黄土丘陵区撂荒农田土壤酶活性及酶化学计量变化特征

明确土壤胞外酶活性及酶化学计量比在农田撂荒过程中的变化特征及驱动因素,对揭示土壤养分可利用性随植被恢复的变化规律和阐明生态系统养分循环机制有重要意义.本文以黄土丘陵区不同撂荒年限坡耕地（0、10、20和30 a）为研究对象,通过测定土壤酶活性及酶计量比、土壤理化性质、植物多样性和科组成,探讨农田撂荒后土壤微生物养分限制状况及酶活性和酶计量比的主控因子.结果表明,β-1,4-N-乙酰氨基葡萄糖苷酶（NAG）、亮氨酸氨基肽酶（LAP）和碱性磷酸酶（ALP）的活性均随撂荒年限增加而显著增加,而β-1,4-葡萄糖苷酶（BG）活性则相反.土壤BG：（NAG+LAP）和BG：ALP呈现出与土壤BG活性相同的随撂荒年限增加而减小的趋势;而（NAG+LAP）：ALP呈先升后降趋势,在撂荒20 a时达到最高值.酶化学计量的向量长度随撂荒年限增加而显著减小,表明撂荒过程中土壤微生物受碳（C）限制程度的减弱.撂荒前10 a酶化学计量的向量角度小于45°,后20 a大于45°,说明撂荒前期微生物受氮（N）限制,后期受磷（P）限制.冗余分析结果揭示土壤有机碳含量、总氮含量、C：N、C：P、pH以及植被多样性是调控酶活性和酶计量比变化的主要因子.分类变异分析表明,土壤和植物因素可解释不同撂荒年限下土壤酶活性及酶计量比差异的62.0%,植被特征与土壤理化特性之间的交互作用是土壤酶活性及酶计量比变化的主控因子,解释度为37.1%.综上所述,黄土丘陵区农田撂荒过程中应考虑外源P的投入以缓解生态系统中有效P的不足,研究结果可为理解脆弱生境恢复生态系统中微生物介导的生物地球化学循环机制以及指导土壤养分管理和生态可持续发展提供理论依据.     

不同大气污染区林木根区土壤重金属和酶活性研究

黄埔区是广州市污染较严重的地区,其中林木也受到了大气等污染物的危害。林木根区的土壤重金属和酶活性是探讨污染对林木影响机制和反映污染程度的重要指标。作者分别在该区的石化厂、硫酸厂附近林地和非污染的华南农业大学校园(对照)共3个区选择了台湾相思、马尾松、尾叶桉和荔枝4个树种、11个采样点,共采集了33个供试土壤样品,分析了林木根区土壤重金属(Cu、Zn、Pb、Cd)全量、有效量和土壤酶(脲酶、过氧化氢酶、酸性磷酸酶和蛋白酶)活性。结果表明,(1)石化厂重金属含量总体上与对照区差异不大,而硫酸厂区重金属含量则显著地高于对照区,污染严重。(2)不同调查区根区土壤酶活性存在显著差异,各调查区平均土壤酶活性大小顺序基本上表现为:对照区>石化厂区>硫酸厂区,尤其是硫酸厂区显著地低于对照区;而同一调查区不同树种之间的酶活性也存在差异,台湾相思根区土壤脲酶的活性均比其它树种高;从酶活性看,在硫酸厂严重污染胁迫下,台湾相思比尾叶桉更耐污染。(3)对土壤重金属含量和酶活性进行典型相关分析得出:根区土壤有效Zn含量对过氧化氢酶和酸性磷酸酶活性有明显的刺激作用,但抑制了蛋白酶活性;有效Cd则抑制了过氧化氢酶和酸性磷酸酶活性,但刺激了蛋白酶活性。     

邻苯二甲酸二(2-乙基己基)酯酶促降解性的研究

从处理石化厂废水的活性污泥中分离出一株邻苯二甲酸酯降解菌FS1（Pseudomonas fluorescens FS1),测定了P.fluorescens FS1的邻苯二甲酸酯降解酸对邻苯二甲酸二（2－乙基已基）酯（DEHP）的降解特性。P.fluorescens FS1细胞中的颗粒部分、溶液部分对DEHP都具有降解作用，初步认为P.fluorescens FS1降解酶属胸内酶。P.fluorescens FS1降解酶对DEHP的最适酸度为pH6.5-8.0，温度为25－35℃，米氏常数Km为190.48nmol/mL。在好氧条件下，DEHP与P.fluorescens FS1降解酯酶作用，形成邻苯二甲酸单酯和邻苯二甲酸后，可进一步降解成苯甲酸、对羟基苯甲酸，最终转化为CO2与H2O。     

Soil enzymatic activities and microbial community structure with di erent application rates of Cd and Pb

This study focused on the changes of soil microbial diversity and potential inhibitory effects of heavy metals on soil enzymatic activities at different application rates of Cd andor Pb. The soil used for experiments was collected from Beijing and classified as endoaquepts. Pots containing 500 g of the soil with different Cd andor Pb application rates were incubated for a period of 0, 2, 9, 12 weeks in a glasshouse and the soil samples were analyzed for individual enzymes, including catalase, alkaline phosphatase and dehydrogenase, and the changes of microbial community structure. Results showed that heavy metals slightly inhibited the enzymatic activities in all the samples spiked with heavy metals. The extent of inhibition increased significantly with increasing level of heavy metals, and varied with the incubation periods. The soil bacterial community structure, as determined by polymerase chain reaction-denaturing gradient gel electrophoresis techniques, was different in the contaminated samples as compared to the control. The highest community change was observed in the samples amended with high level of Cd. Positive correlations were observed among the three enzymatic activities, but negative correlations were found between the amounts of the heavy metals and the enzymatic activities.