模擬水淹對(duì)水杉苗木生長(zhǎng)與生理生化特性的影響

白林利, 韓文嬌, 李昌曉

(西南大學(xué)生命科學(xué)學(xué)院,三峽庫(kù)區(qū)生態(tài)環(huán)境教育部重點(diǎn)實(shí)驗(yàn)室,重慶400715)

模擬水淹對(duì)水杉苗木生長(zhǎng)與生理生化特性的影響

白林利, 韓文嬌, 李昌曉*

(西南大學(xué)生命科學(xué)學(xué)院,三峽庫(kù)區(qū)生態(tài)環(huán)境教育部重點(diǎn)實(shí)驗(yàn)室,重慶400715)

通過(guò)對(duì)在不同土壤水分處理下水杉(Metasequoiaglyptostroboides)保護(hù)酶系[超氧化物歧化酶(superoxide dismutase,SOD)、過(guò)氧化物酶(peroxidase,POD)、抗壞血酸過(guò)氧化物酶(ascorbate peroxidase,ASP)、過(guò)氧化氫酶(catalase,CAT)]活性及滲透調(diào)節(jié)物質(zhì)(可溶性蛋白質(zhì)、游離脯氨酸)和細(xì)胞膜脂過(guò)氧化產(chǎn)物[丙二醛(malondialdehyde,MDA)]含量以及光合特性、生物量的測(cè)定,探討水杉對(duì)三峽庫(kù)區(qū)水位變化的響應(yīng)特性和耐水淹適應(yīng)能力。模擬三峽庫(kù)區(qū)消落帶土壤水分變化格局,以二年生水杉苗木為試驗(yàn)材料,設(shè)置對(duì)照組(control,CK)、半淹組(half-submersion,HS)和全淹組(full-submersion,FS)3個(gè)處理。結(jié)果表明:在水淹脅迫下,SOD、POD、ASP、CAT活性以及游離脯氨酸含量均升高。在水淹脅迫下,水杉葉片MDA含量與CK相比差異不顯著,無(wú)統(tǒng)計(jì)學(xué)意義。HS凈光合速率(net photosynthetic rate,Pn)顯著高于CK；FS的根冠比顯著高于CK,但與HS相比差異不顯著,無(wú)統(tǒng)計(jì)學(xué)意義。全淹植株呈葉芽形式,水淹植株存活率均達(dá)100%。在淹水期間,由于抗氧化酶、滲透調(diào)節(jié)物質(zhì)、光系統(tǒng)Ⅱ的積極響應(yīng),水杉表現(xiàn)出極強(qiáng)的水分適應(yīng)能力。因此,可以考慮將水杉列為三峽庫(kù)區(qū)消落帶植被構(gòu)建的候選樹(shù)種之一。

水杉； 水分脅迫； 生長(zhǎng)； 生理生化

三峽工程給長(zhǎng)江流域的生態(tài)環(huán)境帶來(lái)了巨大影響[1],因三峽工程的興建,三峽庫(kù)區(qū)生態(tài)系統(tǒng)的水文循環(huán)、生物多樣性格局和庫(kù)區(qū)氣候等正在發(fā)生著一系列改變[2],在庫(kù)區(qū)消落帶內(nèi)人工構(gòu)建植被、減少污染物質(zhì)進(jìn)入水體、保持庫(kù)岸水土、維持和增強(qiáng)消落帶的生態(tài)功能尤為重要?，F(xiàn)有消落帶與原有消落帶相比,水淹時(shí)間更長(zhǎng)、水淹程度更深,并且是在冬季水淹,這將很可能打亂庫(kù)岸帶植物的生理節(jié)律,影響這些庫(kù)岸植物的光合作用與生長(zhǎng)發(fā)育。重建和恢復(fù)消落帶植被面臨嚴(yán)峻的考驗(yàn),而其中的關(guān)鍵就是對(duì)耐水淹樹(shù)種的篩選[3]。因此,本文將耐水淹作為切入點(diǎn),研究樹(shù)種耐水淹的生理生化機(jī)制,為三峽庫(kù)區(qū)消落帶植被構(gòu)建提供參考。

水杉(Metasequoiaglyptostroboides)是三峽庫(kù)區(qū)庫(kù)岸帶典型的鄉(xiāng)土樹(shù)種,別稱(chēng)水沙,屬杉科水杉屬；其根系發(fā)達(dá),耐寒與耐受多種水分逆境的能力較強(qiáng),是亞熱帶地區(qū)平原綠化的優(yōu)良樹(shù)種[4]。目前對(duì)水杉的研究多集中于基因結(jié)構(gòu)[5-7]、膜結(jié)構(gòu)[8]、化學(xué)成分[9-14]、生長(zhǎng)特性[15-17]和光合作用[18-19]等方面。但關(guān)于水杉對(duì)水分脅迫的響應(yīng)缺乏生長(zhǎng)、生化、光合特性的系統(tǒng)性研究,尤其是在三峽庫(kù)區(qū)消落帶土壤水分變化條件下水杉苗木的生理生態(tài)學(xué)特性鮮有報(bào)道,特別是對(duì)全淹條件下的變化情況不得而知。

本文擬對(duì)不同水淹深度下水杉的生長(zhǎng)與生理生化特性進(jìn)行研究,探索水杉在不同水淹條件下的生理生化響應(yīng)機(jī)制,為其在三峽庫(kù)區(qū)消落帶高海拔地段栽植提供理論依據(jù)。

1 材料與方法

1.1 試驗(yàn)材料與處理方法

考慮到庫(kù)岸防護(hù)林體系建設(shè)多采用二年生苗木,本試驗(yàn)以二年生的水杉苗木(取自四川省鄰水縣苗圃)為試驗(yàn)材料。2012年11月20日帶土盆栽樹(shù)苗(土壤類(lèi)型為紫色土,其性質(zhì)見(jiàn)表1),每盆1株(盆中央內(nèi)徑20 cm,盆高17 cm),共36株。置于西南大學(xué)三峽庫(kù)區(qū)生態(tài)環(huán)境教育部重點(diǎn)實(shí)驗(yàn)室實(shí)驗(yàn)基地大棚(海拔249 m,透明頂棚,四周開(kāi)敞)進(jìn)行培養(yǎng),于2013年1月18日進(jìn)行試驗(yàn)處理[苗高(97.05±1.53) cm]。結(jié)合三峽庫(kù)區(qū)消落帶水位變化情況,設(shè)置對(duì)照組(control,CK)、半淹組(half-submersion,HS)和全淹組(full-submersion,FS)3個(gè)處理,每組12株。其中,CK為常規(guī)供水組,保持土壤含水量為田間持水量的75%～80%[2]；HS苗盆放入水池中,池水保持淹沒(méi)至植物中段；FS苗盆也放入水池中,但池水保持沒(méi)過(guò)植物頂端20 cm。于2013年4月3日結(jié)束試驗(yàn)進(jìn)行各項(xiàng)指標(biāo)的測(cè)定。

表1 供試土壤營(yíng)養(yǎng)元素含量初始值

1.2 分析方法

2013年4月3日開(kāi)始對(duì)不同處理組進(jìn)行測(cè)定,每個(gè)處理組6株水杉苗木用于生長(zhǎng)測(cè)定,6株用于生理生化測(cè)定。

1.2.2 生長(zhǎng)與生物量測(cè)定 采用卷尺測(cè)量苗高、冠幅,用游標(biāo)卡尺測(cè)量地徑,每個(gè)處理6株,測(cè)定時(shí)間2013年4月3日。隨后將試驗(yàn)盆缽中的苗木小心挖出,用自來(lái)水沖凈根系,用根系分析儀(WinRHIZO,LC4800-Ⅱ LA2400)分析根系的總根長(zhǎng)、總表面積和總體積。然后將根(收集斷根,并用吸水紙吸干根表面水分)、莖、葉分別放置在80 ℃烘箱中烘干至恒重,用分析天平稱(chēng)量,計(jì)算根冠比。

1.2.3 生理生化指標(biāo)的測(cè)定 2013年4月3日,將每個(gè)處理的6株水杉苗木葉片分別全部取完,保存于-80 ℃冰箱中,用于生理生化指標(biāo)測(cè)定。超氧化物歧化酶(superoxide dismutase,SOD)活性測(cè)定采用氮藍(lán)四唑(nitro-blue tetrazolium,NBT)法[24]。過(guò)氧化物酶(peroxidase,POD)活性測(cè)定采用愈創(chuàng)木酚法[24]?？箟难徇^(guò)氧化物酶(ascorbate peroxidase,ASP)的測(cè)定采用文獻(xiàn)[25]的方法。過(guò)氧化氫酶(catalase,CAT)活性測(cè)定采用過(guò)氧化氫氧化法,以每分鐘內(nèi)吸光值減少0.1為1個(gè)酶活力單位[24]。超氧根離子(O2-)測(cè)定采用高俊鳳[26]的方法,以μg/g表示O2-的含量。丙二醛(malondialdehyde,MDA)含量的測(cè)定采用硫代巴比妥酸(thiobarbituric acid,TBA)氧化法,可溶性蛋白質(zhì)含量測(cè)定采用考馬斯亮藍(lán)顯色法,游離脯氨酸含量測(cè)定采用磺基水楊酸法,用茚三酮比色法測(cè)定其含量[24]。吸光值測(cè)定均采用紫外分光光度計(jì)。

1.2.4 數(shù)據(jù)處理 根據(jù)測(cè)定的各項(xiàng)指標(biāo),采用單因素方差分析(One-way ANOVA)揭示水分處理對(duì)水杉生長(zhǎng)與光合生理的影響(GLM程序,SPSS 16.0),并用Tukey檢驗(yàn)法進(jìn)行多重比較,檢驗(yàn)每個(gè)指標(biāo)在處理間(α=0.05)的差異顯著性，結(jié)果用平均值±標(biāo)準(zhǔn)誤表示。

2 結(jié)果與分析

2.1 光合色素含量變化

不同處理對(duì)水杉苗木光合色素含量的影響顯著(圖1)。與CK相比,HS的葉綠素b(chlorophyll b,Chl b)、光合色素(photosynthetic pigments，Pp)均顯著降低,分別降低35.06%和21.21%；葉綠素a(chlorophyll a,Chl a)、類(lèi)胡蘿卜素(carotene,Car)、葉綠素/類(lèi)胡蘿卜素(chlorophyll/yellow carotene,Chl/Car)亦降低,相比差異不顯著,無(wú)統(tǒng)計(jì)學(xué)意義；而葉綠素a/b升高了22.89%,FS中的Chl a、Chl b、Car、Pp和Chl/Car卻均顯著低于CK與HS。與之相反,FS中的Chl a/b顯著高于CK與HS。

2.2 光合指標(biāo)

水淹結(jié)束時(shí),與CK相比,HS中的Pn、CUE顯著增加,而Sc、Ci/Ca則顯著降低。HS中的Fv/Fm、PhiPS2有所增加,但與CK相比差異不顯著,無(wú)統(tǒng)計(jì)學(xué)意義(表2)。因FS中的葉芽呈未展開(kāi)形式,無(wú)法測(cè)定其光合參數(shù).此外,各處理組水杉苗木存活率都達(dá)100%,即水淹未影響水杉樹(shù)苗存活率。

2.3 滲透調(diào)節(jié)物質(zhì)含量變化

在淹水脅迫下,水杉苗木體內(nèi)脯氨酸含量不斷積累,且隨著脅迫程度的加劇積累越多。與CK相比,

CK:對(duì)照組;HS:半淹組;FS:全淹組.柱狀圖上的不同小寫(xiě)字母表示在0.05水平差異有統(tǒng)計(jì)學(xué)意義。 CK: Control; HS: Half-submersion; FS: Full-submersion. Different lowercase letters above the histogram indicate significant difference at the 0.05 probability level．圖1 不同處理組光合色素的比較Fig.1 Comparison of photosynthetic pigments among treatment groups

表2 不同處理組光合參數(shù)的變化

Table 2 Changes of photosynthetic parameters among treatment groups

變量Variable對(duì)照組CK半淹組HSPn/[μmolCO2/(m2·s)]11.39±0.34b13.86±0.84aSc/[molH2O/(m2·s)]0.11±0.00a0.08±0.00bCi/Ca/(μmolCO2/mol)0.58±0.01a0.27±0.02bCUE=Pn/Ci0.05±0.00b0.16±0.02aFv/Fm0.77±0.00a0.78±0.00aPhiPS2=(F'm-Fs)/F'm0.08±0.00a0.09±0.00aETR39.98±1.10b46.70±1.17a

Pn：凈光合速率；Sc：氣孔導(dǎo)度；Ci：胞間CO2濃度；Ca：大氣CO2濃度；CUE：羧化效率；Fv/Fm：光系統(tǒng)Ⅱ的最大量子產(chǎn)量；PhiPS2：光系統(tǒng)Ⅱ的實(shí)際量子產(chǎn)量；ETR：電子傳遞速率。同行數(shù)據(jù)后不同小寫(xiě)字母表示在0.05水平差異有統(tǒng)計(jì)學(xué)意義。

Pn: Net photosynthetic rate; Sc: Stomatal conductance; Ci: Intercellular CO2concentration; Ca: Atmospheric CO2concentration; CUE: Carboxylation efficiency;Fv/Fm: The maximum quantum yield of PSⅡ; PhiPS2: The actual quantum yield of PSⅡ; ETR: Electron transfer rate. Values within a row followed by different lowercase letters show significantly different at the 0.05 probability level.

HS和FS的游離脯氨酸含量均顯著升高了34.46%和57.29%,而HS與FS相比差異不顯著,無(wú)統(tǒng)計(jì)學(xué)意義;與CK相比,在水淹結(jié)束時(shí),HS可溶性蛋白質(zhì)升高,但未達(dá)顯著水平,而FS則顯著降低(圖2).

2.4 葉片MDA與超氧根離子含量變化

在水淹結(jié)束時(shí),HS、FS水杉苗木的MDA含量有所升高,但均與CK相比差異不顯著,無(wú)統(tǒng)計(jì)學(xué)意義；與CK相比,HS、FS水杉苗木的超氧根離子均有所降低,但均未達(dá)顯著水平(圖3)。

2.5 葉片保護(hù)酶系活性變化

在水淹脅迫下,SOD表現(xiàn)為上升的趨勢(shì),HS顯著高于CK,而FS與CK相比差異不顯著,無(wú)統(tǒng)計(jì)學(xué)意義;與CK相比,HS、FS中的CAT活性均升高,但未達(dá)顯著水平;不同水分處理對(duì)水杉苗木POD活性的影響顯著,FS水杉苗木的POD活性顯著高于CK,HS顯著高于FS;與CK相比,HS、FS中CAT活性均升高,HS顯著高于CK與FS(圖3)。

CK:對(duì)照組;HS:半淹組;FS:全淹組.柱狀圖上的不同小寫(xiě)字母表示在0.05水平差異有統(tǒng)計(jì)學(xué)意義。 CK: Control; HS: Half-submersion; FS: Full-submersion. Different lowercase letters above the histogram indicate significant difference at the 0.05 probability level．圖2 不同處理組脯氨酸、可溶性蛋白質(zhì)含量的比較Fig.2 Comparison of free proline and soluble protein content among treatment groups

CK:對(duì)照組;HS:半淹組;FS:全淹組.柱狀圖上的不同小寫(xiě)字母表示在0.05水平差異有統(tǒng)計(jì)學(xué)意義。 CK: Control; HS: Half-submersion; FS: Full-submersion. Different lowercase letters above the histogram indicate significant difference at the 0.05 probability level．圖3 不同處理組MDA、超氧根離子、SOD、POD、ASP、CAT的比較Fig.3 Comparison of MDA, O2-, SOD, POD, ASP, CAT among treatment groups

2.6 生長(zhǎng)指標(biāo)

2.6.1 苗高、地徑、冠幅 在水淹結(jié)束時(shí),各處理組的苗高、地徑、冠幅都呈上升趨勢(shì)；與CK相比,HS、FS苗高的凈增長(zhǎng)顯著降低,地徑的凈增長(zhǎng)與CK相比差異不顯著,無(wú)統(tǒng)計(jì)學(xué)意義；HS水杉苗木冠幅的凈增長(zhǎng)顯著高于FS,而與CK相比差異不顯著,無(wú)統(tǒng)計(jì)學(xué)意義(圖4)。

2.6.2 根長(zhǎng)、根表面積、根體積 在水淹脅迫下,水杉苗木的根長(zhǎng),根表面積,根體積表現(xiàn)出一個(gè)共同的變化趨勢(shì),即與CK相比,HS升高,FS降低；HS水杉苗木的根長(zhǎng)、根表面積顯著高于FS,而與CK相比差異不顯著,無(wú)統(tǒng)計(jì)學(xué)意義(圖5)。

2.6.3 生物量分配 與CK相比,HS與FS的根所占比例顯著升高;HS葉所占比例與CK相比差異不顯著,FS莖所占比例與CK相比差異也不顯著,無(wú)統(tǒng)計(jì)學(xué)意義。同時(shí),FS的根冠比顯著高于CK,但與HS相比差異不顯著,無(wú)統(tǒng)計(jì)學(xué)意義(表3)。

CK:對(duì)照組;HS:半淹組;FS:全淹組.柱狀圖上的不同小寫(xiě)字母表示在0.05水平差異有統(tǒng)計(jì)學(xué)意義。 CK: Control; HS: Half-submersion; FS: Full-submersion. Different lowercase letters above the histogram indicate significant difference at the 0.05 probability level．圖4 不同處理組水杉的苗高、地徑、冠幅變化Fig.4 Changes of height, ground diameter, crown diameter of M. glyptostroboides among treatment groups

CK:對(duì)照組;HS:半淹組;FS:全淹組.柱狀圖上的不同小寫(xiě)字母表示在0.05水平差異有統(tǒng)計(jì)學(xué)意義。 CK: Control; HS: Half-submersion; FS: Full-submersion. Different lowercase letters above the histogram indicate significant difference at the 0.05 probability level．圖5 不同處理組根長(zhǎng)、根表面積、根體積的比較Fig.5 Comparison of root length, root surface area, root volume among treatment groups

表3 不同處理組水杉各器官在生物量中所占的比例

同行數(shù)據(jù)后的不同小寫(xiě)字母表示在0.05水平差異有統(tǒng)計(jì)學(xué)意義。

CK： Control; HS: Half-submersion； FS： Full-submersion. Values within row followed by different lowercase letters show significantly differences at the 0.05 probability level.

3 討論

3.1 水淹對(duì)水杉苗木細(xì)胞膜的影響及其滲透調(diào)節(jié)物質(zhì)的響應(yīng)

滲透調(diào)節(jié)是植物適應(yīng)逆境的一種重要的生理機(jī)制,植物通過(guò)代謝活動(dòng)增加細(xì)胞內(nèi)的溶質(zhì)降低滲透勢(shì),維持膨壓,從而使體內(nèi)各種與膨壓有關(guān)的生理過(guò)程正常進(jìn)行[27-28]。脯氨酸被認(rèn)為是有效的滲透調(diào)節(jié)物質(zhì)之一,有助于細(xì)胞或組織持水[29]。在水淹脅迫下,水杉苗木游離脯氨酸含量增加(圖2),超氧根離子含量與對(duì)照相比差異不顯著(圖3),表明水杉產(chǎn)生脯氨酸能適應(yīng)水分脅迫,調(diào)節(jié)細(xì)胞的滲透勢(shì)和清除活性氧[30]。FS可溶性蛋白質(zhì)含量顯著降低,HS有所增加,但未與CK產(chǎn)生顯著差異(圖2),說(shuō)明全淹脅迫使水杉苗木的正常代謝過(guò)程受到干擾,抑制蛋白質(zhì)的合成并誘導(dǎo)蛋白質(zhì)的降解,從而使植株體內(nèi)的蛋白質(zhì)含量降低[31]；同時(shí)也表明水杉苗木對(duì)水淹逆境有一種內(nèi)在的生理適應(yīng)機(jī)制[32]。就本研究所測(cè)的滲透調(diào)節(jié)物質(zhì)而言,從可溶性蛋白質(zhì)含量相對(duì)較低,增幅平穩(wěn)并沒(méi)有對(duì)脅迫表現(xiàn)出明顯增幅加大來(lái)看,脯氨酸是水杉應(yīng)對(duì)水分脅迫較為主導(dǎo)的滲透調(diào)節(jié)物質(zhì),它對(duì)活性氧有專(zhuān)一的消除作用,可保護(hù)細(xì)胞膜免受損害[33]。

在水分脅迫下,植物體內(nèi)丙二醛(MDA)和活性氧的產(chǎn)生及積累是植物的主要生理響應(yīng)特征之一[34]。MDA是膜脂過(guò)氧化產(chǎn)物之一,其對(duì)細(xì)胞具有很強(qiáng)的毒性,并且參與破壞生物膜的結(jié)構(gòu)和功能,通常利用其表示細(xì)胞膜脂過(guò)氧化程度及植物對(duì)逆境條件反應(yīng)的強(qiáng)弱[35-36]。超氧根離子傷害植物的機(jī)制之一在于參與啟動(dòng)膜脂過(guò)氧化或脂膜脫酯作用[37],從而破壞膜結(jié)構(gòu)。HS、FS水杉葉片MDA含量與CK相比差異不顯著,說(shuō)明水淹脅迫未對(duì)水杉苗木造成膜脂損害,顯示出水杉具有良好的耐水淹特性。本研究同時(shí)發(fā)現(xiàn),在淹水結(jié)束時(shí),淹水處理組水杉苗木的O2-含量與CK相比差異不顯著，SOD、POD、ASP和CAT均比CK高(圖3),說(shuō)明水杉苗木為了抵御水分脅迫的毒害作用,形成了復(fù)雜的抗氧化防御系統(tǒng)[38]。水杉苗木保護(hù)酶系統(tǒng)在短期內(nèi)能維持活性氧的動(dòng)態(tài)平衡,通過(guò)提高保護(hù)酶活性以加強(qiáng)清除活性氧、減少其對(duì)細(xì)胞膜傷害[36],這應(yīng)是水杉苗木適應(yīng)水淹環(huán)境的重要機(jī)制之一[39]。

3.2 水杉對(duì)水分脅迫的保護(hù)酶系統(tǒng)響應(yīng)

SOD、POD、ASP和CAT是植物體內(nèi)參與活性氧代謝的主要酶,SOD催化分解O2-,使之轉(zhuǎn)化為過(guò)氧化氫(H2O2)；POD、ASP和CAT則被認(rèn)為是植物清除H2O2的酶[40],它們的活性變化在一定程度上反映了植物體內(nèi)活性氧的代謝情況[41]。在本研究中,HS水杉苗木的SOD、POD顯著高于CK；而O2-含量、ASP和CAT均與CK相比差異不顯著,表明在半淹脅迫下,水杉苗木啟動(dòng)SOD表達(dá),產(chǎn)生大量的SOD清除O2-；在清除H2O2的過(guò)程中,POD起到了最主要的作用,這與Takemura等[42]對(duì)木欖(Bruguieragymnorrhiza)的研究結(jié)果相似,這些酶的表達(dá)是水杉苗木對(duì)水淹脅迫的適應(yīng)性響應(yīng)[43]。FS水杉苗木的SOD、O2-含量和CAT與CK相比差異均不顯著,而POD、ASP顯著高于CK,但POD顯著低于HS。說(shuō)明與半淹脅迫相比,在全淹脅迫下,水杉苗木主要通過(guò)升高ASP活性來(lái)清除H2O2,這應(yīng)和其清除活性氧從而誘導(dǎo)提高保護(hù)酶活性與保護(hù)細(xì)胞膜有關(guān),同時(shí)也是對(duì)水淹脅迫適應(yīng)的結(jié)果[44]。

3.3 水杉對(duì)水分脅迫的光合與生長(zhǎng)響應(yīng)

水淹會(huì)使植株葉片的葉綠素降解,含量下降[45]。本研究發(fā)現(xiàn),水淹使水杉苗木Chl、Car、Chl/Car下降,表明光合色素的降解是水杉苗木應(yīng)對(duì)水淹脅迫的方式之一[46-47]。與CK相比,盡管水淹組水杉苗木Chl/Car下降,但其比值仍大于3(植物葉片內(nèi)的葉綠素與類(lèi)胡蘿卜素含量之比通常約為3∶1[48]),提高了葉綠素在光合色素中的相對(duì)含量,確保有足夠的反應(yīng)中心色素,進(jìn)而提高光合能力。而與CK相比,水淹組水杉苗木Chl a/b卻顯著上升(圖1),表明水淹后水杉苗木的捕光色素降解得快,而光系統(tǒng)反應(yīng)中心色素降解得慢[49],通過(guò)調(diào)節(jié)葉片Chl a與Chl b的比值來(lái)維持其較高的光合能力[50]。有研究表明,在水淹脅迫下,Chl a/b的比值上升[51],但也有研究認(rèn)為下降[52]。本研究發(fā)現(xiàn),淹水處理組的Chl a/b顯著高于CK(圖1),支持了Smethurst等[51]的研究結(jié)果。這極有可能是樹(shù)種的不同所引起,不同的樹(shù)種可能具有不同的耐水淹能力和響應(yīng)特性,產(chǎn)生這種差異的原因還有待進(jìn)一步研究。

植物葉片氣孔變小甚至關(guān)閉是植物對(duì)水淹逆境脅迫的通常響應(yīng)方式之一[53]。本研究發(fā)現(xiàn),在水淹脅迫下,水杉苗木的Sc降低,與Mielke等[54]對(duì)美洲格尼帕樹(shù)(Genipaamericana)的研究結(jié)果相同。羅芳麗等[55]認(rèn)為水淹導(dǎo)致植株部分葉組織無(wú)法進(jìn)行光合作用而使植株的整體光合能力受到影響,植株未被水淹的葉組織光合能力可能會(huì)增強(qiáng)。淹水后HS水杉苗木Pn顯著高于CK(表2),其原因可能是植物的光合能力受光合產(chǎn)物需求的負(fù)反饋調(diào)節(jié)[56],這可能與水杉葉片在水淹期間具有較高羧化能力有關(guān)(表2),也是水杉苗木抗氧化酶、滲透調(diào)節(jié)物質(zhì)與光合色素綜合作用的結(jié)果。本研究發(fā)現(xiàn),與CK相比,HS水杉苗木的Pn增加了33%,高于相同水淹深度處理后耐淹樹(shù)種水翁(Cleistocalyxoperculatus)[57]和落羽杉(Taxodiumdistichum)[58]?？梢?jiàn),在短暫的水淹時(shí)間(2013-01-18—2013-04-03)內(nèi),水杉苗木與一些耐淹樹(shù)種相比其光合能力受水淹影響較小。本研究還發(fā)現(xiàn),在半淹脅迫下,水杉苗木的Pn、Sc和Ci/Ca的變化(表2)表明,水杉苗木Pn升高的原因極有可能是在短期水淹脅迫下水杉苗木的光合酶活性和利用CO2的能力較強(qiáng)所致[59]。

葉綠素?zé)晒鈾z測(cè)可以快速、靈敏地了解植物光合作用對(duì)外界環(huán)境因子的響應(yīng)[60],植物葉片PSⅡ的最大光化學(xué)效率(Fv/Fm)可以作為PSⅡ潛在光化學(xué)活性的度量,在非脅迫條件下該參數(shù)變化極小,不受物種和生長(zhǎng)條件的影響；在脅迫條件下該參數(shù)明顯下降,表明有功能的反應(yīng)中心含量降低[55]。HS水杉葉片的Fv/Fm與CK相比差異不顯著,表明半淹脅迫對(duì)水杉有功能的PSⅡ反應(yīng)中心影響較小,加之水杉苗木抗氧化系統(tǒng)與光合色素的積極響應(yīng),表明水杉確實(shí)有較強(qiáng)的水分適應(yīng)能力[61]。與CK相比,HS水杉苗木有較高PhiPS2、電子傳遞速率(表2),表明水淹對(duì)水杉葉片光合器官及羧化酶的活性影響較小。

植物的生物量、苗高和地徑與其生長(zhǎng)發(fā)育及營(yíng)養(yǎng)物質(zhì)的形成密切相關(guān),對(duì)其所處的生長(zhǎng)環(huán)境綜合表征作用明顯[62]。本研究發(fā)現(xiàn),不管是HS還是FS,水杉苗木苗高的凈增長(zhǎng)都低于CK,淹水脅迫抑制了植物苗高的生長(zhǎng)[63]。本研究還發(fā)現(xiàn),半淹脅迫對(duì)水杉的生長(zhǎng)具有部分促進(jìn)作用,與東北玉簪(Hostaclausa)[64]和烏桕(Sapiumsebiferum)[65]等表現(xiàn)相似。HS水杉根長(zhǎng)、根表面積均比CK高,HS葉所占的比例,地徑、冠幅的凈增長(zhǎng)與CK相比差異不顯著,這有可能與半淹脅迫下水杉苗木Pn顯著高于CK有關(guān)。而水淹組水杉苗木根所占比例,根冠比顯著高于CK(表3),說(shuō)明二年生水杉苗木生物量較多分配在根部,加大根部化合物的貯存,以有效應(yīng)對(duì)水淹脅迫下逆境條件[66-67]。

4 結(jié)論

本研究發(fā)現(xiàn),水杉苗木的生長(zhǎng)和生理生化代謝受到水淹脅迫的影響,其水分適應(yīng)性較強(qiáng)。在水淹脅迫下,水杉苗木引起膜脂過(guò)氧化以及光合色素含量降低,但由于體內(nèi)滲透調(diào)節(jié)物質(zhì)含量的增加和抗氧化防御系統(tǒng)的積極防御,可以緩解過(guò)多水分對(duì)水杉苗木造成的損害,從而沒(méi)有對(duì)Fv/Fm和Pn造成影響。在不同淹水條件下,水杉苗木存活率均達(dá)100%,表現(xiàn)出極強(qiáng)的適應(yīng)水環(huán)境的能力。從本研究結(jié)果來(lái)看,水杉可以作為三峽庫(kù)區(qū)消落帶植被恢復(fù)的候選樹(shù)種之一。

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Effects of simulated waterlogging on growth, physiological and biochemical characteristics ofMetasequoiaglyptostroboidesseedlings.

Bai Linli, Han Wenjiao, Li Changxiao*

(KeyLaboratoryfortheEco-EnvironmentoftheThreeGorgesReservoirRegionoftheMinistryofEducation,CollegeofLifeSciences,SouthwestUniversity,Chongqing400715,China)

The disruption of natural flow regimes in river systems poses many challenges to riparian ecosystems and their native species. The construction of the Three Gorges Dam has altered the flow regimes of the upper Yangtze River and created a riparian zone with a vertical gap of 30 m. Because of the anti-seasonal change of the water level caused by annual water regulation, plants grown on the riparian zone of the Three Gorges Reservoir Area (TGRA) may suffer from submergence, and often display dynamic change characteristics. Such water level change is likely to disturb the normal ecophysiological rhythm of the native tree species of the riparian zone. These hydrological changes highlight the importance of screening suitable tree species for reforestation in the TGRA and similar environments. Thus, the native tree speciesMetasequoiaglyptostroboides, will most likely to experience continuous submergence or inundation. Current research onM.glyptostroboidesseedlings is more focused on genetic structure, membrane composition, chemical property, growth and photosynthesis, and the like. However, the eco-physiological implications of submersion onM.glyptostroboidesseedlings are not well known, especially under the condition of full-submersion.

The aim of this study was to investigate the responding characteristics of theM.glyptostroboidesseedlings to the water level change in the TGRA, and provide theoretical basis for species selection for revegetation in the riparian zone of the TGRA.

Measured indexes included protective enzymes such as superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (ASP) and catalase (CAT), osmotic adjustment substances such as soluble protein and free proline, and membrane lipid peroxidation such as malondialdehyde (MDA), as well as photosynthetic characteristics and biomass accumulation of the two-year oldM.glyptostroboidesseedlings to submergence, upon mimicking the water level change in the riparian zone of the TGRA. Based on soil moisture change pattern in the TGRA, water treatments including control (CK), half-submersion (HS), and full-submersion (FS) were applied.

The activities of SOD, POD, ASP, CAT and content of free proline ofM.glyptostroboidesseedlings in HS and FS group were higher than that in CK after submersion. Under submersion, MDA content in HS and FS group increased as compared with that in CK. The net photosynthetic rate ofM.glyptostroboidesseedlings in HS was significantly higher than that in CK. Root-shoot ratio in FS was significantly higher than that in CK, but no significant difference was detected between FS and HS. Leaves ofM.glyptostroboidesseedlings in FS were leaf bud, and survival rates were 100%.

The results indicated that antioxidant enzymes, osmotic adjustment substances and photosystem Ⅱ have a positive response during submersion,M.glyptostroboidesseedlings show strong adaptability to the submersion. Thus,M.glyptostroboidesshould be considered as one of the potential species for revegetation in the TGRA.

Metasequoiaglyptostroboides; water stress; growth; physiology and biochemistry

Journal of Zhejiang University (Agric. & Life Sci.), 2015,41(5):505-515

重慶市基礎(chǔ)與前沿研究計(jì)劃重點(diǎn)項(xiàng)目(CSTC2013JJB00004)；中央高?；究蒲袠I(yè)務(wù)費(fèi)專(zhuān)項(xiàng)資金(XDJK2013A011)；國(guó)家林業(yè)公益性行業(yè)科研專(zhuān)項(xiàng)(201004039)；留學(xué)回國(guó)人員科研啟動(dòng)基金(教外司留[2010]1561號(hào))。

聯(lián)系方式:白林利(http://orcid.org/0000-0002-0956-844X),E-mail:895845358@qq.com

2014-09-29;接受日期(Accepted):2015-01-21；網(wǎng)絡(luò)出版日期(Published online):2015-09-18

Q 945.78; S 718.43; S 791.35

A

*通信作者(Corresponding author):李昌曉(http://orcid.org/0000-0002-5090-6201),E-mail:lichangx@swu.edu.cn

URL:http://www.cnki.net/kcms/detail/33.1247.s.20150918.1743.004.html