土壤呼吸不仅是反映土壤生物活性的重要指标，也是全球碳循环研究中备受关注的热点问题。在地处典型干旱区的石羊河下游，以流动沙丘和去除土壤结皮人工梭梭林为对照，采用LI-8100土壤碳通量监测系统研究了栽植约40 a、30 a、10 a和5 a的人工梭梭林生长季和非生长季的土壤呼吸日变化，并分析了土壤水分和温度对土壤呼吸的影响。结果表明：（1）不同林龄梭梭林生长季和非生长季土壤呼吸速率的日变化均为明显的单峰曲线，且呈现出一定的波动性，日最大排放速率出现在12:00～14:00时，最小值出现在8:00时左右。（2）梭梭林营造和去结皮处理显著提高了沙漠土壤呼吸速率，而且不同林龄土壤呼吸速率大体上随着种植年限的增加而递增，表现为MC >40 a>30 a>10 a>MS >5 a，非生长季表现为MC >40 a>10 a>5 a>30 a>MS。（3）不同林龄梭梭林土壤呼吸速率均具有明显的季节变化特征，生长季（8 月）的土壤呼吸作用明显强于非生长季（1月）。（4）相关性分析表明，生长季和非生长季土壤呼吸均与0～5 cm土壤水分显著相关，且均呈二次曲线关系，分别为Y =-0.205 8X 2+0.946 5X-0.316 6（R 2 =0.506 2，P= 0.041 7）和Y= 0.118 7 X 2+0.156 3X+0.118 8（R 2=0.675 7，P =0.001 1）；但与10 cm土壤温度的相关性不显著，土壤水分是影响人工梭梭林土壤呼吸的关键因素。该研究进一步证明了人工梭梭林的营造有效改善了沙漠土壤的生物活性，提高了土壤碳通量水平，以土壤结皮破坏为基本特征的人工梭梭林退化和沙漠化必然在短期内加剧碳排放。因此，需要在沙漠地区合理营造人工林，并在造林和林业管理过程中注意保护土壤结皮，以减少CO2排放。
Soil respiration is not only one of important indexes of soil biological activity but also a hot issue in the studies of global carbon cycle.In order to reveal the characters of the soil respiration of an artificial Haloxylon ammodendron forest at its different life stages (40 a, 30 a,10 a and 5 a) in the lower reaches of Shiyang River,Gansu Province,China which is located in the typical arid region,the LI-8 100 automated soil CO2 flux system was used to investigate the daily change of the soil respiration of the forest in both growing and nongrowing seasons,with the mobile sand dunes and the artificial Haloxylon ammodendron forest after soil crust removal as the control samples.The influence of soil moisture and temperature on its respiration was also evaluated.The four results were found as follows: (1) Diurnal changes in the soil respiration rate of the artificial Haloxylon ammodendron forest at different life stages in both growing and nongrowing seasons were showing an obvious singlepeak curves with certain volatility.The maximum rate appeared from 12:00 PM to 14:00 PM while the minimum around 8:00 AM.(2) Planting Haloxylon ammodendron forest and breaking soil crusts significantly improved the respiration rate of the desert soil and the respiration rates of the forest in different life stages generally were progressively increased with the planting age,following a descent order as MC= >40 a>30 a>10 a>MS >5 a in the growing season and MC>40 a>10 a>5a>30 a>MS in the nongrowing season respectively. (3) There are obvious seasonal variations in the soil respiration rate of the artificial TBX]Haloxylon ammodendron forest at different life stages.The value of the rate in the growing season (August) is much higher than that in the nongrowing season (January). (4) The correlation analysis showed that the soil respiration rate (Y ) of artificial Haloxylon ammodendron forest was significantly correlated with the soil water content (X ) at the depth from 0 to 5cm in both growing and nongrowing seasons.Their relationships were described by the following square curve regression equations: Y=-0.205 8X2+0.946 5X-0.316 6 (R2=0.506 2,P=0.041 7) for the growing season and Y=0.118 7X2+0.156 3X+0.118 8 (R2=0.675 7,P =0.001 1） in the nongrowing season,respectively.However,there were no significant correlations between soil respiration rate and soil temperature at 10 cm depth.Thus,the soil water content is the critical factor for soil respiration of artificial Haloxylon ammodendron forest.The findings further proved the importance of planting Haloxylon ammodendron forest to promote the biological activity and carbon flux in the desert soil.Nevertheless,degradation of artificial Haloxylon ammodendron forest and land desertification reflected by the destructed soil crusts will inevitably increase carbon emission in the short run.Therefore,artificial afforestation in desert areas and soil crust protection in this process as well as effective forest administration should be adopted to reduce CO2 emissions.
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