Growth response of Praxelis clematidea seedlings to water and nitrogen coupling

The response mechanism of invasive species of Praxelis clematidea seedling growth to different water and nitrogen (WN) coupling models were investigated by determining the relationship between WN and bio-invasion. This experiment incorporated three irrigation levels and four levels of nitrogen, for a total of 12 processes to study the coupling effect of different WN processing on P. clematidea parameters including morphological, biomass and chlorophyll content. P. clematidea seedlings were significantly affected by the WN coupling (P<0.05). The seedlings grew better with higher root, stem and leaf morphological indexes, such as plant height, stem diameter, leaf area, total root length and root surface area, and more biomass accumulation under suitable moisture and nutrient conditions, such as treatment with the intermediate level of WN (saturated sand water content 60%~70%, water supply 60 mL·kg-1, nitrogen supply 0.30 g·kg-1). P. clematidea seedlings exposed to each nitrogen treatment coupled with low level of water (saturated sand water content 30%~40%, water supply 30 mL·kg-1) or high level of water (saturated sand water content 90%~100%, water supply 90 mL·kg-1) displayed lower root, stem and leaf morphological indexes and less biomass accumulation than the corresponding nitrogen treatment coupled with the intermediate level of water. Leaf chlorophyll content of P. clematidea was more sensitive to nitrogen, which increased with the increase of nitrogen. We can draw the conclusion that P. clematidea easily invades an environment with a certain content of WN, but has more restricted distribution in an environment with excessive or insufficient water or nutrients, which is closely related to its invasion.