| Litter is fundamental to the productivity components of terrestrial ecosystem,it decomposition has a pivotal role in the chemical and nutritional cycle of terrestrial ecosystem.At the same time,litter contains a large number of allelochemicals,which decompose and release allelochemicals in soil has considerable impact on plant allelopathy.Invasive plant Solidago canadensis is a typical malignant weed,but previous studies of litter decomposition in the in situ ecological environment have not dealt with its dynamic effects on soil nutrient cycle and allelopathy.Therefore,both field in-situ and indoor supplementary experiments were performed in this paper to study the litter dynamics of Solidago canadensis and native plant Phragmites communis.An objective of this study was to investigate the decomposition dynamics of litter of Solidago canadensis and its effect on soil feedback under different invasion degrees.The purpose of this paper is tantamount to explore the dynamics of litter decomposition and its impact on its invasion,and to provide some theoretical reference for the study of the invasion mechanism and ecological control of Solidago canadensis.The main results of this study are as follows:1.A field in-situ degradation experiment was conducted to study the chemical properties of litter and the effects of invasive plots on litter decomposition rate and the effect of litter decomposition dynamics on soil carbon and nitrogen cycle.The results showed that:(1)The C/N ratio and the relative content of cellulose in litter of Solidago canadensis were significantly lower than those of Phragmites communis.The decomposition rate of litter in individual plots was as follows: Solidago canadensis >Phragmites communis.Results of RDA analysis showed that the C/N ratio of litter and the relative content of cellulose were negatively correlated with the decomposition rate of litter.Compared with the single plots,the mixed plots significantly promoted the litter decomposition of Solidago canadensis and inhibited the litter decomposition ofPhragmites communis.(2)The contents of soil total C and total N increased significantly in the four stages of litter decomposition,and there was no significant difference between the two species,but the increase of total N in mixed plots was significantly higher than that in single plots.At the same time,litter decomposition increased the content of nitrate nitrogen and inorganic nitrogen in soil.The results of this study indicate that the C/N ratio of litter and the invasion sample land affected the litter decomposition rate of Solidago canadensis,and it showed that long-term effects of litter of Solidago canadensis continued to the content of soil total C and total N in the decomposition stage.2.The release rate and change law of allelochemicals during litter decomposition of Solidago canadensis were studied,and the dynamic effects of allelochemicals released into soil were studied by a pot experiment.The results showed that:(1)Solidago canadensis contained a lot of allelochemicals,and the contents of two main allelochemicals(total phenols and total flavonoids)were significantly higher than those of Phragmites communis litter.From the perspective of allelopathic effect,the two litter extracts significantly inhibited the germination and growth of lettuce seed,and the allelopathic inhibitory effect decreased markedly with the release of allelopathic substances.The time of litter decomposition and soil sample land significantly affected the content of allelochemicals in litter leaves: allelochemicals decomposed rapidly to the lowest level at the initial stage(60 days for litter of Solidago canadensis and 30 days for litter of Phragmites communis).The mixed plot promoted the release of allelochemicals from Solidago canadensis,and the time for reducing the lowest level of allelochemicals in litter was shortened to 30 days.(2)Soil allelopathic experiments showed that allelochemicals would not be decomposed immediately when they entered the soil,but some of them would accumulate in the soil,and continued to inhibit the germination and growth of nativeplants from 60 to 120 days.The results of this study indicate that Solidago canadensis has a strong allelopathic effect,which may inhibit plant growth at the initial stage of litter decomposition,and also shows that the decomposition rate of allelochemicals is also affected by the invasion of the sample plots;and it also shows that the timeliness of allelochemicals may depend to a large extent on the decomposition rate of litter and the residence time in the soil.3.The effect of litter decomposition of Solidago canadensis on the structure of soil microbial community was studied.The results showed that the litter decomposition of Solidago canadensis and Phragmites communis significantly affected the richness and diversity of fungi in soil,and the litter decomposition of Solidago canadensis significantly increased the number of Mortierella and Rumex fungi,while significantly decreased Fusarium,Brassica and Coreopsis fungi.Litter of Solidago canadensis and Phragmites communis in mixed plots significantly increased Brassica,Rumex and Amaranthus fungal genera and Brassica,Amaranthus and Geranium fungal genera,respectively,while significantly decreased Mortierella and Salix fungal genera.CCA results showed that there was a significant correlation between soil physical and chemical properties and fungal community structure.The results of this study indicate that litter significantly increased the diversity and richness of fungal community and changed the soil ecosystem,which may be beneficial to the growth of Solidago canadensis.4.A pot experiment was conducted to study the soil feedback effect of litter decomposition of Solidago canadensis.The results showed that:(1)The plant height and total biomass of Solidago decurrens were significantly increased by litter decomposition(Sc)and Phragmites communis litter decomposition(Pa)treatment;compared with Pa treatment,the plant height of Phragmites communis was inhibited by Sc treatment,while Sc and Pa treatment had no significant effect on the plant height of Pterocypsela laciniata and Solidago canadensis.The soil treated with Sc and Pahad no effect on the biomass of Phragmites communis and Pterocypsela laciniata,but the soil treated with Sc inhibited the biomass of Solidago decurrens.(2)Soil feedback index showed that Sc treatment inhibited the growth of Phragmites communis,Solidago decurrens and Pterocypsela laciniata,and had the most significant effect on the growth of native plant Solidago decurrens,but significantly promoted the growth of invasive plant Solidago canadensis,while soil treatment with Pa significantly promoted the growth of Solidago canadensis,and inhibited the growth of Pterocypsela laciniata,but had no significant effect on the growth of Phragmites communis.The results of this study indicate that the soil had a feedback effect after litter decomposition,which significantly promoted its own growth. |
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