中文摘要：

应用微量热法研究了长期轮作下麦田不同土层中的微生物活性, 以及施肥对微生物垂直分布的影响。结果表明, 微生物活性基本随深度的增加而下降; 随着土层加深, 可培养细菌菌落数减少, 且可培养细菌菌落数目与最大时间（Peak time）Pt值（表示从微生物生长开始到达到峰值的时间）呈负相关; 热功率（P）-时间（t）曲线由陡变缓, 由规则变得起伏不定, 侧翼变得更短, 峰高也降低; 不同土层的微生物生长速率常数（Microbial growth rate constant） μ、峰高（Peak height）Ph值变化明显, 基本随深度增加而减小。施肥土样和不施肥土样的曲线形状不同, 特别是上层土样施肥后的曲线明显比不施肥的曲线陡, 侧翼也明显变短; 施肥土样的μ和Ph值都大于不施肥土样, 且施肥土样的Pt都小于对照。这说明, 在不同的土壤深度有不同的微生物群落结构, 长期的施肥处理改变了土壤微生物的垂直分布特征。

英文摘要：

Aims Soil depth and fertilizer application affect soil biological properties. A few studies in China have focused on the influence of soil depth and long-term fertilizer application on microbial activity. Our objective was to study changes in microbial activity in different soil layers under 28-year fertilizer treatments in wheat （Triticum aestivum） field soil to provide basic data on microbial activity and structure and function of farmland ecosystems. Methods In 1978, six different treatments were established in the Gaoping Agricultural Experimental Station in Pingliang, Gansu Province of China for an experiment on long-term fertilization and wheat-maize rotation. We chose two treatments, no fertilizer application treatment （CK） and mineral fertilizer plus manure application treatment （MNP）. The amount of fertilizer per year was 75 000 kg.hm-2 manure, 90 kg·hm^-2 N, and 75 kg·hm^-2 P. Five soil layers were sampled in both treatments： 5-15, 15-20, 25-30, 35-40 and 45-50 cm. The microbial activity of the different soil layers and the effect of fertilizer on its vertical distribution were determined with microcalorimetry. All experiments were repeated three times. Analysis was done using integrative method combining correlation and component analyses in SPSS. Important findings With an increase of soil depth, the number of bacteria colonies decreased. This was negatively correlated with Pt values, which indicates time from the growth of microbes to the peak. Thermal power-time curves changed from steep to flat and from regular to irregular, shoulders were shorter and peak height lower. The microbial growth rate constant u and the peak height Ph values in different soil layers also varied significantly, and both decreased with increased soil depth. There were different kinds of curve shapes in CK and MNP, particularly in the former two layers of soil samples. Curves of MNP were steeper than for CK, and their shoulders before the peak were significantly much shorter. The Ph and u values of MNP were g