Abstract

Invasive alien species (IAS) may threaten native biodiversity and cause considerable economic loss, so more and more attention has been directed towards the assessment of the impact of IAS on native ecosystems. Here, the effects of invasive Canadian goldenrod (Solidago canadensis) on soil properties were examined both in common gardens and under natural conditions. In the common garden experiment, S. canadensis and Chinese goldenrod (S. decurrens) were grown together. After a growing season, soil properties were measured, including pH, pools of soil nitrogen (N), carbon (C), organic matters (SOM) and extractable inorganic nitrogen (NH4-N and NO3-N), and fluxes of net mineralization rate (MIN), net ammonification rate (AMO) and net nitrification rate (NIT). Similar variables representing soil properties were also measured in a field infested with S. canadensis. Our results show that the effects of S. canadensis invasions on soil properties observed in common gardens were similar to those under natural conditions. The invasion of S. canadensis increased the pools of N, C and SOM, but reduced the NH4-N and NO3-N; and S. canadensis also changed soil pH to ca. 8.2 in both garden and field experiments. However, the magnitude of change in several soil properties was larger in field experiments than in garden experiments, which might be the result of the difference in invasion time. C and N contents were only 10% higher in soil planted with S. canadensis than in the soil without S. canadensis in the garden experiments. In contrast, C and N contents were 100% higher in the soil colonized by S. canadensis than in the soil without S. canadensis in the field experiments. Similarly, SOM and NH4-N in the soil showed considerable difference between garden and field experiments. No significant difference in NO3-N was detected, either in garden or field experiments. Interms of fluxes, MIN increased by 3 times when the field was invaded by S. canadensis, indicating that S. canadensis invasions increased the inorganic nitrogen supply. Independent fertilization experiments controlling inorganic nitrogen form and total nitrogen concentration suggest that S. canadensis grew better at a higher ratio of NH4-N to NO3-N or at higher nitrogen levels. This study provided experimental data both for assessment of impacts of plant invaders on soil and for exploration of the mechanism of their successful invasions.