楊思存， 霍 琳， 王成寶， 姜萬禮

(甘肅省農(nóng)業(yè)科學(xué)院土壤肥料與節(jié)水農(nóng)業(yè)研究所， 農(nóng)業(yè)部甘肅耕地保育與農(nóng)業(yè)環(huán)境科學(xué)觀測(cè)實(shí)驗(yàn)站， 蘭州 730070)

綠洲鹽化潮土施鎂對(duì)玉米幼苗生長(zhǎng)、活性氧自由基代謝和鋅營(yíng)養(yǎng)的影響

楊思存， 霍 琳， 王成寶， 姜萬禮

(甘肅省農(nóng)業(yè)科學(xué)院土壤肥料與節(jié)水農(nóng)業(yè)研究所， 農(nóng)業(yè)部甘肅耕地保育與農(nóng)業(yè)環(huán)境科學(xué)觀測(cè)實(shí)驗(yàn)站， 蘭州 730070)

鹽化潮土； 土壤交換鎂； 鋅營(yíng)養(yǎng)； 活性氧自由基代謝； 玉米幼苗

1 材料與方法

1.1 試驗(yàn)材料

1.2 試驗(yàn)設(shè)計(jì)

試驗(yàn)采用盆栽方法，供試盆缽為塑料盆，高30 cm、直徑20 cm，將土壤和肥料均勻混合后裝盆，每盆裝風(fēng)干土5 kg。以硫酸鎂為鎂源，設(shè)加入鎂(Mg)0、74、147、221、515 mg/kg 5個(gè)水平，混合后，土壤交換性Mg含量分別為287.3、349.2、411.6、487.9和755.2 mg/kg，依次代表綠洲鹽化潮土含鎂量低、較低、中等、較高、極高5種類型。除試驗(yàn)設(shè)計(jì)鎂用量外，每個(gè)處理施N 100 mg/kg、P 50 mg/kg和K 63 mg/kg。所施肥料均以溶液形式施入，充分與土壤混勻后灌水至飽和，平衡1天后播種。玉米經(jīng)催芽于4月20日播種，每盆8粒，7 d后定苗，每盆5株。玉米生長(zhǎng)期間澆灌去離子水，用重量法控制水分供應(yīng)。各處理均重復(fù)6次。玉米生長(zhǎng)到6葉期時(shí)(45 d)收獲，測(cè)定株高后，其中3次重復(fù)采集心葉下第二個(gè)葉片鮮樣用于測(cè)定葉綠素含量，超氧化物歧化酶(SOD)、過氧化物酶(POD)、過氧化氫酶(CAT)活性和丙二醛(MDA)含量。另外3次重復(fù)分為地上部莖葉和地下部根系兩部分收獲，洗凈后先在90℃下殺青30 min，再在60℃下烘干至恒重，分別稱重后用不銹鋼粉碎機(jī)粉碎，過0.25 mm篩備用。同時(shí)采集土壤樣品，自然風(fēng)干、磨碎后過1 mm篩備用。

1.3 測(cè)定項(xiàng)目與方法

葉片葉綠素含量測(cè)定采用丙酮浸提分光光度法，超氧化物歧化酶(SOD)活性測(cè)定采用氮藍(lán)四唑(NBT)法，過氧化物酶(POD)活性測(cè)定采用愈創(chuàng)木酚法，過氧化氫酶(CAT)活性測(cè)定采用高錳酸鉀滴定法，丙二醛(MDA)含量測(cè)定采用硫代巴比妥酸法，具體方法參照文獻(xiàn)[16]。

1.4 統(tǒng)計(jì)分析

采用Excel 2003和SAS 9.0軟件對(duì)數(shù)據(jù)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 施鎂對(duì)玉米幼苗生長(zhǎng)的影響

表1 不同施鎂水平玉米株高和干物質(zhì)產(chǎn)量

注(Note): 同列數(shù)據(jù)后不同字母表示處理間差異達(dá)5%顯著水平 Values followed by different letters in a column are significantly among treatments at the 5% leve1.

2.2 施鎂對(duì)玉米葉片葉綠素含量和活性氧自由基代謝的影響

圖1 不同施鎂量玉米幼苗葉綠素含量Fig.1 Chlorophyyll contents of maize seendling under different Mg application amount[注(Note)： 方柱上不同字母表示處理間差異達(dá)5%顯著水平 Different letters above the bars mean significant among treatments at the 5% level.]

2.2.1 葉綠素含量 隨著施鎂量的增加或土壤含鎂量水平的提高，玉米葉片葉綠素含量顯著下降(圖1)。與不施鎂處理相比，施鎂74、147、221、515 mg/kg處理的葉綠素含量分別降低了9.4%、21.6%、25.4%和45.9%，特別是在土壤施鎂量達(dá)到515 mg/kg時(shí)，葉綠素含量幾乎降低了一半，導(dǎo)致玉米葉片枯黃，出現(xiàn)明顯的鎂中毒現(xiàn)象和典型缺鋅癥狀。

2.2.2 活性氧自由基代謝 隨著施鎂量的增加或土壤含鎂量水平的提高，玉米幼苗葉片中SOD、POD、CAT活性的變化趨勢(shì)基本一致，三者都是先升高再迅速降低(表2)。SOD和CAT活性的峰值均出現(xiàn)在施鎂量147 mg/kg，施鎂74、147 mg/kg處理分別比不施鎂處理增加9.93%、13.54%和13.06%、23.31%，施鎂221、515 mg/kg處理分別比不施鎂處理降低19.24%、49.75%和0.51%、32.21%；POD活性的峰值出現(xiàn)在施鎂量74 mg/kg，但與不施鎂處理差異不顯著；施鎂221、515 mg/kg處理分別比不施鎂處理降低了20.93%和48.06%。這說明在適量施鎂范圍內(nèi)，3種保護(hù)酶能起到協(xié)同作用，提高保護(hù)酶活性，減輕活性氧自由基對(duì)膜脂的毒害，從而起到保護(hù)植物的作用；但當(dāng)施鎂量或土壤含鎂量超出正常范圍后，就會(huì)對(duì)保護(hù)酶活性造成傷害。

丙二醛(MDA)是自由基對(duì)細(xì)胞膜脂進(jìn)行過氧化傷害的最終產(chǎn)物之一，其含量變化可代表細(xì)胞的脂質(zhì)過氧化水平和生物膜損傷程度的大小，是判斷膜脂過氧化作用的一個(gè)重要指標(biāo)[17]。由表2可以看出，隨著施鎂量的增加或土壤含鎂量水平的提高，玉米幼苗葉片中MDA含量始終呈增加趨勢(shì)。與不施鎂處理相比，施鎂74、147、221、515 mg/kg處理分別增加了20.39%、66.74%、102.71%和183.58%。說明高鎂脅迫能增強(qiáng)脂質(zhì)過氧化作用，造成MDA在玉米葉片中大量積累。

表2 不同施鎂量玉米幼苗SOD、POD、CAT活性和MDA含量

注(Note): 同列數(shù)據(jù)后不同字母表示處理間差異達(dá)5%顯著水平 Values followed by different letters in a column are significantly among treatments at the 5% leve1.

2.3 施鎂對(duì)玉米鋅含量的影響

2.3.1 土壤及玉米的鋅含量 施鎂顯著降低了玉米幼苗的Zn含量(表3)，與不施鎂相比，莖葉的Zn含量分別降低了4.05%、34.80%、44.59%和57.09%，根系的Zn含量分別降低了7.55%、14.90%、16.82%和18.99%?？梢钥闯?，根系Zn含量的降低幅度明顯低于莖葉，之所以出現(xiàn)這種差異，一方面與莖葉和根系對(duì)鋅吸收能力的不同有關(guān)；另一方面也可能與鋅的轉(zhuǎn)運(yùn)受阻有關(guān)。

表3 不同施鎂量下玉米幼苗及土壤有效鋅含量

注(Note): 同列數(shù)據(jù)后不同字母表示處理間差異達(dá)5%顯著水平 Values followed by different letters in a column are significantly among treatments at the 5% leve1.

2.3.2 玉米的鋅吸收量 與Zn含量相似，施鎂也顯著降低了玉米幼苗的Zn吸收量(表4)，與不施鎂相比，莖葉的Zn吸收量分別降低了15.41%、46.45%、58.89%和73.55%，根系的Zn吸收量分別降低了11.62%、23.35%、29.16%和37.40%，植株總體Zn吸收量分別降低了13.73%、36.18%、45.67%和57.48%?？梢钥闯觯滴樟康慕档头让黠@低于莖葉，說明施鎂雖然抑制了Zn的吸收量，但對(duì)莖葉和根系的抑制程度不同，仍有一部分Zn累積到了根系而沒有向地上部轉(zhuǎn)運(yùn)。

表4 不同處理玉米幼苗鋅的吸收量(μg/plant)

注(Note): 同列數(shù)據(jù)后不同字母表示處理間差異達(dá)5%顯著水平 Values followed by different letters in a column are significantly among treatments at the 5% leve1.

2.3.3 Zn從根系向地上部的轉(zhuǎn)運(yùn) Rengel等[18]將養(yǎng)分的轉(zhuǎn)運(yùn)率定義為植株地上部養(yǎng)分的吸收量與整株吸收量的比值。在本研究中，我們對(duì)不同施鎂條件下玉米幼苗的Zn轉(zhuǎn)運(yùn)情況進(jìn)行了分析。從圖2可以看出，隨著施鎂量的增加或土壤交換態(tài)鎂含量的提高，Zn從根系向地上部的轉(zhuǎn)運(yùn)顯著降低，施鎂147 mg/kg，土壤交換性鎂含量為411.6 mg/kg時(shí)，Zn的轉(zhuǎn)運(yùn)率還有46.60%，施鎂515 mg/kg，土壤交換性鎂含量為755.2 mg/kg時(shí)只有34.55%，僅達(dá)到不施鎂水平的62%，表明施鎂或高土壤交換性鎂對(duì)地上部莖葉的抑制作用較根系更為明顯(表1)，導(dǎo)致根系累積了更多的鋅的緣故；對(duì)Zn含量和Zn吸收量的分析也有相同的結(jié)論(表3、表4)。

圖2 施鎂對(duì)玉米幼苗鋅轉(zhuǎn)運(yùn)的影響 Fig.2 Effects of Mg applied in soil on Zn transported to shoots of maize plants

3 討論

3.1 高鎂土壤對(duì)作物生長(zhǎng)發(fā)育的影響

3.2 高鎂環(huán)境對(duì)土壤Zn有效性的影響

3.3 高鎂環(huán)境對(duì)Zn吸收轉(zhuǎn)運(yùn)的影響

鋅在植物體內(nèi)以自由離子狀態(tài)存在或與各種低分子化合物配合，其吸收和轉(zhuǎn)運(yùn)受多種因素制約，其中供鋅水平和離子間的交互作用是植物營(yíng)養(yǎng)學(xué)家研究較多的問題。大量研究結(jié)果表明，缺鋅條件下作物體內(nèi)鋅濃度顯著下降，施鋅能大幅度提高作物體內(nèi)鋅含量和累積量[29-31]。本研究是在潛在缺鋅的石灰性土壤上進(jìn)行，有效鋅含量(DTPA-Zn)只有0.89 mg/kg，土壤供鋅水平很低，因此不同處理玉米體內(nèi)鋅含量和吸收量都很低。蘆滿濟(jì)[5]等認(rèn)為鎂與鋅之間存在拮抗作用，Zn的生物毒性試驗(yàn)也證明Mg2+可以減少Zn的毒害作用[32]，本研究中隨著施鎂量的增加，土壤和作物根際Mg2+含量都大幅度增加，充足的Mg2+充分滿足了作物對(duì)鎂素營(yíng)養(yǎng)的需求，但對(duì)于玉米幼苗的鋅營(yíng)養(yǎng)來說，其作用是相反的，高濃度的Mg2+有可能在質(zhì)外體交換位點(diǎn)上與Zn2+產(chǎn)生競(jìng)爭(zhēng)[33]，從而造成玉米莖葉和根系中的鋅含量、鋅吸收量都顯著降低，這與上述研究者的結(jié)論是一致的。另外，本研究中施鎂221 mg/kg時(shí)，玉米莖葉含鋅量為16.4 μg/g，已表現(xiàn)出缺鋅脅迫；施鎂515 mg/kg時(shí)，莖葉含鋅量只有12.7 μg/g，表現(xiàn)出缺鋅癥狀，這與大多數(shù)研究者所認(rèn)同的作物潛在性缺鋅和缺鋅臨界值(莖葉含鋅量<20 mg/kg和15 mg/kg)是一致的[13]。本研究中隨著施鎂量的增加，Zn從根系向地上部的轉(zhuǎn)運(yùn)顯著降低，這一方面與施鎂對(duì)莖葉和根系的抑制程度不同有關(guān)(表1)，另一方面也可能與環(huán)境中大量存在的Mg2+離子搶先占據(jù)了轉(zhuǎn)運(yùn)蛋白上的有利位置，導(dǎo)致根系吸收的鋅不能向地上部運(yùn)輸有關(guān)[34]。

4 結(jié)論

1)綠洲鹽化潮土上的玉米缺鋅問題與土壤含鎂量水平密切相關(guān)，隨著施鎂量的增加，玉米幼苗的生長(zhǎng)受到抑制，達(dá)到515 mg/kg時(shí)表現(xiàn)出明顯的鎂中毒癥狀和典型缺鋅癥狀，株高、干重、葉片中的葉綠素含量和SOD、POD、CAT活性都顯著降低，MDA含量顯著增加。

2)施鎂抑制了玉米幼苗對(duì)鋅的吸收，但對(duì)莖葉的抑制程度明顯高于根系，導(dǎo)致玉米根系的鋅含量和吸收量都普遍高于莖葉，鋅從根系向地上部的轉(zhuǎn)運(yùn)率顯著降低，施鎂515 mg/kg時(shí)只有34.55%，僅達(dá)到不施鎂水平的62%。

3)施鎂降低了土壤有效鋅含量，用量達(dá)到515 mg/kg時(shí)，土壤有效鋅含量已降至0.47 mg/kg，超過了土壤缺鋅臨界值(DTPA-Zn<0.5 mg/kg)。

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Inhibition of high Mg concentration on seedling growth, free radical metabolism of reactive oxygen and zinc nutrition of maize in saline fluvo-aquic soils

YANG Si-cun, HUO Lin, WANG Cheng-bao, JIANG Wan-li

(InstituteofSoil,FertilizerandWater-savingAgriculture,GansuAcademyofAgriculturalSciences/GansuScientificObservingandExperimentStationofAgro-EnvironmentandArableLandConservation,MinistryofAgriculture,Lanzhou730070,China)

【Objectives】 Zinc deficiency is very often happened in maize in saline fluvo-aquic soils in Hexi Oasis Area of Gansu Province, the high soil magnesium levels have been regarded as a major contributor to this deficiency. The inhibition effect of magnesium to zinc in saline fluvo-aquic soils in Hexi Oasis Area were discussed in this paper. 【Methods】 A pot experiment was conducted with maize as materials. Exchangeable magnesium contents of 287.3, 349.2, 411.6, 487.9 and 755.2 mg/kg were obtained by irrigating different amount of MgSO4solution. The maize plants were harvested at 46 days, the biomass of above and under ground parts were dried and weighed, the Zn contents were measured. The second leaf under the interior leaf was used for the determination of active oxygen and some enzyme activities. 【Results】 1)More high and extremely high exchangeable Mg level in soil inhibits the growth of maize seedlings. When magnesia applied levels is 221 mg/kg, i.e. the exchangeable Mg content in soil is over 487.9 mg/kg, the growth of maize is stressed, when the Mg2+applied level is 515 mg/kg, i.e. the exchangeable Mg content in soil is over 755.2 mg/kg, the plant height is markedly decreased by 14.5%, showing symptoms of magnesia poison and zinc deficiency, such as withered leaf margins and partial white stripes on the leaves (P<0.01). 2)With the increase of or exchangeable Mg levels, the dry weight in the of Mg2+addition maize are reduced by 11.9%-38.3% and 4.6%-11.9% respectively. The reduction in stem weight is significantly higher than in roots. 3)Maize leaf chlorophyll contents are reduced by 9.4%-45.9% with the increase of the Mg2+addition . The Mg level of 515 mg/kg would lead to withered and yellow leaves. The blade superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities are increased at first and then reduced quickly, the peak value appears at the exchangeable Mg levels of 147, 74 and 147 mg/kg respectively. When the dose reaches 515 mg/kg, the values are reduced by 49.75%, 48.06% and 32.21% respectively. The malondialdehyde (MDA) contents are increased consistently in the range of 20.39%-183.58%. 4)The exchangeable Mg levels significantly inhibit the uptake of Zn. Compared with the CK, the zinc contents in above ground parts are reduced by 4.05%-57.09%, the uptake reduced by 15.41%-73.55%; the root zinc contents are reduced by 7.55%-18.99%, and the uptake reduced by 11.62%-37.40%. The zinc content and absorption in stems/leaves are reduced more than in roots. High exchangeable Mg level would also lead to lower upward transfer of zinc. 5)Soil available zinc contents are significantly reduced with the increase of exchangeable Mg levels. When the Mg level reaches 515 mg/kg, i.e. the exchangeable Mg content in soil is over 755.2 mg/kg, the available zinc content falls to 0.47 mg/kg, which is below the critical value of zinc deficiency (DTPA-Zn<0.5 mg/kg).【Conclusions】 Zinc deficiency of maize in saline fluvo-aquic soil in Hexi Oasis Area is closely related to soil magnesium content. The high levels of exchangeable Mg contents show significant restraining effects on the maize seedling growth and biomass, the leaf chlorophyll content and the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT). Over high exchangeable Mg levels decrease the zinc absorption by maize seedlings, and the inhibition in stem/leaf is significantly higher than in root system, which inhibites the upward transfer of Zn from root to shoot. The available zinc content in soil will also be reduced, when the Mg level reaches 515 mg/kg, the available zinc content is below the critical value of zinc deficiency.

saline fluvo-aquic soil; soil exchangeable Mg level; zinc nutrition; free radical metabolism; maize seedling

2014-01-06 接受日期: 2014-12-09

國(guó)家自然科學(xué)基金項(xiàng)目(41261072)；農(nóng)業(yè)部公益性行業(yè)(農(nóng)業(yè))科研專項(xiàng)(200903001)資助。

楊思存(1971—)，男，甘肅靖遠(yuǎn)人，副研究員，主要從事土壤養(yǎng)分管理與鹽堿地改良利用研究。E-mail: yangsicun@sina.com

S153.6+21

A

1008-505X(2015)02-0354-08