景航,劉國彬,?,王國梁,,薛萐,,姚旭,梁楚濤

(1.西北農(nóng)林科技大學(xué)水土保持研究所,712100,陜西楊凌;2.中國科學(xué)院水土保持與生態(tài)環(huán)境研究中心,712100,陜西楊凌)

恢復(fù)措施對皆伐油松林團聚體活性有機碳含量的影響
——以黃土丘陵區(qū)松峪溝流域為例

景航1,劉國彬1,2?,王國梁1,2,薛萐1,2,姚旭1,梁楚濤2

(1.西北農(nóng)林科技大學(xué)水土保持研究所,712100,陜西楊凌;2.中國科學(xué)院水土保持與生態(tài)環(huán)境研究中心,712100,陜西楊凌)

團聚體中的活性有機碳對土壤質(zhì)量改善以及碳庫動態(tài)平衡具有重要意義。為了研究皆伐后土壤團聚體活性有機碳的分布狀況,本實驗選取黃土高原典型油松林為對象,以未皆伐人工油松林為對照,采用高錳酸鉀氧化法研究皆伐后不同恢復(fù)植被群落(幼林、撂荒、灌木)地表0～20 cm層土壤團聚體中活性有機碳變化特征。結(jié)果表明: 1)研究區(qū)土壤以大團聚體(＞250 μm)為主,自然恢復(fù)的灌木地以及撂荒地大團聚體質(zhì)量分數(shù)顯著增加(P＜0.05)。2)有機碳質(zhì)量分數(shù)隨團聚體粒徑的增大而增加,大團聚體是有機碳積累的主要場所,并且自然恢復(fù)的灌木地團聚體有機碳質(zhì)量分數(shù)最高。3)研究區(qū)油松林團聚體低活性有機碳質(zhì)量分數(shù)＞中活性有機碳質(zhì)量分數(shù)＞高活性有機碳質(zhì)量分數(shù),大團聚體活性有機碳質(zhì)量分數(shù)大于微團聚體。研究表明,皆伐會造成團聚體有機碳趨于活化,其中自然恢復(fù)的灌木地活性有機碳質(zhì)量分數(shù)顯著增加。本研究還進一步發(fā)現(xiàn)大團聚體中的高活性有機碳能更好地預(yù)測土壤碳庫變化。

土壤團聚體;活性有機碳;油松人工林;皆伐;土壤有機碳

團聚體是土壤結(jié)構(gòu)的重要組成部分[1],是評價土壤質(zhì)量的一個重要指標[2]。有機碳能黏合礦物顆粒形成穩(wěn)定的土壤團聚結(jié)構(gòu),是團聚體形成過程中的主要膠結(jié)物質(zhì)[3]。團聚體和有機碳是土壤肥力的基礎(chǔ),二者之間關(guān)系密切[4]。目前關(guān)于團聚體有機碳的研究報道已有很多。陳建國等[5]研究指出土壤的固碳過程伴隨著團聚體的形成、穩(wěn)定和周轉(zhuǎn),而有機碳中的活性組分在這個過程中最為活躍。W.Logninow等[6]根據(jù)土壤有機碳被濃度為333、167和33 mmol/L的高錳酸鉀氧化的數(shù)量將活性有機碳分為高、中和低3個活性級別。雖然活性有機碳只占土壤有機碳很少的一部分,但是它在土壤碳庫源、匯的狀態(tài)轉(zhuǎn)換及反映和預(yù)測土壤質(zhì)量變化方面具有重要意義[7]。以往研究主要針對全土活性碳變化進行分析[8],而團聚體中的活性有機碳由于其特殊的結(jié)構(gòu)以及團聚體的保護作用可能會對土壤的碳匯功能產(chǎn)生深刻影響[9];因此開展團聚體及其活性有機碳的研究是揭示土壤碳庫動態(tài)變化的重要途徑[10]。

森林生態(tài)系統(tǒng)是全球碳循環(huán)的重要組成部分,全球土壤有機碳庫的70%～73%是森林土壤有機碳[11]。森林土壤碳庫的微弱變化都會導(dǎo)致大氣CO2的顯著變化[12]。研究森林土壤團聚體和活性有機碳可以揭示森林土壤碳庫動態(tài)過程,為探索全球碳循環(huán)提供參考[10]。當(dāng)前森林土壤活性有機碳研究中,存在的問題主要是影響因子和變化過程不清楚,這也是不能預(yù)測氣候變化的主要原因[13]。已有的研究表明,森林皆伐后土壤有機碳變化各異[14],并且皆伐后恢復(fù)的不同植被群落對土壤有機碳組分和團聚體含量的影響目前還不清楚;因此探索皆伐后恢復(fù)的不同植被群落對土壤團聚體和活性有機碳分布的影響,評價不同恢復(fù)群落的固碳效益,對黃土高原地區(qū)水土保持工作具有指導(dǎo)意義,可為林業(yè)經(jīng)營管理和生態(tài)安全建設(shè)提供參考依據(jù)。

1 研究區(qū)概況

實驗在陜西省延安東南部宜川縣鐵龍灣林場松峪溝半陽坡進行(E 110°06＇,N 35°39＇),坡度25°,土壤類型為灰褐色森林土,樣地為典型的黃土丘陵區(qū)油松(Pinus tabuliformisCarrière)林。實驗區(qū)地質(zhì)、土壤、植被條件基本一致,具有開展研究森林水土保持效益實驗的條件。實驗區(qū)屬黃龍山系,海拔1 000～1 200 m,年平均氣溫9.8℃,年平均降水量574.4 mm,多集中在7—9月。土壤表層有機質(zhì)含量豐富,達13.6 mg/g。林下土壤屬堿性土,pH值約8.6,每100 g干土陽離子交換量為13.01 mg,全氮、全磷質(zhì)量分數(shù)分別為0.39 mg/g和0.63 mg/g。

供實驗用油松人工林為1963年植造,現(xiàn)保存1 400～1 800株/hm2,樹高9.5～12.5 m,胸徑10～12 cm,郁閉度0.7。森林群落組成特征為:喬木層油松,零星伴生有杜梨(Pyrus betulifoliaBunge)、山杏(Armeniaca sibirica(L.)Lam);灌木層有黃刺梅(Rosa xanthinaL.)、繡線菊(Spiraea salicifoliaL.)、胡枝子(Lespedeza bicolorTurcz)等,覆蓋度10%～20%;草本層優(yōu)勢種有大披針苔草(Carex lanceolataBoott),蓋度約40%。

2 試驗設(shè)計與方法

1999年皆伐后,在油松人工林地,用鐵絲圍封12塊面積為50 m2實驗用小區(qū),保證不同小區(qū)之間環(huán)境條件基本一致。參考前人對皆伐后不同恢復(fù)群落類型的相關(guān)研究結(jié)果[14-15]并結(jié)合當(dāng)?shù)爻Ｒ娭脖环N群以及坡耕地特征。設(shè)置3種常見皆伐后恢復(fù)的植被群落:皆伐后更新為油松幼林、皆伐后自然更新為灌木、皆伐后翻耕并撂荒形成草地共3種恢復(fù)林地,并以未皆伐林地為對照(CK)進行實驗,每種措施設(shè)置4個重復(fù)。共16塊實驗小區(qū)用鐵絲圍封管理。灌木地以胡枝子群落為主,而撂荒地以披針苔草群落為主。

2015年10月采集不同處理原狀土壤樣品,土壤質(zhì)地為中壤土,結(jié)構(gòu)較疏松,平均土壤密度2.635 g/cm3,表層土壤密度1.1 g/cm3左右。樣品采集時要去除地表植被與枯枝落葉,取樣深度為0～20 cm,每個樣地采3個原狀土樣裝入方形塑料盒運回實驗室。將同一樣地內(nèi)的3個原狀土混合均勻,立刻將土樣過8 mm土篩,較大的土塊沿著自然裂隙輕輕破碎最后風(fēng)干土樣,以便進行土壤團聚體及活性有機碳的測定。

采用濕篩法[16]測定土壤水穩(wěn)性團聚體質(zhì)量分數(shù):取100 g過8 mm篩的土樣在去離子水中靜置5 min,撇去水面上漂浮的雜質(zhì),在250 μm樣品篩內(nèi)濕篩2 min,頻率控制在50次/min,振幅約3 cm;通過250 μm篩的土樣在53 μm篩上濕篩2 min;＞250 μm的土粒為大團聚體,250～53 μm為微團聚體,沖出來的土壤黏粉結(jié)構(gòu)通過離心處理,在270g下離心3 min得到黏粒,加入凝絮劑在2 000g下離心10 min得到粉粒。所有樣品測定土壤質(zhì)量后用于活性有機碳的測定。

活性有機碳含量測定采用Logninow提出的KMnO4氧化法測定[6]:根據(jù)KMnO4濃度的變化得出活性有機碳的質(zhì)量分數(shù)。稱取3 g土壤樣品于50 mL離心管,根據(jù)所要測定有機碳的活性加入不同濃度(333、167和33 mmol/L)的KMnO4溶液25 mL,放入震蕩器震蕩1 h后以2 000 r·min-1離心5 min。用去離子水稀釋上清液250倍,然后在565 nm光下比色得出不同活性有機碳質(zhì)量分數(shù)?？傆袡C碳采用重鉻酸鉀氧化外加熱法測定。

數(shù)據(jù)統(tǒng)計整理以及做圖基于Excel 2010;不同恢復(fù)群落之間各指標的差異性檢驗采用SPSS中的LSD和Duncan方法(P＜0.05)。

3 結(jié)果與分析

3.1 不同恢復(fù)群落團聚體分布

土壤結(jié)構(gòu)以大團聚體為主,皆伐后不同恢復(fù)群落會造成水穩(wěn)性團聚體分布的顯著變化(表1)。與不采取任何干擾的對照處理相比,撂荒地和灌木地的大團聚體比例顯著增加而幼林地大團聚體比例下降但變化不顯著。另外,撂荒地和灌木地的微團聚體比例有顯著降低的趨勢而幼林地微團聚體比例增加不顯著。不同恢復(fù)群落土壤黏粒、粉粒團聚體比例很少,并且不同處理變化不明顯。

3.2 不同恢復(fù)群落團聚體有機碳質(zhì)量分數(shù)

團聚體有機碳質(zhì)量分數(shù):大團聚體＞微團聚體＞黏粉粒。灌木地團聚體有機碳質(zhì)量分數(shù)與對照相比顯著增加(表2),其他處理下變化不顯著。如表2所示,不同處理下林地全土的有機碳質(zhì)量分數(shù)沒有顯著變化,而團聚體中的有機碳質(zhì)量分數(shù)變化顯著。

表1 不同恢復(fù)群落土壤水穩(wěn)性團聚體組成Tab.1 Composition of soil water-stable aggregate at different restoration communities%

表2 不同恢復(fù)群落水穩(wěn)性團聚體有機碳質(zhì)量分數(shù)Tab.2 Soil organic carbon concentration of water-stable aggregates at different restoration communitiesmg/g

3.3 不同恢復(fù)群落團聚體活性有機碳質(zhì)量分數(shù)

如圖1所示,團聚體活性有機碳質(zhì)量分數(shù)隨其活性的提高而降低,大團聚體中的活性碳質(zhì)量分數(shù)普遍高于微團聚體。與對照相比,皆伐后不同恢復(fù)群落團聚體活性有機碳呈增加趨勢,皆伐后自然恢復(fù)的灌木地團聚體中活性碳的質(zhì)量分數(shù)最高,大團聚體中的活性有機碳對群落的變化響應(yīng)最顯著。

圖1 不同恢復(fù)群落水穩(wěn)性團聚體活性有機碳質(zhì)量分數(shù)Fig.1 Labile organic carbon contents in soil water-stable aggregates of different restoration community

3.4 團聚體活性有機碳與土壤總有機碳的相關(guān)性

團聚體中的中、高活性有機碳與全土有機碳均極顯著相關(guān)(表3),大團聚體活性有機碳與全土有機碳相關(guān)性較微團聚體更為顯著,而活性越高相關(guān)性越顯著。

表3 土壤總有機碳與水穩(wěn)性團聚體活性有機碳的相關(guān)系數(shù)RTab.3 Correlation between total soil organic carbon and aggregate labile organic carbon in soil water-stable_________

4 討論

4.1 不同恢復(fù)群落團聚體分布

不同的土壤利用方式會改變土壤結(jié)構(gòu),導(dǎo)致團聚體的重新分布[17]。研究發(fā)現(xiàn),大團聚體是研究區(qū)土壤的主要組成結(jié)構(gòu),這與李娟等[17]、孫天聰?shù)萚18]和魏亞偉等[19]的研究結(jié)果基本一致。土壤肥力與大團聚體含量的多少直接相關(guān),而且大團聚體含量越高土壤穩(wěn)定性也越高[16],可見,研究區(qū)人工油松林土壤質(zhì)量有所改善。與對照相比,撂荒地和灌木地的大團聚體含量顯著增加,而微團聚體含量顯著降低,幼林地土壤大團聚體的減小和微團聚體增加趨勢均不顯著。由等級發(fā)育模型[20]可知,大團聚體是由微團聚體在各類膠結(jié)物質(zhì)的作用下形成的,而各種有機碳就是最重要的膠結(jié)物質(zhì)。皆伐后自然恢復(fù)的灌木地能促進微團聚體向大團聚體轉(zhuǎn)化可能是由于形成灌木地后自然恢復(fù)提高土壤各種有機碳的輸入造成的,撂荒地大團聚體含量增加可能主要是由于草本植物根系影響表層土壤團聚體組成導(dǎo)致的,而皆伐后恢復(fù)的油松幼林地因地表枯落物的減少而導(dǎo)致土壤有機碳含量降低,但是短期內(nèi)不會顯著改變團聚體組成。

4.2 不同恢復(fù)群落團聚體有機碳分布

團聚體的形成過程需要有機碳的膠結(jié)作用,而形成的團聚結(jié)構(gòu)也是有機碳穩(wěn)定存在的主要場所,兩者之間相互依存[21]。有機碳質(zhì)量分數(shù)隨著團聚體粒徑的增大而增加,與安韶山等[22]和趙世偉等[23]的研究結(jié)果相似。這主要是由于有機碳可以將微團聚體膠結(jié)成大團聚體[24],并且大團聚體中處于分解狀態(tài)的枯落物可以增加有機碳含量[25]。大團聚體是有機碳積累的主要場所,因此大團聚體中有機碳成為研究區(qū)土壤總有機碳的主要貢獻部分。皆伐后自然恢復(fù)的灌木地處理團聚體有機碳質(zhì)量分數(shù)顯著增加(P＜0.05),而其他處理沒有顯著變化。胡枝子灌木群落土壤團聚體有機碳含量相比于對照有所增加,結(jié)合不同處理間團聚體的分布特征可表明灌木地土壤有機碳積累較對照有所增加。其主要原因可能是胡枝子屬豆科植物,而栽植豆科植物后土壤氮、有機碳以及微生物量均能顯著增加[26]。其他群落團聚體有機碳質(zhì)量分數(shù)沒有顯著變化可能與有機碳含量指標受多種組分影響變化遲緩有關(guān)。另外,從表2中可以看出不同恢復(fù)群落全土有機碳質(zhì)量分數(shù)相比團聚體有機碳質(zhì)量分數(shù)變化更小,與毛霞麗等[27]在浙江稻田中取得的研究結(jié)果一致,而這與全土有機碳組成成分復(fù)雜有很大關(guān)系。

4.3 不同恢復(fù)群落團聚體活性有機碳分布

團聚體中的活性有機碳由于受到物理保護的作用而隔離微生物的分解作用可能會造成土壤碳匯功能的轉(zhuǎn)變,因此團聚體中活性有機碳對土壤碳庫穩(wěn)定和碳匯具有重要意義[8]。團聚體中低活性有機碳質(zhì)量分數(shù)＞中活性有機碳質(zhì)量分數(shù)＞高活性有機碳質(zhì)量分數(shù);大團聚體活性有機碳質(zhì)量分數(shù)大于微團聚體(圖1),與安娟娟等[28]、Blair等[29]得出的結(jié)論一致。團聚體活性有機碳對外界變化有很強的敏感性,研究皆伐后不同恢復(fù)群落團聚體活性碳分布的變化可以用來預(yù)測土壤碳庫對人為干擾與自然恢復(fù)響應(yīng)的動態(tài)過程。研究表明油松林皆伐后恢復(fù)的群落團聚體活性碳質(zhì)量分數(shù)均不同程度增加,土壤碳庫活性組分積累加快。其中,皆伐后自然恢復(fù)的灌木地團聚體活性有機碳質(zhì)量分數(shù)最高,相比于其他恢復(fù)群落而言,其土壤活性有機碳積累量最大且土壤質(zhì)量相對明顯提高。大團聚體活性有機碳對恢復(fù)群落改變的響應(yīng)最顯著,這主要是由于大團聚體中累積了土壤活性碳組分的絕大部分。類似的研究表明不同土地利用方式下土壤活性有機碳會有顯著變化,但也有研究指出土地利用方式對土壤活性有機碳含量沒有顯著影響。這些不同的結(jié)果說明土地利用方式對土壤活性碳的影響過程十分復(fù)雜,不同區(qū)域環(huán)境會有不同的響應(yīng)結(jié)果[30]。本研究顯示皆伐會擾動森林土壤團聚體活性有機碳動態(tài)過程,其中大團聚體活性有機碳對皆伐的響應(yīng)最明顯;不同恢復(fù)群落團聚體有機碳不同程度的活化,其中皆伐后自然恢復(fù)的灌木地團聚體有機碳活化最顯著。這可能與胡枝子群落改變土壤表層有機碳輸入和輸出動態(tài)平衡以及土壤中不同活性有機碳相互轉(zhuǎn)化有關(guān),還需進一步的研究來揭示這其中的機理。

4.4 團聚體活性有機碳與土壤總有機碳的相關(guān)性

活性有機碳含量可以作為預(yù)測和評價土壤質(zhì)量的敏感指標[31]。相關(guān)研究也證實即使在不同區(qū)域環(huán)境下活性有機碳都可以作為評價土壤碳庫變化的敏感指標[8,17],本研究的結(jié)果也對此進行了證實

(圖3)。另外,通過對不同粒徑團聚體3種活性有機碳與土壤總碳的相關(guān)分析發(fā)現(xiàn),團聚體活性有機碳與土壤總有機碳之間的相關(guān)性隨著團聚體粒徑的增大和有機碳活性的提高而增大,大團聚體中的高活性有機碳與土壤總有機碳的相關(guān)性最為顯著。因此,大團聚體中的高活性有機碳可以更好的作為預(yù)測和評價土壤碳庫動態(tài)變化的敏感指標。

5 結(jié)論

黃土高原油松林土壤以大團聚體(＞250 μm)為主,皆伐會造成團聚體分布顯著變化,自然恢復(fù)的灌木地以及撂荒地大團聚體含量顯著增加說明自然恢復(fù)過程有助于土壤質(zhì)量的提高。團聚體中的有機碳是土壤碳庫的重要組成部分,黃土高原油松林土壤團聚體有機碳質(zhì)量分數(shù)隨團聚體粒徑的增大而增加,表明大團聚體是有機碳積累的主要部分。相比于對照和其他恢復(fù)群落而言,自然恢復(fù)的灌木地團聚體有機碳質(zhì)量分數(shù)顯著增加。人工油松林團聚體活性有機碳組分中,低活性有機碳質(zhì)量分數(shù)＞中活性有機碳質(zhì)量分數(shù)＞高活性有機碳質(zhì)量分數(shù),并且大團聚體中的活性有機碳質(zhì)量分數(shù)大于微團聚體。皆伐會造成團聚體有機碳庫趨于活化,其中皆伐后自然恢復(fù)的灌木地活性有機碳質(zhì)量分數(shù)顯著增加,土壤有機碳活性成分積累量提高,土壤碳庫變化波動最大,不過其中的機理有待于進一步探索。另外,在活性有機碳可以用來預(yù)測土壤碳庫變化的基礎(chǔ)上,證實土壤大團聚體中的高活性有機碳可以作為未來預(yù)測土壤碳庫變化的更佳指標。

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Effects of restoration measure on labile organic carbon in aggregates after clear-cutting Chinese pine forest: A case study of Songyugou Watershed of the Loess Plateau

JING Hang1,LIU Guobin1,2,WANG Guoliang1,2,XUE Sha1,2,YAO Xu1,LIANG Chutao2
(1.Institute of Soil and Water Conservation,Northwest A&F University,712100,Yangling,Shaanxi,China; 2.Institute of Soil and Water Conservation,Chinese Academy of Sciences and Ministry of Water Resources,712100,Yangling,Shaanxi,China)

[Background]Labile organic carbon(LOC)is an important factor of soil organic carbon pool,and it can be more sensitive to environment change than any other factor.LOC in aggregate significantly influences soil quality and protection of carbon pool.In order to achieve the scientific management of restoration communities after clear-cutting,it is of great significance to investigate the relationship between soil aggregates and LOC in the area.[Methods]Concentrations of soil aggregates and LOC of restoration communities in Chinese pine plantations of the Loess Plateau after clear-cutting were investigated.There were 3 types of restoration community(shrub land,abandoned forestland and young plantation land.)and no clear-cutting forest as control(CK).Undisturbed soil samples were collected at 0-20 cm soil layer,the volume fraction of aggregate were tested using wet screening,theconcentrations of soil total organic carbon were determined using H2SO4-K2Cr2O7oxidation,and the concentrations of soil LOC were measured using KMnO4oxidation.Analysis of variance and linear regression analyses were done using SPSS(12.0).[Results]1)Macro-aggregate(＞250 μm)was dominant in aggregate composition.Compared with CK,the types of restoration community after clearcutting presented significant effects on the distribution of aggregates.The percentage of micro-aggregate significantly decreased(P＜0.05)while that of macro-aggregate significantly increased(P＜0.05)in shrub land and abandoned forestland.Aggregate composition in young plantation land showed no significant changes.2)The concentration of aggregate organic carbon increased with aggregate size increasing.There was the highest concentration of organic carbon in shrub land.The concentration of aggregate organic carbon was more sensitive than that of bulk soil organic carbons to different type of restoration community.3)The concentration of LOC in soil aggregate decreased with the improvement of labile state,and LOC concentration of macro aggregate was greater than micro aggregates.Compared with CK,the organic carbon of soil aggregate became more highly labile under different restoration communities.The concentration of aggregate LOC significantly increased in shrub land,and the concentration of LOC in macro-aggregate was more sensitive to different type of restoration community than that in any other aggregate size.4)Results of correlation analysis showed that LOC in aggregates presented a significant correlation with organic carbon in bulk soil.The correlation of LOC in macroaggregate with organic carbon in bulk soil was better than micro-aggregate.Highly LOC showed better correlation with organic carbon in bulk soil than lowly LOC.Therefore,highly LOC in macro-aggregate correlated best with organic carbon in bulk soil.[Conclusions]These results proved that different type of restoration community resulted in soil organic carbon unstable,and aggregate LOC in shrub land significantly increased.To some degree,our results uncovered the distribution characteristics of soil aggregate LOC in the Loess Plateau and indicated the effect of clear-cutting on aggregate labile organic carbon.According to these results,shrub land in restoration community can be a considerable management measure after clear-cutting Chinese pine forest in the Loess Plateau.Based on previous researches,our findings indicate that highly LOC in macro-aggregate can be a better index for measuring the dynamic of soil organic carbon than LOC in bulk soil.

soil aggregate;labile organic carbon;Chinese pine forest;clear-cutting;soil organic carbon

S714.2

:A

:2096-2673(2017)01-0113-08

10.16843/j.sswc.2017.01.014

2016- 07- 11

2016- 09- 13

項目名稱:國家科技支撐課題“陜北水蝕區(qū)植被功能調(diào)控技術(shù)與示范”(2015BAC01B03);中國科學(xué)院重點部署項目“黃土丘陵區(qū)集約經(jīng)營型流域生態(tài)經(jīng)濟協(xié)同發(fā)展技術(shù)研究與示范”(KFZD-SW-306-2)

景航(1991—),男,碩士研究生。主要研究方向:土壤生態(tài)學(xué)研究。E-mail:h8170166069@163.com

?通信作者簡介:劉國彬(1958—),男,博士,教授,博士生導(dǎo)師。主要研究方向:流域管理。E-mail:gbliu@ms.iswc.ac.cn