土壤微生物量氮含量、矿化特性及其供氮作用

Contents of soil microbial biomass nitrogen and its mineralized characteristics and relationships with nitrogen supplying ability of soils

论述了土壤中微生物体氮的含量及其影响因素 ,土壤微生物量氮的矿化特性及其与土壤矿化氮间的关系 ,土壤微生物量氮含量与土壤供氮指标间的关系等。提出研究不同生态系统中土壤微生物量氮的含量及其变化规律 ,不同耕作栽培措施对土壤微生物量氮含量的影响 ;土壤微生物量氮在土壤氮素保持和释放中的作用 ;土壤微生物量氮的转化率与其供氮量间的关系 ;土壤微生物量氮与作物氮素吸收间的关系等 ,是土壤微生物量氮方面应重点研究的问题。

As soil microorganisms decompose the organic matter,they also assimilate a portion of the nutri- ent in soils to build their body.The nutrients in soil microbial biomass are mineralized from the dead mi- croorganisms.Therefore,soil microbial biomass is considered as a source and sink for nutrients,and is an active pool of organic matter in soils.Because of its important role in various ecological systems,nitrogen contained in soil microbial biomass(i.e.,SMBN) has got much attention in recent years.This article in- tends to briefly review the advances in studying the content of SMBN in soils,its mineralization character- istics and the relationships with nitrogen supplying ability of soils.Areas,which need further research,are stressed. The content of SMBN in soils in the different ecosystems depends on climate,vegetation,soil types and cultivation practices.Contributions of organic matter to soil from manure,plantresidues or root secre- tion usually increase the levels of SMBN.The rate of increase depends on the amounts of organic matter added and its properties.Soils with fine texture were found to have high contents of SMBN,perhaps due to the ability to better protectsoil microbial biomassfrom decomposition.The effects ofinorganic N fertilizers on SMBN were not consistent.The effects of various managementpractices on the changes of SMBN were perhaps related to their different influences and contributions to the organic matter pool in soils. Compared to the other pools of organic- N in soils,N in microbial biomass,fractionated by the acid hy- drolysis method,is lower in unhydrolysable N and higher in amino acid and acid hydrolysably unidentified forms.This indicatesthe easy decompositions of SMBN.The turnover of SMBN varies with soils,however, itwas fasterthan otherpools of organic N in soil.Therefore,SMBN can be considered as a source of easily mineralizable organic- N in soilsSignificant correlation between SMBN and the mineralizable N in soils was found in several studied. As for the contribution of SMBN to mineralized N in soils,there were some controversial reports.Some re- searchers showed that the SMBN were the main source of easily mineralizable organic- N in soils.Others concluded that SMBN contributed only a part of the easily mineralizable organic- N.Although its contentis low,the short- term turnover of SMBN makes it an importantsource for the mineralizable N in soils. SMBN can be extracted chemically.Mild extractants,such as0 .0 1 mol/L Ca CI2 ,or0 .0 1 mol/L Na H- CO3 solutions,were found to be preferential for extracting the SMBN.Due to the active role of SMBN in N transformation in soils,chemical methods used to extractthe available N from soils,and which are sensitive to SMBN,are also importantfor evaluation of N availability in soils.Such methods could also be used to as- sess the N supplying ability of soils. Researchers have recognized the importantrole of SMBN in adjusting N transformations in soils,and used the SMBN as an index to evaluate the effects of fertilization and tillage on soil properties.To under- stand the exact role of SMBN in N dynamics in soil- plant systems there are still many issues to be re- solved.Among these are: A.Quantifying the changes in the SMBN in soils of various ecosystems and under different manage- ment practices.This could help understand the role of SMBN in affecting the mineralization and immobi- lization of N in soil- plant systems,and to explain the fate of N- fertilizer applied to soils. B.Evaluating the relationship between the contentand turnoverrate of SMBN and N supplying ability of soils in differentecosystems.This includes the mineralization characteristics of SMBN under aerobic and anaerobic conditions,and the relationship between the SMBN and other N availability indices of soils. C.Assessing the contribution of SMBN to N uptake by the plant in various ecosystems,including its role at different growth stages of plants. In summary,the core of the needed research is to understand the relationships of SMBN with other