Physio-Ecological Responses Of Invasive Plant Flaveria Bidentis To Clipping, Simulating Herbivory And Fertilizing Management

Flaveria bidentis，an exotic plant with the strong invasiveness, spreads at the most regions ofTianjin, Hebei, Henan and Shandong Province, China, and there is an evidence that it has high potentialto expand to other provinces. This article aims to find out an effective, economic and environmentallyfriendly measure to manage F. bidentis. During2010and2011, the experiments of control andmanagement, including clipping, simulated herbivory and fertilizing management on F. bidentis wasconducted to search effective measures for controlling and management this invasive plant. The growthprameters of biomass accumulation, plant height, branch numbers, flower bud numbers and thephysiological characteristics of chlorophyll content, photosynthesis characteristics, chlorophyllfluorescence parameters were measured to clarify the effects of different treatments. The mainconclusions were as follows:1. Clipping reduced the biomass accumulation of F. bidentis. Compared with the control,three-time clipping treatment was most efficient, and a reduction of82.57%,44.53%,80.04%and91.76%in total biomass, root biomass, stem biomass and leaf biomass was found respectively. Theplant height and the flower bud numbers decreased significantly with clipping times, especially underthree-time clipping treatment, the flower bud numbers declined to0. The maximum branch numberswas recorded under one-time clipping treatment (so-called super-compensation phenomenon), whilethree-time clipping yielded the lowest branch numbers. Compared with control, chlorophyll contenttended to decrease with increasing clipping times. In addition, clipping treatments significantlyenhanced net photosynthetic (Pn), stomatal conductance (Cond) and transpiration rate (Tr). Themaximum photochemical efficiency of photosystem II (Fv/Fm) and potential activity of photosystem II(Fv/F_o) under three-time clipping were significantly lower than other treatments, whereas initialfluorescence yield (F_o) increased obviously. At same time, there was a trend of rise in parameters, suchas Pn, Cond and Tr upon clipping, In short, the impact of every growth and physiological index of F.bidentis was greatest by three clipping, three-time clipping affected growth and physiological indices ofF. bidentis greatly, restricting its regeneration, flowering and eventually fructifying. The index ofgrowth plasticity was higher than that of physiological plasticity, suggesting that growth plasticity wasan important acclimation characteristic for clipping regimes for this invasive species.2. Compared with the control, the overcompensation effect was observed in low level damage andapical removal with increased total biomass, root biomass, stem biomass, plant height, branch numbers,flower bud numbers, net photosynthetic (Pn), water use efficiency (WUE) of F. bidentis. Theseparameters were only reduced by severe damage level (3/4) in our study. Initial fluorescence yield (F_o)under three leaf damages was significantly higher than other treatments, whereas the maximumphotochemical efficiency of photosystem II (Fv/Fm) and potential activity of photosystem II (Fv/F_o)were significantly suppressed. Higher phenotypic plasticity were observed with biomass related parameters, indicating these parameters of F. bidentis have great herbivore tolerance, which might makean important acclimation under herbivores regimes for this invasive species.These results suggest thatnatural enemies may have little impact on fecundity of F. bidentis unless it results in very high levels ofdamage. In practice, more swift management strategy such as clipping, plant replacement and integratedcontrol measure is required to prevent the reproduction of this weed.3. We compared the growth and physiological response of F. bidentis to two different forms ofnitrogen (nitrate and ammonium) under varying concentrations. The result showed that: F. bidentisrespond preferentially to ammonium addition. In this experiment, the carbon (C) addition, which canreduce N availability to plant, resulted in significant inhibiting effect in Chlorophyll fluorescence of Fbidentis. Significant responses to C addition were observed by decreasing growth and biomass.Nitrogen application increased the invasion ability and the risk of proliferation and pervasion of F.bidentis. Nitrogen fixation treatment can inhibit the growth and biomass accumulation of F. bidentis,but the practicality of C addition should consider the effect to native species and the cost input. Inpractice, more swift management strategy such as clipping, plant replacement and integrated controlmeasure, combined with fertilizing management, is required for preventing and controlling this invasiveplant.