| In this experiment,the effects of acid rain on the physicochemical properties of litter,C-,N-and P-decomposition related enzyme activities and microbial community structure were studied by spraying simulated acid rain on three types of crop(corn,rice,soybean)straw that have been widely planted in southern China.Three treatments were set up in the experiment: severe acid rain with pH 3.0(pH3),mild acid rain with pH 5.0(pH5),and a control(CK)with pH=7.80,and 4 replicates per treatment.The experiment was conducted for six months in which the straw samples were collected at 1,2,4,and 6 months after treatment.Each bag of the sample was baked in an oven to constant weight and the dry weight residual ratio and C,N,and P contents were calculated.The other samples were cut into 1 mm sieves,some were placed in a refrigerator at 4℃ for enzyme activity determination of carbon,nitrogen and phosphorus decomposition,and the other was stored in a refrigerator at-40℃ for storage of phospholipid fatty acids(PLFA).The main results are as follows:Compared with CK,mild acid pH5 treatment increased the total PLFA content and bacterial PLFA content of three crop straws,and had no obvious effect on fungal PLFA content and actinomycete PLFA content;strong acid pH3 treatment increased compared with CK.The G+/G-ratio of soybean straw is not significant for the structure of bacteria and other microbial communities.Acid treatment reduced the activity of BG and CB enzymes in soybean straw,but had no obvious effect on the activities of BG and CB enzymes in corn and rice straw.The acid treatment inhibited the activity of NAG enzyme in corn straw,but the effect was not obvious with the increase of time.The effect of NAG enzyme activity on rice and soybean straw was not obvious;acid treatment inhibited AP enzyme activity in corn stover,and the effect of acid treatment on soybean was reflected in the early stage of acid treatment,and the effect was not obvious in the later stage of treatment.With the increase of treatment time,the residual weight ratio of corn,rice and soybean straw decreased gradually,and it became gentle after the rapid decomposition in the first month.However,the decomposition rate of soybean straw was significantly higher than that of corn and rice during the whole observation period.Corn stalks first responded to acid rain,followed by rice straw,and soybean stalks did not respond significantly to acid rain.The residual amount of corn and rice straw C is increased in the early stage of decomposition,and the acid treatment increases the residual amount of C compared with CK.However,the acid treatment reduces the residual amount of corn C compared with CK in the late stage of decomposition,which may be difficult for acid to dissolve corn stover.The decomposed substances lead to a decrease in the organic carbon content;the effect of acid treatment on the residual amount of soybean straw C is not significant compared with CK.The change trend of carbon decomposition-related enzyme activities(BG,CB)of corn stover is basically consistent with the change of C residue.The change of carbon can be verified from the enzyme activity;the decomposition of soybean straw is related to carbon decomposition after CK treatment.The activities of enzymes BG and CB decrease,which leads to the decrease of the utilization rate of carbon sources by microorganisms,thereby promoting the preservation of soil organic carbon.The effect of acid treatment on the residual N of crop straw was not obvious,but the effect on C/N ratio was obvious.The C/N ratio of soybean straw was less obvious than that of CK in the early stage of treatment.In the later stage of treatment,acid treatment significantly increased the C/N ratio of soybean straw compared with CK.The C/N ratio of corn stalks was significantly negatively correlated with G-content.The C/N ratio of rice straw was significantly positively correlated with the PLFA content of actinomycetes.The C/N ratio of soybean straw was significantly correlated with the content of fungal PLFA.Acid treatment compared with CK had no significant effect on the P residue of corn and rice straw,but significantly increased the P residue of soybean.The reason for the difference between species may also be because soybean is weaker than corn and rice straw.In summary,this study found that heavy acid pH3 treatment promoted the decomposition of corn and rice crop straw,and the effect on soybean straw was not significant,which may be related to the difference between species.From the microbial community structure of three crop straws,the mild acid pH5 treatment increased the microbial biomass of three crops,but the correlation with the nutrient release of crop straw was not obvious.Comprehensive comparative analysis,proper acid treatment is conducive to the storage of nutrients,and excessive acid treatment will be detrimental to nutrient storage,thus increasing the nutrient scarcity of farmland ecosystems.The response of crop straw decomposition to acid deposition is a complex process.To reveal its specific response mechanism,long-term positioning research is still needed to provide a scientific basis for the trend of straw decomposition. |
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