| Wedelia trilobata(L.)Hitchc.is a stoloniferous herb native to South America,and its native congener Wedelia chinensis(Osb.)Merr.has the same family and genus.They share the same life history.W.trilobata has rapidly became a harmful weed in the field after introduced as the ground cover plant in 1970 s,which caused certain harm to the ecosystem of many areas in China.It is a “new weapon” for the successful invasion of W.trilobata to inhibit the growth and development of native plants by secreting allelochemicals,and the nutrient availabilities can affect the potential of allelopathy.In recent years,the spread of W.trilobata to farmland has become more and more common,which has had a negative impact on the yield and quality of crops.Therefore,this paper studies allelopathic effects of the invasive alien plant W.trilobata and its native congener W.chinensis on the physiological growth characteristics of common crop Lycopersicon esculentum Mill.under different nutrient availabilities,in order to provide a certain theoretical basis for regulating plant allelopathy potential and protecting crops in production practice.The main research contents and conclusions are as follows:(1)Allelopathic effects of W.trilobata and W.chinensis on morphological growth and root antioxidant enzyme activities of L.esculentum under different nutrient availabilities.Main root length and seedling height of L.esculentum planted with W.trilobata were remarkably lower than those of single L.esculentum and L.esculentum planted with W.chinensis under 15%,25% and 75% nutrient availabilities,the activities of superoxide dismutase,peroxidase,catalase and ascorbate peroxidase reached the highest level at 25% nutrient availability,indicating that allelopathic effects of W.trilobata significantly inhibited the growth of the roots and stems of neighboring L.esculentum.During the increase of nutrient availabilities,main root length and seedling height increased significantly,and the activity of antioxidant enzymes decreased significantly.The results showed that high nutrient availabilities could significantly alleviate this inhibition effect,and the root vitality and morphological growth of L.esculentum were restored.However,the allelopathic effects of W.chinensis on the main root length and seedling height of neighboring L.esculentum was not significant,indicating that the allelopathic effects of W.chinensis was lower than that of W.trilobata.The increase of nutrient availabilities weakens the resource competition between W.chinensis and L.esculentum,and ensures the growth of roots and stems of neighboring L.esculentum.(2)Allelopathic effects of W.trilobata and W.chinensis on photosynthetic physiological characteristics of L.esculentum leaf under different nutrient availabilities.The nitrogen content,chlorophyll content,net photosynthetic rate and chlorophyll fluorescence parameters of mixed L.esculentum leaves were significantly lower than those of single L.esculentum,indicating that both compositae plants had significant allelopathic effects on the photosynthetic physiological characteristics of neighboring L.esculentum leaves.The nitrogen uptake,chloroplast synthesis and Photosynthesis of leaves were inhibited.Among them,the parameters of L.esculentum planted with W.trilobata were significantly lower than those of L.esculentum planted with W.chinensis.It showed that the allelopathic effects of W.trilobata was stronger and the ability to secrete allelochemicals was more stable.With the increase of nutrient availabilities,the parameters of leaves increased significantly,indicating that allelopathy was negatively correlated with nutrient availabilities.(3)Allelopathic effects of W.trilobata and W.chinensis on biomass and biomass allocation of L.esculentum plant under different nutrient availabilities.Under 15% nutrient availability,there was no significant difference in biomass and biomass allocation among different cropping systems,indicating that the nutrient availability was near threshold,and the growth of plants was too poor to support the synthesis of allelochemicals in roots.At 25% nutrient availability,the total biomass of L.esculentum planted with W.trilobata was significantly lower than those of single L.esculentum and L.esculentum planted with W.chinensis,and the ratio of belowground biomass was significantly higher than those of single L.esculentum and L.esculentum planted with W.chinensis,while the total biomass and biomass allocation of L.esculentum planted with W.chinensis were not significantly different from those of single L.esculentum,indicating that W.trilobata has higher ecological tolerance and can regulate its own growth strategy according to the environment.It has been able to successfully release allelochemicals to inhibit the growth and development of neighboring L.esculentum under the condition of low nutrient availability.When the nutrient availability was up to 50% and 75%,the total biomass and the ratio of aboveground biomass of L.esculentum planted with W.trilobata increased significantly,indicating that the allelopathic effects of W.trilobata to neighboring L.esculentum was significantly reduced,and the ability to acquire resources in the environment was remarkable enhanced. |
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