甘肅中部沿黃灌區(qū)馬鈴薯連作對(duì)土壤化學(xué)和生物學(xué)性質(zhì)的影響*

劉 星,邱慧珍,張文明,張春紅,朱 靜,馬 興,程萬(wàn)莉

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甘肅中部沿黃灌區(qū)馬鈴薯連作對(duì)土壤化學(xué)和生物學(xué)性質(zhì)的影響*

劉 星1,2,邱慧珍1**,張文明1,張春紅1,朱 靜1,馬 興1,程萬(wàn)莉1

(1. 甘肅農(nóng)業(yè)大學(xué)資源與環(huán)境學(xué)院/甘肅省干旱生境作物學(xué)重點(diǎn)實(shí)驗(yàn)室 蘭州 730070; 2. 河南科技學(xué)院資源與環(huán)境學(xué)院 新鄉(xiāng) 453003)

甘肅中部沿黃灌區(qū)是全國(guó)重要的加工型馬鈴薯和種薯生產(chǎn)基地, 但集約化種植帶來(lái)的連作障礙問(wèn)題已嚴(yán)重影響到產(chǎn)業(yè)的健康發(fā)展。設(shè)置不同連作年限(0~5年)馬鈴薯種植處理, 通過(guò)田間試驗(yàn)評(píng)估連作對(duì)土壤化學(xué)和生物學(xué)性質(zhì)的影響, 探討馬鈴薯連作的土壤障礙因子。結(jié)果表明: 土壤有機(jī)碳含量隨連作年限延長(zhǎng)逐漸降低, 而堿解氮和速效鉀含量以及電導(dǎo)率與之相反; 連作顯著增加土壤速效磷含量, 但對(duì)全氮含量、碳氮比和pH無(wú)明顯影響。長(zhǎng)期連作(3~5年)較非連作(0年)土壤平均酶活性顯著降低33.07%~61.78%, 脲酶、蔗糖酶和脫氫酶活性亦隨連作年限延長(zhǎng)逐漸降低。長(zhǎng)期連作降低土壤微生物生物量碳含量, 土壤基礎(chǔ)呼吸量和FDA水解活性與連作年限呈極顯著負(fù)相關(guān)。Biolog ECO分析顯示, 長(zhǎng)期連作顯著降低土壤微生物總活性和功能多樣性, Shannon多樣性指數(shù)較非連作降低11.75%~13.65%。碳源利用圖譜分析表明, 連作明顯改變土壤微生物群落結(jié)構(gòu), 碳水化合物是區(qū)分不同連作年限土壤微生物群落結(jié)構(gòu)差異的最敏感碳源類型; 長(zhǎng)期連作顯著降低土壤微生物對(duì)碳水化合物類、氨基酸類、羧酸類和胺類碳源的相對(duì)利用率, 且土壤微生物對(duì)單一碳源的利用呈現(xiàn)集中化的趨勢(shì)。線性逐步回歸分析和通徑分析表明, 土壤微生物群落結(jié)構(gòu)、微生物生物量碳、全氮和脫氫酶對(duì)塊莖產(chǎn)量有顯著影響, 以微生物群落結(jié)構(gòu)貢獻(xiàn)最大, 微生物生物量碳次之。土壤微生物因子變化可能是導(dǎo)致甘肅中部沿黃灌區(qū)馬鈴薯連作障礙發(fā)生的重要原因。

馬鈴薯; 連作; 土壤化學(xué)性質(zhì); 生物學(xué)性質(zhì)

甘肅中部沿黃灌區(qū)是全國(guó)重要的加工型馬鈴薯()生產(chǎn)基地和種薯繁殖基地, 但集約化生產(chǎn)和訂單農(nóng)業(yè)經(jīng)營(yíng)模式帶來(lái)的連作障礙問(wèn)題已嚴(yán)重影響到產(chǎn)業(yè)的健康發(fā)展。闡明連作障礙形成機(jī)制并尋求有效的防控措施已成為當(dāng)?shù)伛R鈴薯生產(chǎn)環(huán)節(jié)亟需解決的課題。早前學(xué)者從植株生長(zhǎng)發(fā)育和生理生態(tài)響應(yīng)角度來(lái)解析馬鈴薯連作障礙機(jī)理, 并指出植株源端生產(chǎn)性能降低和庫(kù)源關(guān)系失衡是導(dǎo)致連作馬鈴薯塊莖產(chǎn)量下降的重要生理機(jī)制[1-2]。健康的土壤環(huán)境是作物高產(chǎn)高效的基礎(chǔ), 盡管不同作物連作障礙機(jī)理可能存在差別, 但主要源自土壤[3]。長(zhǎng)期連作導(dǎo)致土壤頹敗發(fā)生, 并對(duì)植株生長(zhǎng)發(fā)育和經(jīng)濟(jì)產(chǎn)量形成產(chǎn)生負(fù)反饋調(diào)節(jié)[4-5]。究竟這種負(fù)反饋調(diào)節(jié)由哪些土壤障礙因子觸發(fā), 不同研究者仍然存在爭(zhēng)議。部分學(xué)者從土壤理化層面開展研究[6-10], 認(rèn)為馬鈴薯連作導(dǎo)致土壤養(yǎng)分虧缺、土壤酸化或次生鹽漬化等。也有學(xué)者從土壤酶角度開展研究[11], 指出馬鈴薯連作影響土壤中相關(guān)酶類的活性, 而這將影響土壤生態(tài)功能發(fā)揮。健康高效的微生物區(qū)系是土壤質(zhì)量的重要保證, 有學(xué)者認(rèn)為馬鈴薯連作導(dǎo)致土壤微生物多樣性降低, 群落結(jié)構(gòu)改變, 土傳病害泛濫, 帶來(lái)塊莖產(chǎn)量降低[12-20]。還有學(xué)者從自毒/化感作用角度探討馬鈴薯連作障礙機(jī)理[21-25]。盡管上述研究的背景存在氣候環(huán)境、施肥狀況和供試品種以及土壤質(zhì)地等方面的差異, 但馬鈴薯連作障礙的發(fā)生應(yīng)該受到多種土壤因子驅(qū)動(dòng)。因此, 評(píng)估連作土壤環(huán)境變化特征是探索馬鈴薯連作障礙機(jī)理的前提。目前, 關(guān)于連作土壤障礙因子的研究更多地集中在設(shè)施蔬菜、大田經(jīng)濟(jì)作物、中藥材和園藝花卉上, 在馬鈴薯上研究相對(duì)較少, 在甘肅省中部沿黃灌區(qū)這一馬鈴薯優(yōu)勢(shì)產(chǎn)區(qū)更是鮮有報(bào)道。本研究依托田間定位試驗(yàn), 試圖從連續(xù)的時(shí)間尺度上來(lái)探討土壤化學(xué)和生物學(xué)性質(zhì)對(duì)馬鈴薯連作的響應(yīng), 評(píng)估可能的連作土壤障礙因子, 旨在為明確馬鈴薯連作障礙機(jī)理以及探索連作土壤障礙因子的消減技術(shù)提供依據(jù)。

1 材料與方法

1.1 試驗(yàn)區(qū)概況

田間試驗(yàn)設(shè)置在地處甘肅中部沿黃灌區(qū)的白銀市景泰縣條山農(nóng)場(chǎng)(37°12′252N, 104°1′162E), 海拔約1 500 m, 屬溫帶大陸性干旱氣候, 年平均氣溫9.1 ℃, 無(wú)霜期141 d左右。年平均降水量185.6 mm, 年平均蒸發(fā)量1 722.8 mm。年平均日照時(shí)數(shù)2 713 h, 光熱資源豐富, 日照百分率62%, 太陽(yáng)年平均輻射量618.1 kJ·m-2, 年≥0 ℃活動(dòng)積溫3 614.8 ℃, ≥10 ℃有效積溫3 038 ℃, 是我國(guó)除青藏高原外光熱資源最為豐富的地區(qū)之一。供試土壤為灰鈣土, 質(zhì)地為砂壤。

1.2 試驗(yàn)設(shè)計(jì)與方法

選擇前茬為制種玉米、地勢(shì)平坦整齊且土壤肥力均勻的地塊, 于2005年開始隨機(jī)劃區(qū)種植馬鈴薯, 而該地塊其余部分繼續(xù)種植制種玉米, 此后逐年增加新的馬鈴薯種植小區(qū), 這樣在同一地塊上形成不同連作年限的馬鈴薯種植處理, 得以同時(shí)采集連續(xù)時(shí)間尺度下的連作馬鈴薯植株和土壤樣品[2]。當(dāng)年種植馬鈴薯的小區(qū)即為連作0年處理, 連續(xù)種植兩年馬鈴薯的小區(qū)為連作1年處理, 依次類推。田間定位試驗(yàn)開始前供試小區(qū)耕層土壤基礎(chǔ)理化性質(zhì)為: 有機(jī)質(zhì)10.2 g·kg-1, 全氮0.55 g·kg-1, 堿解氮76.5 mg·kg-1, 速效磷9.6 mg·kg-1, 速效鉀192.2 mg·kg-1, pH為8.43(水土比為5︰1)。2014年選擇連作0年處理(未連作, 前茬為制種玉米, 用RP表示)和連作1~5年處理(分別用CP1-CP5表示)進(jìn)行田間試驗(yàn), 每個(gè)處理4次重復(fù), 小區(qū)面積為5.4 m×10 m。采用統(tǒng)一的馬鈴薯栽培種植模式和施肥量, 寬壟雙行覆膜種植, 在播種前一天切種薯, 并用濃度為1.5%的高錳酸鉀溶液消毒, 壟寬和行距分別為1.35 m和0.70 m, 株距為0.20 m, 種植密度約為7.5×104株·hm-2。年化肥施用量為210 kg(N)·hm-2, 150 kg(P2O5)·hm-2, 300 kg(K2O)·hm-2,化肥分別用養(yǎng)分含量為15-15-15的復(fù)合肥、含N 46%的尿素和含K2O 51%的硫酸鉀, 無(wú)有機(jī)肥施用。播種和施肥均采用機(jī)械化一次進(jìn)行, 人工覆膜?；试诓シN時(shí)全部基施, 無(wú)追肥, 其余栽培、灌溉和田間管理措施均按農(nóng)場(chǎng)統(tǒng)一方法進(jìn)行, 且各處理保持一致。當(dāng)年4月30日播種, 9月8日收獲。供試材料為當(dāng)?shù)刂髟缘募庸ば婉R鈴薯品種‘大西洋’, 由條山農(nóng)場(chǎng)提供。

1.3 樣品采集與分析

土壤樣品采集在2014年馬鈴薯收獲時(shí)進(jìn)行, 采用五點(diǎn)取樣法, 在壟上馬鈴薯行間靠近植株根系處進(jìn)行, 采樣深度0~20 cm。新鮮土樣混合均勻后等分兩份, 一份置于室內(nèi)風(fēng)干, 分別研磨通過(guò)0.25 mm和1 mm篩, 測(cè)定土壤化學(xué)性質(zhì); 另一份快速研磨通過(guò)1 mm篩, 置于4 ℃冰箱中, 測(cè)定土壤生化性質(zhì)。馬鈴薯收獲時(shí)采集植株樣品進(jìn)行考種, 而后分根、莖、葉和塊莖4個(gè)部分在105 ℃下殺青30 min, 80 ℃烘干至恒重, 稱量生物量, 并對(duì)每個(gè)小區(qū)實(shí)測(cè)記產(chǎn)。

有機(jī)碳、全氮、堿解氮、速效磷和速效鉀等土壤理化性質(zhì)測(cè)定參考文獻(xiàn)[26], 電導(dǎo)率和pH測(cè)定在5︰1的水土比條件下進(jìn)行。土壤蔗糖酶、脲酶、堿性磷酸酶和多酚氧化酶活性采用風(fēng)干土樣測(cè)定, 脫氫酶和熒光素二乙酸酯(FDA)水解活性采用新鮮土樣測(cè)定, 測(cè)定結(jié)果全部以干基計(jì)算。土壤酶活性測(cè)定參考李振高等[27]的方法, 并根據(jù)Zhang等[28]的方法計(jì)算如下: 土壤平均酶活性＝(蔗糖酶×脲酶×堿性磷酸酶×多酚氧化酶×脫氫酶)1/5。

FDA水解活性參考Adam和Duncan[29]的方法。土壤基礎(chǔ)呼吸量參考Giovannini等[30]的方法, 暗培養(yǎng)進(jìn)行。微生物生物量碳測(cè)定采用氯仿熏蒸法, 0.5 mol·L-1K2SO4溶液浸提, 重鉻酸鉀消化, FeSO4滴定[31]。微生物熵(%)＝微生物生物量碳/土壤有機(jī)碳[32], 微生物代謝熵(%)＝土壤基礎(chǔ)呼吸量/微生物生物量碳[33]。

土壤微生物功能多樣性測(cè)定采用Biolog ECO方法, 96孔微生態(tài)板包括31種單一碳源, 分別為氨基酸類(6種)、碳水化合物類(10種)、羧酸類(7種)、胺類(2種)、酚酸類(2種)、聚合物類(4種), 及1個(gè)空白對(duì)照, 均重復(fù)3次。土壤預(yù)處理和測(cè)定過(guò)程參見早前報(bào)道[34]。平均顏色變化率(AWCD)＝(C-)/, 其中C為第個(gè)非對(duì)照孔的吸光值,為對(duì)照孔的吸光值,為培養(yǎng)基碳源種類數(shù), 當(dāng)C-計(jì)算為負(fù)值時(shí)直接按0處理。功能多樣性指數(shù)和碳源相對(duì)利用率的計(jì)算參見鄒春嬌等[35]的報(bào)道, 以不同連作年限處理下6類碳源AWCD值中最大的值為100%, 其余AWCD值與最大值的比值即為相對(duì)利用率, 同時(shí)將每一種碳源的利用率與31種碳源的總利用率的比值定為每一種碳源的相對(duì)利用率, 采用168 h時(shí)的吸光值進(jìn)行計(jì)算。

1.4 數(shù)據(jù)處理

試驗(yàn)數(shù)據(jù)計(jì)算和圖表繪制在Microsoft Excel 2007軟件上進(jìn)行, 使用SPSS 21.0軟件進(jìn)行處理間差異顯著性檢驗(yàn)(One-way,<0.05)。微生物群落結(jié)構(gòu)采用主成分分析方法。采用線性逐步回歸分析和通徑分析方法評(píng)估不同土壤因子對(duì)塊莖產(chǎn)量的影響及其相對(duì)貢獻(xiàn)。

2 結(jié)果與分析

2.1 不同連作年限馬鈴薯土壤化學(xué)性質(zhì)的變化

不同連作年限土壤化學(xué)性質(zhì)測(cè)定結(jié)果如表1所示。CP1-CP3處理有機(jī)碳含量與RP無(wú)顯著差異, 而CP4和CP5處理分別顯著下降15.68%和11.47%。連作土壤全氮含量與非連作均無(wú)顯著差異。與RP相比, CP1處理碳氮比顯著增加, CP2處理顯著降低22.69%, CP3-CP5處理無(wú)顯著變化。CP1、CP2和CP4處理土壤堿解氮含量與RP無(wú)顯著差異, CP3和CP5分別顯著增加55.52%和84.04%。與RP比較, 連作處理土壤速效磷含量顯著增加49.00%~93.12%。CP1和CP3處理土壤速效鉀含量與RP無(wú)顯著差異, 其余處理則顯著增加30.52%~60.06%。連作處理土壤電導(dǎo)率比非連作均不同程度增加, 且CP2、CP3和CP5達(dá)顯著水平, 增幅分別為55.74%、57.28%和51.22%。CP1-CP4處理土壤pH較RP顯著下降, 而CP5處理無(wú)顯著變化。線性相關(guān)分析表明, 土壤有機(jī)碳含量與連作年限極顯著負(fù)相關(guān), 而速效氮、速效鉀含量及電導(dǎo)率與連作年限顯著或極顯著正相關(guān)。

2.2 不同連作年限馬鈴薯土壤酶活性的變化

不同連作年限土壤的酶活性測(cè)定結(jié)果如表2所示。連作處理土壤脲酶活性較RP有不同幅度下降, 僅CP4處理達(dá)顯著水平。連作處理蔗糖酶活性較RP顯著下降31.72%~75.19%, 堿性磷酸酶和多酚氧化酶活性無(wú)顯著差異。連作處理脫氫酶活性較RP有不同幅度下降, 僅CP4處理顯著下降83.53%。綜合計(jì)算表明, CP1和CP2處理土壤平均酶活性與RP無(wú)顯著差異, CP3-CP5處理顯著下降33.07%~61.78%。脲酶、蔗糖酶、脫氫酶和土壤平均酶活性與連作年限均顯著或極顯著地線性負(fù)相關(guān)。

表1 馬鈴薯連作年限對(duì)土壤化學(xué)性質(zhì)的影響

RP為連作0年(未連作), CP1-CP5為連作1~5年處理。同列不同小寫字母表示各連作年限處理間5%差異顯著水平。RP, CP1, CP2, CP3, CP4 and CP5 are treatments of continuous potato monoculture for 0, 1, 2, 3, 4 and 5 years, respectively. Different lowercase letters in the same column mean significant differences at 5% level by Duncan’s test. YCPM: year of continuous potato monoculture.

表2 馬鈴薯連作年限對(duì)土壤酶活性的影響

RP為連作0年(未連作), CP1-CP5為連作1~5年處理。同列不同小寫字母表示各連作年限處理間5%差異顯著水平。RP, CP1, CP2, CP3, CP4 and CP5 are treatments of continuous potato monoculture for 0, 1, 2, 3, 4 and 5 years, respectively. Different lowercase letters in the same column mean significant differences at 5% level by Duncan’s test. YCPM: year of continuous potato monoculture.

2.3 不同連作年限馬鈴薯土壤微生物活性的變化

不同連作年限土壤微生物活性測(cè)定結(jié)果如表3所示。CP1、CP2和CP5處理微生物生物量碳含量較RP無(wú)顯著變化, 而CP3和CP4處理分別顯著下降28.63%和24.85%; 與CP1相比, CP2-CP5處理土壤微生物生物量碳含量顯著降低23.55%~38.29%。相似的變化趨勢(shì)也表現(xiàn)在土壤基礎(chǔ)呼吸量和FDA水解活性上, 連作處理與非連作無(wú)顯著差異, 但CP2- CP5處理較CP1出現(xiàn)大幅降低, 且除CP3處理外均達(dá)到差異顯著水平。連作處理土壤微生物熵和微生物代謝熵較非連作相比均無(wú)顯著差異。土壤微生物生物量碳、基礎(chǔ)呼吸量和FDA水解活性與連作年限均極顯著負(fù)相關(guān)。

2.4 不同連作年限馬鈴薯土壤微生物功能多樣性的變化

由圖1可知, 在整個(gè)培養(yǎng)周期內(nèi), CP1和CP2處理較RP無(wú)明顯差異, 而CP3-CP5處理顯著下降, 至培養(yǎng)第168 h, CP3-CP5處理平均顏色變化率較RP顯著降低50.23%~56.80%。功能多樣性指數(shù)的計(jì)算結(jié)果如表4所示, 除Pielou均勻度指數(shù)和豐富度指數(shù)外, CP3-CP5處理Shannon多樣性指數(shù)、Simpson優(yōu)勢(shì)度指數(shù)和McIntosh 指數(shù)均顯著低于RP。馬鈴薯長(zhǎng)期連作顯著降低土壤微生物總活性和微生物功能多樣性。

表3 馬鈴薯連作年限對(duì)土壤微生物活性的影響

RP為連作0年(未連作), CP1-CP5為連作1~5年處理。同列不同小寫字母表示各連作年限處理間5%差異顯著水平。RP, CP1, CP2, CP3, CP4 and CP5 are treatments of continuous potato monoculture for 0, 1, 2, 3, 4 and 5 years, respectively. Different lowercase letters in the same column mean significant differences at 5% level by Duncan’s test. YCPM: year of continuous potato monoculture.

RP為連作0年(未連作), CP1-CP5為連作1~5年處理。RP, CP1, CP2, CP3, CP4 and CP5 are treatments of continuous potato monoculture for 0, 1, 2, 3, 4 and 5 years, respectively.

基于Biolog Eco測(cè)定的微生物對(duì)碳源底物利用結(jié)果, 通過(guò)主成分分析評(píng)估馬鈴薯連作對(duì)土壤微生物群落結(jié)構(gòu)的影響(圖2)。在31個(gè)因子中共提取7個(gè)主成分, 其中第1主成分和第2主成分分別解釋整體方差變異的48.26%和9.58%, 而其余各主成分的貢獻(xiàn)率相對(duì)較小。在PC1軸上, RP和CP1處理、CP2處理以及CP3-CP5處理3組供試土壤樣品出現(xiàn)明顯的分異, 表明三者對(duì)碳源利用能力存在較大差別, 顯示馬鈴薯長(zhǎng)期連作已經(jīng)改變土壤微生物群落結(jié)構(gòu)。31種單一碳源的利用情況與PC1的相關(guān)分析表明, 共有8種碳源的利用程度與PC1存在高度線性正相關(guān)關(guān)系(>0.8,<0.01), 其中7種屬于碳水化合物, 1種屬于氨基酸類化合物(表5), 暗示土壤微生物群落結(jié)構(gòu)的改變可能與不同連作年限下以碳水化合物為主要碳源利用類型的微生物的差異有關(guān)。

微生物對(duì)6大類碳源的相對(duì)利用率計(jì)算結(jié)果如圖3所示。馬鈴薯長(zhǎng)期連作顯著降低土壤微生物對(duì)碳水化合物類、氨基酸類、羧酸類和胺類碳源的相對(duì)利用率, 且以碳水化合物類的降幅最大, CP3-CP5處理較RP顯著降低約54.39%~67.36%。由表6可知, 相對(duì)利用率較低的碳源(<2.5%)在RP處理下是10種, 在CP1-CP5處理下分別是10種、11種、15種、16種和16種; 相對(duì)利用率處于中等水平的碳源(2.5%~ 5.0%)在RP處理下是17種, 在CP1-CP5處理下分別是15種、12種、9種、8種和8種; 而相對(duì)利用率較高的碳源(>5.0%)在RP處理下是4種, 在CP1-CP5處理下分別是6種、8種、7種、7種和7種。碳源低利用率預(yù)示著微生物對(duì)其利用能力的衰退, 高利用率表明微生物對(duì)其利用需求較高。就31種單一碳源而言, 隨著馬鈴薯連作年限延長(zhǎng), 土壤微生物對(duì)碳源的利用表現(xiàn)出從分散化到集中化的趨勢(shì)。在CP3-CP5處理下, 土壤微生物更多地是利用L-天冬酰胺酸、丙酮酸甲酯、D-蘋果酸、4-羥基苯甲酸、吐溫40和吐溫80等碳源。統(tǒng)計(jì)分析表明,b-甲基-D-葡萄糖苷、D-纖維二糖、L-蘇氨酸和D-葡萄胺酸等碳源的相對(duì)利用率與連作年限均呈現(xiàn)顯著或極顯著線性負(fù)相關(guān)關(guān)系, 而丙酮酸甲酯和吐溫80則與連作年限存在顯著或極顯著線性正相關(guān)關(guān)系。盡管4-羥基苯甲酸、吐溫40、D-蘋果酸、D-半乳糖酸-g-內(nèi)酯和L-天冬酰胺酸等碳源的相對(duì)利用率整體上也表現(xiàn)出隨連作年限延長(zhǎng)而增加的趨勢(shì), 但線性相關(guān)測(cè)試未達(dá)到統(tǒng)計(jì)顯著水平。

表4 馬鈴薯連作年限對(duì)土壤微生物功能多樣性的影響

RP為連作0年(未連作), CP1-CP5為連作1~5年處理。同列不同小寫字母表示各連作年限處理間5%差異顯著水平。RP, CP1, CP2, CP3, CP4 and CP5 are treatments of continuous potato monoculture for 0, 1, 2, 3, 4 and 5 years, respectively. Different lowercase letters in the same column mean significant differences at 5% level by Duncan’s test. YCPM: year of continuous potato monoculture.

RP為連作0年(未連作), CP1-CP5為連作1~5年處理。RP, CP1, CP2, CP3, CP4 and CP5 are treatments of continuous potato monoculture for 0, 1, 2, 3, 4 and 5 years, respectively.

2.5 回歸分析和通徑分析

以塊莖產(chǎn)量作因變量, 以土壤因子作自變量, 采用線性逐步回歸分析方法, 探討不同土壤因子對(duì)塊莖產(chǎn)量的影響。結(jié)果顯示主成分因子1、微生物生物量碳、全氮和脫氫酶對(duì)塊莖產(chǎn)量具有顯著影響, 且均表現(xiàn)為明顯的正效應(yīng), 而其余土壤因子均未達(dá)到統(tǒng)計(jì)顯著水平(>0.05)?；貧w方程如下:= 13.188 2+3.061 11+0.093 82+6.586 53+22.472 14(=0.961 1,=0.022 6,=24), 其中表示塊莖產(chǎn)量,1表示主成分因子1,2表示微生物生物量碳,3表示全氮,4表示脫氫酶。結(jié)合線性相關(guān)分析, 計(jì)算得到上述4個(gè)土壤因子對(duì)塊莖產(chǎn)量的通徑系數(shù), 結(jié)果如表7所示。主成分因子1的直接通徑系數(shù)為0.553 6, 遠(yuǎn)高于其他3個(gè)因子, 顯示其對(duì)塊莖產(chǎn)量的直接影響作用最大。微生物生物量碳對(duì)塊莖產(chǎn)量的影響作用次之, 其直接通徑系數(shù)為0.382 1, 并且微生物生物量碳可通過(guò)主成分因子1在較大程度上來(lái)間接影響塊莖產(chǎn)量(間接通徑系數(shù)為0.336 4)。全氮和脫氫酶的直接通徑系數(shù)分別為0.197 5和0.187 5, 表明二者對(duì)塊莖產(chǎn)量的直接影響作用相對(duì)較小, 但脫氫酶通過(guò)主成分因子1對(duì)塊莖產(chǎn)量的間接影響作用要高于其直接影響作用(間接通徑系數(shù)為0.216 3)。

表5 微生物對(duì)碳源的利用情況與PC1的相關(guān)分析

“—”表中相關(guān)系數(shù)<0.8或>-0.8。*,< 0.05; **,< 0.01. When symbol “—” was given in the table, the correlation coefficient was < 0.8 or >-0.8.

RP為連作0年(未連作), CP1-CP5為連作1~5年處理。CH: 碳水化合物類; AA: 氨基酸類; CA: 羧酸類; AM: 胺類; PC: 酚酸類; PO: 聚合物類。RP, CP1, CP2, CP3, CP4 and CP5 are treatments of continuous potato monoculture for 0, 1, 2, 3, 4 and 5 years, respectively. CH: carbohydrates; AA: amino acids; CA: carboxylic acids; AM: amines; PC: phenolic compounds; PO: polymers.

3 結(jié)論和討論

3.1 馬鈴薯連作對(duì)土壤化學(xué)性質(zhì)的影響

有機(jī)碳是維持土壤可持續(xù)生產(chǎn)力的關(guān)鍵因素,且有機(jī)碳庫(kù)與土壤質(zhì)量和作物生產(chǎn)力有密切關(guān)系。本研究表明, 馬鈴薯長(zhǎng)期連作降低土壤有機(jī)碳含量, 隨著連作年限延長(zhǎng), 土壤有機(jī)碳含量呈逐漸降低趨勢(shì), 相似結(jié)果也被早前學(xué)者報(bào)道[36-37]。長(zhǎng)期連作能夠?qū)е峦寥烙袡C(jī)質(zhì)中穩(wěn)定性結(jié)構(gòu)減少, 而易分解結(jié)構(gòu)增加, 有機(jī)質(zhì)結(jié)構(gòu)趨于簡(jiǎn)單化, 易被分解, 碳含量降低[38]。棉花長(zhǎng)期連作導(dǎo)致0~40 cm深度內(nèi)土壤有機(jī)碳的活性指數(shù)顯著增加, 但難降解指數(shù)則顯著降低[39]。團(tuán)聚體的物理保護(hù)是土壤有機(jī)碳重要的穩(wěn)定機(jī)制, 長(zhǎng)期連作可能是通過(guò)改變土壤中不同粒級(jí)團(tuán)聚體的比例及其碳含量進(jìn)而降低有機(jī)碳的穩(wěn)定性[40]。長(zhǎng)期耕種和缺乏有機(jī)投入, 使得土壤有機(jī)碳庫(kù)輸入少、輸出多, 這也會(huì)導(dǎo)致連作土壤有機(jī)碳含量降低[41]。也有學(xué)者報(bào)道了長(zhǎng)期連作下土壤有機(jī)碳含量高于非連作或短期連作的現(xiàn)象[42-43], 但作物產(chǎn)量依然隨連作而降低。沈?qū)氃频萚44]研究顯示, 即使大量施用普通有機(jī)肥或生物有機(jī)肥, 連作馬鈴薯塊莖產(chǎn)量同樣會(huì)大幅下降。盡管本研究中土壤有機(jī)碳含量和塊莖產(chǎn)量存在著顯著正相關(guān)關(guān)系, 然而逐步回歸分析顯示前者對(duì)后者并無(wú)顯著影響。有研究推測(cè), 相比較于土壤有機(jī)碳含量, 土壤有機(jī)碳質(zhì)量可能與連作障礙的關(guān)系更為密切[43], 但目前仍然缺乏直接證據(jù)。

表6 不同馬鈴薯連作年限下土壤微生物對(duì)單一碳源的相對(duì)利用率比較

RP為連作0年(未連作), CP1-CP5為連作1~5年處理。LCA: 單一碳源的相對(duì)利用率與連作年限間的線性相關(guān)分析(=24)。RP, CP1, CP2, CP3, CP4 and CP5 are treatments of continuous potato monoculture for 0, 1, 2, 3, 4 and 5 years, respectively. LCA: linear correlation analysis between year of continuous potato monoculture and the relative utilization ratio of sole-carbon source substrate (=24).

表7 土壤性質(zhì)與塊莖產(chǎn)量的通徑分析

PC1: principal component factor 1; MBC: microbial biomass carbon; TN: total nitrogen; DE: dehydrogenase.

田間試驗(yàn)結(jié)果表明, 馬鈴薯長(zhǎng)期連作增加土壤堿解氮、速效磷、速效鉀含量和電導(dǎo)率, 且除速效磷外, 均與連作年限有顯著或極顯著線性正相關(guān)關(guān)系。馬鈴薯連作條件下植株生長(zhǎng)發(fā)育變差, 對(duì)養(yǎng)分消耗減少, 伴隨常年化肥施用, 使得土壤養(yǎng)分輸入多、輸出少, 逐漸累積[45], 引起電導(dǎo)率上升。與早前報(bào)道相比[46], 本研究未發(fā)現(xiàn)土壤pH隨連作出現(xiàn)規(guī)律性變化, 可能與供試土壤性質(zhì)差異有關(guān)。農(nóng)作物由于其自身營(yíng)養(yǎng)特性的原因?qū)τ谕寥鲤B(yǎng)分并非均衡性吸收, 有學(xué)者據(jù)此認(rèn)為長(zhǎng)此以往所帶來(lái)的土壤養(yǎng)分虧缺、比例失調(diào)或不平衡會(huì)導(dǎo)致連作障礙發(fā)生[47-49],但本試驗(yàn)結(jié)果并不支持該論斷。

3.2 馬鈴薯連作對(duì)土壤酶活性的影響

馬鈴薯連作導(dǎo)致土壤脲酶、蔗糖酶和脫氫酶活性降低, 且后兩者與連作年限顯著或極顯著線性負(fù)相關(guān)。整體來(lái)看, 連作土壤平均酶活性較非連作顯著下降。土壤酶來(lái)源于動(dòng)植物殘?bào)w分解、微生物生產(chǎn)和根系分泌物, 故而土壤有機(jī)質(zhì)、微生物代謝強(qiáng)度和作物長(zhǎng)勢(shì)是影響土壤酶活性的主要因子[50]。通常來(lái)看, 有機(jī)質(zhì)含量高的土壤同樣具有高水平的酶活性[51], 土壤有機(jī)質(zhì)含量的增加能促進(jìn)有機(jī)質(zhì)或礦質(zhì)膠體與酶分子之間復(fù)合體的形成[52]。本研究結(jié)果也證明土壤有機(jī)質(zhì)含量與脲酶、堿性磷酸酶、蔗糖酶和脫氫酶活性均顯著或極顯著正相關(guān), 馬鈴薯連作土壤有機(jī)碳含量降低應(yīng)是酶活性下降的重要原因。此外, 長(zhǎng)期連作土壤微生物生物量碳含量、土壤基礎(chǔ)呼吸量、FDA水解活性和AWCD降低, 土壤微生物代謝受到抑制, 這將使得土壤微生物對(duì)酶的生產(chǎn)量減少[53]。

脫氫酶活性表征土壤氧化還原狀況并與微生物的氧化能力關(guān)聯(lián)。本研究證明脫氫酶活性與土壤基礎(chǔ)呼吸量、FDA水解活性和AWCD均顯著或極顯著正相關(guān)。土壤脫氫酶活性和塊莖產(chǎn)量隨連作雙雙下降, 并且前者對(duì)后者的影響作用達(dá)到統(tǒng)計(jì)顯著水平, 而通徑分析則表明這種影響作用更多地是借由土壤微生物群落結(jié)構(gòu)作為橋梁來(lái)間接實(shí)現(xiàn)。多酚氧化酶能酶促一、二及三元酚氧化為醌, 在土壤芳香族有機(jī)化合物轉(zhuǎn)化為腐殖質(zhì)組分的過(guò)程中起重要作用。酚酸是常見的化感/自毒物質(zhì), 有學(xué)者認(rèn)為多酚氧化酶活性降低能夠?qū)е峦寥乐蟹铀犷惢衔锓e累, 帶來(lái)潛在的自毒效應(yīng)并改變土壤微生物群落結(jié)構(gòu)[54-56]。但本研究中土壤多酚氧化酶活性并未因馬鈴薯連作而出現(xiàn)顯著變化。

3.3 馬鈴薯連作對(duì)土壤微生物功能多樣性和碳源利用的影響

本研究結(jié)果表明, 馬鈴薯長(zhǎng)期連作顯著降低土壤微生物活性和微生物功能多樣性, 土壤微生物群落結(jié)構(gòu)隨連作明顯改變。張雪艷等[57]研究表明, 溫室黃瓜()連作顯著降低土壤微生物對(duì)碳水化合物類、羧酸類、聚合物類、氨基酸類和胺類碳源的利用強(qiáng)度。岳冰冰等[58]指出, 烤煙()輪作與連作相比, 土壤微生物對(duì)碳源的利用強(qiáng)度除胺類以外均有顯著提高。李玉娣等[59]也證明, 大棚蔬菜種植土壤微生物對(duì)碳水化合物類和氨基酸類碳源的利用隨連作年限出現(xiàn)巨大分異。馬鈴薯長(zhǎng)期連作下土壤微生物對(duì)碳水化合物類、氨基酸類、羧酸類和胺類碳源的相對(duì)利用率均有顯著降低, 其中又以碳水化合物類碳源的平均降幅最大, 而微生物群落結(jié)構(gòu)變化特別是以碳水化合物為碳源的微生物群落改變應(yīng)是直接原因, 碳水化合物是區(qū)分不同連作年限處理微生物群落結(jié)構(gòu)差異的最敏感碳源。碳水化合物是自然界中存在最多、具有廣譜化學(xué)結(jié)構(gòu)和生物功能的有機(jī)化合物, 是微生物利用最廣的碳源, 在微生物分解代謝中占有重要地位?；诟咄繙y(cè)序發(fā)現(xiàn), 馬鈴薯長(zhǎng)期連作顯著降低土壤細(xì)菌群落的結(jié)構(gòu)多樣性和豐富度[19], 這直接導(dǎo)致微生物對(duì)碳水化合物類碳源相對(duì)利用率的快速下降。馬玲等[60]發(fā)現(xiàn), 土壤微生物對(duì)碳水化合物的相對(duì)利用率隨著馬鈴薯連作年限延長(zhǎng)而顯著下降, 但其他類碳源則變化不明顯, 并認(rèn)為代謝功能強(qiáng)弱可能與微生物主要類群組成有關(guān), 功能的變化由特定微生物類群決定。微生物對(duì)單一碳源利用與PC1的相關(guān)分析顯示, 微平板上所包含的10種碳水化合物類碳源其中有7種的利用強(qiáng)度與PC1高度正相關(guān)(>0.8,<0.01), 這間接證實(shí)了上述報(bào)道。

根系分泌物是根際微生物利用碳源的主要來(lái)源。有研究指出[21-22], 馬鈴薯連作較非連作根系分泌物組分變化明顯, 糖類所占比例降低, 而有機(jī)酸類比例增加。但本研究中長(zhǎng)期連作土壤微生物對(duì)氨基酸類、羧酸類和酚酸類碳源的相對(duì)利用率較非連作反而顯著降低, 這可能一方面與微平板內(nèi)碳源種類的選擇有關(guān), 另一方面也與連作土壤微生物數(shù)量減少有關(guān)。31種單一碳源相對(duì)利用率的分級(jí)顯示, 長(zhǎng)期連作改變土壤微生物對(duì)碳源的利用模式, 使之更為集中地利用少數(shù)幾種碳源底物, 這與早前學(xué)者對(duì)連作黃瓜的報(bào)道一致[35]。長(zhǎng)期連作土壤微生物對(duì)L-天冬酰胺酸、丙酮酸甲酯、D-蘋果酸、4-羥基苯甲酸、吐溫40和吐溫80等碳源的相對(duì)利用率較高, 其中前4種均屬于有機(jī)酸。

3.4 土壤微生物因子與馬鈴薯連作障礙的關(guān)系

線性逐步回歸分析顯示, PC1和微生物生物量碳顯著影響塊莖產(chǎn)量, 通徑分析表明, 前者的直接貢獻(xiàn)遠(yuǎn)高于后者。PC1和微生物生物量碳實(shí)質(zhì)是表征土壤微生物群落結(jié)構(gòu)和微生物數(shù)量?jī)蓚€(gè)概念。本研究條件下, 微生物群落結(jié)構(gòu)是影響連作馬鈴薯生產(chǎn)力最重要的土壤因子。馬鈴薯連作顯著影響土壤微生物群落結(jié)構(gòu), 相似的結(jié)果也在其他作物上得到證明[36,45,61-66]。長(zhǎng)期連作導(dǎo)致甘肅中部沿黃灌區(qū)馬鈴薯干腐病、立枯病和黃萎病等土傳病害泛濫, 降低塊莖產(chǎn)量?；赑CR-DGGE、Real-time PCR以及高通量測(cè)序等方法研究發(fā)現(xiàn), 土壤中、、sp.等土傳致病菌隨馬鈴薯連作大量積累[14-20]。馬鈴薯長(zhǎng)期連作導(dǎo)致土壤從抑病型向?qū)Р⌒娃D(zhuǎn)變, 而微生物群落結(jié)構(gòu)的變化是主要原因[14,67]。土傳病害的抑制在一定程度上是土壤微生物群體的作用, 當(dāng)微生物群落結(jié)構(gòu)越豐富、多樣性越高時(shí), 作物對(duì)抗病原菌的綜合能力就越強(qiáng)。長(zhǎng)期連作破壞土壤微生物群落結(jié)構(gòu), 微生物種間互作呈現(xiàn)無(wú)序和弱化狀態(tài)[14,65], 有益微生物或具有潛在生防能力的微生物豐度降低[68], 對(duì)土傳致病菌的競(jìng)爭(zhēng)能力下降。有學(xué)者直接指出, 連作土壤中土傳致病菌的積累是以有益微生物的減少作為代價(jià)[68-69]。但導(dǎo)致連作土壤微生物群落結(jié)構(gòu)出現(xiàn)這種定向性變化的深層次機(jī)理尚不明確, 推測(cè)可能與根系分泌物有關(guān)。

根系分泌物是土壤-微生物-植物體系重要的調(diào)節(jié)者。根系分泌物影響土壤微生物群落結(jié)構(gòu), 而微生物自身也能夠直接作用于根系分泌物或者通過(guò)影響植物生長(zhǎng)發(fā)育來(lái)改變根系分泌物的組成和種類。不同于早前學(xué)者的傳統(tǒng)理解, 已有報(bào)道指出[5,56], 連作障礙的發(fā)生更多地是與根系分泌物對(duì)土壤微生物群落的改變有關(guān), 而非根系分泌物對(duì)植株直接的自毒作用。對(duì)連作花生的研究表明[5], 根系分泌物對(duì)土壤微生物的影響具有選擇性, 表現(xiàn)為增加等致病菌的相對(duì)豐度, 而抑制PGPRs和菌根真菌等有益菌的相對(duì)豐度。張文明等[21]研究發(fā)現(xiàn), 輪作和連作馬鈴薯根系分泌物都可促進(jìn)立枯病病原菌的生長(zhǎng), 但后者的促進(jìn)作用更為顯著。因此, 在本研究的基礎(chǔ)上明確連作馬鈴薯根系分泌物和土壤微生物群落結(jié)構(gòu)之間的關(guān)系將是未來(lái)厘清甘肅中部沿黃灌區(qū)馬鈴薯連作障礙機(jī)理和形成高效連作土壤障礙因子消減技術(shù)的關(guān)鍵點(diǎn)。

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Effect of continuous potato monoculture on soil chemical and biological properties in Yellow River Irrigation Area incentral Gansu Province*

LIU Xing1,2, QIU Huizhen1**, ZHANG Wenming1, ZHANG Chunhong1, ZHU Jing1, MA Xing1, CHENG Wanli1

(1. College of Resources and Environmental Sciences, Gansu Agricultural University/ Gansu Provincial Key Lab of Aridland Crop Science,Lanzhou 730070, China;2. College of Resources and Environmental Sciences,Henan Institute of Science and Technology,Xinxiang 453003,China)

The irrigation area along the Yellow River in central Gansu Province is an important growing region of processing potato and seed potato in China. Continuous potato monoculture (CPM) stemming from intensive cultivation has severely affected the healthy development of local potato industry. It is necessary to increase our understanding about the barrier associated with CPM. To that, a long-term field experiment was conducted, which contained 5 potato cropping treatments corresponding to continuous potato cropping for 1–5 years, with maize-potato rotation cropping as the control. In the study, we focused on how the soil chemical and biological properties changed in CPM system, and which soil variables contributed principally to the barriers of CPM. The study showed that contrary to alkaline hydrolyzable nitrogen, NH4OAc extractable potassium and electrical conductivity, soil organic carbon content gradually decreased with increasing years of CPM. Also compared with the control, CPM significantly increased soil NaHCO3extractable phosphorus content. However, there were no significant changes in total nitrogen, C/N ratio and pH. Compared with the control, long-term CPM (over 3–5 years) decreased mean soil enzyme activity by 33.07%–61.78%. The activities of urease, sucrose and dehydrogenase decreased with increasing years of CPM. Long-term CPM decreased the content of soil microbial biomass carbon, while both soil basal respiration and FDA hydrolysis activity exhibited highly significant linear negative correlation with the number of year of CPM. Results of Biolog ECO assessment indicated that long-term CPM significantly decreased total activity and function diversity of soil microbes, where Shannon diversity index for long-term CPM decreased by 11.75%–13.65% compared with the control. Principal component analysis of carbon utilization profile of soil microbes showed that long-term CPM clearly changed the structure of soil microbial community compared with the control. Among the 6 groups of carbon source substrates, carbohydrates type was most sensitive to the changes in soil microbial communities in CPM system. Long-term CPM significantly decreased the relative utilization ratio of selected carbon source substrates for soil microbes, including carbohydrates, amino acids, carboxylic acids and amines. For 31 sole-carbon source substrates, the utilization pattern of soil microbes under long-term CPM was more centralized than under the control or short-term CPM. Linear models of stepwise regression analysis and path analysis confirmed that a total of 4 soil variables (soil microbial community structure, soil microbial biomass carbon, total nitrogen and dehydrogenase) significantly affected tuber yield under CPM system, and that soil microbial community structure contributed most, followed by soil microbial biomass carbon. The results of the study suggested that soil microbial variables were the main causes of the barriers of CPM system in the Yellow River Irrigation Area in central Gansu Province.

Potato; Continuous monoculture; Soil chemical property; Biological property

10.13930/j.cnki.cjea.160848

S154.1; S154.4; S154.36

A

1671-3990(2017)04-0581-13

2016-09-21

2016-11-23

Sep. 21, 2016; accepted Nov. 23, 2016

* 公益性行業(yè)(農(nóng)業(yè))科研專項(xiàng)(201103004)、國(guó)家科技支撐計(jì)劃項(xiàng)目(2012BAD06B03)、國(guó)家馬鈴薯產(chǎn)業(yè)技術(shù)體系(CARS-10-P18)和甘肅省科技重大專項(xiàng)(1102NKDA025)資助

* Supported by the Special Fund for Agro-scientific Research in the Public Interest of China (201103004), the National Key Technologies R&D Program of China (2012BAD06B03), the Special Fund for the Industrial Technology System Construction of Modern Agriculture (CARS- 10-P18), and the Municipal Science and Technology Project of Gansu Province (1102NKDA025)

** Corresponding author, E-mail: hzqiu@gsau.edu.cn

**通訊作者:邱慧珍, 主要研究方向?yàn)橹参餇I(yíng)養(yǎng)與根際生態(tài)學(xué)。E-mail: hzqiu@gsau.edu.cn

劉星, 從事植物營(yíng)養(yǎng)和土壤生態(tài)學(xué)研究。E-mail: liuxingnice@163.com

劉星, 邱慧珍, 張文明, 張春紅, 朱靜, 馬興, 程萬(wàn)莉. 甘肅中部沿黃灌區(qū)馬鈴薯連作對(duì)土壤化學(xué)和生物學(xué)性質(zhì)的影響[J].中國(guó)生態(tài)農(nóng)業(yè)學(xué)報(bào), 2017, 25(4): 581-593

Liu X, Qiu H Z, Zhang W M, Zhang C H, Zhu J, Ma X, Cheng W L. Effect of continuous potato monoculture on soil chemical and biological properties in Yellow River Irrigation Area in central Gansu Province[J]. Chinese Journal of Eco-Agriculture, 2017, 25(4): 581-593