倪 奎

(安徽新聞出版職業(yè)技術(shù)學(xué)院 新聞傳播系， 合肥 230061)

野生矮桃生物量分布及其對(duì)硒與礦質(zhì)元素的利用特性

倪 奎

(安徽新聞出版職業(yè)技術(shù)學(xué)院 新聞傳播系， 合肥 230061)

分析野生矮桃生物量分布規(guī)律，以及對(duì)硒與礦質(zhì)元素的吸收、遷移及其相關(guān)性的探究。采取野生矮桃樣本，測(cè)出其生物量；分別采用原子發(fā)光色譜法和原子熒光法，對(duì)不同居群的矮桃植株及土壤中礦質(zhì)元素和硒元素進(jìn)行測(cè)定，并進(jìn)行相關(guān)性分析。結(jié)果顯示：矮桃葉的生物量分配率最高，矮桃根和果實(shí)中的硒與鉀含量成顯著負(fù)相關(guān)，矮桃葉中的硒含量最高。為探究矮桃作為富硒植物開發(fā)提供了基本科學(xué)依據(jù)。

矮桃;生物量;礦質(zhì)元素;硒;相關(guān)性

矮桃(LysimachiaclethroidesDuby)隸屬報(bào)春花科(Primulaceae)珍珠菜屬(LysimachiaL.)[1]。我國(guó)珍珠菜屬植物資源十分豐富，是一類具有豐富利用價(jià)值的植物類群，常生于山坡林緣和草叢中[2]，是一種具有較高食用價(jià)值的綠色食品[3]，種子脂肪油含量達(dá)32%，可用于制作肥皂等[2]。其植物體含14 種以上黃酮類化合物，在抗腫瘤方面具有重要應(yīng)用前景與價(jià)值[4-6]。

硒是人體和動(dòng)物的必需營(yíng)養(yǎng)元素[7]，缺硒可導(dǎo)致人、畜產(chǎn)生多種疾病[8-10]，我國(guó)大約有72 %的縣處于缺硒或嚴(yán)重缺硒狀態(tài)[11]。研究顯示，安徽池州產(chǎn)野生珍珠菜中的鋅硒含量高[3]。研究從矮桃的個(gè)體生物量分布規(guī)律、矮桃對(duì)硒及礦質(zhì)元素的吸收、轉(zhuǎn)移與利用等特性角度探究矮桃作為富硒植物開發(fā)具有一定價(jià)值。

我國(guó)珍珠菜屬植物資源十分豐富，有138種[1]?！栋不罩参镏尽酚涊d安徽廣布有該屬植物23種1變型[2]。近年還發(fā)現(xiàn)右旋過路黃(L.dextralflora)與祁門過路黃(L.qimenensis)兩新種及距萼過路黃(L.crista-galli)一個(gè)地理分布新記錄種[12-13]。研究表明，該屬植物在民間作為藥用植物資源非常普遍[14]，多數(shù)種類具有清熱解毒、利尿排石、活血散瘀等功效，可用于治療跌打損傷、骨折、風(fēng)濕疼痛及咳喘等病癥；現(xiàn)代醫(yī)學(xué)研究也證明該屬植物在治療腎炎、肝炎、尿路結(jié)石、心肌缺血、婦科疾病、抗腫瘤等方面具有明顯療效[15-17]。該屬植物除了具有上述重要的藥用價(jià)值外，還具有較好的觀賞價(jià)值、工業(yè)價(jià)值及食用價(jià)值[18]。有研究表明，安徽池州產(chǎn)野生珍珠菜中的鋅硒含量高。然而，關(guān)于矮桃的個(gè)體生物學(xué)基礎(chǔ)研究較為缺乏，如生物量分布規(guī)律，矮桃對(duì)硒及礦質(zhì)營(yíng)養(yǎng)元素的吸收、轉(zhuǎn)移、分布與利用等特性。本研究通過對(duì)安徽產(chǎn)不同地區(qū)的矮桃為研究材料，初步掌握其相關(guān)規(guī)律，為矮桃的合理高效持續(xù)的開發(fā)利用提供依據(jù)。

1 材料和方法

1.1 材料來源

2012年8月，分別在安徽金寨縣青山鎮(zhèn)湯店村、岳西縣天堂鎮(zhèn)葉畈村和蕪湖市南陵縣籍山鎮(zhèn)千峰村采集野生矮桃結(jié)果期樣品。在3個(gè)采集地分別選取3個(gè)代表性野生矮桃居群，生境條件皆為林緣，分根、莖、葉、果實(shí)4大植物功能器官以及土壤(0～30 cm)同時(shí)收集，每個(gè)居群重復(fù)采集3次，并分裝于牛皮紙袋中帶回實(shí)驗(yàn)室。

1.2 研究方法

1.2.1 土壤樣品采集與處理

在每個(gè)調(diào)查居群內(nèi)用內(nèi)徑 25 mm 的土鉆鉆取0～30 cm土壤樣品，帶回實(shí)驗(yàn)室，晾置于通風(fēng)處風(fēng)干，用研缽將土壤碾碎，過100目篩，裝入自封袋，待測(cè)。

1.2.2 植物樣品采集與處理

將來自不同地區(qū)，分不同器官的樣品首先用自來水沖洗掉泥沙及污染物，然后用去離子水清洗3次，再將其置于75℃烘箱中烘干24 h至恒重，待測(cè)。

1.2.3 矮桃生物量測(cè)定

將烘干至恒重的不同樣品用萬(wàn)分之一電子天平分別稱量質(zhì)量。

1.2.4 礦質(zhì)元素測(cè)定

將烘干的植物器官樣品用粉碎機(jī)粉碎，以及土壤樣品各稱取0.5 g于開氏瓶中，加濃HNO3∶HClO4混合酸(12∶3)15 mL，放置數(shù)小時(shí)后，在電爐上慢慢升溫加熱，使黃棕色煙慢慢揮發(fā)，再適當(dāng)提高溫度繼續(xù)消化，至冒出大量白煙，消化液呈白色透明狀，約2 mL時(shí)為止，取下，待冷卻后定容至50 mL。然后采用原子發(fā)色光譜法測(cè)定礦質(zhì)元素含量。共檢測(cè)K、Na、Mg、Ca、Al、Cu、Fe、Zn、Mn等9種礦質(zhì)元素含量。

1.2.5 硒元素測(cè)定

將烘干的植物器官樣品用粉碎機(jī)粉碎，再用研缽研磨后過100目篩，以及土壤樣品各稱取0.2 g于開氏瓶中，加濃HNO3∶HClO4混合酸(8∶2)10 mL，放置數(shù)小時(shí)后，在電爐上慢慢升溫加熱，使黃棕色煙慢慢揮發(fā)，再適當(dāng)提高溫度繼續(xù)消化，至冒出大量白煙，消化液呈白色透明狀，約2 mL時(shí)為止，取下，待冷卻加5 mL HCl(優(yōu)級(jí)純)過夜，定容至25 mL。然后采用原子熒光法測(cè)定硒元素含量。

1.3 數(shù)據(jù)處理與分析

生物吸收系數(shù)(Ax) =Ep/Es。式中，Ep和Es分別代表化學(xué)元素在植物干物質(zhì)中的含量與其生長(zhǎng)地土壤中的含量。

元素累積量=器官生物量×元素含量

本實(shí)驗(yàn)以生物吸收系數(shù)衡量矮桃對(duì)9種礦質(zhì)元素及硒的富集能力，以元素含量及累積量衡量9種礦質(zhì)元素及硒從土壤到生物體及生物體形態(tài)學(xué)下端到形態(tài)學(xué)上端的吸收與遷移特性。

以不同器官生物量差異性反應(yīng)矮桃植株的生物量分布特征。

采用SPSS 13.0 for Windows軟件進(jìn)行差異顯著性檢驗(yàn)與多重比較，差異顯著性檢驗(yàn)前對(duì)數(shù)據(jù)進(jìn)行轉(zhuǎn)換，以確保符合方差分析的基本條件。數(shù)據(jù)結(jié)果以“平均值±標(biāo)準(zhǔn)誤”表示，采用Microsoft Office Excel 2007軟件作圖。

2 結(jié)果與分析

2.1 矮桃生物量分布特征

2.1.1 不同地區(qū)單株矮桃總生物量及根冠比

不同地區(qū)矮桃單株平均總生物量如圖1所示，其中岳西縣產(chǎn)矮桃單株平均總生物量最高，為(8.796±1.239)g。方差分析與多重比較結(jié)果顯示，3個(gè)不同地區(qū)產(chǎn)矮桃單株總生物量無顯著差異(F=2.194,P>0.05)。從實(shí)驗(yàn)結(jié)果分析，在相似生境條件下，矮桃表現(xiàn)出對(duì)資源競(jìng)爭(zhēng)利用能力的一致性特點(diǎn)。

圖1 不同地區(qū)矮桃單株平均總生物量Fig 1 The average general biomass of L. clethroides in different areas

如表1所示，不同地區(qū)產(chǎn)矮桃植株根冠比表現(xiàn)出顯著差異(F=13.415,P﹤0.05)，從大到小為金寨縣>岳西縣>蕪湖市，總平均根冠比為(0.396±0.070)。這表明矮桃在資源分配上具有一定可塑性，以增加其在不同生境條件下的生態(tài)適應(yīng)性。

表1 不同地區(qū)矮桃植株根冠比(平均值±標(biāo)準(zhǔn)誤)Table1 The root-shoot ratio of L. clethroidesin different areas )

注：根冠比值后不同字母表示在0.05水平上有顯著差異

從圖2可以看出，不同地區(qū)矮桃植株的根、莖、葉及果實(shí)生物量分布有顯著差異(金寨縣樣本，F(xiàn)=13.219,P﹤0.05；岳西縣樣本，F(xiàn)=14.989,P﹤0.05；蕪湖市樣本，F(xiàn)=59.914,P﹤0.05)。從營(yíng)養(yǎng)器官生物量與繁殖器官生物量比較看，3個(gè)地區(qū)的矮桃都表現(xiàn)出兩者間均具有顯著差異，即矮桃對(duì)營(yíng)養(yǎng)器官的資源投入明顯大于對(duì)繁殖器官的資源投入。從對(duì)根、莖及葉3大營(yíng)養(yǎng)器官的資源投入分析來看，不同地區(qū)表現(xiàn)出不同差異性，其中岳西縣樣本差異性不明顯，而金寨縣樣本與蕪湖市樣本存在顯著差異；從對(duì)繁殖器官的資源投入分析來看，3個(gè)不同地區(qū)樣本間卻未表現(xiàn)出差異性(F=0.992,P=0.424)。以上分析也表明，矮桃在對(duì)營(yíng)養(yǎng)器官的資源投入上具有一定可塑性，但對(duì)繁殖器官的資源投入上卻表現(xiàn)出一定程度的穩(wěn)定性，這是矮桃生活史對(duì)策中的一種生殖資源保障對(duì)策。

圖2 矮桃植株生物量分布Fig 2 The biomass distribution of clethroides

2.1.2 矮桃生物量分配特征

從表2可以看出，矮桃根、莖、葉與果實(shí)的生物量分配率在不同地區(qū)表現(xiàn)出一定的變異幅度。從整體而言，矮桃葉的生物量分配率最高，平均達(dá)37.5%，其次是莖，平均為28.4%，兩者生物量分配率之和達(dá)到65.9%，占較大比例。從表2可有看出，作為依靠葉和莖類資源植物開發(fā)對(duì)象，葉和莖其在生物量指標(biāo)上具有一定優(yōu)勢(shì)。

2.2 土壤中總硒及礦質(zhì)元素含量特征

植物所需的礦質(zhì)營(yíng)養(yǎng)元素來自于土壤，因此土壤的礦質(zhì)元素組成、含量及其供應(yīng)養(yǎng)料的能力對(duì)于植物生長(zhǎng)發(fā)育十分重要。表3為土壤中總硒及9種礦質(zhì)營(yíng)養(yǎng)元素的測(cè)定結(jié)果。從元素相對(duì)含量水平看，不同地區(qū)土壤硒及9種礦質(zhì)元素含量存在一些差異。其中，金寨縣土壤總硒及9種礦質(zhì)營(yíng)養(yǎng)元素順序?yàn)椋篈l> Fe> Mg> Ca> K> Na> Mn> Zn> Cu> Se；岳西縣土壤總硒及9種礦質(zhì)營(yíng)養(yǎng)元素順序?yàn)椋篈l> Fe> Mg> K> Ca> Na> Mn> Zn> Cu> Se；蕪湖市土壤總硒及9種礦質(zhì)營(yíng)養(yǎng)元素順序?yàn)椋篈l> Fe> K> Ca> Mg> Na> Mn> Cu> Zn> Se。這些元素按相對(duì)含量可分為3級(jí)：A級(jí)，含量大于10 000 μg/g，有Al和Fe；B級(jí)，含量介于500～10 000 μg/g，有Na、Ca、Mg、K和Mn(金寨縣)；C級(jí)，含量小于500 μg/g，有Zn、Cu、Mn(除金寨縣)和Se。分類中，除Mn元素在不同地區(qū)存在分類差異外，其他元素按含量分類均一致。但從3個(gè)取樣品點(diǎn)來看，蕪湖的硒含量明顯高于金寨縣和岳西縣。

表2 不同地方矮桃不同器官生物量分配率Table 2 The biomass distribution rates different organs ofL. clethroides in from different areas

表3 土壤中硒及礦質(zhì)元素含量Table 3 The contents of mineral elements and selenium in soil

2.3 矮桃植物體內(nèi)總硒及礦質(zhì)元素含量及分布特征

植物對(duì)礦質(zhì)營(yíng)養(yǎng)元素的吸收、遷移、分配和利用具有重要生態(tài)學(xué)意義。植物根冠比、對(duì)礦質(zhì)營(yíng)養(yǎng)元素的生物吸收系數(shù)及累積量常被用于衡量礦質(zhì)營(yíng)養(yǎng)元素從土壤庫(kù)到生物庫(kù)遷移特征的實(shí)驗(yàn)統(tǒng)計(jì)指標(biāo)。以分析和評(píng)價(jià)土壤養(yǎng)分與植物生長(zhǎng)之間的生態(tài)適應(yīng)性。

2.3.1 矮桃植物體內(nèi)硒元素總含量及分布特征

圖3 矮桃植株內(nèi)硒元素分布Fig 3 The content distribution of selenium in L. Clethroides

由圖3可知，不同地區(qū)矮桃植株體內(nèi)不同器官硒元素含量存在明顯差別。但從形態(tài)學(xué)下端向形態(tài)學(xué)上端遷移中，一般都表現(xiàn)出先增加后減少的趨勢(shì)。其中，葉的硒元素總含量較高，尤其是金寨縣樣本葉硒總含量最高，達(dá)到955.53 μg/kg，比來自岳西縣樣本葉硒總含量104.52 μg/kg高9倍多。這可能與該地區(qū)土壤中硒存在形態(tài)及其他環(huán)境因子有關(guān)。

2.3.2 矮桃植物體內(nèi)礦質(zhì)元素含量及分布特征

圖4 礦質(zhì)元素在矮桃植株內(nèi)分布Fig 4 The confent distribution of the mineral elements in L. Clethroides

由圖4可以看出，不同地方矮桃中的各礦質(zhì)元素總體含量大小順序?yàn)椋篕>Ca>Mg>Na>Al>Fe>Mn，Zn和Cu含量最少，兩者含量差異不明顯；各地矮桃中的K的總體含量大小順序?yàn)椋涸牢骺h>金寨縣>蕪湖市；Ca和Mg在各器官中的含量大小順序?yàn)椋喝~>果實(shí)>莖>根；3個(gè)地區(qū)矮桃中的Na含量基本相同，在各器官中的含量也大致相同，說明Na含量比較穩(wěn)定；Al和Fe的含量在各器官中以根含量最高，莖含量最少；Mn的含量在各器官中以葉中最高；Zn和Cu的含量在各器官中偏低，分布差異不明顯。

2.4 矮桃各營(yíng)養(yǎng)器官對(duì)硒及礦質(zhì)元素的富集特征

由表4可以看出，矮桃各器官中K的吸收系數(shù)最大(葉除外，葉中Ca的吸收系數(shù)最大)，Ca、Na、Zn、Cu、Mn、Mg、Se的吸收系數(shù)較大，F(xiàn)e的吸收系數(shù)較小，Al的吸收系數(shù)最小，在矮桃各器官對(duì)硒的吸收系數(shù)中，葉的吸收系數(shù)最大。Al、Fe、Zn、Na元素在根中的吸收系數(shù)大于在莖、葉、果實(shí)中的吸收系數(shù)，Mg、Mn、Ca、Se元素在葉中的吸收系數(shù)大于在根、莖、果實(shí)中的吸收系數(shù),Cu、K在果實(shí)中的吸收系數(shù)大于在根、莖、葉中的吸收系數(shù)。

由表5可以看出，矮桃各器官中K的累積量最高(葉除外，葉中Ca的累積量最高，其次是K)，其次是Ca，Al、Mg、Na、Fe的累積量較高，Mn、Zn、Cu的含量較低，在矮桃各器官中，葉中的Se累積量最高。Al、Fe元素在根中的累積量大于在莖、葉、果實(shí)的累積量，在根中富集，Cu、Mg、Mn、Zn、Na、Ca、K、Se元素在葉中的累積量大于在根、莖、果實(shí)的累積量，在葉中富集。

2.5 矮桃各營(yíng)養(yǎng)器官中硒及礦質(zhì)元素含量之間的相關(guān)性

2.5.1 矮桃根中硒及礦質(zhì)元素含量之間相關(guān)性分析

由表6可以看出，在安徽省3個(gè)地方的矮桃中，根中的Zn和Cu、Ca和Mg含量具顯著差異，存在正相關(guān)性，相關(guān)系數(shù)都為0.998；Ca和Mn、Se和K含量具顯著差異，存在負(fù)相關(guān)性，相關(guān)系數(shù)分別為-0.915、-0.997。

表4 矮桃不同器官對(duì)硒及礦質(zhì)元素的吸收系數(shù)Table 4 The absorption coefficients of selenium and mineral elements in L. clethroides′ different organs

表5 矮桃不同器官硒及礦質(zhì)元素累積量Table 5 The accumulation of mineral elements and selenium in L. clethroides′ different organs

2.5.2 矮桃莖中硒及礦質(zhì)元素含量之間相關(guān)性分析

由表7可以看出，在安徽省3個(gè)地方的矮桃中，莖中的Fe和Zn、 Mn和Zn、Na和Zn的含量具顯著差異，存在負(fù)相關(guān)性，其相關(guān)系數(shù)分別為-0.997、-0.999、-0.998，Na和Mn具極顯著差異，存在正相關(guān)性，其相關(guān)系數(shù)為0.99。

2.5.3 矮桃葉中硒及礦質(zhì)元素含量之間相關(guān)性分析

由表8可以看出，在安徽省3個(gè)地方的矮桃中，葉中各礦質(zhì)元素之間，以及硒和礦質(zhì)元素含量之間無相關(guān)性，這可能與矮桃不同器官對(duì)礦質(zhì)元素的吸收作用不同以及生理需求不同有關(guān)。

2.5.4 矮桃果實(shí)中硒及礦質(zhì)元素含量之間相關(guān)性分析

表6 矮桃根中硒及礦質(zhì)元素含量之間相關(guān)性Table 6 The content correlation between the selenium and mineral elements in the L. clethroides′ roots

*：0.05水平上差異顯著

表7 矮桃莖中硒及礦質(zhì)元素含量之間相關(guān)性Table 7 The content correlation between the selenium and mineral elements in the L. clethroides′ stem

*：0.05水平上差異顯著；**：0.01水平上差異顯著

表8 矮桃葉中硒及礦質(zhì)元素含量之間相關(guān)性Table 8 The content correlation between the selenium and mineral elements in the L.clethroides′ leaves

由表9可以看出，在安徽省3個(gè)地方的矮桃中，果實(shí)中的Zn和Cu，Na和Al含量具顯著差異，存在正相關(guān)性，相關(guān)系數(shù)分別為0.997、0.998；Se和K含量具顯著差異，存在負(fù)相關(guān)性，相關(guān)系數(shù)為-0.999。

通過表6～9的數(shù)據(jù)可以看出，矮桃根中的Zn和Cu、Ca和Mg含量具顯著正相關(guān)性，Ca和Mn含量具顯著負(fù)相關(guān)性；莖中的Fe和Zn、 Mn和Zn、Na和Zn的含量具顯著負(fù)相關(guān)性，Na和Mn具極顯著正相關(guān)性; 果實(shí)中的Zn和Cu，Na和Al含量具顯著正相關(guān)性；根和果實(shí)中的Se和K含量有顯著負(fù)相關(guān)性。由數(shù)據(jù)可知，Zn、Cu、Mn在矮桃植株中含量雖偏低，但與其他礦質(zhì)元素吸收具相關(guān)性，說明它們?cè)诰S持礦質(zhì)元素吸收的化學(xué)特性上發(fā)揮重要的作用，在矮桃植物的生長(zhǎng)發(fā)育過程中起積極作用；矮桃中的K元素對(duì)Se元素吸收關(guān)系密切,對(duì)矮桃作為富硒植物的開發(fā)上需進(jìn)一步研究。

表9 矮桃果實(shí)中硒及礦質(zhì)元素含量之間相關(guān)性Table 9 The content correlation between the selenium and mineral elements in the L. clethroides fruits

*：0.05水平上差異顯著

3 討論與總結(jié)

3.1 矮桃的生物量特征

不同地區(qū)矮桃單株總生物量無顯著差異；不同地方產(chǎn)矮桃植株根冠比表現(xiàn)出顯著差異，表明矮桃在資源分配上具有一定可塑性，以增加其在不同生境條件下的生態(tài)適應(yīng)性。不同地方矮桃植株的根、莖、葉及果實(shí)生物量分布有顯著差異。從營(yíng)養(yǎng)器官生物量與繁殖器官生物量比較看，矮桃對(duì)營(yíng)養(yǎng)器官的資源投入明顯大于對(duì)繁殖器官的資源投入。矮桃在對(duì)營(yíng)養(yǎng)器官的資源投入上具有一定可塑性，但對(duì)繁殖器官的資源投入?yún)s表現(xiàn)出一定程度的穩(wěn)定性，這是矮桃生活史對(duì)策中的一種生殖資源保障對(duì)策。從整體而言，矮桃葉的生物量分配率為最高，其次是莖，兩者生物量分配率之和達(dá)到65.9%，占較大比例。作為利用葉類資源植物開發(fā)對(duì)象，其在生物量指標(biāo)上具有一定優(yōu)勢(shì)。

3.2 矮桃對(duì)礦質(zhì)元素的吸收與分布特征

不同地方矮桃的各器官礦質(zhì)元素含量中，K的累積量最高(葉除外，葉中Ca的累積量最高，其次是K)，其次是Ca，Al、Mg、Na和Fe的累積量較高，Mn、Zn、Cu的含量較低，在矮桃各器官中， Al、Fe元素在根中的累積量最高，Cu、Mg、Mn、Zn、Na、Ca和K元素在葉中的累積量最高。這與藍(lán)芙寧等[19]對(duì)巖溶山區(qū)巖石-土壤-牧草系統(tǒng)礦質(zhì)元素的分布、遷移、富集特征的研究基本一致。這可能與葉片既是矮桃植物的光合器官，又是消耗能量的營(yíng)養(yǎng)器官有關(guān)，某些礦質(zhì)元素分配偏高，以滿足其生理作用。表明矮桃植物在生長(zhǎng)發(fā)育過程中需要多種大量的礦質(zhì)元素營(yíng)養(yǎng)，元素在矮桃體內(nèi)的分布和富集,不僅取決于元素自身在矮桃體內(nèi)的移動(dòng)性能,還與矮桃各部位生理需要以及元素在其體內(nèi)相互作用有關(guān)。

3.3 矮桃對(duì)硒及礦質(zhì)元素的利用特征

不同地方矮桃植株體內(nèi)不同器官硒元素含量存在明顯差別。但從形態(tài)學(xué)下端向形態(tài)學(xué)上端遷移中，一般都表現(xiàn)出先增加后減少的趨勢(shì)。其中，葉中的硒元素總含量較高。

通過數(shù)據(jù)分析可知，矮桃根中的Zn和Cu、Ca和Mg含量具顯著正相關(guān)性，Ca和Mn含量具顯著負(fù)相關(guān)性；莖中的Fe和Zn、 Mn和Zn、Na和Zn的含量具顯著負(fù)相關(guān)性，Na和Mn具極顯著正相關(guān)性; 果實(shí)中的Zn和Cu，Na和Al含量具顯著正相關(guān)性；根和果實(shí)中的Se和K含量有顯著負(fù)相關(guān)性。由數(shù)據(jù)可知，Zn、Cu和Mn在矮桃植株中含量雖偏低，但與其他礦質(zhì)元素吸收具相關(guān)性，在矮桃植物生長(zhǎng)發(fā)育中有積極作用；矮桃中的K元素對(duì)其Se元素吸收關(guān)系密切，在引進(jìn)矮桃人工栽植中，利于Se元素在矮桃體內(nèi)富集的土壤鉀肥和硒肥的最適比例有待進(jìn)一步研究。

本研究結(jié)果表明，常量與微量營(yíng)養(yǎng)元素、微量有益元素之間、微量營(yíng)養(yǎng)元素與微量有益元素呈正相關(guān)，微量非營(yíng)養(yǎng)元素與常量營(yíng)養(yǎng)、微量營(yíng)養(yǎng)和微量有益元素常呈負(fù)相關(guān)。這與杜占池等[20]對(duì)紅三葉與鴨茅對(duì)礦質(zhì)元素吸收的相關(guān)性研究結(jié)果一致。

從對(duì)矮桃各器官的生物量分布研究來看，矮桃葉中的生物量分配率最大，作為利用葉類資源植物開發(fā)對(duì)象，其在生物量指標(biāo)上具有一定優(yōu)勢(shì)。硒是人體和動(dòng)物必需的營(yíng)養(yǎng)元素，葉中硒元素和多數(shù)礦質(zhì)元素的累積量最高，在矮桃根與葉中的硒與鉀元素的含量具有負(fù)相關(guān)性，在以后開發(fā)矮桃作為富硒植物的研究中可以具體研究硒肥與鉀肥的合適比例。總體來說，矮桃作為待開發(fā)的富硒植物是很有前景的。

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收稿日期：2016-12-18；修回日期：2016-12-26

作者簡(jiǎn)介：劉智敏，博士，研究方向?yàn)楦邷貐捬醢l(fā)酵有機(jī)廢物生產(chǎn)沼氣、污水處理，E-mail: zliu14@ncsu.edu

doi∶10.3969/j.issn.2095-1736.2017.01.058

Abstract With the increasing concerns of global climate change caused by the consumption of fossil fuels, much efforts have been spent on the exploration of renewable energy sources in the last couple of decades. Biogas produced from the treatment of organic waste materials is one of the renewables that have attracted a lot of attentions. This paper provides a summary of the studies on thermophilic anaerobic digestion or co-digestion of various organic waste materials for biogas production. Discussions in this paper include main advantages of thermophilic anaerobic digestion technology over mesophilic one, factors that critically impact the efficiency of the anaerobic digestion such as temperature, pH, total solids, carbon/nitrogen ratio, and hydraulic retention time, the effect of the pretreatment of lignocellulosic materials on the biogas production from anaerobic co-digestion of animal manure and agricultural residues, and mathematical models describing the anaerobic digestion processes.

Keywords anaerobic digestion; biogas; organic wastes; renewable energy; thermophilic

摘 要 隨著化石燃料消耗導(dǎo)致越來越嚴(yán)重的全球氣候變化問題，可再生能源在近20年被人們大量的研究和探索。通過厭氧發(fā)酵處理有機(jī)廢物產(chǎn)生的沼氣作為一種可再生能源得到了廣泛的關(guān)注。匯總了高溫混合厭氧發(fā)酵有機(jī)廢物生產(chǎn)沼氣的相關(guān)研究, 探討了高溫厭氧發(fā)酵相比中溫厭氧發(fā)酵的優(yōu)點(diǎn)，影響厭氧發(fā)酵效率的因素(例如溫度、pH值、總固體量、碳氮比和水力停留時(shí)間)，以及木質(zhì)纖維素原料的預(yù)處理方法對(duì)動(dòng)物糞便和農(nóng)作物廢棄物混合厭氧發(fā)酵生產(chǎn)沼氣的影響,并描述了厭氧發(fā)酵產(chǎn)生沼氣過程的數(shù)學(xué)模型。

關(guān)鍵詞 厭氧發(fā)酵；沼氣；有機(jī)廢物;可再生能源；高溫發(fā)酵

1 Introduction

With the rapid development of industry and agriculture, large volume of organic wastes is generated. Organic wastes can be treated using physical, chemical and biological treatment methods. Among different types of biological treatment methods, anaerobic digestion (AD) is regarded as the most cost-effective one because of its environment friendly operations, net high energy recovery and carbon neutral impact[1].

AD involves the breakdown of complex organic wastes and produces biogas by a consortiumof anaerobic microorganisms[2]. Biogas is mainly composed of 48%-70% methane, 30%-49% carbon dioxide, 100-2 000 ppm hydrogen sulfide and traces of other gases[3]. In comparison with other biological treatment methods, AD offers signification advantages including:

● Biogas produced can be used for heat and electricity generation;

● Thedigestate can be used as fertilizer due to its high nutrients content;

● AD reduces disposed waste volume and weight;

● AD eliminates odor;

● AD is a low cost and low technology system to provideenergy for rural areas.

In order to create a stable and optimized AD process, there are many factors that need to be taken into consideration. Among them, temperature is the most important one because it alone can affect the rate of biochemical reactions in the AD process[1]. AD can be carried out under psychrophilic (15-25℃), mesophilic (30-40℃), and thermophilic (50-60℃) conditions, of which mesophilic and thermophilic conditions are commonly used in applications. In comparison with mesophilic digestion, thermophilic digestion offers many advantages such as higher specific growth rate for the anaerobic microorganisms, higher kinetic advantage in fermentation, higher percentage destruction of pathogens and weed seeds, improved solid-liquid separation and more stability of organic wastes[1]. Thermophilic AD is attracting more and more attentions because of the advantages. In this paper a critical review is presented on themophilic anaerobic digestion of organic wastes including the characteristics of the microorganisms, critical factors, applications, challenges and modeling of the process.

2 Basic Scheme of Thermophilic Anaerobic Digestion Process

Under thermophilic conditions, the basic scheme of digestion process remains almost the same as that undermesophilic conditions. The thermophilic AD is mainly comprised of four steps: hydrolysis, acidogenesis, acetogenesis, and methanogenesis. A schematic diagram of the AD process is shown in Figure 1.

3 Critcal Factors in Maintaining a Stable Thermophilic Anaerobic Digestion Process

3.1 Temperature

The temperature range for thermophilic AD is considered to be between 48-60℃, with the optimum temperature around 55℃[4]. Compared with mesophilic AD, thermophilic AD has higher rates in biogas production and pathogen destruction. However, thermophilic AD is more sensitive to temperature fluctuations and requires a longer time to adapt to a new environment[5]. Zinder et al.[6]found that only a few degrees increase in temperature resulted in a completely irreversible deterioration of the thermophilic process. This might be attributed to the temperature limitation of aceticlastic methanogens[7]. A fluctuation in temperature results in low biogas production, VFA accumulation and a decrease in pH values[4]. In order to maintain the stability of the digester performance, keeping the temperature at the optimum level is very important. De la Rubiaet et al.[4]indicated that the reactor temperature fluctuations in modern thermophilic digesters should be 0.1-0.2℃ on a daily basis.

Fig 1 Anaerobic digestion of organic materials into biogas 圖1 有機(jī)物質(zhì)通過厭氧發(fā)酵轉(zhuǎn)化為沼氣的過程

1. Hydrolysis; 2. Acidogenesis; 3. Acetogenesis; 4. Methanogenesis, 4.1.Hydrogenotrophicmethanogenesis, 4.2.Aceticlasticmethanogenesis

1: 水解；2: 酸化；3: 乙酸化；4: 甲烷化，4.1:氫營(yíng)養(yǎng)型甲烷化，4.2:乙酸發(fā)酵型甲烷化

3.2 pH

A pH range of 6.8 to 7.2 is ideal for the AD[3]. However, the optimum pH of methangenesis and hydrolysis are different. The optimal pH for the methanogenesis is at 6.5-8.2 while the optimum pH for the hydrolysis and acidogenesis is between 5.5 and 6.5[8-9].Liu et al.[10]found that the maximum biogas yield was achieved when the pH was between 7.2 and 7.3 for the treatment of organic fraction of municipal solid waste under thermophilic condition.

3.3 Total Solids (TS)

AD can be categorized into wet, semi-dry and dry digestion based on the TS content in the feed material. The wet digestion processes are operated with TS concentration below 10% which is quite applicable for conventional anaerobic digesters such as continuously stirred tank reactors(CSTRs). The TS content in semi-dry process is usually between 10% and 20%, while the dry digestion is operated with a TS content inside the reactor between 20% and 40%[5]. Compared with the wet AD, dry AD has several advantages such as higher organic loading rate and more efficient energy performance[11]. Many studies have been conducted by researchers investigating the influence of TS content on the performance of AD. Desai et al.[12]found that the biogas production was enhanced with the increased TS reaching a maximum at 6% (w/v) in the biomethanation of the mixture of cattle dung, poultry waste and whey. However, contrary result was found when Itodo et al.[13]tested the effect of different TS concentrations (5%, 10%, 15% and 20% TS) of poultry, cattle and piggery waste slurries on the biogas yield in anaerobic batch digesters. The result indicated that the gas yield increased with the decreasing TS concentration of the slurries. In this case, higher gas yield was obtained from the lower TS.This is because when the TS was too high, the slurry became too thick to digest[13].

3.4 Carbon/Nitrogen (C/N) Ratio

Methane production would be enhanced if the C/N ratio in the feed to an anaerobic digester was balanced in the optimum range. Hills[14]investigated the effects of C/N ratio on the AD of dairy manure. The C/N ratio in the study was determined using available carbon (total organic carbon minus the lignin carbon) tototal Kjeldahl nitrogen (TKN). Different C/N ratios between 8.0 and 51.7 was studied by combining the dairy manure with glucose. The result showed that the highest methane production was achieved when the C/N of the feed was 25. Backus et al.[15]tested four C/N ratios of 8.4, 13.9, 22.2 and 27.6 on the performance of AD of raw sweet cheese whey in a semi-batch, fixed film anaerobic digester. The C/N ratio was defined as TOC/TKN in their study. It was observed that the highest percentage of methane and methane production rate occurred when the C/N ratio was between 22 and 28.

3.5 Hydraulic Retention Time (HRT)

HRT is an important design parameter since it determines the microbe/substrate reaction and further influences the consumptionefficiency of the substrate[16]. Typical HRT for mesophilic anaerobic digestion is 20-25 days, while the HRT for thermophilic anaerobic digestion is 10-15 days.

4 Applications of Thermophilic Anaerobic Digestion/Co-Digestion

Thermophilic AD has been widely applied in the past decades because of its efficient hygienic treatment and higher biogas production rate. Compared with traditional mesophilic AD process which has lower energy requirements, the operational cost of thermophilic AD isslightly higher. However, the real benefit of thermophilic AD is total (99.9%) reduction of pathogens and thereby reducing the risk of disease transmission[17]. Substrates that can be used for thermophilic AD are sewage sludge, municipal solid waste, organic fraction of municipal solid waste, animal manure, energy crops and crop residues. Previous studies on thermophilic AD are summarized in Table 1.

Anaerobic co-digestion (AcoD) is defined as a waste treatment method in which two or more substrates are mixed and treated together, so the biogas production is improved through their joint treatment[25]. The potential benefits of AcoD include dilution of toxic compounds, increased load of biodegradable matter, improved nutrients balance, synergistic effect of microorganisms and better biogas yield[25]. AcoD of animal manure with agricultural residues had been extensively investigated in the past decades[26-27]. Cuetos et al.[26]studied the AcoD of swine manure with maize, rapseed and sunflower residues under batch and semi-continuous conditions. The results indicated that the AcoD system resulted in a major increase in the amount of daily biogas production. Similar results were achieved by Wu et al.[27]when they co-digested swine manure with corn stalks, oat straw, and wheat straw. They found the daily maximum biogas production increased by 11.4-fold when the swine manure is co-digested with corn stalks in comparison with the only manure as the substrate. These studies supported that the idea of AcoD of animal manure/wastewater with corn stover could be an effective method in converting organic wastes into biogas.

Table 1 Summary of previous studies on thermophilic anaerobic digestion (AD) of organic wastes表1 有機(jī)廢物高溫厭氧發(fā)酵研究匯總

5 Application of Pretreatment on Lignocellulosic Materials in Enhancing Biogas Production in Anaerobic Co-Digestion

One of the main challenges in converting lignocellulosic materials such as agricultural residues into biogas is the recalcitrant compact structure of the materials. Lignocellulosic materials mainly consist of three components: cellulose, hemicellulose and lignin. Cellulose chains are embedded in a cross-linked matrix of hemicellulose surrounded by lignin. The lignin barrier prevents the enzymes from accessing into the cellulose fraction, making the hydrolysis process difficult. The objective of pretreatment is to break the lignin seal and disrupt the crystalline structure to make cellulose more accessible to the enzymes that convert the carbohydrate polymers into fermentable sugars[28].

Pretreatment can be categorized into physical pretreatment, physical-chemical pretreatment, chemical pretreatment and biological pretreatment:

5.1 Physical Pretreatment

The objective of physical pretreatment is to reduce the particle size of the influent substrate. Physical pretreatment process can not only increase the available surface area but also decrease the crystallinity and degrees of polymerization of cellulose.

5.2 Physical-Chemical Pretreatment

Physical-chemical pretreatment combines both the physical and chemical processes. Typical form of physical-chemical pretreatment includes steam explosion, ammonia fiber explosion, carbon dioxide explosion. In comparison with the untreated wheat straw, pretreated wheat straw using wet explosion method can produce 20% more methane production[29].

5.3 Chemical Pretreatment

Chemical pretreatment methods include ozonolysis, acid hydrolysis, alkaline hydrolysis and oxidative dilignification. Among all these methods, alkaline pretreatment proves to be a particularly advantageous method in treating agricultural residuesin anaerobic digestion due to its low cost and effectiveness. NaOH and lime are commonly used in the alkaline pretreatment. Pretreated corn stover with 2% of NaOH would increase the accessibility and digestibility of cellulose[30]. Pang et al.[31]showed that NaOH pretreatment can improve the biodegradability of corn stover and improve the biogas yield. When the NaOH dose was 6% and the loading rate was 65 g/L, 48.5%, more biogas were produced compared with the untreated ones. Corn stover which is pretreated by NaOH, resulted in 72.9% and 73.4% increase of biogas and methane production, respectively[32].

5.4 Biological Pretreatment

Biological pretreatment process uses microorganisms to degrade lignocellulosic materials. The microbes include brown-, white-, and soft-rot fungi. Compared with chemical pretreatment processes, biological pretreatment process needs less energy and no requirement of chemicals. Biological pretreatment can not only degrade the lignin, but also hemicelluloses and cellulose. Romano et al.[33]studied the cellulase, hemicellulase and glucosidase effect in the ananerobic digestion process of wheat grass. They found that the solubility of the wheat grass increased; however, the biogas and methane production was similar compared with the control.

6 Mathematical Modeling of Anaerobic Digestion Process

Considerable effort has been put into the mathematical modeling of anaerobic digestion in the past decades. The development of mathematical models results in a better understanding of the process dynamics, reveals optimization opportunities and is an overall prerequisite for improvement of digester performance[34]. The first anaerobic digestion models were simple kinetic models that describe only the rate-limiting step of the biological process, i.e., the slowest step that limits the rate of the overall process[35-36]. According to the digester operating conditions and influent characteristics, the limiting step of the anaerobic digestion process is different. Hydrolysis, being the first step in overall process, is normally the rate-limiting step of the overall anaerobic digestion process[37]. Several kinetic equations for hydrolysis are reported in the literature. Vavilin et al.[38]used traditional first-order kinetics (Equations (1) and (2)) and Contois kinetics (Equation (3)) to describe the hydrolysis of biodegradable solids.

(1)

(2)

(3)

(4)

whereMisthemassofsubstrate,tisthetime(days),Ksbkisthesurfacebasedhydrolysisconstant(kg/m2-day),Aisthesurfaceavailableforhydrolysis(m2).Acetogenesisandmethanogenesishadbeenreportedasrate-limitingstepsaswell[42-43].ThekineticsofthesestepsistraditionallyexpressedbyMonodtypekineticswhichconsiderasinglegrowth-limitingsubstrate(Equation(5)):

(5)

whereμ(d-1)isthespecificgrowthrate,μmax(d-1) the maximum specific growth rate, [S] (g/L) the substrate concentration andKS(g/L) the substrate saturation constant.

It has been found that several chemical compounds at certain concentration are inhibitory to the anaerobic digestion process. These chemical compounds include ammonia, sulfide, metals and some organic compounds such as long-chain fatty acids[44]. Inhibition usually results in decreased or a complete stop in methane production[44].

Organic acids accumulation at neutral pH is regarded as the most common product inhibition in the biological model[45]. Costello et al.[45]proposed a competitive and a non-competitive inhibition model to account for product inhibition by acetic acid. The concentration of the inhibitor [I] is the millimolar concentration of acetic acid in the reactor. It is assumed that the inhibition of the bacteria by the volatile acid substrates or lactic acid is insignificant. The general equation for the competitive inhibition of the acetogenic bacteria is written as follows:

(6)

A noncompetitive model for substrate uptake was used to model product inhibition, the equation is presented in Equation (7):

(7)

In 2002, the International Water Association (IWA) Task Group for Mathematical Modeling of Anaerobic Digestion Processes developed a comprehensive mathematical model known as Anaerobic Digestion Model no.1 (ADM1)[46]. The model includes both biochemical and physicochemical processes. The biochemical steps include extracellular disintegration that coverts homogeneous particulate into carbohydrates, proteins and lipids; extracellular hydrolysis that converts these particulate substrates into sugars, amino acids and long chain fatty acids (LCFA); acidogenesis or fermentation that converts sugars and amino acids into volatile fatty acids (VFA) and hydrogen; acetogenesis that converts LCFA and VFA into acetic acid; and acetoclastic and hydrogenotrophicmethanogenesis[34]. The physicochemical process include ion association and dissociation and gas-liquid transfer[46].

The structured ADM1 model had been successfully applied to simulate the behaviour of a bioreactor for anaerobic digestion of a wide variety of substrates such as municipal waste mixed with activated sludge[47], olive mill wastewater mixed with solid waste[48]and manure mixed with vegetable waste[49].

Recently, some effort has been made to model the solid waste digestion. Esposito et al.[50], for instance, extended the ADM1 to simulate the organic solid particle disintegration and the effect of LCFA production on pH for a sewage sludge and organic fraction of municipal solid waste co-digestion system. In the future, considerable effort will put into the biological aspect of the modelling that is how to mathematically model the anaerobic digestion performance based on microbial diversity and activity[34].

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Uncultivated lysimachia clethroides biomass distribution and its feature of utilizing celenium and mineral element

NI Kui

(Department of Journalism and Communication, Anhui News and Publishing Vocational College, Hefei 230061， China)

The research analyzed the biomass distribution of uncultivated lysimachia clethroides and the absorbing ability, migration and correlation between the content of selenium and mineral elements； the samples of uncultivated lysimachia clethroides were gathered to measure the biomass. The contents of mineral elements and selenium were determined respectively by the atomic luminescence chromatography and the atomic fluorescent method，and the correlation analysis was done meantime. The result showed the biomass distribution rates in the leaves of the lysimachia clethroides were the highest, and the content of selenium was negatively correlated to potassium in the roots and fruits. Besides, the leaves possessed the highest content of selenium.

Lysimachiaclethroides; biomass; mineral elements; selenium; correlation

Thermophilic anaerobic digestion of organic wastes for biogas production: a review

LIU Zhi-min1, ZHU Jian-hang2, CHENG Jia-yang1

(1. Biological and Agricultural Engineering Department, North Carolina State University,Raleigh, NC 27695, USA; 2. School of Environmental Resources and Chemical Engineering, Nanchang University, Nanchang 330031, China)

高溫厭氧發(fā)酵有機(jī)廢物生產(chǎn)沼氣綜述

劉智敏1， 朱建航2， 成家楊1

(1. 北卡羅來納州立大學(xué) 生物與農(nóng)業(yè)工程系， 美國(guó) 羅利 NC27695;2. 南昌大學(xué) 資源環(huán)境與化工學(xué)院, 中國(guó) 南昌 330031)

參考文獻(xiàn)

2016-03-07；

2016-03-24

2015年高校人文社科重點(diǎn)項(xiàng)目“基于景觀生態(tài)學(xué)的高校校園規(guī)劃研究”(SK2015A688)

倪 奎，碩士，講師，研究方向?yàn)樯锕こ蹋珽-mail：ahcbxy@126.com

S662.1

A 文章編號(hào) 2095-1736(2017)01-0052-06

成家楊，博士，教授，研究方向?yàn)閰捬醢l(fā)酵有機(jī)廢物生產(chǎn)沼氣、利用木質(zhì)纖維素制備燃料酒精、微藻生物柴油、生物廢水處理，E-mail: jay_cheng@ncsu.edu

16.4 文獻(xiàn)標(biāo)識(shí)碼 A

2095-1736(2017)01-0058-07

doi∶10.3969/j.issn.2095-1736.2017.01.052