摘要:【目的】研究喀斯特區(qū)植被恢復(fù)過程中植物光、溫、水環(huán)境資源策略及其變化規(guī)律,以期為該區(qū)域植被撫育管理提供理論依據(jù)?!痉椒ā恳再F州茂蘭國(guó)家級(jí)自然保護(hù)區(qū)喀斯特植被為研究對(duì)象,采用空間替代時(shí)間的方法,以植物功能性狀為切入點(diǎn),分析由草灌群落—灌木群落—喬灌群落階段恢復(fù)過程中的群落優(yōu)勢(shì)種適應(yīng)性狀變化過程,結(jié)合主成分分析與隸屬函數(shù)法對(duì)植被恢復(fù)過程中的18個(gè)群落優(yōu)勢(shì)種進(jìn)行光、溫、水適應(yīng)性評(píng)價(jià);通過優(yōu)勢(shì)種適應(yīng)性評(píng)價(jià)值(D)變化,闡明其資源策略,并采用K-means法劃分適應(yīng)功能群,揭示植被恢復(fù)過程中功能群結(jié)構(gòu)變化規(guī)律及對(duì)策?!窘Y(jié)果】群落優(yōu)勢(shì)種對(duì)光適應(yīng)性狀中,葉綠素a含量(1.213~1.851mg/g)和葉綠素a/b(2.321~2.994)隨植被恢復(fù)先降低后升高,比葉面積(125.491~215.580cm2g)隨植被恢復(fù)逐漸降低;對(duì)水適應(yīng)性狀中,葉干物質(zhì)含量(0.272-0.386)和葉組織密度(0.060-0.151g/cm3)隨植被恢復(fù)逐漸增加,葉片相對(duì)含水量(0.671%~0.840%)隨植被恢復(fù)先降低后升高;對(duì)溫適應(yīng)性狀中,丙二醛含量(39.116~63.162nmoVg)隨植被恢復(fù)先降低后升高,過氧化氫酶活性[117.555~1618.869""" nmol(g·min)]隨植被恢復(fù)逐漸增加。主成分分析表明,D反映優(yōu)勢(shì)種光波長(zhǎng)吸收的范圍與光資源轉(zhuǎn)換速率,D反映優(yōu)勢(shì)種對(duì)極端溫度脅迫的耐受程度,D反映優(yōu)勢(shì)種在干旱環(huán)境下維持正常生長(zhǎng)的能力;隨植被恢復(fù)進(jìn)行,群落優(yōu)勢(shì)種D呈先降后升的變化趨勢(shì),D由0.428逐漸升至0.612,D溫在各恢復(fù)階段間無(wú)明顯差異,群落優(yōu)勢(shì)種由開放型光資源獲取策略轉(zhuǎn)變?yōu)楸J匦退Y源競(jìng)爭(zhēng)策略。依據(jù)D劃分出3個(gè)功能群,即FG1(低光—低溫—低水適應(yīng)功能群)、FG2(高光—高溫—高水適應(yīng)功能群)和FG3(低光—低溫—高水適應(yīng)功能群);隨植被恢復(fù)進(jìn)行,F(xiàn)G1的重要值占比逐漸降低,在草灌群落階段達(dá)最高值(49.275%),在灌木群落階段為36.931%,而喬灌群落階段不存在該資源類型物種;FG2物種僅在草灌和喬灌群落階段存在且重要值占比較??;FG3的重要值占比逐漸升高?!窘Y(jié)論】低光合速率、低光資源捕捉面積、不耐水熱脅迫的物種在恢復(fù)早期占據(jù)優(yōu)勢(shì)地位;自灌木群落階段起,逐漸被低光合速率、低光資源捕捉面積、不耐極端溫度、耐旱的物種替代??λ固貐^(qū)域植被撫育應(yīng)在恢復(fù)早期保留光資源獲取策略物種,且多種資源策略物種共存,恢復(fù)中后期主要保留水資源競(jìng)爭(zhēng)策略物種。
關(guān)鍵詞:喀斯特區(qū)域;功能性狀;適應(yīng)評(píng)價(jià);功能群;資源策略;植被恢復(fù)
中圖分類號(hào):S718.54文獻(xiàn)標(biāo)志碼:A文章編號(hào):2095-1191(2024)01-0086-10
Adaptability evaluation and resource strategy of community dominant species in the process of vegetation restoration in karst area of Guizhou
LIU Xiong'2,YULi-fei12°,CHEN Jin12,ZHANG Hui-min12,YAN Ling-bin1-2,WANG Yang3
('College of Life Sciences,Guizhou University,Guiyang,Guizhou550025,China;2Key Laboratory of Plant Resources Conservation and Germplasm Innovation in Mountainous Region(Ministry of Education)/Institute of Agro-bioengineering,Guizhou University,Guiyang,Guizhou550025,China;'Guizhou University of Enginering Science,Bijie,Guizhou551700,China)
Abstract:[Objective]Thispaper studied the strategies of plant light,temperature and water environmental resources and their changing rules in the process of vegetation restoration in karst area,with aview to providing theoretical basis for vegetationnourishment management in the region.【Method]This paper took the karst vegetation in Maolan National Na-ture Reserve in Guizhou as the research object,used spatial substitution time method and plant functional traits as the en-try point,analyzed the adaptive trait change process of community dominant species during the restoration process from grass-shrub community stage to shrubcommunity stage to arbor-shrub community stage,and combined principal compo-nent analysis and membership function method to evaluate the light,temperature,and water adaptability of18community dominant species during the vegetation restoration process;by analyzing the changes in the adaptive evaluation value(D)of dominant species,the resource strategy of dominant species was elucidated,and the K-means method was used to di-videthe adaptive functional groups,in order to reveal the structural changes and countermeasures of functionalgroups du-ring vegetation restoration.[Result]Among the light adaptation traits of the dominant species in the community,chloro-phyll acontent(1.213-1.851mg/g),chlorophyll a/b(2.321-2.994)decreased and then increased with vegetation restora-tion,and specific leaf area(125.491-215.580cm2/g)gradually decreased with vegetation restoration;among the water adaptation traits,leaf dry matter content(0.272-0.386),leaftissue density(0.060-0.151g/cm3)gradually increased with vegetation restoration,and leaf relative water content(0.671%-0.840%)decreased and then increased with vegetation res-toration;among the temperature adaptation traits,malonaldehyde content(39.116-63.162nmol/g)decreased and then in-creased with vegetation restoration,and catalase activity[117.555-1618.869nmol(g·min)]gradually increased with vegetation restoration.Principal component analysis showed that Dis reflected the absorption range of light wavelengths and the strength of light resource conversion rate of the dominant species,Dempenme reflcted the tolerance level of the dominant species to peroxidation produced by extreme temperature stress,and Dwa reflected the ability of the dominant species to maintain normal growth under drought conditions;as vegetation restoration proceded,Diom of the dominant species of the community showed atrend ofdecreasing and then increasing,Da gradually increased from0.428to0.612,Demeram did not differ greatly among the restoration stages,and the dominant species of the community changed froman open light resource acquisition strategy to aconservative water resource competition strategy.In this paper,three func-tional groups were classified based on D,namely FG1(low light-low temperature-low water adaptation functional group),F(xiàn)G2(high light-high temperature-high water adaptation functional group)and FG3(low light-low temperature-high water adaptation functional group);the percentage of important values for FG1gradually decreased with vegetation restoration,reaching the highest value(49.275%)in the grass-shrub community stage and36.931%in the shrub community stage whereas no species of this resource type existed in the arbor-shrub community stage;the species of FG2existed in the grass-shrub and arbor-shrub community stages only and their percentage of important values was small;the percentage of important values for FG3gradually increased with vegetation restoration.【Conclusion]Species with lowphotosynthetic rate,low light resource capture area,and intolerance to water and heat stress dominate in the early stages of recovery;since the shrub community stage,it has gradually been replaced by species with low photosynthetic rate,low light re-source capture area,intolerance to extreme temperatures and drought tolerance.Vegetation nurturing in karst areas should retain light resource acquisition strategy species in the early stages of restoration,with multiple resource strategy species coexisting,and mainly retain water resource competition strategy species in the middle and later stages ofrestoration
Key words:karst area;functional trait;adaptation evaluation;functional group;resource strategy;vegetation resto-ration
Foundation items:National Key Research and Development Program of China(2016YFC0502604);Construction Project of Biology First-class Discipline in Guizhou(GNYL〔2017〕009)
0引言
【研究意義】植被恢復(fù)是群落結(jié)構(gòu)與內(nèi)部環(huán)境相互協(xié)變、匹配的有序過程,隨其變化的生境條件則作為“環(huán)境篩”淘汰不具特定生態(tài)功能的物種(Qin et al.,2023),這種作用在成土慢、地形破碎、滲透性干旱、高生態(tài)脆弱性的喀斯特地區(qū)更為明顯(Chen et al.,2021)。通常植物會(huì)改變自身性狀來(lái)提高耐受性以適應(yīng)變化的環(huán)境條件(Wang and Chen,2013),以葉性狀最敏感(Zhou et al.,2023)。植物是否成功定居,通常取決于其對(duì)環(huán)境適應(yīng)的生態(tài)策略特征(Wen et al.,2023)。因此,在喀斯特區(qū)探究植被恢復(fù)過程中群落優(yōu)勢(shì)種生態(tài)策略特征及其變化規(guī)律,對(duì)指導(dǎo)該區(qū)域植被恢復(fù)具有重要意義?!厩叭搜芯窟M(jìn)展】在生態(tài)策略中,植物資源策略特征更受學(xué)者關(guān)注,即定居種生長(zhǎng)—防御權(quán)衡關(guān)系(黃林娟等,2022)。相較于非喀斯特區(qū),喀斯特區(qū)植物通常具有獨(dú)特的喜鈣、耐瘠和巖生耐旱生態(tài)特性以適應(yīng)環(huán)境(鐘巧連等,2018),具體表現(xiàn)為低比葉面積、高葉組織密度、高葉干物質(zhì)含量等性狀特征(程雯等,2019;王琪等,2022)。研究表明非生物環(huán)境驅(qū)動(dòng)群落物種性狀變異,物種性狀組合決定其資源策略特征,而物種資源策略類型主導(dǎo)其在群落中的優(yōu)勢(shì)地位(Zhou et al.,2023)。在喀斯特區(qū)植被演替中,早期物種性狀主要采取開放型策略以維持種群數(shù)量,后期則轉(zhuǎn)為保守型策略以提高資源利用能力(Wanget al.,2022b)。Geekiyanage等(2019)研究認(rèn)為喀斯特森林主要由土壤水、表巖水、地下水、空氣水和干旱落葉等5類水環(huán)境資源策略類型的物種構(gòu)成,這些物種的分布取決于喀斯特山地水分空間分布格局。Liu等(2022)研究顯示土壤磷是喀斯特森林物種采取保守資源競(jìng)爭(zhēng)策略的驅(qū)動(dòng)因子,且這類物種以降低比葉面積,提高干物質(zhì)含量與組織密度來(lái)增強(qiáng)環(huán)境資源競(jìng)爭(zhēng)力。同樣,在物種繁殖特性上,開放型策略物種繁殖成本低,以加強(qiáng)種子擴(kuò)散能力提高定居機(jī)會(huì),而保守型策略物種的繁殖成本較高,種子成熟緩慢以提高存活率(Han et al.,2019)。在生長(zhǎng)型上,稅偉等(2022)認(rèn)為灌木物種資源策略較喬木物種更穩(wěn)定,且在外在環(huán)境的驅(qū)動(dòng)下,同一混交群落不同亞型間物種資源策略也存在趨同或趨異的發(fā)展趨勢(shì)(Wang et al.,2023)。雖然在同一地區(qū)存活的同類物種存在不同的資源策略(Yang et al.,2022),但整體上性狀適應(yīng)度越高的物種其資源利用效率越高,即入侵、定居、存活的能力越強(qiáng)(Godoy et al.,2012)。綜上,物種的資源策略類型主要取決于定居群落的環(huán)境特征(Wang et al.,2022a),且植物資源策略研究有助于揭示群落構(gòu)建過程中生物與非生物要素間的內(nèi)在協(xié)調(diào)規(guī)律(Doudová and Douda,2020),從而綜合體現(xiàn)群落資源結(jié)構(gòu)特征與生態(tài)系統(tǒng)功能(Zirbel et al.,2017)?!颈狙芯壳腥朦c(diǎn)】目前,對(duì)喀斯特植被資源策略的研究多集中于物種資源獲取與資源競(jìng)爭(zhēng)類型的劃分(鐘巧連等,2018;喻陽(yáng)華等,2021;Wu et al.,2021;Wang et al.,2023),而有關(guān)物種對(duì)不同環(huán)境類型的資源策略及其隨植被恢復(fù)的變化研究鮮有報(bào)道。【擬解決的關(guān)鍵問題】以貴州茂蘭喀斯特區(qū)群落優(yōu)勢(shì)種為研究對(duì)象,采用空間代替時(shí)間的方法,以優(yōu)勢(shì)種為單元,結(jié)合其葉片光、溫、水適應(yīng)功能性狀等屬性,對(duì)優(yōu)勢(shì)種進(jìn)行適應(yīng)性評(píng)價(jià),進(jìn)而明確喀斯特植被恢復(fù)過程中群落優(yōu)勢(shì)種對(duì)光、溫、水資源策略變化規(guī)律;并在此基礎(chǔ)上對(duì)優(yōu)勢(shì)種進(jìn)行適應(yīng)功能群劃分,從群落尺度上揭示植被恢復(fù)過程中功能群結(jié)構(gòu)變化特征,以期為喀斯特區(qū)植被撫育管理提供理論依據(jù)。
1材料與方法
1.1研究區(qū)概況
研究區(qū)位于貴州茂蘭國(guó)家級(jí)自然保護(hù)區(qū),以喀斯特峰叢地貌為主,海拔430~1078m,屬亞熱帶季風(fēng)溫潤(rùn)氣候,年均溫15.3℃,年降水量1752.5mm,年平均相對(duì)濕度83%,主要為黑色石灰土,土層薄且不連續(xù),土壤鈣質(zhì)化。頂極植被類型為常綠落葉闊葉混交林,同時(shí)存在退化植被恢復(fù)各階段群落,恢復(fù)過程沿草本群落、草灌群落、灌木群落、喬灌群落、喬林群落和頂極群落6個(gè)階段進(jìn)行(安明態(tài),2019)。
1.2試驗(yàn)方法
于2021年6月,在植被恢復(fù)樣帶中選取草灌群落階段、灌木群落階段和喬灌群落階段3類連續(xù)的過渡階段群落,并選擇其中優(yōu)勢(shì)植物種的葉片,測(cè)定其對(duì)光、溫、水適應(yīng)的形態(tài)生理性狀指標(biāo),分析不同恢復(fù)階段優(yōu)勢(shì)種性狀變化特征,并分別對(duì)植物性狀開展光、溫、水適應(yīng)性評(píng)價(jià),以闡明植被恢復(fù)過程中群落優(yōu)勢(shì)種資源策略特征及其變化規(guī)律;在此基礎(chǔ)上,劃分植物對(duì)光、溫、水的適應(yīng)功能群,分析不同恢復(fù)階段優(yōu)勢(shì)種適應(yīng)功能群結(jié)構(gòu)及其變化特征。
1.2.1樣地調(diào)查在貴州茂蘭國(guó)家級(jí)自然保護(hù)區(qū)植被恢復(fù)區(qū)設(shè)20m×120m的2條水平樣帶(表1),且每條樣帶均由草灌群落階段(Grass-shrub commu-nity stage,簡(jiǎn)稱gscs)、灌木群落階段(Shrub commu-nity stage,簡(jiǎn)稱scs)和喬灌群落階段(Arbor-shrub community stage,簡(jiǎn)稱ascs)組成。其中,各樣帶分別由6個(gè)20m×20m的植被恢復(fù)樣地構(gòu)成,按其恢復(fù)序列依次命名為gscs-1、gscs-2、sCs-1、scs-2、ascs-1、ascs-2。將各樣地均分為10個(gè)4m×10m的樣方,每個(gè)樣方中隨機(jī)各設(shè)1個(gè)1m×1m草本樣方、4m×4m灌木樣方和4m×10m喬木樣方,調(diào)查優(yōu)勢(shì)層植物種名、多度、密度、胸徑、蓋度、頻度等信息,計(jì)算其重要值,同時(shí)記錄海拔、地形等生境信息。
1.2.2樣品采集及處理于植物生長(zhǎng)最旺盛的6月采集各樣地優(yōu)勢(shì)層共計(jì)18個(gè)優(yōu)勢(shì)種葉片,每種3株混合取樣?,F(xiàn)場(chǎng)用游標(biāo)卡尺(FS=0.01mm)測(cè)定葉厚,稱重后部分鮮葉密封保存,部分葉片速凍后干冰保存下迅速帶回實(shí)驗(yàn)室測(cè)定各樣本形態(tài)生理性狀指標(biāo)(表2)。其中,鮮葉利用掃描儀(HP Scanjet N9120)測(cè)定葉面積,浸泡與烘干稱重后計(jì)算葉干物質(zhì)含量和葉片相對(duì)含水量,并結(jié)合葉面積計(jì)算比葉面積和葉組織密度;采用試劑盒(蘇州科銘生物技術(shù)有限公司)測(cè)定葉綠素和丙二醛(MDA)含量,以及過氧化氫酶(CAT)、過氧化物酶(POD)和超氧化物歧化酶(SOD)活性,所選試劑型號(hào)依次為CPL-2-G、MDA-1-Y、CAT-1-Y、POD-1-Y和SOD-1-W。
1.2.3優(yōu)勢(shì)種適應(yīng)性評(píng)價(jià)及功能群劃分適應(yīng)性評(píng)價(jià):以植物優(yōu)勢(shì)種為單元,以其性狀指標(biāo)為屬性進(jìn)行主成分分析(PCA),選累積貢獻(xiàn)率gt;80%主成分,根據(jù)公式計(jì)算PCA得分及其隸屬函數(shù)值,并結(jié)合各主成分的權(quán)重計(jì)算各優(yōu)勢(shì)種適應(yīng)性評(píng)價(jià)值(D)(馮月等,2022)。
式中,Xij為j主成分中種i得分,aj為主成分j的標(biāo)準(zhǔn)化特征向量值,T為種i指標(biāo)標(biāo)準(zhǔn)化后各性狀值,Uij為j主成分得分中種i隸屬函數(shù)值,Xjmin為j主成分得分最小值,Xjmas為j主成分得分最大值,W為主成分j權(quán)重,Pj為主成分j貢獻(xiàn)率。
功能群劃分:以植物優(yōu)勢(shì)種為單元,以其D為屬性,采用Elbow method和K-means法,利用R語(yǔ)言(ggplot2、factoextra、cluster和vegan包)對(duì)優(yōu)勢(shì)種進(jìn)行功能群聚類。
1.3統(tǒng)計(jì)分析
采用R4.2.1、Excel2016和SPSS22.0對(duì)數(shù)據(jù)進(jìn)行統(tǒng)計(jì)分析。正態(tài)分布數(shù)據(jù)利用參數(shù)檢驗(yàn),非正態(tài)分布數(shù)據(jù)進(jìn)行對(duì)數(shù)轉(zhuǎn)換后,若服從正態(tài)分布則采用參數(shù)檢驗(yàn),否則作非參數(shù)檢驗(yàn)。
2結(jié)果與分析
2.1植被恢復(fù)過程中優(yōu)勢(shì)種適應(yīng)性狀變化特征
由表3可知,在對(duì)光適應(yīng)性狀中,群落優(yōu)勢(shì)種Chla/b和SLA隨植被恢復(fù)分別由草灌群落階段的2.994和215.580cm2/g顯著降低至喬灌群落階段的2.352和125.491cm2/g(Plt;0.05,下同),Chla和Tchl含量則隨植被恢復(fù)先顯著降低后緩升,即灌木群落階段的含量最低,分別為1.213和140.797mg/g。表明在恢復(fù)早期優(yōu)勢(shì)種主要采取吸收紅光(波長(zhǎng)620~760nm)、光資源捕捉面積大的喜陽(yáng)策略以適應(yīng)早期強(qiáng)光照、直輻射的光環(huán)境條件;隨恢復(fù)至中后期,優(yōu)勢(shì)種吸收藍(lán)紫光(波長(zhǎng)380~475nm)比重增加,光資源捕捉面積減少,同時(shí)在灌木群落階段優(yōu)勢(shì)種光合速率與紅光吸收速率最弱。在對(duì)水分適應(yīng)性狀中,群落優(yōu)勢(shì)種LRWC、LDMC和LTD隨植被恢復(fù)分別由草灌群落階段的0.767%、0.272和0.060g/cm3增至喬灌階段的0.840%、0.386和0.151g/cm3,即群落優(yōu)勢(shì)種早期水養(yǎng)存儲(chǔ)能力低、葉片延展性差,而中后期水養(yǎng)存儲(chǔ)能力強(qiáng),葉片延展性好。在對(duì)溫度適應(yīng)性狀中,群落優(yōu)勢(shì)種CAT活性[1618.869nmol/(g·min)]和MDA含量(63.162nmol/g)均在喬灌群落階段達(dá)最大值,表明植被恢復(fù)中后期優(yōu)勢(shì)種通過提高體內(nèi)H?O?分解能力以應(yīng)對(duì)較強(qiáng)的環(huán)境脅迫。
2.2植被恢復(fù)過程中優(yōu)勢(shì)種適應(yīng)性評(píng)價(jià)結(jié)果
以18個(gè)優(yōu)勢(shì)種為單元,分別以其對(duì)光、溫、水適應(yīng)性狀為屬性進(jìn)行PCA,結(jié)果如表4所示。為更好進(jìn)行適應(yīng)性綜合評(píng)價(jià),各環(huán)境類型適應(yīng)性狀PCA均提取3個(gè)主成分,累積貢獻(xiàn)率均大于85%。結(jié)合表5特征向量分別計(jì)算得出各優(yōu)勢(shì)種光、溫、水適應(yīng)性評(píng)價(jià)值,即D光、D溫和D水。由表5的載荷系數(shù)可知,D光反映優(yōu)勢(shì)種光波長(zhǎng)吸收的范圍與光資源轉(zhuǎn)換速率,D光越大表明物種葉綠素含量高、Chla/b和SLA大,即吸收光波長(zhǎng)范圍廣、光資源轉(zhuǎn)換速率高、喜陽(yáng)、光資源捕捉面積大,反之光波長(zhǎng)吸收范圍窄、光資源轉(zhuǎn)換速率低、耐蔭、光資源捕捉面積?。籇反映優(yōu)勢(shì)種對(duì)極端溫度脅迫的耐受程度,D溫越大表明植物受極端溫度脅迫較強(qiáng),但其體內(nèi)保護(hù)性酶活性較高以消除脂膜過氧化帶來(lái)的危害,反之同理;D水反映優(yōu)勢(shì)種在干旱環(huán)境下維持正常生長(zhǎng)的能力,D越大則植物葉片越薄且具有較高的LDMC、LTD和LRWC,即植物具有較強(qiáng)的水養(yǎng)分存儲(chǔ)能力與葉片延展度以適應(yīng)干旱生境,反之同理。
2.3植被恢復(fù)過程中優(yōu)勢(shì)種D的變化特征
對(duì)不同恢復(fù)階段優(yōu)勢(shì)種間D光、D溫和D水進(jìn)行方差分析可知,草灌群落階段優(yōu)勢(shì)種D光最高(0.385),使其能適應(yīng)早期強(qiáng)光環(huán)境,灌木群落階段D晃最低(0.255),二者間差異顯著(圖1-A);而各恢復(fù)階段間優(yōu)勢(shì)種D溫?zé)o顯著差異(Pgt;0.05,下同)(圖1-B);D水則表現(xiàn)為喬灌群落階段(0.612)gt;灌木群落階段(0.492)gt;草灌群落階段(0.428),三者間差異顯著,表明高D物種為植被恢復(fù)中后期的主要組成部分(圖1-C)。綜上,強(qiáng)光環(huán)境可能主導(dǎo)草灌群落階段物種的生長(zhǎng)分布,而環(huán)境水分條件是灌木和喬灌群落階段優(yōu)勢(shì)種生長(zhǎng)發(fā)育的主要限制因子。
通過回歸分析(圖2)可知,在水平樣帶樣地上,隨植被的恢復(fù),群落優(yōu)勢(shì)種D,呈先降低后升高的變化趨勢(shì),表明在草灌群落與灌木群落過渡階段,群落優(yōu)勢(shì)種具有較好的光適應(yīng)能力,即光合速率較高、光資源捕捉面積較大。群落優(yōu)勢(shì)種D永隨植被恢復(fù)呈線性極顯著增加趨勢(shì)(Plt;0.01),表明在植被恢復(fù)中后期群落優(yōu)勢(shì)種具有較強(qiáng)的耐旱性,即對(duì)環(huán)境水資源具有較強(qiáng)競(jìng)爭(zhēng)力。群落優(yōu)勢(shì)種D溫隨植被恢復(fù)無(wú)顯著變化,其在喬灌群落階段達(dá)最大值。
由圖3可知,草灌群落階段優(yōu)勢(shì)種核密度集中分布在D軸(23.511%~49.557%)和Dk軸(28.901%~49.976%);灌木群落階段優(yōu)勢(shì)核密度在D光軸上的分布權(quán)重為12.308%~33.097%,而在D軸上為35.588%~59.256%;喬灌群落階段優(yōu)勢(shì)種核密度在D光軸上的分布權(quán)重為14.230%~38.275%,而在D水軸上為35.973%~63.454%,同時(shí)在植被恢復(fù)中后期,優(yōu)勢(shì)種在D溫軸上分布的權(quán)重呈逐漸增加趨勢(shì)。表明隨植被恢復(fù)進(jìn)行,群落優(yōu)勢(shì)種對(duì)環(huán)境光、溫、水適應(yīng)性分配逐漸由光、水資源策略轉(zhuǎn)變?yōu)樗?、溫資源策略。
2.4植被恢復(fù)過程中適應(yīng)功能群劃分及其群落結(jié)構(gòu)變化特征
由圖4-A可知,當(dāng)K為3時(shí)圖像逐漸趨于平緩,即簇內(nèi)畸變程度低,故將優(yōu)勢(shì)種劃分為3種適應(yīng)功能群較合適;聚類結(jié)果如圖4-B所示,第1類功能群共有7種優(yōu)勢(shì)種,第2類功能群共有3種優(yōu)勢(shì)種,第3類功能群共有8種優(yōu)勢(shì)種。對(duì)各適應(yīng)性功能群D光、D溫和D水分別進(jìn)行方差分析(表6),根據(jù)各類D的生態(tài)意義,按照其均值大小并結(jié)合檢驗(yàn)水平對(duì)各功能群進(jìn)行命名,分別為FG1:低光—低溫—低水適應(yīng)功能群,物種組成多為草本物種,這類物種通常光合速率較低,比葉面積較小,對(duì)極端水熱環(huán)境耐受性差;FG2:高光一高溫—高水適應(yīng)功能群,物種組成較少,由草本和喬木物種構(gòu)成,屬于偶見資源類型;FG3:低光—低溫—高水適應(yīng)功能群,多為喬木物種,這類物種光合速率低,光資源捕捉面積小,對(duì)極端溫度耐受性差,但具有較強(qiáng)的耐旱性。
由圖5可知,群落植物種功能群結(jié)構(gòu)隨植被恢復(fù)發(fā)生變化,F(xiàn)G1的重要值占比隨植被恢復(fù)逐漸降低,其在草灌群落階段達(dá)最高值(49.275%),在灌木群落階段為36.931%,而喬灌群落階段不存在該資源類型物種;FG3的重要值占比隨植被恢復(fù)由草灌群落階段的27.851%經(jīng)灌木群落階段的63.069%升至喬灌群落階段的84.534%,反映出低光合速率、低光資源捕捉面積、不耐極溫、不耐旱策略物種的優(yōu)勢(shì)地位逐漸被低光合速率、低光資源捕捉面積、不耐極端溫度、耐旱的植物種類所替代;而FG2物種僅在草灌和喬灌群落階段存在且重要值占比始終較小,屬于偶見資源類型。
3討論
物種資源獲取策略是研究喀斯特區(qū)環(huán)境篩選作用及物種生存機(jī)制的重要研究手段(Yu et al.,2022)。本研究中,群落優(yōu)勢(shì)種D晃隨植被恢復(fù)呈先降后升的變化趨勢(shì),D錄隨植被恢復(fù)而顯著上升,這是因?yàn)榭λ固厝郝溲萏嬖缙谖锓N通常以犧牲耐旱性為代價(jià),提高光合能力以獲取更多資源,而中后期物種提高其耐旱性生態(tài)位,有助于增加存活率(Wu et al.,2021)。隨植被恢復(fù)進(jìn)行,本研究草灌群落優(yōu)勢(shì)種Chla含量、Chla/b、Tchl含量及SLA達(dá)最大值,使其具有較高的D光,進(jìn)一步體現(xiàn)亞熱帶喀斯特區(qū)草灌群落階段植被具有較強(qiáng)的光資源捕捉能力與相對(duì)生長(zhǎng)速率(陳文等,2016);同時(shí),較高的Chla含量和到生長(zhǎng)目的(王亞楠等,2020),使其D光顯著低于其他階段,即Chla含量和Chla/b顯著降低。雖然喬灌群落階段部分優(yōu)勢(shì)種提高自身光合速率與波長(zhǎng)吸收范圍致使D光顯著高于灌木群落階段,但這類物種在該階段占比較小,這是由喬灌群落生物結(jié)構(gòu)的不穩(wěn)定性及隨植被恢復(fù)逐漸穩(wěn)定的非生物環(huán)境驅(qū)使的結(jié)果,以促進(jìn)群落在恢復(fù)進(jìn)程中逐漸形成更為穩(wěn)定的群落層次與資源競(jìng)爭(zhēng)關(guān)系(文麗等,2015)。整體而言,草灌群落優(yōu)勢(shì)種對(duì)光照資源采取較開放的獲取策略,以達(dá)到適應(yīng)強(qiáng)光、快速生長(zhǎng)目的,而中期木本植物占據(jù)較上層資源空間、冠層分布廣且在D晃軸上的分布占比較小,即光資源限制作用弱而受土壤環(huán)境影響顯著(Wu et al.,2021),群落優(yōu)勢(shì)種對(duì)光照資源獲取采取較保守的耐蔭策略。
植被恢復(fù)早期的不穩(wěn)定水熱環(huán)境預(yù)示資源空間多樣化,使得恢復(fù)早期LTD、LRWC和LDMC較低的物種得以占據(jù)優(yōu)勢(shì)地位,而中后期穩(wěn)定的水熱環(huán)境使物種資源策略具有趨同性(李亞錦等,2021),環(huán)境水熱條件對(duì)物種選擇作用增強(qiáng)。本研究中,優(yōu)勢(shì)種LTD呈草灌群落階段低,灌木和喬灌群落階段高的現(xiàn)象,與喀斯特植被恢復(fù)中后期群落結(jié)構(gòu)分層,水分資源逐級(jí)截取,土壤水分季節(jié)性虧缺嚴(yán)重等因素有關(guān);物種通過提高LTD和LRWC以減少其水分喪失、防止高溫干旱環(huán)境損傷葉片,進(jìn)而導(dǎo)致SLA趨于減?。ǘ悅サ龋?022)。同樣,植物在面對(duì)這種惡劣環(huán)境脅迫時(shí)通常會(huì)提高自身LDMC,較高的LDMC可增強(qiáng)植物對(duì)外來(lái)物理傷害的抗性,提高資源競(jìng)爭(zhēng)力,維持自身正常生長(zhǎng)(吳陶紅等,2023)。本研究認(rèn)為喀斯特區(qū)隨著植被恢復(fù)進(jìn)行,群落優(yōu)勢(shì)種通過降低水分蒸發(fā)面積,增加葉片伸展度,加強(qiáng)水養(yǎng)吸收存儲(chǔ)能力,以提高環(huán)境水資源競(jìng)爭(zhēng)力。整體而言,植被恢復(fù)早期群落環(huán)境異質(zhì)性高,群落結(jié)構(gòu)單一,優(yōu)勢(shì)種水分存儲(chǔ)能力弱,屬水分獲取策略,而恢復(fù)中后期資源空間分布逐步穩(wěn)定,優(yōu)勢(shì)種資源策略更多分配在水分吸收、儲(chǔ)存與減少蒸發(fā)上,提高了物種對(duì)環(huán)境水分資源的競(jìng)爭(zhēng)能力。
植物功能群作為研究植被—環(huán)境相互協(xié)調(diào)機(jī)制的重要單位,較多學(xué)者認(rèn)為功能群劃分應(yīng)基于植物對(duì)環(huán)境限制因子的響應(yīng)上(Jakobet al.,2022),以明確各植物種組間的類型界定及解釋生態(tài)系統(tǒng)過程對(duì)物種的作用機(jī)理(Hu et al.,2023)。通過環(huán)境適應(yīng)功能群劃分表明,草灌群落階段優(yōu)勢(shì)資源類型為低光合速率、低光資源捕捉面積、不耐水熱脅迫的適應(yīng)物種組合,且與FG2、FG3共存,反映出生境資源多樣性較高的草灌階段允許多種資源類型物種共存;同時(shí),本研究認(rèn)為灌木群落階段是喀斯特植被恢復(fù)優(yōu)勢(shì)種資源類型轉(zhuǎn)變的關(guān)鍵階段,可能與其逐漸穩(wěn)定的土壤養(yǎng)分及物種生活史階段有關(guān)(Meng et al.,2021),自灌木群落階段起,具有低光合速率、低光資源捕捉面積、不耐極端溫度、耐旱資源類型的物種占據(jù)優(yōu)勢(shì)地位,屬保守型資源競(jìng)爭(zhēng)策略,以應(yīng)對(duì)植物群落競(jìng)爭(zhēng)排斥作用(Lohbeck et al.,2014)。相應(yīng)地,耐極端溫度FG2在恢復(fù)后期重要值占比較低,故環(huán)境溫度對(duì)物種分布限制作用較弱,而環(huán)境水分是主要限制因子。綜上,喀斯特植被生態(tài)修復(fù)過程中,應(yīng)注重不同恢復(fù)階段物種資源類型以確定保留種,早期階段允許多種資源類型物種共存,且以保留光資源獲取策略物種為主,中后期保留較強(qiáng)水資源競(jìng)爭(zhēng)能力物種,以促進(jìn)植被恢復(fù)。
4結(jié)論
隨植被恢復(fù)進(jìn)行,早期優(yōu)勢(shì)種主要采取開放型光資源獲取策略,低光合速率、低光資源捕捉面積、不耐水熱脅迫物種占據(jù)優(yōu)勢(shì);自灌木群落階段起,優(yōu)勢(shì)種采取保守型水資源競(jìng)爭(zhēng)策略,低光合速率、低光資源捕捉面積、不耐極端溫度、耐旱資源類型物種占據(jù)優(yōu)勢(shì)。喀斯特區(qū)域植被撫育應(yīng)在恢復(fù)早期保留光資源獲取策略物種,且多種資源策略物種共存,恢復(fù)中后期主要保留水資源競(jìng)爭(zhēng)策略物種。
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(責(zé)任編輯 羅麗)