兰州大学机构库 >生命科学学院
河西走廊干旱气候条件下盐渍土微生物生态研究
Alternative TitleMicrobial Biomass and Activity in Salt-Affected Soils Under Arid Conditions in the Hexi Corridor
元炳成
Thesis Advisor李自珍
2007-04-12
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name博士
Keyword盐渍度 镁碱度 微生物量 微生物活动性 代谢熵 水解酶活动性
Abstract

研究了镁碱化盐土的化学性质特征指标电导率和Mg2+/Ca2+对土壤微生物群落大小、活动性以及群落结构的影响。微生物碳、微生物熵、微生物氮以及微生物氮占全氮的百分比与电导率、Mg2+/Ca2+之间为负相关关系,它们随电导率的升高而指数下降,随Mg2+/Ca2+的升高而线性下降。微生物C/N和电导率、Mg2+/Ca2+之间都呈线性负相关关系。土壤基础呼吸值很低,且随电导率的升高而指数下降,随Mg2+/Ca2+的升高而线性下降。代谢熵和电导率之间为正相关二次函数关系,和g2+/Ca2+之间正相关线性关系。可矿化氮随电导率和Mg2+/Ca2+的升高而指数下降。精氨酸氨化率和FDA水解率随电导率的升高而指数下降,随Mg2+/Ca2+的升高而线性下降。脲酶、磷酸酶、β-葡萄糖苷酶、BAA-蛋白酶和casein-蛋白酶的活动性低,和电导率之间为负相关指数关系,和Mg2+/Ca2+之间为负相关线性关系。这些不同水解酶的活动性之间相互正相关,酶的活动性和度量微生物活动性的其它指标间也存在正相关关系。微生物碳与土壤有机碳之间为正相关线性关系,而且这种关系在大多数情况下也成立。虽然如此,高盐渍度和镁碱度对微生物的危害仍然是显而易见的,这主要表现在随着盐渍度和镁碱度的升高,微生物系数不断地下降。平均微生物熵远低于Anderson和Domsch (1989)以及Sparling (1992)等人提出的值。在盐渍度最高的土壤中,微生物碳的含量显著地偏低,使得最低微生物熵仅为0.53%。因为基础呼吸代表微生物碳的活性部分,所以我们的结果表明全部和活性微生物都受
到盐渍化和镁碱化的不利影响。这表明CO2的产生量反映了干旱地区的镁碱化盐土对土壤微生物的胁迫作用。代谢熵和电导率、 Mg2+/Ca2+之间的正相关关系表明盐渍化和镁碱化对土壤微生物而言是一种胁迫环境。所以,随着盐渍度和镁碱度的升高,土壤微生物群落变小且其碳资源的利用效率降低。低的微生物C/N比可能反映镁碱化盐土微生物群落中细菌占优势。土壤微生物群落是由不同的微生物所组成,而不同的微生物其微生物量的C/N是不同的。随着盐渍度和镁碱度的升高, FDA水解率明显降低,这可能归因于盐渍化和镁碱化胁迫条件下微生物细胞对FDA的吸收降低。此外,盐渍化和镁碱化条件下土壤微生物量减少,与FDA水解活动有关的酶的合成也减少,这些都是导致FDA水解率降低的原因。精氨酸氨化率的变化模式与FDA水解率相似,进一步表明盐渍度和镁碱度对土壤微生物的活动会产生强烈的抑制作用。盐渍度和镁碱度通过直接抑制微生物生长及其活动降低土壤微生物对有机质的分解。盐渍度和镁碱度升高引起微生物量的减少,由此导致可矿化氮呈现出指数下降。氮的矿化也和土壤微生物的组成有关,因为不同的微生物在分解有机化合物方面的能力不同。细菌的优势地位可能会造成盐渍土中复杂有机化合物分解的困难。微生物本身也是土壤易矿化有机氮的来源之一,低的可矿化氮可能和盐渍环境中微生物氮的量低有关。和其它土壤相比,镁碱化盐土水解酶的活动性很低。部分原因可能是盐渍度和镁碱度使土壤微生物产生的酶的数量减少, 因为盐渍度和镁碱度使土壤微生物量减少且活动性降低。此外,高浓度的盐可降低酶蛋白的溶解性,盐也能破坏蛋白质的三级结构而使酶蛋白变性,而蛋白质的三级结构是酶的活动性所必需的。值得注意的是,电导率和镁碱度对水解酶的抑制作用是因酶而异的。镁碱化盐土水解酶的活动性相互间正相关,这表明虽然每一种酶都依赖于特定的酶作用物和参与特定的生化反映,但是,盐渍度和镁碱度对所有的酶都会产生抑制作用。酶的活动性和土壤有机碳的含量正相关,就如同微生物群落的活动性和土壤有机碳的含量正相关一样。一般地讲,上述微生物指标和电导率之间的负相关关系表现为指数型,而和Mg2+/Ca2+之间的负相关关系为线性;另外,微生物指标和电导率之间的负相关性系数比它们和Mg2+/Ca2+之间的负相关性系数要小。这说明可溶盐对土壤微生物的抑制性要比镁碱度大。随着电导率的增加,微生物群落的大小和活动性呈现出指数下降,这说明电导率的小幅度增加会对土壤微生物产生极为有害的影响。总之,盐渍度和镁碱度对土壤的微生物群落有极为不利的影响。而且,相对而言,盐渍度的负面影响比镁碱度更大。

Other Abstract

The effects of salinity and Mg2+ alkalinity on the size and activity and structure of the soil microbial community in Mg2+ alkalized soils were investigated.There was a negative exponential relationship between EC and biomass C,biomass N, microbial quotient, indices of microbial activity and the activities of the hydrolases,but the negative relationships with Mg2+/Ca2+ were best described by linear functions. Potentially mineralizable N decreased exponentially with increasing EC and Mg2+/Ca2+. Basal soil respiration rate was very low,and declined exponentially with increasing EC, linearly with increasing Mg2+/Ca2+.The metabolic quotient (qCO2) showed a quadratic relationship with EC and positive linear relationships with Mg2+/Ca2+,indicating that increasing salinity and Mg2+ alkalinity resulted in a progressively smaller,more stressed microbial community which was less metabolically efficient.The biomass C/N tended to be lower in soils with higher salinity and Mg2+ alkalinity,reflecting the bacterial dominance in microbial biomass in Mg2+ alkalized soils.The activities of the enzymes urease,phosphatase,
β-glucosidase,protease-BAA,protease-casein were low and declined exponentially with increasing EC and linearly with increasing Mg2+/Ca2+.The activities of different hydrolases were positively interrelated,and there were also positive
relationships between the measures as good indices for soil microbiological activity and enzymatic activities.In present study there was a positive linear relationship between microbial biomass C and soil organic C and this is generally the case in most situations.Nonetheless,with increasing salinity and Mg2+ alkalinity the conditions were becoming increasingly detrimental to soil microorganisms and this was demonstrated by the decline in microbial quotient. The average microbial quotient is far below the alue suggested by Anderson and Domsch (1989) and Sparling (1992):about 4% of soil organic C belongs to the microbial biomass.Microbial biomass C content in the soil with the highest salt concentration was markedly low, leading to a minimum microbial quotient of 0.53% only. Since basal respiration represents the living component of microbial biomass C, both the active and total microbial communities decreased with increasing salinity and Mg2+ alkalinity. This suggests that CO2-C emission reflects the stress existing in Mg2+ alkalized soils of arid regions.
The positive relationships between qCO2 and EC and Mg2+/Ca2+ found in this study reflected increasing environmental stress as a result of salinity and Mg2+ alkalinity conditions on the soil microbial community.Consequently,increasing salinity and Mg2+ alkalinity resulted in a smaller,more stressed,microbial community which was less efficient in using C resources than its less stressed counterparts.Soil microflora is a composite of several groups of organisms and each microbial group may have a different biomass C/N ratio. The declining trend in biomass C/N with increasing salinity and Mg2+ alkalinity may reflect the bacterial dominance in soil microbial biomass.
The remarkable reduction of FDA hydrolysis rate with increasing salinity and Mg2+ alkalinity might be ascribed to the lower uptake of FDA by the soil microbial cells due to the salinity and Mg2+ alkalinity stress conditions. The similar pattern of decline for arginine ammonification rate as for FDA hydrolysis rate indicates that microbial activity was greatly decreased by increasing salinity and Mg2+ alkalinity.Salinity and Mg2+ alkalinity may decrease organic matter decomposition directly by inhibiting microbial growth and activity. Reduction in soil microbial biomass due to increased salinity and Mg2+ alkalinity caused a substantial exponential decline in potentially mineralizable N. In addition, N mineralization may be affected by species composition of soil microorganisms, as species differ in their ability to degrade various organic compounds.The salinity induced reduction of fungi may reduce the decomposition of complex organic material in saline soils.
The values of hydrolases activity in this study were very low with regards to those of nondisturbed soils.Moreover,the lowest values corresponded to the soils with highest salinity and Mg2+ alkalinity.The decreased enzyme activity may be partially
attributed to the less enzymes released by the smaller, less active microbial biomass due to salinity and Mg2+ alkalinity. In addition, high salt concentrations tend to reduce the solubility and denature enzyme proteins through disruption of the tertiary protein structure which is essential for enzymatic activity.It is worth noting that the inhibitory effect of both EC and Mg2+ alkalinity on the hydrolases activity is enzyme specific. The positive correlation between the hydrolases of the soils studied indicates that although each individual enzyme depends on specific substrates and takes part in specific reactions, the soil degradation induced by salinity and Mg2+ alkalinity affects all the enzymatic activities equally. Enzyme activity was positively related to soil organic C content as was the relationship between the size and activity of the microbial community and organic C.
In general, the negative relationships between the indices analysed and EC were exponential, while the negative relationships with Mg2+/Ca2+ were linear.In addition,measures of the size and activity of the microbial community were more negatively correlated to EC than to Mg2+/Ca2+. Thus, soluble salt concentrations were apparently more important in inhibiting the growth and activity of soil microorganisms than Mg2+ alkalinity.The exponential decline in the size and activity of the microbial community with increasing EC demonstrates the extremely detrimental effect of small increases in salinity.Our data show that high salinity and Mg2+ alkalinity tend to result in a small bacteria dominated soil microbial community with low microbiological activity.

URL查看原文
Language中文
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/221254
Collection生命科学学院
Recommended Citation
GB/T 7714
元炳成. 河西走廊干旱气候条件下盐渍土微生物生态研究[D]. 兰州. 兰州大学,2007.
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