Effect Of Warming On Quantity And Composition Of Soil Dissolved Organic Matter In Subtropical Forest

Dissolved organic matter(DOM)is an important mobile carbon pool in forest soil,and its small changes will affect the carbon and nitrogen cycle of forest soil.The global temperature rise has become an indisputable fact,but the physical and chemical properties of the soil and soil microbes will change after the temperature changes,and the DOM cycle in the soil will also change,but this change is not yet clear.In order to explore the effect of warming on the quantity and composition of soil dissolved organic matter in subtropical evergreen broad-leaved forest,the research team set a 6 m x 6 m heating capacity in the Castanopsis kawakamii Hayata Nature Reserve of Sanming,Fujian Province in 2014.Samples,including control CT(no warming)and warming W(+4?)treatments,5 replicates per treatment,10 samples in total,10 cm,20 cm,and 30 cm in each sample A zero-strength penetrometer was installed on the 40 cm soil layer,soil solution was extracted,and the quantity and composition spectroscopic properties of the soil solution DOM were analyzed.Through a one-year dynamic study,it was found that the range of DOC concentration in the control soil solution was 3.88 mg·L-1-31.24 mg·L-1,and the DOC flux ranged from 0.08 kg · ha-1d-1to 2.44 kg · ha-1d-1.The DOC concentration in soil solution after warming ranged from 2.86 mg L-1to 33.12 mg·L-1.The DOC flux ranged from 0.04 kg · ha-1d-1to 2.11 kg · ha-1d-1.Compared with the control,the warming treatment significantly increased the DOC concentration of the soil solution in the 20 cm layer by 16.3%(P<0.05),but had no significant effect on other soil layers,but decreased the annual DOC flux of all soil layers and reduced the range.It was 26.9%to 47.7%(P<0.05).The warming treatment significantly reduced the DOC flux in soil solution from 10 to 20 cm soil layers from March to July,but the effect on the monthly DOC was not significant.For the 30 cm and 40 cm soil layers,the temperature increase treatment significantly decreased.The DOC monthly flux of soil solution in May had no significant effect on the pernod from June to February.Temperature increase decreased the annual fluxes of DON and NH4-N by 10 cm and 20 cm layer,and the decrease range was 63.5%?65.8%,46.1%51.2%(P<0.05)for TN and HO3-N,respectively.Annual flux had no significant effect(iP>0.05).Compared with the control,the aromatization coefficient of the soil solution in each layer of the temperature-increasing treatment decreases,the hydrophobic component decreases,and the molecular weight decreases.The control and warming soil solution DOM mainly has three strong absor:ption regions(1000-1260 cm"',1300-1550 cm'1,3200-3600 cm-1)and two weakly absorbing regions(460-680 cm-1,2850-3000 cm-1).However,after warming treatment,the 1000-1260 cm-1,1300-1550 cm-1,and 3200-3600 cm-1 bands of the soil solution were deepened and widened,indicating that small molecules of carbohydrates such as fats and carbohydrates were present in the soil solution.Increase in content.Three-dimensional fluorescence data showed that there were two fluorescence peaks in the DOM of the two soil treatments,namely,fulvic acid(Ex/Em 300-360/370-440 nm)and protein-like substances(250-300/300-350 nm).In the visible region,the content of fulvic acid first decreased and then increased with the increase of soil depth,and protein-like substances decreased with the increase of soil depth.After the temperature rise,the peaks of fulvic acid and protein-like substances in the visible region decreased,and the soil solution was obtained by EMMs-PARAFAC analysis.There is also a small amount of humic acid species C1(Ex/Em 250/520).The main conclusions are as follows:The increase of the temperature of the soil solution after the temperature treatment decreases,the hydrophobic substance decreases,and the aromatization index decreases.Both indicate that the DOM composition and structure of the soil solution after the temperature increase become simpler.The soil preferentially adsorbs hydrophobic components and macromolecules in the DOM.The increase in temperature increases the microbial activity,the turnover of organic matter is accelerated,the DOM small molecule material increases,and the ability of DOM to bind to soil minerals decreases.Over time,long-term warming may lead to soil organic matter.As the decomposition increases,the risk of nutrient loss from organic matter increases,and the amount of carbon in soil decreases.