模拟氮沉降对云杉人工林土壤有机碳组分及理化性质的影响

Effects of Simulated Nitrogen Deposition on Soil Organic Carbon Fractions and Soil Physico-chemical Properties in Picea asperata Plantation in Sichuan

大气氮沉降已成为目前全球性的环境问题之一。氮沉降可能影响森林生态系统碳循环的过程,研究氮沉降对森林土壤有机碳库的影响,有利于正确评估森林生态系统碳循环过程及其对全球气候变化的响应。为探究氮沉降对森林生态系统碳循环的影响,以四川云杉Picea asperata人工林为研究对象,研究了氮沉降(N0,N 0 kg·hm^(-2)·a^(-1);N1,N 60 kg·hm^(-2)·a^(-1);N2,N 120 kg·hm^(-2)·a^(-1);N3,N 240 kg·hm^(-2)·a^(-1))对云杉人工林土壤有机碳组分的影响。结果表明,模拟氮沉降处理下,土壤总孔隙度(TPO)与土壤容重(BD)变化趋势相反;土壤pH值变化范围在6.58~7.02之间,随N浓度的增加而降低。土壤养分(有机碳SOC、全氮TN、全钾TK、有效磷AP和有效钾AK)和有效养分均呈现出一致性规律,随着N浓度的增加而增加,模拟氮沉降处理下土壤全磷含量差异均不显著(P>0.05)。与对照相比(N0),土壤易氧化有机碳(EOC)、颗粒有机碳(POC)、轻组有机碳(LFOC)、水溶性有机碳(WSOC)和微生物量碳(SMBC)明显受氮沉降的影响。EOC、POC、轻组有机碳(LFOC)和WSOC均呈现出一致性规律,随N处理水平的增加而增加。EOC/SOC比例和微生物熵(MBC/SOC)均随N浓度的增加而增加。通径分析结果表明:1~0.05 mm粒径和TPO对土壤有机碳组分产生直接效应;<0.002 mm和pH对土壤有机碳组分产生间接效应;土壤理化性质对土壤有机碳组分产生的总效应值具体表现为1~0.05 mm>pH>TPO=(<0.002)mm>BD>0.05~0.002 mm;土壤养分对土壤有机碳组分产生直接和间接负作用,其中SOC、TN和AK对土壤有机碳组分产生直接效应;TK和AP对土壤有机碳组分产生间接效应;总效应值大小依次为SOC>TN>AK>TK>TP>AP。综合分析表明,氮沉降有利于云杉人工林土壤有机碳组分稳定性的提高,利于土壤有机碳的累积。

The impacts of nitrogen deposition on soil labile carbon at different age poplar plantations were examined in this study. As an essential indicator of soil quality, soil organic carbon（SOC） and its fractions play an important role in many soil chemical, physical and biological properties. We conducted a field experiment to simulate nitrogen deposition（N0, N 0 kg·hm-2·a-1; N1, N 60 kg·hm-2·a-1; N2, N 120 kg·hm-2·a-1; N3, N 240 kg·hm-2·a-1） with Picea asperata plantation in Sichuan Province. The results as follows： soil total porosity（TPO） had the opposite trend with bulk density（BD） in order of N3〉N2〉N1〉N0. Soil p H decreased with the increasing of nitrogen concentration. Soil nutrients（soil organic carbon and total nitrogen） had the same variation trend which showed N3〉N2〉N1〉N0, while there was no significantly difference in soil total phosphorus（P〉0.05）, and there was a spatial variability with the higher variable coefficient. Compared with N0, the easy oxidation of soil organic carbon（EOC）, particulate organic carbon（POC）, light group of organic carbon（LFOC）, water soluble organic carbon（WSOC）, soil microbial biomass carbon（MBC） had the same change trends, which showed N3〉N2〉N1〉N0. Further, the ratio of EOC/SOC increased with the increasing of nitrogen concentration. Path analysis showed that TPO and 1～0.05 mm particle size had the direct effect to soil organic carbon fractions, and 〈0.002 mm particle size and p H had the indirect effect to soil organic carbon fractions. Also, SOC, TN and AK had the direct effect to soil organic carbon fractions, and TK and AP had the indirect effect to soil organic carbon fractions. Overall, nitrogen deposition is beneficial to the stability of the soil organic carbon in spruce plantation soil, which is beneficial to the accumulation of soil organic carbon.