Ecological stoichiometry and invasive strategies of two alien species ( Bidens pilosa and Mikania micrantha ) in subtropical China

To understand the growth and nutritional strategies of two alien Asteraceae species in both nutrient‐rich and nutrient‐poor environments by measuring the stoichiometric characteristics of plants and soil nutrients, two alien species Bidens pilosa and Mikania micrantha from subtropical zone of southeast China was studied. The two species grow in P‐rich environments and/or have a strong capacity for absorption and utilization of P. The two invasive alien species studied used diverse nutrition and growth strategies under different habitats. For B. pilosa under low‐N environments, leaves showed lower N:P and C:P than in other habitats. In contrast, roots showed greater N:P, C:P and C:N ratios, suggesting a “resource conservative strategy,” whereas under high‐N and high‐P, or high‐N and low‐P environments, B. pilosa roots had lower N:P and C:P ratios, suggesting a “growth competitive strategy.” Conversely, M. micrantha did not match either strategy in high‐ or low‐resource habitats. The growth of B. pilosa is resource‐dependent, mainly driven by C and N content, and C:N ratio in the soil, as well as allocation of P within the plant. The growth of M. micrantha is less limited by soil resources, but mainly by tradeoffs between allocation to leaves versus roots. There are various growth and nutrient strategies under different resource environments (e.g., resource conservative strategy, and/or growth competitive strategy), as well as fundamental trade‐offs between life history traits, which all contribute to the successful invasion by alien species.