朱麗琴, 黃榮珍, 黃國(guó)敏, 黃詩(shī)華, 易志強(qiáng), 張文鋒, 賈龍, 王赫, 劉勇
(南昌工程學(xué)院,江西省退化生態(tài)系統(tǒng)修復(fù)與流域生態(tài)水文重點(diǎn)實(shí)驗(yàn)室,330099,南昌)
不同人工恢復(fù)林對(duì)退化紅壤團(tuán)聚體組成及其有機(jī)碳的影響
朱麗琴, 黃榮珍?, 黃國(guó)敏, 黃詩(shī)華, 易志強(qiáng), 張文鋒, 賈龍, 王赫, 劉勇
(南昌工程學(xué)院,江西省退化生態(tài)系統(tǒng)修復(fù)與流域生態(tài)水文重點(diǎn)實(shí)驗(yàn)室,330099,南昌)
研究土壤團(tuán)聚體的組成及其有機(jī)碳的分布,有助于從微觀角度理解土壤結(jié)構(gòu)與功能的相互作用。采用干篩法和濕篩法,研究南方紅壤退化地實(shí)施人工恢復(fù)30年后, 馬尾松與闊葉復(fù)層林(PB)、木荷+馬尾松混交林(SP)和闊葉林(BF) 3種典型林分在0~60 cm土層的團(tuán)聚體組成及其有機(jī)碳分布特征,分析土壤團(tuán)聚體有機(jī)碳與總有機(jī)碳相關(guān)關(guān)系。結(jié)果表明:各恢復(fù)林分土壤機(jī)械穩(wěn)定性團(tuán)聚體質(zhì)量分?jǐn)?shù),以>2 mm粒徑所占比例最大(均在60%以上),而在水穩(wěn)性團(tuán)聚體中,以<0.05 mm粒徑占優(yōu)勢(shì)。不同林分土壤團(tuán)聚體結(jié)構(gòu)破壞率順序依次為BF(53.38%~84.27%)>SP(52.22%~70.86%)>PB(22.70%~47.83%)。機(jī)械穩(wěn)定性和水穩(wěn)性團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)均以PB最高,隨著土層深度的增加,各林分土壤團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)呈下降趨勢(shì)。水穩(wěn)性大團(tuán)聚體(>0.25 mm粒徑)有機(jī)碳質(zhì)量分?jǐn)?shù)總體高于相應(yīng)土層的總有機(jī)碳質(zhì)量分?jǐn)?shù),而微團(tuán)聚體的(<0.25 mm粒徑)則低于后者,說(shuō)明有機(jī)碳對(duì)于大團(tuán)聚體的形成和水穩(wěn)性具有積極作用。土壤團(tuán)聚體有機(jī)碳與總有機(jī)碳的相關(guān)關(guān)系分析表明,土壤團(tuán)聚體有機(jī)碳的增加,對(duì)總有機(jī)碳的積累具有正面影響。保留密度大、灌木(草)層蓋度高的馬尾松與闊葉復(fù)層林土壤團(tuán)聚體的數(shù)量和質(zhì)量更高;因此,在紅壤侵蝕退化地森林恢復(fù)初期,可通過(guò)適當(dāng)密植、增加林下灌草覆蓋等措施,增加有機(jī)碳的輸入,促進(jìn)團(tuán)聚體的形成和穩(wěn)定,從而加速了退化土地的土壤結(jié)構(gòu)改善和功能恢復(fù)。該研究可為南方嚴(yán)重紅壤退化地生態(tài)恢復(fù)中的林分類(lèi)型選擇和優(yōu)化配置提供科學(xué)依據(jù)。
人工恢復(fù)林; 機(jī)械穩(wěn)定性團(tuán)聚體; 水穩(wěn)性團(tuán)聚體; 有機(jī)碳; 紅壤
我國(guó)南方紅壤丘陵區(qū)由于山高坡陡、降水集中,生態(tài)環(huán)境較為脆弱,對(duì)人類(lèi)活動(dòng)的響應(yīng)極為敏感。該區(qū)原生植被的破壞,造成水土流失嚴(yán)重,有機(jī)質(zhì)大量流失,土地不斷退化,使其成為不毛之地的“紅色沙漠”;而土壤退化中,最重要的一個(gè)過(guò)程是土壤結(jié)構(gòu)的退化,其顯著特征表現(xiàn)為土壤團(tuán)聚體比例的失調(diào)和穩(wěn)定性的下降[1]。土壤團(tuán)聚體實(shí)質(zhì)上是土壤有機(jī)質(zhì)、鐵鋁氧化物和硅酸鹽等有機(jī)無(wú)機(jī)體,通過(guò)靜電引力、氫鍵和羥基等官能團(tuán)作用復(fù)合而成,這些有機(jī)無(wú)機(jī)體質(zhì)量分?jǐn)?shù)及作用機(jī)制,均會(huì)對(duì)團(tuán)聚體的穩(wěn)定性產(chǎn)生影響[2]。其中,作為土壤團(tuán)聚體的主要膠結(jié)劑,有機(jī)質(zhì)在土壤結(jié)構(gòu)遭到破壞時(shí),將因失去大團(tuán)聚體的保護(hù)而暴露于空氣中,從而增加了微生物與有機(jī)碳的接觸機(jī)會(huì),及對(duì)后者的分解礦化,導(dǎo)致有機(jī)碳質(zhì)量分?jǐn)?shù)降低、膠結(jié)物質(zhì)減少,大團(tuán)聚體穩(wěn)定性隨之下降,有機(jī)質(zhì)在大團(tuán)聚體的形成與穩(wěn)定性方面,展現(xiàn)出極其重要的作用。
千煙洲作為我國(guó)紅壤丘陵區(qū)較早開(kāi)展退化生態(tài)系統(tǒng)恢復(fù)的典型,經(jīng)過(guò)30年的治理和恢復(fù),森林覆蓋率有大幅度的提升,水土流失得到有效控制。隨著植被的恢復(fù),生物歸還量增多,有機(jī)碳輸入增加,有助于有機(jī)聚合體對(duì)礦質(zhì)土粒的連接、植物根系與菌絲對(duì)土粒的纏繞,從而促進(jìn)土壤團(tuán)聚體的形成,提高團(tuán)聚體有機(jī)碳的分配比例,進(jìn)而改善土壤結(jié)構(gòu),增強(qiáng)土壤抗侵蝕能力[3]。謝錦升等[4]研究發(fā)現(xiàn),裸地植被恢復(fù)后,表層土壤大團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)占總有機(jī)碳的比例從15%提高到32%~42%。A.F.WICK等[5]研究也證實(shí),植被的恢復(fù)能夠提高土壤有機(jī)碳質(zhì)量分?jǐn)?shù)。目前,國(guó)內(nèi)外學(xué)者有關(guān)土壤團(tuán)聚體的研究,多集中在不同恢復(fù)年限、土地利用方式和土壤施肥等方面[6-8],而對(duì)于紅壤退化地森林恢復(fù)后,土壤團(tuán)聚體的響應(yīng)和演變探討不多,尤其是團(tuán)聚體穩(wěn)定性對(duì)土壤結(jié)構(gòu)影響的研究還不夠深入;因此,本文以南方紅壤退化地典型人工恢復(fù)林(馬尾松與闊葉復(fù)層林、木荷×馬尾松混交林和闊葉林)為研究對(duì)象,研究土壤團(tuán)聚體及其有機(jī)碳的分布特征,分析土壤團(tuán)聚體有機(jī)碳與總有機(jī)碳相關(guān)關(guān)系,試圖從土壤有機(jī)碳-土壤結(jié)構(gòu)-土壤穩(wěn)定性-土壤回復(fù)力角度,理解土壤結(jié)構(gòu)與功能的相互作用,為南方嚴(yán)重紅壤退化地生態(tài)恢復(fù)中的林分類(lèi)型選擇和優(yōu)化配置提供科學(xué)依據(jù)。
中國(guó)科學(xué)院江西省千煙洲紅壤丘陵綜合開(kāi)發(fā)試驗(yàn)站 (E 115°04′13″,N 26°44′48″),屬典型紅壤丘陵地貌,海拔100 m左右,相對(duì)高差20~50 m。該區(qū)年均氣溫17.9 ℃,年均降水量1 489 mm,年均日照時(shí)間1 406 h,無(wú)霜期323 d,屬亞熱帶濕潤(rùn)季風(fēng)氣候。站內(nèi)原生植被以中亞熱帶常綠闊葉林為主,由于長(zhǎng)期開(kāi)發(fā)和破壞,其原生植被遭到嚴(yán)重破壞,在1984年建站初期,已退化為灌草叢,且多處出現(xiàn)不同程度的水土流失。實(shí)驗(yàn)地現(xiàn)狀植被以人工林為主,土壤類(lèi)型為紅砂巖發(fā)育的紅壤。各實(shí)驗(yàn)地基本情況詳見(jiàn)表1。
表1 實(shí)驗(yàn)地概況
注:PB:馬尾松與闊葉復(fù)層林;SP:木荷+馬尾松混交林;BF:闊葉林。以下類(lèi)同。Note:PB:Pinusmassoniana-multiple layer broadleaf forest; SP:Schimasuperba-Pinusmassonianamixed forest;BP:broadleaf forest. The same below.
馬尾松與闊葉復(fù)層林(PB):主要喬木樹(shù)種為馬尾松(Pinusmassoniana)、楓香(Liquidambarformosana)、白櫟(Quercusfabri)、黃瑞木(Adinandramillettii)和三角槭(Acerbuergerianum)。林下植被主要有烏飯樹(shù)(Vacciniumbracteatum)、三葉赤楠(Syzygiumgrijsii)、秤星樹(shù)(Llexasprella)、淡竹葉(LophatherumgracileBrongn)、檵木(Loropetalunchinense)、菝葜(SmilacischinaeRhizoma)、芒萁(Dicranopterisdichotoma)和狗脊蕨(Woodwardiajaponica)等。
木荷+馬尾松混交林(SP):主要喬木樹(shù)種為木荷(Schimasuperba)和馬尾松。林下植被主要有青岡櫟(Cyclobalanopsisglauca)、黃瑞木、檵木、白櫟、六月雪(Serissajaponica)、含笑(Micheliafigo)、麥冬(Ophiopogonjaponicus)、淡竹葉、海金沙(Lygodiumjaponicum)、金銀花(Lonicerajaponica)、鐵線蕨(Adiantumcapillus-veneris)、烏蕨(StenolomachusanumChing)、鱗毛蕨(Dryopteris)、狗脊蕨、羊角藤(MorindaumbellataLinn)等。
闊葉林(BF):主要喬木樹(shù)種為鵝掌楸(Liriodendronchinense)、厚樸(Magnoliaofficinalis)、樟樹(shù)(Cinnamomumcamphora)、楓香、青岡櫟。林下植被主要有黃瑞木、石斑木(Rhaphiolepisindica)、香椿(Toonasinensis)、三葉赤楠、秤星樹(shù)、深山含笑(Micheliamaudiae)、桂花(Osmanthusfragrans)、檵木、朱砂根(Ardisiacrenata)、麥冬、淡竹葉、芒萁、狗脊蕨、鐵線蕨和鱗毛蕨等。
2.1 土壤樣品采集
2014年4月,在PB、SP和BF 3種人工恢復(fù)林中,分別設(shè)立3塊20 m×20 m固定標(biāo)準(zhǔn)地,共9塊。每個(gè)標(biāo)準(zhǔn)地內(nèi)按“S”型布設(shè)5個(gè)取樣點(diǎn),在每個(gè)取樣點(diǎn)處挖土壤剖面,用不銹鋼飯盒按0~10、10~20、20~40和40~60 cm 4個(gè)層次分層取樣,用來(lái)測(cè)定土壤團(tuán)聚體相關(guān)指標(biāo)。另用自封袋分層取樣,用來(lái)測(cè)定土壤總有機(jī)碳。
2.2 測(cè)定方法
根據(jù)李輝信等[9]方法(干篩法),對(duì)土壤機(jī)械穩(wěn)定性團(tuán)聚體測(cè)定稍做修改:將飯盒采回的原狀土,在室內(nèi)用手沿著土壤自然結(jié)構(gòu)脆弱帶,輕輕掰成直徑約為1 cm的小塊,放于室溫條件下風(fēng)干;按照四分法稱(chēng)取200 g風(fēng)干后的土壤樣品,用震擊式標(biāo)準(zhǔn)振篩機(jī)篩分5 min(上下振幅5 mm,頻率147次/min),分離出>2、1~2、0.5~1、0.25~0.5、0.05~0.25和<0.05 mm的土壤團(tuán)聚體。土壤水穩(wěn)性團(tuán)聚體,根據(jù)E.T.Elliott[10]方法(濕篩法)稍做修改:將干篩得到的各粒徑團(tuán)聚體,按照各自比例組合成100 g混合土樣,放在頂端2 mm的篩子上,置于水中浸泡5 min,用團(tuán)聚體篩分儀篩分30 min(上下振幅3 cm,頻率30次/min),分離出上述相同粒徑的團(tuán)聚體,置于60 ℃下烘干,稱(chēng)量(扣除沙子的總量)。土壤總有機(jī)碳和團(tuán)聚體有機(jī)碳采用K2Cr2O7氧化—外加熱法測(cè)定。
2.3 數(shù)據(jù)計(jì)算與處理
試驗(yàn)數(shù)據(jù)為各重復(fù)實(shí)測(cè)值的平均值,采用Microsoft Excel 2003進(jìn)行數(shù)據(jù)統(tǒng)計(jì)、分析及制圖,采用SPSS 19.0進(jìn)行方差和相關(guān)分析,顯著性水平設(shè)定為0.05。
3.1 不同人工恢復(fù)林土壤團(tuán)聚體分布
由表2可知,不同林分機(jī)械穩(wěn)定性團(tuán)聚體質(zhì)量分?jǐn)?shù),以>2 mm粒徑所占比例最大,均>60%,最高達(dá)80.29%。表明該粒徑團(tuán)聚體在整個(gè)團(tuán)聚體中占主導(dǎo)地位,這與李瑋等[6]研究的不同植茶年限土壤,以>2 mm粒徑團(tuán)聚體為主的結(jié)果一致;同時(shí),也說(shuō)明森林植被恢復(fù),通過(guò)增加有機(jī)碳輸入,促進(jìn)機(jī)械穩(wěn)定性團(tuán)聚體形成,大粒徑團(tuán)聚體效果更好。郭曼等[11]也發(fā)現(xiàn),隨著植被演替,土壤團(tuán)聚體由小粒徑向大粒徑轉(zhuǎn)變。從不同土層來(lái)看,0~10 cm土層>0.25 mm的團(tuán)聚體(大團(tuán)聚體)質(zhì)量分?jǐn)?shù),在不同林分中表現(xiàn)為BF(95.31%)>PB(93.66%)>SP(89.77%),而<0.25 mm的團(tuán)聚體(微團(tuán)聚體)質(zhì)量分?jǐn)?shù),則表現(xiàn)為SP(10.23%)>PB(6.35%)>BF(4.69%)。表明SP土壤團(tuán)聚體機(jī)械穩(wěn)定性相對(duì)較差,在強(qiáng)降雨時(shí),土壤易受到雨滴擊濺破壞而分散、堵塞土壤孔隙,減小水分下滲速率,形成地表徑流,造成水土流失。同樣的規(guī)律亦出現(xiàn)在其他土層。
水穩(wěn)性團(tuán)聚體數(shù)量的多少可表征土壤的結(jié)構(gòu)變化。在0~10、10~20和20~40 cm土層,PB中>2 mm的水穩(wěn)性團(tuán)聚體質(zhì)量分?jǐn)?shù)顯著高于其他2種林分,分別是SP和BF的3.09~5.84倍和1.75~4.21倍。與機(jī)械穩(wěn)定性團(tuán)聚體結(jié)果有所差異:SP和BF水穩(wěn)性團(tuán)聚體質(zhì)量分?jǐn)?shù)以<0.05 mm粒徑所占比例最大,分別為37.04%~51.48%和27.01%~44.41%;PB中0~10和10~20 cm土層,仍以>2 mm的團(tuán)聚體所占比例較大,而在20~40和40~60 cm土層,則以<0.05 mm的團(tuán)聚體占優(yōu)勢(shì)。說(shuō)明土壤團(tuán)聚體在遭水濕潤(rùn)時(shí),首先受影響的是大粒徑團(tuán)聚體,其對(duì)人為干擾或外界環(huán)境變化更敏感。小粒徑團(tuán)聚體因孔隙較小、容積密度較大、彎曲程度更大,使小粒徑團(tuán)聚體內(nèi)聚力要大于大粒徑團(tuán)聚體,從而致使大粒徑團(tuán)聚體穩(wěn)定性不如小粒徑團(tuán)聚體[12];另外,小粒徑團(tuán)聚體較穩(wěn)定是由于某些聚合物及芳香腐殖質(zhì)等持久介質(zhì)的作用,也存在多糖等瞬時(shí)介質(zhì)的作用,而大粒徑團(tuán)聚體則主要通過(guò)瞬時(shí)介質(zhì)及菌絲等暫時(shí)介質(zhì)膠結(jié)而成。>0.25 mm的水穩(wěn)性團(tuán)聚體的數(shù)量是衡量土壤抗侵蝕能力強(qiáng)弱的重要指標(biāo),不同林分土壤水穩(wěn)性大團(tuán)聚體質(zhì)量分?jǐn)?shù)在0~10、10~20和20~40 cm土層,均表現(xiàn)為PB>BF>SP,可能是由于PB凋落物中,針葉所含的樹(shù)脂等物質(zhì)是疏水性的,容易阻礙水的浸潤(rùn)速度,使團(tuán)聚體內(nèi)部空氣能夠緩慢釋放,從而增強(qiáng)團(tuán)聚體抵抗被破壞的能力[13];而在40~60 cm土層,3種林分水穩(wěn)性大團(tuán)聚體質(zhì)量分?jǐn)?shù)差異不顯著,變化范圍為48.80%~51.64%。
3.2 不同人工恢復(fù)林土壤團(tuán)聚體穩(wěn)定性
穩(wěn)定的團(tuán)聚體結(jié)構(gòu),對(duì)于改良土壤肥力、提高土壤抗侵蝕能力具有重要作用。團(tuán)聚體結(jié)構(gòu)破壞率是評(píng)價(jià)土壤團(tuán)聚體穩(wěn)定性的一項(xiàng)重要指標(biāo),破壞率越小,土壤的穩(wěn)定性則越高。圖1表明,不同林分土壤團(tuán)聚體結(jié)構(gòu)破壞率,以PB最小(22.70%~47.83%),SP的破壞率是其1.36~3.01倍,BF是其1.76~3.01倍,可能有機(jī)碳對(duì)團(tuán)聚體穩(wěn)定性的作用,不僅與有機(jī)碳的數(shù)量有關(guān),還受有機(jī)碳質(zhì)量的影響,不同數(shù)量和質(zhì)量的碳源,對(duì)團(tuán)聚體的穩(wěn)定性同時(shí)起作用,而前期研究發(fā)現(xiàn),BF中土壤有機(jī)碳是以活性有機(jī)碳為主,可正向激發(fā)土壤中已有有機(jī)碳活性[14],使其被氧化和礦化的潛力更大,導(dǎo)致土壤穩(wěn)定性相對(duì)較差。筆者研究表明,不同恢復(fù)林分表層土壤團(tuán)聚體結(jié)構(gòu)破壞率為22.70%~53.38%,遠(yuǎn)大于劉曉利等[15]在中科院紅壤生態(tài)實(shí)驗(yàn)站林地表層研究的7.16%~18.2%。其主要原因?yàn)樵撛囼?yàn)地在恢復(fù)前,原生植被被完全破壞,水土流失嚴(yán)重,表土沖刷殆盡,有機(jī)質(zhì)大量流失。經(jīng)過(guò)30年的恢復(fù),雖然森林覆蓋率有了大幅度提高,水土流失得到有效控制,土壤結(jié)構(gòu)得到一定程度的改善;但與侵蝕退化前的原生植被(中亞熱帶常綠闊葉林)下的土壤相比,其土壤結(jié)構(gòu)和功能仍然存在巨大差距,要達(dá)到亞熱帶地帶性森林的土壤功能,還需要一個(gè)漫長(zhǎng)的過(guò)程,需要后續(xù)進(jìn)一步管護(hù)。
表2 不同人工恢復(fù)林土壤團(tuán)聚體的分布
注:表中數(shù)據(jù)表示平均值±標(biāo)準(zhǔn)差,不同小寫(xiě)字母表示不同人工恢復(fù)林間差異達(dá)顯著水平(P<0.05)。下同。Note: The datas in the table are mean ± standard deviation, and different lowercase letters mean significant at 5% lever among different artificially restored forests. The same below.
圖1 不同人工恢復(fù)林團(tuán)聚體結(jié)構(gòu)破環(huán)率Fig.1 Broken rate of soil aggregate structure in different artificially restored forests
PB和BF土壤團(tuán)聚體結(jié)構(gòu)破壞率隨土層的加深逐漸增大,而SP則在10~20 cm土層,達(dá)到70.86%,隨后逐漸減小。土壤團(tuán)聚體水穩(wěn)性下降,可能與有機(jī)碳質(zhì)量分?jǐn)?shù)下降有關(guān):因?yàn)橛袡C(jī)碳能夠增強(qiáng)土壤團(tuán)聚體間的黏結(jié)力及抗張強(qiáng)度,減緩水分濕潤(rùn)速率,提高團(tuán)聚體穩(wěn)定性;而有機(jī)碳質(zhì)量分?jǐn)?shù)的下降,會(huì)加速水穩(wěn)性團(tuán)聚體間膠結(jié)物的分解,使大團(tuán)聚體分解為小團(tuán)聚體,導(dǎo)致對(duì)有機(jī)碳的物理保護(hù)作用減弱,進(jìn)而加劇有機(jī)碳的礦化,降低團(tuán)聚體的穩(wěn)定性。但在有機(jī)碳質(zhì)量分?jǐn)?shù)相對(duì)偏低的土壤,弱結(jié)晶氧化鐵質(zhì)量分?jǐn)?shù)對(duì)團(tuán)聚體的穩(wěn)定性更重要[16]。R.Spaccini等[17]指出,土壤質(zhì)地對(duì)土壤物理性質(zhì)和結(jié)構(gòu)也能產(chǎn)生明顯影響,黏粒質(zhì)量分?jǐn)?shù)高的土壤,其大團(tuán)聚體數(shù)量及穩(wěn)定性更高。從團(tuán)聚體結(jié)構(gòu)破壞率考慮,PB土壤穩(wěn)定性程度更好。
3.3 不同人工恢復(fù)林土壤團(tuán)聚體有機(jī)碳分布
團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)是土壤有機(jī)質(zhì)平衡及礦化速率的微觀表征[6]。由表3可知:在機(jī)械穩(wěn)定性團(tuán)聚體中,0~10 cm土層,土壤團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)PB以0.05~0.25 mm、SP和BF以0.25~0.5 mm粒徑最高;PB土壤團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)顯著高于SP和BF,分別是SP和BF的1.17~1.36倍和1.25~1.56倍,而SP和BF差異不顯著。10~20 cm土層,土壤團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)PB以0.05~0.25 mm、SP以<0.05 mm、BF以0.25~0.5 mm粒徑最高;PB團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)依然顯著高于SP和BF,比SP高出30.84%~76.36%,比BF高出31.94%~58.08%。20~40 cm土層,土壤團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)PB和BF以<0.05 mm、SP以0.25~0.5 mm粒徑最高;不同林分土壤團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)大小依次為PB>SP>BF。40~60 cm土層,PB、SP和BF團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)在不同粒徑中,分別為6.29~7.38、5.87~7.85和6.11~7.65 g/kg,各林分間團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)差異不顯著。各林分機(jī)械穩(wěn)定性團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)隨土層的加深而降低,這與總有機(jī)碳在垂直剖面的變化趨勢(shì)一致,且團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)在各粒徑均總體高于相應(yīng)土層的總有機(jī)碳質(zhì)量分?jǐn)?shù)。
在水穩(wěn)性團(tuán)聚體中,0~10 cm土層,土壤團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)PB以1~2 mm、SP以0.5~1 mm、BF以>2 mm粒徑最高;PB土壤團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)顯著高于SP和BF,分別是SP和BF的1.17~1.40倍和1.31~1.66倍。10~20 cm土層,土壤團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)PB和BF以1~2 mm、SP以>2 mm粒徑最高;PB土壤團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)依然顯著高于SP和BF,分別比SP和BF高出35.0%~59.66%和40.77%~68.78%,而SP和BF差異不顯著。20~40和40~60 cm土層,土壤水穩(wěn)性團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)分別以1~2和>2 mm粒徑最高;不同林分土壤團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)大小均依次為PB>SP>BF。各林分土壤團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)在相鄰粒徑間較為接近,如>2與1~2 mm、0.5~1與0.25~0.5 mm、0.05~0.25與<0.05 mm粒徑間的差值,僅分別為0.06~0.19、0.14~0.67和0.16~0.48 g/kg。
表3 不同人工恢復(fù)林土壤團(tuán)聚體有機(jī)碳的分布
從土壤垂直剖面上看,水穩(wěn)性團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)隨土層的加深而降低,與機(jī)械穩(wěn)定性團(tuán)聚體結(jié)果一致。這是因?yàn)榈蚵湮锝?jīng)微生物分解后,形成的有機(jī)質(zhì)首先進(jìn)入表層土壤,為微生物生長(zhǎng)繁殖提供了大量能源,從而促進(jìn)土壤生物(包括根系、菌類(lèi)和土壤動(dòng)物等)的活性,有利于增強(qiáng)團(tuán)聚體內(nèi)部黏結(jié)力,而形成微粒有機(jī)質(zhì)[18],而下層土壤受生物的影響小,其有機(jī)碳來(lái)源主要是表層腐殖質(zhì)的淋溶下滲、植被根系及其分泌物等,故有機(jī)碳質(zhì)量分?jǐn)?shù)降低。與總有機(jī)碳相比,除PB>2和1~2 mm粒徑外,3種林分水穩(wěn)性團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)在0~10 cm土層,均低于總有機(jī)碳質(zhì)量分?jǐn)?shù);在其他土層,各林分基本呈現(xiàn)出水穩(wěn)性大團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)高于總有機(jī)碳質(zhì)量分?jǐn)?shù),而微團(tuán)聚體的則低于后者,說(shuō)明有機(jī)碳對(duì)于水穩(wěn)性大團(tuán)聚體的形成具有積極作用,而微團(tuán)聚體因黏粒對(duì)有機(jī)碳的物理保護(hù),或鐵鋁氧化物膠體對(duì)有機(jī)碳的化學(xué)保護(hù),成為有機(jī)碳長(zhǎng)期固存的場(chǎng)所[19]。閆靖華等[20]研究也表明,連續(xù)人工種植后,土壤增碳顯著提高了水穩(wěn)性大團(tuán)聚體中有機(jī)碳的質(zhì)量分?jǐn)?shù)。原因在于微團(tuán)聚體主要是通過(guò)有機(jī)質(zhì)與黏?;蚺c陽(yáng)離子相互膠結(jié)而成,而大團(tuán)聚體又可通過(guò)微團(tuán)聚體與自身或與周?chē)W酉嗷ツz結(jié)而成;因此,大團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)更高[4]。
無(wú)論機(jī)械穩(wěn)定性還是水穩(wěn)性團(tuán)聚體,其有機(jī)碳質(zhì)量分?jǐn)?shù)均以馬尾松為優(yōu)勢(shì)樹(shù)種的PB最高。與大多數(shù)研究顯示的針葉林土壤有機(jī)碳質(zhì)量分?jǐn)?shù)一般要低于闊葉林和混交林的結(jié)果不同[21],主要是因?yàn)橄鄬?duì)于SP,PB保留密度更高,其灌木層蓋度是SP的4倍(表1),且林下植被地上生物量和地下生物量分別是SP的1.73和1.23倍。已有研究表明,林分密度或植被蓋度的不同,會(huì)對(duì)凋落物量產(chǎn)生差異,從而對(duì)土壤有機(jī)碳具有顯著影響[22]。覃勇榮等[23]研究也發(fā)現(xiàn):土壤有機(jī)碳與植被蓋度存在顯著的正相關(guān)關(guān)系,相對(duì)于PB和BF,兩者林下植被地上和地下生物量數(shù)值相近;但PB保留密度卻是BF的2.11倍,且凋落物量是其1.46倍,大量凋落物進(jìn)入土壤,為微生物提供充足碳源,而微生物的生長(zhǎng)有利于提高土壤酶的活性,進(jìn)一步促進(jìn)有機(jī)碳的分解和轉(zhuǎn)化,使土壤有機(jī)碳降解為活性小分子有機(jī)碳,直接被植物根系吸收利用,或轉(zhuǎn)化成腐殖質(zhì),形成團(tuán)聚體[24]。從表3還可看出,機(jī)械穩(wěn)定性團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)大部分高于水穩(wěn)性團(tuán)聚體,這可能與濕篩使水溶性有機(jī)碳流失有關(guān)。
3.4 土壤團(tuán)聚體有機(jī)碳與總有機(jī)碳的關(guān)系
由表4可知:0~10 cm土層,土壤機(jī)械穩(wěn)定性和水穩(wěn)性團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)在各粒徑上,均與總有機(jī)碳質(zhì)量分?jǐn)?shù)呈顯著正相關(guān),尤其在機(jī)械穩(wěn)定性團(tuán)聚體的0.05~0.25 和<0.05 mm粒徑、水穩(wěn)性團(tuán)聚體的1~2 mm粒徑上,呈極顯著正相關(guān),Pearson相關(guān)系數(shù)分別為0.528、0.527和0.428;10~20 cm土層,兩者均與總有機(jī)碳質(zhì)量分?jǐn)?shù)呈極顯著正相關(guān),相關(guān)系數(shù)分別為0.478~0.714和0.529~0.704;20~40 cm土層,亦呈顯著或極顯著正相關(guān);40~60 cm土層,僅機(jī)械穩(wěn)定性團(tuán)聚體的1~2和<0.05 mm粒徑、水穩(wěn)性團(tuán)聚體的0.25~0.5 mm粒徑有機(jī)碳質(zhì)量分?jǐn)?shù),與總有機(jī)碳質(zhì)量分?jǐn)?shù)呈顯著正相關(guān),而其他粒徑上相關(guān)性不顯著。結(jié)果表明,各土層機(jī)械穩(wěn)定性和水穩(wěn)性團(tuán)聚體有機(jī)碳的增加,均對(duì)總有機(jī)碳的積累有不同程度的正面影響。邱陸旸等[25]研究也證明了團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)與總有機(jī)碳質(zhì)量分?jǐn)?shù)顯著相關(guān),表明團(tuán)聚體的形成與有機(jī)質(zhì)的膠結(jié)作用關(guān)系密切。
紅壤侵蝕退化地經(jīng)過(guò)30年的森林恢復(fù),雖然喬木層林木的生長(zhǎng)逐漸趨于成熟,但土壤團(tuán)聚體穩(wěn)定性仍然較差,土壤團(tuán)聚過(guò)程相對(duì)緩慢,要達(dá)到亞熱帶地帶性森林的土壤結(jié)構(gòu)和質(zhì)量,還需要一個(gè)漫長(zhǎng)的過(guò)程,需要加強(qiáng)后續(xù)的管理和維護(hù)。馬尾松與闊葉復(fù)層林因保留密度大、灌木(草)層蓋度高,表現(xiàn)出土壤團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)更高、團(tuán)聚體結(jié)構(gòu)破壞率更?。灰虼耍诩t壤侵蝕退化地森林恢復(fù)初期,可通過(guò)適當(dāng)密植和增加林下灌草覆蓋等措施,增加有機(jī)碳的輸入,以促進(jìn)團(tuán)聚體的形成和穩(wěn)定,加速退化土地土壤的結(jié)構(gòu)改善和功能恢復(fù)。
表4不同人工恢復(fù)林土壤團(tuán)聚體有機(jī)碳質(zhì)量分?jǐn)?shù)與總有機(jī)碳質(zhì)量分?jǐn)?shù)的相關(guān)關(guān)系
Tab.4Correlation between the mass fractions of soil aggregate organic carbon and soil total organic carbon in different artificially restored forests
團(tuán)聚體粒徑Aggregateparticlesize/mm0~10cm10~20cm20~40cm40~60cm干篩Drysieve濕篩Wetsieve干篩Drysieve濕篩Wetsieve干篩Drysieve濕篩Wetsieve干篩Drysieve濕篩Wetsieve>20.400*0.383*0.649**0.643**0.523**0.606**0.2770.3121~20.409*0.428**0.714**0.704**0.405*0.480**0.365*0.2780.5~10.391*0.384*0.601**0.609**0.513**0.360*0.1720.2550.25~0.50.413*0.387*0.478**0.558**0.511**0.338*0.2840.359*0.05~0.250.528**0.375*0.636**0.539**0.573**0.3220.3160.282<0.050.527**0.1220.692**0.529**0.470**0.333*0.349*0.324
注:*和**分別表示在0.05和0.01水平上(雙側(cè))顯著相關(guān)。Note: * and ** in the table indicate significance level of 0.05 and 0.01, respectively.
[1] 朱紅球,謝振華,李紅.衡陽(yáng)紫色土丘陵坡地土地退化/恢復(fù)過(guò)程中土壤水穩(wěn)性團(tuán)聚體的動(dòng)態(tài)變化[J].中國(guó)農(nóng)學(xué)通報(bào),2013,29(35):289.
ZHU Hongqiu, XIE Zhenhua, LI Hong. Dynamic change of water stable aggregate in land degradation/restoration process on sloping-land with purple soils in Hengyang [J]. Chinese Agricultural Science Bulletin,2013,29(35):289.
[2] 王小紅,楊智杰,劉小飛,等.天然林轉(zhuǎn)換成人工林對(duì)土壤團(tuán)聚體穩(wěn)定性及有機(jī)碳分布的影響[J].水土保持學(xué)報(bào),2014,28(6):177.
WANG Xiaohong,YANG Zhijie,LIU Xiaofei, et al. Effects of natural forest converted to plantations on soil organic carbon distribution and stability of aggregates in middle-subtropics of China [J].Journal of Soil and Water Conservation,2014,28(6):177.
[3] 藍(lán)良就,張野,黃炎和,等.退化花崗巖植被恢復(fù)對(duì)團(tuán)聚體及其有機(jī)碳的影響[J].水土保持學(xué)報(bào),2012,26(1):190.
LAN Liangjiu,ZHANG Ye,HUANG Yanhe, et al. Soil water-stable aggregates and organic carbon affected by forestland restoration of degraded granite[J]. Journal of Soil and Water Conservation,2012,26(1):190.
[4] 謝錦升,楊玉盛,陳光水,等.植被恢復(fù)對(duì)退化紅壤團(tuán)聚體穩(wěn)定性及碳分布的影響[J].生態(tài)學(xué)報(bào),2008,28(2):702.
XIE Jinsheng, YANG Yusheng, CHEN Guangshui, et al. Effects of vegetation restoration on water stability and organic carbon distribution in aggregates of degraded red soil in subtropics of China [J]. Acta Ecologica Sinica,2008,28(2):702.
[5] WICK A F, INGRAM L J, STAHL P D. Aggregate and organic matter dynamics in reclaimed soils as indicated by stable carbon isotopes[J]. Soil Biology and Biochemistry,2009,41(2):201.
[6] 李瑋,鄭子成,李廷軒,等.不同植茶年限土壤團(tuán)聚體及其有機(jī)碳分布特征[J].生態(tài)學(xué)報(bào),2014,34 (21):6326.
LI Wei, ZHENG Zicheng, LI Tingxuan, et al. Distribution characteristics of soil aggregates and its organic carbon in different tea plantation age[J].Acta Ecologica Sinica,2014,34 (21):6326.
[7] 羅友進(jìn),魏朝富,李渝,等.土地利用對(duì)石漠化地區(qū)土壤團(tuán)聚體有機(jī)碳分布及保護(hù)的影響[J].生態(tài)學(xué)報(bào),2013,44(6):1356.
LUO Youjin, WEI Chaofu, LI Yu, et al. Effects of land use on distribution and protection of organic carbon in soil aggregates in karst rocky desertification area [J]. Acta Ecologica Sinica,2013,44(6):1356.
[8] 王曉娟,賈志寬,梁連友,等.旱地施有機(jī)肥對(duì)土壤有機(jī)質(zhì)和水穩(wěn)性團(tuán)聚體的影響[J].應(yīng)用生態(tài)學(xué)報(bào),2012,23(1):159.
WANG Xiaojuan, JIA Zhikuan, LIANG Lianyou, et al. Effects of organic manure application on dry land soil organic matter and water stable aggregates [J]. Chinese Journal of Applied Ecology,2012,23(1):159.
[9] 李輝信,袁穎紅,黃欠如,等.不同施肥處理對(duì)紅壤水稻土團(tuán)聚體有機(jī)碳分布的影響[J].土壤學(xué)報(bào),2006,3(42):422.
LI Huixin, YUAN Yinghong, HUANG Qianru,et al.Effects of fertilization on soil organic carbon distribution in various aggregates of red paddy soil[J]. Acta Pedologica Sinica,2006,3(42):422.
[10] ELLIOTT E T. Aggregate structure and carbon, nitrogen and phosphorus in native and cultivated soils [J].Soil Science Society of America Journal,1986,50(3):627.
[11] 郭曼, 鄭粉莉,安韶山,等. 應(yīng)用Le Bissonnais法研究黃土丘陵區(qū)土壤團(tuán)聚體穩(wěn)定性[J].中國(guó)水土保持科學(xué),2010,8(2):68.
GUO Man, ZHENG Fenli, AN Shaoshan, et al. Application of Le Bissonnais method to study soil aggregate stability in the Hilly-gully region[J].Science of Soil and Water Conservation,2010,8(2):68.
[12] 楊建國(guó),安韶山,鄭粉莉.寧南山區(qū)植被自然恢復(fù)中土壤團(tuán)聚體特征及其與土壤性質(zhì)關(guān)系[J].水土保持學(xué)報(bào),2006,20(1):72.
YANG Jianguo, AN Shaoshan, ZHENG Fenli. Characteristics of soil water stable aggregates and relationship with soil properties during vegetation rehabilitation in Ningxia loess hilly region [J]. Journal of Soil and Water Conservation,2006,20(1):72.
[13] WRIGHT A L, HONS F M. Carbon and nitrogen sequestration and soil aggregation under sorghum cropping sequences[J].Biology and Fertility Soils,2005,41(2): 95.
[14] ERKTANA, CECILLON L, GRAF F, et al. Increase in soil aggregate stability along a Mediterranean successional gradient in severely eroded gully bed ecosystems: combined effects of soil, root traits and plant community characteristics [J].Plant and Soil,2016,398(1): 121.
[15] 劉曉利,何園球,李成亮,等. 不同利用方式和肥力紅壤中水穩(wěn)性團(tuán)聚體分布及物理性質(zhì)特征[J].土壤學(xué)報(bào),2008,45(3):459.
LIU Xiaoli, HE Yuanqiu, LI Chengliang, et al. Distribution and physical properties of soil water-stable aggregates in red soils different in land soil fertility[J]. Acta Pedolologica Sinica, 2008,45(3):459.
[16] DUIKER S W, RHOTON F E, TORRENT J , et al. Iron(Hydr)oxide crystallinity effects on soil aggregation[J],Soil Science Society of America Journal,2003,67(2):606.
[17] SPACCINI R, PICCOLO A. Effects of field managements for soil organic matter stabilization on water-stable aggregate distribution and aggregate stability in three agricultural soils[J].Journal of Geochemical Exploration,2013,129(6):45.
[18] CAMBARDELLA C A, EILLIOTT E T. Particulate soil organic-matter changes across a grassland cultivation sequence [J]. Soil Science Society of America Journal, 1992,56(3):777.
[19] 徐文靜,叢耀輝,張玉玲,等.黑土區(qū)水稻土水穩(wěn)性團(tuán)聚體有機(jī)碳及其顆粒有機(jī)碳的分布特征[J].水土保持學(xué)報(bào),2016,30(4):210.
XU Wenjin, CONG Yaohui, ZHANG Yuling, et al. Distribution of organic carbon and particulate organic carbon in water-stable aggregates of paddy soil in black soil area[J]. Journal of Soil and Water Conservation,2016,30(4):210.
[20] 閆靖華,張鳳華,譚斌,等.不同恢復(fù)年限對(duì)土壤有機(jī)碳組分及團(tuán)聚體穩(wěn)定性的影響[J].土壤學(xué)報(bào),2013,50(6):1183.
YAN Jinghua, ZHANG Fenghua, TAN Bin, et al. Effects of reclamation history of deserted salinized farmlands on organic carbon composition and aggregate stability of the soils[J]. Acta Pedologica Sinica,2013,50(6):1183.
[21] 耿玉清,余新曉,岳永杰,等. 北京山地針葉林與闊葉林土壤活性有機(jī)碳庫(kù)的研究[J].北京林業(yè)大學(xué)學(xué)報(bào),2009,31(5):19.
GENG Yuqing, YU Xinxiao, YUE Yongjie, et al. Soil active organic carbon pool of coniferous and broadleaved forests in the mountainous area of Beijing [J]. Journal of Beijing Forestry University,2009,31(5):19.
[22] 張海東,于東升,王寧,等.植被恢復(fù)過(guò)程中侵蝕紅壤有機(jī)質(zhì)變化研究[J].土壤,2013,45(5):856.
ZHANG Haidong, YU Dongsheng, WANG Ning, et al. The change of soil organic matter under vegetation restoration on the eroded red soil[J].Soils,2013,45(5):856.
[23] 覃勇榮,王燕,劉旭輝,等.馬尾松對(duì)喀斯特石漠化地區(qū)土壤有機(jī)質(zhì)的影響[J].中國(guó)農(nóng)學(xué)通報(bào),2009,25(5):104.
QIN Yongrong, WANG Yan, LIU Xunhui, et al. Influence ofPinusmassonianaon soil organic matter content of the karst rocky desertification area,north-west of Guangxi province[J]. Chinese Agricultural Science Bulletin,2009,25(5):104.
[24] 馬瑞萍,安韶山,黨廷輝,等.黃土高原不同植物群落土壤團(tuán)聚體中有機(jī)碳和酶活性研究[J].土壤學(xué)報(bào),2014,51(1):104.
MA Ruiping, AN Shaoshan, DANG Tinghui, et al. Soil organic carbon and enzymatic activity in aggregates of soils under different plant communities in Hilly-gully regions of Loess Plateau[J].Acta Pedologica Sinica,2014,51(1):104.
[25] 邱陸旸,連琳琳,張麗萍,等.林下土壤水穩(wěn)性團(tuán)聚體特征及其影響因素研究[J].揚(yáng)州大學(xué)學(xué)報(bào),2016,37(2):74.
QIU Luyang, LIAN Linin, ZHANG Liping, et al. Study on the characteristics and influencing factors of water stable aggregates of forest soil[J].Journal of Yangzhou University,2016,37(2):74.
Effectsofdifferentartificiallyrestoredforestsonaggregatecompositionandorganiccarbonindegradedredsoil
ZHU Liqin, HUANG Rongzhen, HUANG Guomin, HUANG Shihua, YI Zhiqiang, ZHANG Wenfeng,JIA Long, WANG He, LIU Yong
(Jiangxi Key Laboratory of Degraded Ecosystem Restoration and Watershed Eco-hydrology, Nanchang Institute of Technology, 330099, Nanchang, China)
BackgroundResearch on the composition of aggregates and the distribution of organic carbon in soil will be beneficial for understanding the interaction between soil structure and function at the molecular scale.MethodsThree typical artificially restored forests after a 30-year restoration in degraded red soil were selected in this study, which werePinusmassoniana-multiple layer broadleaf forest (PB),Schimasuperba-Pinusmassonianamixed forest (SP), and broadleaf forest (BF), respectively. Methods of dry sieve and wet sieve were applied to investigate the composition of aggregates and the distribution of organic carbon in different layers (0-60 cm) of soil in each of the three forests, following which the correlations between soil aggregate organic carbon and soil total organic carbon were also determined.ResultsFor all three forests, particles larger than 2 mm in diameter constituted more than 60% of mechanical-stable aggregates in soil, while particles less than 0.05 mm in diameter made up the majority of water-stable aggregates in soil. The broken rate of aggregate structure in the three forests ranked as: BF (53.38%-84.27%) > SP (52.22%-70.86%) > PB (22.0%-47.83%). The organic carbon mass fractions of both mechanical- and water-stable aggregates were the highest in the soil of PB. Along with the increase of soil depth, organic carbon mass fraction of soil aggregates all showed a decreasing trend in the three forests. Compared with the total organic carbon at all soil layers, macro water-stable aggregates (>0.25 mm in diameter) had higher organic carbon mass fraction, while micro water-stable aggregates (<0.25 mm in diameter) showed lower mass fraction, suggesting that organic carbon may play an active role in the formation and the water-stability of macro aggregates. Furthermore, soil aggregate organic carbon showed a positive correlation with soil total organic carbon.ConculsionsPB had the best quantity and quality of soil aggregates among the three forests, which can be attributed to the high density and coverage of shrubs/herbs. Therefore, to accelerate the improvement of soil structure and the recovery of soil functions in degraded lands, we should increase the input of organic carbon by appropriately creating a higher density and coverage of shrubs/herbs at the early stage of forest restoration, which would promote the formation and the stability of soil aggregates. This may provide a scientific basis for the selection and optimal allocation of forest types in the restoration of degraded red soil in the south of China.
artificially restored forest; mechanical-stable aggregate; water-stable aggregate; organic carbon; red soil
S151.9
A
2096-2673(2017)05-0058-09
10.16843/j.sswc.2017.05.008
2016-11-24
2017-06-25
項(xiàng)目名稱(chēng): 國(guó)家自然科學(xué)基金 “生態(tài)恢復(fù)對(duì)紅壤嚴(yán)重侵蝕地土壤水庫(kù)重建的影響與機(jī)制” (31160179);江西省自然科學(xué)基金目“侵蝕紅壤碳吸存對(duì)植被恢復(fù)的響應(yīng)及其微生物學(xué)機(jī)制”(20151BAB204033);江西省高等學(xué)?!笆濉彼帘3峙c荒漠化防治重點(diǎn)學(xué)科培育基金“紅壤侵蝕地不同植被恢復(fù)模式對(duì)土壤團(tuán)聚體有機(jī)碳的影響”
朱麗琴(1986—),女,碩士,實(shí)驗(yàn)師。主要研究方向:植被恢復(fù)與重建。E-mail: zhuliqin@nit.edu.cn
?
黃榮珍(1975—),男,博士,教授,碩士生導(dǎo)師。主要研究方向:坡地水文與生態(tài)修復(fù)。E-mail: huangrz@nit.edu.cn