亚热带森林生物多样性与生态系统功能实验研究基地(BEF-China)研究进展

生物多样性与生态系统功能的关系(BEF)及其内在机制是当前生物多样性研究领域的热点问题。长期以来,以草地生态系统为主的BEF研究积累了大量研究成果,而基于森林生态系统的相关研究则相对较少。亚热带森林生物多样性与生态系统功能实验研究基地(BEF-China)是目前包含树种最多、涉及多样性水平最高的大型森林控制实验样地。该文总结了基于BEF-China平台的研究进展,特别是生物多样性对生态系统生产力、养分循环以及多营养级相互作用关系等方面的影响,并提出了未来BEF-China的研究应注重高通量测序和遥感等新兴技术的应用,在生物多样性的多维度、生态系统的多种组分与多种功能以及BEF研究的多种尺度等交叉方向上持续开展深入研究。针对BEF-China研究成果的梳理有助于理解驱动亚热带森林生物多样性与生态系统功能关系的内在机理,为生物多样性保护和生态修复提供科学依据。

基于BEF-China平台下的人才培养探索实践——以景德镇学院生物工程专业为例

“科教融合”源于19世纪著名的德国科学家洪堡的大学理念,科研创造知识,教学传播知识,两者既相互补充又相互促进。随着我国高等教育大众化,以教师讲授为中心的传统教育模式已很难适应时代发展的步伐。大学生普遍存在着实践动手能力不足、创新能力欠缺的现象。为有效培养大学生实践创新能力,围绕“科教融合”理念,实施“准研究生”式的本科生培养模式,解决高等教育中缺乏实践训练的问题。

Effects of tree sapling diversity and nutrient addition on herb-layer invasibility in communities of subtropical species

Exotic species are assumed to alter ecosystem functioning. However, little is known of the relationships within vertically structured plant communities such as forests, where tree saplings interact with herbaceous species, especially in the early phases of succession. This relationship was tested in a common garden experiment which assessed the impacts on tree saplings and herbaceous species following nutrient addition and the introduction of exotic herb species. The experiment was established in South- East China using four broad-leaved tree species (Elaeocarpus decipiens, Schima superba, Castanea henryi and Quercus serrata) to study the relationships between tree sapling diversity, herb-layer productivity and invasibility. Tree saplings were planted in monoculture and in mixtures of two and four species. A full factorial design was applied, within which species composition was crossed with nutrient and exotic seed-addition treatments. The seed-addition treatment included mixtures of seeds from eight exotic herb species, and herb community attributes were assessed after a four month growing season. Results indicate that certain tree species negatively affect native as well as exotic herbs;however, the high productivity of native herbs had a stronger negative impact on exotic species than tree saplings. Nutrient addition increased the productivity of exotic herbs but had no effect on native herbs. Remarkably, exotic species introduction had a negative feedback effect on the growth of tree saplings, which highlights the potential of exotic herbs to diminish tree recruitment. Although tree saplings reduced invasive effects on the herb-layer during the earliest phase of forest succession, nutrient addition had a more profound and opposite effect on these invaders.

亚热带森林中环境和物种多样性对灌木存活的影响

灌木是森林生态系统的重要组成部分,在维持物种多样性、促进养分循环、保护幼苗更新以及促进营养级相互作用等方面具有重要作用,其存活情况对森林群落组成和生态系统功能具有重要意义。但亚热带森林中灌木的存活情况及其影响因素仍有待探究。本研究依托于中国亚热带森林生物多样性与生态系统功能实验研究平台(BEF-China),利用105个不同乔木与灌木多样性相嵌套样方中2012年和2019年的灌木个体存活数据,以及样方水平的土壤养分数据、地形数据、物种多样性数据和物种水平的功能性状数据,通过构建一系列广义线型混合模型(GLMM)探讨了非生物因素、生物因素以及灌木功能性状对灌木存活的影响。结果表明:不同灌木物种的存活率具有显著差异。坡度较小的山谷、山鞍部位以及土壤碳氮比较高的环境更有利于灌木存活;乔木和灌木多样性对灌木存活影响有限,但乔木多样性的增加可通过形成更郁闭的林冠提高灌木存活;灌木功能性状显著影响灌木存活,且倾向于保守型生活策略(即较小的比叶面积、叶片氮含量、气孔大小,较高的叶干物质含量、木质密度)的灌木物种具有更易于存活。通过模型比较发现,包含所有因素的全模型对灌木存活的解释度最高,不同影响因素的贡献率由大到小依次为非生物因素、灌木功能性状以及生物因素。本研究表明灌木存活受到多方面因素的共同影响,尽管土壤和地形等非生物因素的变化影响了灌木的存活,但不同灌木由于功能性状间的差异同样形成了不同的存活表现,而物种多样性的直接影响可能需要更长时间的监测才能更加显著。

中国亚热带森林筑巢独栖蜂类群及其寄生者多样性

筑巢独栖蜂包括捕食者和传粉者,在生态系统中具有重要的生态功能。巢管法用于研究筑巢蜂的生物学、生活史、多样性和生态学特性,但此前较少用于研究亚热带森林中的独栖蜂。经过在生物多样性-生态系统功能实验(BEF-China)新岗山样地5年的长期定点监测和实验样本积累,我们发现了独栖蜂的主要类群和发生规律。巢管法共获得128个物种,隶属于3目25科。其中传粉者占全部独栖蜂的26.6%,共2科12种,主要为分舌蜂和切叶蜂;捕食者约占全部独栖蜂的73.4%,有4科44种,以蜾蠃、蛛蜂、泥蜂和方头泥蜂为主;独栖蜂寄生者有19科72种,主要类群是麻蝇、蜂虻、青蜂、钩腹蜂和姬小蜂。独栖蜂物种组成中传粉者多样性显著低于捕食者。同时独栖蜂中普遍存在着雌雄羽化异律现象,即雄性先羽化,并在越冬个体中更明显。切叶蜂科和方头泥蜂科的发生时间比蜾蠃亚科和蛛蜂科的发生时间更集中。此外,通过构建独栖蜂及其寄生者的互作网络,我们发现寄生者多度和多样性受较低营养级寄主的上行控制效应调节。上述结果揭示了对中国亚热带森林地区独栖蜂及其寄生者多样性,有利于更好地保护野生独栖蜂资源,发挥其生态服务功能。

植物多样性对亚热带森林土壤微生物群落的影响

植物群落组成的改变能够直接或间接地影响土壤生态过程并调节参与这些过程的土壤生物,树种特性和多样性是影响土壤微生物多样性和群落结构的关键因素。本项目利用江西新岗山建立的中国亚热带森林生物多样性与生态系统功能(Biodiversity-Ecosystem Functioning Experiment China)BEF-China研究平台,观测了样方水平下不同多样性组成(单物种、2物种、4物种和8物种)对土壤微生物群落结构的影响。结果表明:在森林生态系统演替初期,植物多样性的改变对土壤微生物群落结构具有显著影响,在不同多样性水平处理下,微生物磷脂脂肪酸含量随着植物多样性的增加,表现出先升高后降低的趋势,但各类群微生物磷脂脂肪酸含量并未表现出对植物多样性的明显响应。其中,土壤和凋落物的理化指标能够分别解释微生物群落结构变异的28.4%和12.3%。森林生态系统较高的异质性和地下生态过程响应的滞后性,导致了土壤微生物对植物多样性组成的响应需要较长时间才能显现出来,因此,为了更好地评价地上生物多样性与生态系统功能的关联,应长期监测森林生态系统多样性组成对地下生态过程的影响。

亚热带不同树种组成森林中土壤甲螨群落结构特征:以江西新岗山为例

在全球环境变化的大背景下,生物多样性丧失日益加剧。土壤动物作为生物多样性重要组成之一,受到广泛的关注。位于我国江西省新岗山的亚热带森林生物多样性与生态系统功能实验样地(BEF-China)是全世界25个森林生物多样性控制实验样地之一。本研究自2019年9月至2022年4月在BEF-China两个不同树种组成的样地(A样地和B样地)内采样,共获得甲螨23,704头,隶属于34科50属61种。本文分析和对比了两个样地内甲螨群落结构的差异,及其多度、物种丰富度、Shannon多样性指数的季节性差异;通过Pearson检验探讨了甲螨多度与环境因子的关系。结果表明:在A、B两个不同树种组成的森林生态系统内,土壤甲螨群落结构及其季节动态具有显著差异。具体表现在:A样地奥甲螨科、罗甲螨科、若甲螨科和尖棱甲螨科的相对多度高于B样地;B样地菌甲螨科、盖头甲螨科和礼服甲螨科的相对多度高于A样地。A样地中夏季和秋季甲螨多度、物种丰富度和Shannon多样性指数显著低于春季和冬季;而B样地中秋季甲螨多度和物种丰富度与春季差异不显著。Pearson检验结果显示,凋落物木质素含量与单翼甲螨科和菌甲螨科多度呈负相关关系,而与奥甲螨科多度呈正相关关系。菌甲螨科多度与土壤和凋落物同一理化因子的相关性基本相同(碳氮比除外),但与凋落物碳氮比呈正相关关系而与土壤碳氮比呈负相关关系。

地形、邻株植物及自身大小对红楠幼树生长与存活的影响

在山地森林中,树木生长不仅受地形的影响,也与邻株植物存在各种相互作用,而且具有个体大小依赖性。然而这些影响都具有物种特异性,即不同物种即使在同类地形或与同种植物相邻也会受到不同乃至相反的影响。此外,不同物种个体生长的自身大小依赖性也存在差异。作者利用中欧合作项目"中国亚热带森林生物多样性与生态系统功能实验研究(BEF)"实验样地,以渐危的常绿阔叶木本植物红楠(Machilus thunbergii)为研究对象,连续两年观测了存活的1,452株红楠幼树基径和树高,分析坡向和坡度等地形、邻株植物丰富度及其功能群组成、红楠自身大小对红楠幼树生长和存活率的影响。结果表明:(1)红楠幼树位于阴坡时比位于阳坡具有更高的生长速率和存活率,而坡度只对树高生长量有显著影响;(2)邻株植物物种丰富度对红楠幼树的基径、树高和存活率影响不显著;(3)邻株植物功能类型对红楠幼树生长具有极显著的影响,影响程度大小依次为落叶阔叶型>落叶阔叶与常绿阔叶的混交型>常绿阔叶型>常绿针叶型,而对存活率无显著影响;(4)红楠幼树的生长与自身大小呈正相关幂函数关系,即基径和树高的生长速率都会随着其自身大小的增加而增加。可见,构建树木生长模型,不仅要考虑地形等环境因子差异,而且要充分考虑邻株植物的功能类群差异、邻株植物相互作用的性质和程度,以及自身个体大小等因素,为渐危和濒危树种的保护提供更为可靠的理论依据。

On the combined effect of soil fertility and topography on tree growth in subtropical forest ecosystems—a study from SE China

Aims The aim of our research was to understand small-scale effects of topography and soil fertility on tree growth in a forest biodiversity and ecosystem functioning(BEF)experiment in subtropical SE China.Methods Geomorphometric terrain analyses were carried out at a spatial resolution of 5×5 m.Soil samples of different depth increments and data on tree height were collected from a total of 566 plots(667 m2 each).The soils were analyzed for carbon(soil organic carbon[SOC]),nitrogen,acidity,cation exchange capacity(CEC),exchangeable cations and base saturation as soil fertility attributes.All plots were classified into geomorphological units.Analyses of variance and linear regressions were applied to all terrain,soil fertility and tree growth attributes.Important Findings In general,young and shallow soils and relatively small differences in stable soil properties suggest that soil erosion has truncated the soils to a large extent over the whole area of the experiment.This explains the concurrently increasing CEC and SOC stocks downslope,in hollows and in valleys.However,colluvial,carbon-rich sediments are missing widely due to the convexity of the footslopes caused by uplift and removal of eroded sediments by adjacent waterways.The results showed that soil fertility is mainly influenced by topography.Monte-Carlo flow accumulation(MCCA),curvature,slope and aspect significantly affected soil fertility.Furthermore,soil fertility was affected by the different geomorphological positions on the experimental sites with ridge and spur positions showing lower exchangeable base cation contents,especially potassium(K),due to leaching.This geomorphological effect of soil fertility is most pronounced in the topsoil and decreases when considering the subsoil down to 50 cm depth.Few soil fertility attributes affect tree height after 1-2 years of growth,among which C stocks proved to be most important while pH_(KCl)and CEC only played minor roles.Nevertheless,soil acidity and a high proportion of Al on the exchange complex affected tree height even after only 1-2 years growth.Hence,our study showed that forest nutrition is coupled to a recycling of litter nutrients,and does not only depend on subsequent supply of nutrients from the mineral soil.Besides soil fertility,topography affected tree height.We found that especially MCCA as indicator of water availability affected tree growth at small-scale,as well as aspect.Overall,our synthesis on the interrelation between fertility,topography and tree growth in a subtropical forest ecosystem in SE China showed that topographic heterogeneity lead to ecological gradients across geomorphological positions.In this respect,small-scale soil-plant interactions in a young forest can serve as a driver for the future development of vegetation and biodiversity control on soil fertility.In addition,it shows that terrain attributes should be accounted for in ecological research.

Positive effects of tree species diversity on litterfall quantity and quality along a secondary successional chronosequence in a subtropical forest

Aims Litterfall,as an important link between aboveground and belowground processes,plays a key role in forest ecosystems.Here,we test for effects of tree species richness on litter production and litter quality in subtropical forest.The study further encompasses a factorial gradient of secondary succession that resulted from human exploitation.Given that a large percentage of subtropical forests are in secondary successional stages,understanding the role of biodiversity on forest re-growth after disturbance appears critical.Methods From January 2009 to December 2014,we monitored forest litterfall in 27 Comparative Study Plots that spanned a gradient of tree species richness(3-20 species)and secondary successional ages(~20 to 120 years)in Gutianshan Natural Nature Reserve,Zhejiang Province,China.The experiment is part of the biodiversity-ecosystem functioning research platform‘BEF-China’.Tree litterfall was collected in monthly intervals using litter traps.Samples were separated into leaf and non-leaf components.Leaf litter was further sorted into dominant and other species.Community level monthly leaf litter C and N contents were analysed through a full year.General linear mixed-effects models were applied to test for effects of tree species richness and successional age on litter quantity and leaf litter C/N.Important Findings Litterfall increased with species richness among and within successional age and this effect was consistent across years.Successionally older stands had higher litterfall and this effect was related to increased tree species richness.However,species richness did not change the intra-and inter-annual temporal stability of litterfall.Increasing tree species richness increased leaf litter quality(decreased C/N),while successional age had no effect.Our study indicates that more diverse forest stands produce more leaf litter and that this litter has higher N concentrations,which could promote forest growth through accelerated nutrient re-cycling.

Opposing intraspecific vs.interspecific diversity effects on herbivory and growth in subtropical experimental tree assemblages

Aims Positive plant diversity-ecosystem function relations are ultimately driven by variation in functional traits among individuals that form a community.To date,research has largely focused on the role of species diversity for ecosystem functioning.However,substantial intraspecific trait variation is common and a significant part of this variation caused by genetic differences among individuals.Here,we studied the relative importance of species diversity and seed family(SF)diversity within species for growth and herbivory in experimental subtropical tree assemblages.Methods In 2010,we set up a field experiment in subtropical China,using four species from the local species pool.Trees were raised from seeds,with seeds from the same mother tree forming an SF.We established 23 plots containing one or four species(species diversity treatment)and one or four SFs per species(SF diversity treatment).Tree growth(stem diameter,plant height and crown expansion)and herbivory(percentage leaf loss due to leaf chewers)were monitored annually from 2011 to 2013.Important findings Tree species richness promoted growth but had no effect on herbivory.In contrast,SF diversity reduced growth and increased herbivory but only so in species mixtures.Most of the observed effects were time dependent,with the largest effect found in 2013.Our results suggest that biodiversity can affect plant performance directly via tree species-species interactions,or context dependent,via potential effects on inter-trophic interactions.Two important conclusions should be drawn from our findings.Firstly,in future studies regarding biodiversity and ecosystem functioning(BEF)relationships,intraspecific genetic diversity should be given similar weight as species diversity as it has often been neglected and its effects are not well understood.Secondly,we demonstrate opposite effects of biodiversity among and within species,stressing the importance to consider the effects of multiple levels of biodiversity simultaneously.

Leaf area increases with species richness in young experimental stands of subtropical trees

Aims Most biodiversity-ecosystem functioning research has been carried out in grassland ecosystems,and little is known about whether forest ecosystems,in particular outside the temperate zone,respond similarly.Here,we tested whether productivity,assessed as leaf area index(LAI),increases with species richness in young experimental stands of subtropical trees,whether this response is similar for early-season leaf area(which is dominated by evergreens)and seasonal leaf area increase(which is dominated by deciduous species),and whether responses saturate at high species richness.Methods We used a planted tree biodiversity experiment in south-east China to test our hypotheses.LAI was determined three times by digital hemispheric photography in 144 plots that had been planted with 400 trees each,forming communities with 1,2,4,8 or 16 tree species.Important Findings LAI increased significantly with tree species richness in the fifth year of stand establishment.Similar,but weaker,statistically non-significant trends were observed 1 year before.We did not observe leaf area overyielding and the presence of particularly productive and unproductive species explained large amounts of variation in leaf area,suggesting that selection-type effects contributed substantially to the biodiversity effects we found in this early phase of stand establishment.Effects sizes were moderate to large and comparable in magnitude to the ones reported for grassland ecosystems.Subtropical(and tropical)forests harbor substantial parts of global net primary production and are critical for the Earth’s carbon and hydrological cycle,and our results suggest that tree diversity critically supports these ecosystem services.

Seasonal characteristics and determinants of tree growth in a Chinese subtropical forest

Aims To quantify the seasonal differences in effects of leaf habit,species identity,initial diameter,neighborhood interaction and stand environment on tree absolute diameter growth rates in a subtropical forest in China.Methods We used man-made dendrometer bands to record radial increments of all trees with diameter at breast height(DBH)≥5 cm and height≥3 m within 25 comparative study plots(30×30 m for each)of the‘Biodiversity-Ecosystem Functioning Experiment China’(BEF-China)in the Gutianshan National Nature Reserve,Zhejiang Province,China.We measured stem circumferences twice a year from 2011 to 2014 to calculate absolute diameter growth rate of a warm and wet season(WWS,April to September)and a dry and cold season(DCS,October to the next March)for each individual tree:annual growth(GR_(year)),growth during the WWS(GR_(WWS))and growth during the DCS(GR_(DCS)).We firstly tested the differences in growth rates between different seasons using paired t-tests with Bonferroni correction.Then we applied linear mixed models to explore the effects of leaf habit,species identity,initial diameter,neighborhood interaction(indicated by richness,density and total basal area of all neighboring trees within a radius of 5 m around target trees),stand age and topography(elevation,slope and aspect)on tree growth rates of the two different seasons in three deciduous and 14 evergreen species.Important Findings GR_(year),GR_(WWS)and GR_(DCS)varied between 0.04-0.50 cm year^(−1)(mean=0.21),0.03-0.46 cm season^(−1)(mean=0.18)and 0.01-0.05 cm season^(−1)(mean=0.03)across the 17 species,respectively.GR_(WWS)was significantly higher than GR_(DCS)for all species.Growth rates of faster growing species tended to have larger absolute differences between the WWS and DCS.Tree growth rates of both seasons and of the year(GR_(year),GR_(WWS)and GR_(DCS))varied significantly among leaf habit and species,and increased allometrically with initial diameter,decreased with stand age,but were not significantly related to topography and neighborhood richness or density.GR_(WWS)decreased with neighborhood total basal area,while GR_(DCS)did not.In conclusion,species might the temporally complementary,contributing to plot growth at different times of the year.

Tree diversity and nectar composition affect arthropod visitors on extrafloral nectaries in a diversity experiment

Aims Plants with extrafloral nectaries(EFNs)are common in tropical and subtropical habitats and,despite many other arthropods also forage for EFN,most studies solely focused on the defense mutualisms between EFN plants and ants.This study aims at a quantitative assessment of the entire arthropod community that visits EFN trees to compare visitor communities between different tree species to disentangle the mechanisms that may drive EFN visitor community composition.We also test for tree diversity effects on EFN visitors,as it is unknown if local tree species richness relates to the abundance and species richness of arthropods foraging for EFN.Methods We sampled EFN-visiting arthropods in the experimental tree species richness gradient of the BEF-China Experiment,the currently largest forest diversity experiment in the world,and tested if tree species richness affects EFN visitors and if visitor community composition differs between EFN tree species.In a second step,we analyzed the EFN of Ailanthus altissima and Triadica cochinchinensis,the two EFN tree species with highest visitor abundance,for sugars and amino acids(AA)to test if tree species-specific differences in nectar chemistry translate to differing visitor communities.Lastly,we conducted a choice experiment using different artificial nectar solutions to test if nectar quality affects foraging decisions of ants,the most frequent EFN visitors in our study sites.Important Findings EFN trees in young successional forests in subtropical South-East China are visited by a diverse assemblage of arthropods including ants,beetles,flies,and spiders.Albeit ants accounted for about 75%of all individuals,non-ant visitors were by far more species rich.Visitor abundance and species richness declined with increasing tree species richness,suggesting a resource dilution effect,because plots with more tree species had proportionally less EFN tree individuals and thus lower nectar availability.Ailanthus altissima and T.cochinchinensis were visited by different arthropods and their nectar had species-specific AA composition and sugar concentration,indicating that differences in visitors may,at least partly,be explained by differences in nectar chemistry.These findings are supported by the choice experiment,in which artificial nectars containing sugar solutions supplemented with essential AAs attracted more ants than pure sugar solutions or sugar solutions supplemented with non-essential AAs.Our results improve the understanding of the complex ecology of EFN trees,a plant life form that might be crucial for understanding how tree diversity influences patterns of tree growth in young successional tropical and subtropical forests.

Impact of tree diversity and environmental conditions on the survival of shrub species in a forest biodiversity experiment in subtropical China

Aims Although shrubs are an important component of forests,their role has not yet been considered in forest biodiversity experiments.In the biodiversity-ecosystem functioning(BEF)experiment with subtropical tree species in south-east China(BEF-China),we factorially combined tree with shrub species-diversity treatments.Here,we tested the hypotheses that shrub survival differs between the 10 planted shrub species,with lower survival rates of late-than early-successional species and is affected by environmental conditions,such as topography and top soil characteristics,as well as by biotic factors,represented by tree,shrub and herb layer characteristics.Methods We analyzed the survival of 42000 shrub individuals in 105 plots varying in tree and shrub species richness of the BEF-China project four years after planting.Shrub survival was analyzed with generalized linear mixed effects models at the level of individuals and with variance partitioning at the plot level.Random intercept and random slope models of different explanatory variables were compared with respect to the Bayesian Information Criterion(BIC).Important Findings Survival rates differed largely between the 10 shrub species,ranging from 26%to 91%for Ardisia crenata and Distylium buxifolium,respectively.Irrespective of species identity,single abiotic factors explained up to 5%of species survival,with a negative effect of altitude and slope inclination and a positive effect of the topsoil carbon to nitrogen ratio,which pointed to drought as the major cause of shrub mortality.In contrast,neither tree nor shrub richness affected shrub survival at this early stage of the experiment.Among the biotic predictors,only herb layer species richness and cover of the dominant fern species(Dicranopteris pedata)affected shrub survival.Overall,our models that included all variables could explain about 65%in shrub survival,with environmental variables being most influential,followed by shrub species identity,while tree species diversity(species richness and identity)and herb layer characteristics contributed much less.Thus,in this early stage of the experiment the biotic interactions among shrubs and between shrubs and trees have not yet overruled the impact of abiotic environmental factors.

Early positive effects of tree species richness on soil organic carbon accumulation in a large-scale forest biodiversity experiment

Aims tree species richness has been reported to have positive effects on aboveground biomass and productivity,but little is known about its effects on soil organic carbon(SOC)accumulation.Methods to close this gap,we made use of a large biodiversity-ecosystem functioning experiment in subtropical china(BEF-china)and tested whether tree species richness enhanced SOC accumulation.In 2010 and 2015,vertically layered soil samples were taken to a depth of 30 cm from 57 plots ranging in tree species richness from one to eight species.Least squares-based linear models and analysis of variance were used to investigate tree diversity effects.Structural equation modeling was used to explore hypothesized indirect relationships between tree species richness,leaf-litter biomass,leaf-litter carbon content,fine-root biomass and SOC accumulation.Important Findings Overall,SOC content decreased by 5.7 and 1.1 g C kg^(-1) in the top 0-5 and 5-10 cm soil depth,respectively,but increased by 1.0 and 1.5 g C kg^(-1) in the deeper 10-20 and 20-30 cm soil depth,respect-ively.converting SOC content to SOC stocks using measures of soil bulk density showed that tree species richness did enhance SOC accumulation in the different soil depths.these effects could only to some extent be explained by leaf-litter biomass and not by fine-root biomass.Our findings suggest that carbon storage in new forests in china could be increased by planting more diverse stands,with the potential to contribute to mitigation of climate warming.

Limited tree richness effects on herb layer composition,richness and productivity in experimental forest stands

Aims In forests,the herbaceous understory vegetation plays an important role for ecosystem functioning as it represents a significant component of total aboveground productivity.In addition,the herb layer contributes to overall forest species richness and controls tree species regeneration.Vice versa,trees in the overstory control understory herb and shrub growth through competition for resources.Using an experimental forest plantation with manipulated tree richness,we asked to which degree tree species richness and identity affect herb layer composition,richness and productivity and how these relationships across strata change with abiotic environmental conditions and competition intensity.Methods In the context of the Biodiversity-Ecosystem Functioning project in subtropical China(BEF-China),we made use of the integrated BEFmod experiment arranged along a tree species richness gradient at two sites,with additional subplot treatments of phosphorus addition,herb layer weeding and no weeding.We recorded the understory vegetation and determined herb layer biomass production on a total of 201 subplots.Important Findings We found only minor effects of tree layer richness on herb layer species composition and no significant effect on herb layer richness or productivity yet.However,there were strong tree layer identity effects on all response variables,which were partly explained by differences in leaf area index and by a high share of woody species both in total herb layer species richness and biomass.There were strong treatment effects,which were largest in the‘no weeding’treatment but we did not find any treatment×tree layer richness interaction in herb layer responses.Thus,these effects are mainly explained by increased competition intensity within the herb layer in the absence of weeding.Despite the young age of the experiment,the interactions between tree species identity,tree richness and the herb layer did already emerge and can be expected to become stronger with ongoing runtime of the experiment.

Shifts in community leaf functional traits are related to litter decomposition along a secondary forest succession series in subtropical China

Aims We investigated shifts in community-weighted mean traits(CWm)of 14 leaf functional traits along a secondary successional series in an evergreen broadleaf forest in subtropical southeast China.most of the investigated traits have been reported to affect litter decomposition in previous studies.We asked whether changes in CWms along secondary succession followed similar patterns for all investigated traits and whether the shifts in CWm indicated a change in resource use strategy along the successional gradient.using community decomposition rates(k-rates)estimated from annual lit-ter production and standing litter biomass,we asked whether the dynamics of litter decomposition were related to changes in leaf functional traits along the successional series.Methods twenty-seven plots were examined for shifts in leaf CWm traits as well as in k-rates along a series of secondary forest succession cov-ered in the framework of the bEF-China project.We investigated whether the changes in CWms followed similar patterns for all traits with ongoing succession.three alternative linear models were used to reveal the general patterns of shifts in CWm trait values.moreover,multiple regression analysis was applied to investigate whether there were causal relationships between the changes in leaf functional traits and the dynamics of litter decomposition along secondary succession.We furthermore assessed which traits had the highest impact on community litter decomposition.Important Findingsshifts in CWm values generally followed logarithmic patterns for all investigated traits,whereas community k-rates remained stable along the successional gradient.In summary,the shifts in CWm values indicate a change in community resource use strategy from high nutrient acquisition to nutrient retention with ongoing succession.stands with higher CWm values of traits related to nutrient acquisition had also higher CWm values of traits related to chemical resistance,whereas stands with higher CWm values of traits related to nutrient retention exhibited higher CWm values in leaf physical defense.moreover,high values in CWm values related to nutritional quality(such as high leaf phosphorus concentrations)were found to promote com-munity k-rates,whereas high values in physical or chemical defense traits(such as high contents in polyphenols or high leaf toughness)decreased litter decomposition rates.In consequence,litter decom-position,which was simultaneously affected by these characteristics,did not change significantly along succession.our findings show that leaf decomposition within the investigated communities is dependent on the interplay of several traits and is a result from interactions of traits that affect decomposition in opposing directions.

林下生物量影响因素:幼龄林树种特性比丰富度更重要

生物多样性与生态系统功能的正相关关系己被广泛报道,其主要来源于对草原生态系统的研究。然而,该结论并不一定适用于更复杂的环境,例如具有不同垂直层次的森林。举例而言,己有研究表明上层乔木树种丰富度与林下生产力降低有关。树种丰富度是否会通过增加(由于生境异质性)或降低(通过增强竞争)资源的可利用性进而影响林下生产力,以及林下生产力是否受树种特性的影响更大,这些影响机制都可能会随着时间的推移而改变。此外,研究还表明,丰富度-生产力关系随着环境背景的变化而改变。本研究利用可以操控树种丰富度的实验林场研究了这些不同垂直层位里的时间和环境动态。在中国亚热带森林生物多样性与生态系统功能(BEF-China)研究计划的框架下,我们在3年时间里沿树种丰富度梯度反复采集林下生物量样本,研究了不同环境处理中树种丰富度、树种特性和时间对林下生物量的影响。尽管我们发现乔木层特性对林下生物量有显著和一致的影响,但是树种丰富度对后者却不具有这种影响。另外,在森林结构层之间,可能并不存在单一的、具有普遍性的上层乔木树种丰富度与林下生产力的相关关系,并且与上层乔木相关的环境因素(如透光率)对林下生产力的贡献程度会随着时间而变化。总体而言,我们的结果表明,在研究森林结构层之间的关系时应将时间动态变化考虑在内。

Estimation of Throughfall Erosivity in a Highly Diverse Forest Ecosystem Using Sand-Filled Splash Cups

Sand-fflled splash cups were used to study the erosive power of rainfall and throughfall in the humid subtropics of Southeast China. The splash cup measurements yielded precise and reproducible results under both open field conditions and forest vegetation. The splash cups were exposed to specific forest stands of different ages and to selected species （Schima superba, Castanopsis eyrei, Daphniphyllum oldhamii, Lithocarpus glaber） in the Gutianshan （古田山） National Nature Reserve （GNNR）. The results of the measurements under forest vegetation show that the erosive power of throughfall drops to be 2.59 times higher compared to the open field. This accentuates the importance of shrub, herb and litter layers in forest ecosystems to protect the soil against erosion. Coalescing drops from leaves and branches （drips） are responsible for this notable gain in erosive power. Moreover, differences in sandloss between the investigated tree species （deciduous, evergreen） revealed that the erosion potential and the spatial heterogeneity of throughfall are species-specific. This highlights the importance of selecting specific species for afforestation projects considering the prevention of soil erosion.