Fluctuated water depth with high nutrient concentrations promote the invasiveness of<i>Wedelia trilobata</i>in Wetland

Abstract

The distribution of invasive and native species in wetlands is determined by hydrological conditions; whereas conditions such as water depth fluctuations, variations in the nutrient concentrations are expected to affect the growth and physiological traits of plants. For the assessment of such effects, we conduct greenhouse experiment with three factors; 1) water depth of 5 cm and 15 cm (static and fluctuated); 2) three levels of nutrient concentrations (i) full-strength Hoagland solution (N1), (ii) ¼-strength Hoagland solution (N2), and (iii) ¹/₈-strength Hoagland solution (N3); and 3) species, invasive <i>Wedelia trilobata</i> (L.) and its congener, native <i>Wedelia chinensis</i> (Osbeck.) under mono and mixed culture. Water depth of 5 cm combined with any of the nutrient treatments significantly restrained the photosynthesis, intracellular CO₂ concentration and leaf chlorophyll of both <i>W. trilobata</i> and <i>W. chinensis</i>. Increase in the water depth to 15 cm with low-nutrient treatment N3 did not sustain the physiological traits of <i>W. chinensis</i> under mono and mixed planting. A great loss was noted in the growth of <i>W. chinensis</i> at 15 cm static and fluctuated water depth with low-nutrient treatment (N3) and under mixed culture. In addition, water depth fluctuations with both low- and high-nutrient treatments significantly affected the root-shoot ratio, relative growth rate, and interspecific interaction among these two species. <i>W. trilobata</i> benefited more from competitive interaction index (CII) under fluctuated water depth at 15 cm with high nutrients, and the value of CII was clearly positive. Therefore, higher competitive ability may contribute to the invasiveness of <i>W. trilobata</i> in wetlands.