土壤增溫對(duì)杉木幼苗細(xì)根生理生態(tài)性質(zhì)的影響

馮建新, 熊德成,史順增,許辰森,鐘波元,鄧 飛,陳云玉,陳光水,*,楊玉盛

1 福建師范大學(xué)地理科學(xué)學(xué)院, 福州 350007 2 福建師范大學(xué)濕潤(rùn)亞熱帶山地生態(tài)國(guó)家重點(diǎn)實(shí)驗(yàn)室培育基地, 福州 350007

土壤增溫對(duì)杉木幼苗細(xì)根生理生態(tài)性質(zhì)的影響

馮建新1,2, 熊德成1,2,史順增1,2,許辰森1,2,鐘波元1,2,鄧 飛1,2,陳云玉1,2,陳光水1,2,*,楊玉盛1，2

1 福建師范大學(xué)地理科學(xué)學(xué)院, 福州 350007 2 福建師范大學(xué)濕潤(rùn)亞熱帶山地生態(tài)國(guó)家重點(diǎn)實(shí)驗(yàn)室培育基地, 福州 350007

為了揭示我國(guó)最重要人工林樹(shù)種杉木對(duì)全球變暖的地下響應(yīng)及其適應(yīng)性,通過(guò)在福建省三明市陳大國(guó)有林場(chǎng)設(shè)置杉木(Cunninghamialanceolata)幼苗土壤增溫實(shí)驗(yàn)(增溫 +5 ℃和不增溫兩個(gè)處理,各5個(gè)重復(fù)),用土鉆法和內(nèi)生長(zhǎng)環(huán)法探討土壤增溫約1年后的杉木幼苗細(xì)根生物量和形態(tài)特征(比根長(zhǎng),SRL;比表面積,SRA),化學(xué)計(jì)量學(xué)特征(C、N、P)和代謝特征(包括呼吸和非結(jié)構(gòu)性碳水化合物,NSC)的變化。結(jié)果表明：1)與對(duì)照相比,土壤增溫處理0—1 mm細(xì)根生物量顯著下降,1—2 mm細(xì)根生物量沒(méi)有變化,細(xì)根形態(tài)亦未有顯著變化;2)土壤增溫處理細(xì)根N濃度顯著增加,細(xì)根P濃度沒(méi)有顯著變化,細(xì)根C/N顯著降低而N/P顯著增加;3)土壤增溫處理細(xì)根呼吸沒(méi)有出現(xiàn)馴化現(xiàn)象,細(xì)根NSC顯著下降?？梢?jiàn),土壤增溫改變了杉木細(xì)根生物量分配格局,并引起一定的營(yíng)養(yǎng)失衡和代謝失衡現(xiàn)象,從而對(duì)杉木生長(zhǎng)和生產(chǎn)力產(chǎn)生影響。

土壤增溫;細(xì)根;生物量;形態(tài);化學(xué)計(jì)量學(xué);呼吸;非結(jié)構(gòu)性碳水化合物

Effects of soil warming on the ecophysiological properties of the fine roots of

IPCC(2013)第五次報(bào)告指出,由于大氣溫室氣體上升引起的氣候變化導(dǎo)致最近130年(1880—2012)全球海陸表面平均溫度升高了0.85 ℃,預(yù)計(jì)2016—2035年全球地表平均溫度將上升0.3—0.7 ℃;到21世紀(jì)末將升高0.3—4.8 ℃[1]。溫度升高可能直接或間接影響森林生態(tài)系統(tǒng)的地上和地下生態(tài)過(guò)程[2]。雖然森林細(xì)根占根系總生物量的比例不足30%[3],但在森林生態(tài)系統(tǒng)養(yǎng)分循環(huán)和能量流動(dòng)中起到重要作用。而且,細(xì)根本身是植物養(yǎng)分、水分的吸收器官,因而細(xì)根生理生態(tài)性質(zhì)的變化與林木生長(zhǎng)和森林生產(chǎn)力緊密相關(guān)。相關(guān)的研究表明,細(xì)根生長(zhǎng)與土壤或者空氣溫度相關(guān)[4]。但至目前為止,關(guān)于溫度升高對(duì)地下部分尤其是對(duì)細(xì)根的生理生態(tài)性質(zhì)的研究還很缺乏。

植物細(xì)根對(duì)增溫的生理生態(tài)響應(yīng)可能體現(xiàn)在諸多方面,如細(xì)根生物量分配、細(xì)根形態(tài)(比根長(zhǎng),SRL;比表面積,SRA)、細(xì)根元素化學(xué)計(jì)量學(xué)(C、N、P)、細(xì)根代謝(呼吸;非結(jié)構(gòu)性碳水化合物,NSC)等,這些變化均體現(xiàn)了植物對(duì)全球變暖的適應(yīng)性。增溫可能會(huì)對(duì)細(xì)根生物量產(chǎn)生增加、減少或者無(wú)影響。例如在加拿大湯普森南部的黑云杉(Piceamariana)森林發(fā)現(xiàn)活細(xì)根(<2 mm)生物量在增溫樣地下降了24%—46%[5]。與對(duì)照地區(qū)相比,黃石國(guó)家公園增溫地區(qū)生長(zhǎng)的翦股穎(Agrostisscabra)和匍莖剪股穎(Agrostisstolonifera)細(xì)根生物量分別降低了8%、15%[6]。研究發(fā)現(xiàn)美國(guó)佛羅里達(dá)州蓋恩斯維爾地區(qū)橙樹(shù)幼苗細(xì)根生物量(<4 mm)和總細(xì)根生物量隨著溫度升高而略有增加[7]。細(xì)根SRL,SRA是根系生長(zhǎng)發(fā)育和反應(yīng)根功能情況的重要特征之一,但只有極少數(shù)的研究考慮到溫度對(duì)細(xì)根形態(tài)的影響[8]。增溫對(duì)細(xì)根元素化學(xué)計(jì)量學(xué)的影響主要集中在對(duì)細(xì)根C、N的影響上,而對(duì)細(xì)根P含量的影響較小。例如在美國(guó)馬薩諸塞州的落葉林中,土壤增溫雖然沒(méi)有顯著的改變細(xì)根C含量,但在增溫地區(qū)活細(xì)根N含量比對(duì)照地區(qū)高出10.5%[9]。目前細(xì)根呼吸對(duì)溫度的敏感性受到較大關(guān)注,如已有的研究證明根呼吸隨著溫度呈指數(shù)遞增[10-11]并且Q10值往往在1.8—3.0之間[12-13]。但根呼吸是否對(duì)溫度產(chǎn)生馴化仍是一個(gè)爭(zhēng)議的問(wèn)題,且增溫后根系呼吸的變化如何影響根系代謝平衡(如NSC的消耗)目前亦不清楚。

我國(guó)人工林面積占世界1/3,濕潤(rùn)亞熱帶是我國(guó)最重要的人工林基地。其中杉木林是最重要的人工林之一,占世界人工林面積的6%,在我國(guó)林業(yè)生產(chǎn)和森林碳匯中發(fā)揮著重要作用[14]。之前的增溫研究主要集中在高緯度溫帶地區(qū)[15- 17],但是更多的證據(jù)顯示熱帶亞熱帶森林對(duì)全球變暖的響應(yīng)更加敏感[18]。基于以上方面,本研究以杉木為研究對(duì)象,采用野外土壤增溫方式,探討增溫對(duì)杉木幼苗細(xì)根生理生態(tài)特性(包括細(xì)根生物量、形態(tài)(SRL、SRA)、化學(xué)計(jì)量學(xué)(C、N、P)、呼吸和NSC)的影響。這對(duì)預(yù)測(cè)全球變暖背景下我國(guó)濕潤(rùn)亞熱帶人工林生產(chǎn)力變化和人工林的適應(yīng)性管理具有重要作用。

1 試驗(yàn)地概況和研究方法

1.1 試驗(yàn)地概況

試驗(yàn)地位于福建三明森林生態(tài)系統(tǒng)與全球變化研究站陳大觀測(cè)點(diǎn),金絲灣森林公園陳大林業(yè)國(guó)有林場(chǎng)內(nèi)(26°19′N(xiāo),117°36′E)。平均海拔300 m,屬中亞熱帶季風(fēng)氣候,年均氣溫19.1 ℃,年平均降雨量1749 mm(主要集中在3—8月份),年均蒸發(fā)量1585 mm,相對(duì)濕度81%。

1.2 試驗(yàn)設(shè)計(jì)

試驗(yàn)采用完全隨機(jī)設(shè)計(jì),設(shè)置增溫(+5 ℃)、不增溫(對(duì)照)兩種處理,小區(qū)面積2 m×2 m,每個(gè)處理5個(gè)重復(fù)。試驗(yàn)小區(qū)四周采用4塊PVC板(200 cm×70 cm深)焊接而成,與周?chē)寥栏糸_(kāi),防止小區(qū)之間相互干擾。小區(qū)土壤取自附近的杉木林土壤,分層(0—10、10—20、20—70 cm)取回,剔除粗根、石塊和其他雜物后,土壤分層混合均勻,并按20—70、10—20和0—10 cm重填回2 m×2 m實(shí)驗(yàn)小區(qū)內(nèi),同時(shí)采用壓實(shí)法調(diào)整土壤容重與原位土壤容重接近。于2013年10月安裝加熱電纜(增溫和不增溫小區(qū)都布設(shè)相同電纜),平行布設(shè),深度為10 cm,間距20 cm,并在最外圍環(huán)繞一圈,保證樣地增溫的均勻性。2013年11月,每個(gè)2 m×2 m小區(qū)均勻種植4棵1年生2代半短側(cè)枝杉木幼苗,杉木位置均處于兩條電纜線(xiàn)之間。電纜布設(shè)完成后5個(gè)月(2014年3月)開(kāi)始通電增溫。2015年1月末(增溫后1年左右)對(duì)照(CK)和增溫(W)樣地土壤各理化性質(zhì)(0—20 cm)見(jiàn)表1。

表1 2015年1月末對(duì)照和增溫樣地土壤各理化性質(zhì)(0—20 cm)

1.3 細(xì)根生物量測(cè)定

2015年1月末(增溫后1年左右),采用土芯法在CK和W小區(qū)內(nèi)對(duì)根系進(jìn)行隨機(jī)取樣,每個(gè)小區(qū)取4個(gè)土鉆,土鉆直徑3.5 cm,取樣深度分0—10、10—20、20—40和40—60 cm。按照土層深度將杉木根挑出后立即帶回實(shí)驗(yàn)室清洗,剔除死根后按照0—1 mm和1—2 mm分徑級(jí)。分別裝入信封袋中放進(jìn)65 ℃烘箱中烘至恒重并稱(chēng)重。細(xì)根生物量是4個(gè)土層相加累計(jì)而得。

1.4 細(xì)根呼吸、形態(tài)、元素含量和NSC測(cè)定

1.4.1 根系取樣與處理

采用半徑為10 cm、高度為20 cm的內(nèi)生長(zhǎng)環(huán)在CK和W每個(gè)小區(qū)中心位置進(jìn)行取樣,每個(gè)小區(qū)取一個(gè)樣,并立即在野外把細(xì)根挑出,然后帶回實(shí)驗(yàn)室清洗干凈。根據(jù)細(xì)根的顏色、外形等區(qū)分出活死根,再按照0—1 mm和1—2 mm分出徑級(jí)。取少量的各徑級(jí)活根放入盛有生理緩沖液(10 mmol/L MES,1 mmol/L CaSO4)的燒杯中,然后進(jìn)行恒溫(18 ℃)水浴,以備細(xì)根呼吸測(cè)定之用;其他的活根用微波爐殺青3 min后裝入信封袋并放入烘箱中烘干至恒重。殺青烘干后的細(xì)根樣品用球磨儀進(jìn)行粉碎后待用。

1.4.2 細(xì)根呼吸測(cè)定

根系呼吸使用Oxytherm液相氧電極測(cè)定。將已經(jīng)水浴過(guò)的活根放入氧電極的反應(yīng)杯里,并吸取2 ml緩沖液倒入,當(dāng)呼吸反應(yīng)達(dá)到穩(wěn)定狀態(tài)后開(kāi)始測(cè)定氧消耗量,每個(gè)小區(qū)各徑級(jí)的活根測(cè)定3次。本試驗(yàn)測(cè)定的細(xì)根呼吸從分根到測(cè)定完成在2 h內(nèi)。

1.4.3 細(xì)根形態(tài)測(cè)定

呼吸樣品測(cè)定完后用數(shù)字化掃描儀Espon scanner 對(duì)根進(jìn)行掃描,掃描完成后放入65 ℃烘箱中烘干并稱(chēng)重。而掃描后的根系圖像運(yùn)用 Win-RHIZO(Pro 2009b)根系圖像分析軟件進(jìn)行形態(tài)特征分析。

1.4.4 細(xì)根元素含量與非結(jié)構(gòu)性碳測(cè)定

細(xì)根的C、N使用VarioEL III元素分析儀進(jìn)行測(cè)定。稱(chēng)取粉碎的樣品8—10 mg進(jìn)行包樣,把包好的樣品放入進(jìn)樣盤(pán)進(jìn)行測(cè)定。每個(gè)處理各徑級(jí)測(cè)定3次。

細(xì)根P的測(cè)定方法：精確稱(chēng)取0.25 mg(±0.0001 g)細(xì)根樣品,加入4 mL硫酸和1 mL高氯酸搖勻,靜置1d后消煮3 h,冷卻后定容至100 mL。取上清液應(yīng)用流動(dòng)分析儀進(jìn)行測(cè)定。

細(xì)根NSC的測(cè)定：包括可溶性糖和淀粉使用改進(jìn)后的酚-硫酸法[19-20]。

1.5 數(shù)據(jù)分析

采用雙因素ANOVA檢驗(yàn)處理、徑級(jí)以及其交互作用對(duì)細(xì)根生物量、SRL、SRA、C、N、P、C/N、N/P、比呼吸速率(SRR)、可溶性糖、淀粉及NSC的影響。同一徑級(jí)不同處理之間、同一處理不同徑級(jí)之間細(xì)根生物量、SRL、SRA、C、N、P、C/N、N/P、SRR、可溶性糖、淀粉及NSC的差異采用獨(dú)立樣本t檢驗(yàn)。所有的統(tǒng)計(jì)分析均在SPSS 19.0軟件上進(jìn)行,顯著性水平設(shè)定為P=0.05。

2 結(jié)果

2.1 細(xì)根生物量和形態(tài)

處理、徑級(jí)以及兩者之間的交互作用對(duì)細(xì)根生物量(0—60 cm)的影響達(dá)到顯著水平(P<0.05),其中處理對(duì)細(xì)根生物量的影響達(dá)到極顯著水平(P<0.01)(表2)。土壤增溫后0—1 mm的細(xì)根生物量顯著降低(P<0.05);1—2 mm的細(xì)根生物量差異不顯著(P>0.05)(圖1)。同一處理,與0—1 mm相比,CK的1—2 mm的細(xì)根生物量顯著降低(P<0.05),而W的1—2 mm的細(xì)根生物量差異不顯著(P>0.05)(圖1)。處理以及處理與徑級(jí)之間的交互作用對(duì)細(xì)根SRL、SRA(0—20 cm)沒(méi)有影響(P>0.05),而徑級(jí)對(duì)細(xì)根SRA的影響達(dá)到顯著水平(P<0.05),對(duì)細(xì)根SRL沒(méi)有影響(P>0.05)(表2)。W與CK間各徑級(jí)細(xì)根SRL、SRA的差異均不顯著(P>0.05)。與0—1 mm相比,CK和W的1—2 mm的細(xì)根SRL顯著降低(P<0.05)(圖2A),而細(xì)根SRA的差異不顯著(P>0.05)(圖2B)。

表2 處理、徑級(jí)及其交互作用對(duì)細(xì)根生理生態(tài)各指標(biāo)影響的雙因素方差分析表

圖1 不同處理各徑級(jí)的細(xì)根生物量 Fig.1 Fine root biomass of different diameter class under different treatmentsCK,對(duì)照 control;W,增溫 warming.不同大寫(xiě)字母表示同一徑級(jí)不同處理差異顯著,不同小寫(xiě)字母表示同一處理不同徑級(jí)差異顯著;圖中數(shù)據(jù)為平均值±標(biāo)準(zhǔn)差

圖2 不同處理各徑級(jí)的細(xì)根比根長(zhǎng)與比表面積Fig.2 Fine root specific root length and specific root surface area of different diameter class under different treatments不同大寫(xiě)字母表示同一徑級(jí)不同處理差異顯著,不同小寫(xiě)字母表示同一處理不同徑級(jí)差異顯著;圖中數(shù)據(jù)為平均值±標(biāo)準(zhǔn)差

圖3 不同處理各徑級(jí)的細(xì)根C濃度、N濃度、P濃度和C/N、N/PFig.3 Concentrations of C,N,P and ratios of C/N,N/P of different diameter class of fine roots under different treatments不同大寫(xiě)字母表示同一徑級(jí)不同處理差異顯著,不同小寫(xiě)字母表示同一處理不同徑級(jí)差異顯著;圖中數(shù)據(jù)為平均值±標(biāo)準(zhǔn)差

2.2 細(xì)根元素化學(xué)計(jì)量學(xué)(C、N、P、C/N、N/P)

處理對(duì)細(xì)根N、C、C/N、N/P的影響達(dá)到極顯著水平(P<0.01),對(duì)細(xì)根P沒(méi)有影響(P>0.05);徑級(jí)對(duì)細(xì)根C的影響達(dá)到極顯著水平(P<0.01),對(duì)細(xì)根N的影響達(dá)到顯著水平(P<0.05),對(duì)細(xì)根P、C/N、N/P沒(méi)有影響(P>0.05);處理與徑級(jí)的交互作用對(duì)細(xì)根N、C的影響達(dá)到極顯著水平(P<0.01),對(duì)細(xì)根C/N的影響達(dá)到顯著水平(P<0.05),對(duì)細(xì)根P、N/P沒(méi)有影響(P>0.05)(表2)。與CK相比,W處理各徑級(jí)細(xì)根N、N/P均顯著增加(P<0.05)(圖3),細(xì)根C/N顯著降低(P<0.05)(圖3),而在0—1 mm細(xì)根C顯著降低(P<0.05)(圖3)、細(xì)根P差異不顯著(P>0.05)(圖3),在1—2 mm細(xì)根C、P差異不顯著(P>0.05)(圖3)。與0—1 mm相比,CK的1—2 mm的細(xì)根N、C、P均顯著降低(P<0.05)(圖3),細(xì)根C/N顯著升高(P<0.05)(圖3),細(xì)根N/P差異不顯著(P>0.05)(圖3);W的1—2 mm的細(xì)根N、C、P、C/N、N/P差異均不顯著(P>0.05)(圖3)。

2.3 細(xì)根代謝特征

處理以及處理與徑級(jí)間的交互作用對(duì)細(xì)根SRR沒(méi)有影響(P>0.05),徑級(jí)對(duì)細(xì)根SRR的影響達(dá)到極顯著水平(P<0.01)(表2)。與CK相比,土壤增溫后各徑級(jí)細(xì)根SRR差異均不顯著(P>0.05)(圖4)。與0—1 mm相比,CK和W的1—2 mm的細(xì)根SRR差異不顯著(P>0.05)(圖4)。處理對(duì)可溶性糖和NSC的影響達(dá)到極顯著水平(P<0.01),對(duì)淀粉的影響達(dá)到顯著水平(P<0.05),徑級(jí)以及處理與徑級(jí)間的交互作用對(duì)可溶性糖、淀粉和NSC沒(méi)有影響(P>0.05)(表2)。與CK相比,土壤增溫后各徑級(jí)細(xì)根淀粉和NSC均顯著降低(P<0.05)(圖4),而細(xì)根可溶性糖在0—1 mm差異不顯著(P>0.05),在1—2 mm顯著降低(P<0.05)(圖4)。與0—1 mm相比,CK和W的1—2 mm的可溶性糖、淀粉和NSC差異均不顯著(P>0.05)(圖4)。

圖4 不同處理各徑級(jí)的細(xì)根比呼吸速率、可溶性糖、淀粉和非結(jié)構(gòu)性碳水化合物Fig.4 Fine root specific respiration rate,soluble sugar,starch and nonstructural carbohydrate of different diameter class under different treatments不同大寫(xiě)字母表示同一徑級(jí)不同處理差異顯著,不同小寫(xiě)字母表示同一處理不同徑級(jí)差異顯著;圖中數(shù)據(jù)為平均值±標(biāo)準(zhǔn)差

3 討論

3.1 土壤增溫對(duì)細(xì)根生物量和形態(tài)的影響

本研究結(jié)果顯示,土壤增溫后,0—1 mm細(xì)根生物量(0—60 cm)顯著降低,這與許多研究報(bào)道相一致[21- 24]。例如Wan等[25]發(fā)現(xiàn)與對(duì)照相比,增溫樣地紅楓(Acerrubrum)和糖楓(Acersaccharum)細(xì)根生物量顯著降低。造成土壤增溫細(xì)根生物量下降的原因一方面是土壤增溫后,土壤變得干旱,影響了植物光合作用和生長(zhǎng),導(dǎo)致地上和地下生物量的減少[26-27]。另一方面是增溫促進(jìn)土壤氮有效性增加[15, 28],導(dǎo)致細(xì)根特別是0—1 mm細(xì)根分配(投入)的相對(duì)降低。本試驗(yàn)中,土壤增溫后,0—1 mm細(xì)根生物量顯著降低,而1—2 mm細(xì)根生物量卻沒(méi)有變化。一種原因是0—1 mm細(xì)根是養(yǎng)分吸收的主要器官,土壤增溫后養(yǎng)分有效性增加引起吸收根的降低;而1—2 mm細(xì)根主要是結(jié)構(gòu)根,養(yǎng)分有效性增加可能對(duì)結(jié)構(gòu)根的影響較小。另一種原因可能是增溫引起直徑較小的細(xì)根分解死亡更快[29],也相對(duì)更容易成為食物或者被分解[30]。

本研究結(jié)果還表明,土壤增溫對(duì)細(xì)根形態(tài)(SRL、SRA)(0—20 cm)沒(méi)有影響。Alvarez-uria等[31]研究表明土壤增溫對(duì)瑞士的綠赤楊(Alnusviridis)、普通赤楊(Alnusglutinosa)、挪威云杉(Piceaabies)、樟子松(Pinussylvestris)、瑞士石松(Pinuscembra)、垂枝樺(Betulapendula)6個(gè)物種細(xì)根SRL沒(méi)有影響,Equiza等[32]研究指出土壤—空氣增溫對(duì)春季小麥細(xì)根SRA沒(méi)有作用,這與本研究結(jié)果相一致。造成這種結(jié)果的原因可能是根系對(duì)養(yǎng)分有效性的響應(yīng)更多地通過(guò)細(xì)根生物量特別是0—1 mm細(xì)根的調(diào)整(即分配的調(diào)整),而細(xì)根形態(tài)上的調(diào)整相對(duì)很小[33]。

3.2 土壤增溫對(duì)細(xì)根化學(xué)計(jì)量學(xué)特征的影響

本試驗(yàn)發(fā)現(xiàn)土壤增溫顯著的增加了細(xì)根N濃度,顯著的降低了C/N比率,而對(duì)1—2 mm細(xì)根C濃度沒(méi)有影響,這個(gè)結(jié)果與Zhou等[9]研究結(jié)果一致。Zogg[34]、 Bassirirad[35]和Wan[25]等人研究發(fā)現(xiàn)土壤增溫增加了細(xì)根N濃度是因?yàn)樵诟叩臏囟认录?xì)根活性更強(qiáng),土壤N有效性增加,導(dǎo)致活細(xì)根吸收N濃度增加。土壤增溫后0—1 mm細(xì)根C濃度下降,而1—2 mm細(xì)根C濃度卻沒(méi)發(fā)生變化,可能是因?yàn)?—1 mm細(xì)根主要是吸收根,土壤增溫增加了土壤N有效性,導(dǎo)致土壤C向0—1 mm細(xì)根分配的比例相對(duì)減少,而1—2 mm細(xì)根主要是結(jié)構(gòu)根,土壤增溫雖然增加了土壤N有效性,但細(xì)根吸收N濃度只是積累于細(xì)根中而不參與代謝,導(dǎo)致土壤C向1—2 mm細(xì)根分配的比例并未變化。土壤增溫細(xì)根C/N比率顯著降低是因?yàn)榧?xì)根吸收N顯著增加而吸收C顯著降低或沒(méi)有變化。本試驗(yàn)還發(fā)現(xiàn)土壤增溫對(duì)細(xì)根P濃度沒(méi)有影響,這可能是因?yàn)橥寥繮是很容易被固定的元素,特別是亞熱帶土壤P極易被固定,P有效性極低,即使是土壤增溫也未能明顯促進(jìn)土壤P的礦化速率,導(dǎo)致根系對(duì)P的吸收并未明顯變化。但土壤增溫后細(xì)根N濃度的升高導(dǎo)致N/P比率顯著升高表明了土壤增溫可能導(dǎo)致?tīng)I(yíng)養(yǎng)元素失衡,特別是受P營(yíng)養(yǎng)的限制可能更為強(qiáng)烈[36]。

3.3 土壤增溫對(duì)細(xì)根代謝特征的影響

本試驗(yàn)發(fā)現(xiàn)在18 ℃參考溫度下測(cè)得CK與W兩個(gè)處理的SRR沒(méi)有變化,說(shuō)明土壤增溫后細(xì)根呼吸還沒(méi)有出現(xiàn)馴化現(xiàn)象,即在增溫條件下W處理的細(xì)根呼吸應(yīng)更高于CK。Burton等[37]研究表明,在6 ℃和18 ℃參照溫度下對(duì)密歇根州90a的糖槭(sugarmaple)進(jìn)行細(xì)根呼吸測(cè)定,發(fā)現(xiàn)土壤溫度的季節(jié)性變化沒(méi)有對(duì)細(xì)根呼吸產(chǎn)生溫度馴化,這與本試驗(yàn)的結(jié)果類(lèi)似。造成土壤增溫后細(xì)根呼吸未出現(xiàn)馴化的原因可能有以下原因：1)試驗(yàn)樣地增溫才1a,增溫時(shí)間跨度還不大;2)增溫樣地的溫度未能達(dá)到細(xì)根呼吸馴化的閥值[37]。但也有一些研究發(fā)現(xiàn)細(xì)根呼吸會(huì)產(chǎn)生部分溫度馴化,馴化受到底物限制和腺苷酸控制的影響[38]。多數(shù)研究發(fā)現(xiàn)植物組織N濃度與呼吸速率往往存在強(qiáng)烈的正相關(guān)性[39-40],而本試驗(yàn)發(fā)現(xiàn)在18 ℃參照溫度下,W細(xì)根的N濃度顯著高于CK,但W和CK處理細(xì)根呼吸沒(méi)有差異。這可能是因?yàn)橥寥繬濃度超出了杉木幼苗所需的N濃度,超出的部分N濃度不參與N的吸收和同化而只是積累于細(xì)根中。

本試驗(yàn)結(jié)果顯示土壤增溫后,細(xì)根NSC顯著下降。Karst等[41]研究表明加拿大阿爾伯塔省羅奇波爾附近的處于生長(zhǎng)期的黑云杉和黑松(Pinuscontorta)幼苗隨著土壤溫度降低根系NSC濃度升高,這與本試驗(yàn)結(jié)果類(lèi)似。同時(shí),本試驗(yàn)發(fā)現(xiàn)對(duì)照試驗(yàn)中可溶性糖、淀粉分別占NSC的31.25%、68.75%,增溫試驗(yàn)中可溶性糖、淀粉分別占NSC的36.81%、63.19%,說(shuō)明增溫促使貯存的淀粉更多的相對(duì)比例轉(zhuǎn)化為可溶性糖,這亦表明了增溫后細(xì)根對(duì)NSC消耗增加,更多地動(dòng)用了NSC貯存。造成這種結(jié)果可能是因?yàn)橐韵聨讉€(gè)原因：1)土壤增溫,土壤變得干旱,降低了植物的光合速率,致使淀粉和可溶性碳向細(xì)根的運(yùn)輸減少;2)W處理的細(xì)根呼吸沒(méi)有發(fā)生馴化,所以導(dǎo)致NSC加速消耗。這表明增溫后導(dǎo)致了細(xì)根出現(xiàn)一定的代謝失衡現(xiàn)象,這有可能引起根系功能障礙,并引起細(xì)根死亡增加,壽命縮短(未刊資料),從而對(duì)杉木的養(yǎng)分、水分吸收和杉木生長(zhǎng)產(chǎn)生影響。

4 結(jié)論

本試驗(yàn)可以發(fā)現(xiàn)：1)土壤增溫后0—1 mm細(xì)根生物量顯著下降,1—2 mm細(xì)根生物量沒(méi)有變化,細(xì)根形態(tài)也沒(méi)有發(fā)生變化,說(shuō)明了根系對(duì)養(yǎng)分有效性的響應(yīng)更多地通過(guò)細(xì)根生物量特別是0—1 mm細(xì)根的調(diào)整,而細(xì)根形態(tài)上的調(diào)整相對(duì)較少;2)土壤增溫后細(xì)根N濃度和N/P顯著增加,細(xì)根C/N顯著降低,0—1 mm細(xì)根C濃度顯著降低,而1—2 mm細(xì)根C濃度沒(méi)有變化,細(xì)根P濃度也沒(méi)有變化,表明土壤增溫后細(xì)根營(yíng)養(yǎng)元素失衡,對(duì)N/P的分析說(shuō)明了增溫樣地杉木幼苗更易受到P素的限制;3)土壤增溫后細(xì)根呼吸沒(méi)有出現(xiàn)馴化現(xiàn)象,細(xì)根NSC顯著下降,表明增溫后細(xì)根出現(xiàn)一定的代謝失衡現(xiàn)象,并引起細(xì)根死亡增加,壽命縮短,從而對(duì)杉木的養(yǎng)分、水分吸收和杉木生長(zhǎng)產(chǎn)生影響。

[1] IPCC.Climate change 2013:The physical science basis.Contribution of Working Group I to the Fifth Assessment Report of the Intergovernment Panel on Climate Change.Cambridge:Cambridge University Press.2013.

[2] Way D A, Oren R. Differential responses to changes in growth temperature between trees from different functional groups and biomes: a review and synthesis of data. Tree physiology, 2010, 30(6):669- 688.

[3] Vogt K A, Grier C C, Vogt D J. Production, turnover, and nutrient dynamics of above-and belowground detritus of world forests. Advances in ecological research, 1986, 15: 303- 377.

[4] Tierney G L, Fahey T J, Groffman P M, Hardy J P, Fitzhugh R D, Driscoll C T, Yavitt J B. Environmental control of fine root dynamics in a northern hardwood forest. Global Change Biology, 2003, 9(5): 670- 679.

[5] Bronson D R, Gower S T, Tanner M, Linder S, Van Herk I. Response of soil surface CO2flux in a boreal forest to ecosystem warming. Global Change Biology, 2008, 14(4): 856- 867.

[6] Lyons E M, Pote J, DaCosta M, Huang B R. Whole-plant carbon relations and root respiration associated with root tolerance to high soil temperature forAgrostisgrasses. Environmental and Experimental Botany, 2007, 59(3): 307- 313.

[7] Allen L H, Vu J C V. Carbon dioxide and high temperature effects on growth of young orange trees in a humid, subtropical environment. Agricultural and Forest Meteorology, 2009, 149(5): 820- 830.

[8] Pregitzer K S, King J S, Burton A J, Brown S E. Responses of tree fine roots to temperature. New Phytologist, 2000, 147(1): 105- 115.

[9] Zhou Y M, Tang J W, Melillo J M, Butler S, Mohan J E. Root standing crop and chemistry after six years of soil warming in a temperate forest. Tree Physiology, 2011, 31(7): 707- 717.

[10] Atkin O K, Edwards E J, Loveys B R. Response of root respiration to changes in temperature and its relevance to global warming. New Phytologist, 2000, 147(1): 141- 154.

[11] Apostol K G, Jacobs D F, Wilson B C, Salifu K F, Dumroese R K. Growth, gas exchange, and root respiration of Quercus rubra seedlings exposed to low root zone temperatures in solution culture. Forest ecology and management, 2007, 253(1/3): 89- 96.

[12] Burton A J, Pregitzer K S, Ruess R W, Hendrick R L, Allen M F. Root respiration in North American forests: effects of nitrogen concentration and temperature across biomes. Oecologia, 2002, 131(4): 559- 568.

[13] Piao S L, Luyssaert S, Ciais P, Janssens I A, Chen A P, Cao C, Fang J Y, Friedlingstein P, Luo Y Q, Wang S P. Forest annual carbon cost: a global-scale analysis of autotrophic respiration. Ecology, 2010, 91(3): 652- 661.

[14] Chen G S, Yang Z J, Gao R, Xie J S, Guo J F, Huang Z Q, Yang Y S. Carbon storage in a chronosequence of Chinese fir plantations in southern China. Forest Ecology and Management, 2013, 300: 68- 76.

[15] Melillo J M, Steudler P A, Aber J D, Newkirk K, Lux H, Bowles F P, Catricala C, Magill A, Ahrens T, Morrisseau S. Soil warming and carbon-cycle feedbacks to the climate system. Science, 2002, 298(5601): 2173- 2176.

[16] Schindlbacher A, Zechmeister-boltenstern S, Jandl R. Carbon losses due to soil warming: do autotrophic and heterotrophic soil respiration respond equally? Global Change Biology, 2009, 15(4): 901- 913.

[17] Li D J, Zhou X H, Wu L Y, Zhou J Z, Luo Y Q. Contrasting responses of heterotrophic and autotrophic respiration to experimental warming in a winter annual-dominated prairie. Global change biology, 2013, 19(11): 3553- 3564.

[18] Clark D A, Piper S C, Keeling C D, Clark D B. Tropical rain forest tree growth and atmospheric carbon dynamics linked to interannual temperature variation during 1984—2000. Proceedings of the National Academy of Sciences of the United States of America, 2003, 100(10): 5852- 5857.

[19] Buysse J, Merckx R. An improved colorimetric method to quantify sugar content of plant tissue. Journal of Experimental Botany, 1993, 44(10): 1627- 1629.

[20] 于麗敏, 王傳寬, 王興昌. 三種溫帶樹(shù)種非結(jié)構(gòu)性碳水化合物的分配. 植物生態(tài)學(xué)報(bào), 2011, 35(12): 1245- 1255.

[21] Bassow S J, McConnaughay K D M, Bazzaz F A. The Response of Temperate Tree Seedlings Grown in Elevated CO2to Extreme Temperature Events. Ecological applications, 1994,4(3): 593- 603.

[22] Soussana J F, Casella E, Loiseau P. Long-term effects of CO2enrichment and temperature increase on a temperate grass sward. Plant and soil, 1996, 182(1): 101- 114.

[23] Forbes P J, Black K E, Hooker J E. Temperature-induced alteration to root longevity in Lolium perenne. Plant and Soil, 1997, 190(1): 87- 90.

[24] Kandeler E, Tscherko D, Bardgett R D, Hobbs P J, Kampichler C, Jones T H. The response of soil microorganisms and roots to elevated CO2and temperature in a terrestrial model ecosystem. Plant and Soil, 1998, 202(2): 251- 262.

[25] Wan S Q, Norby R J, Pregitzer K S, Ledford J, O′N(xiāo)eill E G. CO2enrichment and warming of the atmosphere enhance both productivity and mortality of maple tree fine roots. New Phytologist, 2004, 162(2): 437- 446.

[26] Hendrick R L, Pregitzer K S. Patterns of fine root mortality in two sugar maple forests. Nature, 1993, 361(6407).

[27] Norby R J, Long T M, Hartz-Rubin J S, O′neill E G. Nitrogen resorption in senescing tree leaves in a warmer, CO2-enriched atmosephere. Plant and Soil, 2000, 224(1): 15- 29.

[28] Rustad L E J L, Campbell J, Marion G, Norby R, Mitchell M, Hartley A, Cornelissen J, Gurevitch J, GCTE-NEWS. A meta-analysis of the response of soil respiration, net nitrogen mineralization, and aboveground plant growth to experimental ecosystem warming. Oecologia, 2001, 126(4): 543- 562.

[29] Baddeley J A, Watson C A. Influences of root diameter, tree age, soil depth and season on fine root survivorship inPrunusavium. Plant and Soil, 2005, 276(1- 2): 15- 22.

[30] Lin C F, Yang Y S, Guo J F, Chen G S, Xie J S. Fine root decomposition of evergreen broadleaved and coniferous tree species in mid-subtropical China: dynamics of dry mass, nutrient and organic fractions. Plant and soil, 2011, 338(1/2): 311- 327.

[31] Alvarez-Uria P, K?rner C. Low temperature limits of root growth in deciduous and evergreen temperate tree species. Functional Ecology, 2007, 21(2): 211- 218.

[32] Equiza M A, Tognetti J A. Morphological plasticity of spring and winter wheats in response to changing temperatures. Functional Plant Biology, 2002, 29(12): 1427- 1436.

[33] Poorter H, Ryser P. The limits to leaf and root plasticity: what is so special about specific root length? New Phytologist, 2015, 206(4): 1188- 1190.

[34] Zogg G P, Zak D R, Burton A J, Pregitzer K S. Fine root respiration in northern hardwood forests in relation to temperature and nitrogen availability. Tree Physiology, 1996, 16(8): 719- 725.

[35] Bassirirad H. Kinetics of Nutrient Uptake by Roots: Responses to Global Change. New Phytologist, 2000, 147(1):155- 169.

[36] Li Y, Niu S L, Yu G R. Aggravated phosphorus limitation on biomass production under increasing nitrogen loading: a meta-analysis. Global Change Biology, 2016, 22(2):934- 943.

[37] Burton A J, Pregitzer K S. Field measurements of root respiration indicate little to no seasonal temperature acclimation for sugar maple and red pine. Tree physiology, 2003, 23(4): 273- 280.

[38] Atkin O K, Tjoelker M G. Thermal acclimation and the dynamic response of plant respiration to temperature. Trends in plant science, 2003, 8(7): 343- 351.

[39] Burton A J, Jarvey J C, Jarvi M P, Zak D R, Pregitzer K S. Chronic N deposition alters root respiration-tissue N relationship in northern hardwood forests. Global Change Biology, 2012, 18(1): 258- 266.

[40] Reich P B, Tjoelker M G, Pregitzer K S, Wright I J, Oleksyn J, Machado J L. Scaling of respiration to nitrogen in leaves, stems and roots of higher land plants. Ecology letters, 2008, 11(8): 793- 801.

[41] Karst J, Landh?usser S M. Low soil temperatures increase carbon reserves inPiceamarianaandPinuscontorta. Annals of Forest Science, 2014, 71(3): 371- 380.

Chinese fir (Cunninghamialanceolata) seedlings

FENG Jianxin1,2, XIONG Decheng1,2, SHI Shunzeng1,2, XU Chensen1,2, ZHONG Boyuan1,2, DENG Fei1,2, CHEN Yunyu1,2, CHEN Gunagshui1,2,*, YANG Yusheng1,2

1CollegeofGeographicalScience,FujianNormalUniversity,Fuzhou350007,China2StateKeyLaboratoryofSubtropicalMountainEcology(FoundedbyMinistryofScienceandTechnologyandFujianProvince),FujianNormalUniversity,Fuzhou350007,China

Global warming is expected to have profound effects on plant growth. The effects of global climate change on the aboveground parts of plants have been reported in many studies in the past decades. However, limited information regarding how warming affects belowground ecological processes, especially root dynamics, has restricted our ability to predict how roots will respond to increasing temperatures. Changes in ecophysiological properties of fine roots under climate change may play an important part in the growth performance of tree plantations. The aim of the present study was to explore the belowground responses and adaptability of the most important timber species in southern China, the Chinese fir (Cunninghamialanceolata) to global warming. A field soil cable warming experiment was conducted in Chenda State-Own Forest Farm, Sanming, Fujian Province. The experiment included two treatments: soil warming (+5℃) and no-warming (control), and each treatment had 5 replicate plots. We measured changes in fine root biomass, morphology (specific root length and specific root surface area), stoichiometry (C, N, P) and metabolisme (including root respiration and nonstructural carbohydrates (NSCs) ) after approximately one year of soil warming using soil coring and ingrowth core methods. Soil core diameters were 3.5 cm and were divided into 0—10, 10—20, 20—40, and 40—60 cm. Ingrowth core diameters were 20 cm and were divided into 0—10 and 10—20 cm. A two-way ANOVA showed that treatment × diameter class significantly effected the fine root biomass, C and N concentrations, and C/N ratio, whereas it had no effect on the fine root morphology, P concentration, C/P ratio, and metabolism. The one-way ANOVA showed that (1) campared with the control plots, the 0—1 mm fine root biomass increased significantly, whereas the 1—2 mm fine root biomass and fine root morphology did not change in warmed soil plots. These findings indicated that the root system adjusted the fine root biomass, especially the 0—1 mm whereas the fine root morphology responded to nutrient availability; (2) the fine root N concentration increased significantly, but the fine root P concentration showed no change; the fine root C/N decreased significantly, whereas the fine root N/P had increased significantly in warmed soil plots. Collectively, these findings demonstrated that soil warming caused nutritional imbalances, and the growth of Chinese fir seedlings was limited by P avalibility by analyzing the N/P ratio; (3) the fine root respiration did not acclimate to soil warming and the fine root NSCs decreased significantly in warmed soil plots. Soil warming caused a metabolic imbalance, which increased the fine root mortality and shortened the fine root lifespan; thus, could have an effect on nutrient and moisture absorption of the Chinese fir. It can be concluded that soil warming changed the fine root biomass allocation and caused nutritional and metabolic imbalances, which could play important roles in the growth of Chinese fir under global warming.

soil warming;fine roots;biomass;morphology;stoichiometry;respiration;nonstructural carbohydrates

國(guó)家自然科學(xué)基金優(yōu)秀青年基金項(xiàng)目(31422012); 國(guó)家973前期專(zhuān)項(xiàng)課題(2014CB460602); 福建省杰出青年基金項(xiàng)目滾動(dòng)資助項(xiàng)目(2014J07005)

2016- 03- 26;

2016- 07- 11

10.5846/stxb201603260543

*通訊作者Corresponding author.E-mail: gshuichen@163.com

馮建新, 熊德成,史順增,許辰森,鐘波元,鄧飛,陳云玉,陳光水,楊玉盛.土壤增溫對(duì)杉木幼苗細(xì)根生理生態(tài)性質(zhì)的影響.生態(tài)學(xué)報(bào),2017,37(1):35- 43.

Feng J X, Xiong D C, Shi S Z, Xu C S, Zhong B Y, Deng F, Chen Y Y, Chen G S， Yang Y S.Effects of soil warming on the ecophysiological properties of the fine roots of Chinese fir (Cunninghamialanceolata) seedlings.Acta Ecologica Sinica,2017,37(1):35- 43.