水生植物荇菜和菹草分解對(duì)物種混合的響應(yīng)研究

鞏崇賢 王 東

(華中師范大學(xué)生命科學(xué)學(xué)院, 武漢430079)

水生植物荇菜和菹草分解對(duì)物種混合的響應(yīng)研究

鞏崇賢 王 東

(華中師范大學(xué)生命科學(xué)學(xué)院, 武漢430079)

為探討水生植物混合的分解效應(yīng), 研究了浮葉植物荇菜(Nymphoides peltatum)、沉水植物菹草(Potamogeton crispus)及兩物種混合的分解速率和養(yǎng)分動(dòng)態(tài)。結(jié)果顯示: (1)兩單物種的分解速率與初始N含量呈顯著正相關(guān)關(guān)系(P＜0.05, r=0.862), 荇菜和菹草分解90d后的干重剩余率分別為24.74%和44.91%。物種混合干重剩余率在分解初期階段的實(shí)測(cè)值比期望值高6.63% (P＜0.05), 表明物種混合對(duì)分解速率具有拮抗效應(yīng), 但在隨后的分解時(shí)間里無(wú)顯著的混合效應(yīng), 分解90d后干重剩余率為30.39%; (2)在分解初期的N、P釋放階段, 物種混合的N、P剩余率實(shí)測(cè)值比其期望值分別高14.36%和12.88% (P＜0.05), 表明物種混合對(duì)初期N、P元素釋放具有拮抗效應(yīng), 在隨后的分解過(guò)程中對(duì)N元素?zé)o顯著的混合效應(yīng), 但分解后期P剩余率實(shí)測(cè)值比期望值低4.26% (P＜0.05), 表現(xiàn)為協(xié)同效應(yīng); (3)物種混合N、P動(dòng)態(tài)在分解初期呈一個(gè)快速釋放的過(guò)程,但在隨后的分解階段N元素釋放或積累, P元素持續(xù)釋放, 最終N、P均表現(xiàn)為凈釋放, 與兩單物種分解的N、P動(dòng)態(tài)的規(guī)律基本一致。另外, 總酚在物種混合分解初期釋放迅速, 隨后釋放緩慢。研究結(jié)果表明, 荇菜和菹草混合分解存在非加和效應(yīng), 即單物種的分解速率和營(yíng)養(yǎng)動(dòng)態(tài)變化不能用來(lái)預(yù)測(cè)兩物種混合的分解速率和營(yíng)養(yǎng)動(dòng)態(tài)變化。物種混合在分解的不同階段其分解效應(yīng)不同, 這說(shuō)明混合效應(yīng)具出一定的時(shí)間依賴性。此外, 混合效應(yīng)與浮葉植物和沉水植物其初始質(zhì)量特征有較密切的關(guān)系。

水生植物; 混合; 分解速率; N、P動(dòng)態(tài); 非加和效應(yīng)

水生植物是構(gòu)成湖泊生物多樣性的主體之一,植物殘?bào)w的腐爛分解影響湖泊的元素循環(huán)和水體的營(yíng)養(yǎng)平衡[1—3]。在淡水湖泊中, 水生植物以單優(yōu)種群或由多種水生植物組成群落的情況普遍存在, 不同物種的殘?bào)w經(jīng)常在湖泊沿岸帶混合堆積, 其有機(jī)物質(zhì)在分解后歸還水體[1,2]。前人對(duì)混合分解的研究表明, 物種混合對(duì)分解的影響可表現(xiàn)為加和效應(yīng)(Additive effect), 即混合對(duì)分解速率和養(yǎng)分的釋放速率沒(méi)有顯著影響; 或表現(xiàn)為非加和效應(yīng)(Nonadditive effect), 包括協(xié)同效應(yīng)(Synergistic effect)即提高分解速率和養(yǎng)分的釋放速率和拮抗效應(yīng)(Antagonistic effect)即降低分解速率和養(yǎng)分的釋放速率[4,5]。已有的相關(guān)研究關(guān)于陸生植物的較多, 對(duì)水生植物腐爛分解的研究相對(duì)薄弱[6]。目前對(duì)水生植物多涉及單一物種的分解研究[2,3,7,8—10], 有關(guān)物種混合分解的研究報(bào)道很少。

荇菜(Nymphoides peltatum)和菹草(Potamogeton crispus)是長(zhǎng)江中下游湖泊常見(jiàn)的水生植物, 植物組織的 N和P含量不同[11]。荇菜為根生浮葉植物, 菹草為沉水植物, 在擾動(dòng)環(huán)境下它們可產(chǎn)生大量的莖葉殘?bào)w并混合堆積于湖邊沿岸帶。為揭示荇菜和菹草混合的分解效應(yīng), 本文運(yùn)用分解袋法研究了荇菜、菹草及其混合的分解速率及N、P釋放動(dòng)態(tài), 以期為探討水生植物的分解規(guī)律提供資料, 也為認(rèn)識(shí)水生植物的整個(gè)生態(tài)過(guò)程和湖泊生態(tài)系統(tǒng)的管理提供參考。

1 材料與方法

1.1 實(shí)驗(yàn)材料

荇菜、菹草的新鮮莖葉于2012年5月16日取自華中師范大學(xué)南湖校區(qū)水生植物實(shí)驗(yàn)基地(N30°30′, E 114°21′), 材料用池水洗凈帶回實(shí)驗(yàn)室, 自然風(fēng)干后剪成5 cm左右的小段, 在60℃下烘干至恒重, 樣品放入干燥器并于10d后用于實(shí)驗(yàn)。

1.2 實(shí)驗(yàn)方法

將烘干處理后的荇菜、菹草和等量混合的荇菜和菹草三種樣品各10 g分別裝入尼龍網(wǎng)袋(大小20 cm× 15 cm, 網(wǎng)孔1 mm×1 mm)。采用經(jīng)過(guò)篩處理(以去除雜物和根系)、洗干凈的細(xì)沙[TC (0.67±0.20) mg/g、TN (0.07±0.05) mg/g、TP (0.12±0.01) mg/g, 根據(jù)底質(zhì)干重獲得]作為分解實(shí)驗(yàn)的基質(zhì), 沙厚約 1.5 cm,待穩(wěn)定10d后作為植物腐爛分解實(shí)驗(yàn)反應(yīng)器。將分解袋置于塑料盆(54 cm × 27 cm × 6 cm, 長(zhǎng)×寬×高)中, 保持分解袋處于濕潤(rùn)狀態(tài), 一個(gè)處理每個(gè)樣品6袋(按6次取樣計(jì))并置于1個(gè)塑料盆中, 3組重復(fù)。實(shí)驗(yàn)共計(jì)9個(gè)塑料盆、54袋樣品。取部分剩余材料用于實(shí)驗(yàn)材料初始質(zhì)量特征參數(shù)的測(cè)定。在實(shí)驗(yàn)中,塑料盆在生物園室內(nèi)實(shí)驗(yàn)區(qū)有遮雨處隨機(jī)放置, 保持盆中無(wú)雜物和分解袋濕潤(rùn)。

1.3 樣品采集與分析

于2012年5月26日將分解袋放置在塑料盆中,在分解袋放置后的第10、第20、第30、第40、第60和第90天分別取樣, 實(shí)驗(yàn)周期為90d。每種材料每次在每組處理中分別取1袋, 共3袋。帶回實(shí)驗(yàn)室后用純凈水沖去沙子等雜物。60℃烘干至恒重, 稱重后,磨碎過(guò)0.25 mm篩, 用于樣品中TC、TN、TP、總酚含量及干重測(cè)定。采用K2Cr2O7氧化-FeSO4滴定法測(cè)定TC, 材料經(jīng) H2SO4-H2O2消化, 分別采用靛酚藍(lán)比色法和鉬銻抗比色法測(cè)定TN和TP[12]; 采用范氏分析方法(Analysis of Van Soest)測(cè)定木質(zhì)素、纖維素、半纖維素含量[13]; 采用福林酚法測(cè)定總酚含量[14]。

1.4 統(tǒng)計(jì)分析

用指數(shù)分解模型描述分解材料干重變化: Wt=W0×e–kt(t為分解時(shí)間; k為分解常數(shù); W0為初始干重; Wt為經(jīng) t天分解后的剩余干重), 用非線性回歸分析計(jì)算分解速率[15]。為了直觀地反映分解材料的損失情況, 采用剩余率表示分解過(guò)程中干重和養(yǎng)分含量的變化。干重剩余率和養(yǎng)分剩余率分別為分解后材料干重和養(yǎng)分剩余量占初始量的百分率。

根據(jù)Salamanca等[16]采用的方法計(jì)算混合材料的期望干重剩余率和養(yǎng)分剩余率: 期望干重剩余率=[M1/(M1+M2)]×R1+[M2/(M1+M2)]×R2; 期望養(yǎng)分剩余率=[N1/(N1+N2)]×R1+[N2/(N1+N2)]×R2。式中, 以1、 2表示混合物中的兩種組分, M和N分別表示各組分在初始混合物中的干重和養(yǎng)分含量, R表示各組分單一物種的干重剩余率和養(yǎng)分剩余率。對(duì)混合材料混合分解時(shí)是否存在混合效應(yīng)進(jìn)行判斷: 若實(shí)測(cè)值與期望值之間差異顯著(P＜0.05), 則表示混合材料各組分之間存在非加和效應(yīng), 實(shí)測(cè)值大于期望值,則混合效應(yīng)是負(fù)的, 即拮抗效應(yīng), 實(shí)測(cè)值小于期望值, 則混合效應(yīng)是正的, 即協(xié)同效應(yīng)。若實(shí)測(cè)值與期望值之間差異不顯著(P＞0.05), 則表示混合材料各組分之間存在加和效應(yīng), 即無(wú)明顯的相互作用。

使用統(tǒng)計(jì)軟件 SPSS 17.0 進(jìn)行數(shù)據(jù)分析, 采用單因素方差分析(One-way analysis of variance)檢驗(yàn)差異性水平, 若差異顯著, 則采用 Duncan法(Duncan’s multiple comparison test)對(duì)具顯著性差異的處理間進(jìn)行多重比較檢驗(yàn)。對(duì)3種材料的干重剩余率、C、N、P、總酚剩余率、C/N、C/P的比較先進(jìn)行方差齊性檢驗(yàn), 如方差不齊則進(jìn)行對(duì)數(shù)轉(zhuǎn)換(lg-transformed)。實(shí)測(cè)值與期望值的比較, 采用配對(duì)樣本 t檢驗(yàn)其差異性水平。對(duì)于兩單種之間質(zhì)量特征、分解速率的比較采用獨(dú)立樣本 t檢驗(yàn)其差異性水平。對(duì)荇菜和菹草的分解速率與其初始N含量的相關(guān)性進(jìn)行Pearson相關(guān)分析。

2 結(jié)果

2.1 荇菜和菹草的初始質(zhì)量特征

荇菜和菹草在 C、N、P、C/P、木質(zhì)素、纖維素、總酚含量上存在顯著差異(P＜0.05)(表 1)。與菹草相比, 荇菜具有較高的 C、N、C/P、木質(zhì)素、總酚含量和較低的 P和纖維素含量; 荇菜的 C/N、半纖維素含量與菹草的差異不顯著。

2.2 荇菜、菹草及其混合分解的干重動(dòng)態(tài)變化

荇菜和菹草干重動(dòng)態(tài)變化均表現(xiàn)為先快后慢(圖 1), 其分解速率存在顯著差異(P＜0.01), 分解速率分別為 0.032/d和 0.017/d, 實(shí)驗(yàn)結(jié)束時(shí)干重剩余率分別為24.74%和 44.91%。荇菜 20d左右可分解50%的干重。菹草 40d左右可分解 50%的干重。Pearson相關(guān)分析表明, 兩單物種的分解速率與初始N含量呈顯著正相關(guān)關(guān)系(P＜0.05, r=0.862)。荇菜和菹草混合的分解速率為0.023/d, 其分解速率介于兩物種單獨(dú)分解速率之間(表2)。1個(gè)月內(nèi)可分解50%的干重。實(shí)驗(yàn)結(jié)束時(shí)荇菜和菹草混合的干重剩余率為30.39% (表3)。物種混合對(duì)干重剩余率在不同分解階段有不同的分解效應(yīng), 在分解的第10天, 實(shí)測(cè)值比期望值高 6.63%(P＜0.05), 表現(xiàn)出拮抗作用, 隨后的時(shí)間里實(shí)測(cè)值與期望值無(wú)明顯差異(P＞0.05),表現(xiàn)為加和效應(yīng)(表3)。

表1 荇菜和菹草的初始質(zhì)量特征Tab. 1 Initial quality characteristics of N. peltatum and P. crispus materials

圖1 荇菜、菹草及其混合在分解過(guò)程中的干重動(dòng)態(tài)變化Fig.1 Mass loss dynamics of N. peltatum and P. crispus and their mixture in decomposition

2.3 荇菜、菹草及其混合分解的N、P動(dòng)態(tài)變化

荇菜、菹草的N剩余率在最初10d下降明顯, 分別為 62.30%和 64.68%。在隨后的時(shí)間里, 荇菜 N剩余率呈繼續(xù)下降趨勢(shì), 到90d N剩余率略有增加,但仍低于初始值; 菹草N剩余率呈不規(guī)律的變化。在分解90d后荇菜和菹草的N剩余率分別為36.33%和53.09%。荇菜、菹草的P剩余率在最初10d下降明顯, 分別為 21.13%和 36.59%。在隨后的時(shí)間里,荇菜、菹草P剩余率在總體上呈平緩下降趨勢(shì)(荇菜在第90天和菹草在第60天P剩余率略有增加)。在分解90d后荇菜和菹草的P剩余率分別為11.84%和26.93%?？傮w上, 荇菜N、P的釋放速率大于菹草N、P的釋放速率, 最終均表現(xiàn)為凈釋放(圖 2)。

表2 荇菜、菹草及其混合的分解速率比較Tab. 2 Comparison of the decomposition rates among and between N. peltatum and P. crispus and their mixture

荇菜和菹草混合在整個(gè)分解過(guò)程中, N、P剩余率變化均先表現(xiàn)出明顯的快速下降, 隨后呈繼續(xù)平緩下降趨勢(shì)(除N剩余率在第60天略有上升外), 在分解90d后N、P剩余率分別為43.60%和15. 88% (圖3)。在分解的第10天, 物種混合N、P剩余率實(shí)測(cè)值比其期望值分別高 14.36%和 12.88%, 且差異顯著(P＜0.05), 表現(xiàn)出拮抗效應(yīng), 物種混合在分解初期抑制了N、P元素的釋放。在隨后的時(shí)間里, 除在分解的第90天P剩余率實(shí)測(cè)值比期望值低4.26%,且差異極顯著(P＜0.01)外, N、P剩余率實(shí)測(cè)值與期望值均無(wú)顯著差異, 說(shuō)明物種混合對(duì)N元素的釋放無(wú)顯著影響, 對(duì) P的拮抗效應(yīng)逐漸減弱并在最終表現(xiàn)出協(xié)同效應(yīng)。此外, 物種混合N、P動(dòng)態(tài)在分解初期呈一個(gè)快速釋放的過(guò)程, 但在隨后的分解階段N元素表現(xiàn)出釋放或積累, P元素持續(xù)釋放, 最終 N、P均表現(xiàn)為凈釋放。總酚在物種混合分解初期迅速釋放, 隨后緩慢釋放, 與物種混合的N、P釋放規(guī)律表現(xiàn)出一致的趨勢(shì)。

表3 荇菜和菹草混合分解的干重剩余率(%)(實(shí)測(cè)值和期望值)Tab. 3 Observed and expected values of the dry mass remaining percentage (%) of the mixed N. peltatum and P. crispus

圖2 荇菜、菹草及其混合在分解過(guò)程中的N、P剩余率(%)變化Fig. 2 Changes of nitrogen and phosphorus remaining percentage (%) of N. peltatum, P. crispus, and its mixture during the experiment

圖3 荇菜和菹草混合分解的N、P的實(shí)測(cè)剩余率(%)和期望剩余率(%)Fig. 3 The values of observed and expected nitrogen and phosphorus remaining percentage (%) of the mixed N. peltatum and P. crispus materials

表4 荇菜和菹草及其混合在分解過(guò)程中的質(zhì)量特征變化Tab. 4 Changes of quality characteristics of N. peltatum, P. crispus and their mixture during the decomposition

3 討論

3.1 質(zhì)量特征對(duì)荇菜和菹草分解的影響

植物組織的質(zhì)量特征是影響分解快慢的重要生物因素[3,17]。其中, N含量對(duì)初始階段的分解有較大的影響, 初始N含量較高其分解較快。荇菜的初始N含量顯著高于菹草, 荇菜的分解速率顯著高于菹草, 這表明荇菜和菹草的分解快慢也受其初始N含量所控制。另外, 具有較高P含量和較低C/P比的材料其分解也相對(duì)較快[18], 菹草較荇菜具有較高的P含量和較低的 C/P, 但菹草的分解速率小于荇菜,這可能與初始N含量較P含量和C/P對(duì)分解速率的影響更顯著有關(guān)[17]。此外, 有研究表明分解速率與材料初始纖維素、半纖維素、木質(zhì)素含量、酚類化合物的含量呈負(fù)相關(guān)[1,7,19]。在本研究中, 荇菜較菹草有較高的總酚和木質(zhì)素含量, 但荇菜仍表現(xiàn)出較高的分解速率, 荇菜的干重剩余率和N、P剩余率也均小于菹草, 這可能與荇菜在不同的分解階段各種物質(zhì)的化學(xué)組成變化對(duì)微生物活動(dòng)的影響有關(guān)。一些酚類物質(zhì)可能會(huì)改變酶的結(jié)構(gòu)使酶失活, 或與營(yíng)養(yǎng)蛋白結(jié)合后阻礙微生物對(duì)N元素的利用, 從而降低分解速率等[20,21]。荇菜的初始纖維素含量顯著低于菹草, 荇菜的分解速率顯著高于菹草, 這表明荇菜和菹草的分解快慢也與其初始纖維素含量有關(guān)。有研究發(fā)現(xiàn)淋溶作用可導(dǎo)致水生植物組織中的可溶性成分在初期分解階段迅速釋放, 一般在 24h干重?fù)p失率可達(dá)初始重量的25%[1]或50%[22—24]。本研究也發(fā)現(xiàn)在分解前10d荇菜和菹草腐爛分解均有較高的干重?fù)p失率和N、P含量的快速下降過(guò)程, 這在一定程度上表明淋溶使荇菜和菹草喪失了大部分養(yǎng)分。有研究表明, 植物在腐爛分解過(guò)程中其N(xiāo)剩余率的變化與微生物固定N的趨勢(shì)有密切關(guān)系[25], 微生物對(duì)N的固定將導(dǎo)致分解材料N含量的升高。分解材料中N含量越低微生物固定N的趨勢(shì)越強(qiáng)[26],反之亦然。在本實(shí)驗(yàn)中, 荇菜N剩余率呈持續(xù)下降趨勢(shì), 僅在分期后期(第90天時(shí))略有增加。這說(shuō)明由于荇菜初始N含量較高, 其自身N源能夠滿足微生物活動(dòng)的需求, 以至于在分解后的很長(zhǎng)一段時(shí)間內(nèi)微生物沒(méi)有發(fā)生對(duì)外源N元素的固定, 僅在分解后期外源N素被微生物所固定, 使植物殘余物中的氮素濃度有所上升。另外據(jù)Brady和Weil[27]的研究發(fā)現(xiàn), 當(dāng)植物殘余物的C/N比超過(guò)30, N元素的固定就已經(jīng)開(kāi)始, 相反, 如果小于 30, N元素將被礦化。荇菜初始C/N比小于30, 在分解第10、第20、第30、第40和第60天時(shí), 殘余物中的C/N比也小于30, 這說(shuō)明荇菜N的釋放動(dòng)態(tài)與Brady和Weil[27]的研究結(jié)論是一致的。與荇菜N剩余率變化趨勢(shì)比較, 菹草N剩余率表現(xiàn)出不規(guī)律的變化, 如在第20、第 60天略有增加, 而在其他時(shí)間呈下降趨勢(shì)。這與菹草初始N含量較荇菜低, 但初始C/N較荇菜高, 在分解的不同階段微生物對(duì)外源N元素產(chǎn)生固定有關(guān)。

與分解過(guò)程N(yùn)動(dòng)態(tài)相比較, 荇菜和菹草的P剩余量在分解過(guò)程中總體上均呈平緩下降趨勢(shì), 且一直表現(xiàn)為釋放。盡管荇菜的初始P含量較菹草低, 但相對(duì)較低的初始P含量并不導(dǎo)致微生物對(duì)P固定。有研究發(fā)現(xiàn), 當(dāng)初始 C/P＜100時(shí), P元素發(fā)生礦化,相反, 如果大于100, P元素將被固定[28,29]。荇菜和菹草初始 C/P比分別為 110.32±1.90和 82.03±0.59,但本研究中荇菜的初始C/P比似乎并不能解釋荇菜分解過(guò)程中的P元素的釋放動(dòng)態(tài)。對(duì)荇菜和菹草來(lái)說(shuō), 微生物在分解過(guò)程中的營(yíng)養(yǎng)需求沒(méi)有受到 P供給的限制, 或者說(shuō)沒(méi)有發(fā)生微生物對(duì)P元素的固定。

3.2 物種混合對(duì)分解速率和養(yǎng)分釋放的影響

不同物種混合對(duì)分解的響應(yīng)可表現(xiàn)為非加和效應(yīng)或加和效應(yīng)[4,5]。據(jù)Gartner和Cardon[4]統(tǒng)計(jì), 在物種混合分解中出現(xiàn)非加和效應(yīng)的比例約占 70%,其中協(xié)同效應(yīng)占 50%, 拮抗效應(yīng)占 20%, 而出現(xiàn)加和效應(yīng)的比例占30%。同時(shí), 76%的物種混合在分解過(guò)程中表現(xiàn)出非加和的養(yǎng)分動(dòng)態(tài)。在本研究中, 荇菜和菹草混合僅在分解初期對(duì)分解速率和N釋放具有顯著的拮抗效應(yīng), 在隨后的分解階段對(duì)分解速率和N釋放均不產(chǎn)生混合效應(yīng); 但分解過(guò)程中卻在一定程度上都促進(jìn)了 P釋放或積累。有研究表明, 當(dāng)不同質(zhì)量的物種混合時(shí), 由于營(yíng)養(yǎng)物質(zhì)(如 N)通過(guò)被動(dòng)擴(kuò)散和微生物的主動(dòng)運(yùn)輸?shù)葟母哔|(zhì)量材料中向低質(zhì)量材料發(fā)生轉(zhuǎn)移, 改善了質(zhì)量較差材料的營(yíng)養(yǎng)狀況, 從而促進(jìn)混合物的分解速率[30]; 但也有一些研究發(fā)現(xiàn)酚類物質(zhì)可以控制可溶性有機(jī)氮和無(wú)機(jī)氮的釋放比例[31], 酚類物質(zhì)的釋放會(huì)抑制微生物豐度和活性從而降低混合物種的分解速率[32]。在本研究中, 荇菜和菹草的初始N和總酚含量存在顯著差異,但N含量的差異對(duì)分解初期的混合效應(yīng)作用似乎并不明顯, 而總酚釋放動(dòng)態(tài)則與混合后的分解速率和N釋放有相同的趨勢(shì)。具有一面葉氣生的荇菜比完全沉水生長(zhǎng)的菹草具有更高的總酚含量, 在混合分解初期總酚也出現(xiàn)一個(gè)快速釋放過(guò)程, 之后出現(xiàn)緩慢釋放趨勢(shì)。此外, Bonanomi等[5]在研究地中海物種混合分解時(shí)發(fā)現(xiàn), 相對(duì)于對(duì) N動(dòng)態(tài)的影響而言,混合效應(yīng)對(duì)分解速率的影響更具有分解時(shí)間上的依賴性, 非加和效應(yīng)的產(chǎn)生更多發(fā)生在分解初期階段,并認(rèn)為物種質(zhì)量特征對(duì)物種混合是否產(chǎn)生混合效應(yīng)起到了決定性的作用。也有研究發(fā)現(xiàn)物種混合并不影響分解速率, 但顯著加快N元素的釋放[33]。在本結(jié)果中, 在分解初期荇菜和菹草混合抑制了干重的損失, 但在隨后的分解階段分解沒(méi)有發(fā)現(xiàn)顯著的混合效應(yīng), 混合效應(yīng)表現(xiàn)出明顯的時(shí)間依賴性。N釋放動(dòng)態(tài)在混合分解初期之后表現(xiàn)出加和性, 而 P元素的釋放動(dòng)態(tài)在分解初期、后期均表現(xiàn)出顯著的非加和性, 這說(shuō)明P元素對(duì)混合的響應(yīng)比N元素更為敏感。

水生植物腐爛分解對(duì)湖泊生態(tài)系統(tǒng)將產(chǎn)生影響,由于受環(huán)境擾動(dòng)如風(fēng)浪、人類活動(dòng)的(捕撈魚(yú)蝦和打撈水草等)影響, 植物的莖葉殘?bào)w經(jīng)?；旌隙逊e在湖泊沿岸帶。盡管水生植物在人工濕地或極端環(huán)境的水體中也存在單種群落的情況, 但淡水湖泊中由多種水生植物組成群落的情況普遍存在, 水生植物殘?bào)w的混合分解是必然的。本研究初步表明, 荇菜和菹草混合的分解效應(yīng)在干重?fù)p失率和營(yíng)養(yǎng)元素的釋放動(dòng)態(tài)方面不同于兩單種的分解規(guī)律。在分解的初始階段物種混合對(duì)分解速率具有拮抗效應(yīng), 但在隨后的分解時(shí)間里無(wú)顯著的混合效應(yīng); 同時(shí)物種混合對(duì)N、P元素釋放具有拮抗效應(yīng), 在隨后的分解過(guò)程中對(duì)N元素?zé)o顯著的混合效應(yīng), 但在分解后期對(duì) P釋放具有協(xié)同效應(yīng)。由于在野外自然狀態(tài)下, 環(huán)境因子的影響作用復(fù)雜, 另外也不涉及環(huán)境容量對(duì)分解過(guò)程的影響, 以及實(shí)驗(yàn)過(guò)程中材料的減少對(duì)容量影響產(chǎn)生的作用。因此, 很有必要加強(qiáng)野外條件下的相關(guān)研究。

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EFFECT OF MIXED FLOATING AND SUBMERGED MACROPHYTES ON DECOMPOSITION RATE AND NUTRIENT DYNAMICS

GONG Chong-Xian and WANG Dong
(School of Life Sciences, Central China Normal University, Wuhan 430079, China)

Decomposition of aquatic macrophytes can considerably influence nutrient cycling and energy flow in aquatic ecosystems, and may therefore alter aquatic ecosystem structure and functioning. Most studies of decomposition processes have focused on single species of aquatic macrophytes; however, most aquatic ecosystems consist of a mixture of aquatic plant species and fragments they produce which intermingle during decomposition. To explore the effect of species mixtures of aquatic macrophytes with different life forms, decomposition rate and nutrient dynamics were quantified in mixed-species litterbags (containing Nymphoides peltatum, a floating-leaved plant, and Potamogeton crispus, a submerged plant) and in litterbags containing fragments of a single species in a laboratory experiment. There were 10 g of materials used for each species in the litter bags, and for the mixture experiment, also 10 g of the dried macrophyte fragments were used at a mixtures rate of 5:5, Nymphoides:Potamogeton, w/w basis). The decomposition rates, nitrogen and phosphorus content of the remaining materials were determined after 10, 20, 30, 40, 60, and 90 days. Data from single-species litterbags were used to generate expected decomposition rates, nitrogen and phosphorus dynamics for mixed-species litterbags experiments. The result showed that the decomposition rates of N. peltatum (0.032/d) was pronounced higher than that of P. crispus (0.017/d), 24.74% and 44.91% dry mass remaining after 90 days, respectively. The decomposition rates of both N. peltatum and P. crispus were significantly and positively correlated with initial N content (P ＜ 0.05, r = 0.862). The decomposition rate of the mixture was 0.023/d which was intermediate between N. peltatum and P. crispus. The observed remaining mass of the mixture at the early stages of decomposition in ten days was 6.63% (P ＜ 0.05) higher than the expected, indicating the occurrence of negative, non-addtivie effects of mixed species early on. In contrast, there was no significant mixing effect after ten days in subsequent samplings. After 90 days, the remaining dry mass of the mixture was 30.39%. The N and P contents of both N. peltatum and P. crispus released rapidly at the early stages and then slowed down. The remaining percentage of N and P of N. peltatum were lower than that of P. crispus. During the early stages of decomposition of mixed material in ten days, the observed N and P remaining were 14.36% and 12.88% (P ＜ 0.05) higher than the expected, indicating the occurrence of antagonistic effects on N and P release in the mixture. However, there were no significant antagonistic mixing effects in subsequent times for N. After 90 days, the observed P remaining was 4.26% (P ＜ 0.05) lower than expected, indicating a synergistic effect on P release occurred. The remaining percentage of N and P were 43.60% and 15.88%, respectively. Nutrients and polyphenol concentrations in the mixture decreased rapidly at the early stages and then decreased slowly through the end of the study, in a manner similar to that of the single species. Our results indicated that there were negative, non-additive effects on decomposition rate, N and P releases when two species were mixed together at the early stages, while there was a synergistic effect on P release in the final stage of the decomposition. This suggests that neither decomposition nor nutrient release patterns can be assessed on basis of single species dynamics. In addition, there was a significant time-independent non-additive effect of species interactions. We further suggest that different aquatic macrophytes of contrasting life forms such as floating-leaved plants and submerged plants may differ in initial chemical quality and may exhibit major determinants for decomposition of mixed aquatic macrophytes.

Aquatic macrophyte; Mixed-species; Decomposition rate; Nitrogen and phosphorus dynamics; Non-additive effect

Q948.8

A

1000-3207(2014)06-1098-09

10.7541/2014.161

2014-01-14;

2014-04-23

國(guó)家自然科學(xué)基金項(xiàng)目(31270378); 中央高?；究蒲袠I(yè)務(wù)費(fèi)專項(xiàng)(CCNU12A02006)資助

鞏崇賢(1987—), 男, 山東棗莊人; 碩士研究生; 研究方向?yàn)闈竦厣鷳B(tài)學(xué)。E-mail: 1933759109@qq.com

王東, E-mail: dongwang.cn@gmail.com