Root Morphology and Anchorage of Six Native Tree Species from a Tropical Montane Forest and an Elfin Forest in Ecuador

Root architecture of tree species was investigated at two different altitudes in tropical forests in Ecuador. Increasing altitude was accompanied by higher wind speeds and more shallow soils, while slope angles of both sites were comparable (20–50°). Three tree species typical for the montane forest at 1900 m (Graffenrieda emarginata (Ruiz & Pav.) Triana (Melastomataceae), Clethra revoluta (Ruiz & Pav.) Spreng. (Clethraceae), Vismia tomentosa Ruiz & Pav. (Clusiaceae)) and for the elfin forest at 3000 m (Weinmannia loxensis Harling (Cunoniaceae), Clusia spec. (Clusiacaea) Styrax foveolaria Perkins (Styraceae)) were examined. At 1900 m, 92% of the trees grew upright, in comparison to 52% at 3000 m. At 3000 m, 48% of the trees were inclined, lying or even partly uprooted. At this altitude, all trees with tap roots or with shoots connected by coarse rhizomes, 83% of the trees with stilt roots, and 50% of the trees in which stems or roots were supported by other trees grew upright, suggesting that these characteristics were relevant for tree stability. Root system morphology differed markedly between altitudes. In contrast to 1900 m, where 20% of structural roots originated in the deeper mineral soil, root origin at 3000 m was restricted to the forest floor. The mean ratio of root cross sectional area to tree height decreased significantly from 6.1 × 10⁻³ m² m⁻¹ at 1900 m to 3.2 × 10⁻³ m² m⁻¹ at 3000 m. The extent of root asymmetry increased significantly from 0.29 at 1900 m to 0.62 at 3000 m. This was accompanied by a significantly lower number of dominant roots at 3000 m (2.3 compared to 3.8 at 1900 m). In conclusion, native tree species growing in tropical montane and elfin forests show a variety of root traits that improve tree stability. Root system asymmetry is less important for tree stability where anchorage is provided by a deep and solid root–soil plate. When deep rooting is impeded, root traits improving the horizontal extension of the root–soil plate are more pronounced or occur more frequently. Furthermore, mutual mechanical support of roots and stems of neighboring trees seems to be an appropriate mechanism to provide anchorage in soils with low bulk density and in environments with high wind speeds.     

亚热带典型树种根毛特征及其与共生真菌的关系

根毛和共生真菌增加了吸收面积,提高了植物获取磷等土壤资源的能力。由于野外原位观测根表微观结构较为困难,吸收细根、根毛、共生真菌如何相互作用并适应土壤资源供应,缺乏相应的数据和理论。该研究以受磷限制的亚热带森林为对象,选取了21种典型树种,定量了根毛存在情况、属性变异,分析了根毛形态特征与共生真菌侵染率、吸收细根功能属性之间的关系,探讨了根表结构对低磷土壤的响应和适应格局。结果表明:1)在亚热带森林根毛不是普遍存在的, 21个树种中仅发现7个树种存有根毛, 4个为丛枝菌根(AM)树种, 3个为外生菌根(ECM)树种。其中,马尾松(Pinus massoniana)根毛出现率最高,为86%;2)菌根类型是理解根-根毛-共生真菌关系的关键,AM树种根毛密度与共生真菌侵染率正相关,但ECM树种根毛直径与共生真菌侵染率负相关; 3) AM树种根毛长度和根毛直径、ECM树种根毛出现率与土壤有效磷含量呈负相关关系。该研究揭示了不同菌根类型树种根毛-共生真菌-根属性的格局及相互作用,为精细理解养分获取策略奠定了基础。     

Relationship between mycorrhizal fungi and functional traits in absorption roots: research progress and synthesis

吸收根(absorption root)一般是指根枝系统末端少数几级具有初生结构、负责物质吸收的根。吸收根功能性状被广泛用于评价和预测植物个体到生态系统水平上的一系列功能和过程。菌根真菌侵染是吸收根的一个关键性状, 它可以深刻影响吸收根的形态、结构, 以及功能性状之间的关系。该文针对与吸收功能密切相关的菌根真菌与根毛和根直径之间的关系进行了研究综述, 提出了真菌侵染、根毛和化学防御之间关系的一个假说; 探讨了温带和热带不同类型的吸收根如何通过菌根真菌影响根的功能性状, 从而适应不同的水热条件、养分状况和能量消耗; 提出一些需要关注的议题和研究方向, 以期为菌根真菌与吸收根功能性状之间关系的研究提供借鉴。     

四种不同生活型树种细根寿命及影响因素

以4种不同生活型树种(常绿阔叶和针叶树种、落叶阔叶和针叶树种)为研究对象,通过微根管法现地观测细根的生长动态,比较不同生活型树种细根寿命在种内和种间的差异,探讨影响细根寿命的主要因子,研究结果对理解和预测森林生态系统碳及养分循环过程具有重要的理论意义。结果表明:(1)细根形态特征(分枝结构和直径)显著影响种内细根寿命,分枝等级越低、直径越小,细根的寿命越短;(2)4个树种的细根寿命表现出明显的土层效应和季节效应,即随土壤深度增加,细根的累积存活率逐渐增加,寿命延长;而不同季节出生的细根其寿命长短模式在树种间不一致,春季或夏季出生的细根寿命要长于秋冬季;(3)常绿树种(柳杉、石栎)的细根寿命要长于落叶树种(池杉、麻栎),同时,针叶树种(池杉、柳杉)的细根寿命要长于阔叶树种(麻栎、石栎)。在同一树种内,细根寿命受细根直径、根系分枝结构、土壤环境因子(土层)等因素显著影响,但在不同树种间,细根寿命可能更依赖于树木生长速率、碳分配模式等树木整体的功能性状差异。     

Hydraulic and photosynthetic characteristics differ between co-generic tree and liana species: a case study of Millettia and Gnetum in tropical forest

木质藤本是热带森林的重要组成部分, 显著影响森林的结构和功能。已有研究发现木质藤本与乔木的水力结构存在显著差异: 木质藤本的缠绕或攀缘茎细小, 但其木质部具有粗大的长导管, 输水效率高, 抗栓塞能力低。为降低基因型差异对比较结果的影响, 该研究选取热带崖豆藤属(Millettia)和买麻藤属(Gnetum)的乔木和木质藤本, 比较同属内不同生长型植物的水力和光合性状的差异, 分析水分传导效率与抗栓塞能力之间以及水力与光合性状之间的相关关系。结果发现: (1)崖豆藤属植物水力性状的种间差异大, 与生活型和需光性有关。耐阴的木质藤本反而具有较低的水分传导效率和较高的抗栓塞能力。(2)买麻藤属植物是裸子植物较为进化的类群(具有导管和阔叶), 其乔木的水分传导效率很低, 但是其木质藤本的水分传导效率高于其他阳生性的被子植物。(3)不论乔木还是木质藤本, 水分传导的有效性与安全性在枝条和叶片水平上均没有显著的权衡关系。(4)与同属乔木相比, 木质藤本的叶片较枝条的抗栓塞能力更强, 在旱季具有更高的最大净光合速率和气孔导度, 支持了木质藤本的“旱季生长优势假说”。该研究揭示了热带木质藤本水力性状的多样性和重要性, 为阐明环境变化对这一重要植物类群的影响, 需要对它们的水力特征进行更广泛的研究。     

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。     

Architectural characteristics of roots in typical coastal psammophytes of South China

选择华南海岸典型沙地, 采用全挖法, 对4种典型沙生植物木麻黄(Casuarina equisetifolia)、厚藤(Ipomoea pes-caprae)、老鼠艻(Spinifex littoreus)和狗牙根(Cynodon dactylon)的根系构型进行了研究。结果表明: 1)狗牙根和老鼠艻的根系总体分支率显著高于木麻黄, 厚藤最小, 说明大部分草本植物在生长过程中通过增加根系分支率, 提高物质传输效率, 除木麻黄外, 其他3个物种枝系均平卧伸展, 易于受到沙埋生出不定根, 进一步提高其物质传输效率; 2) 4种沙生植物根系平均连接长度最大的为木麻黄, 平均连接长度为19.25 cm, 且相对其他3个物种传导根所占的比例最大, 说明木麻黄通过增加平均连接长度以减少根系内部对土壤资源的竞争, 并提高传导根的比例, 以增加资源传输效率; 3) 4种沙生植物根系构型均倾向于叉状分支, 其中草本植物的根系构型更为接近, 说明草本植物受到的资源胁迫相对较小, 有利于在海岸沙地恢复中快速定居; 与内陆地区沙生植物相比, 海岸沙生植物在土壤资源的获取及空间拓展方面表现出显著的差异, 反映出不同生境条件下物种对生境胁迫的适应策略。因此, 海岸沙地前缘植被恢复应以草本植物为主, 尤其是具有不定根的物种, 乔木则不适合。     

乔木根系和凋落物对南亚热带3种人工林土壤线虫群落的差异化影响

根系分泌物和凋落物为土壤食物网提供了基础的养分资源。然而,不同树种纯林和混交林地下根系和地上凋落物对土壤线虫群落的影响机制尚不清楚。2019年9月在广西凭祥热带林业实验中心选取格木(Erythrophleum fordii Oliv.)纯林、马尾松(Pinus massoniana Lamb.)纯林和格木×马尾松混交林3种林分类型,分别设置对照、阻断乔木根系、去除地上凋落物和阻断乔木根系并去除地上凋落物四组实验处理,于2021年3月对3种林分类型不同处理下的土壤线虫群落和土壤理化性质进行了调查。研究结果表明,无论哪种林分类型,阻断根系改变了土壤线虫群落的营养类群组成,显著降低了食真菌线虫相对多度,增加了植物寄生线虫相对多度;去除凋落物显著降低了土壤线虫密度、类群数、线虫通路比值和结构指数,增加了基础指数,表明去除凋落物降低了土壤食物网的稳定性。无论哪种林分类型,人工林中树木地下根系输入是构建土壤线虫群落营养类群组成的主要驱动因素,地上凋落物在维持土壤食物网稳定性方面发挥着重要的作用。此外,阻断根系和去除凋落物对混交林中土壤线虫群落没有显著的影响,表明含固氮树种的格木×马尾松混交林比人工...     

水分再分配对土壤-植物系统养分循环的生态意义

水分再分配(hydraulic redistribution, HR)作为一个普遍存在的生物物理过程, 在缓解植物干旱胁迫、调节植物种间关系和群落组成、影响生态系统水碳平衡等方面具有重要的生态意义。近年来, 同位素标记示踪技术的应用促进了HR的深入研究, 该文综述了HR对土壤-植被系统养分循环的影响。HR能改善干燥土层的水分状况, 防止根系栓塞, 促进细根存活与生长, 提高微生物活性, 从而促进植物对表层土壤养分(尤其是氮)的吸收; HR还通过水分下传作用促进植物对深层土壤中磷和金属离子的吸收。HR促进土壤养分库的上下交换与流动, 调节植物与土壤的氮磷比, 因此其影响可能具有全球意义。在全球变化(如氮沉降)背景下, 有必要深入探索HR在生物地球化学循环过程中的影响和作用, 并将其纳入生态系统模型中。     

Plant diversity and seasonal dynamics in forest gaps of varying sizes in Pinus massoniana plantations

人工林目前存在结构单一、土壤退化、生物多样性降低等人类普遍关注的生态问题。马尾松(Pinus massoniana)是长江上游低山丘陵区退耕还林的主要人工林树种。研究采伐林窗对植物物种组成和更新的影响, 对马尾松低效人工林的改造, 提升其生态服务功能具有重要的意义。该文以采伐39年生的马尾松人工林形成的7种不同大小的林窗为研究对象, 分析了不同季节林窗内的植物生活型组成及多样性变化。结果表明: 1)马尾松人工林林下植物以高位芽植物居多, 其次是地面、地下芽植物, 一年生植物较少而缺少地上芽植物。在林窗形成初期, 林窗的高位芽植物比例明显低于林下, 大林窗的高位芽植物比例稍高于小林窗, 地下芽和一年生植物的比例低于小林窗。2)林下的物种丰富度和物种多样性指数显著低于大林窗。不同林窗下植物的丰富度指数、优势度指数、多样性指数也存在显著差异。3)夏季林窗下植物多样性最高, 其次是秋季, 春季多样性最低。1225-1600 m²的大林窗能够促进马尾松人工林植物多样性恢复和植被更新。     

山东滨海盐碱地11个造林树种叶解剖特征对土壤条件的响应

叶片作为植物与大气环境连接的重要纽带, 对逆境具有强烈的响应。基于叶性状探讨植物对环境的适应机制对盐碱地植物群落构建具有指导意义。该研究以山东省滨海盐碱地3种不同土壤条件下的11个造林树种为对象, 通过对各树种叶解剖性状的测定分析, 阐明叶片功能性状与盐碱地土壤环境的关系, 以期为盐碱地植被修复与群落构建提供科学依据。主要研究结果: (1) 11个树种的叶片厚度较大, 栅栏组织发达, 紧密排列在叶肉近轴面, 呈3-5层。各树种叶片的栅栏组织与海绵组织厚度比值(PT/ST)普遍较高但差异较大, 可指示叶解剖特征在树种间的差异性。(2)不同树种的叶解剖结构在立地环境间具有显著差异, PT/ST可作为指示指标。(3)相关分析和冗余分析表明, 树种叶片解剖结构与立地土壤条件具有密切联系。PT/ST与土壤理化性质相关程度高, 且与土壤pH以及土壤电导率(25 ℃)均呈显著正相关关系, 与土壤硝态氮含量呈显著负相关关系。叶片特征和叶脉特征可解释叶性状随环境变异约84%的信息量。综上所述,叶解剖结构与盐碱地土壤条件存在密切关系, 基于叶解剖特征可进一步分析树种对盐碱环境的适应性, 并为盐碱地植物群落构建的树种选择提供科学依据。     

Hydraulic architecture of evergreen broad-leaved woody plants at different successional stages in Tiantong National Forest Park,Zhejiang Province,China

Aims Hydraulic architecture is a morphological strategy in plants to transport water in coping with environmental conditions. Change of hydraulic architecture for plants occupying different canopy layers within community and for the same plant at different successional stages reflect existence and adaptation in plant's water transportation strategies. The objective of this study was to examine how hydraulic architecture varies with canopy layers within a community and with forest succession.Methods The study site is located in Tiantong National Forest Park, Zhejiang Province, China. Hydraulic architectural traits studied include sapwood-specific hydraulic conductivity, leaf-specific hydraulic conductivity, Huber value, sapwood channel area of twigs, total leaf area per terminal twig, and water potential of twigs. We measured those traits for species that occur in multiple successional stages (we called it "overlapping species") and for species that occur only in one successional stage (we called it "turnover species") along a successional series of evergreen broadleaved forests. For a given species, we sampled both overstory and understory trees. Hydraulic architectural traits between overstory and understory trees in the same community and at successional stages were compared. Pearson correlation was used to exam the relationship between hydraulic architectural traits and the twig/leaf traits.Important findings Sapwood-specific hydraulic conductivities and leaf-specific hydraulic conductivities were significantly higher in overstory trees than those in understory trees, but did not significantly differ from successional stages. Huber value decreased significantly for understory trees, but did not change for overstory trees through forest successional stages. For overstory trees, a trend of decreasing sapwood-specific hydraulic conductivity was observed for overlapping species but not for turnover species with successional stages. In contrast, for understory trees, a trend of decreasing Huber values was observed for turner species but not for overlapping species with successional stages. Across tree species, sapwood-specific hydraulic conductivity was positively correlated with sapwood channel area and total leaf area per terminal twig size. Huber value was negatively correlated to water potential of twigs and total leaf area per terminal twig size. These results suggest that water transportation capacity and efficiency are higher in overstory trees than in understory trees across successional stages in evergreen broadleaved forests in Tiantong region. The contrasting trends of sapwood-specific hydraulic conductivity between overlapping species and turnover species indicate that shift of microenvironment conditions might lead to changes of hydraulic architecture in overstory trees, whereas species replacement might result in changes of hydraulic architecture in understory trees.     

Characteristics of soil nitrogen mineralization in the rhizosphere of trees,shrubs, and herbs in subtropical forest plantations

为了探讨人工林内优势乔木和林下灌草根际土壤氮矿化特征, 明确乔灌草根际土壤氮转化差异, 该研究以江西泰和千烟洲站区典型人工杉木(Cunninghamia lanceolata)、马尾松(Pinus massoniana)和湿地松(Pinus elliottii)林为对象, 在植被生长季初期(4月)和旺盛期(7月)分析3种人工林内乔木、优势灌木(檵木(Loropetalum chinense)、杨桐(Adinandra millettii)、格药柃(Eurya muricata))和草本(狗脊蕨(Woodwardia japonica)、暗鳞鳞毛蕨(Dryopteris atrata))根际土壤的净氮矿化速率、土壤化学性质及土壤微生物特征。结果发现: 1)物种、林型和取样季节显著影响了根际土壤净氮矿化速率(N_min)、净铵化速率(N_amm)和净硝化速率(N_nit)。马尾松和湿地松林内林下灌草根际土壤净氮矿化的季节敏感性高于乔木: 4月乔木根际土壤N_min和N_amm显著高于大多数林下灌草, 而7月林下灌草根际土壤N_min和N_amm显著提高, 与乔木不再具有显著差异, 与主成分综合得分方差分析的结果一致。一般情况下, 杉木林N_min和N_nit显著高于马尾松林和湿地松林。7月净氮矿化显著高于4月。2)土壤铵态氮、硝态氮、全氮及土壤微生物量氮含量是影响根际土壤净氮矿化的主要因素。土壤化学性质对人工林根际土壤净氮矿化变异的贡献率为29.2%, 显著高于土壤微生物的解释率。充分考虑不同季节林下植被根际土壤的净氮矿化及其关键影响因素可为准确评估人工林生态系统养分循环状况提供重要支撑。     

Variations and Trade‐offs in Functional Traits of Tree Seedlings during Secondary Succession in a Tropical Lowland Rain Forest

The seedling stage is generally the most important bottleneck for the successful regeneration of trees in forests. The traits of seedlings, particularly biomass allocation and root traits, are more easily quantified than the traits of adults. In this study, we tested the hypothesis that seedling traits vary and trade‐off tracking the changing environment during secondary succession. We measured the major morphological traits of 27 dominant species and the major environmental factors in a chronosequence (30‐yr‐old fallow, 60‐yr‐old fallow, and old growth forest) after shifting cultivation in a tropical lowland rain forest on Hainan Island, China. The 30‐yr‐old fallow had higher light and nutrient availability, and the older forests had higher soil water content. Redundancy analysis based on species abundance and environmental factors revealed groups of seedlings that dominate in different stages of succession. Seedlings in different stages of succession had different strategies of biomass allocation for harvesting resources that varied in availability. Species characteristic of younger forest had higher allocation to roots and higher specific leaf area, while species characteristic of older forest had higher allocation to leaves. Our study suggests that the variations and trade‐offs in the major functional traits of tree seedlings among successional classes may reflect changes in environmental conditions during succession.     

Below-ground competition between trees and grasses may overwhelm the facilitative effects of hydraulic lift

Under large East African Acacia trees, which were known to show hydraulic lift, we experimentally tested whether tree roots facilitate grass production or compete with grasses for below‐ground resources. Prevention of tree–grass interactions through root trenching led to increased soil water content indicating that trees took up more water from the topsoil than they exuded via hydraulic lift. Biomass was higher in trenched plots compared to controls probably because of reduced competition for water. Stable isotope analyses of plant and source water showed that grasses which competed with trees used a greater proportion of deep water compared with grasses in trenched plots. Grasses therefore used hydraulically lifted water provided by trees, or took up deep soil water directly by growing deeper roots when competition with trees occurred. We conclude that any facilitative effect of hydraulic lift for neighbouring species may easily be overwhelmed by water competition in (semi‐) arid regions.     

内蒙古典型草原优势种冷蒿和克氏针茅对土壤低磷环境适应策略的比较

为探究典型草原植物长期共存的生理生态机制, 以典型草原的优势物种克氏针茅(Stipa krylovii)和冷蒿(Artemisia frigida)为材料, 采用基质培养方法, 通过比较不同供磷浓度对二者生物量、根系形态、质子分泌、酸性磷酸酶和有机酸分泌以及磷吸收利用效率的影响, 探讨克氏针茅和冷蒿对土壤磷缺乏的适应策略。研究结果表明: 冷蒿主要通过根系分泌酸性磷酸酶和酸化根际来适应低磷环境; 而克氏针茅主要是通过根系分泌有机酸(主要是苹果酸)来适应土壤磷缺乏。在低磷条件下, 克氏针茅和冷蒿的磷吸收效率没有显著差异, 但克氏针茅的磷利用效率显著高于冷蒿。随着供磷浓度增加, 二者的磷吸收速率增加, 磷利用效率降低。在生物量、地上部分性状以及根系生长方面, 克氏针茅和冷蒿对磷供给的响应都表现先增长后降低的趋势; 克氏针茅的生物量在外源供0.25 mmol·L^-1磷时达到最大, 而冷蒿的生物量在外源供0.50 mmol·L^-1磷时达到最大, 表明冷蒿对磷的生理需求高于克氏针茅。因此, 克氏针茅和冷蒿具备各自不同的适应土壤有效磷缺乏的生理策略, 这可能是它们在土壤贫瘠的温带典型草原长期共存的重要机制。     

Tree community structure, dynamics, and diversity partitioning in a Bornean tropical forested landscape

Human-modified forested landscapes are prevalent in the tropics, and the role of complex mosaics of diverse vegetation types in biodiversity conservation remains poorly understood. Demographic traits and the spatial pattern of biodiversity are essential information when considering proper forest management and land use strategies. We compared the tree community structure (stem density, basal area, tree diversity, abundance of rare, endemic, and upper-layer trees, and species composition) and the forest dynamics (mortality, recruitment rate, and increments of basal area, and above- and below-ground biomass) of 39–46 plots among five dominant forest types: young and old fallows, rubber plantations, and fragmented and old-growth forests in Sarawak, Malaysia. We also explored how tree diversity was distributed across different spatial scales using additive partitioning of diversity. Swidden cultivation and rubber plantations showed decreased stem density, basal area, tree diversity, abundance of rare, endemic, and upper-layer trees, and increments of above- and below-ground biomass, which affected tree mortality, dominant trees, and species composition. Little distinction in species composition was observed among young and old fallows and rubber plantations, indicating a relatively quick recovery of the tree community in the early stages. The highest diversity was found among forest types, indicating that the whole forested landscape comprises a suitable scale for tree biodiversity conservation in the region. Our results suggest that although fragmented and old-growth forests have an irreplaceable role and a high priority in conserving biodiversity and sustaining the function of the forest ecosystem, secondary forests may also have a reinforcing role in maintaining tree diversity in the region, especially under the current circumstances in which a large portion of the landscape is human-modified and faces an increasing threat from the expansion of oil palm plantations.     

A review on the effects of nitrogen and phosphorus addition on tree growth and productivity in forest ecosystems

Nitrogen (N) and phosphorus (P) inputs induced by anthropogenic activities and atmospheric N and P deposition have largely increased the availability of soil N and P in terrestrial ecosystems, which have considerably affected terrestrial carbon cycling processes. Tree growth and productivity in forest ecosystems play an important role in global carbon cycling, and determine the magnitude and direction of terrestrial carbon sequestration. Currently, a large number of field manipulation experiments have been conducted to investigate the effects of N and/or P addition on tree growth and forest productivity, but the results from these studies were inconsistent. Such inconsistent results might be affected by multiple factors, including biological, environmental and experimental variables. Here, we reviewed the present research status of the effects of N and P addition on tree growth and forest productivity in forest ecosystems based on three aspects, including the number of publications and experiments with field N and P addition, and the global distributions of these experiments. Then, we summarized the methods for assessing tree growth and forest productivity at ecosystem level in forest ecosystems, including relative growth rate and absolute increment. According to the related results, we reviewed the regulating factors that affect tree growth and productivity, and the potential mechanisms for such factors, including climate, tree size and stand age, plant functional traits (including type of tree-associated mycorrhizal fungi, N-fixation property of trees, and conservative and acquisitive functional traits), plant-microbe interaction, ambient nutrient (i.e., N and P) deposition rate, and experimental variables. Finally, we summarized the current studies, and pointed out five aspects that are urgently needed to provide further insights in future studies, including the physiological mechanism of how tree growth responds to N and P addition, the tradeoff and allocation among growth of various parts of tree under N and P addition, the role of plant functional traits in regulating and predicting the responses of tree growth to N and P addition, how the competition among trees regulates the responses of tree growth to N and P addition, and conducting long-term and coordinated distributed field experiments investigating the effects of N and P addition on tree growth and forest productivity at the global scale.     

广西不同林龄杉木、马尾松人工林根系生物量及碳储量特征

为了解不同林龄杉木、马尾松人工林地地下根系生物量及碳储量特征,以广西杉木、马尾松主产区5个不同林龄阶段(幼龄林、中龄林、近熟林、成熟林、过熟林)的人工林为研究对象,采用全根挖掘法和土钻法获取标准木根系生物量、灌草根系生物量和林分细根生物量,并测定其碳含量,分析其不同林龄阶段地下根系生物量和碳储量分配特征。结果表明:杉木、马尾松林地下根系总生物量分别在9.06—31.40Mg/hm~2和7.91—53.40Mg/hm~2之间,各林龄阶段根系总生物量总体上呈现随林龄增加而增加的趋势,杉木林细根生物量随林龄的增加呈现出先减后增的趋势,马尾松呈现出逐渐减小的趋势;林分各层次根系碳含量表现为乔木灌木草本、细根;杉木、马尾松地下根系碳储量变化趋势与生物量变化趋势相同,杉木、马尾松林不同林龄阶段各层次根系和土壤细根总碳储量分别在7.56—21.97Mg/hm~2和8.86—29.95Mg/hm~2之间;地下根系碳储量总体上以乔木根系占优势,且随林龄的增大其比例呈增加的趋势。     

Estimating the relative nutrient uptake from different soil depths in Quercus robur, Fagus sylvatica and Picea abies

The distribution of fine roots and external ectomycorrhizal mycelium of three species of trees was determined down to a soil depth of 55 cm to estimate the relative nutrient uptake capacity of the trees from different soil layers. In addition, a root bioassay was performed to estimate the nutrient uptake capacity of Rb⁺ and NH₄⁺ by these fine roots under standardized conditions in the laboratory. The study was performed in monocultures of oak (Quercus robur L.), European beech (Fagus sylvatica L.) and Norway spruce [Picea abies (L.) Karst.] on sandy soil in a tree species trial in Denmark. The distribution of spruce roots was found to be more concentrated to the top layer (0–11 cm) than that of oak and beech roots, and the amount of external ectomycorrhizal mycelia was correlated to the distribution of the roots. The uptake rate of [⁸⁶Rb⁺] by oak roots declined with soil depth, while that of beech or spruce roots was not influenced by soil depth. In modelling the nutrient sustainability of forest soils, the utilization of nutrient resources in deep soil layers has been found to be a key factor. The present study shows that the more shallow-rooted spruce can have a similar capacity to take up nutrients from deeper soil layers than the more deeply rooted oak. The distribution of roots and mycelia may therefore not be a reliable parameter for describing nutrient uptake capacity by tree roots at different soil depths.