises the largest number of species of invasive alien plants (IAPs) in China. Two IAPs can co-invade the same habitat. Drought can alter the litter decomposition of IAPs and soil enzyme activities. This study aims to estimate the independent and combined effects of two composite IAPs (Bidens pilosa and Solidago canadensis) on litter decomposition and soil enzyme activities under drought. A polyethylene litterbags experiment (5 g litters of B. pilosa, 5 g litters of S. canadensis or 5 g litters of B. pilosa and S. canadensis in an equal proportion per polyethylene litterbag) was performed. The polyethylene litterbags were treated with a gradient of drought, i.e. control, light level of drought and heavy level of drought. The decomposition coefficient of the two composite IAPs and soil enzyme activities was determined. The co-invasion of the two composite IAPs posed a synergistic effect on urease activity. The mixed litters of two composite IAPs and the litters of B. pilosa had higher decomposition rates than S. canadensis. Urease activity was increased in light droughts, but it was decreased in heavy drought. Heavy drought reduced the decomposition rate of the mixed litters of two composite IAPs and the litters of B. pilosa. Drought did not affect the decomposition rate of S. canadensis litters. Thus, heavy drought can decrease the nutrient cycling rate under the co-invasion of the two composite IAPs and the independent invasion of B. pilosa rather than the independent invasion of S. canadensis.

Automated summary

This study aimed to assess the independent and combined effects of two composite invasive alien plants (Bidens pilosa and Solidago canadensis) on litter decomposition and soil enzyme activities under drought conditions. The results showed that the co-invasion of the two species had a synergistic effect on urease activity, and the decomposition rate of mixed litters was higher than that of S. canadensis. Moreover, heavy drought reduced the decomposition rate of the two composite species and B. pilosa, while it did not affect S. canadensis litter decomposition.