狗牙根对石油污染土壤的修复效果研究

为了研究狗牙根对中原油田地区土壤石油污染的修复效果,通过盆栽实验,设置4组处理,对照组(即不种植狗牙根组)、种植狗牙根组、种植狗牙根并添加尿素组、种植狗牙根并添加有机肥组,分别在15,30,60,90,120 d取样分析.结果表明:经过120 d后,对照组的土壤石油污染去除率为25.40%;种植狗牙根组的土壤石油污染去除率为58.67%,是对照组的2.3倍;添加尿素可以有效的增加狗牙根对石油的去除率,当尿素:土为1:2000时,石油污染去除率达到69.43%;土壤石油污染去除率随着有机肥的增加而增加,施加有机肥水平为12 g/kg时,土壤石油污染去除率达到83.97%,是狗牙根组去除率的1.4倍.因此,种植狗牙根对土壤石油污染修复有较好的作用,合理施肥对狗牙根修复土壤石油污染影响显著.     

复合接种剂对三叶草生长特性和品质的影响

利用从兰州地区红三叶 (Trifolium pratense L.) 和白三叶（Trifolium repens L.）根际分离、 筛选获得的4株植物根际促生细菌（代号:A-Hsg、 B-ls1 3、 C-lhs11、 D-lhs14) 制作微生物接种剂,采用盆栽法测定不同接种剂处理对红三叶草生长特性及品质的影响。结果表明,本研究制作的接种剂符合《农用微生物菌剂》质量标准（GB 20287-2006）。复合接种剂处理AD对红三叶草株高、 根长促进作用显著 (P0.05),分别较对照增加33.62%和46.20%。AB和AD处理红三叶草地上植物量增重显著,较对照增加了101.69%和94.98%。BC和AD处理对地下植物量增加显著,增加了197.63%和151.18%。AC、 AD和BCD处理后红三叶草整株磷含量均高于对照,其中BCD处理较对照差异显著（P0.01）,磷含量较对照增加了15.38%。ABCD处理红三叶草整株的含氮量较对照达到了显著水平（P0.05）,较对照增加了14.77%。ABD、 BCD和ABCD处理均可提高红三叶草地上部分粗蛋白含量,其中处理ABCD粗蛋白含量较对照增加最多,增加了14.62%,达到了显著水平（P0.05）。复合接种剂AD、 AB、 BC、 AC、 ABD、 BCD和ABCD接种后,对红三叶草生长特性和品质的提高表现出良好的促进效果,可作为复合菌肥材料作进一步研究。     

丛枝菌根对芘污染土壤修复及植物吸收的影响

采用温室盆栽试验方法,研究了两种丛枝菌根真菌Glomus mosseae和 Glomus etunicatum对三叶草(Trifolium subterraneum L.)和辣椒（Capsicum annuum L.）修复芘污染土壤的影响。供试土样中芘初始浓度为0 ~ 75.18 mg/kg。结果表明,接种AMF可促进供试植物对土壤中芘的吸收,并且显著提高三叶草根的芘含量、根系富集系数、根和茎叶的芘积累量,但对辣椒根和茎叶芘含量、根系富集系数的影响不显著,这主要与植物的菌根侵染率和“菌根依赖度”不同有关。接种AMF土壤中芘的削减率高于普通植物修复,但植物吸收积累对修复的贡献率小于0.2%;因此推测,AM作用下良好的根际环境对土壤微生物数量和活性的提高、进而对土壤中芘降解的促进可能是菌根修复的主要机理。     

两性磁化炭对牧草生长及土壤铜有效性的影响

为了探究材料添加对植物修复过程中的牧草生长和土壤铜有效性特征的影响,采用盆栽试验研究7种土壤Cu~(2+)污染水平[0,100,200,400,800,1 200,1 600 mg/L]下,两性磁化炭表施(0—3 cm)和混施对苏丹草(Sorghum sudanense(Piper)Stapf.)和黑麦草(Lolium multiflorum L.)发芽率、株高和生物量的影响,并分析了盆栽土壤中水溶态和酸提取态铜含量的变化特征。结果表明:(1)在未经Cu~(2+)处理时,表施和混施两性磁化炭都能大幅度提高黑麦草的发芽率和成活率;Cu~(2+)处理后,表施两性磁化炭有利于苏丹草的发芽,但不利于其成活,混施能够提高苏丹草在Cu~(2+)浓度400～800 mg/L内的成活率;(2)各土样上的苏丹草和黑麦草株高前期增长迅速(2 cm/d左右),25 d后趋于缓和。单施两性磁化炭更有利于黑麦草的生长,其中表施的作用尤为显著。(3)混施两性磁化炭能增加苏丹草在Cu~(2+)400～800 mg/L区间中的生物量,而Cu~(2+)浓度低于200 mg/L时,表施和混施两性磁化炭都有利于两种牧草生长;(4)土壤水溶态Cu~(2+)含量和酸提取态Cu~(2+)含量均保持上层高于下层的趋势,黑麦草降低土壤中Cu~(2+)含量的能力强于苏丹草。综上,在铜污染地区表施两性磁化炭并种植黑麦草对土壤的修复效果最佳。     

喀斯特地区四种草本植物及其基质的优先选择

为弄清植物对喀斯特基质的优先选择,用盆栽法研究了四种植物对喀斯特不同基质的适应性。结果表明:整体上随植物生长,基质理化性质除钾含量降低外,其他均增加;发芽率和存活率以石灰土、<1 mm砂、<1 mm砂+石灰土最高,碎石、碎石+枯落物最低,白三叶草发芽率最高、狗牙根存活率最高;株数、株高、盖度以石灰土、<1 mm砂、<1 mm砂+枯落物高而碎石、碎石+枯落物低,且盖度均呈升高趋势;生物量和叶绿素含量狗牙根和白三叶草高而芒草和高羊茅较低,生物量以石灰土、<1 mm砂、<1 mm砂+枯落物高而碎石、碎石+枯落物低,叶绿素含量以<1 mm砂+石灰土、石灰土+1 mm～5 mm砂高而碎石低;δ13C值芒草和狗牙根高而白三叶草和高羊茅低,且δ13C值与植物及生长基质有关。综上,四种植物对石灰土、<1 mm砂、<1 mm砂+枯落物适应性强,对碎石、碎石+枯落物适应性差;狗牙根和芒草适应性最强,白三叶草次之,高羊茅最差,喀斯特生态修复可优先选择芒草、狗牙根。     

河北省滨海盐碱地土壤与盐生植物养分特征的研究

对滨海盐碱地土壤和植物样品分析结果表明,生长不同盐生植物的土壤含盐量不同,以生长白刺(Nitraria sibirica Pall.)的土壤含盐量最高,达18.5 g/kg,盐地碱蓬(Suaeda salsa L.Pall.)次之,柽柳的最低。盐生植物的生长改变了土壤养分特征,4种生长盐生植物的土壤养分含量均高于光板地,土壤有机质含量增加44％以上,生长木本盐生植物白刺、柽柳(Tamarix chinensis Lour.)的土壤养分含量高于生长草本盐生植物碱蓬、碱茅(Puccinellia distans Jacq.Parl.)的土壤,且不同盐生植物养分特征不同,白刺、柽柳N和P含量均高于盐地碱蓬、碱茅,K含量则与植物耐盐特性有关。     

狗牙根与空心莲对水库消落带土壤氮磷释放影响的模拟

通过水库水位涨落室内模拟试验,探究丹江口库区消落带优势物种狗牙根和空心莲2种草本植物对土壤氮磷释放过程影响。结果表明:(1)水淹结束后(32天),空心莲子草土壤TN、TP分别降低11.75%,25.28%,狗牙根分别降低3.62%,25.77%。(2)干湿交替环境主要影响土壤中NH_4~+-N、NO_3~--N和AP的含量的变化,对土壤中的TN、TP含量的影响较小。(3)狗牙根的死亡增加土壤TN、NH_4~+-N、TP量,即不耐淹植被过滤带虽然能净化径流中N、P等污染物,但截留的污染物和植物吸收的养分随着植物体的分解再次进入水体或土壤,无法达到有效防控农业面源污染的目的。该研究为丹江口水库利用植被缓冲带防控水体富营养化提供一定理论依据。     

三峡水库消落带草本植物对若干土壤物理性质的影响

为明确三峡水库消落带典型草本植物对土壤物理性质的影响,在三峡腹地忠县石宝镇消落带选取牛鞭草(Hemarthria altissima(Poir.)Stapf et C.E.Hubb.)、扁穗牛鞭草(Hemarthria compressa(L.f.)R.Br.)、双穗雀稗(Paspalum paspaeoides(Michx.)Scribn.)和自然恢复草地狗牙根(Cynodon dactylon(L.)Pers.),以裸地为对照,对比研究了4种典型草地土壤容重(Bulk density,BD)、颗粒组成(Soil particle composition,SPC)、磁化率(Soil magnetic susceptibility,SMS)和抗剪强度(Soil shear strength,SSS)等土壤物理性质的差异。结果表明:三峡水库消落带植物及其根系的存在对土壤容重、土壤体积磁化率、颗粒组成和抗剪强度有重要影响。裸地的土壤容重要显著高于4种草地,但表层土壤体积磁化率要弱于草地;草地与裸地的土壤颗粒组成无明显差异;植物根系可以显著增强土壤抗剪强度,其中牛鞭草地0—10cm和10—20cm层土壤粘聚力分别比裸地增加319.81%和46.89%,而狗牙根草地的增加幅度分别为17.69%(0—10cm)和43.13%(10—20cm)。研究结果可以为三峡水库消落带植被恢复和水土保持提供一定依据。     

菌剂与肥料配施对矿区复垦土壤白三叶草生长的影响

采用盆栽试验研究了矿区复垦土壤菌剂与肥料的不同配施对白三叶草(Trifolium repens Linn)生长的影响。结果表明: 双接种VA 菌根真菌(Glomus mossea)和根瘤菌(Rhizobium)能显著提高白三叶草根瘤数、根瘤鲜重和固氮酶活性, 根瘤数在有机肥双接种与无机肥双接种处理之间差异不显著, 而根瘤鲜重和固氮酶活性差异显著; 肥料与各菌剂组合处理中, 有机肥双接种处理的白三叶草分枝数、干物质重最大; 在白三叶草生长40 d 和150 d 时, 双接种处理的叶片数均为各处理中最大值; 接种VA 菌根真菌、根瘤菌和双接种均可增加白三叶草根系的菌根侵染率和土壤孢子数, 总体表现为双接种处理＞接种VA 菌根真菌＞接种根瘤菌, 有机肥相应处理＞无机肥相应处理＞对照; 肥料与菌剂的配合施用可有效提高植物对土壤氮、磷、钾养分的吸收。在矿区复垦土壤上有机肥与VA 菌根真菌和根瘤菌菌剂配施能显著促进白三叶草的生长, 是提高矿区复垦土壤植被恢复中比较适宜的组合方式。     

AM真菌和水分条件对稀土尾矿堆中植物生长的影响

通过温室盆栽试验研究了不同水分处理下接种3种丛枝菌根（AM）真菌（Diversispora spurcum、Glomus aggre gatum和Glomus constrictum）后对稀土矿砂中黑麦草（Lolium perenneL.）和狗牙根（Cynodon dactylon（L.）Pers.）植物株高、地上和地下部分干重及植株内Pb和Zn含量的影响。结果表明：不同水分处理下黑麦草和狗牙根与AM真菌均有一定的结合。在干旱胁迫（W1和W2）下,接种3种AM真菌均提高了黑麦草的株高、地上和地下部分干重,其中,接种Glomus aggregatum促进作用最为显著,重度干旱胁迫（W1）处理下接种后黑麦草株高、地上和地下部分干重比对照分别提高了76.16%、202.86%和481.82%;接种Glomus constrictum显著提高了狗牙根的株高、地上和地下部分干重,W1处理下狗牙根接种后的株高、地上和地下部分干重比对照分别提高了119.17%、290.63%和247.37%。接种AM真菌的植株内Pb和Zn含量与AM真菌种类、植物品种、水分处理及重金属性质等相关,在W1处理下接种Glomus constrictum显著降低了黑麦草植株内Pb的含量,而对Zn的含量影响不大;而对于狗牙根,在W1处理下接种Glomus constrictum显著增加了其Pb和Zn的含量。此外,还测定了植物叶片丙二醛和脯氨酸含量,结果显示接种AM真菌明显降低了干旱处理下黑麦草和狗牙根叶片丙二醛和脯氨酸含量,表明接种AM真菌能有效提高植物的抗逆性。     

Crude Oil-Contaminated Soil Phytoremediation by Using Cyperus brevifolius (Rottb.) Hassk

The degradation of total oil and grease (TOG) in crude oil-contaminated soil in the presence of Cyperus brevifolius (Rottb.) Hassk was investigated in a net house study. C. brevifolius plants were transplanted in to spiked soil containing 8% (w/w) crude oil. The capability of plant for enhancing the biodegradation process was tested in pots containing fertilized and unfertilized soil over a 360-day period. Analysis of the degradation of hydrocarbon contaminants, plant growth, and biomass was conducted at 60-day interval. In the presence of contaminants, plant biomass and height were significantly reduced. The specific root surface area was reduced under the effects of crude oil. Concerning TOG content in soil, C. brevifolius could decrease up to 86.2% in TA (crude oil-contaminated soil with fertilizer) and 61.2% in TC (crude oil-contaminated soil without fertilizer). In the unvegetated pots, the reduction of TOG was 13.7% in TB (crude oil-contaminated soil with fertilizer) and 12.5% in TD (crude oil-contaminated soil without fertilizer). However, biodegradation was significantly more in vegetated pots than in unvegetated pots (p?=?0.05). The addition of fertilizer had positive effect on TOG degradation in the presence of C. brevifolius compared to the unfertilized treatments. Thus, there was evidence of C. brevifolius enhancing the biodegradation of crude oil in soil under the conditions of this experiment.     

Rhamnolipids Increase the Phytotoxicity of Diesel Oil Towards Four Common Plant Species in a Terrestrial Environment

The study focused on assessing the influence of rhamnolipids on the phytotoxicity of diesel oil-contaminated soil samples. Tests evaluating the seed germination and growth inhibition of four terrestrial plant species (alfalfa, sorghum, mustard and cuckooflower) were carried out at different rhamnolipid concentrations (ranging from 0 to 1.200?mg/kg of wet soil). The experiments were performed in soil samples with a different diesel oil content (ranging from 0 to 25?ml/kg of wet soil). It was observed that the sole presence of rhamnolipids may be phytotoxic at various levels, which is especially notable for sorghum (the germination index decreased to 41?%). The addition of rhamnolipids to diesel oil-contaminated soil samples contributed to a significant increase of their phytotoxicity. The most toxic effect was observed after a rhamnolipid-supplemented diesel oil biodegradation, carried out with the use of a hydrocarbon-degrading bacteria consortium. The supplemention of rhamnolipids (600?mg/kg of wet soil) resulted in a decrease of seed germination of all studied plant species and an inhibition of microbial activity, which was measured by the 2,3,5-triphenyltetrazolium chloride tests. These findings indicate that the presence of rhamnolipids may considerably increase the phytotoxicity of diesel oil. Therefore, their use at high concentrations, during in situ bioremediation processes, should be avoided in a terrestrial environment.     

Selective enrichment of a pyrene degrader population and enhanced pyrene degradation in Bermuda grass rhizosphere

Rhizosphere soil has a more diverse and active microbial community compared to nonvegetated soil. Consequently, the rhizosphere pyrene degrader population (PDP) and pyrene degradation may be enhanced compared to nonvegetated bulk soil (NVB). The objectives of this growth chamber study were to compare (1) Bermuda grass (Cynodon dactylon cv. Guymon) growth in pyrene-contaminated and noncontaminated soils and (2) pyrene degradation and PDP among NVB, Bermuda grass bulk (BB), and Bermuda grass rhizosphere soil (BR). Soils were amended with pyrene at 0 and 500 mg kg^–1, seeded with Bermuda grass, and thinned to two plants per pot 14 days after planting (DAP). Pyrene degradation was evaluated over 63 days. The PDP was enumerated via a most probable number (MPN) procedure at 63 DAP. Bermuda grass root growth was more sensitive to pyrene contamination than shoot growth. Pyrene degradation followed first-order kinetics. Pyrene degradation was significantly greater in BR compared to BB and NVB with rate constants of 0.082, 0.050, and 0.052 day^–1, respectively. The PDPs were 8.01, 7.30, and 6.83 log₁₀ MPN g^–1 dry soil for BR, BB, and NVB, respectively. The largest PDP was in soil with the most rapid pyrene degradation. These results indicate that Bermuda grass can grow in pyrene-contaminated soil and enhance pyrene degradation through a rhizosphere effect.     

水土保持边坡固化植草技术研究

通过建立4种形式的边坡植草护坡处理试验小区,并对每种处理各设2组重复试验小区,对边坡防护效果及草籽出芽生长情况进行对比试验。研究结果表明,结合土壤固化剂和撒播草籽进行边坡表土处理后,草籽能够正常萌芽及生长,而且边坡表土层的抗冲刷能力明显增强,坡面侵蚀细沟显著减少。实践证明,边坡固化植草是一种行之有效的护坡绿化技术方法。     

植被混凝土基材2种草本植物根-土复合体直剪试验研究

通过在植被混凝土基材上对狗牙根和紫花苜蓿2种有代表性的草本植物进行样地种植和室内直剪试验,分析植被混凝土基材上不同深度根-土复合体抗剪强度的分布规律,对比基材空白样地相应深度的抗剪强度,证实和量化了草本植物根系增强土壤抗剪切强度的作用。试验表明:根-土复合体在0-10cm土层内摩擦角变化不明显,粘聚力随深度先增大后减小;与基材空白样样地相比,根-土复合体内摩擦角变化不大,粘聚力变化显著,狗牙根粘聚力最大增幅为129.4%,紫花苜蓿粘聚力最大增幅为77%;狗牙根根-土复合体抗剪强度比同期生长的紫花苜蓿根-土复合体的抗剪强度高。     

亚麻荠根系分泌物对胡麻和藜种子萌发及幼苗生长的影响

为了探究亚麻荠根系分泌物对胡麻和杂草藜的化感作用，采用水培法观察了亚麻荠根系分泌物对胡麻和藜种子萌发与幼苗生长的影响。结果表明，亚麻荠根系分泌物对胡麻和藜种子的萌发具有抑制作用，且抑制作用随着处理浓度的增加而增强。亚麻荠根系分泌物对胡麻根长、根鲜重、苗鲜重具有抑制作用，在低处理浓度时对胡麻苗高具有促进作用，在中、高处理浓度时抑制作用较小；对杂草藜幼苗生长具有抑制作用，但抑制作用较小。综合分析，亚麻荠根系分泌物在低处理浓度时对胡麻生长的抑制作用小于对藜的抑制作用，在中、高处理浓度时大于对藜的抑制作用。     

Crude extract of Astragalus mongholicus root inhibits crop seed germination and soil nitrifying activity

Astragalus mongholicus has been of medicinal use within the traditional Chinese system for centuries. However, little information is available on its allelopathic effects on other crop plants and soil biochemical properties. Field experiment showed that the extracted residues of A. mongholicus root inhibited seed germination of wheat. Inhibition of seed germination was further confirmed in laboratory using the same crude extract. When the crude extract was applied to soil at various rates and incubated for 30 days, soil urease activity and denitrifying enzyme activity were significantly increased while soil nitrification rate was significantly decreased at 10% amendment rate as compared to the control. Soil respiration rate was significantly increased by the crude extract when measured at the start of incubation but returned to basal levels after 30 days of incubation. The crude extract supplemented to NB medium significantly decreased the colony numbers of Agrobacterium tumefaciens C58, Paraccocus denitrificans and soil bacteria. The stimulating effects of crude extract observed in the amended soil was attributed to the easily-available carbohydrates in the extract, which might served as external energy sources for heterotrophic microbial activities. It was concluded that A. mongholicus contained some compounds that inhibited seed germination, soil nitrification and bacterial growth in general. Possible links between allelochemicals responsible for the inhibitory effects observed in the present study and the medically bioactive compounds are discussed based on information reported in other fields. Further work is needed to specify and verify the allelochemicals produced by this herbal plant.     

石油对翅碱蓬生长及生理特性的影响

通过盆栽试验,测定不同石油浓度下翅碱蓬的生长生理指标及土壤中石油含量的变化,研究石油对翅碱蓬萌发、生长、生理特性和抗氧化酶系统的影响及翅碱蓬对土壤中石油的降解。结果表明,随着石油含量的升高,翅碱蓬种子发芽率、苗高、苗重和苗中叶绿素、粗蛋白含量逐渐下降,电导率上升,石油浓度在5000mg.kg-1以上,影响显著。石油对翅碱蓬糖的合成有明显抑制作用。当石油浓度为1000~5000mg.kg-1时,翅碱蓬抗氧化酶能够快速、长效地提高活性来抵御逆境,使其不受到伤害或减轻伤害,可溶性蛋白保持在高水平;当石油浓度达到10000mg.kg-1时,抗氧化酶系统迅速作出反应,酶活性急剧提高,但因毒性超出了其可以承受的范围,而无法维持较长时间,随后会降至对照组以下,同时可溶性蛋白也急剧下降,仅为对照组的9。石油浓度为1000~5000mg.kg-1时,石油去除率在63.53~83.21,达到10000mg.kg-1时,则下降到40.14。     

Sensitivity Studies of the Common Bean (Vigna unguiculata) and Maize (Zea mays) to Different Soil Types from the Crude Oil Drilling Site at Kutchalli, Nigeria (7 pp)

Background, Aims and Scope   The economic growth that Nigeria has enjoyed as a result of oil revenue has its drawback through exposure of people in the oil producing areas to environmental contamination, due largely to the increase in the movement of oil. Activities associated with oil well drilling on agricultural lands have led to serious economic losses on the communities affected. The local people in most of these communities are peasants who do not know how to react to drilling wastes or polluted fields where they have their crops. A case under study is the Kutchalli oil drilling area. Methods   Waste pit soil from drilling waste dumps in Kutchalli oil drilling area was tested whole and in combinations with 'clean' soil for their abilities to support plant growth and development in common bean (Vigna unguiculata) and maize (Zea mays). Seed germination, plant height, leaf area, biomass accumulation, respiratory activity as well as soil chemical analysis were used to access the ability of waste pit soil to support plant growth and development in the test plants. Results   Discussion and Conclusions. Waste pit soil completely inhibited the germination of bean and maize seeds. Waste pit soil in combinations with different proportions of Kutchalli soil gave growth (germination, height of plants, number of leaves, leaf area, etc.) values that were inferior to the control soil (Kutchalli) and the independent control soil (Monguno). Seeds planted in the test soil combinations containing waste pit soil showed significantly low respiratory activity. Waste pit soil seems to be toxic to plant growth and development. Drilling mud in combination with native Kutchalli soil significantly enhanced plant growth and development. Recommendations and Outlook   The seed germination, growth and development inhibition by waste pit soil suggests its toxicity. We want to suggest the need for strict control and monitoring of waste pit soil in oil drilling sites.     

两株PGPR对豇豆苗期生长及土著细菌群落的影响

以扬豇40为材料,研究了植物根际促生菌Pseudomonas chlororaphis RA6和Bacillus pumilus WP8对豇豆种子出苗及幼苗生长的作用,评价浸种及拌土处理的差异,揭示一段时间内,两株植物根际促生菌（PGPR）在土壤中的行为特征及其对土著细菌群落结构的影响。结果表明：PGPR对豇豆的促生作用因接种方式、接种量的不同而不同。WP8、RA6浸种处理的出苗率分别比对照提高14.29%和9.52%（P〈0.05）;15 d时的株高分别比对照提高14.39%和10.40%（P〈0.05）;茎叶干物重分别比对照增加19.69%和17.71%（P〈0.05）。WP8、RA6低剂量拌土处理（104cfu·g-1soil,以下简作＂低拌处理＂）各指标与对照相比,均无显著差异（P〉0.05）。WP8、RA6中剂量拌土处理（106cfu·g-1soil,以下简作＂中拌处理＂）出苗率和株高均比对照提高,但未达显著差异（P〉0.05）;茎叶干物重分别比对照增加12.71%和18.59%（P〈0.05）。WP8、RA6高剂量拌土处理（108cfu·g-1soil,以下简作＂高拌处理＂）出苗率分别比对照提高9.52%和14.29%（P〈0.05）;15 d时的株高分别比对照提高6.37%和7.64%（P〈0.05）;茎叶干物重分别比对照增加27.37%和20.43%（P〈0.05）。DGGE指纹图谱分析结果显示：各处理在15 d和45 d时,除WP8浸种处理外,其余土壤微生物群落多样性和对照均已发生明显变化,随时间推延,RA6菌株在土壤中优势地位更趋明显,表现在45 d时仍可明显检测到;WP8在土壤中存活时间不长,但拌土处理改变了土著细菌的群落结构。推测WP8的促生作用很可能与土著微生物群落的变化有关。