景立權(quán)，李凡，趙一函，王訓(xùn)康，趙福成，賴上坤，孫小淋，王云霞，楊連新

稻田伴生浮萍碳、氮匯及對水稻產(chǎn)量影響的研究進(jìn)展

1揚(yáng)州大學(xué)農(nóng)學(xué)院/江蘇省作物遺傳生理重點(diǎn)實(shí)驗(yàn)室/江蘇省作物栽培生理重點(diǎn)實(shí)驗(yàn)室/江蘇省糧食作物現(xiàn)代產(chǎn)業(yè)技術(shù)協(xié)同創(chuàng)新中心，江蘇揚(yáng)州 225009；2浙江省農(nóng)業(yè)科學(xué)院玉米與特色旱糧研究所，浙江東陽 322100；3江蘇省農(nóng)業(yè)科學(xué)院宿遷農(nóng)科所，江蘇宿遷 223800；4上海市農(nóng)業(yè)科學(xué)院生態(tài)環(huán)境保護(hù)研究所，上海奉賢 201403；5揚(yáng)州大學(xué)環(huán)境科學(xué)與工程學(xué)院，江蘇揚(yáng)州 225009

浮萍是一種常見于靜水環(huán)境中的水體漂浮微觀植物。以大氣CO2濃度增高為主導(dǎo)致的溫度上升為特征的氣候變化威脅著糧食安全?；蛞驓夂蜃兣肮喔人w富營養(yǎng)化等，近年來我國稻田浮萍伴生有逐年加重趨勢。本文綜述了浮萍對稻田的影響，發(fā)現(xiàn)了一些重要信息：浮萍伴生降低稻田水體溫度0.8—2.76 ℃及pH 0.10—0.45，改變了微生物群落結(jié)構(gòu)，減少稻田NH3揮發(fā)18.2%—59.0%，提高氮利用率17.2%—78.0%，結(jié)果增加了稻田氮匯及稻谷產(chǎn)量（9.0%—34.6%）；伴生浮萍生長繁殖快，其年產(chǎn)生物量可達(dá)8×103—13×103kg·hm-2，碳匯幾乎與當(dāng)季水稻相當(dāng)；水稻浮萍的互利共生總體大于競爭，二者伴生呈現(xiàn)了稻田生態(tài)系統(tǒng)對環(huán)境變化適應(yīng)的現(xiàn)象。但未來本領(lǐng)域仍需深入研究，包括浮萍伴生，特別是與環(huán)境因子互作（高溫及高CO2濃度等）條件下，對稻田生態(tài)環(huán)境變化、水稻生長、產(chǎn)量、品質(zhì)的影響及機(jī)制和可能帶給稻田的風(fēng)險等，為未來基于水稻-浮萍等生物協(xié)作開發(fā)適應(yīng)氣候及環(huán)境變化、維持農(nóng)業(yè)可持續(xù)發(fā)展的稻作技術(shù)提供理論支撐。

浮萍；水稻；碳匯；氮匯；產(chǎn)量

0 引言

浮萍（L.）是繁殖快、富有營養(yǎng)、遍布全球的水體漂浮微觀植物，常見于靜水環(huán)境中[1-2]。或因氣候變化及灌溉水體富營養(yǎng)化等，近年來我國稻田浮萍伴生有逐年加重趨勢：據(jù)本團(tuán)隊(duì)對海南（圖1-a）、浙江、上海、江蘇（圖1-b、d、e、f）、吉林（圖1-c）、黑龍江等共126個獨(dú)立田塊的調(diào)查，稻田浮萍發(fā)生概率達(dá)69.8%，而極端高溫的2022年[3]相對更為嚴(yán)重（鎮(zhèn)江揚(yáng)州由2021年的70.8%增至2022年80.0%）；且本團(tuán)隊(duì)基地也發(fā)現(xiàn)，環(huán)境CO2濃度及溫度增高條件下浮萍生長繁殖速率有倍增趨勢（圖1-d—1-f）——種種跡象表明稻田伴生浮萍的發(fā)生總體隨施肥水平[4]、大氣CO2濃度及溫度[5]的升高而加重。

圖a，b分別為海南三亞及江蘇鎮(zhèn)江生產(chǎn)稻田——浮萍發(fā)生嚴(yán)重；圖c為吉林乾安生產(chǎn)田——浮萍發(fā)生率低；圖d為水稻大田試驗(yàn)對照區(qū)（常規(guī)處理，江蘇揚(yáng)州）——浮萍生長繁殖相對緩慢；圖e為高溫（+1℃）下，浮萍生長繁殖相對加快；圖f為高CO2濃度（+200 μmol·mol-1）及高溫（+1℃）同時處理下浮萍生長繁殖最快

全球CO2排放量持續(xù)增加，近年來屢創(chuàng)歷史新高[6]。以大氣CO2為代表的溫室氣體及其導(dǎo)致的氣溫上升是全球氣候變化的基本特征[7-9]，是極端氣候事件發(fā)生的關(guān)鍵誘因，抑或是刺激浮萍大面積發(fā)生的重要因素，劇烈地影響著糧食生產(chǎn)[3,10]。2020年，我國政府莊嚴(yán)承諾“雙碳”計劃，實(shí)現(xiàn)“雙碳”目標(biāo)，一要“減排”，二要“碳匯”[11]。陸地生態(tài)系統(tǒng)固碳減排被認(rèn)為是一種經(jīng)濟(jì)可行、環(huán)境友好的中和CO2的有效途徑，是實(shí)現(xiàn)自然“增匯”的主體。盡管增加森林、草地等植被面積是實(shí)現(xiàn)“雙碳”目標(biāo)的重要舉措，但這也加劇了其“與糧爭地”的矛盾，農(nóng)田生態(tài)碳匯依然是我國陸地生態(tài)系統(tǒng)固碳減排的關(guān)鍵[12-13]。

水稻為全球67.0%的人口供應(yīng)主食[14]，為超過全球一半的人口提供蛋白及礦質(zhì)元素等基本營養(yǎng)[15]。稻田占據(jù)我國33.0%的總耕地面積，生產(chǎn)了占全球29.0%的稻谷[16]。與歐、美發(fā)達(dá)國家不同，我國人多地少，包括固碳減排在內(nèi)的所有涉農(nóng)問題的解決都必須基于我國糧食的絕對安全。在野外條件下，浮萍伴生可顯著降低水體溫度[17]及pH[18-19]，其生長快、固氮能力強(qiáng)[20-23]，年產(chǎn)生物量達(dá)8×103—13×103kg·hm-2[24]——伴生浮萍降溫幅度同21世紀(jì)中后期溫度增幅[25]相似，而其碳、氮匯能力則與當(dāng)季水稻相當(dāng)。如能與稻互利共生，稻田伴生浮萍不僅是一種理想的生態(tài)碳匯載體，也將是一種優(yōu)異的稻田應(yīng)對氣候及環(huán)境變化的媒介，這與我國“雙碳”戰(zhàn)略吻合。浮萍在基礎(chǔ)學(xué)科領(lǐng)域的研究已取得重大進(jìn)展，發(fā)達(dá)國家產(chǎn)業(yè)化利用發(fā)展迅速[26-28]。本文從浮萍的植物學(xué)特征、生育特點(diǎn)和稻田碳、氮匯方面剖析其與水稻生長的關(guān)系，展望本領(lǐng)域未來的研究方向，以期為稻田碳、氮固定及水稻增產(chǎn)增效提供參考，為基于生物協(xié)作的適應(yīng)未來氣候及環(huán)境變化稻作技術(shù)開發(fā)提供理論支撐。

1 浮萍植物學(xué)特征及生育特點(diǎn)

浮萍，學(xué)名L.，單子葉綱天南星目浮萍科，結(jié)構(gòu)簡單，是目前世界上最小的單子葉開花植物[29-30]，已廣泛應(yīng)用于植物生理學(xué)、分子生物學(xué)及生態(tài)學(xué)等研究領(lǐng)域[28]。浮萍通常僅由3—6 mm×2—15 mm 的葉狀體和長1—5 cm、直徑小于0.5 mm的1條或多條細(xì)根（甚至無根）組成（圖2）[5]，葉狀體呈綠色，背面有時呈紫色。浮萍全世界共有5屬，其中青萍和紫萍在我國較為常見。與紫萍相比，青萍適應(yīng)溫度及pH范圍大，營養(yǎng)物質(zhì)耐受性強(qiáng)，化學(xué)需氧量濃度范圍廣[27]，因此在碳、氮固定及適應(yīng)力方面更有優(yōu)勢[28]。浮萍富含蛋白質(zhì)、氨基酸、胡蘿卜素及碳水化合物等[31-33]，其含水率因品種及生長環(huán)境差異而不同，通常為86.0%—97.0%。多數(shù)浮萍蛋白含量為干重的15.0%—45.0%[1,29,34]，理想條件下可達(dá)26.3%— 45.5%，介于苜蓿（20.0%）和大豆（41.7%）[35]之間，而粗纖維含量僅為5.0%—15.0%，是一種天然綠肥[36]。浮萍亦廣泛富集水體重金屬、礦質(zhì)元素和有機(jī)污染物等[26,36-37]，鑒于此，美國已將其推薦為深度凈化水體氮、磷及其資源化利用的革新技術(shù)載體[38]。

圖a、b引自AN等[1]，為不同時期浮萍的形態(tài)學(xué)特征；c、d為江蘇省作物遺傳生理重點(diǎn)實(shí)驗(yàn)室及實(shí)驗(yàn)田模擬圖

浮萍有無性和有性兩種生殖方式，生命力強(qiáng)，在5—34 ℃、pH 4.5—9.0環(huán)境下均可生長繁殖[5]，20—30 ℃、pH 6.5—7.5時生命活動最為旺盛[39]。浮萍可通過根或葉狀體直接從空氣中吸收CO2，從水中吸取氮、磷、鉀等營養(yǎng)物質(zhì)，由其葉綠體通過光合作用合成并積累有機(jī)物[29,40]。通常情況下，浮萍以成熟葉狀體分生芽孢進(jìn)行無性繁殖為主，在低于5 ℃時進(jìn)入休眠狀態(tài)，在其夾囊或開口內(nèi)形成休眠芽。浮萍休眠芽小、通氣組織少、細(xì)胞壁厚，逆境（或冬季）時可脫離母體沉入水底，逆境解除后利用儲藏在休眠體內(nèi)的淀粉發(fā)芽而形成完整植株。浮萍的植物學(xué)特征和生育特點(diǎn)為稻田生態(tài)及資源化利用奠定了基礎(chǔ)。

2 國內(nèi)外浮萍研究與應(yīng)用情況

美國最早（1925年，SAEGER[41]）發(fā)表了相關(guān)浮萍的研究。目前，美國羅格斯大學(xué)和中國科學(xué)院成都生物研究所保存眾多浮萍資源。中國科學(xué)院其他單位（植物研究所、水生生物研究所及青島生物能源與過程研究所）及海南大學(xué)也有部分保存[28]。就全球研究熱度和水平來說，美國均居首位，是浮萍研究的主導(dǎo)國家，其次集中在歐、日等發(fā)達(dá)地區(qū)，盡管我國關(guān)于浮萍的發(fā)文量位列全球前五，但研究水平相對還較低[5]。

目前浮萍研究熱點(diǎn)主要集中在污水凈化及能源利用方面[5,42]，而在應(yīng)對環(huán)境污染、全球氣候變暖及食物短缺方面浮萍也具有巨大的潛力[43-45]。因此，2014年美國能源部重點(diǎn)資助了有關(guān)浮萍的基礎(chǔ)研究，計劃從浮萍基因組學(xué)和分子生物學(xué)方面率先取得突破，這也意味著浮萍產(chǎn)業(yè)化應(yīng)用的大門打開了[1]。作為食品開發(fā)的潛力植物，浮萍研究也得到了荷蘭政府資助[28]。但在研究浮萍的所有領(lǐng)域中，農(nóng)學(xué)相關(guān)研究很少，僅占5.0%[5]，且大多集中在伴生浮萍截留水體氮、磷等礦質(zhì)元素流失及抑制雜草方面，而基于農(nóng)學(xué)、農(nóng)藝學(xué)等的稻田伴生浮萍碳、氮匯及其直接對水稻生長影響方面的研究則相對缺乏。

3 稻田伴生浮萍碳、氮匯及對水稻產(chǎn)量的影響

3.1 伴生浮萍碳匯及機(jī)理

適宜條件下，浮萍可呈指數(shù)增長[46-47]，《本草綱目》記載“一葉經(jīng)宿，即生數(shù)葉”，是目前已知生長最快的植物。浮萍無性繁殖時，一個葉狀體母芽體內(nèi)一般包括6—7個處于不同發(fā)育階段的芽孢，通常繁殖一代僅需2—7 d[28,48]，甚至不足1 d[49-50]。研究表明，在實(shí)驗(yàn)室條件下，浮萍物質(zhì)積累可達(dá)每周1—2 kg·m-2（鮮重）[50-51]，生產(chǎn)淀粉的能力平均是玉米的5—6倍[47]，經(jīng)過誘導(dǎo)后淀粉含量甚至可達(dá)干重的65.0%[52]，固碳能力極強(qiáng)，是一種理想的生物碳匯載體。與其他植物相比，浮萍科退化嚴(yán)重，除快速生長繁殖外，浮萍已擺脫大部分基因的束縛[1,53]，這或是浮萍生長繁殖快的本質(zhì)原因；同時浮萍的生長與繁殖受品種和環(huán)境影響也很大[54-55]，這是建立稻-萍生物協(xié)作稻田生態(tài)關(guān)系的基礎(chǔ)。浮萍在稻田中的生長與繁殖，可循環(huán)生產(chǎn)并積累有機(jī)物[56]，其腐解后作為綠肥回歸稻田[36,57]，碳匯的同時增加稻田有機(jī)質(zhì)。

3.2 伴生浮萍氮匯及機(jī)理

糧食供應(yīng)、能源危機(jī)、氮肥利用及環(huán)境污染一直是我國經(jīng)濟(jì)社會發(fā)展的潛在矛盾?；守暙I(xiàn)了全球一半以上的糧食增產(chǎn)[58]，而化肥工業(yè)本身高耗能、高碳排。農(nóng)田是全球氮污染及溫室氣體排放的主要來源[13,20,59-61]。據(jù)早期研究估算，氮污染危害抵消了全球0.3%—3.0%的GDP[62]，與其對作物增產(chǎn)效益相抵[63]。我國農(nóng)田施肥量大[58]，化肥利用率低（僅為40.2%[64]，遠(yuǎn)低于發(fā)達(dá)國家的52.0%—67.0%[63]），地區(qū)間不平衡（22.0%—70.0%）[65]，氮損失嚴(yán)重[39,63]，對環(huán)境的負(fù)面影響大[58,66]。我國化肥約30.0%用于水稻生產(chǎn)[39]，提高稻田化肥利用率對我國農(nóng)業(yè)可持續(xù)綠色發(fā)展、環(huán)境保護(hù)及碳、氮匯等意義重大[58]。

區(qū)別于其他作物，水稻耗水多[67]，水稻整個生育期稻田多有水層覆蓋。NH3揮發(fā)是稻田氮肥損失最主要途徑之一[68]，占氮總損失的40.0%— 50.0%[39]，由于高溫高濕氣候，我國南方稻田更為嚴(yán)重[69]。浮萍的氮含量接近3.0%，高于一般的濕地植物，包括水稻[70-71]，氮匯能力很強(qiáng)。前人研究證明（表1），浮萍伴生可降低稻田水體溫度[18-19,21]及pH（0.10—0.45），降低NH3揮發(fā)達(dá)18.2%—59.0%，進(jìn)而減少稻田總氮損失11.2%—13.6%[20]，結(jié)果提高氮肥利用率17.2%—78.0%，最終增加了稻谷產(chǎn)量，增幅達(dá)9.0%—34.6%（表1）。

浮萍伴生主要通過以下三個方面提高稻田氮利用率：①浮萍植株體上下通透，其根系及葉面等均具有發(fā)達(dá)的氣體交流系統(tǒng)，可將空氣中的氧氣通過葉片及根系轉(zhuǎn)移至根際水中，在浮萍植株體附近形成微生物膜，為氮代謝微生物的活動提供適宜的環(huán)境，從而促進(jìn)氮形式的轉(zhuǎn)化，降低水體銨態(tài)氮濃度，抑制氮的揮發(fā)[20,74-75]；②同時浮萍對水體銨態(tài)氮也具有較好的吸收和吸附作用[75]，浮萍與水體進(jìn)行物質(zhì)交換，主要截留并吸收原本因NH3揮發(fā)而損失的氮（幾乎不與稻爭肥），其凋亡后又將吸收的氮素重新釋放至稻田，浮萍的生長與腐解對水體氮含量的變化起到了“緩沖”作用，進(jìn)而促進(jìn)氮向土壤轉(zhuǎn)移[20]，形成稻田“氮庫”效應(yīng)，滿足水稻生育后期對氮的需求，從而提高稻田氮利用率[72]；③此外，包括浮萍在內(nèi)的水體漂浮微觀植物與水稻伴生時，其物理覆蓋降低了水體受光強(qiáng)度，抑制了遲發(fā)雜草光合作用，增加了CO2的溶解，進(jìn)而降低水體pH及溫度[18,21]，降溫幅度可達(dá)0.86—2.76 ℃[19]?？茖W(xué)家的深入研究表明，浮萍伴生導(dǎo)致的水體pH、溫度變化對減少稻田氮損失起關(guān)鍵作用[20]，通常兩個指標(biāo)的大小與稻田NH3揮發(fā)速率保持顯著正相關(guān)關(guān)系[40,68]。與浮萍相似，同樣作為漂浮植物的滿江紅，盡管植物學(xué)及形態(tài)學(xué)等特征與浮萍迥異，但也具有相似的稻田氮匯能力[57,76-78]。這些說明浮萍與其他微觀漂浮植物作用機(jī)理相似，除物理覆蓋外，對稻田還包括明顯的“透膜”效應(yīng)：吸光、阻光、透氣及碳、氮匯等，并保持與水體進(jìn)行物質(zhì)交換。

表1 浮萍伴生對稻田生態(tài)環(huán)境因子及水稻產(chǎn)量的影響

——表示未被作者報道；↓ 抑制或降低；↑ 促進(jìn)或提高 —— This data wasn’t reported by its authors; ↓ Suppress or reduce; ↑ Promote or enhance

3.3 微生物及化感物質(zhì)

浮萍伴生可通過稻田碳、氮匯及抑制病、草害等間接影響水稻生長[79-81]，但更為復(fù)雜的是，其也可通過自身及自身寄宿的微生物群落釋放次級代謝產(chǎn)物直接作用于水稻的生長。研究發(fā)現(xiàn)，稻田伴生浮萍寄生的微生物菌落與水稻極為相似[30]，這就意味著各自微生物的豐缺彼此影響各自的生命活動：HUANG等[81]研究證實(shí)，從水稻器官分離出的254種優(yōu)勢菌落（）可完全移植于無菌浮萍上，這些細(xì)菌分泌的生長素可同時促進(jìn)稻、萍的生長；LU等[23]也發(fā)現(xiàn)，浮萍根際寄宿的微生物分泌的豆甾醇具有明顯促進(jìn)反硝化細(xì)菌脫氮及其生物膜形成，進(jìn)而促進(jìn)氮在稻田水體的形式轉(zhuǎn)化。當(dāng)?shù)咎锇樯∑济芏冗^高時也會產(chǎn)生一些化感物質(zhì)，如酚酸、長鏈脂肪酸、乙烯及其他生長素類物質(zhì)等[52,82]，其中的脂肪酸甲酯及脂肪酸酰胺可刺激反硝化細(xì)菌脫氮[83]，而浮萍腐解也可增加水體疏水性酸（hydrophobic acids）和類海水腐殖質(zhì)（marine humic-like substances）濃度，進(jìn)而促進(jìn)氮向土壤轉(zhuǎn)移，改變水體微環(huán)境及微生物生存狀態(tài)[52,68]，抑制與其競爭光照及營養(yǎng)的雜草的生長[84-85]。這些化感物質(zhì)自身具有易降解的特點(diǎn)[86]，目前尚未發(fā)現(xiàn)它們威脅水稻生長的報道，但對浮萍自身的生命活動具有明顯的調(diào)控作用，如，有學(xué)者證實(shí)，浮萍在含有細(xì)胞分裂素的水體中生存時間被大大延長[43]。大多數(shù)化感物質(zhì)的生物化學(xué)結(jié)構(gòu)及功能是一致的，同一種物質(zhì)往往對不同植物有相同的作用，浮萍與水稻通過化感物質(zhì)相互作用程度如何？目前尚不清晰。

3.4 浮萍伴生對水稻產(chǎn)量的影響及機(jī)理

近20年，稻田浮萍伴生直接對水稻生長及產(chǎn)量影響的報道很少，國內(nèi)外僅發(fā)現(xiàn)9例（表1），其中7例[12,17,19-20,39,72-73]證實(shí)促進(jìn)水稻產(chǎn)量的形成，平均增產(chǎn)幅度15.8%，1例認(rèn)為不利于水稻生長[44]，而1例效應(yīng)不明顯[36]。2008年，廣西大學(xué)實(shí)驗(yàn)結(jié)果證實(shí)，浮萍處理提高了土壤氮、磷、鉀及有機(jī)質(zhì)含量，促進(jìn)了水稻后期的抗倒伏能力形成，同時提高了水稻產(chǎn)量構(gòu)成的4個因子，與稻糠配合施用效果更好，綜合增產(chǎn)稻谷高達(dá)11.1%[39]；2009年，浙江大學(xué)報道，不同氮水平下浮萍伴生降低了稻田水體pH、溫度及NH3揮發(fā)平均分別為0.45、0.9—2.1 ℃和33.2%—53.7%，結(jié)果使水稻增產(chǎn)9.4%—9.8%[17]；2017年，中國科學(xué)院南京土壤研究所探索稻田土壤氮流失規(guī)律時發(fā)現(xiàn)，伴生浮萍在水稻生育的前期截留并吸收原本因NH3揮發(fā)而損失的氮，后期通過干濕交替或其他栽培措施的調(diào)控使浮萍逐漸凋亡，并將浮萍吸收的氮重新釋放至稻田，滿足水稻生育后期對氮素的需求，從而提高氮利用率35.0%—78.0%，增產(chǎn)水稻9.0%—10.0%[72]；2019，南京林業(yè)大學(xué)聯(lián)合中山大學(xué)等報道，在配施生物炭的情況下浮萍可提高稻田氮利用率17.2%，增產(chǎn)水稻10.9%[12]；而與其相似的滿江紅也具有相同的效果[57,76-77]；2021年，處于亞熱帶海洋性季風(fēng)氣候的上海交通大學(xué)研究浮萍對稻田雜草多樣性時發(fā)現(xiàn)，浮萍覆蓋大幅降低了稻田雜草密度（60.3%—90.4%），極大地緩解了水稻與雜草的資源（肥、光、水及空間等）競爭，從而提高了水稻的每穗粒數(shù)（33.7%）和穗重（28.2%），最終使水稻增產(chǎn)28.0%[73]；次年，其團(tuán)隊(duì)深入分析表明，水稻產(chǎn)量的增加主要與稻田生態(tài)環(huán)境因子值降低有關(guān)：浮萍伴生降低了水/土溫度（0.86—2.76 ℃）、透光率（98.0%）、溶氧量（8.9%）及pH（0.32—0.39）等[19]；WANG等[20]在太湖地區(qū)的實(shí)驗(yàn)結(jié)果也證明了稻田伴生浮萍增產(chǎn)稻谷的結(jié)論，且其還觀察到在不施肥的條件下浮萍盡管仍呈現(xiàn)了增產(chǎn)趨勢，但并未達(dá)顯著水平（見[20]，F(xiàn)ig.3-e）。2003年，中國水稻所也曾觀察到了類似結(jié)果：在不施氮的條件下，浮萍伴生盡管抑制了稻田雜草的生長，但對水稻產(chǎn)量并無顯著影響[36]，這說明浮萍伴生對水稻的增產(chǎn)效果與施肥量有關(guān)。當(dāng)然也有個別報道視萍為雜草，因其與稻競爭養(yǎng)分[87]，降低稻田水/土溫度[44]，特別是降低我國北方稻田的水/土溫度[88]等，從而抑制了水稻分蘗與生長[44]，造成稻谷減產(chǎn)，且這種不利影響隨浮萍覆蓋率增加而增大。綜上，多數(shù)學(xué)者證實(shí)了稻田稻-萍的生物協(xié)作關(guān)系[89]，但或因當(dāng)?shù)赝寥婪柿?、溫光條件、肥水管理及浮萍伴生程度等的差異，少數(shù)情況下伴生浮萍與水稻也存在競爭關(guān)系。然而，浮萍特別是生長失控下的浮萍對稻田綜合風(fēng)險的系統(tǒng)評估目前尚未見報道。

4 未來展望

氣候及稻田生態(tài)環(huán)境在持續(xù)變化，以往學(xué)者多從溫、水、肥、管等非生物及抗性育種等方面研究稻田生態(tài)系統(tǒng)應(yīng)對變化的措施[10,90]，而基于稻-萍生物協(xié)作的研究相對較少。有限的報道認(rèn)為伴生浮萍對稻田影響很大：降低水/土溫度（或可對沖高溫對稻田的負(fù)面影響）及pH，固定碳、氮，提高氮利用率，進(jìn)而大幅增加稻谷產(chǎn)量——稻田生態(tài)系統(tǒng)對氣候及環(huán)境變化呈現(xiàn)了明顯的適應(yīng)現(xiàn)象。浮萍在基礎(chǔ)學(xué)科領(lǐng)域的研究已取得重大進(jìn)展，且在發(fā)達(dá)國家的產(chǎn)業(yè)化利用方面發(fā)展迅速，而在農(nóng)業(yè)領(lǐng)域的理論研究及推廣則很少，導(dǎo)致生產(chǎn)上人們多錯誤地視浮萍為雜草而用藥除之，這不僅提高了稻田農(nóng)藥用量及人工成本，還加重了潛在的環(huán)境壓力。鑒于浮萍特性及其在稻田生態(tài)系統(tǒng)中應(yīng)用的巨大潛力，筆者認(rèn)為未來可從以下幾個方面深入開展稻-萍等生物協(xié)作研究。

4.1 系統(tǒng)調(diào)查浮萍伴生對稻田生態(tài)環(huán)境因子的影響規(guī)律

浮萍伴生可通過改變生態(tài)環(huán)境因子間接影響稻田生態(tài)，也可通過自身及自身寄宿的微生物釋放化感物質(zhì)直接作用于水稻，深入開展浮萍伴生，特別是與環(huán)境因子互作（高溫及高CO2濃度等）下，對稻田生態(tài)環(huán)境影響的研究顯得尤為重要，具體包括：①不同程度不同時期的浮萍伴生對稻田水/土溫度、pH、透光率、溶氧量及水資源利用率的影響規(guī)律；②浮萍伴生對稻田微生物優(yōu)勢群落的影響規(guī)律；③浮萍伴生對稻田水體化感物質(zhì)的影響規(guī)律，包括稻、萍及相關(guān)寄宿微生物釋放的激素等；④稻田浮萍伴生條件下，關(guān)鍵營養(yǎng)元素（氮、磷、鉀及微量礦質(zhì)元素等）在稻、萍、水體和土壤之間的轉(zhuǎn)移及轉(zhuǎn)化關(guān)系；⑤深入對比及分析以上指標(biāo)對水稻生命活動的影響規(guī)律，確定其中的關(guān)鍵因子。

4.2 基于農(nóng)學(xué)及農(nóng)藝學(xué)，深入研究浮萍伴生對水稻生長、產(chǎn)量及稻米品質(zhì)的影響及機(jī)制

目前研究浮萍伴生對水稻的影響僅集中在產(chǎn)量表觀性狀方面，鮮有涉及水稻生長、品質(zhì)及其形成機(jī)制方面的深入探索。因此，在浮萍伴生對水稻直接及間接的影響下，系統(tǒng)調(diào)查水稻響應(yīng)及機(jī)理顯得尤為迫切，包括：水稻生長規(guī)律（分蘗機(jī)制、倒伏抗性及干物質(zhì)積累規(guī)律等）、稻米產(chǎn)量形成機(jī)制（葉片光合及籽粒灌漿生理等）、稻米不同品質(zhì)指標(biāo)響應(yīng)規(guī)律及機(jī)制；同時研究不同稻田生態(tài)環(huán)境下浮萍的生長繁殖規(guī)律及控制技術(shù)，從農(nóng)學(xué)及農(nóng)藝學(xué)栽培調(diào)控角度為稻-浮等互利共生的稻田生物協(xié)作生態(tài)系統(tǒng)的建立提供理論支撐。

4.3 科學(xué)調(diào)研，準(zhǔn)確評估浮萍伴生對稻田可能造成的風(fēng)險

類似并區(qū)別于大豆-根瘤菌的互利共生，稻田伴生浮萍與水稻或也存在競爭關(guān)系，伴生浮萍的快速生長及大量繁殖抑或給稻田帶來潛在的風(fēng)險，準(zhǔn)確評估這一風(fēng)險顯得尤為重要，具體包括：①系統(tǒng)調(diào)查全國浮萍發(fā)生情況及對稻田及水稻的表觀性狀影響規(guī)律；②深入分析浮萍伴生條件下，稻田蟲、草、特別是病害發(fā)生規(guī)律及動力學(xué)特征；③開展長期定位試驗(yàn)，綜合分析稻田伴生浮萍碳、氮匯變化及對稻田水分利用、土壤營養(yǎng)及生態(tài)的影響規(guī)律，特別是稻田重金屬積累與轉(zhuǎn)運(yùn)規(guī)律等。

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Research Progress on the Carbon and Nitrogen Sink of Duckweed Growing in Paddy and Its Effects on Rice Yield

JING LiQuan1, LI Fan1, ZHAO YiHan1, WANG XunKang1, ZHAO FuCheng2, LAI ShangKun3, SUN XiaoLin4,WANG YunXia5, YANG LianXin1

1Agricultural College of Yangzhou University/Jiangsu Key Laboratory of Crop Genetics and Physiology/Jiangsu Key Laboratory of Crop Cultivation and Physiology/Jiangsu Co-Innovation Center for Modern Production Technology of Grain Crops, Yangzhou 225009, Jiangsu;2Institute of Maize and Featured Upland Crops, Zhejiang Academy of Agricultural Sciences, Dongyang 322100, Zhejiang;3Suqian Institute, Jiangsu Academy of Agricultural Sciences, Suqian 223800, Jiangsu;4Eco-Environmental Protection Research Institute, Shanghai Academy of Agricultural Sciences, Shanghai 201403;5College of Environmental Science and Engineering, Yangzhou University, Yangzhou 225009, Jiangsu

Duckweed (L.) is a floating microscopic plant that is usually found in standing water. Climate change is characterized by rising temperature, which is mainly due to increasing atmospheric CO2concentration, and it poses potential risks to food production. Owing to factors such as climate warming and/or the eutrophication of water, duckweed growth in paddy fields has shown an increasing trend year by year in China. This paper focused on the impacts of duckweed on paddy fields and highlighted some vital trends. Duckweed reduced the water temperature of paddy by 0.86-2.76 ℃ and the pH value by 0.10-0.45, changed the structure of microbial community, reduced the NH3volatilization by 18.2%-59.0%, and increased the nitrogen utilization rate by 17.2%-78.0%. As a result, the nitrogen sink of paddy increased and the rice yield rose by 9.0%-34.6% upon duckweed growing in paddy. Duckweed grew and reproduced rapidly, and its annual biomass could reach 8×103-13×103kg·hm-2, making its carbon sink almost equal to that of rice in the same season. The mutualism between duckweed and rice was greater than its competition, and the coexistence of duckweed and rice in paddy showed an adaptation of the rice field ecosystem to environmental changes. Future research in this field should focus on the effect and its mechanism of duckweed on the paddy environment changes, rice growth, yield, and quality, and the risks which might bring to the paddy fields, especially the interaction with environmental factors (elevated temperature and CO2concentration, etc.). Such research would provide theoretical support for the sustainable agricultural development of rice farming technology based on biological collaboration, such as rice-duckweed, which can adapt to future changes in climate and environment.

duckweed (L.); rice; carbon sink; nitrogen sink; yield

10.3864/j.issn.0578-1752.2023.23.013

2023-03-29；

2023-06-21

國家自然科學(xué)基金（32172102，31701352）、江蘇高校優(yōu)勢學(xué)科建設(shè)工程（PAPD）、浙江省重點(diǎn)研發(fā)計劃（2020C02001）

景立權(quán)，E-mail：lqjing@yzu.edu.cn。通信作者楊連新，E-mail：lxyang@yzu.edu.cn

（責(zé)任編輯 李云霞）