Measuring Fine Root Turnover in Forest Ecosystems

Development of direct and indirect methods for measuring root turnover and the status of knowledge on fine root turnover in forest ecosystems are discussed. While soil and ingrowth cores give estimates of standing root biomass and relative growth, respectively, minirhizotrons provide estimates of median root longevity (turnover time) i.e., the time by which 50% of the roots are dead. Advanced minirhizotron and carbon tracer studies combined with demographic statistical methods and new models hold the promise of improving our fundamental understanding of the factors controlling root turnover. Using minirhizotron data, fine root turnover (y⁻¹) can be estimated in two ways: as the ratio of annual root length production to average live root length observed and as the inverse of median root longevity. Fine root production and mortality can be estimated by combining data from minirhizotrons and soil cores, provided that these data are based on roots of the same diameter class (e.g., < 1 mm in diameter) and changes in the same time steps. Fluxes of carbon and nutrients via fine root mortality can then be estimated by multiplying the amount of carbon and nutrients in fine root biomass by fine root turnover. It is suggested that the minirhizotron method is suitable for estimating median fine root longevity. In comparison to the minirhizotron method, the radio carbon technique favor larger fine roots that are less dynamics. We need to reconcile and improve both methods to develop a more complete understanding of root turnover.     

细根分解研究及其存在的问题

细根分解是陆地生态系统C和养分循环的重要环节.主要包括淋溶和破碎等物理过程和以生物作用为主的化学过程.这些过程受复杂的细根化学成分及外部土壤因子的综合控制,如细根本身养分含量、木质素和纤维素含量、土壤温度、水分、养分的有效性以及土壤动物、真菌和细菌等.但是,细根分解发生在不能直接观测的地下部分,人为改变细根分解的自然环境是研究过程中存在的主要问题.埋袋法虽然应用最为普遍,但是它严重地干扰了细根分解环境,导致低估分解速率.最近提出的原状土芯法(intact-core)克服了埋袋法的主要缺陷,是目前细根分解研究中最接近自然分解过程的研究方法,但也存在一些问题.因此,如何设计有效且能够真实的反映细根自然分解过程的试验方法是今后该领域研究最重要和最具挑战性的课题.     

Nutrient Movement in Litter Fall and Precipitation Components for Central Himalayan Forests

The annual total litter fall in six Central Himalayan forestsranged from 2.1 to 3.8 t C ha^–1, of which 54 to 82 percent was leaf litter, 9–20 per cent wood litter and 6–14per cent other litter. In all forests the order of relativeabundance of nutrients (kg ha^-1 year^-1) in litter fall was Ca(50.8–91.6) > N (47.7–72.2) > K (22.8–37.1)> P (4.1–6.4). Leaf litter accounted for 63–95per cent of the total nutrients returned through litter fall. In these forests throughfall ranged from 71.3 to 81.4 per cent,stemflow from 0.50 to 2.16 per cent and canopy interceptionfrom 17.7 to 28.2 per cent of the gross rainfall. In the incidentrainfall the concentration and annual input of Ca was the greatestand of P the least. Canopy precipitation was richer in all nutrientscompared to incident rainfall. Net gain of nutrients from thecanopy ranged from 0.16 kg ha^-1 year^-1, for P, to 17.77 kg ha^-1year^-1 for K. Leaching was greatest for K and least for N. Ofthe total quantity of nutrients returned to the soil, 11 to46 per cent was accounted for by precipitation components. Thusprecipitation inputs play a significant role in nutrient cyclingof these forests. Himalaya, forest, litter fall, precipitation components, nutrients     

Spatial Distribution Patterns and Associations of Woody Plant Species in the Evergreen Broad-Leaved Forests in Central Vietnam

Biology Bulletin - The present study was conducted to elucidate the underlying processes that have maintained and promoted the coexistence of tropical forest tree species. Three 1-ha study plots...     

Central Amazon Floodplain Forests: Root Adaptations to Prolonged Flooding

The floodplains of Central Amazonia represent a complex system of inundated river valleys and shallow lakes along the Solimões–Amazonas river, which is subjected to an annual flood-pulse lasting up to 10 months. Such flooding reaching an amplitude of about ten meters causes dramatic changes in the bioavailability of nutrients and oxygen levels and poses extreme constraints for plant survival and reproductivity. Tree species of inundation forests in Central Amazonia had to evolve adaptive mechanisms to both desiccation of soils and partial or full submergence. To adapt to flooded conditions, some trees overcome the flood period by dormancy accompanied by defoliation and formation of annual rings in the wood. Other species maintain metabolism and retain the foliage during the flooding, representing another adaptive mechanism to low oxygen availability. This investigation focused on the root physiology and morphology of six species typical of white-water inundation areas (várzea) led to a preliminary classification of adaptive strategies of trees inhabiting forest communities in floodplains of the Amazon basin.     

缙云山常绿阔叶林的排序

排序概念由苏联学者拉孟斯基(1930)第一次提出并首先用环境梯度为坐标去排列植物群落。然而,这一方法在60年代电子计算技术的普遍应用和连续性学派(个体学派)兴旺发达起来以后,才迅速发展起来。排序是植物群落样本的一种空间排列,是揭示其空间连续变化的有效技术。至今方法很多,但一般分为两类,一类是用环境因子进行排列,称为直接排序,或称直接梯度分析,或者就叫梯度分析。另一类是用植物群落本身的特征(属性)来排序,称为间接排序,或间接     

泉州常绿阔叶林的特征与分布

泉州的常绿阔叶林包括南亚热带雨林和南亚热带山地照叶林。通过对这两种植被类型的区分成分、生活型、叶的性质以及群落的结构与分布的分析,说明海拔450m以下具有较明显的以厚壳桂、红楠等为优势种的南亚热带雨林的特征和景观;海拔450～900m主要以米槠等拷类为优势种的群落,但仍有南亚热带雨林的某些特征;海拔900～1400m以甜槠为主要建群种的群落,属于中亚热带照叶林的群落特征。     

Community Dynamics of Seed Rain in Mixed Evergreen Broad-leaved and Deciduous Forests in a Subtropical Mountain of Central China

Seed dispersal is a key process within community dynamics.The spatial and temporal variations of seed dispersal andthe interspecific differences are crucial for understanding species coexistence and community dynamics.This might alsohold for the mixed evergreen broadleaved and deciduous forests in the mountains of subtropical China,but until now littleexisting knowledge is available for this question.In 2001,we chose to monitor the seed rain process of our mixed evergreenbroad-leaved and deciduous forest communities in Mount Dalaoling National Forest Park,Yichang,Hubei Province,China.The preliminary analyses show obvious variations in seed rain density,species compositions and timing of seed rain amongfour communities.The average seed rain densities of the four communities are 2.43±5.15,54.13±182.75,10.05±19.30and 24.91±58.86 inds./m~2,respectively;about one tenth the values in other studies in subtropical forests of China.In eachcommunity,the seed production is dominated by a limited number of species,and the contributions from the others aregenerally minor.Fecundity of evergreen broadleaved tree species is weaker than deciduous species.The seed rain of fourcommunities begins earlier than September,and stops before December,peaking from early September to late October.The beginning date,ending date and peak times of seed rain are extensively varied among the species,indicating differenttypes of dispersal strategies.According to the existing data,the timing of seed rain is not determined by the climateconditions in the same period,while the density of seed rain may be affected by the disturbances of weather variations ata finer temporal resolution.     

Indirect Methods Produce Higher Estimates of Fine Root Production and Turnover Rates than Direct Methods

The production and turnover of fine roots play substantial roles in the biogeochemical cycles of terrestrial ecosystems. However, the disparity among the estimates of both production and turnover, particularly due to technical limitations, has been debated for several decades. Here, we conducted a meta-analysis to compare published estimates of fine root production and turnover rates derived from different methods at the same sites and at the same sampling time. On average, the estimates of fine root production and turnover rates were 87% and 124% higher, respectively, by indirect methods than by direct methods. The substantially higher fine root production and turnover estimated by indirect methods, on which most global carbon models are based, indicate the necessity of re-assessing the global carbon model predictions for atmospheric carbon sequestration in soils as a result of the production and turnover of fine roots.     

Biomass, Productivity and Energetics in Himalayan Alder Plantations

Biomass, net primary production and energy fixation in an agesequence of Himalayan alder (Alnus nepalensis D. Don) plantationswere estimated in the Kalimpong forest division of the easternHimalayas. Biomass in the plantations ranged from 106 t ha^–1(7-year stand) to 606 t ha^–1 (56-year stand) demonstratingthe potential of the alder for accumulating large biomass. Netprimary production and net energy fixation rates of the plantationswere reduced by nearly half in the 7-year stand (25 t ha^–1year^–1; 421 x 10⁶ kJ ha^–1 year^–1) comparedwith the 56-year stand (13 t ha^–1 year^–1; 215 x10⁶ kJ ha^–1 year^–1). Compartmental models of energystorage and flow rates were developed for the 7-year and 56-yearstands. The production efficiency, energy conversion efficiencyand energy efficiency in N₂ fixation have inverse relationshipswith plantation age. These efficiencies, when treated with eachother, showed significant exponential functions. Alnus nepalensis D. Don, Himalayan alder, plantation age, biomass, net primary production, energy flow, efficiencies     

Effects of Disturbance on Fine Root Dynamics in the Boreal Forests of Northern Ontario, Canada

Wildfire and clearcutting are two main disturbances in North American forests, but whether root systems may respond differently to such disturbances is unknown. Here, we studied how the dynamics of fine roots (<2 mm in diameter) varied with stand origins in a boreal forest in northern Ontario, Canada. Fine root biomass increased with stand age, but did not differ between stands originating from fire and clearcutting. By contrast, fine root production, mortality and turnover rates were lower in 3- and 11-year-old clearcut-origin than fire-origin stands, but did not differ in 29-year-old stands of different stand origins. The lower rates of production, mortality, and turnover rates in 3- and 11-year-old clearcut-origin than fire-origin stands are attributable to a lower density of shrubs and herbs and larger nutrient pools after clearcutting than fire. The similarities among 29-year-old stands indicate that the effects of stand origin on fine root processes tend to converge at this time scale. Our results illustrate that time scale is critical for assessing ecosystem responses to disturbances.     

Fine Root Production and Turnover in a Norway Spruce Stand in Northern Sweden: Effects of Nitrogen and Water Manipulation

Fine root length production, biomass production, and turnover in forest floor and mineral soil (0–30 cm) layers were studied in relation to irrigated (I) and irrigated-fertilized (IL) treatments in a Norway spruce stand in northern Sweden over a 2-year period. Fine roots (<1 mm) of both spruce and understory vegetation were studied. Minirhizotrons were used to estimate fine root length production and turnover, and soil cores were used to estimate standing biomass. Turnover was estimated as both the inverse of root longevity (RTL) and the ratio of annual root length production to observed root length (RTR). RTR values of spruce roots in the forest floor in I and IL plots were 0.6 and 0.5 y⁻¹, respectively, whereas the corresponding values for RTL were 0.8 and 0.9 y⁻¹. In mineral soil, corresponding values for I, IL, and control (C) plots were 1.2, 1.2, and 0.9 y⁻¹ (RTR) and 0.9, 1.1, and 1 y⁻¹ (RTL). RTR and RTL values of understory vegetation roots were 1 and 1.1 y⁻¹, respectively. Spruce root length production in both the forest floor and the mineral soil in I plots was higher than in IL plots. The IL-treated plots gave the highest estimates of spruce fine root biomass production in the forest floor, but, for the mineral soil, the estimates obtained for the I plots were the highest. The understory vegetation fine root production in the I and IL plots was similar for both the forest floor and the mineral soil and higher (for both layers) than in C plots. Nitrogen (N) turnover in the forest floor and mineral soil layers (summed) via spruce roots in IL, I, and C plots amounted to 2.4, 2.1, and 1.3 g N m⁻² y⁻¹, and the corresponding values for field vegetation roots were 0.6, 0.5, and 0.3 g N m⁻² y⁻¹. It was concluded that fertilization increases standing root biomass, root production, and N turnover of spruce roots in both the forest floor and mineral soil. Data on understory vegetation roots are required for estimating carbon budgets in model studies.     

Root Architecture and Root:Shoot Allocation of Shrubs and Saplings in Two Lowland Tropical Forests: Implications for Life-Form Composition1

Entire root systems of saplings of five canopy species and of six shrub and treelet species growing in lowland mixed dipterocarp forest at Andulau, Brunei were excavated and measured. Referring to a prior study at Gigante, Panama, two-way, fixed-factor ANOVAs were used to compare life–forms and sites. Rooting depth and the proportion of root surface area in the upper 20 cm of soil did not differ significantly between life-forms because some treelets/shrubs at Andulau were deep-rooted; all saplings studied were deep-rooted. The root:leaf area ratios of both saplings and treelets/ shrubs at Andulau were significantly higher than those at Gigante. We attribute this strong difference to the lower soil content of available nutrients at Andulau where rainfall shortage is less severe and regular than at Gigante. Available data on life-form composition and mortality rates in large plots are consistent with our proposal that shallow-rooted shrubs and treelets are more vulnerable to drought than deep-rooted life-forms. We suggest that future studies of water use partitioning, wood anatomy, leaf morphology, and associations with neighboring plants would benefit from an explicit examination of their relation to rooting depth.     

Large-Scale Patterns of Turnover and Basal Area Change in Andean Forests

General patterns of forest dynamics and productivity in the Andes Mountains are poorly characterized. Here we present the first large-scale study of Andean forest dynamics using a set of 63 permanent forest plots assembled over the past two decades. In the North-Central Andes tree turnover (mortality and recruitment) and tree growth declined with increasing elevation and decreasing temperature. In addition, basal area increased in Lower Montane Moist Forests but did not change in Higher Montane Humid Forests. However, at higher elevations the lack of net basal area change and excess of mortality over recruitment suggests negative environmental impacts. In North-Western Argentina, forest dynamics appear to be influenced by land use history in addition to environmental variation. Taken together, our results indicate that combinations of abiotic and biotic factors that vary across elevation gradients are important determinants of tree turnover and productivity in the Andes. More extensive and longer-term monitoring and analyses of forest dynamics in permanent plots will be necessary to understand how demographic processes and woody biomass are responding to changing environmental conditions along elevation gradients through this century.     

Different Relationships between Temporal Phylogenetic Turnover and Phylogenetic Similarity and in Two Forests Were Detected by a New Null Model

Background

Ecologists have been monitoring community dynamics with the purpose of understanding the rates and causes of community change. However, there is a lack of monitoring of community dynamics from the perspective of phylogeny.

Methods/Principle Findings

We attempted to understand temporal phylogenetic turnover in a 50 ha tropical forest (Barro Colorado Island, BCI) and a 20 ha subtropical forest (Dinghushan in southern China, DHS). To obtain temporal phylogenetic turnover under random conditions, two null models were used. The first shuffled names of species that are widely used in community phylogenetic analyses. The second simulated demographic processes with careful consideration on the variation in dispersal ability among species and the variations in mortality both among species and among size classes. With the two models, we tested the relationships between temporal phylogenetic turnover and phylogenetic similarity at different spatial scales in the two forests. Results were more consistent with previous findings using the second null model suggesting that the second null model is more appropriate for our purposes. With the second null model, a significantly positive relationship was detected between phylogenetic turnover and phylogenetic similarity in BCI at a 10 m×10 m scale, potentially indicating phylogenetic density dependence. This relationship in DHS was significantly negative at three of five spatial scales. This could indicate abiotic filtering processes for community assembly. Using variation partitioning, we found phylogenetic similarity contributed to variation in temporal phylogenetic turnover in the DHS plot but not in BCI plot.

Conclusions/Significance

The mechanisms for community assembly in BCI and DHS vary from phylogenetic perspective. Only the second null model detected this difference indicating the importance of choosing a proper null model.     

无量山半湿润常绿阔叶林的区系特征及保护生物学意义

无量山半湿润常绿阔叶林是其垂直带上重要的植被类型,目前面临被彻底毁灭的危险,从这类森林及相应地段的177种优势和常见植物的种类结构分析看,只有热带亚洲的成分,东亚中的中国－喜马拉雅成分和中国特有成分贯穿乔木A,B,C层,灌木层,草本和层外植物几大类中,而中国特有种的进一步分析表明了它的区系成分的亚热带性质,温带性质不是很显著,在无量半山湿润常绿阔叶林地段,还存在一些原生植被破坏后产生的次生落叶阔叶加以保护,因之有这么多的特点,加之其为重要特有类群和保护种类聚集的场所,该类植被明显具有不同层次的保护生物学意义。     

Ground Layer Plant Species Turnover and Beta Diversity in Southern-European Old-Growth Forests

Different assembly processes may simultaneously affect local-scale variation of species composition in temperate old-growth forests. Ground layer species diversity reflects chance colonization and persistence of low-dispersal species, as well as fine-scale environmental heterogeneity. The latter depends on both purely abiotic factors, such as soil properties and topography, and factors primarily determined by overstorey structure, such as light availability. Understanding the degree to which plant diversity in old-growth forests is associated with structural heterogeneity and/or to dispersal limitation will help assessing the effectiveness of silvicultural practices that recreate old-growth patterns and structures for the conservation or restoration of plant diversity. We used a nested sampling design to assess fine-scale species turnover, i.e. the proportion of species composition that changes among sampling units, across 11 beech-dominated old-growth forests in Southern Europe. For each stand, we also measured a wide range of environmental and structural variables that might explain ground layer species turnover. Our aim was to quantify the relative importance of dispersal limitation in comparison to that of stand structural heterogeneity while controlling for other sources of environmental heterogeneity. For this purpose, we used multiple regression on distance matrices at the within-stand extent, and mixed effect models at the extent of the whole dataset. Species turnover was best predicted by structural and environmental heterogeneity, especially by differences in light availability and in topsoil nutrient concentration and texture. Spatial distances were significant only in four out of eleven stands with a relatively low explanatory power. This suggests that structural heterogeneity is a more important driver of local-scale ground layer species turnover than dispersal limitation in southern European old-growth beech forests.     

Root Morphology, Stem Growth and Field Performance of Seedlings of Two Mediterranean Evergreen Oak Species Raised in Different Container Types

Outplanting container-grown oak seedlings with undesirable shoot and root characteristics result in poor establishment and reduced field growth. The objective of this study was to determine the influence of container type on both above-and below-ground nursery growth and field performance of one-year old tap-rooted seedlings Quercus ilex L. and Quercus coccifera L. The experiment was conducted in an open-air nursery and the seedlings were grown in three container types. At the end of the nursery, growth period seedlings’ shoot height, diameter (5 mm above root collar), shoot and root biomass, root surface area, root volume and total root length were assessed. Then the seedlings were planted in the field and their survival and growth were recorded for two growing seasons after outplanting. The results showed a difference between the Quercus species in the effect of container type. Q. ilex seedlings raised in paper-pot had significantly greater height, diameter, shoot and root biomass and root volume than those raised in the other two container types. Similarly, Q. coccifera seedlings raised in paper-pot, had significantly greater above-and below-ground growth than those raised in the other two container types. Both oak species showed relatively low survival in the field; the mortality was mainly observed the first year after outplanting, especially after the summer dry period. However, 2 years after outplanting, the paper-pot seedlings of the two oak species showed better field performance.