Increased forest carbon storage with increased atmospheric CO2 despite nitrogen limitation: a game‐theoretic allocation model for trees in competition for nitrogen and light

Changes in resource availability often cause competitively driven changes in tree allocation to foliage, wood, and fine roots, either via plastic changes within individuals or through turnover of individuals with differing strategies. Here, we investigate how optimally competitive tree allocation should change in response to elevated atmospheric CO₂ along a gradient of nitrogen and light availability, together with how those changes should affect carbon storage in living biomass. We present a physiologically‐based forest model that includes the primary functions of wood and nitrogen. From a tree's perspective, wood is an offensive and defensive weapon used against neighbors in competition for light. From a biogeochemical perspective, wood is the primary living reservoir of stored carbon. Nitrogen constitutes a tree's photosynthetic machinery and the support systems for that machinery, and its limited availability thus reduces a tree's ability to fix carbon. This model has been previously successful in predicting allocation to foliage, wood, and fine roots along natural productivity gradients. Using game theory, we solve the model for competitively optimal foliage, wood, and fine root allocation strategies for trees in competition for nitrogen and light as a function of CO₂ and nitrogen mineralization rate. Instead of down‐regulating under nitrogen limitation, carbon storage under elevated CO₂ relative to carbon storage at ambient CO₂ is approximately independent of the nitrogen mineralization rate. This surprising prediction is a consequence of both increased competition for nitrogen driving increased fine root biomass and increased competition for light driving increased allocation to wood under elevated CO₂.     

Response of fine roots to an experimental gap in a boreal Picea abies forest

We examined the initial response of the quantity and distribution of fine roots to the creation of an experimental canopy gap with a diameter of 50 m in a mature managed Norway spruce forest. Under the canopy, the fine root length densities of trees, shrubs, and grasses and herbs were 3207, 707 and 2738 m m^–2, respectively. The fine root biomass of trees, shrubs, and grasses and herbs were 182, 47 and 52 g m^–2, respectively. Two growing seasons after gap creation hardly any fine tree roots were found in the middle part of the gap. The living tree roots in the gap edge zone were mainly located within a 5-m distance from the standing edge trees. The indices developed here to show the influence of trees on fine root lenght density clearly revealed the effect of the vicinity of living trees on fine root lenght density. The root densities of grasses, herbs and dwarf shrubs did not show a clear response to gap creation despite the increase of their foliage. Our results suggest that in boreal spruce forests a gap disturbance creates a distinct tree root gap and that the gap edge trees do not extend their root systems rapidly into the formed root gap.     

常绿阔叶林外生和丛枝菌根树种细根形态和构型性状对氮添加的可塑性响应

以中亚热带常绿阔叶林外生菌根树种罗浮栲和丛枝菌根树种木荷为研究对象,采用根袋法进行野外原位氮添加试验,研究了细根形态性状(比根长、比表面积、组织密度、平均根直径)和构型性状(分枝数、分枝比、根长增长速率、根尖密度、分枝密度),分析不同菌根树种细根形态和构型性状对氮沉降的响应.结果表明:随序级增加,外生和丛枝菌根树种细根...     

Green islands — predation not nutrition

Summary The existence of green islands around wood-ant nests in otherwise damaged birch forests has been explained by two alternative hypotheses: (1) predation by ants protects the trees against defoliators, and (2) the ants ameliorate tree vigor by concentrating soil nutrients. The size of green islands and the nitrogen content of the soil and foliage do not support the nutrition hypothesis. These data and general knowledge about the foraging strategy of wood ants are consistent with the predation hypothesis.     

Optimal co-allocation of carbon and nitrogen in a forest stand at steady state

Nitrogen (N) is essential for plant production, but N uptake imposes carbon (C) costs through maintenance respiration and fine-root construction, suggesting that an optimal C:N balance can be found. Previous studies have elaborated this optimum under exponential growth; work on closed canopies has focused on foliage only. Here, the optimal co-allocation of C and N to foliage, fine roots and live wood is examined in a closed forest stand. Optimal co-allocation maximizes net primary productivity (NPP) as constrained by stand-level C and N balances and the pipe model. Photosynthesis and maintenance respiration increase with foliar nitrogen concentration ([N]), and stand-level photosynthesis and N uptake saturate at high foliage and fine-root density. Optimal NPP increases almost linearly from low to moderate N availability, saturating at high N. Where N availability is very low or very high, the system resembles a functional balance with a steady foliage [N]; in between, [N] increases with N availability. Carbon allocation to fine roots decreases, allocation to wood increases, and allocation to foliage remains stable with increasing N availability. The predicted relationships between biomass density and foliage [N] are in reasonable agreement with data from coniferous stands across Finland. All predictions agree with our qualitative understanding of N effects on growth.     

核桃-小麦复合系统中细根生长动态及竞争策略

以核桃(Juglans regia)-小麦(Triticum aestivum)间作复合系统为研究对象,用微根窗和根钻相结合的方法采样,研究复合系统中核桃和小麦细根年内年际的生长动态和竞争适应策略,为农林复合系统的经营管理和竞争模型的建立提供理论依据和技术支持。结果表明,间作核桃和小麦根系均在上半年有一个大的生长高峰(5月和4月),在下半年有一个小的生长高峰(9月和11月),二者的竞争主要发生在上半年的大生长高峰期。在各年份各土层,间作核桃的根长密度均低于单作核桃,且在从第7年开始存在显著差异。在0—20 cm土层间作小麦根长密度在第3—7年间获得迅速提高,从第7年开始显著高于单作小麦,但在20 cm以下土层则相反。间作使核桃和小麦细根生态位实现了分离,11年的观察期内间作核桃比单作核桃细根的垂直分布中心下移了6.59 cm,间作小麦比单作小麦的上移了8.59 cm。在根系竞争策略方面,小麦根系是通过短期内的快速生长,迅速占据土壤空间获得竞争优势;而核桃根系是通过根系的逐年积累,逐步占据土壤空间从而获得竞争优势。可以干扰核桃根系积累过程的"竞争-干扰-再平衡"农林复合经营管理策略可以让复合系统中核桃和小麦保持各自竞争优势的情况下实现共存。在根系形态方面,自身细根直径较小者小麦在剧烈竞争区域以增加细根直径减小比根长来适应竞争,而自身细根直径较大者核桃则相反。     

Growth,nutrition and gas exchange of Pinus resinosa following artificial defoliation

Summary In three experiments, red pine (Pinus resinosa Ait.) seedlings and trees were subjected to artificial defoliations of varying intensities and subsequent growth, gas exchange and nutritional responses were monitored. In Experiment 1, 2-year-old seedlings received 0, 1 or 2 50% defoliations during a single growing season and were maintained in 1 of 3 low nutrient supply treatments. In Experiment 2, response of 4-year-old seedlings was monitored in the year following 0, 25, 50 or 75% defoliation, while in Experiment 3, response of 11-year-old trees was measured 1 year after being defoliated by 0, 33 or 66%. Regardless of intensity of defoliation, or plant size, clipped plants made qualitatively similar allocational and metabolic adjustments over time. First, leaf diffusive conductance and rates of net photosynthesis were stimulated, especially by light to intermediate defoliation. However, there was no effect of defoliation on foliar nitrogen concentration, and elevated gas exchange rates apparently resulted from altered root-shoot dynamics. Second, allocation of new biomass was preferentially shifted towards foliage at the expense of roots, gradually restoring (but undershooting or overshooting) the ratio of foliage: roots of control plants. During the period when foliage: root balance was being restored, the stimulation of needle gas exchange rates disappeared. Plants defoliated by 25% overcompensated in terms of whole plant growth (were larger at harvest than controls), due to shifts in allocation and enhanced photosynthesis. Defoliated plants also stored a proportionally greater share of their carbohydrate reserves in roots than did control plants, even 1 year after clipping.     

The vertical distribution of N and K uptake in relation to root distribution and root uptake capacity in mature Quercus robur, Fagus sylvatica and Picea abies stands

We have measured the uptake capacity of nitrogen (N) and potassium (K) from different soil depths by injecting ¹⁵N and caesium (Cs; as an analogue to K) at 5 and 50 cm soil depth and analysing the recovery of these markers in foliage and buds. The study was performed in monocultures of 40-year-old pedunculate oak (Quercus robur), European beech (Fagus sylvatica) and Norway spruce (Picea abies (L.) Karst.) located at an experimental site in Palsgård, Denmark. The markers were injected as a solution through plastic tubes around 20 trees of each species at either 5 or 50 cm soil depth in June 2003. After 65 days foliage and buds were harvested and the concentrations of ¹⁵N and Cs analysed. The recovery of ¹⁵N in the foliage and buds tended to be higher from 5 than 50 cm soil depth in oak whereas they where similar in spruce and beech after compensation for differences in immobilization of ¹⁵N in the soil. In oak more Cs was recovered from 5 than from 50 cm soil depth whereas in beech and spruce no difference could be detected. Out of the three investigated tree species, oak was found to have the lowest capacity to take up Cs at 50 cm soil depth compared to 5 cm soil depth also after compensating for differences in discrimination against Cs by the roots. The uptake capacity from 50 cm soil depth compared with 5 cm was higher than expected from the root distribution except for K in oak, which can probably be explained by a considerable overlap of the uptake zones around the roots and mycorrhizal hyphae in the topsoil. The study also shows that fine roots at different soil depths with different physiological properties can influence the nutrient uptake of trees. Estimates of fine root distribution alone may thus not reflect the nutrient uptake capacity of trees with sufficient accuracy. Our study shows that deep-rooted trees such as oak may have lower nutrient uptake capacity at deeper soil layers than more shallow-rooted trees such as spruce, as we found no evidence that deep-rooted trees obtained proportionally more nutrients from deeper soil layers. This has implications for models of nutrient cycling in forest ecosystems that use the distribution of roots as the sole criterion for predicting uptake of nutrients from different soil depths.     

Tannin,nitrogen, and cell wall composition of green vs. senescent Douglas-fir foliage

Summary Tannin, cell wall, and nitrogen composition of green foliage and needle litter of similar-aged Douglas-fir (Pseudotsuga menziesii Mirb. Franco) from two stands differing in density and crown closure were compared. Trees in the closed-canopy stand had a lower basal area growth rate than those in the open-canopy stand. Stands did not differ in wood basal area/ha or forest floor C/N ratios, but the closed-canopy stand had a significantly larger accumulation of forest floor biomass and significantly higher levels of field-extractable nitrogen and nitrogen mineralization rates. Green foliage from trees in the closed-canopy stand had significantly lower nitrogen, astringency, and lignin contents, but higher cellulose concentration than trees in the open-canopy stand. These trends, inconsistent with the inverse relationship often observed between nitrogen and polyphenol contents of foliage, may result from differences in relative resource availability in the two stands. In contrast to green foliage, needle litter from the two stands had comparable contents of nitrogen, cellulose, and lignin, but astringency was significantly higher in litter from the closed-canopy stand. It is suggested that, within the constraints imposed by site conditions, evergreens may alter the tannin composition of senescing foliage, potentially affecting herbivory and decomposition differently.     

Foliage phenols and nitrogen in relation to growth,insect damage,and ability to recover after defoliation,in the mountain birch Betula pubescens ssp tortuosa

We studied growth of the mountain birch, and the role of foliage phenols, nitrogen, and variance in the timing of bud burst, as potential defensive characters, in Finnish Lapland in 1975–1979. Annual and local variation both in phenol and nitrogen concentration of foliage were significant. Individual trees retained their position in the foliage and nitrogen distribution of the population in successive years, as well as in the order of leaf flush in spring. Growth of twigs, mature leaf size, and ability of trees to recover in the year following artificial defoliation correlated positively with the sum of degree days in the previous growing season. Foliage nitrogen correlated negatively with foliage phenols in within-site comparisons. Twig growth correlated negatively with foliage phenols, particularly in growing seasons following cool summers, but did not correlate with foliage nitrogen. Birches flushing early did not grow more than birches flushing late. Between-site differences in foliage phenol content were mainly determined by abiotic conditions, like temperature and nutrient availability. In a between-site comparison insect chewing marks in leaves correlated positively with foliage phenols as well as with nitrogen; intensity of invertebrate predation presumably explained variable herbivory between the sites. In a within-site comparison trees with the highest foliage phenol content had few herbivores only at the site with the highest average phenol level.     

A Model for Individual Tree Development Based on Physiological Processes

Abstract: A tree growth model is presented which calculates the 3D development of trees and stands in dependence on their individual carbon, water and nitrogen balance. The availability of energy, soil water and nutrients is estimated from field data at the scale of crown and root system fractions, taking into account the individual neighbourhood. The model includes a simple estimation of radiation distribution and the simulation of carbon and nutrient exchange. Senescence is represented by compartment-specific turnover rates. Allocation of carbon and nitrogen into foliage, fine roots, branches, coarse roots, and the stem is calculated according to functional balance and pipe model principles. Dimensional changes are calculated annually according to the distribution of net assimilation. The model describes tree development as a response to individual environmental conditions and changes environmental conditions with individual tree development. Due to this feedback loop, environmental influences can be assessed in any kind of species mixture or stand structure. Furthermore, the physiological-based approach ensures that the model can be used for investigations of complex environmental changes, e.g. CO₂ concentration, precipitation, temperature and nitrogen deposition. Thus, it is particularly suitable to analyse field investigations and to support the cognition process on the ecology of forests. It could also be used, however, to estimate forest responses to given environmental scenarios.     

Wood production response to climate change will depend critically on forest composition and structure

Established forests currently function as a major carbon sink, sequestering as woody biomass about 26% of global fossil fuel emissions. Whether forests continue to act as a global sink will depend on many factors, including the response of aboveground wood production (AWP; MgC ha^?1 yr^?1) to climate change. Here, we explore how AWP in New Zealand's natural forests is likely to change. We start by statistically modelling the present‐day growth of 97 199 individual trees within 1070 permanently marked inventory plots as a function of tree size, competitive neighbourhood and climate. We then use these growth models to identify the factors that most influence present‐day AWP and to predict responses to medium‐term climate change under different assumptions. We find that if the composition and structure of New Zealand's forests were to remain unchanged over the next 30 years, then AWP would increase by 6–23%, primarily as a result of physiological responses to warmer temperatures (with no appreciable effect of changing rainfall). However, if warmth‐requiring trees were able to migrate into currently cooler areas and if denser canopies were able to form, then a different AWP response is likely: forests growing in the cool mountain environments would show a 30% increase in AWP, while those in the lowland would hardly respond (on average, ?3% when mean annual temperature exceeds 8.0 °C). We conclude that response of wood production to anthropogenic climate change is not only dependent on the physiological responses of individual trees, but is highly contingent on whether forests adjust in composition and structure.     

Plant allocation of carbon to defense as a function of herbivory,light and nutrient availability

We use modeling to determine the optimal relative plant carbon allocations between foliage, fine roots, anti-herbivore defense, and reproduction to maximize reproductive output. The model treats these plant components and the herbivore compartment as variables. Herbivory is assumed to be purely folivory. Key external factors include nutrient availability, degree of shading, and intensity of herbivory. Three alternative functional responses are used for herbivory, two of which are variations on donor-dependent herbivore (models 1a and 1b) and one of which is a Lotka–Volterra type of interaction (model 2). All three were modified to include the negative effect of chemical defenses on the herbivore. Analysis showed that, for all three models, two stable equilibria could occur, which differs from most common functional responses when no plant defense component is included. Optimal strategies of carbon allocation were defined as the maximum biomass of reproductive propagules produced per unit time, and found to vary with changes in external factors. Increased intensity of herbivory always led to an increase in the fractional allocation of carbon to defense. Decreases in available limiting nutrient generally led to increasing importance of defense. Decreases in available light had little effect on defense but led to increased allocation to foliage. Decreases in limiting nutrient and available light led to decreases in allocation to reproduction in models 1a and 1b but not model 2. Increases in allocation to plant defense were usually accompanied by shifts in carbon allocation away from fine roots, possibly because higher plant defense reduced the loss of nutrients to herbivory.     

Seasonal respiration of foliage, fine roots, and woody tissues in relation to growth, tissue N, and photosynthesis

Autotrophic respiration may regulate how ecosystem productivity responds to changes in temperature, atmospheric [CO₂] and N deposition. Estimates of autotrophic respiration are difficult for forest ecosystems, because of the large amount of biomass, different metabolic rates among tissues, and seasonal variation in respiration rates. We examined spatial and seasonal patterns in autotrophic respiration in a Pinus strobus ecosystem, and hypothesized that seasonal patterns in respiration rates at a common temperature would vary with [N] for fully expanded foliage and fine roots, with photosynthesis for foliage, and with growth for woody tissues (stems, branches, and coarse roots). We also hypothesized that differences in [N] would largely explain differences in maintenance or dormant‐season respiration among tissues. For April–November, mean respiration at 15 °C varied from 1.5 to 2.8 μmol kg^?1 s^?1 for fully expanded foliage, 1.7–3.0 for growing foliage, 0.8–1.6 for fine roots, 0.6–1.1 (sapwood) for stems, 0.5–1.8 (sapwood) for branches, and 0.2–1.5 (sapwood) for coarse roots. Growing season variation in respiration for foliage produced the prior year was strongly related to [N] (r² = 0.94), but fine root respiration was not related to [N]. For current‐year needles, respiration did not covary with [N]. Night‐time foliar respiration did not vary in concert with previous‐day photosynthesis for either growing or fully expanded needles. Stem growth explained about one‐third of the seasonal variation in stem respiration (r² = 0.38), and also variation among trees (r² = 0.43). We did not determine the cause of seasonal variation in branch and coarse root respiration, but it is unlikely to be directly related to growth, as the pattern of respiration in coarse roots and branches was not synchronized with stem growth. Seasonal variations in temperature‐corrected respiration rates were not synchronized among tissues, except foliage and branches. Spatial variability in dormant‐season respiration rates was significantly related to tissue N content in foliage (r² = 0.67), stems (r² = 0.45), coarse roots (r² = 0.36), and all tissues combined (r² = 0.83), but not for fine roots and branches. Per unit N, rates for P. strobus varied from 0.22 to 3.4 μmol molN^?1 s^?1 at 15 °C, comparable to those found for other conifers. Accurate estimates of annual autotrophic respiration should reflect seasonal and spatial variation in respiration rates of individual tissues.     

A Transport-resistance Model of Forest Growth and Partitioning

The transport-resistance approach to dry-matter partitioningis used to construct a model of forest growth The model is atthe stand level for a monoculture of identical trees of thesame age There are five major organ compartments in the modelfoliage, branches, stem, coarse roots, and fine roots and mycorrhizasThe matter in each compartment is further subdivided into menstem,structure, carbon substrate, and nitrogen substrate The modelis driven by daily radiation including day length, ambient CO₂concentration, and daily means of air and soil temperature Thefine roots are provided with constant values of soil mineralnitrogen pools (ammonium and nitrate) from which uptake occursGrowth over about 100 years is simulated for various environmentalconditions and soil mineral nitrogen levels, thinning is alsosimulated Natural tree death occurs within the model Particularattention is paid to dry matter partitioning patterns, and tothe dry matter per stem when death occurs The model is robustand responsive, and provides a framework for further developmentand application to many ecological and environmental scenarios,as well as to some forest management problems Model, forest, growth, partitioning     

What controls variation in carbon use efficiency among Amazonian tropical forests?

Why do some forests produce biomass more efficiently than others? Variations in Carbon Use Efficiency (CUE: total Net Primary Production (NPP)/ Gross Primary Production (GPP)) may be due to changes in wood residence time (Biomass/NPP_wood), temperature, or soil nutrient status. We tested these hypotheses in 14, one ha plots across Amazonian and Andean forests where we measured most key components of net primary production (NPP: wood, fine roots, and leaves) and autotrophic respiration (R_a; wood, rhizosphere, and leaf respiration). We found that lower fertility sites were less efficient at producing biomass and had higher rhizosphere respiration, indicating increased carbon allocation to belowground components. We then compared wood respiration to wood growth and rhizosphere respiration to fine root growth and found that forests with residence times <40 yrs had significantly lower maintenance respiration for both wood and fine roots than forests with residence times >40 yrs. A comparison of rhizosphere respiration to fine root growth showed that rhizosphere growth respiration was significantly greater at low fertility sites. Overall, we found that Amazonian forests produce biomass less efficiently in stands with residence times >40 yrs and in stands with lower fertility, but changes to long‐term mean annual temperatures do not impact CUE.     

Forest microsite effects on community composition of ectomycorrhizal fungi on seedlings of Picea abies and Betula pendula

Niche differentiation in soil horizons, host species and natural nutrient gradients contribute to the high diversity of ectomycorrhizal fungi in boreal forests. This study aims at documenting the diversity and community composition of ectomycorrhizal fungi of Norway spruce ( Picea abies ) and silver birch ( Betula pendula ) seedlings in five most abundant microsites in three Estonian old-growth forests. Undisturbed forest floor, windthrow mounds and pits harboured more species than brown- and white-rotted wood. Several species of ectomycorrhizal fungi were differentially represented on either hosts, microsites and sites. Generally, the most frequent species in dead wood were also common in forest floor soil. Ordination analyses suggested that decay type determined the composition of EcM fungal community in dead wood. Root connections with in-growing mature tree roots from below affected the occurrence of certain fungal species on seedling roots systems in dead wood. This study demonstrates that ectomycorrhizal fungi differentially establish in certain forest microsites that is attributable to their dispersal and competitive abilities. Elevated microsites, especially decayed wood, act as seed beds for both ectomycorrhizal forest trees and fungi, thus affecting the succession of boreal forest ecosystems.     

Impact of balsam fir flowering on pollen and foliage biochemistry in relation to spruce budworm growth, development and food utilization

The impact of balsam fir (Abies balsamea (L.) Miller) flowering on nutritional and allelochemical quality of pollen, current-year and one-year-old foliage is studied in relation to spruce budworm (Choristoneura fumiferana Clem.) (Lepidoptera: Tortricidae) growth, development and utilization of food and nitrogen. In the laboratory, using fresh food from the field, we simulated conditions of low larval population density, in which there is no current-year foliage depletion during the spruce budworm feeding period. Similarly, we simulated conditions of high larval population density when current-year foliage depletion occurs.Because of the high nutritive value of pollen (high amounts of amino acids and minerals, especially nitrogen; low monoterpene content), insects from flowering trees reached the fifth instar five days earlier than those from non-flowering trees, and had heavier dry- and nitrogen-weights at the beginning of the fifth instar. At budbreak, switching from pollen to current-year foliage negatively affected conversion efficiencies and digestibilities of food and nitrogen (AD; ADN; ECDN; ECI; ECIN). The switch from pollen to new foliage had a detrimental impact on fifth-instar survival and on newly-moulted sixth-instar dry- and nitrogen-weights. Moreover, during the fifth instar, balsam fir flowering reduced the nutritive value of current-year foliage, which in turn, might have contributed to the reduced larval growth. Nevertheless, during the sixth instar, balsam fir flowering affected the biochemistry of current-year foliage in ways that enabled larvae to compensate for their low fifth-instar biological performance; larvae also managed to reach pupal dry weight similar to larvae reared on non-flowering trees. Current-year foliage from flowering trees contained less nitrogen, total soluble sugars and total monoterpenes. Those foliar characteristics enabled larvae to increase food and nitrogen consumption rates (RCR; RNCR), because of lower repellency and/or post-ingestional feedback from monoterpenes.As for current-year foliage, balsam fir flowering reduced nitrogen, total soluble sugar and total monoterpene contents in one-year-old foliage during the sixth-instar feeding period. These characteristics enabled sixth-instar larvae, fed on old foliage from flowering trees, to have high relative food and nitrogen consumption rates (RCR; RNCR). Larvae were also able to reach higher relative growth rates (RGR) and relative nitrogen accumulation rates (RNAR) compared to larvae reared on one-year-old foliage from non-flowering trees. Finally, larvae on flowering trees had pupal dry weight similar to those from non-flowering trees, but reached the adult stage nine days earlier.Regardless the foliage type consumed by spruce budworm larvae during the sixth instar, pollen consumption during early larval stages reduced total development time, and thus exposure time to natural enemies. This phenomenon might increase larval survival. Balsam fir flowering changed the biochemistry of one-year-old and current-year foliages, but did not affect pupal dry weights of larvae reared on flowering trees compared to those reared on non-flowering trees. Thus, at low population density, spruce budworm populations in balsam fir flowering stands might be favoured over those in balsam fir non-flowering stands. In addition, when larvae consumed one-year-old foliage during the entire sixth instar, those on flowering trees are probably favoured over those on non-flowering trees. However, because flowering trees produce less new foliage than non-flowering trees, current-year foliage depletion may occur earlier on flowering trees than on non-flowering trees. Thus, at similar larval population density, larvae on flowering trees might have to feed on one-year-old foliage earlier than those on non-flowering trees. In that case, spruce budworm populations on non-flowering stands would be favoured over those on flowering stands.     

亚热带天然常绿阔叶林林下9种灌木细根形态和C、N化学计量特征

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