Allometric scaling relationship between above‐ and below‐ground biomass within and across five woody seedlings

Allometric biomass allocation theory predicts that leaf biomass (M_L) scaled isometrically with stem (M_S) and root (M_R) biomass, and thus above‐ground biomass (leaf and stem) (M_A) and root (M_R) scaled nearly isometrically with below‐ground biomass (root) for tree seedlings across a wide diversity of taxa. Furthermore, prior studies also imply that scaling constant should vary with species. However, litter is known about whether such invariant isometric scaling exponents hold for intraspecific biomass allocation, and how variation in scaling constants influences the interspecific scaling relationship between above‐ and below‐ground biomass. Biomass data of seedlings from five evergreen species were examined to test scaling relationships among biomass components across and within species. Model Type II regression was used to compare the numerical values of scaling exponents and constants among leaf, stem, root, and above‐ to below‐ground biomass. The results indicated that M_L and M_S scaled in an isometric or a nearly isometric manner with M_R, as well as M_A to M_R for five woody species. Significant variation was observed in the Y‐intercepts of the biomass scaling curves, resulting in the divergence for intraspecific scaling and interspecific scaling relationships for M_L versus M_S and M_L versus M_R, but not for M_S versus M_R and M_A versus M_R. We conclude, therefore, that a nearly isometric scaling relationship of M_A versus M_R holds true within each of the studied woody species and across them irrespective the negative scaling relationship between leaf and stem.     

Biomass partitioning pattern of Rheum tanguticum on the Qinghai–Tibet Plateau was affected by water-related factors

To identify the patterns of aboveground biomass (M_A) and belowground biomass (M_B) partitioning of a tall perennial herbal plant, Rheum tanguticum Maxim. ex Balf. (R. tanguticum), we determined M_A, M_B, total biomass (M_T), and below- to aboveground biomass ratio (M_B/M_A) through three consecutive sampling campaigns during 2016–2018 on the Qinghai-Tibetan plateau. We then documented M_A, M_B, M_T, and M_B/M_A, and their log–log relationship with environmental factors using data from 47 sites. M_B/M_A showed a significant negative relationship with mean annual precipitation (MAP) and altitude but a positive relationship with mean annual temperature (MAT), soil total nitrogen content (TN), and soil humidity (SH). While M_T increased with altitude and decreased with MAT, TN, and SH, but the relationship between MAP and M_T was not significant. Reduced major axis analysis revealed a slope of the log–log relationship between M_A and M_B to be 1.16, supporting an allometric partitioning pattern of R. tanguticum. Furthermore, the scaling exponent revealed different changes to different environmental factors. Specifically, scaling exponent was sensitive to the gradient of MAP and SH, but not to the gradient of altitude, MAT, or TN. This indicated that the scaling exponent was affected by water availability.

     

Scaling relationship between tree respiration rates and biomass

The WBE theory proposed by West, Brown and Enquist predicts that larger plant respiration rate, R, scales to the three-quarters power of body size, M. However, studies on the R versus M relationship for larger plants (i.e. trees larger than saplings) have not been reported. Published respiration rates of field-grown trees (saplings and larger trees) were examined to test this relationship. Our results showed that for larger trees, aboveground respiration rates R_A scaled as the 0.82-power of aboveground biomass M_A, and that total respiration rates R_T scaled as the 0.85-power of total biomass M_T, both of which significantly deviated from the three-quarters scaling law predicted by the WBE theory, and which agreed with 0.81–0.84-power scaling of biomass to respiration across the full range of measured tree sizes for an independent dataset reported by Reich et al. (Reich et al. 2006 Nature 439, 457–461). By contrast, R scaled nearly isometrically with M in saplings. We contend that the scaling exponent of plant metabolism is close to unity for saplings and decreases (but is significantly larger than three-quarters) as trees grow, implying that there is no universal metabolic scaling in plants.     

Stem, branch and leaf biomass-density relationships in forest communities

Defining and quantifying biomass?Cdensity relationships in dense plant stands has been a long-standing issue in both theoretical and empirical studies. Most existing/traditional studies focus on whole plant individuals, without considering different plant components (e.g., stem, branch and leaf). However, the analysis of biomass?Cdensity relationships for different plant parts is linked to those for whole plants, and thus important for understanding plant strategies for utilizing resources and community dynamics. In our study, we investigated standing stem (M _S), branch (M _B) and leaf (M _L) biomass?Cdensity relationships, across a range of forest communities in China. The results showed that there was no constant predicted value (e.g., ?1/2 or ?1/3 for M _S; ?1/2, ?1/3 or 0 for M _B and M _L) that can describe all the relationships, and that the scaling exponents for stem, branch and leaf biomass varied across different forest types. In particular, standing leaf biomass (leaf biomass per unit area) was not constant in these forest communities. Furthermore, stem biomass?Cdensity lines were steeper than corresponding branch and leaf lines across most of these forest communities.     

The difference between above- and below-ground self-thinning lines in forest communities

Quantifying the self-thinning process in various plant communities has been a long-standing issue in both theoretical and empirical studies. Most studies on plant self-thinning have centered only on aboveground parts, and rarely on belowground parts. There is still a general lack of comparison between above- and belowground self-thinning processes, especially for forest communities. The fundamental mechanistic difference and the functional association between above- and belowground competition indicate that the self-thinning process of belowground parts may be different from that of aboveground parts. We investigated the self-thinning lines for above-ground (M _A), below-ground (M _B), and total biomass (M _T), respectively, across forest communities in China. The results showed that neither the classical self-thinning rule (−3/2 exponent) nor the universal scaling rule (−4/3 exponent) can apply to all the self-thinning relationships across these forest communities and that the self-thinning lines for belowground biomass were flatter and lower than those for aboveground biomass across most of these forest communities.     

Standing crop and aboveground biomass partitioning of a dwarf mangrove forest in Taylor River Slough,Florida

The structure and standing crop biomass of a dwarf mangrove forest, located in the salinity transition zone ofTaylor River Slough in the Everglades National Park, were studied. Although the four mangrove species reported for Florida occurred at the study site, dwarf Rhizophora mangle trees dominated the forest. The structural characteristics of the mangrove forest were relatively simple: tree height varied from 0.9 to 1.2 meters, and tree density ranged from 7062 to 23 778 stems ha^–1. An allometric relationship was developed to estimate leaf, branch, prop root, and total aboveground biomass of dwarf Rhizophora mangle trees. Total aboveground biomass and their components were best estimated as a power function of the crown area times number of prop roots as an independent variable (Y = B × X^–0.5083). The allometric equation for each tree component was highly significant (p<0.0001), with all r² values greater than 0.90. The allometric relationship was used to estimate total aboveground biomass that ranged from 7.9 to 23.2 ton ha^–1. Rhizophora mangle contributed 85% of total standing crop biomass. Conocarpus erectus, Laguncularia racemosa, and Avicennia germinans contributed the remaining biomass. Average aboveground biomass allocation was 69% for prop roots, 25% for stem and branches, and 6% for leaves. This aboveground biomass partitioning pattern, which gives a major role to prop roots that have the potential to produce an extensive root system, may be an important biological strategy in response to low phosphorus availability and relatively reduced soils that characterize mangrove forests in South Florida.     

Light capture efficiency decreases with increasing tree age and size in the southern hemisphere gymnosperm Agathis australis

We investigated leaf and shoot architecture in relation to growth irradiance (Q_int) in young and mature trees of a New Zealand native gymnosperm Agathis australis (D. Don) Lindl. to determine tree size-dependent and age-dependent controls on light interception efficiency. A binomial 3-D turbid medium model was constructed to distinguish between differences in shoot light interception efficiency due to variations in leaf area density, angular distribution and leaf aggregation. Because of the positive effect of light on leaf dry mass per area (M_A), nitrogen content per area (N_A) increased with increasing irradiance in both young and mature trees. At a common irradiance, N_A, M_A and the components of M_A, density and thickness, were larger in mature trees, indicating a greater accumulation of photosynthetic biomass per unit area, but also a larger fraction of support biomass in older trees. In both young and mature trees, shoot inclination angle relative to horizontal, and leaf number per unit stem length decreased, and silhouette to total leaf area ratio (S_S) increased with decreasing irradiance, demonstrating more efficient light harvesting in low light. The shoots of young trees were more horizontal and less densely leafed with a larger S_S than those of mature trees, signifying greater light interception efficiency in young plants. Superior light harvesting in young trees resulted from more planar leaf arrangement and less clumped foliage. These results suggest that the age-dependent and/or size-dependent decreases in stand productivity may partly result from reduced light interception efficiency in larger mature relative to smaller and younger plants.     

Biomass estimation models and allocation patterns of 14 shrub species in Mountain Luya,Shanxi, China

Aims Shrub species have evolved specific strategies to regulate biomass allocation among various organs or between above- and belowground biomass and shrub biomass model is an important approach to estimate biomass allocation among different shrub species. This study was designed to establish the optimal estimation models for each organ (leaf, stem, and root), aboveground and total biomass of 14 common shrub species in Mountain Luya, Shanxi Province, China. Furthermore, we explored biomass allocation characteristics of these shrub species by using the index of leaf biomass fraction (leaf to total biomass), stem biomass fraction (stem to total biomass), root biomass fraction (root to total biomass), and root to shoot mass ratio (R/S) (belowground to aboveground biomass).
Methods We used plant height, basal diameter, canopy diameter and their combination as variables to establish the optimal biomass estimation models for each shrub species. In addition, we used the ratios of leaf, stem, root to total biomass, and belowground to aboveground biomass to explore the difference of biomass allocation patterns of 14 shrub species.
Important findings Most of biomass estimation models could be well expressed by the exponential and linear functions. Biomass for shorter shrub species with more stems could be better estimated by canopy area; biomass for taller shrub species with less stems could be better estimated by the sum of the square of total base diameter multiply stem height; and biomass for the rest shrub species could be better estimated by canopy volume. The averaged value for these shrub species was 0.61, 0.17, 0.48, and 0.35 for R/S, leaf biomass fraction, stem biomass fraction, and root biomass fraction, respectively. Except for leaf biomass fraction, R/S, stem biomass fraction, and root biomass fraction for shrubs with thorn was significantly greater than that for shrubs without thorn.     

Nitrogen:phosphorous supply ratio and allometry in five alpine plant species

In terrestrial ecosystems, atmospheric nitrogen (N) deposition has greatly increased N availability relative to other elements, particularly phosphorus (P). Alterations in the availability of N relative to P can affect plant growth rate and functional traits, as well as resource allocation to above‐ versus belowground biomass (M_A and M_B). Biomass allocation among individual plants is broadly size‐dependent, and this can often be described as an allometric relationship between M_A and M_B, as represented by the equation , or log M_A = logα + βlog M_B. Here, we investigated whether the scaling exponent or regression slope may be affected by the N:P supply ratio. We hypothesized that the regression slope between M_A and M_B should be steeper under a high N:P supply ratio due to P limitation, and shallower under a low N:P supply ratio due to N limitation. To test these hypotheses, we experimentally altered the levels of N, P, and the N:P supply ratio (from 1.7:1 to 135:1) provided to five alpine species representing two functional groups (grasses and composite forbs) under greenhouse conditions; we then measured the effects of these treatments on plant morphology and tissue content (SLA, leaf area, and leaf and root N/P concentrations) and on the scaling relationship between M_A and M_B. Unbalanced N:P supply ratios generally negatively affected plant biomass, leaf area, and tissue nutrient concentration in both grasses and composite forbs. High N:P ratios increased tissue N:P ratios in both functional groups, but more in the two composite forbs than in the grasses. The positive regression slopes between log M_A and log M_B exhibited by plants raised under a N:P supply ratio of 135:1 were significantly steeper than those observed under the N:P ratio of 1.7:1 and 15:1. Synthesis: Plant biomass allocation is highly plastic in response to variation in the N:P supply ratio. Studies of resource allocation of individual plants should focus on the effects of nutrient ratios as well as the availability of individual elements. The two forb species were more sensitive than grasses to unbalanced N:P supplies. To evaluate the adaptive significance of this plasticity, the effects of unbalanced N:P supply ratio on individual lifetime fitness must be measured.     

Interactive effects of elevated temperature and drought on plant carbon metabolism: A meta-analysis

Elevated temperature (T_e) and drought often co-occur and interactively affect plant carbon (C) metabolism and thus the ecosystem C cycling; however, the magnitude of their interaction is unclear, making the projection of global change impacts challenging. Here, we compiled 107 journal articles in which temperature and water availability were jointly manipulated, and we performed a meta-analysis of interactive effects of T_e and drought on leaf photosynthesis (A_growth) and respiration (R_growth) at growth temperature, nonstructural carbohydrates and biomass of plants, and their dependencies on experimental and biological moderators (e.g., treatment intensity, plant functional type). Our results showed that, overall, there was no significant interaction of T_e and drought on A_growth. T_e accelerated R_growth under well-watered conditions rather than under drought conditions. The T_e × drought interaction on leaf soluble sugar and starch concentrations were neutral and negative, respectively. The effect of T_e and drought on plant biomass displayed a negative interaction, with T_e deteriorating the drought impacts. Drought induced an increase in root to shoot ratio at ambient temperature but not at T_e. The magnitudes of T_e and drought negatively modulated the T_e × drought interactions on A_growth. Root biomass of woody plants was more vulnerable to drought than that of herbaceous plants at ambient temperature, but this difference diminished at T_e. Perennial herbs exhibited a stronger amplifying effect of T_e on plant biomass in response to drought than did annual herbs. T_e exacerbated the responses of A_growth and stomatal conductance to drought for evergreen broadleaf trees rather than for deciduous broadleaf and evergreen coniferous trees. A negative T_e × drought interaction on plant biomass was observed on species-level rather than on community-level. Collectively, our findings provide a mechanistic understanding of the interactive effects of T_e and drought on plant C metabolism, which would improve the prediction of climate change impacts.     

Canonical rules for plant organ biomass partitioning and annual allocation

Here we review a general allometric model for the allometric relationships among standing leaf, stem, and root biomass (M(L), M(S), and M(R), respectively) and the exponents for the relationships among annual leaf, stem, and root biomass production or "growth rates" (G(L), G(S), and G(R), respectively). This model predicts that M(L) ∝ M(S)(3/4) ∝ M(R)(3/4) such that M(S) ∝ M(R) and that G(L) ∝ G(S) ∝ G(R). A large synoptic data set for standing plant organ biomass and organ biomass production spanning ten orders of magnitude in total plant body mass supports these predictions. Although the numerical values for the allometric "constants" governing these scaling relationships differ between angiosperms and conifers, across all species, standing leaf, stem, and root biomass, respectively, comprise 8%, 67%, and 25% of total plant biomass, whereas annual leaf, stem, and root biomass growth represent 30%, 57%, and 13% of total plant growth. Importantly, our analyses of large data sets confirm the existence of scaling exponents predicted by theory. These scaling "rules" emerge from simple biophysical mechanisms that hold across a remarkably broad spectrum of ecologically and phyletically divergent herbaceous and tree-sized monocot, dicot, and conifer species. As such, they are likely to extend into evolutionary history when tracheophytes with the stereotypical "leaf," "stem," and "root" body plan first appeared.     

Low moisture availability reduces the positive effect of increased soil temperature on biomass production of white birch (Betula papyrifera) seedlings in ambient and elevated carbon dioxide concentration

White birch (Betula papyrifera Marsh.) seedlings were grown under two carbon dioxide concentrations ([CO₂]) (360 vs 720 μmol mol^?1), three soil temperatures (T_soil) (5, 15, 25°C initially, increased to 7, 17, 27°C, respectively, one month later), and three moisture regimes (low: 30–40%, intermediate: 45–55%, high: 60–70% field water capacity) for four months in environment‐controlled greenhouses. The dry mass of stem, leaves, and roots was measured after 2 and 4 months of treatment. Low T_soil decreased stem, leaf and total biomass in both measurements, however, the decrease was significantly greater in the elevated than ambient [CO₂] after 4 months. Intermediate T_soil increased root biomass in both measurements. Low moisture reduced stem, leaf, root and total biomass after both 2 and 4 months of treatment. There was a significant T_soil‐moisture interactive effect on leaf, root, and total biomass after 4 months of treatment, suggesting that the magnitude of biomass enhancement in warmer T_soil was dependent on the moisture regime. For instance, the increase in total biomass from the low to high T_soil was 22, 50, and 47% under the low, intermediate and high moisture regimes, respectively. In contrast, the T_soil×moisture effect on stem biomass was significant after 2 months, but not after 4 months of treatment. High T_soil increased leaf mass ratio (LMR) after 4 months of treatment, but decreased both root mass ratio (RMR) after both 2 and 4 months, and root:shoot ratio (RSR) after 4 months of treatment. The low moisture regime decreased LMR after 2 and 4 months of treatment, but increased RSR after 4 months of treatment. There were no significant [CO₂] effects on biomass allocation or [CO₂]×T_soil×moisture interactions on biomass production/allocation.     

Above‐ and belowground biomass allocation in Tibetan grasslands

Question: Optimal partitioning and isometric allocation are two important hypotheses in plant biomass allocation. We tested these two hypotheses at the community level, using field observations from Tibetan grasslands. Location: Qinghai‐Tibetan Plateau, China. Methods: We investigated allocation between above‐ and belowground biomass in alpine grasslands and its relationship with environmental factors using data collected from 141 sites across the plateau during 2001‐2005. We used reduced major axis (RMA) regression and general linear models (GLM) to perform data analysis. Results: The median values of aboveground biomass (M_A), belowground biomass (M_B), and root:shoot (R:S) ratio in alpine grasslands were 59.7, 330.5 g m^?2, and 5.8, respectively. About 90% of total root biomass occurred in the top 30 cm of soil, with a larger proportion in the alpine meadow than in the alpine steppe (96 versus 86%). As soil nitrogen and soil moisture increased, both M_A and M_B increased, but R:S ratio did not show a significant change. M_A scaled as 0.92 the power of M_B, with 95% confidence intervals of 0.82‐1.02. The slope of the isometric relationship between log M_A and log M_B did not differ significantly between alpine steppe and alpine meadow. The isometric relationship was also independent of soil nitrogen and soil moisture. Conclusions: Our results support the isometric allocation hypothesis for the M_A versus M_B relationship in Tibetan grasslands.     

Biomass structure of exotic invasive plant Galinsona parviflora

Galinsona parviflora (Asteraceae) is a widespread annual weed that is invasive, colonizing new ground where it is able to persist. We studied the biomass structure of the G. parviflora population at the module level by using the methods of field plot investigation and weighing at 10 sample plots. Modular biomass was calculated and used for analysis of relationships between various modules. The results show that there was a positive correlation between plant height and modular biomass, between stem biomass and root biomass, stem biomass and capitulum biomass, aboveground biomass and underground biomass, and lastly, stem biomass and leaf biomass. The preferred model which measured all the relationships was a power function model with absolute coefficients (R²) ranging from 0.6303 to 0.9782. __________ Translated from Chinese Journal of Applied Ecology, 2006, 17(12): 2283–2286 [译自: 应用生态学报]     

Leaf meristems: an easily ignored component of the response to human disturbance in alpine grasslands

Grazing and fencing are two important factors that influence productivity and biomass allocation in alpine grasslands. The relationship between root (R) and shoot (S) biomass and the root:shoot ratio (R/S) are critical parameters for estimating the terrestrial carbon stocks and biomass allocation mechanism responses to human activities. Previous studies have often used the belowground:aboveground biomass ratio (M_b/M_a) to replace the R/S in alpine ecosystems. However, these studies may have neglected the leaf meristem biomass, which belongs to the shoot but occurs below the soil surface, leading to a significant overestimation of the R/S ratio. We conducted a comparative study to explore the differences between the R/S and M_b/M_a at both the species (Stipa purpurea, Carex moorcroftii, and Artemisia nanschanica) and community levels on a Tibetan alpine grassland with grazing and fencing management blocks. The results revealed that the use of the M_b/M_a to express the R/S appeared to overestimate the actual value of the R/S, both at species and community levels. For S. purpurea, the M_b/M_a was three times higher than the R/S. The M_b/M_a was approximately two times higher than the R/S for the species of C. moorcroftii and A. nanschanica and at the community level. The relationships between the R‐S and M_b‐M_a exhibited different slopes for the alpine plants across all the management practices. Compared to the fenced grasslands, the plants in the grazing blocks not only allocated more biomass to the roots but also to the leaf meristems. The present study highlights the contribution of leaf meristems to the accurate assessment of shoot and belowground biomasses. The R/S and M_b/M_a should be cautiously used in combination in the future research. The understanding of the distinction between the R‐S and M_b‐M_a may help to improve the biomass allocation mechanism response to human disturbances in an alpine area.     

Near Isometric Biomass Partitioning in Forest Ecosystems of China

Based on the isometric hypothesis, belowground plant biomass (M_B) should scale isometrically with aboveground biomass (M_A) and the scaling exponent should not vary with environmental factors. We tested this hypothesis using a large forest biomass database collected in China. Allometric scaling functions relating M_B and M_A were developed for the entire database and for different groups based on tree age, diameter at breast height, height, latitude, longitude or elevation. To investigate whether the scaling exponent is independent of these biotic and abiotic factors, we analyzed the relationship between the scaling exponent and these factors. Overall M_B was significantly related to M_A with a scaling exponent of 0.964. The scaling exponent of the allometric function did not vary with tree age, density, latitude, or longitude, but varied with diameter at breast height, height, and elevation. The mean of the scaling exponent over all groups was 0.986. Among 57 scaling relationships developed, 26 of the scaling exponents were not significantly different from 1. Our results generally support the isometric hypothesis. M_B scaled near isometrically with M_A and the scaling exponent did not vary with tree age, density, latitude, or longitude, but increased with tree size and elevation. While fitting a single allometric scaling relationship may be adequate, the estimation of M_B from M_A could be improved with size-specific scaling relationships.     

香根草形态性状和光合特性对三峡库区消落带水陆生境变化的响应

基于定位观测,研究三峡库区消落带淹水区和未淹区香根草的形态性状、生物量、光合参数和资源利用效率,并对其适应机制进行讨论。结果显示:(1)香根草可以在消落带每年淹水期4个月左右、淹水深度小于9m的海拔区段存活。(2)淹水区香根草的地上部分多数形态性状指标较未淹区有所降低,降低幅度随香根草露出水面恢复生长的时间长短而异。(3)淹水区香根草总生物量、地上部分生物量分别减少10.58%、48.46%,而根径、根系长度、根系数量、根幅、地下生物量以及地下/地上生物量的比值分别提高12.50%、24.13%、19.09%、78.46%、30.04%、151.71%;同期香根草的蒸腾速率、气孔导度和胞间CO2浓度分别减少20.75%、9.19%和10.04%,而净光合速率、水分利用效率、表观CO2利用效率分别提高7.23%、36.47%和63.64%。研究表明,加速根系分蘖和生长、增加叶片长度和地下生物量,降低植株高度、减少蒸腾、提高水分和CO2利用效率是香根草对三峡库区消落带水陆生境变化的适应对策。     

Low soil temperature inhibits the stimulatory effect of elevated [CO2] on height and biomass accumulation of white birch seedlings grown under three non‐limiting phosphorus conditions

White birch (Betula papyrifera Marsh.) seedlings were exposed to ambient or doubled ambient carbon dioxide concentration ([CO₂]), three soil temperatures (T_soil) (low, intermediate, high), and three phosphorus (P) regimes (low, medium, high) in environment‐controlled greenhouses. Height (H), root‐collar diameter (RCD), biomass, and leaf phosphorus concentration (leaf P) were determined four months after initiation of treatments. The low T_soil reduced H, RCD, shoot biomass, root biomass and total seedling biomass whereas the high‐P level and the [CO₂] elevation increased all the growth and biomass parameters. Elevated [CO₂] significantly reduced leaf P. There were significant two‐factor interactions suggesting that the effect of elevated [CO₂] on (1) H, total biomass, biomass of plant components, and leaf P was dependent on T_soil, (2) total biomass was contingent on P regime. For instance, the positive response of H and total biomass to elevated [CO₂] was limited to seedlings raised under the intermediate and high T_soil, respectively. In addition, [CO₂] elevation increased total biomass only at the high‐P regime but not at the low‐ or medium‐P level where the effect of [CO₂] was statistically insignificant. No significant main effect of treatment or interaction was observed for root to shoot biomass ratio.     

Isometric scaling of above- and below-ground biomass at the individual and community levels in the understorey of a sub-tropical forest

Background and Aims Empirical studies and allometric partitioning (AP) theory indicate that plant above-ground biomass (M_A) scales, on average, one-to-one (isometrically) with below-ground biomass (M_R) at the level of individual trees and at the level of entire forest communities. However, the ability of the AP theory to predict the biomass allocation patterns of understorey plants has not been established because most previous empirical tests have focused on canopy tree species or very large shrubs.Methods In order to test the AP theory further, 1586 understorey sub-tropical forest plants from 30 sites in south-east China were harvested and examined. The numerical values of the scaling exponents and normalization constants (i.e. slopes and y-intercepts, respectively) of log–log linear M_A vs. M_R relationships were determined for all individual plants, for each site, across the entire data set, and for data sorted into a total of 19 sub-sets of forest types and successional stages. Similar comparisons of M_A/M_R were also made.Key Results The data revealed that the mean M_A/M_R of understorey plants was 2·44 and 1·57 across all 1586 plants and for all communities, respectively, and M_A scaled nearly isometrically with respect to M_R, with scaling exponents of 1·01 for all individual plants and 0·99 for all communities. The scaling exponents did not differ significantly among different forest types or successional stages, but the normalization constants did, and were positively correlated with M_A/M_R and negatively correlated with scaling exponents across all 1586 plants.Conclusions The results support the AP theory’s prediction that M_A scales nearly one-to-one with M_R (i.e. M_A ∝ M_R ^≈1·0) and that plant biomass partitioning for individual plants and at the community level share a strikingly similar pattern, at least for the understorey plants examined in this study. Furthermore, variation in environmental conditions appears to affect the numerical values of normalization constants, but not the scaling exponents of the M_A vs. M_R relationship. This feature of the results suggests that plant size is the primary driver of the M_A vs. M_R biomass allocation pattern for understorey plants in sub-tropical forests.     

煤矸石山不同种植年限香根草生物量分配及异速生长分析

香根草(Vetiveria zizanioides)是一种良好的矿业废弃地生态修复物种,研究其生物量分配和异速生长关系,有助于深入了解香根草在矿区的生存策略与生态功能。该研究以贵州省六盘水市大河煤矿煤矸石山种植年限为4、5、8和15 a的香根草为对象,采用挖掘法和称重法对不同种植年限香根草的器官生物量、分配比例及异速生长关系进行了对比分析。结果表明:(1)随种植年限的增加,根、茎、叶生物量均呈现先增加后减少的趋势,且均在种植年限为5 a时最大,15 a时最小。(2)茎生物量分配比在种植年限15 a时最大(37.3%),叶生物量分配比在种植年限5 a时最大(36.1%),根生物量分配比不随种植年限的增加而发生变化,基本保持在30%左右。(3)种植年限为4、5、8 a时,地上部总生物量与根生物量、叶生物量呈异速生长关系;种植年限为5 a时,叶面积与根、叶生物量呈异速生长关系,与茎生物量呈等速生长关系。不同种植年限间的生物量分配及异速生长关系虽然没有一致规律,但体现了香根草在煤矸石基质中生物量分配的特点,且显示了其特别的生长方式和资源分配策略,为今后香根草在煤矸石山生态治理方面提供了参考依据。