| Human activities have greatly increased the input rate of atmospheric nitrogen to the global surface through agricultural fertilization and fossil fuel combustion.About 90%?95%of soil nitrogen exists in the form of organic nitrogen,of which soluble organic nitrogen(DON)refers to the part of organic nitrogen that can be extracted out by water or salt solution.DON is considered to be one of the important and very active chemical components in terrestrial ecosystems and aquatic ecosystems,as well as a carrier for the movement of nutrients and environmental pollutants.Because DON has strong fluidity,it is prone to leaching loss and runoff migration,resulting in the loss of soil nitrogen.It is of great significance to reveal the process and mechanism of soil DON on the loss of nitrogen,thus it has become a research hotspot in soil nitrogen cycling.In this paper,the typical forest soil of Dashanchong Forest Park was used as the research object,and the deionized water extract of litter was used to simulate DON to study the influence of different forest soil and temperature on the adsorption characteristics of DON.In-situ soil column experiment was carried out to study the addition of litter and ammonium sulfate on the soil DON.The main results were as follows:(1)The adsorption characteristics of DON on three typical forest soils(coniferous and broad-leaved mixed forest,evergreen broad-leaved forest and deciduous broad-leaved forest)in Dashanchong Forest Park were studied using DON extracted from litter The results showed that:According to the adsorption isotherm equation,there was a very significant linear relationship between the amount of soil adsorbed DON and the amount of DON added..Its adsorption capacity was as follows:deciduous broad-leaved forest>coniferous and broad-leaved mixed forest>evergreen broad-leaved forest.With the increase of the concentration of DON added,the adsorption rate tended to decrease.The adsorption capacity of the three forest soils to DON was low,and the average adsorption rate was less than 50%.The problem of leaching loss is worthy of attention.Comparison of the adsorption rate of soil to DON under different temperatures,35?>20?>5?,the increase of temperature increased the ability of soil to release DON.the UV254 absorption value and UV280 absorption value in the equilibrium solution both increased.The UV280 value at 35? was less than 20? and 5?,indicating that the soil had a small adsorption capacity for simple structure substances such as carbohydrates at 35?,and the soil had selective adsorption characteristics for different components of soluble organic matter.(2)A 90-day in-situ soil column experiment was conducted in Dashanchong Forest Park to study the effect of litter and ammonium sulfate addition on soil DON.The results showed that the DON content of the three soil layers(0?5 cm,5?10 cm,10?20 cm)under different N addition treatments basically changed in the same manner during the sampling time.The addition of litter did not increase the DON content in the soil within 30 days of the test.After 30 days,the DON concentration in the treatment of litter addition was higher than that the treatment of without litter the addition of,indicating that the decomposition of litter released soluble nitrogen and increased the content of soil DON.The concentration of DON in the 0-10 cm soil layer with ammonium sulfate addition treatment was lower than that in other treatments.In 90 days,the DON/TSN ratio in soil without litter and ammonium sulfate addition decreased rapidly(P<0.05),the nitrogen mineralization rate in the solution increased,thus DON was consumed.On the 15th to 60th day of the experiment,the DON/TSN ratio decreased rapidly(P<0.05).The ratio of DON/TSN showed a significant upward trend,while the mineralization rate continued to decline,and DON tended to accumulate.(3)In-situ soil column experiment showed that the soil moisture content of the three soil layers treated with addition of litter,ammonium sulfate and no litter addition showed a gradually decrease trend with the increase of sampling time.On the 15th and 60th day,compared with the treatment without litter addition,the addition of litter significantly increased the soil moisture content(P<0.05),indicating that the addition of litter could appropriately increase the soil moisture content.In 0-45 days,the addition of litter in the 0-5cm soil layer significantly increased the soil pH(P<0.05),and on the 15th and 30th day,the 45th day was significantly higher than that without litter addition and ammonium sulfate treatment(P<0.05).Compared with no addition of litter,the addition of litter could appropriately increase the soil moisture content and pH.There was no significant difference between different treatments on soil organic carbon and total phosphorus.In summary,soil DON had strong mobility.The adsorption capacity of the three forest soils to DON was low,and the adsorption rate was less than 50%.Some substances with simple structure were preferentially adsorbed by the soil;the adsorption capacity of DON in deciduous broad-leaved forest soil was stronger than that of coniferous forest and evergreen broad-leaved forest.The adsorption capacity of soil to DON is low,and its leaching loss is worthy of attention.Discussing the changes in soil soluble organic nitrogen in different forest types and the changes in the adsorption capacity of soil DON during the process of vegetation restoration will help to understand the role of soil DON in forest ecosystems. |
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