湖南会同5个亚热带树种的细根构型及功能特征分析

细根(直径2mm)具有复杂的分枝系统,不同树种间的细根在空间分布、形态和大小上有较大差异,研究不同树种的细根构型及不同根序的养分特征,对认识不同树种的细根形态和化学成分的变异格局,及其对树种地下生态位分离(niche segregation)、共存和森林生态系统功能过程的影响有着重要意义。在湖南会同林区选择青冈(Cyclobalanopsis glauca)、枫香(Liquidanbar formosana)、拟赤杨(Alniphyllum fortunei)、杉木(Cunninghamia lanceolata)、马尾松(Pinus massoniana)等5个亚热带树种,用挖掘法采集完整的细根根系,按照Pregitzer细根分级方法对细根分级,用Win-RHIZO根系测定系统对细根构型的参数进行测定,同时测定各级根系的C、N含量,以探讨各树种各级细根的功能特征,揭示不同树种细根构型与养分策略之间的关系。结果表明:5个亚热带树种细根1级根比根长、比表面积最高,直径最细;3级根比根长、比表面积最低,直径最粗。不同树种之间细根形态特征和构型也表现出差异性:枫香的1级根序比根长最大,为31.45m·g-1,杉木的最小,为16.34m·g-1,枫香和杉木之间差异显著。马尾松的1、2级根序的比表面积最大,杉木的1级根序的比表面积最小,青冈2级根序的比表面积最小,3级根序比表面积杉木最大,青冈最小。不同树种之间的细根直径差异达到极显著水平,各根序的平均直径以杉木的最大,拟赤杨的最小。5个树种细根根尖密度大小顺序为马尾松青冈枫香杉木拟赤杨,各树种细根分叉数以拟赤杨和马尾松的较高,杉木最低。除杉木和枫香外,5个树种细根C含量均呈现出随着根序上升而增加的趋势,C/N比也随根序的上升而增加,而细根N含量呈现出随着根序上升而明显下降的趋势。细根平均C含量以杉木的最高,拟赤杨的最低,马尾松、青冈与枫香之间的差异不显著。细根平均N含量以拟赤杨的最高,马尾松的最低。C/N比以马尾松的最高,拟赤杨的最低。5个树种中,马尾松的外生菌根有很强的拓展能力,因此能显著地增强植物根系的养分、水分吸收能力,即使在贫瘠和干旱的土壤环境中,也能有效地利用有限的养分和水分,促进个体生长。而杉木细根吸收养分和水分的效率及能力最小。     

海南岛4个热带阔叶树种前5级细根的形态、解剖结构和组织碳氮含量

细根具有复杂的分支系统, 以根序(root order)为取样单元的细根生理生态学研究正在成为根系生态学研究领域的重要内容。该研究以海南岛尖峰岭4个热带阔叶树种海南蕈树(Altingia obovata)、厚壳桂(Cryptocarya chinensis)、山杜英(Elaeocarpus sylvestris)和黄桐(Endospermum chinense)为研究对象, 测定了1-5级细根的形态、解剖结构和组织碳(C)、氮(N)含量, 旨在探讨这些根系特征之间的联系。研究表明: 4个树种的细根形态差异较大, 但在树种水平上直径、根长和组织密度均随着根序的升高而增加, 比根长则随着根序的升高而降低; 低级根(前2级根或前3级根)具有皮层组织, 是典型的吸收根, 而高级根皮层组织消失, 是典型的运输和储藏根; 影响直径大小最重要的因子是皮层厚度, 它可以解释细根直径变异的97%, 而维管束直径仅能解释细根直径变异的70%; 根组织N和C浓度受维管束-根直径比(维根比)的影响, 随着维根比增加, 组织N浓度显著降低, 组织C浓度显著升高。4个树种细根的C/N比的变异受组织N浓度的影响程度为76%, 而受C浓度的影响程度不足10%。上述结果表明, 细根的形态特征、解剖结构和组织化学含量之间存在着紧密联系, 这为我们理解根系结构与功能变异提供了重要依据。     

华北山地6个外生菌根树种的根属性及其与菌根侵染率的关系

该研究以共存于同一暖温带森林的6个外生菌根(ECM)树种为研究对象,测定分析不同根序(1～5级)和功能根系(吸收细根和运输细根)的主要形态和构型属性及ECM侵染率,探究不同外生菌根树种的根属性变异模式及其与菌根真菌侵染程度的关系。结果表明:(1)随着根序的增加,不同树种根直径和单根长度均增加,而比根长和根分支强度均降低;根属性在同一根序下均存在显著的种间差异,尤其是2个裸子植物(落叶松和油松)的根直径较其他4个被子植物大。(2)同一树种的所有根属性在吸收细根和运输细根之间均有显著差异;吸收细根和运输细根的根直径、比根长和根组织密度在树种间均存在显著差异,而其单根长度和根分支强度在树种间无显著差异。(3)ECM侵染率以落叶松最高,千金榆和白桦最低,且与根尖直径呈显著正相关关系,与根尖比根长呈显著负相关关系。研究发现,基于根序或者功能根系,根属性在种间的变异模式不完全一致,单根长度和根分支强度在两个功能根系中均没有表现出显著的种间差异;吸收细根的比根长和根分支强度的变异系数较大,对环境变化有较敏感的响应;古老树种的根直径相对较粗,对菌根真菌的依赖性更高。     

鼎湖山9种常见树木细根组织N浓度的季节变化

根系在植物养分吸收、生理代谢和生态系统过程中发挥着重要作用, 然而我们对根系结构与功能的了解十分有限。以往对根系的研究往往用直径大小定义细根, 忽略了细根系统内部结构和功能的异质性。近年来的研究表明, 细根系统中的根级(root order)与根的功能有较好的相关性, 低级根个体多属于短命的吸收根。温带森林的研究表明, 非木质化的吸收根在氮(N)浓度上呈现显著的季节变化, 而与木质化的结构性根缺少N浓度的季节变化形成鲜明对比。该研究通过研究亚热带树木不同根级N浓度的季节变化, 试图验证假说: 木本植物中, 非木质化的根中N浓度具有明显的季节变化是一个普遍现象。通过对鼎湖山常见的9种木本植物不同根级的研究, 证实了在1年内的6个采样时段, 各根级的N浓度之间都存在显著差异; 与温带树种不同, 各树种不同根级的N浓度变化呈现不同的季节格局, 这与假说不符。因此认为温带与亚热带森林生态系统之间的环境差异以及树种之间的差异是导致亚热带树种低级根的N浓度季节变化不显著, 而三、四级根变化相对显著的主要原因。这些发现对于认识树木根系统内及个体水平的N分配与利用格局具有重要的意义。     

帽儿山天然次生林20个阔叶树种细根形态

 细根在森林生态系统C分配和养分循环过程中发挥着重要作用。细根形态不但影响养分和水分的吸收, 而且与细根寿命和周转有密切关系。因此, 研究森林树种的细根形态对了解根系结构与功能、预测寿命与周转具有重要理论意义。该文根据细根分枝等级划分方法, 研究了东北帽儿山天然次生林20个阔叶树种1～5级根直径、根长和比根长等形态指标。结果表明, 20个树种中, 除5个树种1级根直径略大于2级和比根长略小于2级根外, 其余15个树种均表现为1级根直径和根长最小、比根长最高, 随着根序增加, 直径和根长增加, 而比根长降低。20个阔叶树种前3级根的累积根长均占前5级根总根长的80%以上。9个内生菌根侵染的树种的平均直径、根长和比根长均大于11个外生菌根侵染的树种。     

川中丘陵区3个树种的细根形态和功能异质性分析

以川中丘陵区柏木低效林林窗改造初期种植的银木和香椿细根为研究对象,以未改造的柏木纯林为对照,采用LI-8100土壤碳通量测量系统测定银木、香椿和柏木1~5级细根的原位呼吸速率,并探讨细根形态结构和养分元素浓度与细根呼吸的相关关系,以揭示细根结构与功能异质性。结果表明:银木、香椿和柏木细根的直径、根长、组织碳浓度均随着根序级别的增加而增加,而它们细根的比根长、组织氮浓度和比根呼吸速率均随着根序的增加而降低,树种、根序级及其交互作用对3个树种细根形态、养分浓度和比根呼吸均有显著或极显著影响。回归分析显示,3个树种比根呼吸速率均随细根直径、比根长、N浓度变化呈现出系统性的变化,三者分别能解释64.7%、87.6%和、67.6%的比根呼吸变异。可见,细根在形态和功能上存在明显的异质性,且细根的形态特征、组织化学含量和生理功能之间存在着紧密的联系,为理解植物根系结构与功能变异提供了依据。     

热带亚热带26种蕨类植物的吸收根解剖特征

植物吸收根的生理功能是从土壤中吸收水分和营养物质, 研究其解剖结构有助于揭示植物的环境适应策略。热带亚热带地区蕨类植物丰富, 生态和经济价值较高, 但目前对这一重要植物类群的吸收根解剖特征的研究仍然缺乏。该研究测定了分布在热带亚热带地区4种典型森林的共26种蕨类植物吸收根的解剖特征, 分析它们的种间差异, 结合系统发育与全球自然分布区的气候因子解释根系性状的变异。同时, 通过收集亚热带木本被子植物和温带蕨类植物相关的已发表数据, 比较不同类群的根系性状相关关系的差异。结果表明: (1)这些蕨类植物吸收根特征的种间差异显著, 8个根系性状的种间变异系数范围为20.61%-41.75%。(2)除皮层厚度外根系性状无显著的系统发育信号, 说明性状变异受系统发育的影响较小; 气候因子显著影响根系特征, 根直径和皮层厚度随着最干月(季)降水量减少而增大。(3)随着吸收根直径的减小, 亚热带木本被子植物趋于具有更低的皮层厚度/中柱直径比值, 而蕨类植物则相反; 与温带蕨类相比, 该研究中蕨类植物具有更大的根直径、皮层厚度和管胞直径。该研究有助于提高对热带亚热带蕨类植物根系生理生态适应性的认识。     

亚热带常绿阔叶林89种木本植物一级根直径的变异

细根直径变异是根系形态变化的常见形式, 对细根变异研究具有重要意义。为了揭示亚热带天然常绿阔叶林一级根直径变异特征, 该研究选取福建省建瓯市万木林自然保护区天然常绿阔叶林的89种木本植物进行研究。每个树种选取胸径或地径相近的3株, 用完整土块法进行根系取样, 用根序法对根系进行分级。采用单因素方差分析分别检验叶片习性(常绿、落叶树种)、生长型(乔木、小乔木或灌木、灌木)和主要科之间一级根直径的差异; 通过计算Blomberg’s K值以检验系统发育信号; 利用线性回归方法, 分析科水平的分化时间与一级根直径的相关性。结果显示: 1)亚热带常绿阔叶林一级根直径变异系数为23%; 2)常绿树种与落叶树种一级根直径没有显著差异, 但灌木一级根直径显著小于小乔木或灌木、乔木; 3)一级根直径系统发育信号不显著, 科水平分化时间与一级根直径呈正相关关系。研究结果表明, 亚热带天然常绿阔叶林木本植物一级根直径变异受系统发育影响较小, 但受生长型影响, 表现为一定的趋同适应。     

亚热带天然常绿阔叶林林下9种灌木细根形态和C、N化学计量特征

林下灌木是亚热带常绿阔叶林重要的构成部分,但林下灌木细根功能性状变异规律及地下生态策略仍不清楚。以福建建瓯万木林自然保护区内9种灌木为研究对象,对细根直径、根长、比根长、组织密度、碳浓度和氮浓度6个细根性状进行研究,采用序级划分法,分析不同树种细根性状序级间的变化特征、常绿和落叶灌木细根性状之间的差异,不同序级细根性状之间的关系以及细根性状变异维度。结果表明:树种和序级对9种灌木细根形态和化学性质有显著影响。直径、根长、根组织密度随着序级的增加而逐渐增加,比根长和氮浓度逐渐减小,碳浓度在序级间的变化趋势不一,未表现出明显的规律。落叶灌木细根直径、根长和氮浓度均显著高于常绿灌木,碳浓度和组织密度显著低于常绿灌木,表明与常绿灌木相比落叶灌木更偏向于资源获取型生态策略,常绿灌木则更偏向于保守型策略。灌木细根在不同序级间的直径与比根长、组织密度,氮浓度与组织密度有较强的相关性,细根其他性状间的关系并不密切或因序级而异。主成分分析结果表明灌木细根性状变异沿一个主成分轴发生变异,该轴表示灌木细根的资源获取和保守的权衡策略。     

水曲柳和落叶松不同根序之间细根直径的变异研究

细根直径大小和根序高低对细根寿命和周转估计具有重要的影响,研究不同根序之间的直径变异对认识细根直径与根序的关系具有重要意义。该文根据Pregitzer等(2002)提供的方法,研究了位于东北林业大学帽儿山实验林场尖砬沟森林培育实验站17年生水曲柳(Fraxinus mandshurica)和落叶松(Larix gmelinii)人工林细根1~5级根序的平均直径的变化、直径的最小值和最大值范围、直径的变异系数。结果表明,水曲柳和落叶松细根直径<2 mm时,包含5个根序,随着根序由小到大的增加,细根直径也在增大。各根序平均直径之间,存在较大的差异。在同一根序内,细根直径范围很大,水曲柳和落叶松一级根最小直径均<0.20 mm,最大直径分别<0.50 mm(水曲柳)和<0.70 mm(落叶松)左右。2~3级根序直径最小值在0.20~0.30 mm之间,最大值≤1.0 mm。5级根直径最小值<1.0 mm,最大值超过2.0 mm。随着根序等级增加,直径变异系数增大。一级根序的直径平均变异系数<10%,2~3级根序直径平均变异系数在10%~15%左右,4~5级根序直径的平均变异系数在20%~30%之间。因此,在细根寿命与周转研究过程中,必须同时考虑直径和根序对细根的寿命估计的影响。     

Anatomical traits associated with absorption and mycorrhizal colonization are linked to root branch order in twenty-three Chinese temperate tree species

* Different portions of tree root systems play distinct functional roles, yet precisely how to distinguish roots of different functions within the branching fine-root system is unclear. * Here, anatomy and mycorrhizal colonization was examined by branch order in 23 Chinese temperate tree species of both angiosperms and gymnosperms forming ectomycorrhizal and arbuscular-mycorrhizal associations. * Different branch orders showed marked differences in anatomy. First-order roots exhibited primary development with an intact cortex, a high mycorrhizal colonization rate and a low stele proportion, thus serving absorptive functions. Second and third orders had both primary and secondary development. Fourth and higher orders showed mostly secondary development with no cortex or mycorrhizal colonization, and thus have limited role in absorption. Based on anatomical traits, it was estimated that c. 75% of the fine-root length was absorptive, and 68% was mycorrhizal, averaged across species. * These results showed that: order predicted differences in root anatomy in a relatively consistent manner across species; anatomical traits associated with absorption and mycorrhizal colonization occurred mainly in the first three orders; the single diameter class approach may have overestimated absorptive root length by 25% in temperate forests.     

Influence of root structure on root survivorship: an analysis of 18 tree species using a minirhizotron method

Fine root survivorship is an important aspect of root ecology and is known to be influenced by a suite of covariates. However, the relative importance of each covariate on root survivorship is not clear. Here, we used minirhizotron-based data from 18 woody species to evaluate the relative strength of influence on root survivorship by root diameter, branch order, soil depth, and season of root birth, and to examine how the relationship between each covariate and root survivorship differed across species. We extracted hazard ratio estimates for 16 species from published studies that performed Cox proportional hazards regression analysis, and from our own unpublished data for two Chinese temperate tree species. The mean change in hazard ratio (CHR) and corresponding coefficient of variation for each factor were calculated across species. On average, root diameter and season of root birth had stronger effects on root survivorship than branch order and soil depth. However, the effects of season varied with species and were stronger in temperate forests, whereas the influence of diameter and order were relatively consistent across species. These results suggest that root structures such as diameter and branch order should be carefully considered in root classification and sampling, and adding season of birth (particularly in temperate forests) as a covariate in root survivorship analysis should further enhance our ability in achieving a better understanding of root demography and more accurate estimates of root turnover in forests of different climate zones.     

中国温带和亚热带8个树种叶和吸收根协同分解

叶和细根(2mm)是森林生态系统的分解主体,二者是否协同分解,将极大影响所属植物在生态系统碳(C)循环中的物种效应。已有研究显示,叶和细根的分解关系具有极大的不确定性,认为很大程度上归因于细根内部具有高度的异质性,导致叶和细根在功能上不相似。为此,使用末梢1级根和细根根枝作为研究对象,它们在功能上同叶类似,称为吸收根。通过分解包法,分别在黑龙江帽儿山和广东鹤山,研究了2个阔叶树种和2个针叶树种(共8个树种)的叶和吸收根持续2a多的分解。结果发现,分解速率k(a~(-1),负指数模型)在8个树种整体分析时具有正相关关系(P0.05),在相同气候带或植物生活型水平上是否相关,受叶的分解环境及吸收根类型的影响;N剩余量整体上并不相关,亚热带树种的叶和细根根枝的N剩余量在分解1a后高度显著正相关,温带树种的叶和1级根的N剩余量在分解2a后显著高度正相关。本研究中,根-叶分解过程是否受控于相同或相关的凋落物性质是决定根-叶分解是否相关的重要原因,其中分解速率与酸溶组分正相关、与酸不溶组分负相关。比较已有研究,总结发现,根-叶分解关系受物种影响较大,暗示气候变化导致物种组成的改变将极大影响地上-地下关系,也因此影响生态系统C循环。     

落叶松和水曲柳不同根序细根形态结构、组织氮浓度与根呼吸的关系

根系具有高度的形态和生理功能异质性, 在森林生态系统碳和养分循环中起重要作用。根系分枝的顺序构成根序,是根系最基本的构型特征, 根序代表根系不同的发育阶段。然而, 目前直接测定不同根序细根生理功能的研究很少。以落叶松(Larix gmelinii)和水曲柳(Fraxinus mandshurica)的细根为研究对象, 使用气相氧电极测定不同根序细根的呼吸速率, 探讨根系呼吸速率与其形态、结构和组织氮浓度的关系。结果表明: 落叶松和水曲柳细根的直径、根长和维管束直径均随着根序的增加(1–5级)而增加, 而比根长、组织氮浓度和呼吸速率随着根序的增加而降低, 各根序之间差异显著(P < 0.05); 1级根比根长最大、皮层组织发达、组织氮浓度最高且呼吸速率也最高, 其呼吸速率分别为17.57 nmolO₂·g^–1·s^–1(落叶松)和18.80 nmolO₂·g^–1·s^–1(水曲柳), 比5级根分别高148%(落叶松)和124%(水曲柳); 并且, 落叶松根的呼吸速率几乎有96%与根系组织氮浓度相关, 而水曲柳根的呼吸速率则有89%与根系组织氮浓度相关。上述结果说明, 细根的形态和生理功能异质性是紧密相连的, 低级根的形态、结构决定其功能是吸收养分和水, 而高级根的形态、结构决定其功能是运输和贮存养分。     

Variation of the Linkage of Root Function with Root Branch Order

Mounting evidence has shown strong linkage of root function with root branch order. However, it is not known whether this linkage is consistent in different species. Here, root anatomic traits of the first five branch order were examined in five species differing in plant phylogeny and growth form in tropical and subtropical forests of south China. In Paramichelia baillonii, one tree species in Magnoliaceae, the intact cortex as well as mycorrhizal colonization existed even in the fifth-order root suggesting the preservation of absorption function in the higher-order roots. In contrast, dramatic decreases of cortex thickness and mycorrhizal colonization were observed from lower- to higher-order roots in three other tree species, Cunninghamia lanceolata, Acacia auriculiformis and Gordonia axillaries, which indicate the loss of absorption function. In a fern, Dicranopteris dichotoma, there were several cortex layers with prominently thickened cell wall and no mycorrhizal colonization in the third- and fourth-order roots, also demonstrating the loss of absorptive function in higher-order roots. Cluster analysis using these anatomic traits showed a different classification of root branch order in P. baillonii from other four species. As for the conduit diameter-density relationship in higher-order roots, the mechanism underpinning this relationship in P. baillonii was different from that in other species. In lower-order roots, different patterns of coefficient of variance for conduit diameter and density provided further evidence for the two types of linkage of root function with root branch order. These linkages corresponding to two types of ephemeral root modules have important implication in the prediction of terrestrial carbon cycling, although we caution that this study was pseudo-replicated. Future studies by sampling more species can test the generality of these two types of linkage.     

Fine root architecture, morphology, and biomass of different branch orders of two Chinese temperate tree species

We have limited understanding of architecture and morphology of fine root systems in large woody trees. This study investigated architecture, morphology, and biomass of different fine root branch orders of two temperate tree species from Northeastern China—Larix gmelinii Rupr and Fraxinus mandshurica Rupr —by sampling up to five fine root branch orders three times during the 2003 growing season from two soil depths (i.e., 0–10 and.10–20 cm). Branching ratio (R _b) differed with the level of branching: R _b values from the fifth to the second order of branching were approximately three in both species, but markedly higher for the first two orders of branching, reaching a value of 10.4 for L. gmelinii and 18.6 for F. mandshurica. Fine root diameter, length, SRL and root length density not only had systematic changes with root order, but also varied significantly with season and soil depth. Total biomass per order did not change systematically with branch order. Compared to the second, third and/or fourth order, the first order roots exhibited higher biomass throughout the growing season and soil depths, a pattern related to consistently higher R _b values for the first two orders of branching than the other levels of branching. Moreover, the differences in architecture and morphology across order, season, and soil depth between the two species were consistent with the morphological disparity between gymnosperms and angiosperms reported previously. The results of this study suggest that root architecture and morphology, especially those of the first order roots, should be important for understanding the complexity and multi-functionality of tree fine roots with respect to root nutrient and water uptake, and fine root dynamics in forest ecosystems.