Response patterns of physiological and ecological parameters of Alternanthera philoxeroides to shading rate and its shading control threshold

Alternanthera philoxeroides is an invasive plant widely distributed in the provinces south of 40º N in China. It has become a malignant weed that seriously threatens the biodiversity and ecosystem stability in China. Light intensity is an important environmental factor that regulates plant growth and development. It is important to investigate the specific response patterns of physiological and ecological parameters of A. philoxeroides to different light stress to explore its shading control threshold. In this experiment, we selected 5 types of shading nets (average shading rates 51.0%, 64.3%, 69.7%, 81.8%, and 88.3%) for the shading treatment of A. philoxeroides. The results were as follows: 1) The aboveground and underground biomass of A. philoxeroides decreased linearly with the increase in the shading rate. 2) Morphological parameters (branch number, proportion of long branches, number of leaves, leaf thickness, and leaf area) had high phenotypic plasticity on shading (mean value 0.66), and a higher phenotypic plasticity index had a higher reduction effect of shading on these parameters. 3) When the shading rate reached 61.9% to 66.7%, the underground biomass and branch number of the plant was reduced by more than half, and the promotion effect of shading on the increase in leaf area and SPAD value was inhibited, thus affecting the photosynthesis of the plant. The changes in growth, morphological, and chlorophyll content parameters of A. philoxeroides showed that the shading rate of 61.9% to 66.7% effectively reduced its propagation diffusion ability. Therefore, this shading rate can be used as the shading threshold for the control of A. philoxeroides.