Evolution Of The Defense Strategy And Resource Use Efficiency In An Invasive Plant Alternanthera Philoxeroides

Rapid post-introduction evolution has been found in many invasive plants, in-cluding changes in growth, constitutive defense traits and their resource capture and utilization efficiency. The mechanism of successful invasion has always been a hot spot for ecologists. One of the most receivable hypotheses is the Evolution of In-creased Competitive Ability (EICA). Following are some hypothesizes complement-ing, such as the Resource-Enemy Release Hypothesis (R-ERH) and the Shifting De-fense Hypothesis (SDH).There are some inconsistency in the results of the testing re-searches, we may need to synthesis these hypothesizes to explain the successful inva-sion. Also high resource capture and utilization efficiency are thought to contribute to plant invasion progress. Here, in order to explore how these hypothesizes synthesis together to explain successful invasion, we conducted common garden experiments using eight native populations and eight invasive populations of Alternanthera philoxeroides (alligator weed) in 2011 and 2012.We compared related traits on growth, defense and resource capture and use efficiency. Conclusions below:1) Compared to native populations, introduced populations showed greater total biomass (Biomass,+14.7%), greater main stem biomass (Main stem,+29%) but lower root shoot ratio (RSR,-18%)2) Compared to native populations, introduced populations showed greater Sap-onin (+34%), greater Trichome (+149%), lower specific stem length (SSL,-25%) and lower specific leaf area (SLA,-13%). C/N was not significantly different.3) Compared to native populations, introduced populations had significantly lower mass-based leaf construction cost (CCmass,-5%) and photosynthetic energy use efficiency (PEUE,-4%). The maximum photosynthesis rate (Pmax), photosyn-thetic nitrogen use efficiency (PNUE), water use efficiency (WUE) was not signifi-cantly differentThese results suggested that the invasive populations increased biomass and de-creased the defense toward the natural enemy, this accords with EICA hypothesis. Also the plant increased the defense toward general enemy; this is coordinated to SDH hypothesis. Higher resource capture and utilization efficiency is not suitable for explaining the successful invasion of Alternanthera philoxeroides.