丁德馨,成 浩,劉晶晶,董 雪,李艾書,譚國熾,馬建洪,張 輝,王永東,胡 南*

交流電場(chǎng)與sp.A-2耦合對(duì)博落回修復(fù)鈾污染土壤的強(qiáng)化作用

丁德馨1,成 浩1,劉晶晶2,董 雪2,李艾書2,譚國熾2,馬建洪1,張 輝1,王永東2,胡 南1*

(1.南華大學(xué),鈾礦冶生物技術(shù)國防重點(diǎn)學(xué)科實(shí)驗(yàn)室,湖南 衡陽 421001；2.南華大學(xué),極貧鈾資源綠色開發(fā)技術(shù)湖南省重點(diǎn)實(shí)驗(yàn)室,湖南 衡陽 421001)

通過盆栽試驗(yàn)研究了交流電場(chǎng)(AC)與sp.A-2(A-2)真菌耦合對(duì)博落回(P)的生物量、富集鈾(U)性能、酶活性以及根際土壤中有機(jī)酸含量、生物可利用態(tài)鈾、根際微生物群落結(jié)構(gòu)的影響.結(jié)果表明,在鈾(U)污染土壤中,與AC+P+U、A-2+P+U和P+U相比,AC+A-2+P+U組博落回的鮮重、株高、總干重分別升高了10.67%～45.76%、26.87%～92.02%和61.99%～159.98%;總超氧化物歧化酶(T-SOD)和過氧化氫酶(CAT)含量分別提高了41.24%～133%和15.35%～63.63%;根際土壤中草酸顯著增加了13.03%～157.09%;與A-2+P+U和P+U組相比,AC+A-2+P+U組土壤中生物可利用態(tài)鈾分別提高了12.5%和28.57%.在AC+A-2+P+U組,植物根際土壤中存在大量的鐮刀型菌()真菌屬和酸桿菌屬()等細(xì)菌菌屬,且鐮刀型菌屬()占比最高,與AC+P+U、A-2+P+U、P+U和A-2+U組相比,分別提高了16.67%、81.03%、299.23%和374.47%.AC和A-2耦合強(qiáng)化博落回修復(fù)鈾污染土壤的可能機(jī)理包括AC提高了鈾在土壤中的流動(dòng)性,增加了植物根部與鈾的接觸,促進(jìn)了鈾的富集;AC刺激了博落回的生理活性,增大了博落回的生物量,提高了抗氧化酶活性,使博落回對(duì)鈾的耐受性增強(qiáng);AC刺激了A-2真菌和酸桿菌屬()的生長(zhǎng),使其比例增大,從而產(chǎn)生大量的有機(jī)酸,與鈾形成螯合物,降低了鈾對(duì)植物的脅迫作用,提高了生物可利用態(tài)鈾的占比,促進(jìn)了博落回對(duì)鈾的富集.AC與A-2真菌耦合對(duì)P修復(fù)鈾污染土壤有顯著的強(qiáng)化作用,是一種有潛在應(yīng)用前景的強(qiáng)化方法.

交流電場(chǎng)；sp.A-2真菌；博落回；植物修復(fù)；鈾污染土壤

鈾礦采冶產(chǎn)生的鈾尾礦、鈾廢水導(dǎo)致了土壤的鈾污染.鈾污染土壤中的鈾,極易通過食物鏈進(jìn)入人體,由于鈾具有放射毒性和重金屬毒性,對(duì)人體健康產(chǎn)生較大威脅.因此,鈾污染土壤的修復(fù),是環(huán)境保護(hù)領(lǐng)域亟需開展的工作.

過去幾十年內(nèi),已經(jīng)提出了鈾污染土壤的物理、化學(xué)和生物修復(fù)法.物理修復(fù)法如覆土法、客土法等,成本高而且修復(fù)效果不佳[1-2].化學(xué)修復(fù)法如土壤淋洗法,會(huì)改變土壤的理化性質(zhì)[3-4].生物修復(fù)法如植物修復(fù),成本低、綠色環(huán)保且無二次污染,是被認(rèn)為最具潛力的修復(fù)方式[5],然而,由于大部分植物的生物量小、富集量低,導(dǎo)致了植物修復(fù)的效率低[6].目前修復(fù)重金屬污染土壤的微生物-植物聯(lián)合修復(fù)技術(shù)、電場(chǎng)-植物聯(lián)合修復(fù)技術(shù)、電場(chǎng)-微生物聯(lián)合修復(fù)技術(shù),都存在一定的缺陷.微生物修復(fù)是一種綠色環(huán)保、廉價(jià)、對(duì)土壤理化性質(zhì)擾動(dòng)小的修復(fù)方法[7],但在處理大面積、高濃度污染土壤時(shí),存在修復(fù)時(shí)間長(zhǎng)、效率低等問題;電動(dòng)修復(fù)是一種高效、可行的鈾污染土壤修復(fù)技術(shù),但存在能耗高、成本過大、土壤酸堿化等問題[8-9].已有研究[10]發(fā)現(xiàn)采用耐鈾微生物sp.A-2菌能夠提高植物的生物量、抗氧化能力、提高根際土壤中植物可利用態(tài)鈾的比例.研究表明,交流電場(chǎng)不僅能夠有效加強(qiáng)重金屬在土壤中的移動(dòng)性,提高植物對(duì)重金屬的吸收,而且也對(duì)微生物的生理特性產(chǎn)生了刺激作用,從而提高微生物的新陳代謝,提高植物的生物量、促進(jìn)土壤中金屬離子的遷移[11-12].因此,在植物修復(fù)鈾污染的土壤中,同時(shí)加入交流電場(chǎng)和耐鈾微生物,能夠有效地提高植物對(duì)鈾污染土壤的修復(fù)效率.

本文采用盆栽試驗(yàn)研究交流電場(chǎng)和sp.A-2真菌的耦合對(duì)博落回的生物量、富集U性能、酶活性以及根際土有機(jī)酸、生物可利用態(tài)鈾、根際微生物群落結(jié)構(gòu)的影響,揭示電場(chǎng)與sp.A-2真菌耦合強(qiáng)化博落回修復(fù)鈾污染土壤的機(jī)理,從而提出交流電場(chǎng)與sp.A-2真菌耦合強(qiáng)化博落回修復(fù)鈾污染土壤的方法.

1 材料與方法

1.1 試驗(yàn)材料

1.1.1 試驗(yàn)土壤 土壤取于南華大學(xué)校內(nèi)西山山腳,該土壤與我國南方某尾礦庫周邊地區(qū)的土壤屬于同一種類型,且理化性質(zhì)一致,因此,可被用來作為鈾尾礦庫周邊區(qū)域的模擬供驗(yàn)土壤[13-14].根據(jù)鈾尾礦庫周邊污染土壤中鈾含量及有關(guān)文獻(xiàn)[15]來設(shè)置土壤中鈾的濃度為30mg/kg.具體操作如下:(1):將土壤和粗沙按2:1的質(zhì)量比混勻得到3kg的供試土壤,將其滅菌2h;(2):把配制好的六水硝酸鈾酰標(biāo)準(zhǔn)液分2次均勻地添加到步驟(1)中,攪拌均勻;(3)將步驟(2)中配置好的含鈾土壤裝入到花盆中,其土層厚度為18cm,用薄膜封住花盆口,定期澆定量的滅菌水并重新混勻,使土壤的含水率保持在65%.放于溫室大棚中平衡1個(gè)月,經(jīng)檢測(cè),土壤的理化性質(zhì)如表1.

表1 土壤理化性質(zhì)

1.1.2 試驗(yàn)植物 本試驗(yàn)所用植物為罌粟科類-博落回,是一種多年生草本植物,由Li等[16]對(duì)鈾尾礦庫周圍的植物進(jìn)行調(diào)查采樣分析后,發(fā)現(xiàn)博落回對(duì)鈾具有較強(qiáng)的富集效果.試驗(yàn)中所用的博落回種子購買于衡陽市花鳥市場(chǎng),具體操作處理如下:先將種子浸泡在1%(質(zhì)量分?jǐn)?shù))的次氯酸鈉溶液中,消毒0.5h,再用去離子水沖洗種子2～3次,其次將清洗干凈的種子放在去離子水中浸泡10h,然后將種子濾出撒在滅菌的營(yíng)養(yǎng)土中,放于溫室大棚10～15d左右,等到長(zhǎng)出幼苗.待其生長(zhǎng)穩(wěn)定后,挑選生長(zhǎng)一致的幼苗用于試驗(yàn).

1.1.3 試驗(yàn)真菌 本試驗(yàn)所用微生物為sp.A-2鐮刀型真菌,在CDA固體培養(yǎng)基上,菌落正面凸起呈絮狀且為白色;菌落反面為淡黃色,隨著時(shí)間增加,菌落顏色逐漸加深;具有耐鈾、產(chǎn)酸、提高植物生物量和修復(fù)效率的功能[10].

1.2 試驗(yàn)方法

1.2.1 試驗(yàn)設(shè)計(jì) 盆栽實(shí)驗(yàn)在衡陽市南華大學(xué)西山溫室大棚中進(jìn)行,大棚溫度維持在25 ℃左右,相對(duì)濕度為55%～75%,16h/8h的光照(150mmol/ (m2.s)).結(jié)合之前的預(yù)實(shí)驗(yàn)和相關(guān)文獻(xiàn),選擇耐鈾微生物-sp.A-2真菌,電場(chǎng)為1V/cm的交流電場(chǎng)強(qiáng)度,植物為多年生博落回,電極材料為石墨電極棒.具體操作如下:將1.1.2中生長(zhǎng)一致的幼苗,栽種到花盆中,待幼苗生長(zhǎng)穩(wěn)定一段時(shí)間后,把培養(yǎng)好的sp.A-2真菌接種到博落回根部,待植物生長(zhǎng)3個(gè)月時(shí),將電極垂直插入到離博落回同等距離(植物在中間,兩根電極位于植物兩邊,電極間距為16cm,在土壤中的深度為18cm)的土壤中,開始通電,24h/d,持續(xù)4周后,收獲植物.實(shí)驗(yàn)設(shè)置12個(gè)處理組,每組共有3個(gè)平行樣,具體試驗(yàn)分組如表2.

表2 試驗(yàn)分組

注:AC表示交流電場(chǎng)、A-2表示sp.A-2真菌、P表示博落回、U表示鈾.

1.2.2 植物生物量的測(cè)定 用自來水沖洗掉已收割植物的地上和地下部分表面上殘留的土壤、灰塵及鈾等雜質(zhì)后,用去離子水沖洗2～3次,再次將沖洗好的地上和地下部分分別放在20mmol/L的乙二胺四乙酸二鈉溶液中浸泡0.5h,使得植物表面殘余的鈾以絡(luò)合物的形式得以去除,并用吸水紙吸干植物表面的水分,稱重即可得到鮮重[17].將植物樣品放于105℃的干燥箱中殺青0.5h后,調(diào)節(jié)溫度至70℃直到烘至恒重,冷卻后稱其質(zhì)量即為干重,將烘干后的植物樣品放入馬弗爐中,逐漸升溫至550℃,灰化6h,冷卻取出,稱重即為灰重[18].

1.2.3 植物中鈾含量的測(cè)定 將上述1.2.2中灰化的地上、地下植物樣品,分別放于100mL燒杯中,按照濃鹽酸:濃硝酸:高氯酸=3:1:2的體積比加入到燒杯中,放在電熱爐進(jìn)行消解.消解完成后,用3%(質(zhì)量分?jǐn)?shù))熱的稀硝酸溶液定容至50mL,再用0.22μm的濾頭過濾,最后利用電感耦合等離子體質(zhì)譜儀(ICP-MS, 7700X,Agilent,USA)測(cè)地上、地下消解樣品中的鈾.

1.2.4 植物體內(nèi)相關(guān)性酶活的測(cè)定 利用南京建成生物研究所生產(chǎn)的試劑盒,測(cè)定植物地上部分的總蛋白(TP)、可溶性糖、總超氧化物歧化酶(T-SOD)、丙二醛(MDA)以及過氧化氫酶(CAT)的含量.

1.2.5 根際土壤有機(jī)酸含量的測(cè)定 將新鮮根際土壤過2mm篩,稱取5.0g置于50mL離心管中,加入10mL超純水,再置于25℃、150r/min的搖床中震蕩45min,使其充分混勻后取出,然后以5000r/min的轉(zhuǎn)速離心5min,再用0.22μm的濾頭過濾,濾液在-20℃下保存.采用離子色譜儀(萬通883)分析檢測(cè)濾液中有機(jī)酸的含量,最佳色譜條件為Metroseporganic Acid-250/7.8,5mmol/L H2SO4作為流動(dòng)相,流速為0.5mL/min,壓力為5.1MPa,總記錄時(shí)間為27min[13].6種酸的出峰順序依次為草酸、檸檬酸、酒石酸、蘋果酸、丁二酸和乳酸,檢出時(shí)間分別為8.28, 8.86, 9.42, 10.87, 13.28和13.36min.

1.2.6 土壤中鈾結(jié)合形態(tài)的測(cè)定 土壤中鈾結(jié)合形態(tài)的提取基于Tessier法[19]和BCR法[20]相結(jié)合的方法進(jìn)行.

1.2.7 根際土壤微生物群落測(cè)定 待植物生長(zhǎng)至設(shè)定周期后,取植物根部新鮮土壤,采用高通量測(cè)序分析土壤中群落結(jié)構(gòu).高通量測(cè)序由上海生工生物工程有限公司提供.細(xì)菌引物:338F-806R(5′-AC- TCCTACGGGAGGCACAGG-3′);真菌引物為: SSU0817F-1196R(5′-TTAGCATGGAATAATRRA-ATAGGA-3′).

1.2.8 數(shù)據(jù)處理與分析 試驗(yàn)結(jié)果采用3次重復(fù)試驗(yàn)結(jié)果的平均值+標(biāo)準(zhǔn)誤差表示,并采用單因素方差分析檢測(cè)不同組別均值間差異的顯著性.

2 結(jié)果與討論

2.1 不同處理模式對(duì)植物生物量的影響

如表3所示,在U污染土壤中,與AC+P+U、A-2+P+U及P+U組相比,AC+A-2+P+U處理組,博落回的鮮重、株高、總干重均顯著性(<0.05)升高,分別升高了10.67%～45.76%、26.87%～92.02%和61.99%～ 159.98%.實(shí)驗(yàn)結(jié)果表明,AC和A-2菌有利于促進(jìn)博落回的生長(zhǎng),提高博落回的的生物量[10,17],這結(jié)果與Acosta-Santoyo等[17]研究結(jié)論一致.其原因可能是在AC和A-2菌耦合作用下,一方面AC刺激了博落回的生理特性,其與博落回體內(nèi)細(xì)胞間隙液中的離子相互作用,導(dǎo)致植物細(xì)胞內(nèi)外的代謝活性變得更強(qiáng);另一方面A-2菌提高博落回體內(nèi)酶的活性,有效地緩解鈾對(duì)博落回光合系統(tǒng)的抑制作用,減輕鈾對(duì)植物葉片的損壞,從而提高植物的生物量[10].

表3 不同處理模式下植物生物量的測(cè)量結(jié)果

注:數(shù)據(jù)為平均值±標(biāo)準(zhǔn)偏差(=3),同一列不同小寫字母表示組間具有顯著差異(<0.05).

2.2 不同處理模式對(duì)博落回富集U性能的影響

表4 不同處理模式下博落回鈾富集量的測(cè)量結(jié)果

注:數(shù)據(jù)為平均值±標(biāo)準(zhǔn)偏差(=3),同一列不同小寫字母表示組間具有顯著差異(<0.05).

如表4所示,AC+P+U與P+U組相比,地上部分和地下部分鈾含量分別提高了69.17%和177.81%, A-2+P+U組與P+U組相比,地上部分和地下部分鈾含量分別提高了34.10%和79.30%,AC+A-2+P+U組與P+U組相比,地上部分和地下部分鈾含量分別提高了128.98%和436.21%,博落回對(duì)鈾的富集主要在地下部分.AC+A-2+P+U組富集系數(shù)最高為2.97,與AC+P+U、A-2+P+U和P+U組相比,分別顯著性提高了27.40%、60.34%和119.69%. AC和A-2真菌耦合,有利于強(qiáng)化博落回對(duì)鈾的富集.其原因可能是,在AC作用下,鈾酰離子在土壤中的流動(dòng)性增加,植物根系接觸到鈾酰離子的概率也隨之增加,從而提高了植物對(duì)鈾的富集量.該機(jī)理與O’Connor等[22]的研究一致,其認(rèn)為在土壤中施加電場(chǎng)后,重金屬和間隙液體會(huì)流動(dòng)起來,增加金屬離子與植物根系的碰撞概率,從而提升植物的修復(fù)效率.周麗瑋等[23]也進(jìn)一步證明了O’Connor等[22]的研究.而A-2菌能緩解鈾對(duì)植物的毒性作用[10],提高植物的耐受性.

2.3 不同處理模式對(duì)博落回體內(nèi)相關(guān)性生理指標(biāo)的影響

圖1 不同處理模式下植物體內(nèi)生理活性指標(biāo)檢測(cè)結(jié)果

不同小寫字母表示不同處理下植物體內(nèi)相關(guān)性酶含量具有顯著差異(<0.05)

如圖1所示,在U污染土壤中,與A-2+P、AC+P和P組相比,A-2+AC+P組博落回體內(nèi)T-SOD和CAT含量分別顯著(<0.05)提高了41.24%～133%和15.35%～63.63%.這說明在AC和A-2菌耦合作用下,通過改變T-SOD、CAT含量,緩解鈾脅迫對(duì)植物膜脂過氧化作用,有效阻止過多的活性氧自由基侵害細(xì)胞,在一定范圍內(nèi)平衡了細(xì)胞內(nèi)的活性氧自由基,提高了植物抗鈾耐性的能力,增強(qiáng)了植物對(duì)逆境環(huán)境的耐受性[9-10,24].

2.4 不同處理模式對(duì)根際土壤有機(jī)酸含量的影響

表5 不同處理模式下根際土壤有機(jī)酸含量測(cè)量結(jié)果

注:數(shù)據(jù)為平均值±標(biāo)準(zhǔn)偏差(=3),同一列不同小寫字母表示組間具有顯著差異(<0.05).“-”表示未檢測(cè)到.

如表5所示,在含U土壤中,與AC+P+U、A-2+P+U和P+U相比,AC+A-2+P+U組中草酸、酒石酸、蘋果酸、乳酸分別顯著性(<0.05)增加了13.03%～157.09%、23.81%～563.83%、30.75%～ 283.73%和25.62%～92.75%.本實(shí)驗(yàn)結(jié)果表明在AC和A-2菌耦合作用下,提高了土壤中有機(jī)酸的含量.在重金屬的脅迫下,植物會(huì)通過分泌有機(jī)酸來改變根際的生存狀況從而來適應(yīng)惡劣的環(huán)境.徐衛(wèi)紅等[25]將蘋果酸添加到芥菜中后,蘋果酸不僅強(qiáng)化了芥菜對(duì)鈾的吸收,而且還提高了鈾在芥菜體內(nèi)中的遷移.Shahandeh等[26]將草酸添加到印度芥菜中,最后發(fā)現(xiàn)草酸不僅提高了印度芥菜對(duì)鈾的富集量,而且也提高了轉(zhuǎn)運(yùn)系數(shù).有大量研究發(fā)現(xiàn),有機(jī)酸把土壤中碳酸鹽結(jié)合態(tài)、鐵錳氧化態(tài)以及有機(jī)結(jié)合態(tài)的鈾部分分解、解吸和轉(zhuǎn)化,通過降低植物根系周圍土壤的pH值或以螯合作用將其轉(zhuǎn)換成可交換的鈾酰離子,進(jìn)入到土壤溶液中,被植物更好的利用吸收,并使鈾由植物的地下部分向地上部分轉(zhuǎn)移,使鈾的生物有效性大大提高[27-29].

2.5 不同處理模式對(duì)土壤中鈾結(jié)合形態(tài)的影響

如圖2所示,在其他條件相同的情況下,與AC+U、A-2+P+U和P+U相比,AC+A-2+P+U組生物可利用態(tài)鈾分別提高了34.04%、12.50%和28.57%.AC+A-2+P+U組可利用態(tài)高的原因可能是在AC和A-2菌耦合的作用下,AC提高了鈾酰離子在土壤中流動(dòng)性,同時(shí)也刺激了A-2菌及土壤中其他的微生物,分泌出了大量的有機(jī)酸,而有機(jī)酸使部分碳酸鹽結(jié)合態(tài)、鐵錳氧化態(tài)發(fā)生分解,可交換態(tài)鈾的占比增加,進(jìn)入土壤溶液,從而被植物吸收[27].而這一結(jié)論與Cameselle等[30]和雷鳴等[31]研究的結(jié)果一致.Montiel-Rozas等[32]發(fā)現(xiàn)根系分泌物-小分子有機(jī)酸(如草酸、蘋果酸以及丁二酸等)會(huì)影響土壤中重金屬的生物可利用性,可促使鈾從不可利用態(tài)向潛在可利用態(tài)轉(zhuǎn)化,這可能是AC和A-2菌耦合作用增強(qiáng)博落回富集鈾的原因.

圖2 不同處理模式對(duì)土壤中鈾形態(tài)含量的檢測(cè)結(jié)果

2.6 不同處理模式對(duì)根際土壤微生物群落的影響

2.6.1 微生物豐度和多樣性分析 如表6所示,其中Coverage數(shù)值越高,說明樣品文庫覆蓋率高,數(shù)據(jù)可靠,且均在0.99以上.細(xì)菌Shannon指數(shù)的變化范圍為4.23～5.36,平均值為4.82,與A-2+P+U、AC+ P+U和P+U組比,AC+A-2+P+U組中Shannon指數(shù)偏低為4.23,此外細(xì)菌ace指數(shù)和chao指數(shù)最低,說明在AC和A-2菌耦合作用下降低了土壤中細(xì)菌的多樣性和豐度.真菌的Shannon指數(shù)變化范圍為2.30～3.88,平均值為2.99,AC+A-2+P+U組中Shannon指數(shù)、ace指數(shù)和chao指數(shù)最高,分別為3.88、141.41和140.75,表明AC和A-2菌耦合作用提高了土壤中真菌的多樣性和豐度,原因可能是在AC和A-2菌的作用下,與根系分泌物的數(shù)量和種類增多有關(guān)[34],而這些分泌物為真菌提供了更多的生長(zhǎng)所需的營(yíng)養(yǎng),所以真菌的數(shù)量會(huì)有所增加[35].此外,另有可能是在AC和A-2菌耦合作用下,引起了土壤酸堿性輕微的變化,如草酸等有機(jī)酸分泌的增加和有關(guān)土壤酶含量的變化,為微生物提供了生長(zhǎng)基質(zhì)或改善了微生物生長(zhǎng)的微環(huán)境[36],最終導(dǎo)致土壤真菌數(shù)量的增加.

表6 不同處理模式對(duì)植物根際土壤微生物多樣性指數(shù)檢測(cè)結(jié)果

2.6.2 功能性微生物群落組成分析 根際土壤中細(xì)菌的群落構(gòu)成如圖3所示,根際土壤樣品中優(yōu)勢(shì)細(xì)菌是假單胞菌屬()、羅河桿菌屬()、鞘氨醇單胞菌屬()、固氮螺菌屬()、酸桿菌屬()等.在含U土壤中,AC+A-2+P+U組與A-2+P+U、AC+P+U、P+U組相比,土壤中酸桿菌屬()、鞘氨醇單胞菌屬()的比例升高,假單胞菌屬(s)等菌屬比例降低.在施加AC和A-2菌的含U處理組中,植物對(duì)鈾富集系數(shù)和生物量都有提高,這可能是根際土壤中存在的具有耐重金屬和產(chǎn)酸功能的優(yōu)勢(shì)微生物酸桿菌()[13,37],可使土壤中可交換態(tài)鈾的濃度增大,從而促進(jìn)博落回富集更多游離的鈾酰離子[37].

圖3 根際土壤中細(xì)菌屬水平的群落構(gòu)成(物種豐度>10%)

圖4 根際土壤中真菌屬水平的群落構(gòu)成(物種豐度>10%)

根際土壤中真菌的群落構(gòu)成如圖4所示,根際土壤中優(yōu)勢(shì)真菌是鐮刀菌屬()、子囊菌綱()、子囊菌門()等.在含U土壤中,與AC+P+U、A-2+P+U、P+U、A-2+U組相比,AC+A-2+P+U組鐮刀菌屬()分別提高了16.67%、81.03%和299.23%和374.47%.鐮刀菌屬()比例升高的原因,可能是在AC作用下,刺激了博落回的代謝功能,提高了博落回的生物量,為菌屬提供了生長(zhǎng)所需的碳水化合物[10].優(yōu)勢(shì)微生物spA-2菌可以顯著提高博落回富集鈾總量(表4)的機(jī)理是,鈾污染土壤中的A-2菌分泌的小分子有機(jī)酸對(duì)土壤中的鈾具有鰲合固定和溶解釋放兩種作用.A-2菌分泌的草酸與土壤中的鈾酰離子發(fā)生螯合作用生成微溶于水的草酸鈾酰[10],從而降低鈾對(duì)植物的毒性,如圖2所示,添加A-2菌后,土壤中有機(jī)質(zhì)結(jié)合態(tài)鈾的占比顯著增加.A-2菌分泌的酒石酸可與土壤中的鈾發(fā)生螯合作用,生成鈾酰-酒石酸-二元羧酸的混合絡(luò)合物[38],使土壤中不溶態(tài)鈾轉(zhuǎn)變成可溶態(tài)鈾,如圖2所示,添加A-2菌后,土壤中碳酸鹽結(jié)合態(tài)和鐵錳氧化態(tài)鈾的占比降低,可交換態(tài)鈾的占比增加,進(jìn)入到土壤溶液,從而被植物吸收,提高植物對(duì)鈾的修復(fù)效率[10,27,39].此外,有機(jī)酸還能通過緩解氧化應(yīng)激、提升相關(guān)抗氧化酶活性以及促進(jìn)植物對(duì)營(yíng)養(yǎng)元素的吸收等多種間接方式進(jìn)一步體現(xiàn)其在植物修復(fù)中的強(qiáng)化作用[40-41].優(yōu)勢(shì)微生物子囊菌門(),如子囊菌門()下的曲霉菌屬(),以植物中的纖維素為碳源通過胞外酶的形式進(jìn)行代謝,將大分子纖維素轉(zhuǎn)化為自身生長(zhǎng)所需的營(yíng)養(yǎng)物質(zhì),同時(shí)分泌有機(jī)酸[42-44],從而鰲合鈾酰離子、緩解鈾對(duì)博落回的脅迫和提高博落回的鈾富集量.

3 結(jié)論

3.1 在AC和A-2菌的耦合作用下,博落回的鮮重、株高和總干重分別提高了10.67%～45.76%、26.87%～92.02%和61.99%～159.98%;植物地上和地下部分鈾含量分別提高了35.35%～128.98%和93.01%～436.21%,主要富集在地下部分;鈾富集總量分別提高了186.80%、249.51%和798.34%.

3.2 在AC和A-2菌耦合作用下,AC刺激了植物根系與根際微生物分泌小分子有機(jī)酸,有機(jī)酸以草酸含量最多,提高了13.03%～157.09%,接種A-2后,通過調(diào)控T-SOD、CAT的含量,使其分別提高了41.24%～133%和15.35%～63.63%,來緩解鈾對(duì)植物光合系統(tǒng)的脅迫,提高了植物抗氧化的能力,增強(qiáng)了博落回對(duì)鈾的耐受性,表現(xiàn)為博落回生物量的提高,根際土壤中生物可利用態(tài)鈾提高了12.5%～28.57%.

3.3 在AC和A-2菌耦合作用下,土壤根際微生物群落的豐度與多樣性發(fā)生了變化,使屬和酸桿菌()屬比例增加,提高博落回對(duì)鈾的耐受性和富集能力.

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Enhancement effects of the coupling between AC electric field andsp. A-2 on the remediation of uranium contaminated soil by.

DING De-Xin1, CHENG Hao1, LIU Jing-Jing2, DONG Xue2, LI Ai-Shu2, TAN Guo-Chi2, MA Jian-Hong1, ZHANG Hui1, WANG Yong-Dong2, HU Nan1*

(1.Key Discipline Laboratory for National Defense for Biotechnology in Uranium Mining and Hydrometallurgy, University of South China, Hengyang 421001, China；2.Hunan Province Key Laboratory of Green Development Technology for Extremely Low Grade Uranium Resources, University of South China, Hengyang 421001, China)., 2022,42(1)：258～266

Pot experiments were conducted to study the effects of the coupling between alternating current electric field (AC) andsp. A-2 (A-2) fungi on the biomass, uranium (U) enrichment and enzyme activity of(P), as well as the organic acid content, bioavailable uranium and microbial community structure in the rhizosphere soil. The results showed that compared with AC+P+U, A-2+P+U, and P+U groups, the fresh weight, plant height and total dry weight ofin AC+A-2+P+U group were significantly increased by 10.67%～45.76%, 26.87%～92.02% and 61.99%～159.98%, respectively, and the contents of the total superoxide dismutase (T-SOD) and catalase (CAT) were increased by 41.24%～133% and 15.35%～63.63%, respectively, and the oxalic acid was increased by 13.03%～157.09%. Compared with the A-2+P+U and P+U groups, the bioavailabluranium in soil in AC+A-2+P+U group was increased by 12.5% and 28.57%, respectively. In the AC+A-2+P+U groups, there were a large number offungi andin rhizosphere soil, and the proportion offungi was the highest. Compared with AC+P+U, A-2+P+U, P+U, and A-2+U groups, the proportion offungi in AC+A-2+P+U group was increased by 16.67%, 81.03%, 299.23% and 374.47%, respectively. The mechanisms of AC and A-2 coupling enhanced the remediation of uranium contaminated soil bymay be include that AC improved the mobility of uranium in soil, increased the contact between plant roots and uranium, and promoted the enrichment of uranium by; that AC stimulated the physiological activity and increased the biomass of, improved the activity of antioxidant enzymes, and enhanced the tolerance ofto uranium; and that AC stimulated the growth of A-2 fungi and, increased their proportion, and produced a large number of organic acids which can form chelates with uranium, reduced the stress of uranium on plants, increased the proportion of bioavailable speciation of uranium, and promoted the enrichment of uranium by. AC and A-2 coupling exhibited a significant enhancement effect on the remediation of uranium contaminated soil by, and there coupling was a promising enhancement method.

AC electric field；sp.A-2 fungi；；phytoremediation；uranium contaminated soil

X53

1000-6923(2022)01-0258-09

丁德馨(1958-),男,教授,博士,主要研究方向?yàn)殁櫟V采冶技術(shù)及相關(guān)環(huán)境問題.發(fā)表論文200余篇.

2021-04-12

國家自然科學(xué)基金資助項(xiàng)目(U1967210,11775106);湖南省科技人才托舉項(xiàng)目(2020TJ-Q03);湖南省教育廳重點(diǎn)資助項(xiàng)目(19A436)

* 責(zé)任作者, 高級(jí)實(shí)驗(yàn)師, hn12352000@163.com