| Alternanthera philoxeroides is a perennial root herb of the genus Alternanthera?Amaranthaceae?,native to Brazil.It is a global malignant weed and widely distributed in China.The growth and spread of A.philoxeroides were rapid and the biological invasion was serious.In order to inhibit the invasion of A.philoxeroides according to the principle of substitution between plants,this study chooses grows fast and has high economic value of crops sweet potato?Ipomoea batatas?l.?Lam.?to curb the spread of the farmland A.philoxeroides,and the order of replacement control for sweet potato of A.philoxeroides resources competition and allelopathy research,for the use of sweet potato inhibit invasion of A.philoxeroides which provide a scientific basis for ecological management.The main results are as follows:From the perspective of allelopathy,it is an effective approach to control invasive plants based on the allelopathic effect of native plants with higher economic values.The aim of the present study was to test the allelopathic effect of local crop sweet potato?Ipomoea batatas?on the invasive plant A.philoxeroides.Water extracts from different sweet potato organs?roots,stems,leaves?and three concentrations(0.025,0.05,0.1 g·m L-1)of each were used in the study.To test the effect of sweet potato on growth of A.philoxeroides,the morphological index?ramets number,node number,leaf number,leaf area,plant height,total dry weight and root number of new ramets?,allelopathic response index,trait values?succulent degree,root-shoot ratio,specific leaf area,leaf mass ratio,stem mass ratio,root mass ratio?,CAT,POD,MDA and SOD of young leaves were measured.The results showed that?1?Water extracts from different parts of sweet potato with different concentrations had various effects on the growth of A.philoxeroides.The root water extract with 0.1 g·m L-1significantly inhibited all morphological indexes.Except total dry weight and root number,other morphological indexes decreased significantly with the increasing concentration of water extract from all parts.?2?The synthetic allelopathic response index?RI?was negative under all treatments,indicating that the water extract of sweet potato had negative effects on all indexes of A.philoxeroides and thus inhibited their regular growth.Among the all treatments,the root water extract with 0.1 g·m L-1had the strongest allelopathic inhibition?RI=-0.73?,followed by the stem water extract with 0.1 g·m L-1?RI=-0.44?and root water extract with 0.05 g·m L-1?RI=-0.44?.?3?The water extract of sweet potato had significant inhibitory effects on the degree of succulence,root-shoot ratio,specific leaf area and leaf mass ratio,whereas it had no significant effects on the stem mass ratio and root mass ratio.?4?The water extract of sweet potato significantly increased the contents of MDA and SOD in the fresh leaves of A.philoxeroides,while had no significant effect on the contents of CAT and POD.All these results indicates that the water extract of sweet potato significantly suppress the ramets growth of A.philoxeroides.Under the condition of field experiment,the competition effect of sweet potato on A.philoxeroides was studied by De Wit substitution method.The results showed that:?1?The fresh weight,branching number,net photosynthetic rate?Pn?,water use efficiency?WUE?,chlorophyll a?Ca?and Ca/Cb in the mono-plant were all significantly higher than that in the mixed condition,while the underground fresh weight,intercellular carbon dioxide concentration?Ci?and chlorophyll b?Cb?were significantly lower than that in the mixed condition.The aboveground fresh weight,underground fresh weight and net photosynthetic rate of sweet potato were significantly lower under mono-plant than under mixed-plant.?2?Under the mixed-plant condition,photosynthesis and growth of A.philoxeroides were significantly inhibited.?3?relative yield of sweet potato?RYa?was significantly greater than 1.0,and relative yield of A.philoxeroides?RYb?was significantly less than 1.0,indicating that intra species competition was greater than inter-species competition,while that of A.philoxeroides was opposite.?4?when the planting ratio of two species was greater than 1?the planting ratio of sweet potato to A.philoxeroides was 8:4 and 9:3?,the relative total yield?RYT?was significantly less than 1.0,indicating that the two species had a strong competitive effect.When the mixture ratio was less than 1?the ratio of sweet potato to A.philoxeroides was 3:9 and 4:8?,RYT was greater than 1,indicating that there was no competitive effect between the two species.Under mixed planting conditions,the competitive equilibrium index?CBb?was less than 0,indicating that the competitive power of A.philoxeroides was less than that of sweet potato.In order to explore the influence of sweet potato on the soil physical and chemical properties and the microorganisms in the soil under different substitution degrees of A.philoxeroides,this paper carried out field experiments based on Illumina high-throughput sequencing technology to compare the structure and diversity of soil microbial community under the conditions of the same planting density and different planting ratios of sweet potato and A.philoxeroides.The results showed that:?1?From the perspective of soil physical and chemical properties,AP content significantly decreased with the decrease of planting proportion of sweet potato and the increase of planting proportion of A.philoxeroides?P<0.05?,and the content of AK and AN increased significantly.?2?the main phyla in the soil bacterial community were Acidobacteria,Proteobacteria,Bacteroidetes,Chloroflexi,and Verrucobacteria.The main fungi in the fungal community are Ascomycota,Basidiomycetes,Chytridiomycota and zygomycetes.?3?With the increase of the planting proportion of invasive species,the alpha diversity of soil bacteria decreased,but there was no significant difference in the alpha diversity of fungi.?4?The structure of soil bacteria was most affected by TP,TK,AK and AN,and least affected by organic matter.The fungal community structure was most affected by TK,AK,AN,organic matter,AP and TN,and least affected by TP and p H.The effects of nutrient levels on the growth of sweet potato and A.philoxeroides were studied in pot experiment.The results showed that?1?under the condition of the same nutrient level and mixed planting ratio,the plant height of sweet potato was significantly lower than that of A.philoxeroides,but the biomass was significantly higher than that of A.philoxeroides.There was no significant change in root-shoot ratio of sweet potato under different nutrient levels and planting ratio.When the two species were mixed according to the ratio of 1:1,the root-shoot ratio was significantly higher than other treatments,and the root-shoot ratio was significantly lower than other treatments when planted according to the ratio of 3:1.?2?nutrient level and planting ratio can affect the competitiveness level of the two species,but in general,the competitiveness of A.philoxeroides is weaker than that of sweet potato.?3?with the change of nutrient level,the contents of P and K in different parts of the two species did not change significantly under the same planting ratio,but the contents of nitrogen changed significantly with the increase of nutrient level,and the contents of nitrogen in the two species significantly increased. |
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