Patch isolation and shape predict plant functional diversity in a naturally fragmented forest

Aims It is known that taxonomic diversity can be predicted by the spatial configuration of the habitat, in particular by its area and degree of isolation. However, taxonomic diversity is a poor predictor of ecosystem functioning. While functional diversity is strongly linked to the functionality and stability of ecosystems, little is known about how changes in the spatial configuration of the habitat affect functional diversity. In this study, we evaluated whether the spatial configuration of forest patches predicts the functional diversity of plants in a fragmented forest.Methods Five functional leaf traits (leaf dry matter content, leaf punch force, specific leaf area, leaf size and leaf thickness) were measured for 23 dominant plant species in 20 forest patches in a naturally fragmented forest on the Yucatan Peninsula. Abundance-weighted multivariate and individual trait metrics of functional diversity were calculated and correlated with size, degree of isolation and the shape of forest patches.Important findings Patch shape was negatively correlated with multivariate and individual trait (leaf dry matter content and leaf size) metrics of functional diversity. Patch isolation measures were also negatively correlated with individual trait (leaf dry matter content, leaf punch force and leaf size) metrics of functional diversity. In other words, greater patch shape irregularity and isolation degree impoverish plant functional variability. This is the first report of the negative effects of patch shape irregularity and isolation on the functional diversity of plant communities in a forest that has been fragmented for a long time.     

亚热带次生常绿阔叶林植物功能性状及多样性对人工抚育的响应

亚热带次生常绿阔叶林普遍存在生长滞缓、固碳功能和经济价值低下等问题,迫切需要通过人工抚育提高其生态系统功能。对植物功能性状及其多样性的深入研究,能够找寻植物共存与群落稳定发展的内在机制,为提升森林生态系统功能的实践提供基础。为了探究人工抚育对亚热带次生常绿阔叶林质量提升的影响,以杭州午潮山国家森林公园内的次生常绿阔叶林为研究对象,实施了不同强度的抚育措施,通过群落植被复查,分析群落植物功能性状以及功能多样性对不同强度人工抚育的响应。结果发现:抚育2年后,群落最大潜在树高与叶片氮、磷、钾含量显著上升,而叶片干物质含量和叶片叶绿素含量均有显著下降,比叶面积有下降趋势,两种强度的抚育之间差异不显著;叶片干物质含量、叶绿素含量与叶片氮含量间的相关性由不显著变为了显著负相关,而叶片干物质含量与叶片叶绿素含量,叶片磷、钾含量与叶片氮含量,叶片磷含量与叶片钾含量间的相关性由不显著变为显著正相关;在20%强度抚育下,功能丰富度指数均值从对照的0.52显著下降为0.16,功能均匀度指数与功能分离度指数的均值则分别上升到0.61和0.67,显著高于对照组的0.51和0.56;在10%强度抚育下,功能丰富度有所下降,功能均匀度与功能分离度均有所上升,但差异不显著。研究表明,人工抚育在一定程度上改变了群落水平的植物功能性状与功能多样性,提高了群落植物利用资源的能力和效率;而适度的抚育强度更能解放资源空间,对群落产生的影响更加明显。该结果为亚热带次生常绿阔叶林的经营与管理提供依据与参考。     

博斯腾湖湖滨湿地植物多样性对季节变化的响应

研究生物多样性对季节的响应对于维持生态系统稳定、保护生物多样性、解析群落构建机制具有重要意义。本文以博斯腾湖湖滨湿地为研究对象,探究不同季节植物群落的物种多样性与功能多样性的变化规律。结果显示：(1)物种多样性指数随季节变化没有显著改变;功能多样性指数中,功能丰富度由春季到夏季逐渐减小,功能离散度逐渐增大;不同季节的功能均匀度差异性不显著;(2)植物功能性状在不同季节间差异显著;春季叶绿素含量显著低于夏季;夏季比叶面积和叶干物质含量显著高于秋季;叶片含水量和厚度由春季到秋季呈递增趋势;(3)影响Pielou指数和功能丰富度的主要环境因子分别为土壤铵态氮和速效磷;影响Shannon-Wiener指数、Simpson指数和功能均匀度的主要环境因子为土壤有机质;影响功能离散度的主要环境因子为土壤含水量;(4)影响最大株高的主要环境因子为土壤pH值;影响叶干物质含量的主要环境因子为土壤速效钾;影响叶片厚度和比叶面积的主要环境因子为土壤总磷;而影响叶片含水量的主要环境因子为土壤硝态氮;叶绿素含量与土壤因子无显著相关关系。     

围封与放牧管理对高寒草甸植物功能性状和功能多样性的影响

植物功能性状能够响应生存环境的变化并直接决定着生态系统功能。为了揭示围封与放牧管理对物种共存和驱动群落构建的影响机理,该研究以青藏高原东缘高寒草甸为对象,分析了围封与放牧处理对植物功能性状和功能多样性的影响。结果显示:(1)在群落水平,放牧显著降低了比叶面积和植物高度;在物种水平,放牧群落中多数杂类草比叶面积减小,而莎草类和禾草类的比叶面积在处理间无显著差异。(2)叶干物质含量与比叶面积在围封和放牧处理中均呈显著负相关关系,在放牧处理中,叶干物质含量与植物高度呈显著的二次函数关系,即随着叶干物质含量的增大,植物高度先减小后增大;在同等比叶面积的情况下,与围封相比,放牧降低了叶干物质含量;在相同叶干物质含量的情况下,与围封相比,放牧降低了植物高度。(3)放牧在总体上降低了种间性状的平均差异,植物性状表现出趋同响应,具体表现为放牧减小了叶干物质含量和植物高度的种间差异;与围封相比,放牧显著提高了功能均匀度,减小了功能分离度。研究表明,不同植物种对放牧的响应模式存在差异,放牧降低了种间对光资源的竞争,可能增加了对土壤养分的竞争,放牧驱动群落构建的过程中,土壤养分是非常重要的作用因子,说明放牧影响物种共存依赖于对多种资源的竞争。     

退化草地物种种内和种间功能性状变异对放牧的响应

研究草地植物功能性状变异对放牧干扰的响应机制,有助于解析草地生态系统群落构建和功能多样性维持机制及植物对环境的适应及权衡策略。以科尔沁沙地退化草地为对象,研究围封和放牧草地物种多种功能性状(植株高度、根系长度、叶面积、根面积、叶片干物质含量、地上干物质含量、根系干物质含量、比叶面积、比根长和根冠比)变异特征及其对放牧干扰的响应机制。结果表明: 退化草地物种种间性状变异明显高于种内变异,种间性状变异对总体变异的贡献率占比高达70.2%～95.1%,而种内变异仅为4.9%～29.8%,但群落构建中物种的种内变异仍不可忽视。放牧草地物种种间性状变异低于围封草地,且放牧草地种内变异增加而种间变异减小。放牧导致不耐牧的优良禾本科牧草叶面积和叶片干物质含量下降而比根长增加,但耐牧的杂类草则通过增加叶面积和叶片干物质含量并降低比根长来提高在群落中的优势地位。退化草地对放牧响应较为敏感的功能性状有叶面积、叶片干物质含量、比根长和比叶面积。植物叶片性状和根系性状自身及彼此间均呈显著正相关,但放牧会增强根系性状的协同效应而减弱叶片性状的协同效应。说明放牧会驱动植物个体和种群功能性状权衡策略发生改变,进而起到调控植物群落结构和功能的作用。     

Aboveground resilience to species loss but belowground resistance to nitrogen addition in a montane plant community

Aims Decades of empirical work have demonstrated how dominant plant species and nitrogen fertilization can influence the structure and function of plant communities. More recent studies have examined the interplay between these factors, but few such studies use an explicit trait-based framework. In this study, we use an explicit trait-based approach to identify potential mechanisms for community-level responses and to test ecological niche theory.Methods We experimentally manipulated plant communities (control, ?dominant species, ?random biomass) and nitrogen (N) inputs (control, +organic N, +inorganic N) in a fully factorial design. We predicted that traits related to plants' ability to take up different forms of soil N would differ between dominant and subordinate species, resulting in interactive effects of dominant species loss and N fertilization on plant community structure and function. The study took place in a montane meadow in the Rocky Mountains, Colorado, USA.Important findings After four years, the plant community in removal plots converged toward a species composition whose leaf and root functional traits resembled those of the previously removed dominant species. Ecosystem productivity generally increased with N addition: soil carbon efflux was ~50% greater when either form of N was added, while inorganic N addition increased aboveground biomass production by ~60% relative to controls. The increase in production was mediated by increased average height, leaf mass:area ratio and leaf dry matter content in plant communities to which we added inorganic N. Contrary to our predictions, there were no interactive effects of N fertilization and dominant species loss on plant community structure or ecosystem function. The plant community composition in this study exhibited resistance to soil N addition and, given the functional convergence we observed, was resilient to species loss. Together, our results indicate that the ability of species to compensate functionally for species loss confers resilience and maintains diversity in montane meadow communities.     

Plant trait responses to the environment and effects on ecosystem properties

A combined analysis of plant trait responses to the environment, and their effects on ecosystem properties has recently been proposed. In this study, we related the trait composition of plant communities to soil nutrients and disturbance as environmental drivers and to productivity, decomposition and soil carbon as ecosystem properties. We surveyed two sites, one comprising intensively grazed and fertilized grasslands, the other consisting of semi-natural grassland and open heathland. Species abundance and trait values of 49 species were recorded in 69 plots, as well as parameters describing soil resources, land-use disturbances, and ecosystem properties. Our main goal was to test whether the average or the diversity of the trait values of the vegetation had stronger effects on ecosystem properties (mass ratio vs. diversity hypothesis). Structural equation modeling was used to perform a simultaneous analysis of trait responses and effects. Specific leaf area and leaf nutrient contents were always negatively correlated with stem dry matter content and canopy height, indicating greater investments in supportive and nutrient-conserving tissue as plants increased in size. In the agricultural site, disturbance was the single most important factor decreasing plant height, while leaf traits such as specific leaf area and leaf nutrient contents increased with soil resources in heathlands. Productivity was directly or indirectly driven by leaf traits, and investments in structural tissue increased standing biomass and soil carbon. Different environmental drivers in the two sites produced opposing leaf trait effects on litter decomposition. Ecosystem properties were explained by the community mean trait value as predicted by the mass ratio hypothesis. Evidence for effects of functional diversity on productivity and other ecosystem properties was not detected, suggesting that diversity–productivity relationships depend on the length of the investigated environmental gradients. We conclude that changes in community composition and dominance hierarchies deserve the most attention when ecosystem properties must be maintained.     

天坑森林植物群落叶功能性状、物种多样性和功能多样性特征

以天坑内部-边缘-外部森林植物群落为研究对象,通过调查植物的群落结构、叶功能性状,探究天坑内外森林植物群落叶功能性状、物种多样性和功能多样性变化特征及其内在关联,为深入了解负地形森林生态系统的功能和恢复退化喀斯特地区的植被提供一定参考。研究结果如下：（1）比叶面积（SLA: 198.75 cm2/g)）、叶面积（LA: 42.70 cm2）、叶磷含量（LPC: 1.70 g/kg）和叶钾含量（LKC: 10.27 g/kg）在天坑内部最高,叶组织密度（LTD: 0.32 g/cm3）和叶干物质含量（LDMC: 0.41 g/g）在天坑外部最高,天坑内外森林均易受到磷限制,表明随天坑内部-边缘-外部生境变化,植物对环境的适应机制和生存策略发生了部分调整,物种的防御策略增强,生长投入策略减弱。（2）Shannon-Wiener指数（2.82）、Simpson指数（0.92）和Pielou’s均匀度指数（0.87）均以天坑外部最高,功能丰富度（1.05）、功能离散度（1.88）和Rao’s二次熵（4.52）以天坑内部最高,表明随天坑内部-边缘-外部生境的变化,植物功能性状的差异减少,物种分布及其功能性状分布总体上更为均匀、物种数量增多。（3）物种多样性指数之间、功能多样性指数之间存在较强的相关性,表明物种多样性指数之间、功能多样性指数之间存在不同的制约关系。（4）叶功能性状与物种多样性、功能多样性的相关性强,物种多样性和功能多样性之间相关性较弱,表明叶性状对生态学过程的变化较为敏感,叶功能性状与物种多样性之间存在较强的耦合关系。     

Predicting individual plant performance in grasslands

Plant functional traits are widely used to predict community productivity. However, they are rarely used to predict individual plant performance in grasslands. To assess the relative importance of traits compared to environment, we planted seedlings of 20 common grassland species as phytometers into existing grassland communities varying in land‐use intensity. After 1 year, we dug out the plants and assessed root, leaf, and aboveground biomass, to measure plant performance. Furthermore, we determined the functional traits of the phytometers and of all plants growing in their local neighborhood. Neighborhood impacts were analyzed by calculating community‐weighted means (CWM) and functional diversity (FD) of every measured trait. We used model selection to identify the most important predictors of individual plant performance, which included phytometer traits, environmental conditions (climate, soil conditions, and land‐use intensity), as well as CWM and FD of the local neighborhood. Using variance partitioning, we found that most variation in individual plant performance was explained by the traits of the individual phytometer plant, ranging between 19.30% and 44.73% for leaf and aboveground dry mass, respectively. Similarly, in a linear mixed effects model across all species, performance was best predicted by phytometer traits. Among all environmental variables, only including land‐use intensity improved model quality. The models were also improved by functional characteristics of the local neighborhood, such as CWM of leaf dry matter content, root calcium concentration, and root mass per volume as well as FD of leaf potassium and root magnesium concentration and shoot dry matter content. However, their relative effect sizes were much lower than those of the phytometer traits. Our study clearly showed that under realistic field conditions, the performance of an individual plant can be predicted satisfyingly by its functional traits, presumably because traits also capture most of environmental and neighborhood conditions.     

Functional traits composition predict macrophytes community productivity along a water depth gradient in a freshwater lake

Functional trait composition of plant communities has been proposed as a helpful key for understanding the mechanisms of biodiversity effects on ecosystem functioning. In this study, we applied a step‐wise modeling procedure to test the relative effects of taxonomic diversity, functional identity, and functional diversity on macrophytes community productivity along water depth gradient. We sampled 42 plots and 1513 individual plants and measured 16 functional traits and abundance of 17 macrophyte species. Results showed that there was a significant decrease in taxonomic diversity, functional identity (i.e., stem dry mass content, leaf [C] and leaf [N]), and functional diversity (i.e., floating leaf, mean Julian flowering date and rooting depth) with increasing water depth. For the multiple‐trait functional diversity (FD) indices, functional richness decreased, while functional divergence increased with water depth gradient. Macrophyte community productivity was strongly determined by functional trait composition within community, but not significantly affected by taxonomic diversity. Community‐weighted means (CWM) showed a two times higher explanatory power relative to FD indices in determining variations in community productivity. For nine of sixteen traits, CWM and FD showed significant correlations with community productivity, although the strength and direction of those relations depended on selected trait. Furthermore, functional composition in a community affected productivity through either additive or opposite effects of CWM and FD, depending on the particular traits being considered. Our results suggested both mechanisms of mass ratio and niche complementarity can operate simultaneously on variations in community productivity, and considering both CWM and FD would lead to a more profound understanding of traits–productivity relationships.     

Direct and indirect facilitation affect community productivity through changes in functional diversity in an alpine system

Background and AimsFacilitation is an important ecological process for plant community structure and functional composition. Although direct facilitation has accrued most of the evidence so far, indirect facilitation is ubiquitous in nature and it has an enormous potential to explain community structuring. In this study, we assess the effect of direct and indirect facilitation on community productivity via taxonomic and functional diversity.MethodsIn an alpine community on the Tibetan Plateau, we manipulated the presence of the shrub Dasiphora fruticosa and graminoids in a fenced meadow and a grazed meadow to quantify the effects of direct and indirect facilitation. We measured four plant traits: height, lateral spread, specific leaf area (SLA) and leaf dry matter content (LDMC) of forbs; calculated two metrics of functional diversity [range of trait and community-weighted mean (CWM) of trait]; and assessed the responses of functional diversity to shrub facilitation. We used structural equation modelling to explore how shrubs directly and indirectly drove community productivity via taxonomic diversity and functional diversity.Key ResultsWe found stronger effects from herbivore-mediated indirect facilitation than direct facilitation on productivity and taxonomic diversity, regardless of the presence of graminoids. For functional diversity, the range and CWM of height and SLA, rather than lateral spread and LDMC, generally increased due to direct and indirect facilitation. Moreover, we found that the range of traits played a primary role over taxonomic diversity and CWM of traits in terms of shrub effects on community productivity.ConclusionsOur study reveals that the mechanism of shrub direct and indirect facilitation of community productivity in this alpine community is expanding the realized niche (i.e. expanding range of traits). Our findings indicate that facilitators might increase trait dispersion in the local community, which could alleviate the effect of environmental filters on trait values in harsh environments, thereby contributing to ecosystem functioning.     

黄土高原典型小流域草地群落功能性状对土壤水分的响应

植物功能性状可以响应生境的变化并决定生态系统的功能,探究植物功能性状间的关系及其随土壤有效水分梯度的变化规律,对认识不同水分条件下植被在群落水平碳水代谢关系和维持水分平衡的生理生态学机制具有重要意义。以甘肃定西典型半干旱黄土小流域草地群落为研究对象,采用排序分析和回归拟合方法,分析了30个代表性草地样地中7个植物功能性状加权均值对土壤有效水分的响应以及响应性状间的相关关系。结果显示:(1)7个性状中,除叶宽与土壤有效水分无明显相关外,叶长、株高、叶面积、比叶面积、叶厚和叶干物质含量均与土壤有效水分显著性相关,可识别为草地在群落水平对土壤水分的响应性状。(2)草地群落通过降低株高,减小叶长、叶面积和比叶面积,增加叶厚和叶干物质含量以适应土壤有效水分减少;其中叶干物质含量的解释度最大,是土壤水分的最优响应性状。(3)除叶厚与叶长无显著相关外,其余功能性状均存在显著相关,说明草地群落的功能性状在土壤水分梯度上已基本形成了一个相互权衡或协同变化的功能性状组合。     

Nitrogen Productivity Depends on Photosynthetic Nitrogen Use Efficiency and on Nitrogen Allocation Within the Plant

The concept of plant nitrogen productivity was introduced atthe end of the 1970s to interpret the dependency of plant growthon internal nitrogen. It is defined as the increase in plantdry matter per unit time and per unit plant nitrogen content.Recently, plant nitrogen productivity has been expressed asthe product of two terms: the leaf nitrogen ratio, which isthe proportion of the plant's nitrogen present in the leaves,and the leaf nitrogen productivity, which is defined as theincrease in plant dry matter per unit time and leaf nitrogencontent. In the present paper we use two data sets obtainedfrom C₃ herbaceous species to evaluate the relative importanceof variation in leaf nitrogen ratio and leaf nitrogen productivityin determining interspecific variation in plant nitrogen productivity.Further, we analyse to what extent leaf and plant nitrogen productivitiesdepend on photosynthetic nitrogen use efficiency. Results showthat in all cases, photosynthetic nitrogen use efficiency isa major determinant of both plant and leaf nitrogen productivities.A positive relationship between leaf nitrogen ratio and plantnitrogen productivity was found only when comparisons were madeover broad taxonomic groups.Copyright 1995, 1999 Academic Press Interspecific variation, leaf nitrogen ratio, nitrogen productivity, photosynthetic nitrogen use efficiency     

星斗山常绿落叶阔叶混交林木本植物叶功能性状及其多样性特征分析

为探究亚热带常绿落叶阔叶混交林中木本植物叶功能性状的变异特征,以及群落功能多样性在海拔梯度下的响应规律。该研究以鄂西南地区的星斗山国家级自然保护区海拔1 200～1 700 m的常绿落叶阔叶混交林为研究对象,对群落内木本植物的叶面积(LA)、比叶面积(SLA)、叶干物质含量(LDMC)、叶厚度(LT)、叶氮含量(LNC)、叶磷含量(LPC)6种叶功能性状的变异特征进行了分析,并分析了群落水平下木本植物叶功能性状和功能多样性对海拔变化的响应。结果表明:(1)星斗山保护区内木本植物叶面积、比叶面积、叶干物质含量、叶厚度、叶氮含量和叶磷含量平均值分别为151.49 cm~2、247.98 cm~2/g、34.08%、0.21 mm、16.59 mg/g和0.04 mg/g,其变异幅度依次为206.96%、57.00%、28.15%、52.38%、24.83%和76.92%。(2)在植物科、叶习性、生活型和树高4个因素中,科类群对6种叶功能性状的影响最大,其次为叶习性。(3)海拔对叶面积、叶干物质含量、叶磷含量影响极显著(P0.001),但对比叶面积、叶厚度和叶氮含量无显著影响(P0.05)。(4)不同海拔梯度上群落生物承载量、功能丰富度、功能分离度和功能离散度均达到显著差异(P0.05),仅功能均匀度在海拔梯度上差异不显著。     

Grazing increases functional richness but not functional divergence in Tibetan alpine meadow plant communities

Plant community diversity and ecosystem function are conditioned by competition among co-occurring species for multiple resources. Previous studies suggest that removal of standing biomass by grazing decreases competition for light, but coincident grazing effects on competition for soil nutrients remain largely unknown in Tibetan rangelands where grazing tends to deplete soil phosphorus availability. We measured five functional traits indicative of plant productivity and stoichiometry leaf carbon concentration (LCC), leaf nitrogen concentration (LNC), leaf phosphorus concentration (LPC), specific leaf area (SLA), leaf dry matter content (LDMC) for component species of plant communities in grazed and ungrazed plots in five Tibetan alpine meadows. We examined the diversity of traits singly Rao index of functional diversity (FDrao) and in aggregate functional richness (FRic), functional divergence (FDiv), and functional evenness (FEve) in response to grazing. We tested whether foliar trait diversity increases with nutrient competition but decreases with light competition when competitive exclusion is reduced by grazing. The FDrao of LPC significantly increased under grazing, but FDrao for LCC, LNC and SLA tended to decrease. The FDrao of LDMC increased at the drier site but decreased at the wettest site. There was a strong negative association between increase in FDrao of LPC and decrease in soil nutrients, especially soil phosphorus availability. The FRic for all five traits together increased with species diversity following grazing, but neither FDiv nor FEve differed significantly between grazed and ungrazed plots at most sites. Grazing in Tibetan alpine meadows tends to increase competition for soil phosphorus while decreasing competition for light, resulting in an increase in the functional richness in grazed plant communities without any significant changes in the overall functional diversity of foliar traits. Our study highlights the potential importance of grazing mediated competition for multiple resources in alpine meadow ecosystems.     

Niche and Neutral Processes Together Determine Diversity Loss in Response to Fertilization in an Alpine Meadow Community

Fertilization via nutrient deposition and agricultural inputs is one of the most important factors driving decreases in plant diversity. However, we still do not fully understand which processes (niche process or neutral process) are more important in leading to decreases in plant diversity caused by fertilization. A hypothesis-based approach was used to test the relative importance of niche versus neutral processes along a fertilization gradient in an alpine meadow community on the eastern Tibetan plateau, China. Niche overlap values were calculated for species biomass, and the null model was used to generate the values of niche overlap expected at random. A linear regression modeling was used to evaluate the relationship between functional traits (specific leaf area, leaf dry matter content, and leaf total nitrogen concentration) and species relative abundance. Our results demonstrated that observed niche overlap for species biomass was significantly higher than expected at lower fertilization gradients. Moreover, we also found a significantly negative correlation between species relative abundance and specific leaf area and leaf dry matter content, but a significantly positive correlation between relative abundance and leaf nitrogen concentration at lower fertilization gradients. However, these relationships were not significant at higher fertilization gradients. We concluded that community assembly is dynamic progression along the environmental gradients, and niche and neutral processes may together determine species diversity loss in response to fertilization.     

氮对冬玉米干物质生产及生理特性的影响

通过对不同施氮水平下冬玉米的干物质生产及其生理特性的研究表明 :(1 )随着施氮量的提高 ,叶面积指数增大 ,叶片衰老延缓 ,花后保持有更大的叶面积持续期和光合势 ,有利于干物质的生产 ;(2 )施氮量的增加促进了花丝期前后植株各部分氮和干物质的累积 ,产量显著提高 ,但是营养体干物质和氮的转移率降低 ,尤其高氮条件下尚有大量干物质不能转移 ,库 /源比不协调 ,氮的生产力随之降低。     

湖北星斗山地形变化对不同生活型植物叶功能性状的影响

探究地形变化对不同生活型植物叶功能性状的影响有助于深入理解森林群落物种组成的维持特征。该研究以湖北星斗山常绿落叶阔叶混交林为研究对象, 测量了50个样地中224种木本植物的叶面积、叶厚度、叶干质量、叶干物质含量和比叶面积, 运用单因素方差分析揭示了乔木、灌木和木质藤本的叶功能性状变异特征, 并采用偏曼特尔检验分别从群落水平和物种水平分析了地形变化对不同生活型木本植物叶功能性状的影响。研究发现: 不同生活型植物叶性状变异系数分布范围为23.42%-110.45%; 不同生活型之间的植物叶功能性状差异明显。群落水平上, 海拔与乔木叶干质量、灌木叶面积和木质藤本叶厚度显著正相关, 坡度仅对灌木和木质藤本比叶面积具有显著影响, 坡向与灌木叶厚度、叶干质量和比叶面积显著正相关。物种水平上, 海拔比坡度和坡向对植物叶功能性状影响更为显著, 且不同物种对地形变化的敏感度不一致; 在控制空间结构影响后, 地形因子对植物叶功能性状的影响降低。该研究结果表明, 不同生活型植物的叶功能性状对地形变化的响应格局不同, 这可能是星斗山常绿落叶阔叶混交林植物多样性的主要维持机制。     

火烧强度对兴安落叶松群落叶片功能性状及功能多样性的影响

林火是北方针叶林的重要生态因子,直接影响火烧迹地物种多样性及功能多样性,进而影响森林群落的演替.以牙克石地区火后自然恢复12年的兴安落叶松群落为研究对象,在群落尺度上分析火烧迹地土壤养分含量、叶片功能性状、物种多样性和功能多样性在不同火烧强度(轻、中和重度火烧)下的变化规律.结果表明: 火烧显著降低了土壤全氮含量,对土壤全磷含量无显著影响.轻、中度火烧有助于维持群落较高的物种多样性和功能多样性;中度火烧显著增加了群落的物种多样性,物种丰富度指数、Shannon指数、Simpson指数和Pielou均匀度指数均在中度火烧时有最大值;火烧降低了群落的功能丰富度和功能离散度指数,二者分别在中、轻度火烧时最大(除未过火外),而群落的功能均匀度和二次熵指数在林火干扰后增加,轻度火烧后最大.随火烧强度增加,叶干物质含量、叶组织密度和叶磷含量总体呈显著增大趋势,而比叶面积、叶含水量、叶氮含量和叶N∶P则表现出未过火>中度火烧>轻度火烧>重度火烧的规律,叶片厚度呈先增大后减小的变化规律.火烧强度对森林群落的叶片功能性状和功能多样性均有显著影响,且适度的火干扰对森林群落的恢复具有促进作用.     

Impact of twospotted spider mite (Acari: Tetranychidae) on growth and productivity of glasshouse cucumbers

Experiments were conducted to assess the damage of the glasshouse cucumber by twospotted spider mite, Tetranychus urticae Koch, and to investigate when the economic yield begins to decrease after T. urticae infestations. To assess the damage, dry matter partitioning in the cucumber plant was quantified and plant growth analyses were conducted at four different T. urticae infestation levels. T. urticae infestations decreased leaf productivity by reducing the total number of leaves per plant. Approximately 14% reductions of total leaf areas could result in significant yield loss. The decreased leaf productivity by T. urticae feeding caused biomass reductions and altered the pattern of dry matter partitioning in the plant; damaged plants accumulated more dry matter in the leaf, and partitioning of dry matter to fruits was hindered. The economic yield of cucumber began to significantly decrease as early as 4 wk after heavy mite infestations. This study also showed the seasonal differences in T. urticae-cucumber damage interactions among mite infestation levels.