It has been estimated that a typical gram of soil contains around 90–100 million bacteria and about 200000 fungi,with the majority of these organisms being located around the roots of plants.This localization reflects the fact that plant roots typically exude a large fraction of the carbon that they fix by photosynthesis,and soil microbes utilize this exuded carbon as a food source.The interaction between plants and soil microbes may be beneficial,harmful or neutral for the plant.Bacteria that are beneficial for plant growth and development are commonly called plant growthpromoting bacteria(PGPB).It is thought that these PGPB began to develop mutually beneficial relationships with plants approximately 80–100 million years ago.Moreover,it has been estimated that some fungi began to develop beneficial relationships with plants as long as 450 million years ago.In recent years,based on the successful interaction between PGPB(and/or mychorrhizal fungi)and plants in nature,scientists have endeavored to utilize PGPB(and/or mychorrhizal fungi)in agriculture,horticulture,and environmental cleanup(Glick et al.,1998;Glick,2004;Gamalero et al.,2010;Gamalero and Glick,2012).

The successful implementation of the above-mentioned microbes in agriculture,horticulture,and environmental cleanup requires a detailed in-depth understanding of the many mechanisms that these organisms use to promote plant growth and development.In particular,PGPB may facilitate plant growth either directly or indirectly.Direct promotion of plant growth occurs when PGPB either facilitate the acquisition of nutrients from the environment,including nitrogen,iron,and phosphate,or modulate levels of plant hormones,including auxin,cytokinin,gibberellin,and ethylene.Indirect promotion of plant growth occurs when bacteria decrease the deleterious effects of a plant pathogen.This inhibition of pathogens may occur by any one of a variety of mechanisms including antibiotic synthesis,hydrogen cyanide,siderophores,cell walldegrading enzymes,competition,volatile organic compounds,lowering plant ethylene levels,induced systemic resistance,and quorum quenching.

从圈闭与有效烃源岩的位置关系看，除断层沟通的构造-岩性油气藏外，已发现的孤立砂体岩性油气藏均分布在有效烃源岩范围内或接触有效烃源岩，处于有效烃源岩中心被其包裹的圈闭，其含油性要好于与烃源岩呈侧向接触的岩性圈闭，离有效烃源岩中心的距离越近，圈闭含油气性越好，反之越差。

In the past 20 years or so,scientists worldwide have developed a relatively detailed understanding of many of the mechanisms used by PGPB(Glick et al.,1998;Glick,2004,2015;Sheng et al.,2008;Singh et al.,2011).It is therefore reasonable to conclude that the use of PGPB as an integral component of modern agricultural practice is a technology whose time has come.In fact,a number of PGPB strains have already been commercialized and are being used successfully in a number of different countries throughout the world.Moreover,as the world’s population continues to grow,the pressure for increased food production intensifies,and our concern for the environment becomes paramount(Glick et al.,2007;FAO,2011;Glick,2014,2015;Baligar and Fageria,2015),environmentally friendly methods of food production will no doubt replace traditional agricultural practices including the use of potentially dangerous chemicals(Banat et al.,2000;Scott and Jones,2000;Ying,2006).

局部PUE适合用于同一建筑内有多个数据中心的局部能效评估。对于电网企业数据中心来说，自动化机房与通信机房，甚至自动化机房或通信机房中的各个独立分区都可独立计算pPUE。通过计算自动化机房或通信机房的PUE，可对其中计算值较高的机房进行针对性的优化，从而提升整体数据中心的能效状况。

If we intend to utilize PGPB on a large scale worldwide,then it is first necessary to address several different issues.In the first instance,to go from the current small-scale laboratory and greenhouse experiments to commercial scale field growth of crops using PGPB will necessitate the development of large-scale methods for the growth,handling,storage,shipping,formulation,and application of PGPB.Second,since most people think of bacteria as primary agents of disease,it will be necessary to educate the public worldwide regarding the nature of PGPB and their potential benefits compared to the widespread use of agricultural chemicals.Third,while it is likely that selection of naturally occurring PGPB strains will provide considerable benefit for crop growth and development,eventually signi ficant improvement of PGPB efficacy is likely to come from the genetic manipulation of PGPB strains.However,for such genetic manipulation to be more than a laboratory exercise,scientists will need to convince both the public at large and governmental regulatory agencies that such genetic manipulation does not present any risk or hazard to the food supply.Fourth,it is necessary to develop a more thorough understanding of the functioning of bacterial endophytes and their interaction with plants.This is important since despite the fact that endophytes are likely to be more effective in the field,most of the PGPB research to date has used rhizospheric bacteria.Fifth,since more than 90%of higher plants naturally interact with mychorrhizae,beneficial fungi that utilize mechanisms that are distinct from the mechanisms used by PGPB,it is essential that scientists develop a much better understanding of how PGPB and mychorrhizae can work together to facilitate plant growth.

Notwithstanding the constraints regarding the more widespread use of PGPB that have been mentioned above,the world is at the start of a paradigm shift in agricultural practice where the use of PGPB is becoming much more widespread.The papers in this special issue are an early step in this paradigm shift.These papers include reviews on biosurfactants as a biological tool to increase micronutrient availability in soil(Singh et al.)and microbial degradation of organophosphate pesticides(Kumar et al.),as well as research papers dealing with various aspects of environmental stress including the effect of silver nanoparticles on soil enzyme activities involved in carbon and nutrient cycling(Eivazi et al.),the effect of geogenic lead on fungal and collembola communities in garden topsoil(Joimel et al.),drought-tolerant Pseudomonas spp.for improving the growth performance of finger millet(Eleusine coracana(L.)Gaertn.)under non-stressed and drought-stressed conditions(Chandra et al.),extracts from marine macroalgae and Opuntia ficus-indica cladodes for enhancing diazotrophic PGPR halotolerance,their enzymatic potential,and their impact on wheat germination under salt stress(RAI et al.),carbon and nitrogen amendments leading to differential growth of bacterial and fungal communities in a high-pH soil(Kamble and B˚a˚ath),arsenic bioremediation potential of arsenite-oxidizing Micrococcus sp.KUMAs15 isolated from contaminated soil(Paul et al.),and enhanced lead uptake by an association of plant and earthworm bioaugmented with bacteria(Das and Osborne).In addition to the manuscripts contained in this special issue,several recent issues of this journal have contained a host of manuscripts that address some of the important mechanisms involved in the microbial promotion of plant growth,including those of Wang et al.(2016),Wu et al.(2016),Zabaloy et al.(2016),Raj et al.(2017),Fan et al.(2017),He et al.(2017),Li et al.(2017),and Wang et al.(2017).

A number of other papers on a range of both basic and applied topics involving soil microbes and sustainable agriculture are part of this special issue;they include production of FAPSF from rapeseed meal fermentation using Bacillus flexus NJNPD41 for promoting plant growth(Liu et al.),indication of soil microbial activity by electrical signals of microbial fuel cells with re-vegetated red soils(Jiang et al.),shortterm responses of soil microbial biomass to different chabazite zeolite amendments(Ferretti et al.),effect of long-term soil management on the mutual interaction among soil organic matter,microbial activity,and aggregate stability within a vineyard(Belmonte et al.),responses of soil enzyme activities and microbial community composition to moisture regimes in paddy soils under long-term fertilization practices(Li et al.),nitrogen release from slow-release fertilizers in soils with different microbial activities(Nardi et al.),effect of soil organic matter on adsorption and insecticidal activity of toxin from Bacillus thuringiensis(Zhou et al.),and significant changes in microbial communities along the ecological succession of biological soil crusts in the Tengger Desert of China revealed using pyrosequencing(Zhang et al.).

REFERENCES

Banat I M,Makkar R S,Cameotra S S.2000.Potential commercial applications of microbial surfactants.Appl Microbiol Biotechnol.53:495–508.

Baligar V C,Fageria N K.2015.Nutrient use efficiency in plants:An overview.In Rakshit A,Singh H B,Sen A(eds.)Nutrient Use Efficiency:From Basics to Advances.Springer,New Delhi.pp.1–14.

Food and Agricultural Organization of the United Nations(FAO).2011.The State of Food and Agriculture Report 2010–2011.Women in Agriculture:Closing the Gender Gap for Development.FAO,Rome.

Fan X H,Zhang S A,Mo X D,Li Y C,Fu Y Q,Liu Z G.2017.Effects of plant growth-promoting rhizobacteria and N source on plant growth and N and P uptake by tomato grown on calcareous soils.Pedosphere.27:1027–1036.

Gamalero E,Berta G,Massa N,Glick B R,Lingua G.2010.Interactions between Pseudomonas putida UW4 and Gigaspora rosea BEG9 and their consequences for the growth of cucumber under salt-stress conditions.J Appl Microbiol.108:236–245.

Gamalero E,Glick B R.2012.Plant growth-promoting bacteria and metal phytoremediation.In Anjum N A,Pereira M E,Ahmad I,Duarte A C,Umar S,Khan N A(eds.)Phytotechnologies:Remediation of Environmental Contaminants.CRC Press,Boca Raton.pp.361–376.

Glick B R.2004.Bacterial ACC deaminase and the alleviation of plant stress.Adv Appl Microbiol.56:291–312.

Glick B R.2014.Bacteria with ACC deaminase can promote plant growth and help to feed the world.Microbiol Res.169:30–39.

Glick B R.2015.Beneficial Plant-Bacterial Interactions.Springer,Heidelberg.

Glick B R,Cheng Z,Czarny J,Duan J.2007.Promotion of plant growth by ACC deaminase containing soil bacteria.Eur J Plant Pathol.119:329–339.

Glick B R,Penrose D M,Li J.1998.A model for the lowering of plant ethylene concentrations by plant growth-promoting bacteria.J Theor Biol.190:63–68.

He H D,Li W C,Yu R,Ye Z H.2017.Illumina-based analysis of bulk and rhizosphere soil bacterial communities in paddy fields under mixed heavy metal contamination.Pedosphere.27:569–578.

Li C Y,Hu W C,Pan B,Liu Y,Yuan S F,Ding Y Y,Li R,Zheng X Y,Shen B,Shen Q R.2017.Rhizobacterium Bacillus amyloliquefaciens strain SQRT3-mediated induced systemic resistance controls bacterial wilt of tomato.Pedosphere.27:1135–1146.

Raj V,Shankar S,Kumar A,Surendra S.2017.Soil-plant-microbe interactions in stressed agriculture management:A review.Pedosphere.27:177–192.

Scott M J,Jones M N.2000.The biodegradation of surfactants in the environment.Biochim Biophys Acta(BBA)-Biomembr.1508:235–251.

Sheng X F,He L Y,Wang Q Y,Ye H S,Jiang C Y.2008.Effects of inoculation of biosurfactant-producing Bacillus sp.J119 on plant growth and cadmium uptake in a cadmium-amended soil.J Hazard Mater.155:17–22.

Singh A,Parmar N,Kuhad R C,Ward O P.2011.Bioaugmentation,biostimulation,and biocontrol in soil biology.In Singh A,Parmar,N,Kuhad R C(eds.)Bioaugmentation,Biostimulation and Biocontrol.Springer,Berlin,Heidelberg.pp.1–23.

Wang B B,Shen Z Z,Zhang F G,Raza W,Yuan J,Huang R,Ruan Y Z,Li R,Shen Q R.2016.Bacillus amyloliquefaciens strain W19 can promote growth and yield and suppress Fusarium wilt in banana under greenhouse and field conditions.Pedosphere.26:733–744.

Wang J,Shu K H,Zhang L,Si Y B.2017.Effects of silver nanoparticles on soil microbial communities and bacterial nitri fication in suburban vegetable soils.Pedosphere.27:482–490.

Wu Z P,Wu W D,Zhou S L,Wu S H.2016.Mycorrhizal inoculation affects Pb and Cd accumulation and translocation in Pakchoi(Brassica chinensis L.).Pedosphere.26:13–26.

Ying G G.2006.Fate,behavior and effects of surfactants and their degradation products in the environment.Environ Int.32:417–431.

Zabaloy M C,Garland J L,Allegrini M,Gomez D V.2016.Soil microbial community-level physiological pro filing as related to carbon and nitrogen availability under different land uses.Pedosphere.26:216–225.