| The decomposition of the ecosystem is the process of the gradual degradation of organic matter into small molecules.Decomposition,the organic matter releases inorganic nutrients,which affect the material circulation of the ecosystem,causing changes in the structure and function of the ecosystem.Green plants,as primary producers of nature,are able to produce primary production volumes,so it occupies an important position in the ecosystem,and the organic synthesis-decomposition processes and dynamics directly affect the elemental cycle of ecosystems.The decomposition of plants is controlled by biological factors and non-biological factors.The process characteristics and rate are determined by the quality characteristics of decomposition materials,the biological species of decomposers,and the physical and chemical environment when decomposed.In the ecosystem,predation is a common food chain interaction,herbivorous animal husbandry can change the chemical quality characteristics of plant leaves,causing secondary plant compounds increased,is an important factor affecting the decomposition of biological factors one.Previous studies on the effects of herbivorous stress on plant decomposition mainly related to terrestrial ecosystems.In the aquatic ecosystem,the herbivorous behavior of herbivores will also change the chemical quality characteristics of aquatic plants,which in turn affect the decomposition process is not clear.In addition,it has been found that the presence of living plants in terrestrial ecosystems can stimulate the activity of microorganisms,thus accelerating the rate of plant decomposition.In aquatic ecosystems,whether the living plants can affect the decomposition rate and its mechanism of decomposition unclear.In order to explore whether the effects of grazing pressure on the decomposition of aquatic plants,we studied the decomposition rate and nutrient dynamics of Trapa natans with or without grazing pressure,and by comparing the changes in microbial and invertebrates during the decomposition process,try to explain the mechanism of the impact of the grazing pressure on the decomposition in the aquatic ecosystems.In order to explore whether the living plants will affect the decomposition of aquatic plant with different grazing pressure.We studied the decomposition rate and nutrient dynamics of the Trapa natans with different grazing pressure under the condition of the presence or absence of the live plant Nymphoides,and by comparing the changes in microbial and invertebrates during the decomposition process,try to explain the mechanism of the impact of the living plant on the decomposition of different material in the aquatic ecosystems.The main results are as follows:1.In order to discuss whether the stress of the grazing can affect the decomposition of aquatic plants,this paper studied the decomposition rate and nutrient dynamics of two difference Trapa natans,also studied the change of microbes and invertebrates in the process of decomposition,Try to explain the impact of grazing pressure on the mechanism of decomposition,the experimental period is 50d.The results show:(1)There was no significant difference in the rate of decomposition between the two materials(P>0.05).(2)Under 0.5mm mesh treatment,the Trapa natans with grazing pressure inhibited the release of N.Under 5mm mesh treatment,the two kinds of Trapa natans N,P in the decomposition process continued to release.(3)Under the 0.5 mm mesh treament,there was no significant difference in respiration rate between the two materials(P>0.05),under the 5 mm mesh treament,the microbial respiration rate was the lowest at 30 days after decomposition and there was significant difference in this time(P<0.05),there was no significant difference in the rest of time(P>0.05);Under the 0.5mm mesh treament,during the whole process of decomposition,the number of bacterial CFU decreased of grazing pressure material and the number of bacterial CFU without grazing pressure was fluctuated,but the overall trend was decreased.The number of bacterial CFU without grazing pressure was more,two kinds of materials bacterial colonies only at the later stage of decomposition have significant difference(P<0.05).Under the 0.5 mm mesh treament,the number of fungus CFU of the two materials showed a decreasing trend at the early stage of decomposition,and then rise in the two kinds of materials,at the later stage of decomposition,the fungus CFU zooming,there was a significant difference in the number of fungal CFU of two kinds of Trapa natans materials at the time of 30 days(P<0.05).Under the 5mm mesh treament,the number of fungus CFU of the two materials showed a decreasing trend at the early stage of decomposition,and then rise,the last time continue decreasing in the two kinds of material,only at the late stage of decomposition,there were have significant difference(P<0.05).Decomposition rate and Pearson correlation analysis of microbes showed that there was no correlation between the rate of decomposition and microbial respiration,bacterial diversity and fungal diversity(P>0.05).(4)Under 0.5mm mesh treatment,the density of invertebrates of two kinds materials first rise and the decline during the decomposition.There was no significant difference in the density of invertebrates in the whole decomposition process(P>0.05).Under 5mm mesh treatment,there was no significant difference in the density of invertebrates in the whole decomposition process(P>0.05);In the whole process of decomposition,there is no difference between the invertebrate abundance of the two materials.Pearson correlation analysis of decomposition rate and invertebrate density and abundance showed that there was a significant correlation between the rate of decomposition and invertebrate density(P<0.05),and the decomposition rate was also significantly correlated with the abundance of invertebrates(P<0.05).The results showed that in the aquatic ecosystem,the herbivore pressure of herbivores could cause the change of chemical quality of plant leaves,which had some influence on the decomposition of aquatic plant residues,but the effect was not significant.The results of the study can provide information for the mechanism of the effects of feed pressure on the decomposition of aquatic plant residues and provide a reference for understanding the effect of aquatic plant debris decomposition on nutrient dynamics in aquatic ecosystems.2.In order to investigate whether the living plants in aquatic ecosystems will affect the decomposition of aquatic plant material in different grazing pressures.In this paper,two kinds of Trapa natans leaves(with and without herbivore grazing)were used as experimental materials to study the decomposition rate and nutrient dynamics of Trapa natans materials with different grazing stress.also studied the change of microbes and invertebrates in the process of decomposition,try to explain the impact of living plants on the mechanism of decomposition,the experimental period is 50d.The results show:(1)In the 0.5mm and 5mm two kinds of mesh processing under the two kinds of Trapa natans materials are in Nymphoides habitat decomposition faster,in the absence of Nymphoides habitat decomposition slower.(2)The material,mesh and decomposition time had a significant effect on the release of N,and the habitat,material,mesh and time had a significant effect on P release,And there was no significant difference(P>0.05)in the whole decomposition process.The results showed that there was no significant difference between the two treatments(P>0.05),Under 5mm mesh treatment,under the two habitat conditions,the N remaining was only significant during the first 10 days decomposition,.Under 0.5mm mesh treatment,under the two habitat conditions,the N remaining was only significant during the decomposition of 40 days.The P remaining was decreased in the whole process of decomposition and the P element was released under the condition of 5mm mesh treatment,under the two habitat conditions.During the whole decomposition,there were no significant difference of the two habitat conditions(P>0.05).Under the condition of 0.5mm mesh treatment,the P remaining under the two habitat conditions have significant difference on the 10th days and 20th days of the decomposition(P<0.05);Under the condition of 5mm mesh treatment and two habitat conditions,the P remaining of leaf without herbivore have no significant difference during the whole decomposition(P>0.05);Under the 0.5mm mesh treatment,the P remaining in the two habitats have no significant difference(P>0.05).(3)Under the 5mm mesh treatment,the microbial respiration rate of the two materials under the habitat of Nymphoides,was much higher than absence of the Nymphoides habitat;Under the 0.5mm mesh treatment,the microbial respiration rate of leaf with herbivore under two habitats have significant difference only 50th day decomposition.Leaf without herbivore during the decomposition the microbial respiration rate under the habitat of Nymphoides,was much higher than absence of the Nymphoides habitat,,and during the whole decomposition there was no significant difference of the microbial respiration rate(P>0.05).Under the condition of 5mm large mesh,leaf with herbivore under two habitats the fungal CFU have no significant difference during the whole decomposition(P>0.05),for leaf without herbivore,there were significant differences in the fungal CFU at the 20th day,40th day and 50th day under the two habitats(P<0.05);under the condition of 0.5mm large mesh,leaf with herbivore under two habitats the fungal CFU have significant difference at the 40th day and 50th day(P<0.05).Under the condition of 5mm large mesh,leaf with herbivore under two habitats the bacteria CFU have significant difference at the 50th day of decomposition(P<0.05),leaf without herbivore under two habitats the bacteria CFU have significant difference at the 40th day of decomposition(P<0.05),under the condition of 0.5mm small mesh,for leaf with herbivore,there were significant differences in the bacteria CFU at the 40th day,50th day under the two habitats(P<0.05);leaf without herbivore under two habitats the bacteria CFU have significant difference at the 30th day of decomposition(P<0.05).Decomposition rate and Pearson correlation analysis of microbes showed that there was no correlation between the rate of decomposition and microbial respiration,bacterial diversity and fungal diversity(P>0.05).(4)The density of invertebrates under the condition of Nymphoides habitat was higher than that of non-Nymphoides habitat under the condition of 5mm mesh treatment,the density of invertebrates under the two habitat conditions showed that the invertebrate density changed irregularly.Under the 0.5mm mesh treatment,the invertebrate density of the leaf with herbivore have no significantly different during the whole decomposition process(P>0.05).The density of invertebrates of leaf without herbivore under the habitat of Nymphoides was higher than that of non-Nymphoides habitat in the whole decomposition process.During the whole decomposition process,the abundance of invertebrates under the two habitats of the leaf with herbivore was not much different,and the abundance of invertebrates of leaf without herbivore under the habitat of Nymphoides was better than that of non-Nymphoides.Pearson correlation analysis of decomposition rate and invertebrate density and abundance showed that there was a significant correlation between the rate of decomposition and invertebrate density(P<0.05),and the decomposition rate was also significantly correlated with the abundance of invertebrates(P<0.05).The results showed that the presence of living plants promoted the decomposition of two Trapa natans materials in aquatic ecosystems.In the presence of living plants,the rate of decomposition of under grazing Trapa natans was greater than that of non-grazing pressure.The effect of large invertebrates on the decomposition of aquatic plant was greater than microorganisms.The results can provide information for the mechanism of the decomposition of aquatic plant in living plants habitat and provide a reference for understanding the nutrient dynamics of aquatic ecosystems in the presence of living plants. |
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