孫彩麗，肖列，李鵬，薛萐,3，劉國(guó)彬,3*

（1西北農(nóng)林科技大學(xué)水土保持研究所黃土高原土壤侵蝕與旱地農(nóng)業(yè)國(guó)家重點(diǎn)實(shí)驗(yàn)室，陜西楊凌712100；2西安理工大學(xué)西北旱區(qū)生態(tài)水利工程國(guó)家重點(diǎn)實(shí)驗(yàn)室培育基地，陜西西安710048；3中國(guó)科學(xué)院水利部水土保持研究所，陜西楊凌712100）

氮素添加和干旱脅迫下白羊草碳氮磷化學(xué)計(jì)量特征

孫彩麗1，肖列2，李鵬2，薛萐1,3，劉國(guó)彬1,3*

（1西北農(nóng)林科技大學(xué)水土保持研究所黃土高原土壤侵蝕與旱地農(nóng)業(yè)國(guó)家重點(diǎn)實(shí)驗(yàn)室，陜西楊凌712100；2西安理工大學(xué)西北旱區(qū)生態(tài)水利工程國(guó)家重點(diǎn)實(shí)驗(yàn)室培育基地，陜西西安710048；3中國(guó)科學(xué)院水利部水土保持研究所，陜西楊凌712100）

【目的】氮素和水分是干旱半干旱區(qū)生態(tài)系統(tǒng)的主要限制因子，研究?jī)烧呓换プ饔脤?duì)干旱半干旱區(qū)植物碳(C)、氮(N)、磷(P)化學(xué)計(jì)量特征的影響有助于深入了解干旱半干旱生態(tài)系統(tǒng)對(duì)全球變化的響應(yīng)?！痉椒ā恳渣S土丘陵區(qū)退耕地典型草本植物白羊草(Bothriochloa ischaemum)為研究對(duì)象，采用盆栽控制試驗(yàn)，設(shè)置添加氮0(對(duì)照)、2.5g/(m2·a)(低氮)、5.0g/(m2·a)(高氮)三個(gè)水平；供水處理設(shè)75%～80%FC(充分供水)、55%～60%FC(輕度干旱脅迫)和35%～40%FC(重度干旱脅迫)三個(gè)水平。測(cè)定了白羊草地上部分和根系碳氮磷含量，討論了氮素和水分供應(yīng)對(duì)其化學(xué)計(jì)量特征的影響?！窘Y(jié)果】氮素添加和干旱脅迫對(duì)白羊草地上部分和根系碳含量無(wú)顯著影響，氮素添加使白羊草地上部分氮含量提高9.7%～48.8%(P<0.001)，而干旱脅迫使其降低2.8%～28.3%(P<0.001)。氮素添加和干旱脅迫對(duì)白羊草根系氮含量的影響表現(xiàn)為正常水分條件下氮素添加使根系氮含量提高25.0%～26.1%(P<0.01)，而干旱條件下氮素添加無(wú)顯著作用。氮素添加和干旱脅迫使白羊草地上部分磷含量分別降低17.4%～31.8%和12.0%～22.1%(P<0.001)。氮素添加和干旱脅迫對(duì)白羊草地上部分C∶N的影響表現(xiàn)為在干旱脅迫條件下氮素添加使地上部分C∶N降低24.9%～32.9%(P<0.05)，在正常供水條件下氮素添加無(wú)顯著影響。氮素添加對(duì)根系部分C∶N有顯著影響，在正常供水條件下氮素添加使根系部分C∶N降低19.8%～24.5%(P<0.05)。氮素添加和干旱脅迫使白羊草地上部分C∶P分別提高24.4%～42.3%和12.2%～31.0%(P<0.001)，對(duì)根系C∶P無(wú)顯著影響。氮素添加顯著提高白羊草地上部分N∶P，干旱脅迫對(duì)白羊草地上部分N∶P無(wú)顯著影響。氮素添加和干旱脅迫對(duì)白羊草根系部分N∶P表現(xiàn)為在正常供水條件下氮素添加使根系部分N∶P提高26.8%～54.8%(P<0.05)，在干旱脅迫條件下氮素添加無(wú)顯著影響?！窘Y(jié)論】氮素添加條件下白羊草C∶P和N∶P的提高表明氮沉降增加一定程度上改善了土壤供氮狀況，進(jìn)一步加劇了磷素限制作用。氮素增加條件下干旱脅迫對(duì)N∶P無(wú)顯著影響，表明白羊草的生長(zhǎng)將逐漸受到氮素和磷素的共同限制。

白羊草；化學(xué)計(jì)量學(xué)；干旱；氮素添加；養(yǎng)分限制；黃土高原

植物碳(C)、氮(N)、磷(P)化學(xué)計(jì)量特征是了解碳、氮、磷素分配規(guī)律和確定植物生長(zhǎng)限制性元素類型的重要依據(jù)，對(duì)于認(rèn)識(shí)生態(tài)系統(tǒng)元素生物地球化學(xué)循環(huán)具有重要意義[1–3]。近年來(lái)，隨著氮肥的大量生產(chǎn)和使用以及畜牧業(yè)迅猛發(fā)展等，氮沉降增加帶來(lái)的生態(tài)效應(yīng)逐漸成為國(guó)內(nèi)外生態(tài)學(xué)家關(guān)注的熱點(diǎn)問(wèn)題[4–5]。隨著對(duì)全球變化認(rèn)識(shí)的逐漸深入，人們也開始關(guān)注多個(gè)全球變化因子交互作用對(duì)生態(tài)系統(tǒng)的影響[2,6–7]。干旱半干旱地區(qū)的生態(tài)系統(tǒng)受氮素和水分雙重限制，研究氮沉降增加和干旱脅迫對(duì)植物生態(tài)化學(xué)計(jì)量特征的影響對(duì)于深入了解全球變化下干旱生態(tài)系統(tǒng)的響應(yīng)具有重要意義。

人類活動(dòng)直接或間接導(dǎo)致生態(tài)系統(tǒng)氮沉降量的顯著增加[8–9]。氮沉降增加提高了土壤中可利用氮素含量，為植物的生長(zhǎng)提供了氮素的來(lái)源，導(dǎo)致植物組織中C∶N的降低[10–11]。同時(shí)，短期氮沉降增加通過(guò)提高植物體氮素含量，增大了植物組織的N∶P[12–14]。但是長(zhǎng)期氮沉降研究表明，氮沉降增加對(duì)植物體N∶P沒(méi)有顯著影響[15–16]。此外，由于植被種類、管理措施、氮添加量和初始土壤養(yǎng)分條件的差異也會(huì)造成植物體N∶P對(duì)氮沉降的響應(yīng)不同[5,8,14–15]。與此同時(shí)，隨著全球氣候變暖，干旱成為世界范圍內(nèi)普遍存在的問(wèn)題，而且有愈演愈烈的趨勢(shì)[17–18]。干旱導(dǎo)致土壤中可利用水分含量顯著降低，土壤含水量會(huì)通過(guò)影響枯落物分解[19]和元素的礦化過(guò)程[20–21]來(lái)改變土壤中營(yíng)養(yǎng)元素的含量。長(zhǎng)期的干旱脅迫會(huì)顯著抑制土壤中參與氮磷元素循環(huán)轉(zhuǎn)化的酶活性[22]，導(dǎo)致土壤中可利用性氮磷元素含量降低，尤其是可利用性磷素的含量[23]，從而改變植物組織中C∶P、C∶N和N∶P[24–26]。在全球變化的背景下，氮沉降增加和干旱脅迫相互伴生、相互耦合，共同對(duì)陸地生態(tài)系統(tǒng)產(chǎn)生顯著影響[27]。氮沉降的顯著增加能否減輕干旱脅迫對(duì)植物生長(zhǎng)的氮素限制，而磷素限制作用是否會(huì)進(jìn)一步加劇還鮮有研究。

黃土丘陵區(qū)地處干旱半干旱地區(qū)，水分是限制植物生長(zhǎng)的重要因素，研究表明近50年來(lái)該區(qū)降水量逐漸減少，且降水年際間變化大，月際間分配不均勻，干旱將會(huì)進(jìn)一步限制該區(qū)的植被恢復(fù)過(guò)程[28]。該區(qū)目前的氮沉降量為N2.2g/(m2·a)[29–30]，據(jù)預(yù)測(cè)，未來(lái)該區(qū)氮沉降量將會(huì)持續(xù)增加[31]。研究氮沉降量持續(xù)增加和干旱脅迫加劇情況下，植物體碳、氮、磷含量及其化學(xué)計(jì)量特征的響應(yīng)，對(duì)于預(yù)測(cè)未來(lái)氣候變化對(duì)全球植被的影響具有重要的意義。

1 材料與方法

1.1 試驗(yàn)材料

試驗(yàn)材料采用黃土丘陵區(qū)地帶性草原建群種白羊草(Bothriochloa ischaemum)，種子于2013年秋季采自中國(guó)科學(xué)院安塞水土保持綜合試驗(yàn)站(36°51′30″N、109°19′23″E，海拔1068~1309m)的試驗(yàn)田中。供試土壤為陜北安塞縣的黃綿土，其基本理化性質(zhì)為：田間持水量20%，土壤有機(jī)質(zhì)2.58g/kg，全氮0.21 g/kg，全磷0.57g/kg，速效氮11.55mg/kg，pH為8.24。采用自制的PVC圓筒(內(nèi)徑15cm、高20cm)作為盆栽器皿，每盆裝入等量風(fēng)干的土壤3.8kg，以盆栽方式培育白羊草幼苗。播種前，測(cè)定白羊草種子的發(fā)芽率在90%以上。2014年6月1日播種，每盆點(diǎn)取三個(gè)穴，每穴播3粒種子，待種子發(fā)芽生長(zhǎng)穩(wěn)定后，每盆每穴留健壯苗1株。育苗期間充分供水，保持幼苗正常生長(zhǎng)。

1.2 試驗(yàn)設(shè)計(jì)

本試驗(yàn)采用水分和施氮雙因素完全隨機(jī)試驗(yàn)設(shè)計(jì)。2014年8月1日將盆栽移入人工氣候室(AGCD003N逆境型，浙江求是人工環(huán)境有限公司)，設(shè)定氣候室光照為500μmol/(m2·s)，空氣溫度為28℃/ 22℃(晝/夜)，濕度為55%。待盆栽幼苗穩(wěn)定幾天后開始進(jìn)行干旱脅迫和施氮處理。試驗(yàn)設(shè)3個(gè)水分水平，分別為田間持水量的75%～80%(WW)、55%～60%(MD)和35%～40%(SD)，依次代表正常供水、中度干旱脅迫和重度干旱脅迫。每天下午6點(diǎn)左右稱重，補(bǔ)充消耗的水分，控制在設(shè)定的土壤水分水平。設(shè)置3個(gè)氮素添加水平：0、2.5和5g/(m2·a)，以N0、N2.5、N5表示。N2.5和N5分別代表低氮和高氮添加水平。將含氮濃度為18.4mmol/L的NH4NO3溶液0、5和10mL分別均勻的噴灑到N2.5和N5處理的土壤表面，每?jī)芍苓M(jìn)行一次，共6次。試驗(yàn)共計(jì)6個(gè)處理，每個(gè)處理5個(gè)重復(fù)。

2014年11月15日，盆栽試驗(yàn)結(jié)束。用剪刀將每盆中的3株白羊草貼土壤表面取植株的地上部分。將土柱從PVC管中取出，分離根系和土壤，用鑷子挑取土壤中殘留的根系，將獲得的根系用蒸餾水沖洗干凈。將所采集的植物地上部分和根系在80℃的烘箱中烘至恒重，用粉碎機(jī)磨碎后用于植物樣品碳、氮、磷元素含量的測(cè)定。

1.3 測(cè)定項(xiàng)目及方法

植物樣品碳含量采用重鉻酸鉀硫酸氧化法測(cè)定，氮含量采用半微量開氏法測(cè)定，磷含量采用鉬銻抗比色法測(cè)定。碳氮磷的化學(xué)計(jì)量比為植物組織中全碳氮磷含量的質(zhì)量比。

1.4 數(shù)據(jù)處理

試驗(yàn)數(shù)據(jù)在Excel2007統(tǒng)計(jì)軟件中進(jìn)行整理。采用SPSS16.0軟件對(duì)數(shù)據(jù)進(jìn)行統(tǒng)計(jì)分析。不同處理間碳氮磷含量及其化學(xué)計(jì)量比采用單因素(one-way ANOVA)和Duncan法進(jìn)行方差分析和多重比較(P< 0.05)。采用雙因素方差分析(two-way ANOVA)檢驗(yàn)水分水平和施氮水平及其交互作用。采用SigmaPlot 12.5軟件繪圖。

2 結(jié)果與分析

2.1 氮素和干旱脅迫對(duì)白羊草碳氮磷含量的影響

氮素添加和干旱脅迫對(duì)白羊草地上部分和根系碳含量無(wú)顯著影響(表1、圖1)。氮素添加使白羊草地上部分氮含量提高9.7%～48.4%(P<0.001)，干旱脅迫白羊草地上部分氮含量降低2.8%～28.3%(P< 0.001)，兩種處理因素對(duì)地上氮含量無(wú)顯著交互作用。氮素添加和干旱脅迫對(duì)白羊草根系氮含量的影響具有顯著交互作用(表1)，表現(xiàn)為正常水分條件下氮素添加使根系氮含量提高25.0%～26.1%(P< 0.01)，干旱條件下氮素添加無(wú)顯著作用(圖1)。氮素添加和干旱脅迫使白羊草地上部分磷含量分別降低17.4%～31.8%和12.0%～22.1%(P<0.001)(表1、圖1)，兩種處理因素對(duì)地上磷含量無(wú)顯著交互作用。氮素添加和干旱脅迫對(duì)白羊草根系磷含量有顯著影響，在正常水分條件下，高施氮處理使根系磷含量降低18.4%(P<0.05)，在重度干旱脅迫下，中等施氮處理使根系磷含量降低15.0%(P<0.05) (表1、圖1)。

2.2 氮素和干旱脅迫對(duì)白羊草碳、氮、磷化學(xué)計(jì)量比的影響

氮素添加和干旱脅迫對(duì)白羊草地上部分C∶N的影響具有顯著交互作用(表1)，表現(xiàn)為在干旱脅迫條件下氮素添加使地上部分C∶N降低24.9%～32.9% (P<0.05)，在正常供水條件下氮素添加無(wú)顯著影響(圖2)。氮素添加對(duì)根系部分C∶N有顯著影響，在正常供水條件下氮素添加使根系部分C∶N降低19.8%～24.5%(P<0.05)(表1、圖2)。氮素添加和干旱脅迫使白羊草地上部分C∶P分別提高24.4%～42.3%和12.2%～31.0%(P<0.001)，對(duì)根系C∶P無(wú)顯著影響(表1、圖2)。氮素添加使白羊草地上部分N∶P提高40.0%～99.0%(P<0.05)，干旱脅迫對(duì)白羊草地上部分N∶P無(wú)顯著影響(表1、圖2)。氮素添加和干旱脅迫對(duì)白羊草根系部分N∶P具有顯著交互作用，表現(xiàn)為在正常供水條件下氮素添加使根系部分N∶P提高26.8%～54.8%(P<0.05)，在干旱脅迫條件下氮素添加無(wú)顯著影響。

表1 氮素添加和干旱脅迫對(duì)白羊草碳、氮、磷含量及其化學(xué)計(jì)量比的方差分析結(jié)果Table 1 ANOVA analysis for the effects of nitrogen addition (N), water stress (D) and their interaction (N × D) on C, N, P concentrations and their stoichiometry in B. ischaemum

3 討論

碳、氮、磷是地球上所有生命化學(xué)組成的重要元素，也是植物生長(zhǎng)發(fā)育所必需的基本營(yíng)養(yǎng)元素。光合作用同化的碳是植物生理生化過(guò)程的底物和能量來(lái)源，氮和磷是各種蛋白質(zhì)和遺傳物質(zhì)的重要組成元素[32]。因此，碳、氮、磷對(duì)植物的生長(zhǎng)和生理代謝調(diào)節(jié)起著重要作用。水分和氮素是干旱半干旱區(qū)生態(tài)系統(tǒng)的主要限制性因素，氮沉降增加(氮素添加)直接提高了土壤中有效態(tài)氮素含量，土壤水分可以通過(guò)影響微生物驅(qū)動(dòng)的枯落物分解和氮磷元素的礦化過(guò)程間接影響土壤中有效態(tài)氮磷元素含量，進(jìn)而對(duì)植物體氮磷元素含量產(chǎn)生顯著影響。本研究中，干旱脅迫顯著降低了白羊草體內(nèi)氮和磷含量，施氮?jiǎng)t顯著提高了白羊草氮含量，降低了磷含量。安卓等[4]研究表明，氮素添加顯著提高了長(zhǎng)芒草葉片碳、氮和立枯物氮、磷含量。羊留冬等[33]發(fā)現(xiàn)人工施氮顯著提高了冷杉幼苗葉片氮和磷含量。張文瑾等[34]研究發(fā)現(xiàn)氮素添加對(duì)油蒿、披針葉黃華葉片碳、氮和磷含量無(wú)顯著影響。Ye等[35]對(duì)水稻研究表明干旱脅迫降低了磷含量，對(duì)碳和氮含量影響不大，而元分析結(jié)果表明干旱脅迫降低了植物體氮和磷含量[25]。造成這種差異的原因可能是不同研究所采用植物種類以及土壤本身特性的差異造成的。黃土高原地處干旱半干旱地區(qū)，土壤氮磷俱缺[36]，因此水分和氮素都是影響植物生長(zhǎng)發(fā)育的重要限制因素。大量研究表明，干旱脅迫顯著抑制土壤中參與氮磷元素循環(huán)轉(zhuǎn)化酶的活性[22,37]，減弱了土壤中氮磷元素的礦化過(guò)程，導(dǎo)致土壤中可利用性氮磷元素含量的降低，從而導(dǎo)致白羊草體內(nèi)氮磷含量的降低。氮素添加直接提高了土壤中可利用性氮素含量，從而提高了白羊草體內(nèi)氮素含量。說(shuō)明在黃土丘陵區(qū)干旱脅迫進(jìn)一步加劇情況下，氮沉降增加有助于減輕氮素對(duì)白羊草生長(zhǎng)的限制作用。

氮和磷是自然陸地生態(tài)系統(tǒng)的主要限制性元素，相互獨(dú)立又相互影響，并對(duì)植物碳固定產(chǎn)生影響[38]。土壤養(yǎng)分和水分狀況的改變會(huì)顯著影響植物的光合作用和礦質(zhì)代謝過(guò)程，進(jìn)而影響植物體化學(xué)計(jì)量特征。本研究發(fā)現(xiàn)，氮素和土壤水分對(duì)植物體生態(tài)化學(xué)計(jì)量特征存在顯著的交互作用。在正常水分條件下，氮素添加顯著降低了C∶N，提高了N∶P，而在土壤水分增加條件下，氮素添加對(duì)植物C∶N無(wú)顯著影響，而N∶P不變或者顯著降低[2]。這種變化可能是由于土壤水分條件改善和氮素添加導(dǎo)致的植被的快速生長(zhǎng)對(duì)氮磷素含量的稀釋作用高于植物對(duì)氮磷素吸收量的提高。在本研究中，干旱處理和氮素添加對(duì)白羊草地上部分C∶N和根系部分N∶P的影響具有顯著交互作用，表現(xiàn)為在正常供水條件下氮素添加對(duì)地上部分C∶N無(wú)顯著影響，而根系部分N∶P顯著提高，在干旱脅迫條件下氮素添加顯著降低了地上部分C∶N，根系部分N∶P無(wú)顯著變化。氮素添加和干旱脅迫對(duì)植物體碳含量無(wú)顯著影響，說(shuō)明在干旱條件下氮素添加導(dǎo)致植物體將更多的氮素轉(zhuǎn)移至地上部分，將更多的磷素轉(zhuǎn)移至根系部分，這反映了植物對(duì)不同環(huán)境條件的適應(yīng)策略[39]。在土壤持續(xù)干旱而可利用性氮素含量提高的條件下，植物體將更多的氮素分配至植物葉片提高葉綠體含量，促進(jìn)植物正常生長(zhǎng)，而將磷素更多分配至植物根系，以促進(jìn)根系生長(zhǎng)吸收水分，緩解干旱脅迫對(duì)植物生長(zhǎng)的限制作用。作為重要的生理指標(biāo)，C∶N和C∶P反映了植物的生長(zhǎng)速度[40]，碳作為結(jié)構(gòu)性元素，在植物體中含量普遍較高而且變異小，因此，氮、磷含量是影響C∶N和C∶P值的主要因素[41]。本研究不同處理?xiàng)l件下，白羊草地上部分和根系C∶N均值分別為74.69和92.82，C∶P均值分別為325.76和588.80，高于全球平均水平(22.5、232)[42]，進(jìn)一步說(shuō)明黃土丘陵區(qū)植物葉片氮、磷含量較低。同時(shí)較高的C∶N和C∶P值代表植物氮、磷利用率較高，這是植物適應(yīng)養(yǎng)分貧瘠土壤的一種策略。氮和磷是陸地生態(tài)系統(tǒng)的重要的限制性元素，N∶P可以用來(lái)作為環(huán)境對(duì)植物生長(zhǎng)養(yǎng)分供應(yīng)狀況的指標(biāo)，本研究中白羊草氮磷比在4.74～7.93之間，低于全球平均水平(13.8)[41]。Güsewell[32]認(rèn)為，植物體氮磷小于10時(shí)，植物生長(zhǎng)主要受氮素限制，氮磷比大于20時(shí)，植物生長(zhǎng)受磷素限制，氮磷比在10和20之間時(shí)，植物生長(zhǎng)受氮素和磷素共同限制。本研究結(jié)果表明黃土高原地區(qū)天然草地群落生長(zhǎng)主要受氮素的限制，施氮在一定程度上改善了黃土高原地區(qū)氮素的缺乏狀況。但是，未來(lái)干旱脅迫的進(jìn)一步加劇，會(huì)顯著抑制植物體對(duì)氮素和磷素的吸收，從而限制該區(qū)植物的生長(zhǎng)。

圖1 不同氮素添加和干旱脅迫白羊草地上部分和根系的碳、氮、磷含量Fig. 1 C, N and P concentrations in the shoot and root of B. ischaemum under different N addition and drought stress

圖2 不同氮素添加和干旱脅迫白羊草地上部分和根系碳、氮、磷化學(xué)計(jì)量比Fig. 2 C, N and P stoichiometry in the shoot and root of B. ischaemum under different N addition and drought stress

4 結(jié)論

干旱脅迫顯著降低了白羊草體內(nèi)氮、磷含量以及C∶N和C∶P比，但對(duì)N∶P影響不大。氮素添加提高了白羊草體內(nèi)氮含量，降低了磷含量，導(dǎo)致白羊草C∶N降低，C∶P和N∶P比提高。施氮在一定程度上改善了黃土高原地區(qū)氮素的缺乏狀況，減輕了干旱脅迫下白羊草生長(zhǎng)的氮素限制作用。但是隨著干旱脅迫的持續(xù)和大氣沉降導(dǎo)致的氮素的不斷添加，白羊草的生長(zhǎng)將逐漸受到氮素和磷素的限制。

[1]劉超,王洋,王楠,等.陸地生態(tài)系統(tǒng)植被氮磷化學(xué)計(jì)量研究進(jìn)展[J].植物生態(tài)學(xué)報(bào),2012,36(11):1205–1216. Liu C,Wang Y,Wang N,et al.Advances research in plant nitrogen, phosphorus and their stoichiometry in terrestrial ecosystems:areview[J].Chinese Journal of Plant Ecology,2012,36(11): 1205–1216.

[2]LüX T,Kong DL,Pan QM,et al.Nitrogen and water availability interact to affect leaf stoichiometry in asemi-arid grassland[J]. Oecologia,2012,168(2):301–310.

[3]趙亞芳,徐福利,王渭玲,等.華北落葉松針葉碳、氮、磷含量及化學(xué)計(jì)量比的季節(jié)變化[J].植物營(yíng)養(yǎng)與肥料學(xué)報(bào),2015,21(5): 1328–1335. Zhao YF,Xu FL,Wang WL,et al.Seasonal variations of leaf C,N, P contents and stoichiometry of Larix principis-rupprechtii[J]. Journal of Plant Nutrition and Fertilizer,2015,21(5):1328–1335.

[4]安卓,牛得草,文海燕,等.氮素添加對(duì)黃土高原典型草原長(zhǎng)芒草氮磷重吸收率及C∶N∶P化學(xué)計(jì)量特征的影響[J].植物生態(tài)學(xué)報(bào), 2011,35(8):801–807. An Z,Niu DC,Wen HY,et al.Effects of Naddition on nutrient resorption efficiency and C∶N∶P stoichiometric characteristics in Stipa bungeana of steppe grasslands in the Loess Plateau,China[J]. Chinese Journal of Plant Ecology,2011,35(8):801–807.

[5]Song XZ,Gu HH,Wang M,et al.Management practices regulate the response of Moso bamboo foliar stoichiometry to nitrogen deposition[J].Scientific Reports,2016,6:24107.

[6]Gargallo-Garriga A,Sardans J,Perez-Trujillo M,et al.Warming differentially influences the effects of drought on stoichiometry and metabolomics in shoots and roots[J].New Phytologists,2015,207(3): 591–603.

[7]Huang WJ,Houlton BZ,Marklein AR,et al.Plant stoichiometric responses to elevated CO2vary with nitrogen and phosphorus inputs: evidence from aglobal-scale meta-analysis[J].Scientific Reports, 2015,5:18225.

[8]Liu JX,Huang WJ,Zhou GY,et al.Nitrogen to phosphorus ratios of tree species in responses to elevated CO2and nitrogen addition in subtropical forests[J].Global Change Biology,2013,19(1):208–216.

[9]Kanakidou M,Myriokefalitakis S,Daskalakis N,et al.Past,present, and future atmospheric nitrogen deposition[J].Journal of the Atmospheric Sciences,2016,73(5):2039–2047.

[10]Novotny AM,Schade JD,Hobbie SE,et al.Stoichiometric response of nitrogen-fixing and non-fixing dicots to manipulations of CO2,nitrogen,and diversity[J].Oecologia,2007,151(4):687–696.

[11]Han X,Sistla SA,Zhang YH,et al.Hierarchical responses of plant stoichiometry to nitrogen deposition and mowing in atemperate steppe[J].Plant and Soil,2014,382(1):175–187.

[12]石賢萌,杞金華,宋亮,等.哀牢山中山濕性常綠闊葉林兩種優(yōu)勢(shì)幼苗C、N、P化學(xué)計(jì)量特征及其對(duì)氮沉降增加的響應(yīng)[J].植物生態(tài)學(xué)報(bào),2015,39(10):962–970. Shi XM,Qi JH,Song L,et al.C,N and Pstoichiometry of two dominant seedlings and their responses to nitrogen additions in the montane moist evergreen broad-leaved forest in Ailao Mountains, Yunnan[J].Chinese Journal of Plant Ecology,2015,39(10):962–970.

[13]王喬姝怡,鄭成洋,張歆陽(yáng),等.氮添加對(duì)武夷山亞熱帶常綠闊葉林植物葉片氮磷化學(xué)計(jì)量特征的影響[J].植物生態(tài)學(xué)報(bào),2016, 40(11):1124–1135. Wang QS Y,Zheng CY,Zhang XY,et al.Impacts of nitrogen addition on foliar nitrogen and phosphorus stoichiometry in a subtropical evergreen broad-leaved forest in Mount Wuyi[J].Chinese Journal of Plant Ecology,2016,40(11):1124–1135.

[14]黃菊瑩,余海龍.四種荒漠草原植物的生長(zhǎng)對(duì)不同氮添加水平的響應(yīng)[J].植物生態(tài)學(xué)報(bào),2016,40(2):165–176. Huang JY,Yu HL.Responses of growth of four desert species to different Naddition levels[J].Chinese Journal of Plant Ecology, 2016,40(2):165–176.

[15]Ostertag R.Foliar nitrogen and phosphorus accumulation responses after fertilization:an example from nutrient-limited Hawaiian forests[J].Plant and Soil,2010,334(1–2):85–98.

[16]Mayor JR,Wright SJ,Turner BL.Species-specific responses of foliar nutrients to long-term nitrogen and phosphorus additions in a lowland tropical forest[J].Journal of Ecology,2014,102(1):36–44.

[17]Trenberth KE,Dai AG,van der Schrier G,et al.Global warming and changes in drought[J].Nature Climate Change,2014,4(1): 17–22.

[18]Dai AG.Increasing drought under global warming in observations and models[J].Nature Climate Change,2013,3(1):52–58.

[19]Liu P,Huang JH,Han XG,et al.Differential responses of litter decomposition to increased soil nutrients and water between two contrasting grassland plant species of Inner Mongolia,China[J]. Applied Soil Ecology,2006,34(40212):266–275.

[20]Wang CH,Wan SQ,Xing XR,et al.Temperature and soil moisture interactively affected soil net Nmineralization in temperate grassland in Northern China[J].Soil Biology and Biochemistry,2006,38(5): 1101–1110.

[21]任艷林.降水變化對(duì)樟子松人工林土壤無(wú)機(jī)氮和凈氮礦化速率的影響[J].北京大學(xué)學(xué)報(bào)(自然科學(xué)版),2012,48(6):925–932. Ren YL.Effects of precipitation change on inorganic nitrogen and net nitrogen mineralization rate at aplantation of Mongolian Pine[J]. Acta Scientiarum Naturalium Universitatis Pekinensis,2012,48(6): 925–932.

[22]Sardans J,Penuelas J.Drought decreases soil enzyme activity in a Mediterranean Quercus ilex L.forest[J].Soil Biology and Biochemistry,2005,37(3):455–461.

[23]Sardans J,Penuelas J.Increasing drought decreases phosphorus availability in an evergreen Mediterranean forest[J].Plant and Soil, 2004,267(1):367–377.

[24]Sardans J,Penuelas J.Drought changes nutrient sources,content and stoichiometry in the bryophyte Hypnum cupressiforme Hedw. growing in aMediterranean forest[J].Journal of Bryology,2008, 30(1):59–65.

[25]He MZ,Dijkstra FA.Drought effect on plant nitrogen and phosphorus:a meta-analysis[J].New Phytologist,2014,204(4): 924–931.

[26]Sardans J,Rivas-Ubach A,Penuelas J.The C∶N∶P stoichiometry of organisms and ecosystems in achanging world:a review and perspectives[J].Perspectives in Plant Ecology and Evolution and Systematics,2012,14(1):33–47.

[27]孫良杰,齊玉春,董云社,等.全球變化對(duì)草地土壤微生物群落多樣性的影響研究進(jìn)展[J].地理科學(xué)進(jìn)展,2012,31(12):1715–1723. Sun LJ,Qi YC,Dong YS,et al.Research progresses on the effects of global change on microbial community diversity of grasslandsoils[J].Process in Geography,2012,31(12):1715–1723.

[28]姚玉璧,李耀輝,王毅榮,等.黃土高原氣候與氣候生產(chǎn)力對(duì)全球氣候變化的響應(yīng)[J].干旱地區(qū)農(nóng)業(yè)研究,2005,23(2):202–208. Yao YB,Li YH,Wang YR,et al.Effects of the climate and climatic productivity in the Loess Plateau of China on global climate change[J].Agricultural Research in the Arid Areas,2005,23(2): 202–208.

[29]魏樣,同延安,喬麗,等.陜西省不同生態(tài)區(qū)大氣氮沉降量的初步估算[J].農(nóng)業(yè)環(huán)境科學(xué)學(xué)報(bào),2010,29(4):795–800. Wei Y,Tong YA,Qiao L,et al.Preliminary estimate of the atmospheric nitrogen deposition in different ecological regions of Shaanxi Province[J].Journal of Agro-Environment Science,2010, 29(4):795–800.

[30]Han XW,Tsunekawa A,Tsubo M,et al.Responses of plant-soil properties to increasing Ndeposition and implications for large-scale eco-restoration in the semiarid grassland of the northern Loess Plateau,China[J].Ecological Engineering,2013,60:1–9.

[31]Galloway JN,Dentener FJ,Capone DG,et al.Nitrogen cycles:past, present,and future[J].Biogeochemistry,2004,70(2):153–226.

[32]Güsewell S.N:P ratios in terrestrial plants:variation and functional significance[J].New Physiologist,2004,164(2):243–266.

[33]羊留冬,王根緒,楊陽(yáng),等.峨眉冷杉幼苗葉片功能特征及其N、P化學(xué)計(jì)量比對(duì)模擬大氣氮沉降的響應(yīng)[J].生態(tài)學(xué)雜志,2012, 31(1):44–50. Yang LD,Wang GX,Yang Y,et al.Responses of leaf functional traits and nitrogen and phosphorus stoichiometry in Abies fabiri seedlings in Gongga Mountain to simulated nitrogen deposition[J]. Chinese Journal of Ecology,2012,31(1):44–50.

[34]張文瑾,張宇清,佘維維,等.氮添加對(duì)油蒿群植物葉片生態(tài)化學(xué)計(jì)量特征的影響[J].環(huán)境科學(xué)研究,2016,29(1):52–58. Zhang WJ,Zhang YQ,She WW,et al.Effects of nitrogen addition on foliar ecological stoichiometric characteristics of Artemisia ordosica community[J].Research of Environmental Sciences,2016, 29(1):52–58.

[35]Ye Y,Liang X,Chen Y,et al.Carbon,nitrogen and phosphorus accumulation and partitioning,and C∶N∶P stoichiometry in lateseason rice under different water and nitrogen managements[J].PLoS One,2014,9:e101776.

[36]Liu ZP,Shao MA,Wang YQ.Spatial patterns of soil total nitrogen and soil total phosphorus across the entire Loess Plateau region of China[J].Geoderma,2013,197/198:67–78.

[37]Steinweg JM,Dukes JS,Wallenstein MD.Modeling the effects of temperature and moisture on soil enzyme activity:Linking laboratory assays to continuous field data[J].Soil Biology and Biochemistry, 2012,55:85–92.

[38]Yan ZB,Li P,Chen YH,et al.Nutrient allocation strategies of woody plants:an approach from the scaling of nitrogen and phosphorus between twig stems and leaves[J].Scientific Reports, 2016,6:20099.

[39]Kleczewski NM,Herms DA,Bonello P.Nutrient and water availability alter belowground patterns of biomass allocation,carbon partitioning,and ectomycorrhizal abundance in Betula nigra[J]. Trees-Structure and Function,2012,26(2):525–533.

[40]Agren GI.The C∶N∶P stoichiometry of autotrophs-theory and observations[J].Ecology Letters,2004,7(3):185–191.

[41]Reich PB,Olkesyn J.Global patterns of plant leaf Nand Pin relation to temperature and latitude[J].Proceedings of the National Academy of Sciences of the United States of America,2004,101(30): 11001–11006.

[42]Elser JJ,Fagan WF,Denno RF,et al.Nutritional constraints in terrestrial and freshwater food webs[J].Nature,2000,408(6812): 578–580.

Effects of nitrogen addition and drought stress on carbon, nitrogen and phosphorus stoichiometry of Bothriochloa ischaemum

SUN Cai-li1,XIAO Lie2,LI Peng2,XUE Sha1,3,LIU Guo-bin1,3*
(1 State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Northwest A&F University, Yangling, Shaanxi 712100, China; 2 State Key Laboratory Base of Eco-hydraulic Engineering in Arid Area, Xi'an University of Technology, Xi'an 710048, China; 3 Institute of Soil and Water Conservation, Chinese Academy of Science and Ministry of Water Resource, Yangling, Shaanxi 712100, China)

【Objectives】Both nitrogen and water shortage are the main limiting factors for plant growth in arid and semiarid ecosystems.Study the carbon(C),nitrogen(N)and phosphorus(P)stoichiometric characteristics of plant under nitrogen deposition and drought stress will help understanding the response characteristics of arid and semiarid ecosystems to global changes.【Methods】A pot experiment was conducted inside aphytotron using Bothriochloa ischaemum as tested martials.N application rates of0,2.5and5.0g/(m2·a)were designed,representing CK,low Nand high Nrate;and water supply levels of field capacity of75%–80%,55%–60%and 35%–40%were setup,representing drought stress level of well-watered,moderate drought stress and severe drought stress in turn.The contents of C,N and Pin the shoot and root were determined and the C,N,and P stoichiometry were calculated.【Results】N addition and drought stress had no significant influence on C concentration in the aboveground and root of B. ischaemum.N addition increased the Nconcentration by 9.7%–48.8%(P<0.001)in the shoot,while drought stress decreased it by2.8%–28.3%(P<0.001).Nitrogen addition and drought stress had significant interactive effects on the root Nconcentration,N addition increased the Nconcentration by25.0%–26.1%(P<0.01)under well-watered condition and had no significant influence on it under drought stress condition.N addition and drought stress significantly decreased the Pconcentration by17.4%–31.8%and12.0%–22.1%in shoot.N addition and drought stress had significant interactive effects on the C∶N ratio in shoot,N addition increased the C∶N ratio by24.9%–32.9%(P<0.05)under drought stress,but not under well-watered condition.The C∶N ratio in the root of B. ischaemum was decreased by 19.8%–24.5%(P<0.05)by Naddition under well watered condition.N addition and drought stress decreased the C∶P ratio by24.4%–42.3%and12.2%–31.0%in the shoot of B. ischaemum,respectively,but not in the root.N addition significantly increased the N∶P ratio in the aboveground part of B. ischaemum,drought stress did not.N addition and drought stress had significant interactive influence on the N∶P ratio in the root of B. ischaemum,N addition increased the N∶P ratio by26.8%–54.8%(P<0.05)under well-watered condition and had no significant influence on it under drought stress condition.【Conclusions】N addition will increase the C∶P and N∶P ratio in the aboveground part of B. ischaemum under drought stress,intimating that the growth of B. ischaemum would be restrained by both Nand Pon the Loess Plateau with the aggravation of drought stress and N deposition to some extent.

Bothriochloa ischaemum;stoichiometry;drought;nitrogen addition;nutrient limitation; Loess Plateau

2017–01–05接受日期：2017–03–17

中科院西部青年學(xué)者項(xiàng)目（XAB2015A05）；國(guó)家自然科學(xué)基金項(xiàng)目（41371510，41371508，41471438）資助。

孫彩麗（1989—），女，河南平頂山人，博士，主要從事水土保持及土壤微生物生態(tài)方面研究。E-mail：suncaili2007@126.com

*通信作者E-mail：gbliu@ms.iswc.ac.cn