The influence of small-scale resource heterogeneity caused by human activities on the growth phenotype of invasive aquatic plants

Climate change caused by human activities leads to nitrogen deposition, phosphorus input and changes in rainfall patterns, which also result in heterogeneous distribution patterns of resources and biological invasion. Clonal plants grow in environments with spatial and temporal heterogeneity; they can effectively adapt to heterogeneous environments and further increase growth performance through their own unique characteristics. The strong clonal ability may help invasive species take advantage of heterogeneous environments. To investigate the combined effects of soil nutrients and water heterogeneity on the growth performance and foraging behavior of exotic and native aquatic plants, we conducted a greenhouse experiment with the notorious invasive species Alternanthera philoxeroides and Myriophyllum aquaticum compared with similar life forms of native species Ludwigia peploides. We grew each species in containers in two heterogeneous soils consisting of patches of nitrogen and phosphorus, mixed evenly, and low-nutrient soils, and in soils where the nitrogen and phosphorus soils were mixed homogeneously. The experiment was carried out with homogeneous or heterogeneous water treatments to examine how the interaction with the soil treatments. Overall, all three species increased or maintained their growth performance in heterogeneous soils compared with homogeneous soils. The heterogeneous nutrient treatment with large nutrient differences between patches produced significantly more total biomass, by 68.83% and 160.59%, than the homogeneous nutrient treatment of A. philoxeroides and L. peploides, respectively. There were no significant effects of water heterogeneity on the growth performance of A. philoxeroides and M. aquaticum. In addition, A. philoxeroides and L. peploides showed obvious preferential selective placements of foraging organs in resource-rich patches and further increased whole plant growth. However, M. aquaticum did not show foraging behavior during the experiment, and the effects of soil nutrient heterogeneity on L. peploides changed with the supply mode of water. Foraging behavior may help A. philoxeroides better adapt to heterogeneous environments. Our results suggest that the combination with soil nutrients and water heterogeneity could promote the expansion and growth of the notorious invasive species A. philoxeroides.