桂西北喀斯特峰丛洼地不同植被演替阶段的土壤脲酶活性

Soil urease activity during different vegetation successions in karst peak-cluster depression area of northwest Guangxi,China

以桂西北喀斯特峰丛洼地不同演替阶段植被群落为研究对象,采用空间代替时间序列的方法,选取立地条件基本相似的草地、乔灌林和次生林3种次生演替植被,并以原生林为对照,通过野外调查取样和室内分析,探讨植被不同演替阶段土壤脲酶活性的变化特征及其与土壤理化性质的关系。结果发现,(1)不同植被演替阶段的土壤脲酶活性存在显著差异,草地最高(0.462 mg.g-.1d-1),次生林次之(0.410 mg.g-.1d-1),灌木林再次(0.371 mg.g-.1d-1),原生林最低(0.194 mg.g-.1d-1);(2)在喀斯特区域,土壤脲酶活性与全钾、粘粒含量、容重、碳氮比(C/N)、碱解氮占全氮的比例(AN/TN)呈正相关(P<0.01),与其他指标,如有机碳、全氮、碱解氮、微生物碳、微生物氮等均呈极显著负相关(P<0.01);(3)与脲酶活性关系密切的理化性质有全氮、碱解氮、微生物量、粘粒含量及C/N、AN/TN等。并不是所有区域的土壤脲酶活性都与SOC、TN、AN、微生物量呈正相关,当土壤养分较高,即土壤中的氮量不再是作物生长的限制因子时,脲酶活性有可能与之呈负相关。

Soil urease activity（URE） was usually put forward to indicate the soil fertility.Former studies in other regions had shown that soil urease activity was an indicator for soil fertility,and more urease activity means more fertile.In karst region,the growth of vegetation may be limited by nitrogen element in earlier revegetation.Compared with most other regions,soil nutrients of karst are higher.Therefore,this study aimed to explore the relationship between soil urease activity and nutrients,and find the main factors that affected soil urease activity. An experiment was designed to compare the distribution of soil nutrients under three mainly vegetations to the original forest.In order to explore the value of soil urease anctivity for different vegetation types and its controlling factors,the soil samples of topsoil（0—15cm） were collected in two typical karst peak-cluster within four vegetation succession stages（grassland,shrubland,plantation forest,original forest） in northwest Guangxi,southwest China.A total of 202 samples were collected from twelve sampling lines（each vegetation type had three sample lines for comparison）,including 48 grassland samples,46 shrubland samples,44 plantation forest samples and 64 original forest samples.Analysis of variance（ANOVA） was utilized to analyze the differences of soil urease activity for different vegetation types.The results showed that there were significant differences of soil urease activity during different vegetation succession stages.Soil urease activity of grassland was the highest,while original forest was the lowest.It indicates that soil urease activity did not increase with vegetation succession.Many influencing factors affected the soil urease activity at the same time,such as TN,AN,soil microbial biomass,clay content,C/N,AN/TN and so on.There was a positive correlation between TK,clay content,bulk density,C/N,AN/TN and URE（P〈0.01）;whereas negative correlation between SOC,TN,AN,soil microbial biomass and URE（P〈0.01）.The result was different from most areas in China,such as Beijing,Shanxi,Hunan and so on,but in the area of high TN,the result was the same as ours. Our study indicates that it is not all regions of the urease activity were positively correlated with SOC,TN,AN,and siol microbial biomass.The URE was possible to be negative correlation with main nutrients in regions that N is no longer a limiting factor for crop growth.Therefore,the demand for crop growing is a stationary extent.Even if peopele provide more N nutrient,the enzyme won′t decompose the excess part to available nitrogen.Additionally,it is dangerous to nitrogen loss and ammonia volatilization.