張水勤，袁亮，林治安，李燕婷，胡樹文，趙秉強(qiáng)*

（1農(nóng)業(yè)部植物營(yíng)養(yǎng)與肥料重點(diǎn)實(shí)驗(yàn)室/中國(guó)農(nóng)業(yè)科學(xué)院農(nóng)業(yè)資源與農(nóng)業(yè)區(qū)劃研究所，北京100081；2中國(guó)農(nóng)業(yè)大學(xué)資源與環(huán)境學(xué)院，北京100193）

腐植酸促進(jìn)植物生長(zhǎng)的機(jī)理研究進(jìn)展

張水勤1,2，袁亮1，林治安1，李燕婷1，胡樹文2，趙秉強(qiáng)1*

（1農(nóng)業(yè)部植物營(yíng)養(yǎng)與肥料重點(diǎn)實(shí)驗(yàn)室/中國(guó)農(nóng)業(yè)科學(xué)院農(nóng)業(yè)資源與農(nóng)業(yè)區(qū)劃研究所，北京100081；2中國(guó)農(nóng)業(yè)大學(xué)資源與環(huán)境學(xué)院，北京100193）

【目的】腐植酸在我國(guó)農(nóng)業(yè)生產(chǎn)中發(fā)揮了重要作用，許多研究證實(shí)，腐植酸具有促進(jìn)植物生長(zhǎng)的功能，本文從腐植酸刺激植物根系生長(zhǎng)、調(diào)控土壤與肥料養(yǎng)分轉(zhuǎn)化及肥料利用率和影響土壤微生物和酶活性方面，系統(tǒng)總結(jié)了國(guó)內(nèi)外施用腐植酸促進(jìn)植物生長(zhǎng)的途徑，闡述了腐植酸對(duì)植物生長(zhǎng)促進(jìn)作用的機(jī)理，旨在梳理腐植酸促進(jìn)植物生長(zhǎng)機(jī)理的研究現(xiàn)狀，為腐植酸的進(jìn)一步研究和應(yīng)用提供參考依據(jù)?！局饕M(jìn)展】1)腐植酸能夠?qū)χ参锂a(chǎn)生類似生物刺激素的效應(yīng)。它能夠提高植物根系H+-ATP酶等的活性、刺激植物根伸長(zhǎng)和側(cè)根生長(zhǎng)點(diǎn)的增加，從而增加根系活力及植物根系與土壤養(yǎng)分的接觸面積，增加植物對(duì)養(yǎng)分的吸收；2)逆境脅迫下，腐植酸能夠通過調(diào)節(jié)植物體內(nèi)的新陳代謝并改善植物生長(zhǎng)環(huán)境，緩解甚至消除逆境脅迫對(duì)植物的傷害，從而促進(jìn)植物生長(zhǎng)；3)腐植酸能夠通過與氮素、磷素和鉀素發(fā)生結(jié)合效應(yīng)，與磷酸鹽產(chǎn)生競(jìng)爭(zhēng)效應(yīng)和對(duì)鉀離子的吸附作用固持與活化土壤與肥料中的養(yǎng)分，提高土壤肥料有效性和緩釋性能，提高肥料利用率，從而促進(jìn)植物生長(zhǎng)；4)腐植酸還能夠影響土壤中與養(yǎng)分轉(zhuǎn)化相關(guān)的酶活性和微生物群落結(jié)構(gòu)及數(shù)量，在活化養(yǎng)分的同時(shí)，保蓄養(yǎng)分，降低養(yǎng)分的損失，為植物生長(zhǎng)保障持久的養(yǎng)分供應(yīng)；5)腐植酸對(duì)植物生長(zhǎng)的促進(jìn)效應(yīng)受腐植酸結(jié)構(gòu)特征、添加量和供試植物種類等因素的影響?！窘ㄗh與展望】由于技術(shù)手段的限制和研究技術(shù)的差異，人們對(duì)腐植酸促進(jìn)植物生長(zhǎng)機(jī)理的認(rèn)識(shí)還不夠系統(tǒng)和深入，因此，腐植酸的基本特征、影響腐植酸作用的主控因子、土壤–植物系統(tǒng)中腐植酸促進(jìn)植物生長(zhǎng)的主要途徑和腐植酸對(duì)土壤功能性微生物等的影響都將成為未來(lái)研究的重要方向。

腐植酸；植物生長(zhǎng)；根系；抗逆性；養(yǎng)分轉(zhuǎn)化

腐植酸是動(dòng)植物殘?bào)w和微生物細(xì)胞等經(jīng)微生物分解和轉(zhuǎn)化，以及一系列地球化學(xué)過程形成和累積的一類成分復(fù)雜的天然有機(jī)高分子混合物[1–2]。它在自然界中具有廣泛的來(lái)源與分布。以humic acid(腐植酸)為檢索詞，對(duì)Web of Science數(shù)據(jù)庫(kù)中1996～2015年間收錄的文獻(xiàn)進(jìn)行統(tǒng)計(jì)分析(檢索時(shí)間為2016年4月19日)，發(fā)現(xiàn)腐植酸在農(nóng)業(yè)領(lǐng)域研究的發(fā)文量為588，占所有研究的15.50%，位居所有研究領(lǐng)域第四位，可見，農(nóng)業(yè)是腐植酸應(yīng)用的重要領(lǐng)域之一。我國(guó)對(duì)腐植酸有組織的研究工作始于上世紀(jì)50年代末期。上世紀(jì)60年代，全國(guó)掀起了使用腐植酸肥料和利用腐植酸改良土壤的熱潮；70年代，國(guó)務(wù)院在1974年和1979年兩次發(fā)文(110號(hào)和200號(hào))，全面推動(dòng)了我國(guó)對(duì)腐植酸的綜合開發(fā)利用，確認(rèn)了腐植酸在農(nóng)業(yè)上“改良土壤，增效肥料，刺激生長(zhǎng)，增強(qiáng)抗逆，改善品質(zhì)”五大作用[3–4]。國(guó)內(nèi)外大量研究證實(shí)，腐植酸具有促進(jìn)植物生長(zhǎng)、提高植物產(chǎn)量的作用，如玉米施用腐植酸后能顯著降低從種植到抽雄和抽絲時(shí)間，顯著增加作物高度和單位面積產(chǎn)量[5–6]；小麥?zhǔn)┯酶菜崮艽龠M(jìn)根系伸展和生物量的增加[7–8]；水稻施用腐植酸能顯著增加株高、分蘗數(shù)、千粒重、秸稈和籽粒產(chǎn)量[9–10]。同時(shí)，腐植酸還具有提高肥料利用率、改善作物品質(zhì)的作用，如提高玉米/小麥/水稻氮磷鉀肥利用率[8,11–13]；改善萵苣/油菜/洋蔥/番茄等的品質(zhì)，降低體內(nèi)硝酸鹽含量[14–17]；降低草莓白粉病、灰霉病和爛果病的發(fā)病率[18]。Trevisan等[19]認(rèn)為，腐植酸能夠通過改善土壤結(jié)構(gòu)、提高土壤肥力、影響?zhàn)B分吸收和根系構(gòu)型對(duì)植物生理產(chǎn)生有益的影響。大量研究證實(shí)，腐植酸通過調(diào)控“植物–土壤–肥料”系統(tǒng)促進(jìn)植物生長(zhǎng)，具體方式及主要作用機(jī)理如圖1所示，即主要包括四個(gè)方面：1)通過直接作用于植物(尤其是植物根系)而影響根系生長(zhǎng)及其對(duì)養(yǎng)分的吸收[20–22]；2)通過調(diào)控植物活性氧系統(tǒng)和細(xì)胞膜滲透性、改善植物生長(zhǎng)環(huán)境增強(qiáng)植物抗逆性[23–24]；3)通過調(diào)控土壤及肥料的養(yǎng)分形態(tài)而影響植物的養(yǎng)分供應(yīng)[14,25]；4)通過影響土壤微生物群落結(jié)構(gòu)及土壤酶活性而影響土壤中及肥料施用后養(yǎng)分形態(tài)[26–27]。鑒于此，本文基于以上四個(gè)方面內(nèi)容對(duì)已有研究進(jìn)行總結(jié)，系統(tǒng)分析腐植酸促進(jìn)植物生長(zhǎng)的機(jī)理，旨在啟發(fā)引導(dǎo)對(duì)腐植酸的系統(tǒng)研究，從而為腐植酸資源高效利用和科學(xué)開發(fā)提供理論與技術(shù)支撐。

1 腐植酸通過刺激植物根系生長(zhǎng)及其對(duì)養(yǎng)分的吸收而促進(jìn)植物生長(zhǎng)

1.1 腐植酸對(duì)植物根系生長(zhǎng)及其對(duì)養(yǎng)分吸收的刺激作用

1.1.1 腐植酸對(duì)植物根系生長(zhǎng)的刺激作用腐植酸對(duì)植物根系生長(zhǎng)的刺激作用是其對(duì)植物生長(zhǎng)促進(jìn)作用的最初動(dòng)力[28]。腐植酸對(duì)植物根系生長(zhǎng)的刺激效應(yīng)主要體現(xiàn)在促進(jìn)根長(zhǎng)度和根數(shù)量增加方面。Dobbss等[29]研究表明，腐植酸處理下，番茄側(cè)根數(shù)量的增加幅度達(dá)150%～264%，而側(cè)根長(zhǎng)度的增加幅度更多，達(dá)405%～2280%。這種作用的產(chǎn)生主要是由于腐植酸作用于植物后，植物表現(xiàn)出類似添加低劑量或大量外源生長(zhǎng)素的刺激反應(yīng)[22]，這跟腐植酸含有細(xì)胞激肽酶類等有機(jī)生物刺激素有關(guān)，因此，施用后能夠提升植物生物化學(xué)活性，對(duì)根系產(chǎn)生類似生長(zhǎng)素的作用，刺激植物內(nèi)生細(xì)胞激肽類和植物生長(zhǎng)素的增加，引起細(xì)胞質(zhì)膜滲透性能的改變，促進(jìn)植物蛋白的合成和細(xì)胞的生長(zhǎng)，從而促進(jìn)植物根系生長(zhǎng)和產(chǎn)量的增加[30–33]。腐植酸對(duì)植物根系的刺激作用使植物根系中與蔗糖代謝、蘋果酸酶、ATP酶、細(xì)胞支架蛋白質(zhì)相關(guān)的基因出現(xiàn)了差異性表達(dá)[21,34]，其中，H+-ATP酶基因的差異性表達(dá)對(duì)作物根系生長(zhǎng)影響最大。研究表明，腐植酸能夠促進(jìn)玉米根系中H+-ATP酶編碼基因亞型Mha2的表達(dá)[35]，能夠作為質(zhì)膜上H+-ATP酶誘導(dǎo)因子提高細(xì)胞活性，誘導(dǎo)質(zhì)膜表面H+-ATP酶數(shù)量的增加，酸化非原質(zhì)體，從而使細(xì)胞壁松弛，允許細(xì)胞伸長(zhǎng)[36–38]；同時(shí)，H+-ATP酶活性的增加也使電化學(xué)質(zhì)子梯度增加，促進(jìn)了通過第二運(yùn)輸系統(tǒng)進(jìn)行的質(zhì)子跨膜運(yùn)輸，進(jìn)而改善了植物的營(yíng)養(yǎng)[39–40]，刺激植物根系生長(zhǎng)。此外，腐植酸能夠通過刺激擬南芥根毛細(xì)胞的負(fù)調(diào)控子基因WEREWOLF和GLABRA2的下調(diào)，促使根形態(tài)發(fā)生重塑，增加根吸收面積，改變根系細(xì)胞分化[41]；腐植酸還能促進(jìn)玉米側(cè)根有絲分裂位點(diǎn)增加，抑制ATP的水解和H+的運(yùn)輸[21]。

圖1 腐植酸促進(jìn)作物生長(zhǎng)的主要途徑及機(jī)理Fig. 1 Main approaches and mechanisms of humic acid prompting plant growth

Trevisan等[42]研究表明，在腐植酸施用30min內(nèi)能夠刺激生長(zhǎng)素誘導(dǎo)擬南芥中基因IAA19的表達(dá)，這與生長(zhǎng)素對(duì)植物刺激的效應(yīng)相似；然而，在其作用2h后，該基因卻沒有表現(xiàn)出與生長(zhǎng)素刺激相一致的恢復(fù)至基準(zhǔn)水平，這可能是由于腐植酸除了具有生長(zhǎng)素類似的調(diào)控效應(yīng)外，還具有其他效應(yīng)。

1.1.2 腐植酸對(duì)植物根系吸收養(yǎng)分的促進(jìn)作用腐植酸對(duì)植物根系養(yǎng)分吸收的促進(jìn)作用主要表現(xiàn)在對(duì)硝酸鹽的吸收上。一方面腐植酸能夠促進(jìn)植物根系中與硝酸鹽吸收同化相關(guān)的基因的表達(dá)。Tomasi等[43]和Quaggiotti等[35]研究表明，在低分子量腐植酸作用下，玉米根系中與硝酸鹽吸收相關(guān)的基因(NRT2.1和MHA2)與硝酸鹽同化基因(NR1)均表現(xiàn)出了上調(diào)表達(dá)。另一方面，腐植酸能夠通過調(diào)節(jié)植物根系體內(nèi)環(huán)境，刺激植物對(duì)硝酸鹽的吸收。腐植酸能夠通過降低根細(xì)胞質(zhì)膜表面的pH，中和NO3–作為氮源所產(chǎn)生的堿，抑制H+/NO3–的同向轉(zhuǎn)移[44]；腐植酸(尤其是小分子量腐植酸)對(duì)質(zhì)膜上分離的H+-ATP酶活性的刺激作用，決定了電化學(xué)質(zhì)子梯度的增加[30,38]，從而促進(jìn)了植物根系對(duì)NO3–的吸收，最終促進(jìn)了植物對(duì)氮的吸收。因此，腐植酸能夠通過調(diào)控硝酸鹽的吸收、同化和轉(zhuǎn)移促進(jìn)植物對(duì)硝態(tài)氮的吸收。此外，腐植酸還能促進(jìn)大麥和燕麥幼苗對(duì)SO42–和K+等養(yǎng)分離子的吸收[45–47]。

腐植酸也能作為營(yíng)養(yǎng)物質(zhì)被植物體所吸收。腐植酸(尤其是小分子量的腐植酸)很容易到達(dá)高等植物細(xì)胞質(zhì)膜，且部分被植物所吸收[20,48–51]；李京淑等[52]和儀明光等[53]通過使用氚標(biāo)記的腐植酸鈉開展砂培試驗(yàn)，也觀察到了腐植酸鈉可以通過根或莖的切面進(jìn)入植物體。

1.2 腐植酸對(duì)植物根系生長(zhǎng)及其養(yǎng)分吸收刺激作用的影響因素

腐植酸對(duì)植物根系生長(zhǎng)及其養(yǎng)分吸收刺激作用效果與腐植酸的添加量、來(lái)源、分子量大小、聚合程度高低和供試植物的種類有關(guān)。

1.2.1 腐植酸對(duì)植物根系生長(zhǎng)促進(jìn)作用的影響因素Berbara和García[54]通過水稻根系施用不同濃度腐植酸，發(fā)現(xiàn)水稻根系施用適量濃度的腐植酸后產(chǎn)生一定量的活性氧促進(jìn)了水稻的生長(zhǎng)和側(cè)根的形成，然而，施用高濃度的腐植酸提高了活性氧含量，導(dǎo)致脂質(zhì)過氧化，從而對(duì)水稻根系的生長(zhǎng)產(chǎn)生不良影響；Zandonadi等[38]和Canellas等[55]研究認(rèn)為，聚合程度低分子量小的腐植酸活性較高，能夠刺激玉米根系質(zhì)膜H+-ATP酶的活性和玉米根系生長(zhǎng)，且對(duì)玉米根區(qū)面積的促進(jìn)作用是聚合程度高的大分子量腐植酸的兩倍；而聚合程度高分子量大的腐植酸對(duì)液泡膜H+泵、玉米根系生長(zhǎng)和玉米根系微粒體中H+-ATP酶活性的刺激作用強(qiáng)于聚合程度低分子量小的腐植酸[38,56]；Jindo等[57]認(rèn)為，污泥堆肥和不堆肥產(chǎn)生的腐植酸樣品均能促進(jìn)玉米根系生長(zhǎng)，提高玉米維管束中質(zhì)子泵活性，且堆肥處理強(qiáng)于不堆肥，這是由于堆肥產(chǎn)生的腐植酸樣品含有更多的羧基，且具有更強(qiáng)的疏水特性，能夠產(chǎn)生更好的形態(tài)學(xué)和生物化學(xué)效應(yīng)。此外，相同的腐植酸作用于不同的植物也有不同的響應(yīng)。腐植酸及其分級(jí)物質(zhì)作用于擬南芥幼苗時(shí)，根系表現(xiàn)出主根變短、誘導(dǎo)側(cè)根生長(zhǎng)等類似于大量添加外源生長(zhǎng)素刺激的反應(yīng)；然而，作用于玉米幼苗時(shí)，根系則表現(xiàn)出主根和側(cè)根均有增長(zhǎng)的類似于添加低劑量的外源生長(zhǎng)素刺激的效應(yīng)[22]。

1.2.2 腐植酸對(duì)植物根系養(yǎng)分吸收刺激作用的影響因素腐植酸對(duì)植物根系養(yǎng)分吸收的促進(jìn)作用受其濃度、異質(zhì)性和分子量大小的影響。Maggioni等[46]研究表明，中間濃度腐植酸對(duì)燕麥根系K+和SO42–吸收的促進(jìn)效果明顯優(yōu)于過低或過高濃度的腐植酸處理。Albuzio等[45]研究表明，異質(zhì)性高且未分級(jí)的腐植酸對(duì)大麥吸收硝酸鹽的促進(jìn)作用顯著高于分級(jí)所得的異質(zhì)性低的樣品；而在分級(jí)所得的腐植酸中，大分子量(>10000D)和小分子量(<9000D)的腐植酸對(duì)大麥吸收硝酸鹽的促進(jìn)效果均強(qiáng)于中間分子量(9000～10000D)的腐植酸。也有研究認(rèn)為，小分子量組分能夠顯著刺激植物根系對(duì)NO3–的吸收，然而大分子量腐殖質(zhì)需要暴露在硝酸鹽溶液中很長(zhǎng)時(shí)間才能表現(xiàn)出較低的刺激作用[20,58]；Nardi等[50]則認(rèn)為，只有小分子量的腐植酸組分才能增加植物根系對(duì)NO3–的吸收，大分子量的腐植酸卻無(wú)此作用。

植物對(duì)腐植酸的吸收因腐植酸的分子量而異。研究認(rèn)為，小分子量的腐植酸組分(最大分子量小于3500D)容易到達(dá)高等植物細(xì)胞質(zhì)膜，且被部分吸收[20,48–50]；而大分子量的腐植酸組分(最小分子量大于3500D)只能與細(xì)胞壁發(fā)生接觸，且不能被吸收[31]。然而，也有文獻(xiàn)報(bào)道，大分子量的腐植酸也并非完全不能被植物所吸收，只是其進(jìn)入根系的數(shù)量低于小分子腐植酸[52–53]；Vaughan等[51]通過比較等添加量(10～250mg/L)條件下豌豆根系對(duì)小分子量腐植酸(富里酸)和大分子量腐植酸(胡敏酸)的吸收作用，發(fā)現(xiàn)，豌豆根系對(duì)富里酸和胡敏酸均具有吸收作用，但對(duì)富里酸的吸收量是胡敏酸吸收量的兩倍以上。因此，很多研究者認(rèn)為，小分子量組分是腐植酸中最具活性的部分，它更易被植物所吸收，且對(duì)植物根系生長(zhǎng)和養(yǎng)分離子的吸收具有更好的刺激效應(yīng)[48–50]。盡管如此，大分子量的腐植酸組分也因能夠調(diào)控植物根系生長(zhǎng)而具有較強(qiáng)的生物活性[29,38]，同時(shí)，大分子量的腐植酸處理誘導(dǎo)更高的根分化且刺激了與植物生長(zhǎng)和分化相關(guān)的新陳代謝過程中酶的活性[49,59]。

大多數(shù)研究認(rèn)為，對(duì)植物根系生長(zhǎng)、養(yǎng)分吸收和激素類活性影響的諸多因素中最為有效的腐植酸組分具有最多酸性基團(tuán)和最小分子量的特征，即腐植酸對(duì)植物的刺激效應(yīng)與其結(jié)構(gòu)及分子量大小有關(guān)，而與脂肪族和芳香族含量等表征其聚合程度的指標(biāo)關(guān)系不大[20,31,35,60]。然而，也有研究認(rèn)為低分子量腐植酸之所以成為影響其作用的主要因素與其具有較高含量的芳香族、羧基的和酚基的官能團(tuán)結(jié)構(gòu)密不可分[20,48–50]；此外，Canellas等[22]認(rèn)為腐植酸的特定生物活性分子含量對(duì)根系生長(zhǎng)和形態(tài)的生理影響大于其分子量大小的影響。因此，對(duì)于影響腐植酸作用于植物的關(guān)鍵因素仍需進(jìn)一步研究。

腐植酸對(duì)植物生長(zhǎng)的促進(jìn)作用，不僅表現(xiàn)在對(duì)植物根系生長(zhǎng)及根系對(duì)養(yǎng)分的吸收方面，其對(duì)植物地上部生長(zhǎng)也表現(xiàn)出一定的促進(jìn)作用。Jannin等[61]通過將生長(zhǎng)一周的油菜幼苗移入含有腐植酸(有機(jī)碳100mg/L)的霍格蘭營(yíng)養(yǎng)液中進(jìn)行培養(yǎng)，對(duì)植物根系和地上部與碳、氮和硫轉(zhuǎn)化相關(guān)的基因進(jìn)行測(cè)定，發(fā)現(xiàn)與不添加腐植酸的處理相比，腐植酸處理3天時(shí)，地上部差異性表達(dá)基因數(shù)量為720，是根系(366)的兩倍；且施用30天時(shí)，地上部有102個(gè)基因呈現(xiàn)出差異性表達(dá)，而根系中的基因均檢測(cè)不到差異性表達(dá)。硝酸還原酶、天冬酰胺合成酶、檸檬酸合成酶、異檸檬酸脫氫酶和蘋果酸脫氫酶是玉米葉片中參與氮素轉(zhuǎn)化與運(yùn)輸和有機(jī)酸合成的重要酶類，腐植酸能夠刺激其編碼基因的表達(dá)，從而促進(jìn)玉米的氮素吸收和氨基酸代謝，進(jìn)而促進(jìn)其生長(zhǎng)[62]。腐植酸還能通過誘導(dǎo)玉米葉片中參與次生代謝的重要酶類(苯基丙氨酸脫氨酶和絡(luò)氨酸解氨酶)基因的表達(dá)來(lái)促進(jìn)植物生長(zhǎng)[63]。Mora等[64]研究表明，不同濃度的腐植酸均能促進(jìn)黃瓜地上部生長(zhǎng)，這一效果在小麥、玉米和辣椒上也得到了證實(shí)[65–67]，產(chǎn)生這種影響的機(jī)理可能是腐植酸對(duì)根系H+-ATP酶活性和硝酸鹽在根部–地上部分布的影響，從而引起根部–地上部中一定的細(xì)胞激肽類、多肽和脫落酸分布的變化，進(jìn)而影響地上部生長(zhǎng)。

2 腐植酸通過增強(qiáng)植物抗逆性促進(jìn)植物生長(zhǎng)

2.1 腐植酸對(duì)逆境脅迫下植物生長(zhǎng)及代謝的影響

腐植酸能夠緩解生物和非生物脅迫對(duì)植物生長(zhǎng)的影響，改善植物形態(tài)生理特征，對(duì)逆境脅迫下植物的生長(zhǎng)具有保護(hù)機(jī)制，在植物生態(tài)安全性中具有預(yù)防氧化應(yīng)激的重要作用[23,68–69]。大量研究表明，水分、溫度、鹽分和重金屬等逆境脅迫下，腐植酸通過刺激植物各器官中蛋白質(zhì)和酶的合成，增強(qiáng)植物體內(nèi)過氧化物酶、過氧化氫酶、超氧化物歧化酶等與活性氧代謝相關(guān)的酶活性，并降低植物體內(nèi)丙二醛和質(zhì)膜透性，調(diào)節(jié)植物體內(nèi)的活性氧含量，減輕膜脂的過氧化程度，使植物保持較快的生長(zhǎng)速度，從而保持了細(xì)胞膜的滲透性能，增強(qiáng)了植物對(duì)干旱、寒冷、鹽分和重金屬等的抗性[23–24,70–72]。除了上述作用與功能，García等[73]認(rèn)為腐植酸還能夠修飾水稻根系中液泡膜水通道內(nèi)在蛋白基因OsTIP的表達(dá)，以增強(qiáng)水稻抵抗水分脅迫的能力。同時(shí)，物理作用也是腐植酸增強(qiáng)植物對(duì)水分脅迫抗性的重要方面。García等[74]研究表明，腐植酸添加后能夠在植物根系表面、根系表皮細(xì)胞和新生根毛中形成腐植酸凝聚體，降低了根系的滲透系數(shù)，增強(qiáng)其抗干旱能力。

腐植酸對(duì)植物抗逆性的改變不僅體現(xiàn)在對(duì)植物形態(tài)及生理特征的改變，還能夠通過改變植物生長(zhǎng)環(huán)境來(lái)增強(qiáng)植物的抗逆性。鹽分脅迫條件下，施用腐植酸肥料能夠降低土壤介質(zhì)的電導(dǎo)率，促進(jìn)挪威楓和銀杏幼苗的生長(zhǎng)，提高其葉綠素含量[75]；腐植酸能夠增加土壤團(tuán)聚體含量、土壤緊實(shí)性、持水能力、陽(yáng)離子交換能力，促進(jìn)植物生長(zhǎng)[24]；此外，干旱脅迫下，植物根系分泌的有機(jī)酸能夠?qū)Ω菜崮z體產(chǎn)生局部破壞作用，使其釋放出個(gè)體生長(zhǎng)調(diào)節(jié)分子，這些分子足夠小，以至于能夠穿透細(xì)胞壁基質(zhì)進(jìn)入細(xì)胞膜，從而影響基因的表達(dá)和酶的活性[76]。

生物脅迫下，腐植酸增強(qiáng)植物抗逆作用主要體現(xiàn)在其對(duì)植物致病菌的抑制作用方面。研究證實(shí)，腐植酸不僅能夠降低土壤真菌鏈格孢菌Alternaria alternate、大刀鐮刀菌Fusarium colmorum和尖孢鐮刀菌Fusarium oxysporum分生孢子的存活率，還能夠抑制分生孢子菌絲的伸長(zhǎng)，且對(duì)分生孢子繁殖的抑制為其主要作用方式[77–78]。通過以上作用的發(fā)揮，腐植酸顯著降低了根須病的發(fā)病率。

2.2 逆境脅迫下腐植酸對(duì)植物作用的影響因素

逆境脅迫下，腐植酸對(duì)植物的作用大小受脅迫程度高低、腐植酸添加量、腐植酸結(jié)構(gòu)等因素的影響[23,72,78]。腐植酸對(duì)植物抗逆性的影響因逆境脅迫程度的高低而異。腐植酸可緩解土壤中輕度Cd污染，顯著抑制小麥幼苗對(duì)Cd的吸收，促進(jìn)小麥幼苗干物質(zhì)積累及其對(duì)Cu、Zn、Fe、Mn等微量營(yíng)養(yǎng)元素的吸收和積累；隨Cd污染程度加重，腐植酸對(duì)植株Cd吸收的抑制能力減弱，并對(duì)Cu、Zn、Fe、Mn等微量營(yíng)養(yǎng)元素吸收產(chǎn)生不同影響[72]，因此，逆境條件下，植物受逆境脅迫的程度影響腐植酸的作用效果。腐植酸對(duì)植物抗逆性的影響還受其添加濃度高低的影響。用濃度為0～500μg/mL的腐植酸對(duì)干旱脅迫下玉米浸種，發(fā)現(xiàn)浸種后的玉米幼苗活性氧系統(tǒng)增強(qiáng)，膜脂過氧化程度降低，且對(duì)玉米抗旱性的促進(jìn)效應(yīng)隨浸種腐植酸濃度的增加而愈加顯著[79]。而García等[23]則認(rèn)為，水分脅迫下，隨著腐植酸施用量(HA34和46mg/L)的增加，植物的生長(zhǎng)速度和含水量增長(zhǎng)加快，但是，對(duì)水稻抗氧化防御系統(tǒng)的酶活性并沒有表現(xiàn)出明顯的差異。通過盆栽試驗(yàn)，研究葉面噴施濃度為20、40、60、80和100mg/L的腐植酸對(duì)高溫脅迫下掌葉半夏幼苗生長(zhǎng)生理指標(biāo)及次生代謝的調(diào)控效應(yīng)，發(fā)現(xiàn)噴施60mg/L的腐植酸處理對(duì)高溫脅迫下掌葉半夏幼苗葉片的調(diào)控效應(yīng)最好，最為有效地減輕了夏季高溫對(duì)掌葉半夏幼苗葉片的傷害、延緩衰老、提高幼苗抗熱性，促進(jìn)生長(zhǎng)、延長(zhǎng)生長(zhǎng)期[80]?？梢姡菜崽砑恿坎⒎窃蕉嘣胶?，而是有一個(gè)適宜的濃度，且過量的腐植酸施用甚至增加了番茄感染根腐病病原菌的可能性，提高了番茄根腐病的發(fā)病率[81]。因此，逆境條件下，腐植酸添加量影響其對(duì)植物抗逆性的作用效果，且存在最適宜的添加濃度。

除添加量之外，腐植酸所具有的烷基、羧基和羰基等官能團(tuán)也是其抵抗逆境脅迫的關(guān)鍵作用因素，甚至有研究認(rèn)為這些官能團(tuán)的作用大于添加量[74,79]。Loffredo等[79]研究表明，腐植酸對(duì)植物枯萎病致病菌尖孢鐮刀菌Fusarium oxysporum的抑制效應(yīng)與其羧基官能團(tuán)性質(zhì)和含量相關(guān)。Gholami等[82]也認(rèn)為結(jié)構(gòu)不同的胡敏酸與富里酸消除鹽分對(duì)車前草的傷害效果不同，且胡敏酸的作用效果強(qiáng)于富里酸。

圖2 1996～2015年Web of Science收錄的腐植酸與氮、磷和鉀作用研究的發(fā)文量Fig. 2 The published papers of humic acid and N, P and K in Web of Science from 1996 to 2015

3 腐植酸通過調(diào)控土壤與肥料中的養(yǎng)分轉(zhuǎn)化促進(jìn)植物生長(zhǎng)

3.1 腐植酸調(diào)控土壤與肥料中的養(yǎng)分轉(zhuǎn)化，提高其有效性

以腐植酸(humic acid，HA)與主要肥料養(yǎng)分(nitrogen/phosphorus/potassium，N/P/K)為檢索詞，對(duì)1996～2015年間Web of Science數(shù)據(jù)庫(kù)收錄的發(fā)文量進(jìn)行統(tǒng)計(jì)(檢索時(shí)間2016年4月19日)，得到如圖2所示雷達(dá)圖。由圖2可知，近20年發(fā)文量逐漸增加，可見研究人員對(duì)腐植酸與養(yǎng)分尤其是氮素的交互作用的關(guān)注度逐年增加。大量研究證實(shí)，腐植酸因具有較多的酸性功能基團(tuán)和較大的陽(yáng)離子交換量，能夠作為土壤調(diào)理劑改善土壤理化性質(zhì)，增強(qiáng)土壤保蓄養(yǎng)分離子的能力[83–84]；且能夠通過與氮素、磷素和鉀素的結(jié)合效應(yīng)[85–88]、與磷酸鹽的競(jìng)爭(zhēng)效應(yīng)[14,89]和對(duì)鉀離子的吸附作用[90–91]固持與活化肥料中的養(yǎng)分，提高肥料有效性和緩釋性能，從而提高肥料利用率。因此，腐植酸能夠與土壤與肥料中的養(yǎng)分發(fā)生作用，調(diào)控土壤與肥料中養(yǎng)分形態(tài)轉(zhuǎn)化，提高其利用效率，進(jìn)而促進(jìn)植物生長(zhǎng)。

3.1.1 腐植酸對(duì)土壤與肥料中養(yǎng)分形態(tài)的調(diào)控腐植酸對(duì)土壤中的養(yǎng)分形態(tài)具有調(diào)控效應(yīng)。腐植酸能夠與磷酸鹽競(jìng)爭(zhēng)土壤礦物表面的吸附位點(diǎn)，降低土壤礦物對(duì)磷酸鹽的吸附；與土壤中的鈣離子發(fā)生結(jié)合作用及與Ca-P發(fā)生作用，減少Ca-P沉淀的生成，提高土壤與肥料中磷素的有效性[14,89,92]。Olk和Cassman[90]研究表明，腐植酸具有結(jié)合土壤中鉀離子、增強(qiáng)其抗土壤吸附的能力，從而認(rèn)為其具有調(diào)控土壤鉀素有效性和防固定的潛力。此外，腐植酸因具有較多的酸性基團(tuán)，施用后可降低土壤pH，從而提高土壤中微量元素(Zn、Mn、Fe、Cu)的有效性[93]。

腐植酸對(duì)肥料中的養(yǎng)分形態(tài)具有調(diào)控效應(yīng)。腐植酸能夠通過自身的羧基和酚羥基與尿素的酰胺基作用生成腐植酸-脲絡(luò)合物，該物質(zhì)具有較高的穩(wěn)定性，能夠抑制尿素分解、提高氮素利用效率，實(shí)現(xiàn)尿素的長(zhǎng)效緩效[84–85,94]。同時(shí)，腐植酸能夠通過非生物作用固定肥料中的銨態(tài)氮，并形成以吲哚和吡咯[86]、酰胺-縮氨酸結(jié)構(gòu)[27,87]等為代表的化學(xué)物質(zhì)與結(jié)合形式。腐植酸中所含的羥基官能團(tuán)能夠與磷酸一銨通過陽(yáng)離子的橋接作用發(fā)生復(fù)合反應(yīng)，生成水溶性的腐植酸磷和腐銨磷[88]，提高了磷肥的有效性。腐植酸還能夠吸附與固定肥料中的鉀素或與肥料中的鉀素反應(yīng)，生成以膠體化合物形式存在的腐植酸鉀，它不易隨水流失，提高了鉀肥的緩釋性能[88,91]。

3.1.2 腐植酸能夠提高土壤與肥料中養(yǎng)分的有效性腐植酸能夠提高肥料養(yǎng)分的有效性。施用添加胡敏酸和富里酸的尿素后，土壤中NH4+-N和NO3

–-N的累積量明顯高于普通尿素處理[3]；而Suntari等[10]則通過開展土壤培養(yǎng)試驗(yàn)，進(jìn)一步研究發(fā)現(xiàn)，腐植酸尿素肥料能夠在水稻種植后第28和42天分別提高土壤中NH4

+-N和NO3–-N的含量。腐植酸與磷肥一起施用后土壤中速效磷含量顯著高于普通磷肥處理，且土壤對(duì)磷的固定率比普通磷肥降低7.32%[95]。

腐植酸能夠降低肥料施用后土壤與肥料中養(yǎng)分的損失。腐植酸主要組分胡敏酸和富里酸的pH分別為1.89～2.27和1.14～1.20，施用于土壤后，造成土壤pH短暫降低，從而緩解甚至抑制了施肥區(qū)域尿素的水解，進(jìn)而降低了尿素的氨揮發(fā)損失[25,27]。同時(shí)，腐植酸還通過短暫降低土壤pH，降低土壤中氨的揮發(fā)損失[84]。Reeza等[25]研究發(fā)現(xiàn)，土壤中施用了添加胡敏酸和富里酸的尿素后，氨揮發(fā)量較普通尿素處理顯著降低了12.92%～20.12%；Yusuff等[96]進(jìn)一步證實(shí)腐植酸與尿素混合施用在培養(yǎng)初期(0～10天)氨揮發(fā)量顯著低于單施尿素處理(P<0.05)，但隨后高于單施尿素處理。因此，腐植酸與尿素混合施用能夠在初期抑制氨揮發(fā)并在后期將保蓄在土壤中的氨緩慢釋放，從而提高氮肥利用率[8,11]。此外，腐植酸施用還能夠降低水稻土中NH4+-N和NO3

–-N隨農(nóng)田排水的損失量[9]。

因此，腐植酸能夠通過調(diào)控土壤與肥料中養(yǎng)分的形態(tài)，提高肥料施用后土壤與肥料中養(yǎng)分的有效性和降低土壤與肥料中的養(yǎng)分損失，提高肥料利用率和土壤供肥能力，促進(jìn)植物生長(zhǎng)[97]。

3.2 腐植酸調(diào)控土壤與肥料養(yǎng)分的影響因素

腐植酸對(duì)土壤與肥料養(yǎng)分的調(diào)控效應(yīng)受腐植酸種類、官能團(tuán)和添加量等因素的影響。腐植酸的種類和來(lái)源不同，導(dǎo)致其對(duì)土壤與肥料養(yǎng)分的調(diào)控效應(yīng)存在差異。不同產(chǎn)地的腐植酸對(duì)小白菜各生育期土壤氮磷鉀含量的影響存在顯著的差異[98]；腐植酸的組分胡敏酸和富里酸對(duì)氨均有一定的固定作用，且與氨結(jié)合的位點(diǎn)基本一致，但富里酸對(duì)氨的固定量大于胡敏酸[86]，這可能是由于腐植酸的羧基和羥基在固定氨方面起著最主要的作用，而這些基團(tuán)在富里酸中具有更廣泛的分布[99–101]。腐植酸某些特定的官能團(tuán)與尿素、銨根離子、磷酸鹽和鉀離子均能夠發(fā)生結(jié)合反應(yīng)，因此，腐植酸結(jié)合位點(diǎn)數(shù)量的多少影響腐植酸對(duì)土壤和肥料養(yǎng)分的調(diào)控效果[88]。腐植酸的添加量對(duì)土壤養(yǎng)分的調(diào)控效果也不相同。一方面，腐植酸添加量影響土壤中養(yǎng)分的釋放率。Bama等[102]研究表明，土壤中N、P和K的釋放與腐植酸的添加量呈線性相關(guān)關(guān)系。另一方面，腐植酸的添加量對(duì)肥料施用后養(yǎng)分的轉(zhuǎn)化影響存在差異，腐植酸施用量達(dá)到一定水平后，對(duì)土壤固定態(tài)磷才具有激活效應(yīng)[103]。Yusuff等[96]研究表明，腐植酸添加量越大，其對(duì)尿素氨揮發(fā)的抑制效果越強(qiáng)。劉增兵等[104]的研究結(jié)果與此一致。此外，環(huán)境pH影響腐植酸與磷酸鹽的競(jìng)爭(zhēng)吸附效應(yīng)。低pH條件下，腐植酸與磷酸鹽對(duì)針鐵礦、三水鋁礦和土壤上的吸附位點(diǎn)具有更強(qiáng)的競(jìng)爭(zhēng)效應(yīng)[105]。

綜上，腐植酸對(duì)肥料及土壤養(yǎng)分有效性的調(diào)控是其降低土壤pH、活化與固持土壤與肥料養(yǎng)分、減少土壤與肥料養(yǎng)分損失和結(jié)合土壤肥料等作用的綜合結(jié)果，且具體效果因腐植酸種類、官能團(tuán)數(shù)量和添加量等因素而異。

4 腐植酸通過調(diào)控土壤微生物及酶活性促進(jìn)作物生長(zhǎng)

4.1 腐植酸對(duì)土壤酶活性的影響

腐植酸是土壤腐殖質(zhì)的重要組成成分，具有穩(wěn)定的碳形態(tài)，對(duì)土壤微生物的生物活性具有重要的作用[30,106]；同時(shí)，腐植酸還能夠通過調(diào)控土壤微生物及酶活性，為植物根系的生長(zhǎng)和肥料養(yǎng)分的保蓄提供良好的生長(zhǎng)環(huán)境來(lái)實(shí)現(xiàn)其促進(jìn)作物生長(zhǎng)的作用。腐植酸施用能夠影響土壤酶的活性。腐植酸對(duì)脲酶的作用是其影響土壤酶的重要方面。研究認(rèn)為，腐植酸能夠在加入初期抑制土壤脲酶活性，降低尿素水解速度，從而減少水解產(chǎn)物氨的揮發(fā)；而加入后期卻能夠穩(wěn)定脲酶活性，使尿素繼續(xù)以相對(duì)穩(wěn)定的速度轉(zhuǎn)化成氨，供給植物生長(zhǎng)[107–108]，而腐植酸之所以能夠抑制脲酶活性，一方面是因?yàn)楦菜嶂写罅坎伙柡玩I可以有效防止脲酶中的活性官能團(tuán)(巰基，–SH)氧化，另一方面腐植酸還能螯合土壤中脲酶巰基的抑制劑(Cu2+和Hg2+)[109]。此外，腐植酸對(duì)其他酶類的影響有：在含大量有機(jī)質(zhì)的土壤中，腐植酸能夠強(qiáng)烈抑制脲酶、酸性磷酸酶和N-乙酰氨基葡萄糖苷酶等的活性[26]；而彭正萍等[15]研究表明，向種植油菜的潮褐土中施用腐植酸復(fù)合肥，較普通復(fù)合肥更能提高土壤堿性磷酸酶活性和過氧化氫酶活性，從而活化土壤中的磷素，提高有效磷含量；此外，劉蘭蘭等[110]通過小區(qū)試驗(yàn)證實(shí)，腐植酸具有提高土壤酸性磷酸酶和蔗糖酶活性的作用；Sellamuthu和Govindaswamy[111]的研究則進(jìn)一步認(rèn)為，腐植酸和肥料配合施用對(duì)土壤中過氧化氫酶、脫氫酶和堿性磷酸酶活性具有提高效果，且隨著腐植酸添加量(10～40kg/hm2)的增加，效果先增強(qiáng)后減弱。

4.2 腐植酸對(duì)土壤微生物結(jié)構(gòu)和數(shù)量的影響

腐植酸還能夠影響土壤中微生物的數(shù)量和多樣性。Sellamuthu和Govindaswamy[111]研究表明，肥料和腐植酸配合施用增加了甘蔗種植條件下根際土壤中細(xì)菌、真菌和放線菌數(shù)量，且隨著腐植酸添加量(10～40kg/hm2)的增加，各種微生物數(shù)量均呈現(xiàn)先增加后降低的趨勢(shì)，30kg/hm2的腐植酸與肥料配合施用條件下，微生物的數(shù)量最多；劉蘭蘭等[103]和楊云馬等[112]的研究結(jié)果與此一致，且認(rèn)為腐植酸對(duì)不同種類的微生物作用效果不同，其中，對(duì)細(xì)菌的影響最大，真菌次之，對(duì)放線菌的影響最?。籇ong等[27]研究表明，褐煤腐植酸能夠通過降低土壤中尿素向氨的水解速度和緩沖土壤pH等作用來(lái)抑制氨化細(xì)菌、氨化古菌等微生物群落組成和數(shù)量的改變，緩沖尿素施用對(duì)土壤中細(xì)胞多樣性和總量的影響，從而降低氨被氧化成亞硝酸和硝酸的速度，以及降低通過反硝化轉(zhuǎn)化成氮?dú)庠斐傻膿p失，最終能夠使更多的氮為植物所吸收利用，對(duì)于植物生長(zhǎng)和作物增產(chǎn)均具有重要的意義。

腐植酸對(duì)土壤微生物的影響受腐植酸種類的影響。Bhardwaj和Gaur[113]研究表明，胡敏酸和富里酸均能明顯促進(jìn)固氮菌生長(zhǎng)，提高固氮菌的固氮能力，且以富里酸的提高效果更為顯著，對(duì)固氮菌數(shù)量的影響大于其對(duì)固氮能力的影響。

此外，腐植酸含有能夠提高土壤肥力和增加土壤養(yǎng)分有效性的大多數(shù)元素，能夠促進(jìn)作物生長(zhǎng)、增加作物產(chǎn)量[114]；腐植酸還能夠通過增加細(xì)胞呼吸和細(xì)胞膜對(duì)養(yǎng)分的吸收，提高作物二磷酸核酮氧合酶/羧化酶活性，增加植物光合活性，提高豆科作物的生物固氮等，從而促進(jìn)作物生長(zhǎng)、增加作物產(chǎn)量[115–117]。

5 研究展望

腐植酸可通過直接刺激植物根系生長(zhǎng)和養(yǎng)分吸收、增強(qiáng)植物抗逆性、間接調(diào)控土壤與肥料中養(yǎng)分的有效性和影響土壤微生物數(shù)量結(jié)構(gòu)和酶活性等調(diào)控養(yǎng)分轉(zhuǎn)化促進(jìn)植物生長(zhǎng)；同時(shí)，腐植酸對(duì)植物生長(zhǎng)的促進(jìn)作用受腐植酸來(lái)源、組成、結(jié)構(gòu)、濃度、植物種類等影響，因此，對(duì)腐植酸促進(jìn)植物生長(zhǎng)主要途徑的研究和影響腐植酸作用發(fā)揮主控因子的研究顯得十分有必要。

近些年來(lái)，人們對(duì)于腐植酸的研究，無(wú)論是在研究技術(shù)、研究方法上都在逐步發(fā)展，然而，隨著對(duì)腐植酸應(yīng)用目標(biāo)要求的逐漸提高和研究?jī)?nèi)容的逐漸深入，現(xiàn)有的研究?jī)?nèi)容已不能滿足未來(lái)發(fā)展的需求，還需要從以下幾個(gè)方面實(shí)現(xiàn)突破：

1)腐植酸基本特征的研究。盡管國(guó)內(nèi)外對(duì)腐植酸結(jié)構(gòu)與組成的研究已有相當(dāng)長(zhǎng)的歷史，但具有高度異質(zhì)性的腐植酸仍然是研究的熱點(diǎn)與難點(diǎn)，因此，利用新的技術(shù)手段，如核磁共振等對(duì)腐植酸的結(jié)構(gòu)和組成等進(jìn)行表征和分析仍需進(jìn)一步開展。

2)影響腐植酸作用的主控因子研究。在研究腐植酸基本特征的基礎(chǔ)上，對(duì)影響腐植酸作用的因子進(jìn)行分析，探究腐植酸作用的主控因子，為腐植酸的深入研究和活化改性提供理論依據(jù)。

3)土壤–植物系統(tǒng)中，腐植酸促進(jìn)植物生長(zhǎng)的主要途徑研究。當(dāng)前對(duì)腐植酸促進(jìn)植物生長(zhǎng)的途徑研究手段存在不一致性，如腐植酸對(duì)根系生長(zhǎng)的刺激作用多采用水培的方法[20–22]，對(duì)土壤微生物和土壤酶的調(diào)控作用多采用室內(nèi)恒溫培養(yǎng)的方法[27]，而對(duì)土壤養(yǎng)分有效性的影響則多是田間試驗(yàn)的結(jié)果[25]，因此，缺乏系統(tǒng)的研究來(lái)綜合比較腐植酸對(duì)植物生長(zhǎng)的促進(jìn)作用，從而分析土壤–植物系統(tǒng)中，腐植酸促進(jìn)植物生長(zhǎng)的主要途徑。

4)腐植酸對(duì)土壤功能性微生物等的影響研究。腐植酸能夠影響土壤微生物結(jié)構(gòu)，但目前多數(shù)研究?jī)H停留在對(duì)微生物數(shù)量的研究層面，未進(jìn)一步深入，而對(duì)功能性微生物的研究有助于探究腐植酸促進(jìn)土壤中養(yǎng)分轉(zhuǎn)化的機(jī)理，為腐植酸的利用提供重要的理論支持。

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Advances in humic acid for promoting plant growth and its mechanism

ZHANG Shui-qin1,2,YUAN Liang1,LIN Zhi-an1,LI Yan-ting1,HU Shu-wen2,ZHAO Bing-qiang1*
(1 Key Laboratory of Plant Nutrition and Fertilizer, Ministry of Agriculture/Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081, China; 2 College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, China)

【Objectives】Humic acid plays an important role in Chinese agricultural production.Many research results have showed that humic acid could prompt plant growth.In this study,the researches on humic acid for prompting plant growth were systematically summarized,and the mechanism was focused on stimulating roots growth,regulating nutrition transformation,and affecting microbial activity.According to review of the research status of humic acid prompting plant growth,we aimed to provide the references for the further researches and application of humic acid at last.【Major advances】1)Humic acid produces effects on plant like biostimulants.In detail,humic acid can improve H+-ATPase activity of roots,simulate root elongation and the increase of lateral root points,which is conducive to the increase of root activity,as well as the expansion of the contact area between roots and soil nutrition.2)Humic acid regulates the metabolism of plant and improves the environment of plant growth under stress.Based on this,the abiotic and biotic stress is eliminated and the plant isprevented from the injury,which is conducive to plant growth.3)Humic acid reacts with nitrogen,phosphorus and potassium,and new compounds are synthetized.In addition,humic acid has competition effects with phosphate,and adsorption effects with potassium ions.All the effects are beneficial to immobilize and activate the nutrients in soil and fertilizer.Thus,the availability and the sustainable release of the nutrients in soil and fertilizer are enhanced,and plant growth is prompted.4)Humic acid also plays an important role in regulating soil enzyme activities related to soil or fertilizer nutrition transformation,and microbial community structure and biomass. Owing to the regulation,the nutrition is activated in soil,and the goal of nutrition preservation is achieved. Therefore,it is ensured that plant growth can get permanent nutrient supply.5)The promotion of humic acid on plant growth is affected by the structural characteristics,addition amounts of humic acid,and crop species.【Suggestions and expectations】The limited technology and the discrepancy of researches impede deeper and systematic research in the mechanism of humic acid prompting plant growth.Therefore,the future study will focus on the basic characteristics of humic acid,the dominating factor analysis of humic acid action,the principal pathway of humic acid prompting plant growth in soil-plant systems,and the effect of humic acid on soil functional microorganism.

humic acid;plant growth;root system;stress resistance;nutrition transformation

2016–06–27接受日期：2016–09–10

“十三五”國(guó)家重點(diǎn)研發(fā)計(jì)劃項(xiàng)目（2016YFD0200402）；國(guó)家自然科學(xué)基金項(xiàng)目（31601827）；中央級(jí)公益性科研院所專項(xiàng)資金項(xiàng)目（IARRP-2014-5）資助。

張水勤（1988—），女，河南新密人，博士研究生，主要從事新型肥料研究。E-mail：shuiqin08@163.com

*通信作者E-mail：zhaobingqiang@caas.cn