植物對鹽分空間不均勻分布的形態(tài)和生理響應(yīng)研究進(jìn)展

孫娟娟,張英俊

1 中國農(nóng)業(yè)科學(xué)院草原研究所, 呼和浩特 010010 2 中國農(nóng)業(yè)大學(xué)動物科學(xué)技術(shù)學(xué)院草業(yè)科學(xué)系, 北京 100193

植物對鹽分空間不均勻分布的形態(tài)和生理響應(yīng)研究進(jìn)展

孫娟娟1,張英俊2,*

1 中國農(nóng)業(yè)科學(xué)院草原研究所, 呼和浩特 010010 2 中國農(nóng)業(yè)大學(xué)動物科學(xué)技術(shù)學(xué)院草業(yè)科學(xué)系, 北京 100193

鹽脅迫是干旱、半干旱地區(qū)以及灌溉土地主要的非生物脅迫,是影響農(nóng)業(yè)生產(chǎn)的主要不利環(huán)境因子之一。隨集約化灌溉農(nóng)業(yè)的發(fā)展、水資源的缺乏、氣候干旱帶來的蒸發(fā)量的增加,土壤及地下水鹽漬化程度不斷增加。自然界中,土壤鹽分在時(shí)空上呈不均勻分布。關(guān)于植物對均勻鹽脅迫的響應(yīng)研究報(bào)到較多,然而植物對不均勻鹽脅迫的響應(yīng)研究報(bào)道較少。分析了國內(nèi)外植物適應(yīng)不均勻鹽脅迫的研究案例,從植物地上部分生長、地下部分生長、水分調(diào)節(jié)、光合作用以及離子調(diào)控等方面闡述植物適應(yīng)鹽分不均勻分布的生理機(jī)制,并提出展望。

不均勻鹽脅迫；水分吸收；離子調(diào)控

鹽脅迫是干旱、半干旱地區(qū)以及灌溉土地主要的非生物脅迫,是影響農(nóng)業(yè)生產(chǎn)的不利環(huán)境因素之一。世界約有7%的陸地面積,20%的栽培土地,幾乎一半的灌溉土地受到鹽脅迫影響[1]。我國鹽堿地面積約有3400多萬公頃[2]。隨集約化灌溉農(nóng)業(yè)的發(fā)展,水資源的缺乏,氣候干旱帶來的蒸發(fā)量的增加,土壤及地下水鹽漬化程度不斷增加[3]。

自然界中土壤鹽分在時(shí)間與空間上呈不均勻狀態(tài)存在[4- 7],并且植物根區(qū)的土壤鹽分也呈不均勻分布[8- 13]。土壤鹽分含量隨地下水位的波動[14]、土層深度的增加、水平范圍距離的不同、季節(jié)的變化[15-16]、灌溉方式的不同[17-18]而變化,降雨對鹽分的淋溶作用也會導(dǎo)致土壤鹽分的不均勻分布[19]。植物吸收水分時(shí)能將90%以上的Na+濾在根外,因此植物本身也會導(dǎo)致土壤鹽分的不均勻分布[20]。鹽土的土壤含鹽量從接近于0到高出海水鹽分濃度幾倍的范圍變化[8, 13-14,21-22]。研究表明,植物在鹽土中能夠維持生長,土壤鹽分濃度的不均勻分布起著極為重要的作用,當(dāng)植物生長在均勻的高鹽含量的鹽土中將面臨死亡[23-24]。然而土壤鹽分的不均勻分布與變化,卻給植物耐鹽品種的選育帶來極大的困難。研究植物對鹽分空間不均勻分布的響應(yīng)機(jī)制,對于篩選和培育耐鹽植物、優(yōu)化鹽堿地植物種植模式、提高鹽堿地植物生產(chǎn)力具有非常重要的理論指導(dǎo)意義。

本文著眼于植物對不均勻鹽脅迫的響應(yīng)機(jī)制,對國內(nèi)外的研究案例進(jìn)行總結(jié)和分析,以明晰該研究領(lǐng)域的發(fā)展趨勢。

1 鹽土對植物的危害

2 土壤鹽分空間不均勻分布及原因

田間土壤含鹽量從0到高出海水鹽分濃度幾倍的范圍變化[13]。研究認(rèn)為甜土植物能夠在表層鹽分含量高的土壤中生存,主要是由于植物能夠從下層土壤吸取淡水[33]。土壤中鹽分的水平變化及垂直變化同時(shí)存在,表1中是不同生境條件下土壤鹽分的變化情況。

土壤中鹽分的變化同時(shí)受到降雨、灌溉及植物的影響[44-45]。滴灌導(dǎo)致土壤鹽分在土壤表層與滴管帶之間的積累[46]。對于溝灌系統(tǒng),水分和鹽分在土壤毛細(xì)管的作用下緩慢上升導(dǎo)致鹽分在苗床中部的積累[22]。過量灌溉或多年生植被的減少往往會導(dǎo)致地下水位上升,從而導(dǎo)致表層土壤含鹽量的增加,特別是在蒸發(fā)量較大的時(shí)期[47-48]。植物本身會導(dǎo)致土壤鹽分不均勻分布。植物的根在吸收水分時(shí)能夠?qū)?0%以上的Na+濾在根外,導(dǎo)致植物根際周圍鹽分的不均勻分布[20,49]。盆栽實(shí)驗(yàn)表明,小麥(Triticumaestivum)根際土壤的含鹽量是根外圍土壤含鹽量的2倍[50]。

3 鹽分空間不均勻分布對植物生長的影響

3.1 鹽分空間不均勻分布對植物地上部分生長的影響

不同植物莖生長對不均勻鹽脅迫的反應(yīng)不同,已開展的研究中除了辣椒[51](Capsicumannuum)在不均勻鹽脅迫下其生物量與均勻鹽脅迫無顯著差異外,多數(shù)植物不均勻鹽脅迫下的地上生物量大于均勻鹽脅迫下的地上生物量,見表2。充分說明不均勻鹽脅迫能夠緩解均勻高鹽脅迫對植物造成的危害。

表1 不同環(huán)境土壤含鹽量在水平方向及垂直方向的分布

表2 不均勻和均勻鹽脅迫下不同植物地上生物量的比較

大洋洲濱藜所受不均勻鹽脅迫處理中低鹽脅迫根部鹽分濃度為10mmol/L NaCl,其他植物的不均勻鹽脅迫處理中低鹽脅迫根部鹽分濃度均為0mmol/L NaCl

關(guān)于不均勻鹽脅迫下植物生長取決于什么存在4個(gè)假設(shè)：(1)不均勻鹽脅迫下植物生長與低鹽脅迫根部的鹽分濃度有關(guān)；(2)不均勻鹽脅迫下植物的生長與根部鹽分濃度平均值有關(guān)；(3)不均勻鹽脅迫下植物生長與整個(gè)根部所受鹽脅迫平均濃度有關(guān)；(4)不均勻鹽脅迫下植物的生長取決于根重加權(quán)鹽分濃度平均值。這些假設(shè)分別在不同的植物中得到驗(yàn)證,也說明了不同植物間對不均勻鹽脅迫表現(xiàn)的差異。早期田間試驗(yàn)研究認(rèn)為植物的產(chǎn)量與土壤平均鹽分濃度有關(guān)[7,58-59]；也有一部分研究認(rèn)為植物的產(chǎn)量與根重加權(quán)鹽分濃度平均值有關(guān)[60]；還有研究認(rèn)為不均勻鹽脅迫下植物地上生物量與水分吸收加權(quán)鹽分濃度平均值有關(guān)[54,61]；對辣椒的研究認(rèn)為不均勻鹽脅迫下,最高鹽脅迫根部的鹽脅迫濃度決定了植物的生長[51]。孫娟娟對紫花苜蓿的研究認(rèn)為,不均勻鹽脅迫下紫花苜蓿的生長與根部鹽分濃度平均值、根重加權(quán)鹽分濃度平均值和根部水分吸收加權(quán)鹽分濃度平均值都有一定的相關(guān)性,但與根部水分吸收加權(quán)鹽分濃度平均值的相關(guān)性最大[62]。

3.2 鹽分空間不均勻分布對植物根生長的影響

關(guān)于不均勻鹽脅迫對植物根生長的影響研究較少。多數(shù)研究認(rèn)為在不均勻鹽脅迫下,植物大部分新生根都會出現(xiàn)在不受鹽脅迫或者鹽脅迫程度較低的根部。通過分根實(shí)驗(yàn),給番茄進(jìn)行不均勻鹽脅迫發(fā)現(xiàn),在非鹽脅迫的根部出現(xiàn)了根的補(bǔ)償生長,不均勻鹽脅迫下非鹽脅迫一側(cè)根的生物量比對照組提高了60%,這部分根生物量占根總生物量的72%[9]。0/150mmol/L NaCl處理冬小麥,其非鹽脅迫一側(cè)根系干重、根長和側(cè)根數(shù)分別比非鹽脅迫對照增加了42.1%、21.3%和60.9%[63]。而不均勻鹽脅迫下在非鹽脅迫根部或者低鹽脅迫根部是否發(fā)生根的補(bǔ)償生長取決于高鹽脅迫根部鹽分濃度的大小。鹽生植物大洋洲濱藜在10/670mmol/L NaCl的脅迫下其兩側(cè)根部生物量沒有顯著不同,因此也沒有出現(xiàn)低鹽脅迫根部的補(bǔ)償生長[55],而當(dāng)高鹽脅迫根部鹽分濃度增加到1500mmol/L NaCl時(shí),大洋洲濱藜低鹽脅迫根部干重顯著高于高鹽脅迫根部根干重[60]。0/75mmol/L NaCl處理紫花苜蓿兩側(cè)根的生物量與0/0mmol/L NaCl處理兩側(cè)根的生物量無顯著差異,隨高鹽脅迫根部鹽分濃度的增加,當(dāng)給紫花苜蓿0/150和0/225mmol/L NaCl處理時(shí)紫花苜蓿非鹽脅迫一側(cè)根部的根生物量分別比0/0mmol/L NaCl處理一側(cè)根的根生物量提高了15%和20%[31],低鹽脅迫根部根的生長會受到高鹽脅迫根部鹽分濃度的影響的原因,還有待于進(jìn)一步研究。對不均勻鹽脅迫下紫花苜蓿根系構(gòu)型研究,發(fā)現(xiàn)當(dāng)高鹽脅迫根部NaCl濃度在75mmol/L和150mmol/L時(shí),非鹽脅迫一側(cè)根部的總根長和總根表面積與對照無顯著差異,然而0—0.3mm直徑的根長比例卻顯著高于對照組；當(dāng)高鹽脅迫根部NaCl濃度為255mmol/L時(shí),發(fā)現(xiàn)非鹽脅迫一側(cè)根部根長及根表面積的增加[62]。

4 植物對鹽分空間不均勻分布的生理響應(yīng)

4.1 植物對水分吸收的調(diào)節(jié)

關(guān)于不均勻鹽脅迫下植物對水分吸收及水勢的研究非常有限。研究認(rèn)為均勻鹽脅迫導(dǎo)致植物對水分吸收的下降[10,60,64-66],然而,不均勻鹽脅迫下植物對水分的吸收量高于均勻鹽脅迫下植物對水分的吸收量。主要是由于低鹽脅迫根部能夠部分地[31,55,60,65,67]或全部地[9-10,54]補(bǔ)償高鹽脅迫根部對水分吸收的減少。0/75、0/150、0/225mmol/L NaCl處理紫花苜蓿，發(fā)現(xiàn)非鹽脅迫一側(cè)根部水分吸收分別比0/0mmol/L NaCl處理一側(cè)根部提高了18%、20%、27%；75/150、75/225mmol/L NaCl處理紫花苜蓿75mmol/L NaCl一側(cè)根部的水分吸收分別比75/75mmol/L NaCl一側(cè)根部水分吸收提高了36%和16%[31]。

不均勻鹽脅迫下,莖水勢與受鹽脅迫最低的根部水勢有關(guān)。對鹽生植物大洋洲濱藜進(jìn)行10/230- 670mmol/L NaCl不均勻鹽脅迫處理,發(fā)現(xiàn)其黎明前莖水勢與對照(均勻的10mmol/L NaCl處理)無顯著差異,表明了莖水勢受低鹽脅迫根部鹽分濃度影響較大,而不受高鹽脅迫根部鹽分濃度影響[55]。對甜土植物的相關(guān)研究也發(fā)現(xiàn)了類似的結(jié)果,0/80mmol/L NaCl處理酸橙的莖水勢為0.2MPa與非鹽脅迫對照的莖水勢相同,而均勻80mmol/L NaCl處理其莖水勢則降到-2.7Mpa[54]；在紫花苜蓿的研究中發(fā)現(xiàn),0/75、0/150、0/225mmol/L NaCl處理黎明前葉片水勢與非鹽脅迫對照均無顯著差異,且分別比均勻的75、150、225mmol/L NaCl處理提高了15%、31%、50%。不均勻鹽脅迫75/150和75/225mmol/L NaCl處理紫花苜蓿葉片水勢與均勻75mmol/L NaCl處理無顯著差異,分別比均勻150和225mmol/L NaCl處理提高了28%和37%[31]?？赡芘c植物能夠從低鹽脅迫根部吸收較多的水分有關(guān),在這些研究中,不均勻鹽脅迫下植物吸收的水分71—91%來自于低鹽脅迫根部[31,54-55]。

4.2 不均勻鹽脅迫對植物光合特征的影響

不均勻鹽脅迫能夠緩解均勻鹽脅迫引起的植物氣孔導(dǎo)度、胞間二氧化碳濃度和蒸騰速率的下降。對冬小麥的研究發(fā)現(xiàn),0/150mmol/L NaCl處理冬小麥14天其光合速率分別比均勻75和150mmol/L NaCl處理提高了8.5%和43.8%、該處理冬小麥的氣孔導(dǎo)度分別比均勻75和150mmol/L NaCl處理提高了8.0%和119.8%、胞間二氧化碳濃度分別提高了52.1%和30.1%、蒸騰速率分別提高了22.1%和121.5%[63]。在紫花苜蓿的研究中發(fā)現(xiàn),0/225mmol/L NaCl處理紫花苜蓿的凈光合速率、氣孔導(dǎo)度和蒸騰速率分別是均勻225mmol/L NaCl處理的1.4倍、1.7倍和1.7倍[62]。不均勻鹽脅迫下鹽生植物氣孔導(dǎo)度與非鹽脅迫時(shí)的氣孔導(dǎo)度無顯著差異[55]。對大麥的研究發(fā)現(xiàn),均勻鹽脅迫18d其氣孔導(dǎo)度急劇下降,而不均勻鹽脅迫27d時(shí),大麥的氣孔導(dǎo)度才發(fā)生急劇下降,說明了不均勻鹽脅迫緩解了大麥葉片的衰老[68]。0/200、50/150mmol/L NaCl不均勻鹽脅迫7d,棉花的凈光合速率分別比均勻100mmol/L NaCl處理提高了41.1%和18.4%、蒸騰速率分別提高了49.1%和33.5%、葉綠素含量分別提高了21.2%和10.9%、氣孔導(dǎo)度分別提高了97.7%和60.2%[65]。

4.3 不均勻鹽脅迫下植物對Na+和K+的調(diào)控

植物維持高耐鹽性的機(jī)制之一就是在高鹽脅迫下能夠使莖中Na+濃度維持在較低水平。研究認(rèn)為鹽脅迫下植物莖生長與莖中Na+濃度呈顯著負(fù)相關(guān)。鹽脅迫下植物莖部低濃度的Na+含量往往與高濃度的K+含量相伴,研究認(rèn)為對于很多植物細(xì)胞能夠維持較高的K+/Na+要比單一的維持低濃度的Na+更重要[69]。Na+是通過根皮層細(xì)胞的被動吸收從土壤進(jìn)入根部的[740]。Na+在植物中的凈積累是Na+被動流入與主動流出的平衡。Na+由根部排出是很多植物的重要耐鹽機(jī)制之一[71]。

不均勻鹽脅迫下植物莖或葉片Na+含量通常高于非鹽脅迫對照組[53,55,60]。大麥、菜豆(Phaseolusvulgaris)和夾竹桃在不均勻的0/100mmol/L NaCl脅迫下,葉片Na+含量分別是對照組的58倍、34倍和57倍[53]。0/200、50/150、100/100mmol/L NaCl處理棉花7d,其葉片Na+含量分別為對照組的4倍、5倍、6倍[65]。10/670、230/670、450/670mmol/L NaCl處理21d大洋洲濱藜葉片Na+含量分別為對照組的1.5倍、1.8倍、1.7倍[55]。海馬齒莧在0/800mmol/L NaCl下,其葉片Na+含量是對照組的20倍[57]。然而,不均勻鹽脅迫下植物莖葉的Na+含量顯著低于均勻鹽脅迫處理組。10/670mmol/L NaCl不均勻鹽脅迫21d,大洋洲濱藜葉片Na+含量為280mmol/L,而均勻的670mmol/L NaCl鹽脅迫其葉片Na+含量為830mmol/L[55]。0/75、0/150和0/225mmol/L NaCl處理紫花苜蓿其葉片Na+濃度分別比均勻的75、150mmol/L和225mmol/L NaCl處理降低了42%、43%和43%[31]。說明不均勻鹽脅迫能夠緩解均勻鹽脅迫對植物造成的Na+的毒害。對棉花[65]和紫花苜蓿[31]進(jìn)行不均勻鹽脅迫處理,發(fā)現(xiàn)非鹽脅迫一側(cè)的根部Na+的含量,顯著高于非鹽脅迫對照組[65],當(dāng)去掉非鹽脅迫一側(cè)根部的韌皮部時(shí),棉花非鹽脅迫一側(cè)根部Na+含量顯著降低,說明了葉片Na+通過韌皮部轉(zhuǎn)移到低鹽脅迫根部。采用非損傷微測技術(shù)對棉花根部進(jìn)行檢測,發(fā)現(xiàn)不均勻鹽脅迫下棉花非鹽脅迫一側(cè)根部Na+外流增加[65],說明來源于高鹽脅迫根部的Na+向非鹽脅迫根部外排。通過添加Na+外排抑制劑阿米洛利和礬酸鈉后,發(fā)現(xiàn)Na+外排速度降低,說明不均勻鹽脅迫下Na+的外排可能是通過激活質(zhì)膜Na+/H+逆向轉(zhuǎn)運(yùn)蛋白實(shí)現(xiàn)的。

伴隨著葉片Na+含量的減少,不均勻鹽脅迫導(dǎo)致海馬齒、大洋洲濱藜、棉花等植物葉片K+含量增加[55-57,65]。0/800mmol/L NaCl處理45d,海馬齒葉片K+含量為均勻鹽脅迫處理的7倍[57]；50/150mmol/L NaCl處理棉花7d,其葉片的K+含量比均勻的100mmol/L NaCl增加了12%[65]。然而不均勻鹽脅迫并沒有導(dǎo)致紫花苜蓿葉片K+含量的增加[31]。不均勻鹽脅迫下棉花兩側(cè)根部K+含量不同[65],而不均勻鹽脅迫下大洋洲濱藜兩側(cè)根部的K+含量并沒有受到兩側(cè)不同的鹽分濃度的影響,表現(xiàn)為兩側(cè)根部K+濃度無顯著差異[55]。研究發(fā)現(xiàn)不均勻鹽脅迫下紫花苜蓿的莖生長速率與葉片K+濃度無顯著相關(guān)性,然而與兩側(cè)根部K+濃度均有顯著正相關(guān)關(guān)系,而且與高鹽脅迫根部K+濃度的相關(guān)性要高于與低鹽脅迫根系K+濃度的相關(guān)性,表明增加非鹽脅迫根部對K+吸收以及減少鹽脅迫根部K+的外流,特別是提高高鹽脅迫根部對K+的持留能力,對于不均勻鹽脅迫緩解高鹽脅迫對紫花苜蓿生長的抑制起非常重要的作用[31]。

5 展望

不均勻鹽脅迫下植物的生理機(jī)制研究取得了一定的進(jìn)展,但與均勻鹽脅迫下植物的生理機(jī)制研究相距甚遠(yuǎn)。目前對很多植物適應(yīng)不均勻鹽脅迫的機(jī)制還不清楚。開展植物對不均勻鹽脅迫的適應(yīng)機(jī)制研究是對植物耐鹽理論的重要補(bǔ)充,也是推動和加速耐鹽植物育種進(jìn)程的重要理論基礎(chǔ)。不均勻鹽脅迫處理更符合植物在鹽土中的實(shí)際生長狀況,在今后的研究中應(yīng)該得到重視。以下問題的解決希望能夠推動植物對不均勻鹽脅迫響應(yīng)機(jī)制的了解：

(1)比較不同物種或者同一物種耐鹽性差異大的不同品種對不均勻鹽脅迫的響應(yīng)機(jī)制。對耐鹽植物或耐鹽品種的篩選具有重要的理論意義；(2)目前關(guān)于植物對垂直方向不均勻鹽脅迫的響應(yīng)機(jī)制研究較少；(3)低鹽脅迫根部對水分的補(bǔ)償性吸收以及根的補(bǔ)償性生長會受高鹽脅迫根部鹽分濃度的影響,低鹽脅迫根部感知高鹽脅迫根部鹽脅迫程度大小的信號傳導(dǎo)機(jī)制也有待于深入研究；(4)不均勻鹽脅迫下植物根系形態(tài)及生理的可塑性研究；(5)植物適應(yīng)不均勻鹽脅迫的分子機(jī)制研究。

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Areviewofplantmorphologyandphysiologicalresponsetospatiallyheterogeneoussalinity

SUN Juanjuan1,ZHANG Yingjun2,*

1InstituteofGrasslandResearchofChineseAcademyofAgriculturalSciences,Hohhot010010,China2DepartmentofGrasslandScience,CollegeofAnimalScienceandTechnology,ChinaAgriculturalUniversity,Beijing100193,China

Salt is a major abiotic stressor in arid, semi-arid, and irrigated areas. The expansion of irrigated agriculture and the intensive use of water resources combined with high evaporation rates, leads to increasing salinity in soil and ground water. Soil salinity is rarely spatially uniform in field conditions. Numerous studies on plant physiological responses to salinity have been conducted using uniform conditions; however, only a few studies have investigated the physiology of plants grown in nonuniform root-zone salinity conditions. This paper summarizes domestic and international case studies of plant response to heterogeneous salinity. Mechanisms of plant growth under heterogeneous salinity were illustrated by plant shoot growth, root growth, water relations, photosynthesis, and ion regulation. Finally, research prospects for this domain are presented.

heterogeneous salinity; water uptake; ion regulation

國家牧草產(chǎn)業(yè)技術(shù)體系(CRAS- 35)；中央級公益性科研院所基本科研業(yè)務(wù)費(fèi)專項(xiàng)(1610332012003,1610332013003,1610332014007)

2017- 03- 20;

2017- 08- 30

*通訊作者Corresponding author.E-mail: zhangyj@cau.edu.cn

10.5846/stxb201703200472

孫娟娟,張英俊.植物對鹽分空間不均勻分布的形態(tài)和生理響應(yīng)研究進(jìn)展.生態(tài)學(xué)報(bào),2017,37(23):7791- 7798.

Sun J J,Zhang Y J.A review of plant morphology and physiological response to spatially heterogeneous salinity.Acta Ecologica Sinica,2017,37(23):7791- 7798.