姜超,陳志彪?,陳志強(qiáng),區(qū)曉琳,任天婧,趙紀(jì)濤

(1.福建師范大學(xué)地理科學(xué)學(xué)院,350007,福州;2.濕潤亞熱帶山地生態(tài)國家重點(diǎn)實(shí)驗(yàn)室培育基地,福州,350007; 3.福建師范大學(xué)地理研究所,350007,福州)

崩崗侵蝕對土壤速效養(yǎng)分質(zhì)量分?jǐn)?shù)及化學(xué)計(jì)量比的影響

姜超1,2,3,陳志彪1,2,3?,陳志強(qiáng)1,2,3,區(qū)曉琳1,任天婧1,趙紀(jì)濤1

(1.福建師范大學(xué)地理科學(xué)學(xué)院,350007,福州;2.濕潤亞熱帶山地生態(tài)國家重點(diǎn)實(shí)驗(yàn)室培育基地,福州,350007; 3.福建師范大學(xué)地理研究所,350007,福州)

為揭示崩崗侵蝕對土壤速效養(yǎng)分及化學(xué)計(jì)量比的影響,選取福建省長汀縣黃泥坑崩崗群微度、中度和強(qiáng)度崩崗3處為研究對象,測定和分析了0～30 cm土層集水坡面、崩壁、崩積體以及溝道部位的土壤基本物理性質(zhì)、速效養(yǎng)分及化學(xué)計(jì)量特征。結(jié)果表明:1)隨著侵蝕強(qiáng)度的增加,硝態(tài)氮和速效磷質(zhì)量分?jǐn)?shù)表現(xiàn)為強(qiáng)度＞中度＞微度,中度侵蝕崩崗銨態(tài)氮質(zhì)量分?jǐn)?shù)最低,速效鉀質(zhì)量分?jǐn)?shù)最高;從水平方向上,各速效養(yǎng)分質(zhì)量分?jǐn)?shù)表現(xiàn)為速效鉀(AK)＞銨態(tài)氮＞硝態(tài)氮＞速效磷(AP);垂直方向上,各速效養(yǎng)分質(zhì)量分?jǐn)?shù)大致隨著土層深度而降低,但同一侵蝕強(qiáng)度內(nèi)各質(zhì)量分?jǐn)?shù)差異較小。2)土壤速效氮為銨態(tài)氮與硝態(tài)氮的總和(AN),AN/AP比表現(xiàn)為微度＞強(qiáng)度＞中度,微度與中度差異顯著(P＜0.05);AK/AN比為中度＞微度＞強(qiáng)度,中度與強(qiáng)度差異顯著(P＜0.05);AK/AP比為微度＞中度＞強(qiáng)度,微度與中度差異顯著(P＜0.05)。3)從集水坡面、崩壁、崩積體至溝道,3種類型崩崗的銨態(tài)氮和硝態(tài)氮平均值都呈降低的趨勢,速效磷逐漸升高,速效鉀在崩積體處最低,其他3個部位變化不大;土壤AN/AP、AK/AP比呈降低的趨勢,AK/AN比在溝道處最高。4)速效養(yǎng)分化學(xué)計(jì)量比與砂粒、粉粒、pH和有機(jī)質(zhì)皆密切相關(guān),黏粒、容重和含水率對其影響相對較小。

崩崗侵蝕;速效養(yǎng)分;化學(xué)計(jì)量比;土壤;部位;質(zhì)量分?jǐn)?shù)

崩崗是南方紅壤區(qū)巖(土)體及其風(fēng)化殼在水力—重力交替作用下,遭受剝蝕、崩塌和堆積而形成的一類侵蝕類型,一般分成集水坡面(位于崩崗壁后緣的匯水坡面)、崩壁(發(fā)生崩塌的部位)、崩積體(上方松散物質(zhì)垮塌形成)、溝道和沖(洪)積扇(主溝末端)等侵蝕部位,崩崗侵蝕造成地力衰退、水域淤積,被稱為該地區(qū)的“生態(tài)潰瘍”[1-2]。崩崗是我國特有的侵蝕地貌,與集中分布于地中海地區(qū)劣地(badland)在地貌形態(tài)、發(fā)生機(jī)制等存在相似之處[3-4]。全國崩崗分布約24萬處,其中,福建省6 714處,侵蝕面積2 631 hm2,崩崗密度0.06個/km2,主要集中于安溪、上杭、永春、長汀、寧化、連城及詔安7縣[5-6]。目前,關(guān)于崩崗研究以揭示其侵蝕機(jī)理為主,并已成為土壤侵蝕領(lǐng)域的重要研究方向,且備受關(guān)注[7-8]。鄧羽松等[9-10]分析了洪積扇土壤理化特征,蔣芳市等[11-12]對崩積體侵蝕過程開展了一系列工作。上述研究多集中于崩壁、崩積體及洪積扇等崩崗子系統(tǒng),且以揭露其物理特性較多。

土壤速效養(yǎng)分是供給植物所易吸收的有效營養(yǎng)成分,其質(zhì)量分?jǐn)?shù)的高低反映土壤肥力狀況,其中,速效氮是銨態(tài)氮與硝態(tài)氮的總和(AN),其與速效磷

(AP)和速效鉀(AK)是植物生長發(fā)育所必需的3大基本元素的直接來源,對土壤質(zhì)量評價及生態(tài)恢復(fù)具有指示意義[13-14]。關(guān)于土壤速效養(yǎng)分的研究多集中于時空變異及尺度效應(yīng)[13,15-16]和外物添加對其質(zhì)量分?jǐn)?shù)的影響[17-18],另有一些學(xué)者開始探討不同土地管理方式下速效養(yǎng)分的流失規(guī)律[19-20];但上述研究大多數(shù)集中于干旱、半干旱農(nóng)地土壤,且作為土壤養(yǎng)分綜合指標(biāo)的一部分(速效態(tài)),而南方紅壤崩崗侵蝕區(qū)土壤速效養(yǎng)分質(zhì)量分?jǐn)?shù)及化學(xué)計(jì)量比還尚無報(bào)道。目前有關(guān)土壤化學(xué)計(jì)量比的研究,以全量養(yǎng)分較多,且研究區(qū)多集中于不同類型濕地[21-22]、西北干旱區(qū)[23-24]及森林[25-26]土壤,而缺乏在亞熱帶紅壤崩崗區(qū)等土壤侵蝕極其嚴(yán)重區(qū)域的基礎(chǔ)數(shù)據(jù)。定量分析不同侵蝕強(qiáng)度下崩崗速效養(yǎng)分質(zhì)量分?jǐn)?shù)及其化學(xué)計(jì)量比在各土層與部位空間分異規(guī)律,對揭示崩崗區(qū)養(yǎng)分狀況及治理措施的篩選具有指導(dǎo)意義。

1 研究區(qū)概況

研究區(qū)位于福建省長汀縣濯田鎮(zhèn)西南約20 km,205省道西側(cè)約1 km處,地理坐標(biāo)E116°16＇52″,N25°31＇50″。區(qū)內(nèi)屬中亞熱帶季風(fēng)性濕潤氣候,年均氣溫18.5℃,年均降雨量1 710mm,年均相對濕度80%,年均日照時間1 754 h,年均蒸發(fā)量1 403mm。黃泥坑崩崗群海拔介于281～359m,共有崩崗34處,侵蝕面積約3萬7 500m2,其中,主溝長度200.3m,寬度4.87～12.10m。地貌以低山緩丘為主,在長期溫?zé)釢駶櫁l件下,形成厚度超過60m的紅色風(fēng)化殼,發(fā)育為抗蝕性極低的酸性侵蝕性紅壤。原生植被破壞后,土壤遭受劇烈崩崗侵蝕作用,大量坡面表土被沖刷和堆積于溝道系統(tǒng)內(nèi),沿途于流路集中處發(fā)生崩塌,形成溝壑叢生的侵蝕地貌。

2 研究方法

2.1樣地布設(shè)

根據(jù)典型性和代表性的原則,于2014年7—8月,在黃泥坑崩崗群內(nèi),選擇處于不同侵蝕強(qiáng)度,且海拔、坡度和坡向等地形條件相似的3條毗鄰崩崗,各崩崗侵蝕強(qiáng)度的判別參考崩崗區(qū)及其周邊未發(fā)生崩崗侵蝕區(qū)域的主要生境特征[27]。

強(qiáng)度侵蝕崩崗:集水坡面海拔359m,坡度18°,坡向南偏西18°,崩壁高度9.43m,寬度3.55～5.09 m,主溝長度13.83m,寬度2.20～4.50m,侵蝕面積520m2,侵蝕模數(shù)6 000～6 500 t/(km2·a)。表層巖土近赤褐色,白色粗粒石英顆粒隨處可見,形成高約1 cm的微土柱,約2mm物理結(jié)皮覆蓋,植被覆蓋度僅為2%。

中度侵蝕崩崗:位于強(qiáng)度侵蝕崩崗西側(cè)約5 m處,集水坡面海拔324 m,坡度3°,坡向南偏西19°,崩壁高度11.80 m,寬度4.62～6.02 m,主溝長度15.10m,寬度1.83～4.45m,侵蝕面積686m2,侵蝕模數(shù)4 500～5 000 t/(km2·a)。深紅色新土裸露,質(zhì)地疏松,約5 mm物理結(jié)皮覆蓋。植被有馬尾松幼樹(Pinusmassoniana)、崗松(Baeckea frutescens)、五節(jié)芒(Miscanthus floridulus)、芒萁(Dicranopteris dichotoma),株高0.03～1.85m,冠幅0.01～1.36m2,植被總覆蓋度約20%。

微度侵蝕崩崗:位于中度侵蝕崩崗西南方向約10m處,集水坡面海拔318m,坡度15°,坡向南偏東26°,崩壁高度6.30 m,寬度2.70～3.42 m,主溝長度16.48m,寬度0.71～1.54m,侵蝕面積96m2,侵蝕模數(shù)＜500 t/(km2·a)。植物群落主要有喬木馬尾松、毛冬青(Ilex pubescens)、石斑木(Rhaphiolepis indica)、黃瑞木(Adinandra millettii)等灌叢及芒萁、五節(jié)芒等草本植物,喬木株高、胸徑和冠幅平均值分別為6.38m,8.26 cm和9.31m2;灌木平均株高、地徑和冠幅3.20 m,4.03 cm和2.39 m2;草本植物平均株高1.42m,總覆蓋度95%,無表土出露。

2.2樣品采集與測定

采樣方案見表1,每一崩崗于集水坡面、崩壁、崩積體和溝道等侵蝕部位分別挖取土壤剖面,0～10,10～20和20～30 cm分層采樣;各崩崗共7個采樣點(diǎn),每樣點(diǎn)內(nèi)各層5點(diǎn)的混合共采集樣品約189份。重復(fù)土樣混合均勻后,立即取約1 kg,裝入聚乙烯自封袋內(nèi),分別貼上標(biāo)簽,暫時放置于保溫箱保存。另外,用環(huán)刀-鋁盒采集各樣點(diǎn)原狀土1份。

土樣迅速帶回實(shí)驗(yàn)室后,剔除植物根系、石礫、殘?bào)w等雜物,用四分法混合均勻后研磨,過2 mm篩,用于銨態(tài)氮和硝態(tài)氮的測定。其余土樣待自然風(fēng)干后,1份過2mm篩,用于樣品顆粒組成、pH值、速效磷及速效鉀的測定,另1份過0.149mm篩,用于有機(jī)質(zhì)測定。土壤密度采用環(huán)刀法;土壤含水量采用鋁盒烘干法;土壤顆粒組成采用德國SEDIMAT4-12粒徑分析系統(tǒng),粒徑劃分標(biāo)準(zhǔn)采用美國制;土壤pH值以水土質(zhì)量比2.5∶1,采用STARTER 300便攜式酸度計(jì)測定;土壤速效氮采用2mol/L KCl浸提,連續(xù)流動分析儀(Skalar san++,荷蘭)測定;速效磷采用乙酸—硝酸銨混合液浸提,連續(xù)流動分析儀測定;速效鉀采用HF 2mL+HClO41mL消煮,火焰光度儀測定;有機(jī)質(zhì)采用重鉻酸鉀-外加熱法測定。

表1　每一崩崗采樣說明Tab.1 Sampling explanations of each collapsemound

各崩崗?fù)寥阑纠砘再|(zhì)見表2。

表2　崩崗?fù)寥阑纠砘再|(zhì)Tab.2 Soil basic physical-chemical properties of collapsemounds

2.3數(shù)據(jù)處理

AN/AP/AK為元素摩爾比,速效氮為銨態(tài)氮與硝態(tài)氮總和。采用SPSS 16.0進(jìn)行數(shù)據(jù)統(tǒng)計(jì)分析,用單因子方差分析(One-way ANOVA),對不同侵蝕強(qiáng)度崩崗?fù)寥繬H4+-N、NO3--N、AP、AK、AN/ AP、AK/AN和AK/AP比進(jìn)行差異性檢驗(yàn),采用Pearson相關(guān)分析土壤AN/AP、AK/AN和AK/AP比與土壤因子的相關(guān)性。繪圖由Origin 9.0完成。

3 結(jié)果與分析

3.1不同侵蝕強(qiáng)度崩崗速效養(yǎng)分的質(zhì)量分?jǐn)?shù)

由表3得知,隨著侵蝕強(qiáng)度的增加,土壤速效養(yǎng)分質(zhì)量分?jǐn)?shù)總體上呈升高的趨勢,其中,硝態(tài)氮和速效磷質(zhì)量分?jǐn)?shù)表現(xiàn)為:強(qiáng)度(均值分別為1.31和0.66mg/kg)＞中度(0.95和0.60 mg/kg)＞微度(0.88和0.33mg/kg),強(qiáng)度侵蝕崩崗銨態(tài)氮質(zhì)量分?jǐn)?shù)最高(10.14mg/kg),速效鉀在中度侵蝕崩崗質(zhì)量分?jǐn)?shù)最高,均值為31.86mg/kg。從水平方向上,崩崗?fù)寥浪傩юB(yǎng)分質(zhì)量分?jǐn)?shù)存在差異,其中,速效磷質(zhì)量分?jǐn)?shù)最小,速效鉀質(zhì)量分?jǐn)?shù)最大,銨態(tài)氮質(zhì)量分?jǐn)?shù)明顯高于硝態(tài)氮;從垂直方向上,各速效養(yǎng)分質(zhì)量分?jǐn)?shù)大致隨著土層深度而降低,在同一侵蝕強(qiáng)度下,其質(zhì)量分?jǐn)?shù)差異較小,除強(qiáng)度侵蝕崩崗銨態(tài)氮和硝態(tài)氮差異顯著(P＜0.05),其余均未達(dá)到顯著水平(P＞0.05)。

表3　不同侵蝕強(qiáng)度崩崗?fù)寥浪傩юB(yǎng)分質(zhì)量分?jǐn)?shù)Tab.3 Content of soil available nutrients in collapsemounds with different erosion intensity mg/kg

3.2不同侵蝕部位崩崗?fù)寥浪傩юB(yǎng)分的質(zhì)量分?jǐn)?shù)

如圖1所示,不同侵蝕強(qiáng)度下銨態(tài)氮表現(xiàn)為崩壁＞集水坡面＞崩積體＞溝道,平均值分別為9.51,8.15,6.50和4.40 mg/kg;相比于集水坡面,崩壁增加16.70%,崩積體減少20.21%,溝道減少46.03%;3種不同侵蝕強(qiáng)度的銨態(tài)氮質(zhì)量分?jǐn)?shù),在集水坡面和溝道差異顯著(P＜0.05);在崩壁及崩積體,中度侵蝕崩崗與微度及強(qiáng)度侵蝕崩崗差異顯著(P＜0.05)。硝態(tài)氮質(zhì)量分?jǐn)?shù)在集水坡面最低,平均值為0.59 mg/kg,其次為溝道,平均值為0.77 mg/kg,崩壁平均質(zhì)量分?jǐn)?shù)為1.18 mg/kg,最高為崩積體,平均值為1.19mg/kg;相比于集水坡面、溝道、崩壁及崩積體,分別增加了29.31%,100.27%和100.70%;各侵蝕強(qiáng)度下崩崗硝態(tài)氮質(zhì)量分?jǐn)?shù),在崩積體和溝道差異性達(dá)到顯著水平(P＜0.05);在崩壁處,中度侵蝕崩崗與微度及強(qiáng)度侵蝕崩崗差異性達(dá)到顯著水平(P＜0.05);集水坡面處微度侵蝕崩崗與中度及強(qiáng)度侵蝕崩崗差異性達(dá)到顯著水平(P＜0.05)。速效磷質(zhì)量分?jǐn)?shù)自集水坡面、崩壁、崩積體至溝道逐漸升高,相比于集水坡面、崩壁、崩積體和溝道分別增加12.14%,15.38%和81.68%;不同侵蝕強(qiáng)度崩崗速效磷質(zhì)量分?jǐn)?shù),在集水坡面、崩積體和溝道差異性均達(dá)到顯著水平(P＜0.05);在崩壁處,微度侵蝕崩崗與中度及強(qiáng)度侵蝕崩崗差異性達(dá)到顯著水平(P＜0.05)。速效鉀質(zhì)量分?jǐn)?shù)在集水坡面、崩壁、崩積體和溝道平均值分別為33.77, 26.27,16.58和28.90 mg/kg;相對于集水坡面,溝道速效鉀質(zhì)量分?jǐn)?shù)減少14.42%,崩壁減少22.19%,崩積體減少50.91%。中度侵蝕崩崗速效鉀質(zhì)量分?jǐn)?shù)最高,微度侵蝕崩崗速效鉀質(zhì)量分?jǐn)?shù)最低。

圖1　不同侵蝕部位崩崗?fù)寥浪傩юB(yǎng)分質(zhì)量分?jǐn)?shù)Fig.1 Content of soil available nutrients in collapsemoundswith different erosion position

3.3不同侵蝕強(qiáng)度崩崗?fù)寥浪傩юB(yǎng)分的化學(xué)計(jì)量比

如表4所示,微度侵蝕崩崗?fù)寥赖腁K/AP比最大(均值74.47),其次為AN/AP比(67.06),AK/ AN比最小(1.22);AN/AP比和AK/AN比隨土層加深增加而逐漸增加,AK/AP比在10～20 cm最低,20～30 cm最高。中度侵蝕崩崗為AK/AP比、AN/AP比和AK/AN比平均值分別為45.06,29.90和2.07;隨著土層深度的增加,AN/AP比先降低后略有上升,AK/AN比先升高后有所下降,AK/AP比保持相對穩(wěn)定。強(qiáng)度侵蝕崩崗,AN/AP比最大(均值42.02),其次為AK/AP比(均值31.67),AK/AN比最小(均值0.87);AN/AP比和AK/AP比隨土層深度的增加呈降低的趨勢,AK/AN比呈升高的趨勢。不同侵蝕強(qiáng)度崩崗,AN/AP比表現(xiàn)為微度＞強(qiáng)度＞中度,微度侵蝕崩崗與中度及強(qiáng)度侵蝕崩崗差異顯著(P＜0.05);AK/AN比為中度＞微度＞強(qiáng)度,中度侵蝕崩崗與微度及強(qiáng)度侵蝕崩崗差異顯著(P＜0.05);AK/AP比為微度＞中度＞強(qiáng)度,微度侵蝕與中度及強(qiáng)度侵蝕崩崗差異顯著(P＜0.05)。

表4　不同崩崗強(qiáng)度土壤速效養(yǎng)分化學(xué)計(jì)量特征Tab.4 Stoichiometry characteristics of soil available nutrients in collapsemounds with different erosion intensity

3.4不同侵蝕部位崩崗?fù)寥浪傩юB(yǎng)分的化學(xué)計(jì)量比

圖2　不同侵蝕部位崩崗?fù)寥浪傩юB(yǎng)分化學(xué)計(jì)量特征Fig.2 Stoichiometry characteristics of soil available nutrients in collapsemounds in different erosion position

崩崗4個部位速效養(yǎng)分化學(xué)計(jì)量比變化特征如圖2所示。不同侵蝕強(qiáng)度下,AN/AP比從集水坡面、崩壁、崩積體至溝道逐漸降低,平均值分別為63.55,52.90,41.94和17.18;相對于集水坡面,其崩壁、崩積體和溝道分別減少16.75%,34.00%和72.96%。不同侵蝕強(qiáng)度崩崗,AN/AP比在集水坡面和溝道差異顯著(P＜0.05);中度侵蝕崩崗與微度及強(qiáng)度侵蝕崩崗,在崩壁處差異顯著(P＜0.05);微度侵蝕崩崗與中度及其強(qiáng)度侵蝕崩崗,在崩積體處顯著(P＜0.05)。AK/AP比表現(xiàn)為集水坡面＞崩壁＞溝道＞崩積體,其平均值分別為73.77, 56.76,32.91和35.37;相比于集水坡面,崩壁、溝道和崩積體分別減少了23.06%,52.05%和55.39%。各侵蝕強(qiáng)度下,AK/AP比在崩壁和崩積體差異性達(dá)到顯著水平(P＜0.05),在集水坡面和溝道處,微度侵蝕崩崗與中度及強(qiáng)度侵蝕崩崗差異性達(dá)到顯著水平(P＜0.05)。AK/AN比在溝道處最大(2.51),其次為集水坡面(1.47),崩積體與崩壁大致相當(dāng),平均值分別為1.08和1.07;相比于集水坡面,崩壁和崩積體減少了27.29%和26.74%,溝道增加了70.73%。中度侵蝕崩崗AK/AN比值最大,且不同侵蝕強(qiáng)度崩崗,在集水坡面、崩壁和溝道差異顯著(P＜0.05),中度侵蝕崩崗與微度及強(qiáng)度侵蝕崩崗,在崩積體處差異顯著(P＜0.05)。

3.5崩崗?fù)寥浪傩юB(yǎng)分化學(xué)計(jì)量特征的影響因子

崩崗侵蝕區(qū)土壤速效養(yǎng)分化學(xué)計(jì)量比除了受到各元素自身含量的調(diào)控外,還受土壤環(huán)境因子影響,不同侵蝕強(qiáng)度下,土壤速效養(yǎng)分化學(xué)計(jì)量比的影響因素也不一致(表5)。微度侵蝕崩崗,AN/AP、AK/ AP比受土壤顆粒組成影響較大,與砂粒、粉粒和黏粒均達(dá)到極顯著相關(guān)(P＜0.01);AK/AN比與pH呈極顯著正相關(guān)(P＜0.01),與有機(jī)質(zhì)呈極顯著負(fù)相關(guān)(P＜0.01)。中度侵蝕崩崗,AN/AP、AK/AP和AK/AN比受到砂粒、pH和有機(jī)質(zhì)影響,但影響程度存在差異。在強(qiáng)度侵蝕崩崗,AN/AP比與砂粒、粉粒極顯著負(fù)相關(guān)(P＜0.01),與含水率和有機(jī)質(zhì)極顯著正相關(guān)(P＜0.01);AK/AP比與砂粒顯著負(fù)相關(guān)(P＜0.05),與pH極顯著負(fù)相關(guān)(P＜0.01),與有機(jī)質(zhì)極顯著正相關(guān)(P＜0.01);AK/AN比僅與含水率達(dá)到極顯著負(fù)相關(guān)水平(P＜0.01)。從整個崩崗區(qū)來看,AN/AP、AK/AP和AK/AN比與砂粒、粉粒、pH和有機(jī)質(zhì)密切相關(guān),黏粒、土壤密度和含水率對AN/AP、AK/AP和AK/AN比影響較小。由此可見,土壤環(huán)境因子對AN/AP、AK/AP比影響較大,而對AK/AN比影響較小。

表5　崩崗?fù)寥浪傩юB(yǎng)分化學(xué)計(jì)量比與環(huán)境因子的相關(guān)性Tab.5 Correlation between soil available nutrient stoichiometry ratios and environmental factors(n=189)

4 討論

4.1崩崗侵蝕區(qū)速效養(yǎng)分質(zhì)量分?jǐn)?shù)的變化特征

土壤速效養(yǎng)分不僅受母質(zhì)、地形及氣候等自然因素影響,毀林等人為干擾的影響也較大,具有高度空間異質(zhì)性的特點(diǎn)[13];然而,本研究中發(fā)現(xiàn),各侵蝕強(qiáng)度崩崗不同土層深度間,土壤銨態(tài)氮、硝態(tài)氮、速效磷和速效鉀質(zhì)量分?jǐn)?shù)變化較小,崩崗區(qū)土壤速效養(yǎng)分質(zhì)量分?jǐn)?shù)整體偏低,特別是速效磷,均值僅為0.63mg/kg。與鄧羽松等[10]在贛縣崩崗洪積扇處得出結(jié)論相比,本文中質(zhì)量分?jǐn)?shù)最高的速效鉀只有其60%左右,速效磷質(zhì)量分?jǐn)?shù)甚至不足其1/5;與長汀縣內(nèi)朱溪小流域撂荒坡地土壤速效養(yǎng)分質(zhì)量分?jǐn)?shù)基本一致,普遍低于采取水土保持措施后的樣地[25]。這說明崩崗區(qū)土壤速效養(yǎng)分質(zhì)量分?jǐn)?shù)已處于極低水平,各速效養(yǎng)分匱缺非常嚴(yán)重,造成這一特征的原因與其自身劇烈的土壤侵蝕有關(guān),并表現(xiàn)出與侵蝕具有協(xié)同效應(yīng);另外,隨侵蝕強(qiáng)度加劇,各速效養(yǎng)分質(zhì)量分?jǐn)?shù)而增加,這主要是因?yàn)榘l(fā)生崩崗侵蝕后,土壤結(jié)構(gòu)遭到破壞,土壤養(yǎng)分流失嚴(yán)重,而微度侵蝕崩崗以馬尾松+毛冬青+芒萁為代表的植物群落生長較好,對速效養(yǎng)分需求相對較高,加之植物凋落物對速效養(yǎng)分質(zhì)量分?jǐn)?shù)變化的影響相對較小[18],總體上呈現(xiàn)出強(qiáng)度＞中度＞微度的趨勢。丘世鈞[28]認(rèn)為,“在自然環(huán)境中,崩崗發(fā)生主要是在降雨和地表水流作用下,沖溝溝頭和溝谷墻壁崩陷作用不斷加強(qiáng),最后由水蝕作用占主導(dǎo)轉(zhuǎn)化為崩陷作用為主導(dǎo)”。與這一結(jié)論已基本得到共識。在水流和重力交替作用下,原坡面土體崩塌坍落形成崩壁,墜落的土體在崩壁底部形成崩積體,崩積體再在降雨徑流的沖刷下,部分土體在溝道內(nèi)沉積,或搬運(yùn)至溝道出口以及下游農(nóng)田發(fā)育成洪積扇;因此,崩崗侵蝕過程可以理解成巖土體沿集水坡面→崩壁→崩積體→溝道遭受沖刷(坍塌)→搬運(yùn)→堆積的輸移過程。崩崗系統(tǒng)內(nèi)銨態(tài)氮和硝態(tài)氮變化規(guī)律與侵蝕過程基本一致,速效磷質(zhì)量分?jǐn)?shù)沿集水坡面→崩壁→崩積體→溝道呈升高的趨勢;而速效鉀在崩積體處質(zhì)量分?jǐn)?shù)最低,其他3個部位差異較小。造成崩崗?fù)寥浪傩юB(yǎng)分質(zhì)量分?jǐn)?shù)具有明顯的空間分異特征的原因可能有2個方面:一是土壤氮、磷、鉀等養(yǎng)分的輸入和輸出途徑存在差異,如氮主要來源于植被凋落物礦化分解,而磷鉀多來自于成土母質(zhì)風(fēng)化釋放[29-30];二是在崩崗強(qiáng)度侵蝕及其植被吸收利用的環(huán)境下,速效養(yǎng)分淋溶和循環(huán)速率可能較快。另外,本研究亦發(fā)現(xiàn),崩崗區(qū)內(nèi)土壤銨態(tài)氮質(zhì)量分?jǐn)?shù)明顯高于硝態(tài)氮,這可能是由于亞熱帶地區(qū)溫暖濕潤的氣候、嚴(yán)重的土壤侵蝕、pH值較低和離子選擇性交換等原因的影響,導(dǎo)致絕大多數(shù)硝態(tài)氮被淋濾流失。

4.2崩崗侵蝕對土壤AN/AP、AK/AP和AK/AN比的影響

研究發(fā)現(xiàn),土壤速效養(yǎng)分化學(xué)計(jì)量比既受到其質(zhì)量分?jǐn)?shù)變化的影響,還與土壤顆粒組成、pH值和有機(jī)質(zhì)關(guān)系密切。土壤AN/AP、AK/AP和AK/AN比,隨侵蝕強(qiáng)度的降低有升高的趨勢,與其速效養(yǎng)分質(zhì)量分?jǐn)?shù)相反,這是因?yàn)榱缀外浽啬枖?shù)較大;但是,不同土層深度的速效養(yǎng)分化學(xué)計(jì)量比的變化規(guī)律與質(zhì)量分?jǐn)?shù)基本一致,造成的原因可能是崩崗侵蝕導(dǎo)致土壤空間結(jié)構(gòu)遭到破壞,垂直分布差異較小。林麗等[31]對高寒區(qū)不同演替序列下矮嵩草土壤研究得出,AN/AP比的變化范圍介于(3.98±0.10)～(34.04±2.80),總體低于本研究結(jié)果,這是因?yàn)楸狙芯恐型寥浪傩Я踪|(zhì)量分?jǐn)?shù)極低所致。土壤AN/AP和AK/AP比從集水坡面、崩壁、崩積體至溝道呈降低的趨勢,與侵蝕過程基本一致,而AK/AN比在溝道處最高,這可能與崩崗侵蝕區(qū)不同部位各元素質(zhì)量分?jǐn)?shù)空間差異相關(guān)。

5 結(jié)論

1)土壤硝態(tài)氮和速效磷隨著崩崗侵蝕強(qiáng)度的增強(qiáng)而增加,中度侵蝕崩崗銨態(tài)氮質(zhì)量分?jǐn)?shù)最低,速效鉀在中度侵蝕崩崗質(zhì)量分?jǐn)?shù)最高,各速效養(yǎng)分質(zhì)量分?jǐn)?shù)間存在差異,呈現(xiàn)出速效鉀＞銨態(tài)氮＞硝態(tài)氮＞速效磷;另外,各速效養(yǎng)分質(zhì)量分?jǐn)?shù)大致隨著土層深度而降低,在同一侵蝕強(qiáng)度下,其質(zhì)量分?jǐn)?shù)差異較小。

2)土壤AN/AP比表現(xiàn)為微度崩崗＞強(qiáng)度崩崗＞中度崩崗,AK/AN比為中度崩崗＞微度崩崗＞強(qiáng)度崩崗,AK/AP比為微度崩崗＞中度崩崗＞強(qiáng)度崩崗,土壤速效養(yǎng)分化學(xué)計(jì)量比隨侵蝕強(qiáng)度的降低,有升高的趨勢,與其速效養(yǎng)分質(zhì)量分?jǐn)?shù)相反。

3)自集水坡面、崩壁、崩積體至溝道,銨態(tài)氮和硝態(tài)氮呈降低的趨勢,速效磷逐漸升高,速效鉀在崩積體處質(zhì)量分?jǐn)?shù)最低,其他3個部位變化較小;而AN/AP、AK/AP比從集水坡面、崩壁、崩積體至溝道呈降低的趨勢,AK/AN比在溝道處最大。

4)速效養(yǎng)分化學(xué)計(jì)量比與砂粒、粉粒、pH和有機(jī)質(zhì)密切相關(guān),黏粒、密度和含水率對其影響相對較小。

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Effects of collapsemound erosion on soil available nutrient contents and their stoichiometry ratios

Jiang Chao1,2,3,Chen Zhibiao1,2,3,Chen Zhiqiang1,2,3,Ou Xiaolin1,Ren Tianjing1,Zhao Jitao1

(1.College of Geographical Science,Fujian Normal University,350007,Fuzhou,China;2.Key Laboratory for Subtropical Mountain Ecology(Ministry of Science and Technology and Fujian Province Funded),350007,Fuzhou,China; 3.Institute of Geography,Fujian Normal University,350007,Fuzhou,China)

[Background]Collapsemound,called“Benggang”in Chinese geomorphic pictograph,has been known to describe a kind of erosion phenomenon in hilly and mountainous area among subtropical and fractional tropical climatic zone of south China thatgully head collapsed,transported and developed a deep-cut shape,concave-deforming deep-seated failure landform.[M ethods]To reveal the effects of collapsemound erosion on soil available nutrients and stoichiometry ratios,we chose 3 collapsemounds of slight,moderate and strong erosion intensities in Huangniken collapsemound groups of Changting County of Southwest Fujian as research object.Soils at0-10 cm,10-20 cm and 20-30 cm in 4 positions of upper catchment,collapsing wall,colluvial deposit and channel were sampled,and the contents ofammonium N(),nitrate N(),available P(AP)and available K(AK)and related physical-chemical properties,such asmechanical composition,bulk density,water content,and organic matter content were measured,finally,the stoichiometric characteristics of available nutrients were analyzed.[Results]The results indicated that:1)With erosion intensity increasing,the contents ofand AP occurred in the collapsemound of strong＞moderate＞slight,and the content ofN was the lowest and AK was the highest in collapse mound under moderate erosion;horizontally,the diminishing order of contents of soil available nutrients were displayed as following:,while the content of each available nutrient decreased vertically as soil depth increasing, and their variance of the same erosion intensity was very little.2)With different erosion intensities,ANAP ratio showed:slight＞moderate＞strong,and there was significant difference(P＜0.05)between slight and moderate collapse mound;AK/AN ratio was in moderate＞slight＞strong,and there was significant difference(P＜0.05)between moderate and strong collapse mound;AK/AP ratio was in slight＞strong＞moderate,and difference was significant(P＜0.05) between slight and moderate.3)From upper catchment,collapsing wall,colluvial deposit and channel, the averaged content ofandshowed a downward tendency,while AP increased gradually,and AK was the lowest at colluvial deposit,but in 3 other sections they varied slightly under different erosion intensities;meanwhile,AN/AP and AK/AP ratios decreased from slope of catchment area to channel,but the value of AK/AN ratiowas the highest at channel.4)Stoichiometric ratios of soil available nutrients were closely correlated to sand,silt,pH value and organic matter,but they were impacted slightly by the clay,bulk density and water content.[Conclusions]collapse mound erosion resulted in variation of soil available nutrients and stoichiometry ratioswith different layers and position.

collapsemound erosion;available nutrients;stoichiometric ratios;soil;position;content

S157.1

A

1672-3007(2016)02-0031-10

10.16843/j.sswc.2016.02.005

2015-09-13

2015-12-27

項(xiàng)目名稱:國家自然科學(xué)基金“南方紅壤侵蝕區(qū)芒萁散布及其時空模擬”(41171232),“南方離子型稀土礦區(qū)芒萁的蔓延格局與稀土遷聚響應(yīng)”(41371512);國家科技支撐計(jì)劃“南方紅壤水土流失治理技術(shù)及示范”(2013BAC08B03)

姜超(1990—),男,碩士研究生。主要研究方向:崩崗侵蝕機(jī)理與災(zāi)害評價。E-mail:jcjiangchengzi@163.com

簡介:陳志彪(1962—),男,博士,教授。主要研究方向:水土保持、資源與環(huán)境等。E-mail:chenzhib408@vip.163. com