張 瑜， 劉海濤, 周亞平, 李春儉

(中國農(nóng)業(yè)大學(xué)資源與環(huán)境學(xué)院，北京 100193)

田間玉米和蠶豆對(duì)低磷脅迫響應(yīng)的差異比較

張 瑜， 劉海濤, 周亞平, 李春儉*

(中國農(nóng)業(yè)大學(xué)資源與環(huán)境學(xué)院，北京 100193)

玉米； 蠶豆； 低磷脅迫； 根際； 根系； 適應(yīng)性反應(yīng)

為了適應(yīng)土壤中有限可利用的磷資源，在長期進(jìn)化過程中，植物逐步形成了一系列適應(yīng)性機(jī)制，以增加從有效磷濃度低的土壤中吸收磷素，并提高體內(nèi)的磷利用效率[3-5]。提高磷吸收效率一方面與根系的形態(tài)和結(jié)構(gòu)改變有關(guān)[3,6-7]，也與根系生理和分子機(jī)制的改變有關(guān)，例如提高磷轉(zhuǎn)運(yùn)蛋白相關(guān)基因的表達(dá)[8-9]，或者通過酸化根際土壤[10-11]以及增加有機(jī)酸和磷酸酶分泌[12-14]，來增加難溶性無機(jī)磷或有機(jī)磷的吸收。提高體內(nèi)的磷利用效率有助于增加單位磷所產(chǎn)生的生物量或籽粒產(chǎn)量，并有助于磷素從營養(yǎng)體器官向籽粒轉(zhuǎn)移[15]。

缺磷條件下，蠶豆根系表現(xiàn)為半徑減小，根長、根表面積和根冠比增加，以及體內(nèi)酸性磷酸酶活性提高[16]；白羽扇豆則會(huì)形成特有的排根，并通過質(zhì)子和有機(jī)酸的釋放顯著增加土壤中磷的有效性[17-20]。具有須根系的玉米對(duì)磷的適應(yīng)性反應(yīng)與蠶豆、白羽扇豆等植物的反應(yīng)有所不同。玉米在缺磷條件下不會(huì)明顯改變根際pH值[10,21]，甚至有機(jī)酸的總分泌降低[10,22]。但在缺磷狀態(tài)下，玉米能夠改變根系生長[7,23]，淺根型的根系比深根型根系具有更高的含磷量、相對(duì)生長率及生物量的積累[24]。磷高效玉米品種在低磷條件下具有較大的根冠比、 更多的側(cè)根數(shù)目和更長的總根長來擴(kuò)大與土壤的接觸范圍，從而增加磷的吸收和生物量的積累[24-26]。上述研究結(jié)果是否意味著與豆科作物相比，玉米主要通過根系形態(tài)的變化來適應(yīng)低磷脅迫？

已有關(guān)于植物對(duì)缺磷適應(yīng)性反應(yīng)的研究主要是在控制條件下、通過營養(yǎng)液培養(yǎng)或盆栽試驗(yàn)進(jìn)行的。已知蠶豆是在缺磷條件下具有包括增加質(zhì)子和酸性磷酸酶分泌等在內(nèi)的明顯生理適應(yīng)性反應(yīng)的代表性植物。在快速生長階段，植物對(duì)養(yǎng)分的需求量大，在養(yǎng)分供應(yīng)不足的條件下更容易出現(xiàn)缺素癥狀。本研究通過連續(xù)兩年田間試驗(yàn)，在長期極度缺磷(Olsen-P <5 mg/kg)和供磷充足的定位試驗(yàn)田上，比較玉米和蠶豆在快速生長階段植株生長及對(duì)磷的吸收、根系在0—40 cm土層中的分布、以及根際土壤pH值和酸性磷酸酶活性的變化，驗(yàn)證玉米主要通過根系形態(tài)的變化來適應(yīng)低磷脅迫的假設(shè)。研究結(jié)果對(duì)了解不同植物在養(yǎng)分缺乏條件下適應(yīng)性反應(yīng)機(jī)制的差異具有理論意義。

1 材料和方法

1.1 供試材料

玉米雜交種鄭單958和臨蠶5號(hào)(ViciafabaL. cv. Lincan No.5)

1.2 試驗(yàn)設(shè)計(jì)和處理

試驗(yàn)于2012年和2013年在中國農(nóng)業(yè)大學(xué)上莊試驗(yàn)站長期定位試驗(yàn)田進(jìn)行。分不供磷(P0)和供磷100 kg/hm2兩個(gè)水平。定位試驗(yàn)從1984年至今，施用磷肥量不變，每年只種一季玉米。在施肥前，利用根鉆法獲取基礎(chǔ)土壤。供試0—30 cm土壤的基礎(chǔ)理化性狀見表1。在播種前灌溉土壤，使土壤含水量保持在約75%。玉米和蠶豆分別于2012年4月28日和2013年5月12日同時(shí)播種，苗期間苗，兩種作物均為單作。兩年玉米的種植密度為100000株/公頃，行距50 cm，株距20 cm，小區(qū)面積為21 m2(5 m×4.2 m)；臨蠶5號(hào)的種植密度250000株/公頃，行距20 cm，株距20 cm，小區(qū)面積為20 m2(5 m×4 m)。試驗(yàn)采用隨機(jī)區(qū)組設(shè)計(jì)，3次重復(fù)。

表1 2012年和2013年土壤0—30 cm土層基礎(chǔ)理化性狀Table 1 Soil chemical properties (0-30 cm soil layer) in 2012 and 2013

在播種玉米和蠶豆前不施用磷肥(P0)或施用P2O5100 kg/hm2(P100)， 磷肥為過磷酸鈣； 同時(shí)均以硫酸鉀形式施入K2O 150 kg/hm2。所有處理氮肥總用量為尿素 240 kg/hm2，其中30%為基肥，其余在玉米十二葉期時(shí)追施。2012年7月3日和7月15日，2013年7月8日和7月18日進(jìn)行兩次取樣，均是在兩種植物快速生長時(shí)期：玉米處于抽雄前的拔節(jié)至大喇叭口期；蠶豆處于初花至盛花期。

1.3 測定項(xiàng)目和方法

1.3.1 生物量和含磷量測定 取樣時(shí)，每個(gè)小區(qū)選取5株地上部生長均勻的玉米和蠶豆植株，從莖基部剪斷。分地上部和根系取樣。樣品取回后洗凈(根系)，在105℃殺青30 min，然后在70℃烘干至恒重，稱重，并用于測定植物組織含磷量。磷含量利用濃H2SO4-H2O2消煮—釩鉬黃比色法測定[27]。

江銅集團(tuán)（德興）橡膠實(shí)業(yè)有限公司煉膠車間主要煉膠生產(chǎn)設(shè)備XK-560A型雙輥筒開放式煉膠機(jī)，原使用衡水電機(jī)Y315L-8（電機(jī)功率90kW），啟動(dòng)方式為星三角降壓啟動(dòng)，控制系統(tǒng)為傳統(tǒng)的繼電器控制，正常運(yùn)行電流在100-200A。由于在初次處理原膠過程中，經(jīng)常出現(xiàn)過載運(yùn)行狀態(tài)，導(dǎo)致電機(jī)轉(zhuǎn)速下降和長時(shí)間過流，引起設(shè)備堵轉(zhuǎn)，從而影響設(shè)備生產(chǎn)處理工效。通過討論分析，決定采用KSM1-315L1-7.5型90kW開關(guān)磁阻電機(jī)替換老式交流異步電動(dòng)機(jī)，用SRD控制系統(tǒng)替換傳統(tǒng)的繼電器控制系統(tǒng)［1, 5］。

1.3.2 分層根系取樣 收獲地上部以后，通過分層挖取法在P0和P100處理的每個(gè)小區(qū)挖取1株玉米根系和2株蠶豆根系。玉米根系是以玉米莖為中心，挖取體積為50 cm×20 cm×10 cm的土體，垂直向下挖4層至距地面以下40 cm。蠶豆是以兩株蠶豆莖中間處為中心，挖取體積為40 cm×20 cm×10 cm的土體，共垂直向下挖4層。每層土體中的所有可見根系在田間由人工挑出后，裝入封口袋，并按順序編號(hào)，帶回實(shí)驗(yàn)室用水沖洗干凈后放入冰箱在-20℃中保存，用于之后的根長掃描。根系經(jīng)掃描儀(Epson 1680, Indonesia)掃描后用分析軟件(WinRhizo Pro Vision 5.0 a)分析，計(jì)算各層土壤中的根長。

1.3.3 根際和非根際土壤取樣 另取一株玉米和多株蠶豆用“抖土法”將植物根表的土壤輕輕抖落，附著在根表的土壤為根際土壤，同時(shí)在行間0—40 cm的土壤剖面取非根際土壤。田間將根際和非根際土壤裝入封口袋中帶回實(shí)驗(yàn)室。風(fēng)干后過2 mm篩，用于測定根際和非根際土壤pH值。pH值的測定以水為浸提液，土液比為1 ∶2.5。

1.4 數(shù)據(jù)處理

本試驗(yàn)數(shù)據(jù)采用Microsoft Excel(2010)和SAS 8.2統(tǒng)計(jì)軟件進(jìn)行統(tǒng)計(jì)分析，LSD法檢驗(yàn)差異顯著性。

2 結(jié)果與分析

2.1 不同供磷水平對(duì)植物生長的影響

兩年兩次取樣均為兩種植物的快速生長時(shí)期。兩年的結(jié)果表明，玉米的生物量遠(yuǎn)遠(yuǎn)大于蠶豆。第二次取樣時(shí)，兩種植物地上部的生物量遠(yuǎn)高于第一次取樣(圖1)。

圖1 兩次取樣時(shí)不同供磷水平下玉米和蠶豆地上部和根系的干重變化Fig.1 Shoot and root dry weight of maize ZD958 and Viciafaba (Lincan No.5) with P0 and P100 supply at two harvests[注(Note)： 圖中每個(gè)柱子代表3個(gè)重復(fù)平均值The bars represent the mean values from three replicates; 方柱上不同字母表示處理間差異在5% 水平顯著Different letters above the bars represent significant difference among different treatments at 5% level.]

兩種植物根冠比值的差異與生物量的差異明顯不同。兩年的結(jié)果表明，第一次取樣時(shí)，P0和P100處理的蠶豆根冠比都高于玉米，但第二次取樣時(shí)，玉米的根冠比則高于蠶豆，說明兩種植物根冠比隨生長時(shí)間延長在發(fā)生變化，與供磷水平無關(guān)。與P100處理相比，2012年第一次取樣時(shí)，P0的玉米和蠶豆地上部干重分別下降57.2%和47.4%，根系干重分別下降了47.2%和10.6%；在2013年，P0處理的玉米和蠶豆地上部干重分別下降29.8%和24.2%，二者的根系干重不但沒有下降，反而分別增加10.7%和33.11%。由于低磷條件下根系干重的下降幅度小于地上部的下降幅度，所以在第一次取樣時(shí)，兩種植物在缺磷條件下的根冠比都高于充足供磷的植株；第二次取樣時(shí)兩種植物在兩個(gè)供磷水平下的根冠之間無顯著差異(圖2)。

2.2 不同供磷水平對(duì)植物磷吸收的影響

2.3 兩種植物根系在不同土層中的分布及單位根長吸磷量

圖2 兩次取樣時(shí)不同供磷水平下玉米和蠶豆植株根冠比的變化Fig.2 Root/shoot DW ratio of maize ZD958 and Viciafaba (Lincan No.5) with P0 and P100 supply at two harvests[注(Note)： 圖中每個(gè)柱子代表3個(gè)重復(fù)平均值The bars represent the mean values from three replicates; 方柱上不同字母表示處理間 差異在5%水平顯著Different letters above the bars represent significant difference among different treatments at 5% level.]

圖3 兩次取樣時(shí)不同供磷水平下玉米和蠶豆地上部和根系的磷含量Fig.3 Shoot and root P content of maize ZD958 and Viciafaba (Lincan No.5) with P0 and P100 at two harvests[注(Note)： 圖中每個(gè)柱子代表3個(gè)重復(fù)平均值The bars represent the mean values from three replicates; 方柱上不同字母表示處理 間差異在5%水平顯著Different letters above the bars represent significant difference among different treatments at 5% level.]

從根系在土壤中的縱向分布看，兩種植物的根系都傾向于分布在0—20 cm表層土壤。兩年兩次取樣時(shí)，無論供磷水平如何，玉米根系在0—10 cm土壤的根長都大于蠶豆根系(圖5)。玉米植株的總根長也大于蠶豆，不受供磷水平和取樣時(shí)間的影響(表2)。

比根長表示單位根重所形成的根長，能夠反映根系的粗細(xì)。蠶豆的比根長明顯大于玉米，而且不受取樣時(shí)間和供磷水平的影響，說明蠶豆用較少的碳投入能夠形成更長的根系(表2)。與蠶豆的比根長明顯大于玉米相反，玉米的單位根長吸磷量遠(yuǎn)遠(yuǎn)高于蠶豆(表2)，說明玉米根系的磷素吸收效率高于蠶豆。

2.4 兩種植物根際土壤pH值及酸性磷酸酶活性

2013年的試驗(yàn)結(jié)果表明，在兩種供磷水平下，蠶豆根表的酸性磷酸酶活性均明顯高于玉米。兩次取樣時(shí)，玉米根表的酸性磷酸酶活性在兩種供磷水平下沒有差別；但缺磷蠶豆根表的酸性磷酸酶活性在第一次取樣時(shí)高于供磷充足的植株(圖6)。2012年比較了兩種供磷水平下兩種植物根際與非根際土壤pH值的差異。兩次取樣結(jié)果表明，缺磷蠶豆根際土壤的pH值明顯低于供磷充足蠶豆；但玉米根際土壤pH值在缺磷和供磷充足條件下無顯著差異(表3)。

圖4 兩次取樣時(shí)不同供磷水平下玉米和蠶豆地上部和根系的磷濃度Fig.4 Shoot and root P concentration of maize ZD958 and Viciafaba (Lincan No.5) with P0 and P100 at two harvests[注(Note)： 圖中每個(gè)柱子代表3個(gè)重復(fù)平均值The bars represent the mean values from three replicates; 方柱上不同字母表示處理間 差異在5%水平顯著Different letters above the bars represent significant difference among different treatments at 5% level.]

圖5 兩次取樣時(shí)不同供磷水平下玉米和蠶豆根系在不同土層中的分布Fig.5 Root length distribution of maize ZD958 and Viciafaba (Lincan No.5) supplied with P0 and P100 in each soil layer (0-40 cm soil with 10 cm increment) at two harvests

3 討論

在植物生長早期，較大比例的光合產(chǎn)物分配到根部；隨著生長時(shí)間的延長，植株根冠比不斷下降。隨著玉米從苗期(播種9天后)到成熟期(播種137天)生長時(shí)間的延長，根冠比從0.68下降到0.16[29]。本試驗(yàn)中，蠶豆的根冠比隨生長時(shí)間延長的下降幅度遠(yuǎn)遠(yuǎn)大于玉米，使得其根冠比由第一次取樣時(shí)大于玉米轉(zhuǎn)變?yōu)樵?0—12天后的第二次取樣時(shí)小于玉米，這一變化顯然與供磷水平無關(guān)(圖2)，

表2 不同供磷水平下玉米和蠶豆的總根長、比根長和單位根長吸磷量Table 2 Total root length, specific root length and P uptake per unit of root length of maize ZD958 and Viciafaba (Lincan No.5) supplied with P0 and P100

注(Note): 比根長SRL—specific root length;單位根長磷吸收P uptake efficiency—兩次收獲期間磷凈增量/第二次取樣時(shí)總根長Net P increment between two harvests/total root length at the 2ndharvest; 數(shù)值后不同字母表示每次取樣處理間的差異在5%水平下顯著 Values followed by different letters are significantly different among treatments at 5% level.

表3 2012年兩次取樣時(shí)不同供磷水平下玉米和蠶豆根際和非根際土壤的pH值Table 3 pH values of rhizospheric and bulk soil of maize ZD958 and Viciafaba (Lincan No.5) supplied with P0 and P100 in 2012

注(Note): 數(shù)值后不同字母表示每次取樣處理間在5%水平下差異顯著 Values followed by different letters are significantly different among treatments at 5% level.

圖6 2013年兩次取樣時(shí)不同供磷水平下玉米 和蠶豆根際的酸性磷酸酶活性Fig.6 Acid phosphatase activity in rhizospheric soil of maize ZD958 and Viciafaba (Lincan No.5) with P0 and P100 supply in 2013[注(Note)： 圖中每個(gè)柱子代表3個(gè)重復(fù)平均值The bars represent the mean values from three replicates; 方柱上不同字母表示處理間差異在5%水平顯著Different letters above the bars represent significant difference among different treatments at 5% level.]

表明兩種植物不同的根冠比變化規(guī)律。但第一次取樣時(shí)，兩種植物在缺磷條件下的根冠比都高于供磷充足的植株，屬于典型的對(duì)缺磷脅迫的適應(yīng)性反應(yīng)。本試驗(yàn)中，根冠比變化的原因是由于在低磷脅迫下，地上部生長的減少幅度大于根系生長的減少幅度。這一方面有利于減少地上部的需求，同時(shí)通過增加根系的生長，來增加與土壤的接觸范圍，以增加對(duì)磷素的吸收。

兩年兩次取樣，玉米的總根長均長于蠶豆根系(表2)，這與玉米的根系生物量明顯大于蠶豆根重有關(guān)(圖1)。由于玉米屬于須根系植物，根系在表層土壤，特別是0—10 cm土層的根長分布比例遠(yuǎn)遠(yuǎn)大于蠶豆根系。盡管玉米的總根長大于蠶豆根系，但蠶豆根系的比根長大于玉米(表2)，表明蠶豆對(duì)根系生長的碳投入更少，或蠶豆的根系更細(xì)。通過兩年兩次取樣期間磷的凈增量與根長的比值結(jié)果看，玉米根系單位根長的磷吸收效率遠(yuǎn)遠(yuǎn)高于蠶豆。因而增加根長有利于玉米對(duì)土壤中磷素的吸收。玉米根系磷吸收效率高的另一個(gè)重要原因是玉米地上部的生物量遠(yuǎn)遠(yuǎn)大于蠶豆(圖1)。根系對(duì)養(yǎng)分的吸收量多少受地上部需求調(diào)控[30-31]。

生理變化是植物適應(yīng)缺磷脅迫的另一種機(jī)制，但不同植物的反應(yīng)明顯不同。白羽扇豆可以利用土壤中大豆不能利用的磷[32]；花生能夠在大豆、高粱和玉米因缺磷而無法生長的貧瘠土壤上生長[33]；蠶豆對(duì)難溶性Fe-P和Al-P的利用能力強(qiáng)于玉米[34]。本試驗(yàn)中，玉米根際土壤的pH并未由于缺磷而降低，支持已有的研究結(jié)果[10,21]。同樣具有須根系的小麥在缺磷條件下也沒有發(fā)生根際pH值的明顯改變[35-36]。說明小麥玉米等作物在缺磷條件下不能通過增加質(zhì)子分泌來活化土壤中的難溶性磷。另一方面包括番茄、鷹嘴豆、菜豆和白羽扇豆在內(nèi)的很多雙子葉植物在缺磷脅迫下，都會(huì)增加根系的質(zhì)子分泌，以酸化土壤，或增加根表酸性磷酸酶活性[16-20, 36]。這與本研究中蠶豆缺磷時(shí)增加質(zhì)子分泌和提高根際酸性磷酸酶活性的結(jié)果相同(表3、 圖6)。說明缺磷條件下，蠶豆除了增加根系的生長之外，還有部分光合產(chǎn)物的投入用于根系質(zhì)子分泌和提高根表酸性磷酸酶活性，以增加土壤中難溶性磷甚至有機(jī)磷的利用。

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Comparison of the responses between maize and faba bean to low phosphorus stress in the field

ZHANG Yu, LIU Hai-tao, ZHOU Ya-ping, LI Chun-jian*

(CollegeofResourceandEnvironment,ChinaAgriculturalUniversity,Beijing100193，China)

【Objectives】 In response to limited P availability, plants have evolved a wide adaptive mechanisms. Thers is a hypothesis that maize responds to P deficiency by modifying root morphological structure rather than by changing physiological processes. Comparision between the root morphological and physiological variations of maize and faba bean under low P condition was performed in the field to prove this hypothesis. 【Methods】 The experiments were conducted in the field of long-term P-fertilizer with two P levels (0 and 100 kg/hm2) at the Shangzhuang Experimental Station of the China Agricultural University, Beijing in 2012 and 2013. Maize and faba bean were planted by monoculture with three replicates. Samples from the treatments in two years were taken at elongation and bell stage for maize and at initial and full bloom stage for faba bean in an interval of 10-12 days .Plant growth, P uptake, root distribution within the 0-40 cm soil profile, and rhizospheric pH and acid phosphatase activity of both plant species were incestigated. 【Results】 Data showed that the dry weight (DW) and P content of maize were significantly higher than those of faba bean. At the first harvest in two years, DW ratio in root versus shoot of faba bean was significantly higher than that of maize, and DW ratios of root versus shoot from both plant species under P0 were higher than that under P100. The total roots distribution of maize plant in the 0-10 cm soil layer were higher than those of faba bean at both harvests in two years, and faba bean has higher the specific root length than maize; While the amount of P taken up per unit in roots of faba bean was less than that of maize, regardless of the harvest time and P supply. The acid phosphatase activity on the root surface of faba bean was significantly higher than that of maize at both harvests, but the root surface of maize grown under P0 and P100 exhibited different activities, while that of faba bean under P0 was higher than that under P100. The value of pH in rhizosphere of faba bean grown under P0 was significantly lower than that grown under P100. However, there was no difference in rhizosphere pH of maize grown both at P0 and P100 levels.【Conclusions】 The DW ratios of root versus shoot of maize and faba bean grown under P0 were significantly higher than those under P100. Maize plants took up more P per unit of root length, and exhibited more roots distribution in the top soil layer riching available P relative to faba bean. However, P deficient maize did not increase the release of proton and acid phosphatase in the rhizosphere soil, indicating that maize responds to P deficiency by mainly modifying root morphology. In comparison, faba bean responds to P deficiency by root morphological and physiological variations.

maize; faba bean; low phosphorus stress; rhizosphere; root; adaptive response

2014-06-14 接受日期： 2014-10-12 網(wǎng)絡(luò)出版日期： 2015-06-01

“973”項(xiàng)目“肥料養(yǎng)分持續(xù)高效利用機(jī)理與途徑”(2013CB127402)資助。

張瑜(1986—)，女，內(nèi)蒙古烏海市人，博士，主要從事植物營養(yǎng)生理研究。E-mail: zhangyu9999666@163.com * 通信作者 E-mail: lichj@cau.edu.cn

S513; S643.6; S506.2

A

1008-505X(2015)04-0911-09