风干土保存时间和湿土培育时间对黄淮海平原潮土酶活性的影响

Effect of Storage Time of Air-drying Soil and Incubation Period Following Rewetting on Soil Enzyme Activities in North China Plain

以经历18年不同施肥管理的土壤为研究对象,阐明它们经过4个不同时间保存或处理后的土壤脲酶、转化酶、脱氢酶、及FDA酶活性的动态变化。处理包括:风干保存30天或鲜土状态、风干保存210天、风干土湿润至田间持水量(25℃)条件下分别培育15天和51天;同时评估这些酶活性的变化程度与土壤本身有机碳含量之间的关系。结果表明,风干土保存时间和风干土湿润后短期培育均对脲酶活性影响很小,但风干土湿润培养51天后其活性则显著降低;随风干土保存时间延长,转化酶活性显著降低;与鲜土相比,风干土湿润培养15天后,脱氢酶活性显著提高,但继续湿润培养至51天后,其活性又降至与鲜土相当,因此风干土湿润培育一定时间后测定的脱氢酶活性可用来代表其田间自然湿度时的状态;FDA酶活性的变异程度最大,与其从鲜土状态至风干状态的活性急剧下降有关。土壤本身有机碳含量与脲酶和脱氢酶的活性变化程度成显著负相关关系,说明土壤有机碳含量是决定它们随环境条件改变而变化的主要因素之一。另外,土壤NH4+-N、NO3--N和可溶性有机碳含量对上述4种处理的响应程度也存在差异。其中风干状态土壤经湿润培育处理后,NH4+-N含量呈先降后升趋势,正好与脲酶活性变化趋势相反;而NO3--N含量整体上呈上升趋势,可溶性有机碳含量则正好相反。

Soil samples that have exposed to different fertilization management practices for 18 years were used to examine the variations of various enzyme activities, including urease, invertase, dehydrogenase activity, and fluorescein diacetate hydrolysis, with storage time of air-drying soil and incubation period after rewetting. Soil enzyme activities were determined, respectively, on fresh samples or samples that have air-dried and stored for 30 d, samples that have air-dried and stored for 210 d, and on rewetted samples that have incubated for 15 or 51 d at field capacity （25℃）. Relationship between the content of soil organic carbon and the change in enzyme activities after storage and incubation was also evaluated. The results showed that urease activity was relatively stable during the storage time of air-drying soil and subsequent 15d incubation at field capacity, while the activity significantly shifted down 51 d after rewetting. A considerable decline in inveaase activity was observed during the storage time of air-drying soil. Relative to the fresh soil, dehydrogenase activity was significantly shifted up 15 d after rewetting, however, the activity shifted down again and was comparable to the fresh soil when the incubation time expanded to 51 d, indicating that dehydrogenase activities determined in the later conditions were representative of fresh soil values. Among the four determined enzyme activities, FDA showed largest fluctuations during the experimental period, probably because of its greater decline when the soil changed from fresh state to air-dried state. The significantly negative relationship between the content of soil organic carbon and the variation coefficient of urease or dehydrogenase activity suggested that soil organic carbon was one of the most important factors in controlling their fluctuations with environment. In addition, the responses of soil NH4＋-N, NO3--N and DOC contents to four kinds of treatments were different. During the incubation period of soil rewetted after drying, the trend of NH4＋-N content descended first and then ascended, which was opposite to urease activity, and NO3--N content ascended during the whole incubation, which was opposite to DOC content.