基于组分区分的亚热带湿地松人工林土壤呼吸对氮添加的响应

Responses of Soil Respiration and Its Main Components to Nitrogen Addition in a Subtropical Pinus elliottii Plantation

氮沉降在很大程度上会对土壤呼吸产生扰动,进而影响到生态系统碳收支.以我国亚热带湿地松人工林为研究对象,通过定位模拟氮沉降控制试验,定量研究根系呼吸和微生物呼吸对氮添加的响应差异,并通过土壤环境的同步监测,初步探讨影响上述过程的生物地球化学与微生物学机理.结果表明:不同氮素添加水平下土壤呼吸速率及其组分总体上都呈现出单峰曲线特征,峰值出现在7月或8月,氮添加对土壤呼吸的季节模式没有明显影响.CK(0,对照)、LN[60 kg/(hm^2·a),低氮]和HN[120kg/(hm^2·a),高氮]处理下土壤总呼吸速率的年均值分别为3.91、2.30和1.73μmol/(m^2·s),各组根系呼吸速率年均值分别为1.41、0.87和0.66μmol/(m^2·s),各组微生物呼吸速率年均值分别为2.50、1.44和1.07μmol/(m^2·s).施氮后土壤总呼吸及其组分都受到明显抑制,并且随着施氮水平的提高,土壤总呼吸及其组分明显减小.与对照样地微生物呼吸占比65.2%相比,低氮和高氮处理下微生物呼吸占比显著降低,降幅分别为62.6%和62.1%,说明氮素添加对微生物呼吸的抑制作用大于根系呼吸.施氮后一年,氮素输入对土壤呼吸的抑制在消退.施氮对表层土壤w(TOC)(TOC为总有机碳)、w(NH_4^+)、w(NO_3^-)、w(DOC)(DOC为可溶性有机碳)、w(DON)(DON为可溶性有机氮)、w(MBC)(MBC为微生物生物量碳)和w(MBN)(MBN为微生物生物量氮)都没有显著影响.氮素添加主要是通过降低土壤pH、加速湿地松人工林土壤酸化,对影响土壤有机质转化的土壤脲酶和蔗糖酶活性产生显著抑制,从而影响到土壤微生物活性,导致土壤微生物呼吸降低,这可能是土壤呼吸对氮添加响应的关键机制.

The increase of nitrogen（N） deposition would obviously disturb the soil respiration,further make important influences on the carbon（C） budget and C sequestration in the terrestrial ecosystem. Taking a subtropical Pinus elliottii Plantation in China as the research object,a quantitative study about the responses of the root autotrophic respiration,microbial heterotrophic respiration to the varying N availability was conducted by field simulation control experiment based on the distinction of different components of soil respiration,and a preliminary discussion on the biogeochemistry and microbiological mechanism of the response were also made. Results showed that：（1） The dynamic characteristics of the total soil respiration,root respiration and microbial respiration displayed obvious single peak curve in both 2015 and 2016,with the maximum respiration rates observed in July or August. Simulated N deposition had no significant influence on the seasonal pattern of soil respiration rates.（2） The annual average rates of the total soil respiration,root respiration and microbial respiration were 3. 91,2. 30 and 1. 73 μmol/（m2·s）,respectively under CK（0）,LN treatment（60 kg/（hm2·a）） and HN treatment（120 kg/（hm2·a））; The annual average root respiration and microbial respiration of CK,LN,HN were 1. 41,0. 87,0. 66 μmol/（m2·s） and 2. 50,1. 44,1. 07 μmol/（m2·s）,respectively. The total soil respiration and its two components were inhibited obviously under simulated N deposition,and the total soil respiration,root respiration and microbial respiration all decreased obviously along with the increase of N input levels.（3） Under CK treatment,the proportion of microbial respiration to total soil respiration（Pm） was 65. 2%,but under LN and HN treatments,the Pmvalues were decreased significantly with 62. 6% and 62. 1%. The N input showed a greater inhibitory effect on microbial respiration than on root respiration. A year after N application,the inhibitory effect of N input on soil respiration was declining.（4） N application had no significant effect on the contents of total organic carbon（TOC）,NH4~＋,NO3^-,dissolved organic carbon（DOC）,dissolved organic nitrogen（DON）,microbial biomass carbon（MBC） and microbial biomass nitrogen（MBN） in surface soil at the depth of 0-10 cm. Simulated N deposition reduced soil p H value,acidized surface soil of P. elliottii Plantation,inhibited the activities of soil urease and soil invertase significantly,and futher affected soil microbial activity,which resulted in the reduction of soil microbial respiration. This may be the key mechanism for the response of soil respiration to N addition in this study.