周文鱗, 婁運(yùn)生

(南京信息工程大學(xué)應(yīng)用氣象學(xué)院，南京 210044)

控釋氮肥對抗除草劑轉(zhuǎn)基因水稻田土壤甲烷排放的影響

周文鱗, 婁運(yùn)生*

(南京信息工程大學(xué)應(yīng)用氣象學(xué)院，南京 210044)

采用溫室盆栽和靜態(tài)箱-氣相色譜法，研究了控釋氮肥對抗除草劑轉(zhuǎn)基因水稻和親本常規(guī)水稻稻田土壤甲烷(CH4)排放的影響。供試土壤為潴育型水稻土，氮肥種類為尿素和控釋氮肥。結(jié)果表明，與對照(尿素)相比，控釋氮肥提高了水稻分蘗數(shù)、株高、生物量及產(chǎn)量。水稻品種對CH4季節(jié)性排放規(guī)律沒有明顯影響，CH4排放通量基本表現(xiàn)為，自水稻移栽后逐漸升高，移栽后62—92 d出現(xiàn)峰值，而后逐漸降低至水稻收獲。與對照相比，控釋氮肥可顯著降低CH4排放通量和全生育期累積排放量?？钩輨┺D(zhuǎn)基因水稻稻田土壤CH4排放通量和累積排放量均顯著低于親本常規(guī)水稻。研究認(rèn)為，一次性基施控釋氮肥和種植抗除草劑轉(zhuǎn)基因水稻對有效減緩稻田甲烷排放具有重要意義。

控釋氮肥；抗除草劑轉(zhuǎn)基因水稻；甲烷；排放通量；水稻土

水稻是主要糧食作物之一，人口增加和耕地減少是影響糧食供給的主要矛盾，增施化肥是提高糧食產(chǎn)量的有效措施。氮是肥料三要素之一，氮肥施用能促進(jìn)農(nóng)作物增產(chǎn)，但其肥料利用率仍普遍較低[1]。低肥效不但造成肥料資源的浪費(fèi)，也會污染水體、土體和農(nóng)產(chǎn)品等，對生態(tài)環(huán)境和食品安全帶來不良影響[2- 3]。

稻田是CH4重要的排放源，年均排放量約為31—112 Tg CH4，占全球CH4排放總量的5%—19%[4]。施肥是影響稻田CH4排放的重要因素之一。研究表明，添加新鮮有機(jī)肥能促進(jìn)稻田CH4的排放[5]，而沼肥經(jīng)發(fā)酵處理后可明顯減少CH4的產(chǎn)生和排放[6]?；瘜W(xué)氮肥對稻田CH4排放的影響較復(fù)雜，與土壤 C/N 比、肥料的種類、施肥量和施肥方式等有關(guān)[7- 8]。

控釋氮肥可延緩氮素釋放速率，減少氮素?fù)p失并供植物持續(xù)吸收利用[9]，目前對水稻施控釋氮肥的研究主要涉及氮的吸收利用、氣態(tài)損失(如反硝化與氨揮發(fā))和水稻產(chǎn)量等方面[10- 12]，而對稻田甲烷排放方面的研究鮮有報(bào)道。轉(zhuǎn)基因水稻可提高產(chǎn)量、減少勞動(dòng)強(qiáng)度、降低成本，減少農(nóng)藥使用造成的環(huán)境污染，但其安全性尚不明確，商業(yè)化種植對生態(tài)環(huán)境及人體健康的影響備受關(guān)注和爭議。因此，開展本研究對于進(jìn)一步完善轉(zhuǎn)基因水稻在施控釋氮肥下生態(tài)風(fēng)險(xiǎn)評價(jià)的內(nèi)容具有重要的理論和實(shí)踐意義。

1 材料與方法

1.1 盆栽試驗(yàn)與管理

盆栽試驗(yàn)于2010年5月—11月在南京信息工程大學(xué)農(nóng)業(yè)氣象試驗(yàn)站(32.0°N，118.8°E)溫室內(nèi)進(jìn)行。該站地處亞熱帶濕潤氣候區(qū)，年均降水量1100 mm，年均氣溫15.6 ℃。供試土壤為潴育型水稻土，灰馬肝土屬，耕層土壤質(zhì)地為壤質(zhì)黏土，粘粒含量為26.1%，土壤pH值為6.2(1∶1土水比)，全碳、全氮的含量分別為19.4和1.45 g/kg。土壤經(jīng)自然風(fēng)干，除雜(石塊和植物殘?bào)w等)，磨碎過10目篩，混勻備用。

該試驗(yàn)為水稻品種和肥料種類雙因子試驗(yàn)，供試水稻為抗除草劑轉(zhuǎn)基因水稻(B2)和親本常規(guī)水稻(秀水63)，供試肥料為控釋氮肥(CRNF)和常規(guī)氮肥尿素(U)。試驗(yàn)采用完全區(qū)組設(shè)計(jì)，設(shè)4個(gè)處理：(1)常規(guī)水稻+常規(guī)施肥(PU)；(2)轉(zhuǎn)基因水稻+常規(guī)施肥 (TU)；(3)常規(guī)水稻+控釋氮肥(PC)；(4)轉(zhuǎn)基因水稻+控釋氮肥(TC)。每處理 3次重復(fù)，共12個(gè)盆缽。

供試控釋氮肥LPS100(N 40%)為樹脂包膜類遲釋型控釋氮肥，施后第30 天開始釋放養(yǎng)分，形成 S 型釋放曲線(CHISSO 公司，日本)。供試常規(guī)肥料為尿素(N46%)、磷酸二氫鉀(P 22.8%、K 28.7%)、氯化鉀(K 52.4%)。本試驗(yàn)各處理施用的氮磷鉀總量養(yǎng)分相等，氮(以N計(jì))、磷(以P2O5計(jì))、鉀(以K2O計(jì))肥料施用量分別為150、150和150 kg/hm2。常規(guī)氮肥50%作基肥，50%分別于分蘗和孕穗期追肥?？蒯尩始案髋枥彽牧租浄嗜炕?。水稻種子經(jīng)消毒處理后，于5月29日播種育苗，6月30日移栽，11月9日收獲。每盆缽定苗2株，盆缽直徑20 cm，高30 cm，每盆裝入土壤5 kg，試驗(yàn)期間各處理盆缽?fù)撩媸冀K保持約5 cm的水層。病蟲害防治依據(jù)實(shí)際情況進(jìn)行。

1.2 測定方法

氣體樣品的采集與分析采用靜態(tài)箱-氣相色譜法。在水稻生長期，采樣間隔為10 d，采樣時(shí)間為當(dāng)日9:00—11:00。PVC靜態(tài)箱底面半徑為8.5 cm，箱高120 cm，箱體直徑與盆缽內(nèi)徑相吻合。采樣時(shí)將PVC靜態(tài)箱與盆缽相扣，通過淹水層液封保證靜態(tài)箱氣密性。封箱后分別于0、15、30 min，用帶有三通閥的針筒采集50 mL氣樣，將所采氣樣注入事先抽成真空的氣袋中。同時(shí)，記錄箱溫、氣溫及土溫(5 cm 和10 cm)。所采氣樣用帶有氫火焰離子檢測器(FID)的氣相色譜儀(GC-9890，上海)檢測CH4濃度。CH4排放通量計(jì)算公式如下：

F=ρ×H×T/(T+t)×60×dc/dt

式中，F(xiàn)為CH4排放通量(mg m-2h-1)；ρ為標(biāo)準(zhǔn)狀態(tài)下CH4氣體密度(0.714 kg/m3)；H為采樣箱氣室高度；T為理想氣體標(biāo)準(zhǔn)狀態(tài)下的空氣氣溫273.15 K；t為采樣時(shí)箱內(nèi)平均溫度；dc/dt為箱內(nèi)目標(biāo)氣體濃度隨時(shí)間變化的回歸曲線斜率。積分求得不同生育階段和全生育期CH4累積排放量。

1.3 數(shù)據(jù)統(tǒng)計(jì)分析

試驗(yàn)數(shù)據(jù)用Excel 2003進(jìn)行整理與繪圖，用統(tǒng)計(jì)軟件SPSS 13.0進(jìn)行差異顯著性檢驗(yàn)和重復(fù)測量的多因素方差分析。

2 結(jié)果

2.1 控釋氮肥對水稻生長的影響

表1表明，與等氮尿素分施相比，一次性基施控釋氮肥提高了水稻分蘗數(shù)、株高、生物量及產(chǎn)量，轉(zhuǎn)基因水稻增產(chǎn)23.99%、親本常規(guī)水稻增產(chǎn)9.66%。水稻生長要素的交互分析表明，水稻品種對分蘗數(shù)及株高的影響達(dá)顯著水平，肥料種類對株高、生物量和產(chǎn)量的影響達(dá)顯著水平，水稻品種×肥料種類的互作效應(yīng)對株高和地上部生物量達(dá)顯著水平(P<0.05)。

表1 控釋氮肥對水稻生長及產(chǎn)量的影響

水稻分蘗數(shù)測定在最大分蘗期；株高和產(chǎn)量測定在完熟期；地上部和根系干重測定在抽穗期；表中數(shù)據(jù)為3次重復(fù)平均值±標(biāo)準(zhǔn)誤差；* 表明與對照相比達(dá)到顯著水平(P< 0.05); TU:轉(zhuǎn)基因水稻+常規(guī)施肥Transgenic rice + urea；PU:常規(guī)水稻+常規(guī)施肥Parental rice + urea；TC:轉(zhuǎn)基因水稻+控釋氮肥Transgenic rice + CRNF；PC:常規(guī)水稻+控釋氮肥Parental rice + CRNF

2.2 控釋氮肥對水稻CH4排放通量的影響

由圖1可見，與對照相比，一次性基施控釋氮肥下稻田CH4排放的季節(jié)性變化并不相同。在水稻生育期內(nèi)，各處理CH4排放通量的變化趨勢均表現(xiàn)為，自水稻移栽后，逐漸升高，在生殖生長期(62—92 d)出現(xiàn)峰值，然后逐漸降低至水稻收獲，說明一次性基施控釋氮肥未改變CH4排放通量的季節(jié)性變化趨勢。但是，不同水稻品種稻田CH4排放通量峰值出現(xiàn)的時(shí)間和大小存在差異。轉(zhuǎn)基因水稻的主峰值低于親本常規(guī)水稻，出現(xiàn)在移栽后的72—82 d，而親本常規(guī)水稻則出現(xiàn)在移栽后的82—92 d。分蘗期后(62—111 d)，一次性基施控釋氮肥處理的CH4排放通量顯著低于等氮尿素分施處理(P<0.05)。

圖1 控釋氮肥對CH4季節(jié)性排放的影響Fig.1 Effect of CRNF (controlled-release nitrogen fertilizer) on seasonal variation of CH4 flux under greenhouse conditions

對試驗(yàn)數(shù)據(jù)進(jìn)行重復(fù)測量多因素方差分析，其中Mauchly球形檢驗(yàn)P=0.000，采用Greenhouse-Geisser校正。方差分析結(jié)果表明，不同采樣時(shí)間之間達(dá)顯著性差異(F=194.071，P=0.000)，時(shí)間與肥料種類(F=76.102，P=0.000)、時(shí)間與水稻品種(F=47.166，P=0.000)，以及時(shí)間與肥料種類、水稻品種之間(F=32.303，P=0.000)均存在交互效應(yīng)。組間效應(yīng)的檢驗(yàn)結(jié)果也說明，肥料種類、水稻品種、及兩者之間的互作效應(yīng)均有統(tǒng)計(jì)學(xué)意義(P<0.05)。由此可見，稻田甲烷排放隨時(shí)間的變化，以及時(shí)間因素作用隨肥料種類、水稻品種和肥料種類×水稻品種的互作效應(yīng)的不同而不同，肥料種類、水稻品種及兩者的互作效應(yīng)對稻田甲烷排放的影響顯著。

2.3 控釋氮肥對水稻不同生育期CH4累積排放量的影響

從水稻不同生育期稻田CH4累積排放量來看(表2)，以水稻灌漿至完熟期的累積排放量較高，占全生育期累積排放量的26.21%—53.94%，但不同處理間存在差異。與等氮尿素分施相比，一次性基施控釋氮肥顯著降低抽穗—揚(yáng)花期、灌漿—完熟期及全生育期稻田CH4累積排放量(P<0.05)，但轉(zhuǎn)基因水稻分蘗期和親本水稻分蘗期與拔節(jié)—孕穗期除外。

表2 控釋氮肥下水稻不同生育期CH4累積排放量的變化

表中數(shù)據(jù)為平均值±標(biāo)準(zhǔn)誤差；同列中標(biāo)記不同字母者代表處理間差異達(dá)顯著水平(P<0.05);TU:轉(zhuǎn)基因水稻+常規(guī)施肥Transgenic rice + urea；PU:常規(guī)水稻+常規(guī)施肥Parental rice + urea；TC:轉(zhuǎn)基因水稻+控釋氮肥Transgenic rice + CRNF；PC:常規(guī)水稻+控釋氮肥Parental rice + CRNF

不同水稻品種對各生育期CH4累積排放量有一定影響(表2)。一次性基施控釋氮肥下，各生育期轉(zhuǎn)基因水稻的CH4累積排放量低于常規(guī)水稻，以拔節(jié)—孕穗期、抽穗—揚(yáng)花期和灌漿—完熟期以及全生育期較為明顯，差異達(dá)顯著水平(P<0.05)。

3 討論

稻田CH4的排放具有明顯的季節(jié)性變化，但因水分狀況、溫度和肥料類型及其相互作用而異。本試驗(yàn)中，水稻移栽后(生長初期)的CH4排放通量較低，原因在于盆栽用土經(jīng)過篩去除了前作根茬等有機(jī)底物，使產(chǎn)CH4菌缺少賴以生存和產(chǎn)生CH4的物質(zhì)基礎(chǔ)，且水稻植株較小，根系及植株通氣組織均不發(fā)達(dá)，CH4排放的植株傳輸效率較低所致。隨著水稻生長，根系分泌物和脫落物逐漸增加，水稻土產(chǎn)CH4潛力不斷提高，導(dǎo)致CH4排放通量逐漸升高并出現(xiàn)峰值。

近年來，有關(guān)控釋肥對水稻生長的影響已有較多報(bào)道。研究表明，一次性基施控釋氮肥能提高水稻分蘗期生物量[13]、生育后期的根干重、根長和根系吸收面積[14]、以及通過增加單位面積有效穗和每穗結(jié)實(shí)粒數(shù)實(shí)現(xiàn)水稻增產(chǎn)[15]。本試驗(yàn)中，與尿素相比，控釋氮肥可提高水稻分蘗數(shù)、生物量和產(chǎn)量(表1)，但控釋氮肥顯著降低了水稻土CH4的排放通量和累積排放量(圖1，表2)。這一發(fā)現(xiàn)與一般認(rèn)識相左，即水稻生物量、分蘗數(shù)與水稻土甲烷排放量一般呈正相關(guān)[16]。有研究表明，控釋氮肥能提高水稻生育中、后期功能葉和根系中的SOD(superoxide dismutase)、POD(peroxidase)等活性氧清除酶的活性，降低MDA(malonaldehyde)含量，從而延緩葉、根的衰老，提高水稻產(chǎn)量[14,17]。SOD、POD 等酶具有清除生物體內(nèi)氧自由基的功能，保護(hù)生物體內(nèi)免受自由基損害[18]。Keppler等[19]報(bào)道，有別于傳統(tǒng)甲烷生物源，在有氧條件下很多植物本身可產(chǎn)生并釋放甲烷?；钚匝踝杂苫?reactive oxygen species，ROS)可能在植物源甲烷的生成中起著關(guān)鍵作用。有報(bào)道指出，凡是引起ROS累積的脅迫條件(UV輻射、干旱、營養(yǎng)缺乏等)都可能刺激其與果膠等物質(zhì)中的甲氧基作用，繼而產(chǎn)生甲烷[18,20- 21]。本研究中，推測控釋氮肥提高了水稻體內(nèi)的活性氧清除酶的活性，清除了ROS的累積，減少了植株源甲烷產(chǎn)生的可能。稻田甲烷排放取決于其產(chǎn)生、氧化和傳輸?shù)木C合效應(yīng)。根系能將來自葉片吸收和光合作用產(chǎn)生的氧氣釋放到土壤中，形成根際微域“氧化圈”。而控釋氮肥能改善根系形態(tài)和延緩根系衰老[14]，由此推測本研究中控釋氮肥處理下良好的根系形態(tài)和活性提高了水稻根系的泌氧能力；而厭氧環(huán)境里，根系泌氧的減少誘發(fā)反硝化、鐵硫還原反應(yīng)導(dǎo)致根系發(fā)育不良甚至腐爛，又為甲烷的產(chǎn)生提供了豐富的底物。所以，尿素處理下水稻根系泌氧的“此消”和根系衰老腐爛的“彼長”導(dǎo)致控釋氮肥下的水稻甲烷排放弱于普通尿素處理。另外，控釋氮肥持續(xù)良好的供氮能力，促進(jìn)了抽穗后光合產(chǎn)物的形成和抽穗前葉鞘和莖稈中臨時(shí)性貯存的碳水化合物向穗部的轉(zhuǎn)移[22]，使更多光合產(chǎn)物流向有機(jī)物積累，降低甲烷的排放。有關(guān)控釋氮肥降低甲烷排放的機(jī)制，還需要通過試驗(yàn)進(jìn)一步研究。

水稻品種在稻田甲烷排放中起著非常重要的作用[23]。本研究中，轉(zhuǎn)基因水稻甲烷排放量顯著低于親本常規(guī)水稻(表2)，說明種植抗除草劑轉(zhuǎn)基因水稻對于減緩稻田甲烷排放有積極作用。其原因在于，一方面與轉(zhuǎn)基因水稻的抗逆性和生長能力不同于親本常規(guī)水稻有關(guān)[24]；另一方面轉(zhuǎn)基因及其親本不同基因型水稻的根際微生態(tài)環(huán)境有所不同。有研究發(fā)現(xiàn)，高產(chǎn)水稻因其根系發(fā)達(dá)，通氣組織發(fā)育好，相應(yīng)的根系徑向泌氧量ROL和根際土壤氧氣含量高于低產(chǎn)水稻[25]。3種不同基因型水稻水培試驗(yàn)中，通過15N 稀釋技術(shù)和10 μm的氧電極原位測定，發(fā)現(xiàn)高產(chǎn)水稻品種根際硝化強(qiáng)度和根表氧氣含量顯著高于低產(chǎn)品種[26]。不同的根系分泌物組成和數(shù)量、不同的根系泌氧能力和通氣組織影響并形成了轉(zhuǎn)基因及其親本常規(guī)水稻稻田甲烷的排放差異。

因此，在施控釋氮肥下，通過進(jìn)一步試驗(yàn)探明水稻根系分泌物的數(shù)量和組成，檢測水稻根際土壤產(chǎn)甲烷菌和甲烷氧化菌的變化，將有助于進(jìn)一步闡明施控釋氮肥降低水稻土甲烷排放，以及抗除草劑轉(zhuǎn)基因水稻降低甲烷排放量的原因。研究認(rèn)為，施用控釋氮肥和種植抗除草劑轉(zhuǎn)基因水稻對減少水稻土甲烷排放有積極意義。

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Effect of controlled-release nitrogen fertilizer on CH4emission in transgenic rice from a paddy soil

ZHOU Wenlin, LOU Yunsheng*

CollegeofAppliedMeteorology,NanjingUniversityofInformationScienceandTechnology,Nanjing210044,China

Nitrogen is one of essential nutrients in rice production. Although nitrogen supply increased productivity, nitrogen utilization efficiency was very low in rice production. Some researchers revealed that nearly two-fifths of nitrogen input was lost in different pathways. Excessive use of nitrogen fertilizer not only caused waste of resources but also brought harmful impacts on eco-environment, such as greenhouse effect and pollution to water body and soil. Rice paddies are regarded as one of major CH4emission sources with annual estimates about 31 to 112 Tg, accounting for 5%—19% of global total CH4emissions. CH4emission was promoted by application of fresh organic fertilizer and significantly reduced by biogas fertilizer after fermentation treatment in rice paddies. Effects of chemical nitrogen fertilizer on CH4emission from rice paddies were complicated, which were controlled by soil C/N ratio, fertilizer type, fertilization amount and mode, etc. Fertilization affected CH4emission through influencing soil physicochemical properties, soil microbial community (methanogens and methanotrophs) and plant growth (e.g. development of aerenchyma, formation of root exudates). Controlled-release nitrogen fertilizer (CRNF), as eco-friendly fertilizer, is able to delay nitrogen release, provide a synchronous N supply for plant, thus reduce the accumulation of inorganic N in soil and the risk of N losses. Fewer reports are available regarding the effect of controlled-release N fertilizer on CH4emission in rice paddies. Genetic transformation in rice has achieved rapid development since therst transgenic modification in 1988. Genes containing traits such as resistant to insects, diseases, and tolerant to herbicides, drought and salt have been effectively transferred into different rice varieties. Transgenic rice brought higher yield with less labor intensity, cost and use of pesticides and environmental pollution. However, it is still under argument about the safety of transgenic rice on eco-environment and human health under commercial cultivation. A pot experiment with rice cultivars was conducted to investigate the effect of nitrogen fertilizers on CH4emission from a paddy soil under greenhouse conditions. The experiment was designed with two fertilizer types, i.e. urea and controlled-release nitrogen fertilizer (CRNF), and two rice cultivars, i.e. herbicide-resistant transgenic rice (japonicaline B2) and its parent conventional rice (japonicacv Xiushui 63), and performed at the Station of Agricultural Meteorology, Nanjing University of Information Science and Technology, Nanjing, China. CH4emission was determined by the closed chamber method at 10-day interval during rice growing period in a loamy clay paddy soil. The results indicated that, compared with control (urea), CRNF supply increased tiller number, plant height, biomass and yield in rice. CH4fluxes gradually increased from 22 d after transplanting, then reached the main peak at reproductive phase (62—92 d after transplanting), and sharply decreased until rice harvest. In comparison with control (urea), one-time basal application of CRNF significantly decreased CH4emission from the paddy soil. The total CH4emission was significantly lower from the transgenic rice cultivar than the conventional rice cultivar. It is suggested that one-time basal application of CRNF and planting herbicide-resistant transgenic rice are helpful in mitigating CH4emission from the paddy soil.

controlled-release nitrogen fertilizer; transgenic rice; methane; flux; paddy soil

國家自然科學(xué)基金(41375159); 江蘇省自然科學(xué)基金(BK20131430); 教育部高校博士點(diǎn)基金(20103228110003); 江蘇省“333工程”項(xiàng)目

2012- 12- 26; 網(wǎng)絡(luò)出版日期:2014- 03- 04

10.5846/stxb201212261871

*通訊作者Corresponding author.E-mail: yunshlou@aliyun.com

周文鱗, 婁運(yùn)生.控釋氮肥對抗除草劑轉(zhuǎn)基因水稻田土壤甲烷排放的影響*.生態(tài)學(xué)報(bào),2014,34(16):4555- 4560.

Zhou W L, Lou Y S.Effect of controlled-release nitrogen fertilizer on CH4emission in transgenic rice from a paddy soil.Acta Ecologica Sinica,2014,34(16):4555- 4560.