Effects of clonal integration on allelopathy of invasive plant Wedelia trilobata under heterogeneous light conditions

Plant invasion is one of the most serious threats to ecosystems worldwide.When invasive plants with the ability of clonal growth invading or colonizing in new habitat,their interconnected ramets may suffer from heterogeneous light.Effects of clonal integration on allelopathy of invasive plants are poorly understood under heterogeneous light conditions.To investigate the effects of clonal integration on allelopathy of invasive plant Wedelia trilobata under heterogeneous light conditions,a pot experiment was conducted by using its clonal fragments with two successive ramets.The older ramets were exposed to full light,whereas the younger ones were subjected to 20%full light.The younger ramets of each clonal fragment were adjacently grown with a target plant(one tomato seedling)in a pot.Stolon between two successive ramets was either severed or retained intact.In addition,two tomato seedlings(one as target plant)were adjacently grown in a pot as contrast.Compared with severing stolon,biomass accumulation,foliar chlorophyll and nitrogen contents,chlorophyll fluorescence parameters and net photosynthetic rates of the target plants as well as their root length and activity,were significantly decreased when stolon between interconnected ramets of W.trilobata retained intact.Under heterogeneous light conditions,transportation or sharing of carbohydrate between two successive ramets enhanced allelopathy of the young ramets subjected to 20%full light treatment.It is suggested that clonal integration may be important for invasion or colonization of invasive plants with ability of clonal growth under heterogeneous light conditions.

Adaptive plasticity in response to light and nutrient availability in the clonal plant Duchesnea indica

Phenotypic plasticity enables plants to buffer against environmental stresses and match their phenotypes to local conditions.However,consistent conclusive evidence for adaptive plasticity has only been obtained for a few traits.More studies on a wider variety of plant functional traits and environmental factors are still needed to further understand the adaptive significance of plasticity.We grew 21 genotypes of the stoloniferous clonal plant Duchesnea indica under different light and nutrient conditions,and used selection gradient analyses to test the adaptive value(benefits)of morphological and physiological plasticity responding to variation in light and nutrient availability.Plants grown in shade exhibited lower values for fitness measures(fruit number,ramet number and biomass),shortened thinner internode length and decreased adult leaf chlorophyll content,but higher petiole length,specific leaf area and old leaf chlorophyll content,than plants grown without shade.Plants grown in the low nutrient condition had shorter petiole length,thicker and smaller leaf area,lower chlorophyll content,but higher fruit number and root:shoot ratio than plants grown under the high nutrient condition.Selection gradient analyses revealed that plasticity of petiole length and old leaf chlorophyll content in response to light variation was adaptive,and plasticity of old and adult leaf chlorophyll content in response to nutrient variation was adaptive.Therefore,the adaptive value of plasticity in different traits depends on the specific ecological context.Our findings contribute to understanding the adaptive significance of phenotypic plasticity of clonal plants in response to environmental variation.