恢復(fù)措施對(duì)皆伐油松林團(tuán)聚體活性有機(jī)碳含量的影響
——以黃土丘陵區(qū)松峪溝流域?yàn)槔?/h1>
2017-04-18 07:46:43景航劉國彬王國梁薛萐姚旭梁楚濤
中國水土保持科學(xué) 2017年1期
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(duì)皆伐油松林團(tuán)聚體活性有機(jī)碳含量的影響
——以黃土丘陵區(qū)松峪溝流域?yàn)槔?/p>
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(tuán)聚體中的活性有機(jī)碳對(duì)土壤質(zhì)量改善以及碳庫動(dòng)態(tài)平衡具有重要意義。為了研究皆伐后土壤團(tuán)聚體活性有機(jī)碳的分布狀況,本實(shí)驗(yàn)選取黃土高原典型油松林為對(duì)象,以未皆伐人工油松林為對(duì)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(tuán)聚體中活性有機(jī)碳變化特征。結(jié)果表明: 1)研究區(qū)土壤以大團(tuán)聚體(＞250 μm)為主,自然恢復(fù)的灌木地以及撂荒地大團(tuán)聚體質(zhì)量分?jǐn)?shù)顯著增加(P＜0.05)。2)有機(jī)碳質(zhì)量分?jǐn)?shù)隨團(tuán)聚體粒徑的增大而增加,大團(tuán)聚體是有機(jī)碳積累的主要場(chǎng)所,并且自然恢復(fù)的灌木地團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)最高。3)研究區(qū)油松林團(tuán)聚體低活性有機(jī)碳質(zhì)量分?jǐn)?shù)＞中活性有機(jī)碳質(zhì)量分?jǐn)?shù)＞高活性有機(jī)碳質(zhì)量分?jǐn)?shù),大團(tuán)聚體活性有機(jī)碳質(zhì)量分?jǐn)?shù)大于微團(tuán)聚體。研究表明,皆伐會(huì)造成團(tuán)聚體有機(jī)碳趨于活化,其中自然恢復(fù)的灌木地活性有機(jī)碳質(zhì)量分?jǐn)?shù)顯著增加。本研究還進(jìn)一步發(fā)現(xiàn)大團(tuán)聚體中的高活性有機(jī)碳能更好地預(yù)測(cè)土壤碳庫變化。
土壤團(tuán)聚體;活性有機(jī)碳;油松人工林;皆伐;土壤有機(jī)碳
團(tuán)聚體是土壤結(jié)構(gòu)的重要組成部分[1],是評(píng)價(jià)土壤質(zhì)量的一個(gè)重要指標(biāo)[2]。有機(jī)碳能黏合礦物顆粒形成穩(wěn)定的土壤團(tuán)聚結(jié)構(gòu),是團(tuán)聚體形成過程中的主要膠結(jié)物質(zhì)[3]。團(tuán)聚體和有機(jī)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(tuán)聚體有機(jī)碳的研究報(bào)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(tuán)聚體的形成、穩(wěn)定和周轉(zhuǎn),而有機(jī)碳中的活性組分在這個(gè)過程中最為活躍。W.Logninow等[6]根據(jù)土壤有機(jī)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(jī)碳分為高、中和低3個(gè)活性級(jí)別。雖然活性有機(jī)碳只占土壤有機(jī)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(cè)土壤質(zhì)量變化方面具有重要意義[7]。以往研究主要針對(duì)全土活性碳變化進(jìn)行分析[8],而團(tuán)聚體中的活性有機(jī)碳由于其特殊的結(jié)構(gòu)以及團(tuán)聚體的保護(hù)作用可能會(huì)對(duì)土壤的碳匯功能產(chǎn)生深刻影響[9];因此開展團(tuán)聚體及其活性有機(jī)碳的研究是揭示土壤碳庫動(dòng)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(jī)碳庫的70%～73%是森林土壤有機(jī)碳[11]。森林土壤碳庫的微弱變化都會(huì)導(dǎo)致大氣CO2的顯著變化[12]。研究森林土壤團(tuán)聚體和活性有機(jī)碳可以揭示森林土壤碳庫動(dòng)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(jī)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(cè)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(jī)碳變化各異[14],并且皆伐后恢復(fù)的不同植被群落對(duì)土壤有機(jī)碳組分和團(tuán)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(duì)土壤團(tuán)聚體和活性有機(jī)碳分布的影響,評(píng)價(jià)不同恢復(fù)群落的固碳效益,對(duì)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(shí)驗(yàn)在陜西省延安東南部宜川縣鐵龍灣林場(chǎng)松峪溝半陽坡進(jìn)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(shí)驗(yàn)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(shí)驗(yàn)的條件。實(shí)驗(yàn)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(jī)質(zhì)含量豐富,達(dá)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?jǐn)?shù)分別為0.39 mg/g和0.63 mg/g。
供實(shí)驗(yàn)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(shì)種有大披針苔草(Carex lanceolataBoott),蓋度約40%。
2 試驗(yàn)設(shè)計(jì)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(shí)驗(yàn)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(duì)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(duì)照(CK)進(jìn)行實(shí)驗(yàn),每種措施設(shè)置4個(gè)重復(fù)。共16塊實(shí)驗(yàn)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(shí)要去除地表植被與枯枝落葉,取樣深度為0～20 cm,每個(gè)樣地采3個(gè)原狀土樣裝入方形塑料盒運(yùn)回實(shí)驗(yàn)室。將同一樣地內(nèi)的3個(gè)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(jìn)行土壤團(tuán)聚體及活性有機(jī)碳的測(cè)定。
采用濕篩法[16]測(cè)定土壤水穩(wěn)性團(tuán)聚體質(zhì)量分?jǐn)?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(tuán)聚體,250～53 μm為微團(tuán)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(cè)定土壤質(zhì)量后用于活性有機(jī)碳的測(cè)定。
活性有機(jī)碳含量測(cè)定采用Logninow提出的KMnO4氧化法測(cè)定[6]:根據(jù)KMnO4濃度的變化得出活性有機(jī)碳的質(zhì)量分?jǐn)?shù)。稱取3 g土壤樣品于50 mL離心管,根據(jù)所要測(cè)定有機(jī)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(jī)碳質(zhì)量分?jǐn)?shù)?？傆袡C(jī)碳采用重鉻酸鉀氧化外加熱法測(cè)定。
數(shù)據(jù)統(tǒng)計(jì)整理以及做圖基于Excel 2010;不同恢復(fù)群落之間各指標(biāo)的差異性檢驗(yàn)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(tuán)聚體分布
土壤結(jié)構(gòu)以大團(tuán)聚體為主,皆伐后不同恢復(fù)群落會(huì)造成水穩(wěn)性團(tuán)聚體分布的顯著變化(表1)。與不采取任何干擾的對(duì)照處理相比,撂荒地和灌木地的大團(tuán)聚體比例顯著增加而幼林地大團(tuán)聚體比例下降但變化不顯著。另外,撂荒地和灌木地的微團(tuán)聚體比例有顯著降低的趨勢(shì)而幼林地微團(tuán)聚體比例增加不顯著。不同恢復(fù)群落土壤黏粒、粉粒團(tuán)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(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)
團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù):大團(tuán)聚體＞微團(tuán)聚體＞黏粉粒。灌木地團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)與對(duì)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(jī)碳質(zhì)量分?jǐn)?shù)沒有顯著變化,而團(tuán)聚體中的有機(jī)碳質(zhì)量分?jǐn)?shù)變化顯著。
表1 不同恢復(fù)群落土壤水穩(wěn)性團(tuán)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(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?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(tuán)聚體活性有機(jī)碳質(zhì)量分?jǐn)?shù)
如圖1所示,團(tuán)聚體活性有機(jī)碳質(zhì)量分?jǐn)?shù)隨其活性的提高而降低,大團(tuán)聚體中的活性碳質(zhì)量分?jǐn)?shù)普遍高于微團(tuán)聚體。與對(duì)照相比,皆伐后不同恢復(fù)群落團(tuán)聚體活性有機(jī)碳呈增加趨勢(shì),皆伐后自然恢復(fù)的灌木地團(tuán)聚體中活性碳的質(zhì)量分?jǐn)?shù)最高,大團(tuán)聚體中的活性有機(jī)碳對(duì)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(tuán)聚體活性有機(jī)碳質(zhì)量分?jǐn)?shù)Fig.1 Labile organic carbon contents in soil water-stable aggregates of different restoration community
3.4 團(tuán)聚體活性有機(jī)碳與土壤總有機(jī)碳的相關(guān)性
團(tuán)聚體中的中、高活性有機(jī)碳與全土有機(jī)碳均極顯著相關(guān)(表3),大團(tuán)聚體活性有機(jī)碳與全土有機(jī)碳相關(guān)性較微團(tuán)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(jī)碳與水穩(wěn)性團(tuán)聚體活性有機(jī)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(tuán)聚體分布
不同的土壤利用方式會(huì)改變土壤結(jié)構(gòu),導(dǎo)致團(tuán)聚體的重新分布[17]。研究發(fā)現(xiàn),大團(tuán)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(tuán)聚體含量的多少直接相關(guān),而且大團(tuán)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(duì)照相比,撂荒地和灌木地的大團(tuán)聚體含量顯著增加,而微團(tuán)聚體含量顯著降低,幼林地土壤大團(tuán)聚體的減小和微團(tuán)聚體增加趨勢(shì)均不顯著。由等級(jí)發(fā)育模型[20]可知,大團(tuán)聚體是由微團(tuán)聚體在各類膠結(jié)物質(zhì)的作用下形成的,而各種有機(jī)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(jìn)微團(tuán)聚體向大團(tuán)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(jī)碳的輸入造成的,撂荒地大團(tuán)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(tuán)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(jī)碳含量降低,但是短期內(nèi)不會(huì)顯著改變團(tuán)聚體組成。
4.2 不同恢復(fù)群落團(tuán)聚體有機(jī)碳分布
團(tuán)聚體的形成過程需要有機(jī)碳的膠結(jié)作用,而形成的團(tuán)聚結(jié)構(gòu)也是有機(jī)碳穩(wěn)定存在的主要場(chǎng)所,兩者之間相互依存[21]。有機(jī)碳質(zhì)量分?jǐn)?shù)隨著團(tuán)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(jī)碳可以將微團(tuán)聚體膠結(jié)成大團(tuán)聚體[24],并且大團(tuán)聚體中處于分解狀態(tài)的枯落物可以增加有機(jī)碳含量[25]。大團(tuán)聚體是有機(jī)碳積累的主要場(chǎng)所,因此大團(tuán)聚體中有機(jī)碳成為研究區(qū)土壤總有機(jī)碳的主要貢獻(xiàn)部分。皆伐后自然恢復(fù)的灌木地處理團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?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(tuán)聚體有機(jī)碳含量相比于對(duì)照有所增加,結(jié)合不同處理間團(tuán)聚體的分布特征可表明灌木地土壤有機(jī)碳積累較對(duì)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(jī)碳以及微生物量均能顯著增加[26]。其他群落團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)沒有顯著變化可能與有機(jī)碳含量指標(biāo)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(jī)碳質(zhì)量分?jǐn)?shù)相比團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?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(jī)碳組成成分復(fù)雜有很大關(guān)系。
4.3 不同恢復(fù)群落團(tuán)聚體活性有機(jī)碳分布
團(tuán)聚體中的活性有機(jī)碳由于受到物理保護(hù)的作用而隔離微生物的分解作用可能會(huì)造成土壤碳匯功能的轉(zhuǎn)變,因此團(tuán)聚體中活性有機(jī)碳對(duì)土壤碳庫穩(wěn)定和碳匯具有重要意義[8]。團(tuán)聚體中低活性有機(jī)碳質(zhì)量分?jǐn)?shù)＞中活性有機(jī)碳質(zhì)量分?jǐn)?shù)＞高活性有機(jī)碳質(zhì)量分?jǐn)?shù);大團(tuán)聚體活性有機(jī)碳質(zhì)量分?jǐn)?shù)大于微團(tuán)聚體(圖1),與安娟娟等[28]、Blair等[29]得出的結(jié)論一致。團(tuán)聚體活性有機(jī)碳對(duì)外界變化有很強(qiáng)的敏感性,研究皆伐后不同恢復(fù)群落團(tuán)聚體活性碳分布的變化可以用來預(yù)測(cè)土壤碳庫對(duì)人為干擾與自然恢復(fù)響應(yīng)的動(dòng)態(tài)過程。研究表明油松林皆伐后恢復(fù)的群落團(tuán)聚體活性碳質(zhì)量分?jǐn)?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(tuán)聚體活性有機(jī)碳質(zhì)量分?jǐn)?shù)最高,相比于其他恢復(fù)群落而言,其土壤活性有機(jī)碳積累量最大且土壤質(zhì)量相對(duì)明顯提高。大團(tuán)聚體活性有機(jī)碳對(duì)恢復(fù)群落改變的響應(yīng)最顯著,這主要是由于大團(tuán)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(jī)碳會(huì)有顯著變化,但也有研究指出土地利用方式對(duì)土壤活性有機(jī)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(duì)土壤活性碳的影響過程十分復(fù)雜,不同區(qū)域環(huán)境會(huì)有不同的響應(yīng)結(jié)果[30]。本研究顯示皆伐會(huì)擾動(dòng)森林土壤團(tuán)聚體活性有機(jī)碳動(dòng)態(tài)過程,其中大團(tuán)聚體活性有機(jī)碳對(duì)皆伐的響應(yīng)最明顯;不同恢復(fù)群落團(tuán)聚體有機(jī)碳不同程度的活化,其中皆伐后自然恢復(fù)的灌木地團(tuán)聚體有機(jī)碳活化最顯著。這可能與胡枝子群落改變土壤表層有機(jī)碳輸入和輸出動(dòng)態(tài)平衡以及土壤中不同活性有機(jī)碳相互轉(zhuǎn)化有關(guān),還需進(jìn)一步的研究來揭示這其中的機(jī)理。
4.4 團(tuán)聚體活性有機(jī)碳與土壤總有機(jī)碳的相關(guān)性
活性有機(jī)碳含量可以作為預(yù)測(cè)和評(píng)價(jià)土壤質(zhì)量的敏感指標(biāo)[31]。相關(guān)研究也證實(shí)即使在不同區(qū)域環(huán)境下活性有機(jī)碳都可以作為評(píng)價(jià)土壤碳庫變化的敏感指標(biāo)[8,17],本研究的結(jié)果也對(duì)此進(jìn)行了證實(shí)
(圖3)。另外,通過對(duì)不同粒徑團(tuán)聚體3種活性有機(jī)碳與土壤總碳的相關(guān)分析發(fā)現(xiàn),團(tuán)聚體活性有機(jī)碳與土壤總有機(jī)碳之間的相關(guān)性隨著團(tuán)聚體粒徑的增大和有機(jī)碳活性的提高而增大,大團(tuán)聚體中的高活性有機(jī)碳與土壤總有機(jī)碳的相關(guān)性最為顯著。因此,大團(tuán)聚體中的高活性有機(jī)碳可以更好的作為預(yù)測(cè)和評(píng)價(jià)土壤碳庫動(dòng)態(tài)變化的敏感指標(biāo)。
5 結(jié)論
黃土高原油松林土壤以大團(tuán)聚體(＞250 μm)為主,皆伐會(huì)造成團(tuán)聚體分布顯著變化,自然恢復(fù)的灌木地以及撂荒地大團(tuán)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(tuán)聚體中的有機(jī)碳是土壤碳庫的重要組成部分,黃土高原油松林土壤團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)隨團(tuán)聚體粒徑的增大而增加,表明大團(tuán)聚體是有機(jī)碳積累的主要部分。相比于對(duì)照和其他恢復(fù)群落而言,自然恢復(fù)的灌木地團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)顯著增加。人工油松林團(tuán)聚體活性有機(jī)碳組分中,低活性有機(jī)碳質(zhì)量分?jǐn)?shù)＞中活性有機(jī)碳質(zhì)量分?jǐn)?shù)＞高活性有機(jī)碳質(zhì)量分?jǐn)?shù),并且大團(tuán)聚體中的活性有機(jī)碳質(zhì)量分?jǐn)?shù)大于微團(tuán)聚體。皆伐會(huì)造成團(tuán)聚體有機(jī)碳庫趨于活化,其中皆伐后自然恢復(fù)的灌木地活性有機(jī)碳質(zhì)量分?jǐn)?shù)顯著增加,土壤有機(jī)碳活性成分積累量提高,土壤碳庫變化波動(dòng)最大,不過其中的機(jī)理有待于進(jìn)一步探索。另外,在活性有機(jī)碳可以用來預(yù)測(cè)土壤碳庫變化的基礎(chǔ)上,證實(shí)土壤大團(tuán)聚體中的高活性有機(jī)碳可以作為未來預(yù)測(cè)土壤碳庫變化的更佳指標(biāo)。
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[28] 安娟娟,陳少鋒,趙發(fā)珠,等.不同人工植被下土壤活性有機(jī)碳及碳庫管理指數(shù)變化[J].農(nóng)業(yè)環(huán)境科學(xué)學(xué)報(bào),2014,33(5):985. AN Juanjuan,CHEN Shaofeng,ZHAO Fazhu,et al. Changes iof soil labile organic carbon and carbon management ndex under different artificial vegetations[J]. Journal of Agro-Environment Science,2014,33(5): 985.
[29] BLAIR G J,CONTEH A.The distribution and relative losses of soil organic carbon fractions in aggregate size fractions from cracking clay soils(Vertisols)under cotton production[J].Australian Journal of Soil Research, 1998,36(2):257.
[30] 吳建國,張小全,徐德應(yīng).六盤山林區(qū)幾種土地利用方式下土壤活性有機(jī)碳的比較[J].植物生態(tài)學(xué)報(bào), 2004,28(5):657. WU Jianguo,ZHANG Xiaoquan,XU Deying.Changes in soil labile organic carbon under different land use in the Liupan mountain forest zone[J].Acta Phytoecologica Sinica,2004,28(5):657.
[31] 許明祥,劉國彬,趙允格.黃土丘陵區(qū)土壤質(zhì)量評(píng)價(jià)指標(biāo)研究[J].應(yīng)用生態(tài)學(xué)報(bào),2005,16(10):1843. XU Mingxiang,LIU Guobin,ZHAO Yunge.Assessment indicators of soil quality in hilly Loess Plateau[J].Chinese Journal of Applied Ecology,2005,16(10):1843.
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(xiàng)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(diǎn)部署項(xiàng)目“黃土丘陵區(qū)集約經(jīng)營型流域生態(tài)經(jīng)濟(jì)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(jiǎn)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
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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(duì)皆伐油松林團(tuán)聚體活性有機(jī)碳含量的影響
——以黃土丘陵區(qū)松峪溝流域?yàn)槔?/p>
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(tuán)聚體中的活性有機(jī)碳對(duì)土壤質(zhì)量改善以及碳庫動(dòng)態(tài)平衡具有重要意義。為了研究皆伐后土壤團(tuán)聚體活性有機(jī)碳的分布狀況,本實(shí)驗(yàn)選取黃土高原典型油松林為對(duì)象,以未皆伐人工油松林為對(duì)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(tuán)聚體中活性有機(jī)碳變化特征。結(jié)果表明: 1)研究區(qū)土壤以大團(tuán)聚體(＞250 μm)為主,自然恢復(fù)的灌木地以及撂荒地大團(tuán)聚體質(zhì)量分?jǐn)?shù)顯著增加(P＜0.05)。2)有機(jī)碳質(zhì)量分?jǐn)?shù)隨團(tuán)聚體粒徑的增大而增加,大團(tuán)聚體是有機(jī)碳積累的主要場(chǎng)所,并且自然恢復(fù)的灌木地團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)最高。3)研究區(qū)油松林團(tuán)聚體低活性有機(jī)碳質(zhì)量分?jǐn)?shù)＞中活性有機(jī)碳質(zhì)量分?jǐn)?shù)＞高活性有機(jī)碳質(zhì)量分?jǐn)?shù),大團(tuán)聚體活性有機(jī)碳質(zhì)量分?jǐn)?shù)大于微團(tuán)聚體。研究表明,皆伐會(huì)造成團(tuán)聚體有機(jī)碳趨于活化,其中自然恢復(fù)的灌木地活性有機(jī)碳質(zhì)量分?jǐn)?shù)顯著增加。本研究還進(jìn)一步發(fā)現(xiàn)大團(tuán)聚體中的高活性有機(jī)碳能更好地預(yù)測(cè)土壤碳庫變化。
土壤團(tuán)聚體;活性有機(jī)碳;油松人工林;皆伐;土壤有機(jī)碳
團(tuán)聚體是土壤結(jié)構(gòu)的重要組成部分[1],是評(píng)價(jià)土壤質(zhì)量的一個(gè)重要指標(biāo)[2]。有機(jī)碳能黏合礦物顆粒形成穩(wěn)定的土壤團(tuán)聚結(jié)構(gòu),是團(tuán)聚體形成過程中的主要膠結(jié)物質(zhì)[3]。團(tuán)聚體和有機(jī)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(tuán)聚體有機(jī)碳的研究報(bào)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(tuán)聚體的形成、穩(wěn)定和周轉(zhuǎn),而有機(jī)碳中的活性組分在這個(gè)過程中最為活躍。W.Logninow等[6]根據(jù)土壤有機(jī)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(jī)碳分為高、中和低3個(gè)活性級(jí)別。雖然活性有機(jī)碳只占土壤有機(jī)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(cè)土壤質(zhì)量變化方面具有重要意義[7]。以往研究主要針對(duì)全土活性碳變化進(jìn)行分析[8],而團(tuán)聚體中的活性有機(jī)碳由于其特殊的結(jié)構(gòu)以及團(tuán)聚體的保護(hù)作用可能會(huì)對(duì)土壤的碳匯功能產(chǎn)生深刻影響[9];因此開展團(tuán)聚體及其活性有機(jī)碳的研究是揭示土壤碳庫動(dòng)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(jī)碳庫的70%～73%是森林土壤有機(jī)碳[11]。森林土壤碳庫的微弱變化都會(huì)導(dǎo)致大氣CO2的顯著變化[12]。研究森林土壤團(tuán)聚體和活性有機(jī)碳可以揭示森林土壤碳庫動(dòng)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(jī)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(cè)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(jī)碳變化各異[14],并且皆伐后恢復(fù)的不同植被群落對(duì)土壤有機(jī)碳組分和團(tuán)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(duì)土壤團(tuán)聚體和活性有機(jī)碳分布的影響,評(píng)價(jià)不同恢復(fù)群落的固碳效益,對(duì)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(shí)驗(yàn)在陜西省延安東南部宜川縣鐵龍灣林場(chǎng)松峪溝半陽坡進(jìn)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(shí)驗(yàn)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(shí)驗(yàn)的條件。實(shí)驗(yàn)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(jī)質(zhì)含量豐富,達(dá)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?jǐn)?shù)分別為0.39 mg/g和0.63 mg/g。
供實(shí)驗(yàn)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(shì)種有大披針苔草(Carex lanceolataBoott),蓋度約40%。
2 試驗(yàn)設(shè)計(jì)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(shí)驗(yàn)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(duì)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(duì)照(CK)進(jìn)行實(shí)驗(yàn),每種措施設(shè)置4個(gè)重復(fù)。共16塊實(shí)驗(yàn)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(shí)要去除地表植被與枯枝落葉,取樣深度為0～20 cm,每個(gè)樣地采3個(gè)原狀土樣裝入方形塑料盒運(yùn)回實(shí)驗(yàn)室。將同一樣地內(nèi)的3個(gè)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(jìn)行土壤團(tuán)聚體及活性有機(jī)碳的測(cè)定。
采用濕篩法[16]測(cè)定土壤水穩(wěn)性團(tuán)聚體質(zhì)量分?jǐn)?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(tuán)聚體,250～53 μm為微團(tuán)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(cè)定土壤質(zhì)量后用于活性有機(jī)碳的測(cè)定。
活性有機(jī)碳含量測(cè)定采用Logninow提出的KMnO4氧化法測(cè)定[6]:根據(jù)KMnO4濃度的變化得出活性有機(jī)碳的質(zhì)量分?jǐn)?shù)。稱取3 g土壤樣品于50 mL離心管,根據(jù)所要測(cè)定有機(jī)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(jī)碳質(zhì)量分?jǐn)?shù)?？傆袡C(jī)碳采用重鉻酸鉀氧化外加熱法測(cè)定。
數(shù)據(jù)統(tǒng)計(jì)整理以及做圖基于Excel 2010;不同恢復(fù)群落之間各指標(biāo)的差異性檢驗(yàn)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(tuán)聚體分布
土壤結(jié)構(gòu)以大團(tuán)聚體為主,皆伐后不同恢復(fù)群落會(huì)造成水穩(wěn)性團(tuán)聚體分布的顯著變化(表1)。與不采取任何干擾的對(duì)照處理相比,撂荒地和灌木地的大團(tuán)聚體比例顯著增加而幼林地大團(tuán)聚體比例下降但變化不顯著。另外,撂荒地和灌木地的微團(tuán)聚體比例有顯著降低的趨勢(shì)而幼林地微團(tuán)聚體比例增加不顯著。不同恢復(fù)群落土壤黏粒、粉粒團(tuán)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(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)
團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù):大團(tuán)聚體＞微團(tuán)聚體＞黏粉粒。灌木地團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)與對(duì)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(jī)碳質(zhì)量分?jǐn)?shù)沒有顯著變化,而團(tuán)聚體中的有機(jī)碳質(zhì)量分?jǐn)?shù)變化顯著。
表1 不同恢復(fù)群落土壤水穩(wěn)性團(tuán)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(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?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(tuán)聚體活性有機(jī)碳質(zhì)量分?jǐn)?shù)
如圖1所示,團(tuán)聚體活性有機(jī)碳質(zhì)量分?jǐn)?shù)隨其活性的提高而降低,大團(tuán)聚體中的活性碳質(zhì)量分?jǐn)?shù)普遍高于微團(tuán)聚體。與對(duì)照相比,皆伐后不同恢復(fù)群落團(tuán)聚體活性有機(jī)碳呈增加趨勢(shì),皆伐后自然恢復(fù)的灌木地團(tuán)聚體中活性碳的質(zhì)量分?jǐn)?shù)最高,大團(tuán)聚體中的活性有機(jī)碳對(duì)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(tuán)聚體活性有機(jī)碳質(zhì)量分?jǐn)?shù)Fig.1 Labile organic carbon contents in soil water-stable aggregates of different restoration community
3.4 團(tuán)聚體活性有機(jī)碳與土壤總有機(jī)碳的相關(guān)性
團(tuán)聚體中的中、高活性有機(jī)碳與全土有機(jī)碳均極顯著相關(guān)(表3),大團(tuán)聚體活性有機(jī)碳與全土有機(jī)碳相關(guān)性較微團(tuán)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(jī)碳與水穩(wěn)性團(tuán)聚體活性有機(jī)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(tuán)聚體分布
不同的土壤利用方式會(huì)改變土壤結(jié)構(gòu),導(dǎo)致團(tuán)聚體的重新分布[17]。研究發(fā)現(xiàn),大團(tuán)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(tuán)聚體含量的多少直接相關(guān),而且大團(tuán)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(duì)照相比,撂荒地和灌木地的大團(tuán)聚體含量顯著增加,而微團(tuán)聚體含量顯著降低,幼林地土壤大團(tuán)聚體的減小和微團(tuán)聚體增加趨勢(shì)均不顯著。由等級(jí)發(fā)育模型[20]可知,大團(tuán)聚體是由微團(tuán)聚體在各類膠結(jié)物質(zhì)的作用下形成的,而各種有機(jī)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(jìn)微團(tuán)聚體向大團(tuán)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(jī)碳的輸入造成的,撂荒地大團(tuán)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(tuán)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(jī)碳含量降低,但是短期內(nèi)不會(huì)顯著改變團(tuán)聚體組成。
4.2 不同恢復(fù)群落團(tuán)聚體有機(jī)碳分布
團(tuán)聚體的形成過程需要有機(jī)碳的膠結(jié)作用,而形成的團(tuán)聚結(jié)構(gòu)也是有機(jī)碳穩(wěn)定存在的主要場(chǎng)所,兩者之間相互依存[21]。有機(jī)碳質(zhì)量分?jǐn)?shù)隨著團(tuán)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(jī)碳可以將微團(tuán)聚體膠結(jié)成大團(tuán)聚體[24],并且大團(tuán)聚體中處于分解狀態(tài)的枯落物可以增加有機(jī)碳含量[25]。大團(tuán)聚體是有機(jī)碳積累的主要場(chǎng)所,因此大團(tuán)聚體中有機(jī)碳成為研究區(qū)土壤總有機(jī)碳的主要貢獻(xiàn)部分。皆伐后自然恢復(fù)的灌木地處理團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?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(tuán)聚體有機(jī)碳含量相比于對(duì)照有所增加,結(jié)合不同處理間團(tuán)聚體的分布特征可表明灌木地土壤有機(jī)碳積累較對(duì)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(jī)碳以及微生物量均能顯著增加[26]。其他群落團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)沒有顯著變化可能與有機(jī)碳含量指標(biāo)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(jī)碳質(zhì)量分?jǐn)?shù)相比團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?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(jī)碳組成成分復(fù)雜有很大關(guān)系。
4.3 不同恢復(fù)群落團(tuán)聚體活性有機(jī)碳分布
團(tuán)聚體中的活性有機(jī)碳由于受到物理保護(hù)的作用而隔離微生物的分解作用可能會(huì)造成土壤碳匯功能的轉(zhuǎn)變,因此團(tuán)聚體中活性有機(jī)碳對(duì)土壤碳庫穩(wěn)定和碳匯具有重要意義[8]。團(tuán)聚體中低活性有機(jī)碳質(zhì)量分?jǐn)?shù)＞中活性有機(jī)碳質(zhì)量分?jǐn)?shù)＞高活性有機(jī)碳質(zhì)量分?jǐn)?shù);大團(tuán)聚體活性有機(jī)碳質(zhì)量分?jǐn)?shù)大于微團(tuán)聚體(圖1),與安娟娟等[28]、Blair等[29]得出的結(jié)論一致。團(tuán)聚體活性有機(jī)碳對(duì)外界變化有很強(qiáng)的敏感性,研究皆伐后不同恢復(fù)群落團(tuán)聚體活性碳分布的變化可以用來預(yù)測(cè)土壤碳庫對(duì)人為干擾與自然恢復(fù)響應(yīng)的動(dòng)態(tài)過程。研究表明油松林皆伐后恢復(fù)的群落團(tuán)聚體活性碳質(zhì)量分?jǐn)?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(tuán)聚體活性有機(jī)碳質(zhì)量分?jǐn)?shù)最高,相比于其他恢復(fù)群落而言,其土壤活性有機(jī)碳積累量最大且土壤質(zhì)量相對(duì)明顯提高。大團(tuán)聚體活性有機(jī)碳對(duì)恢復(fù)群落改變的響應(yīng)最顯著,這主要是由于大團(tuán)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(jī)碳會(huì)有顯著變化,但也有研究指出土地利用方式對(duì)土壤活性有機(jī)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(duì)土壤活性碳的影響過程十分復(fù)雜,不同區(qū)域環(huán)境會(huì)有不同的響應(yīng)結(jié)果[30]。本研究顯示皆伐會(huì)擾動(dòng)森林土壤團(tuán)聚體活性有機(jī)碳動(dòng)態(tài)過程,其中大團(tuán)聚體活性有機(jī)碳對(duì)皆伐的響應(yīng)最明顯;不同恢復(fù)群落團(tuán)聚體有機(jī)碳不同程度的活化,其中皆伐后自然恢復(fù)的灌木地團(tuán)聚體有機(jī)碳活化最顯著。這可能與胡枝子群落改變土壤表層有機(jī)碳輸入和輸出動(dòng)態(tài)平衡以及土壤中不同活性有機(jī)碳相互轉(zhuǎn)化有關(guān),還需進(jìn)一步的研究來揭示這其中的機(jī)理。
4.4 團(tuán)聚體活性有機(jī)碳與土壤總有機(jī)碳的相關(guān)性
活性有機(jī)碳含量可以作為預(yù)測(cè)和評(píng)價(jià)土壤質(zhì)量的敏感指標(biāo)[31]。相關(guān)研究也證實(shí)即使在不同區(qū)域環(huán)境下活性有機(jī)碳都可以作為評(píng)價(jià)土壤碳庫變化的敏感指標(biāo)[8,17],本研究的結(jié)果也對(duì)此進(jìn)行了證實(shí)
(圖3)。另外,通過對(duì)不同粒徑團(tuán)聚體3種活性有機(jī)碳與土壤總碳的相關(guān)分析發(fā)現(xiàn),團(tuán)聚體活性有機(jī)碳與土壤總有機(jī)碳之間的相關(guān)性隨著團(tuán)聚體粒徑的增大和有機(jī)碳活性的提高而增大,大團(tuán)聚體中的高活性有機(jī)碳與土壤總有機(jī)碳的相關(guān)性最為顯著。因此,大團(tuán)聚體中的高活性有機(jī)碳可以更好的作為預(yù)測(cè)和評(píng)價(jià)土壤碳庫動(dòng)態(tài)變化的敏感指標(biāo)。
5 結(jié)論
黃土高原油松林土壤以大團(tuán)聚體(＞250 μm)為主,皆伐會(huì)造成團(tuán)聚體分布顯著變化,自然恢復(fù)的灌木地以及撂荒地大團(tuán)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(tuán)聚體中的有機(jī)碳是土壤碳庫的重要組成部分,黃土高原油松林土壤團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)隨團(tuán)聚體粒徑的增大而增加,表明大團(tuán)聚體是有機(jī)碳積累的主要部分。相比于對(duì)照和其他恢復(fù)群落而言,自然恢復(fù)的灌木地團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)顯著增加。人工油松林團(tuán)聚體活性有機(jī)碳組分中,低活性有機(jī)碳質(zhì)量分?jǐn)?shù)＞中活性有機(jī)碳質(zhì)量分?jǐn)?shù)＞高活性有機(jī)碳質(zhì)量分?jǐn)?shù),并且大團(tuán)聚體中的活性有機(jī)碳質(zhì)量分?jǐn)?shù)大于微團(tuán)聚體。皆伐會(huì)造成團(tuán)聚體有機(jī)碳庫趨于活化,其中皆伐后自然恢復(fù)的灌木地活性有機(jī)碳質(zhì)量分?jǐn)?shù)顯著增加,土壤有機(jī)碳活性成分積累量提高,土壤碳庫變化波動(dòng)最大,不過其中的機(jī)理有待于進(jìn)一步探索。另外,在活性有機(jī)碳可以用來預(yù)測(cè)土壤碳庫變化的基礎(chǔ)上,證實(shí)土壤大團(tuán)聚體中的高活性有機(jī)碳可以作為未來預(yù)測(cè)土壤碳庫變化的更佳指標(biāo)。
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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(xiàng)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(diǎn)部署項(xiàng)目“黃土丘陵區(qū)集約經(jīng)營型流域生態(tài)經(jīng)濟(jì)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(jiǎn)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
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