Scaling relationships of twig biomass allocation in Pinus hwangshanensis along an altitudinal gradient.
ABSTRACT: Understanding the response of biomass allocation in twigs (the terminal branches of current-year shoots) to environmental change is crucial for elucidating forest ecosystem carbon storage, carbon cycling, and plant life history strategies under a changing climate. On the basis of interspecies investigations of broad-leaved plants, previous studies have demonstrated that plants respond to environmental factors by allocating biomass in an allometric manner between support tissues (i.e., stems) and the leaf biomass of twigs, where the scaling exponent (i.e., slope of a log-log linear relationship, ?) is constant, and the scaling constant (i.e., intercept of a log-log linear relationship, log ?) varies with respect to environmental factors. However, little is known about whether the isometric scaling exponents of such biomass allocations remain invariant for single species, particularly conifers, at different altitudes and in different growing periods. In this study, we investigated how twig biomass allocation varies with elevation and period among Pinus hwangshanensis Hsia trees growing in the mountains of Southeast China. Specifically, we explored how twig stem mass, needle mass, and needle area varied throughout the growing period (early, mid-, late) and at three elevations in the Wuyi Mountains. Standardized major axis analysis was used to compare the scaling exponents and scaling constants between the biomass allocations of within-twig components. Scaling relationships between these traits differed with growing period and altitude gradient. During the different growing periods, there was an isometric scaling relationship, with a common slope of 1.0 (i.e., ? ? 1.0), between needle mass and twig mass (the sum of the total needle mass and the stem mass), whereas there were allometric scaling relationships between the stem mass and twig mass and between the needle mass and stem mass of P. hwangshanensis. The scaling constants (log ?) for needle mass vs. twig mass and for needle mass vs. stem mass increased progressively across the growing stages, whereas the scaling constants of stem mass vs. twig mass showed the opposite pattern. The scaling exponents (?) of needle area with respect to needle biomass increased significantly with growing period, changing from an allometric relationship (i.e., ? < 1.0) during the early growing period to a nearly isometric relationship (i.e., ? ? 1.0) during the late growing period. This change possibly reflects the functional adaptation of twigs in different growing periods to meet their specific reproductive or survival needs. At different points along the altitudinal gradient, the relationships among needle mass, twig mass, and stem mass were all isometric (i.e., ? ? 1.0). Moreover, significant differences were found in scaling constants (log ?) along the altitudinal gradient, such that species had a smaller stem biomass but a relatively larger needle mass at low altitude. In addition, the scaling exponents remained numerically invariant among all three altitudes, with a common slope of 0.8, suggesting that needle area failed to keep pace with the increasing needle mass at different altitudes. Our results indicated that the twig biomass allocation pattern was significantly influenced by altitude and growing period, which reflects the functional adaptation of twigs to meet their specific survival needs under different climatic conditions.
Project description:Understanding the scaling between leaf size and leafing intensity (leaf number per stem size) is crucial for comprehending theories about the leaf costs and benefits in the leaf size-twig size spectrum. However, the scaling scope of leaf size versus leafing intensity changes along the twig leaf size variation in different leaf habit species remains elusive. Here, we hypothesize that the numerical value of scaling exponent for leaf mass versus leafing intensity in twig is governed by the minimum leaf mass versus maximum leaf mass (<i>M</i> <sub>min</sub> versus <i>M</i> <sub>max</sub>) and constrained to be ?-1.0. We tested this hypothesis by analyzing the twigs of 123 species datasets compiled in the subtropical mountain forest. The standardized major axis regression (SMA) analyses showed the <i>M</i> <sub>min</sub> scaled as the 1.19 power of <i>M</i> <sub>max</sub> and the -? (-1.19) were not statistically different from the exponents of <i>M</i> <sub>min</sub> versus leafing intensity in whole data. Across leaf habit groups, the <i>M</i> <sub>max</sub> scaled negatively and isometrically with respect to leafing intensity. The pooled data's scaling exponents ranged from -1.14 to -0.96 for <i>M</i> <sub>min</sub> and <i>M</i> <sub>max</sub> versus the leafing intensity based on stem volume (LIV). In the case of <i>M</i> <sub>min</sub> and <i>M</i> <sub>max</sub> versus the leafing intensity based on stem mass (LIM), the scaling exponents ranged from -1.24 to -1.04. Our hypothesis successfully predicts that the scaling relationship between leaf mass and leafing intensity is constrained to be ?-1.0. More importantly, the lower limit to scaling of leaf mass and leafing intensity may be closely correlated with <i>M</i> <sub>min</sub> versus <i>M</i> <sub>max</sub>. Besides, constrained by the maximum leaf mass expansion, the broad scope range between leaf size and number may be insensitive to leaf habit groups in subtropical mountain forest.
Project description:The relationship between leaf and stem biomass as well as the relationship between leaf biomass and stem length and diameter are important to our understanding of a broad range of important plant scaling relationship because of their relationship to photosynthesis and thus growth. To understand how twig architecture (i.e., current year leaves, and stem diameter and length) affects stem diameter and length, and leaf number and biomass, we examined the twigs of 64 woody species collected from three forest types along an elevational gradient in the Wuyi Mountains, Jiangxi Province, China. We also compared the scaling relationships we observed with biomass allocation patterns reported at the whole tree level. Our results revealed isometric relationship between leaf and stem biomass on twigs despite differences in forest communities and despite changes in environmental factors along an elevational gradient. Across the 64 species, from twigs to individual trees, leaf biomass scaled approximately as the 2.0-power of stem diameter (but not for stem length or leaf number). These results help to identify a general rule that operates at two different levels of biological organization (twigs and whole trees). The scaling relationship between leaf biomass and stem diameter in twigs is insensitive to differences in species composition, elevation, or forest type. We speculate that this rule emerges because stem diameter serves as a proxy for the amount of resources supplied per unit cross section to developing leaves and for the flow of photosynthates from mature leaves to the rest of the plant body.
Project description:Allocation of limited nutrients, such as nitrogen (N) and phosphorus (P), among plant organs reflects the influences of evolutionary and ecological processes on functional traits of plants, and thus is related to functional groups and environmental conditions. In this study, we tested this hypothesis by exploring the stoichiometric scaling of N and P concentrations between twig stems and leaves of 335 woody species from 12 forest sites across eastern China. Scaling exponents of twig stem N (or P) to leaf N (or P) varied among functional groups. With increasing latitude, these scaling exponents significantly decreased from >1 at low latitude to <1 at high latitude across the study area. These results suggested that, as plant nutrient concentration increased, plants at low latitudes showed a faster increase in twig stem nutrient concentration, whereas plants at high latitudes presented a faster increase in leaf nutrient concentration. Such shifts in nutrient allocation strategy from low to high latitudes may be controlled by temperature. Overall, our findings provide a new approach to explore plant nutrient allocation strategies by analysing the stoichiometric scaling of nutrients among organs, which could broaden our understanding of the interactions between plants and their environments.
Project description:We compiled a global database for leaf, stem and root biomass representing c. 11 000 records for c. 1200 herbaceous and woody species grown under either controlled or field conditions. We used this data set to analyse allometric relationships and fractional biomass distribution to leaves, stems and roots. We tested whether allometric scaling exponents are generally constant across plant sizes as predicted by metabolic scaling theory, or whether instead they change dynamically with plant size. We also quantified interspecific variation in biomass distribution among plant families and functional groups. Across all species combined, leaf vs stem and leaf vs root scaling exponents decreased from c. 1.00 for small plants to c. 0.60 for the largest trees considered. Evergreens had substantially higher leaf mass fractions (LMFs) than deciduous species, whereas graminoids maintained higher root mass fractions (RMFs) than eudicotyledonous herbs. These patterns do not support the hypothesis of fixed allometric exponents. Rather, continuous shifts in allometric exponents with plant size during ontogeny and evolution are the norm. Across seed plants, variation in biomass distribution among species is related more to function than phylogeny. We propose that the higher LMF of evergreens at least partly compensates for their relatively low leaf area : leaf mass ratio.
Project description:<h4>Background and aims</h4>Biomass partitioning for resource conservation might affect plant allometry, accounting for a substantial amount of unexplained variation in existing plant allometry models. One means of resource conservation is through direct allocation to storage in particular organs. In this study, storage allocation and biomass allometry of deciduous and evergreen tree species from seasonal environments were considered. It was expected that deciduous species would have greater allocation to storage in roots to support leaf regrowth in subsequent growing seasons, and consequently have lower scaling exponents for leaf to root and stem to root partitioning, than evergreen species. It was further expected that changes to root carbohydrate storage and biomass allometry under different soil nutrient supply conditions would be greater for deciduous species than for evergreen species.<h4>Methods</h4>Root carbohydrate storage and organ biomass allometries were compared for juveniles of 20 savanna tree species of different leaf habit (nine evergreen, 11 deciduous) grown in two nutrient treatments for periods of 5 and 20 weeks (total dry mass of individual plants ranged from 0·003 to 258·724 g).<h4>Key results</h4>Deciduous species had greater root non-structural carbohydrate than evergreen species, and lower scaling exponents for leaf to root and stem to root partitioning than evergreen species. Across species, leaf to stem scaling was positively related, and stem to root scaling was negatively related to root carbohydrate concentration. Under lower nutrient supply, trees displayed increased partitioning to non-structural carbohydrate, and to roots and leaves over stems with increasing plant size, but this change did not differ between leaf habits.<h4>Conclusions</h4>Substantial unexplained variation in biomass allometry of woody species may be related to selection for resource conservation against environmental stresses, such as resource seasonality. Further differences in plant allometry could arise due to selection for different types of biomass allocation in response to different environmental stressors (e.g. fire vs. herbivory).
Project description:<h4>Background and aims</h4>Although many hypotheses have been proposed to explain variation in leaf size, the mechanism underlying the variation remains not fully understood. To help understand leaf size variation, the cost/benefit of twig size was analysed, since, according to Corner's rule, twig size is positively correlated with the size of appendages the twig bears.<h4>Methods</h4>An extensive survey of twig functional traits, including twig (current-year shoots including one stem and few leaves) and leaf size (individual leaf area and mass), was conducted for 234 species from four broadleaved forests. The scaling relationship between twig mass and leaf area was determined using standardized major axis regression and phylogenetic independent comparative analyses.<h4>Key results</h4>Leaf area was found to scale positively and allometrically with both stem and twig mass (stem mass plus leaf mass) with slopes significantly smaller than 1.0, independent of life form and habitat type. Thus, the leaf area ratio (the ratio of total leaf area to stem or twig mass) decreases with increasing twig size. Moreover, the leaf area ratio correlated negatively with individual leaf mass. The results of phylogenetic independent comparativeanalyses were consistent with the correlations. Based on the above results, a simple model for twig size optimization was constructed, from which it is postulated that large leaf size-twig size may be favoured when leaf photosynthetic capacity is high and/or when leaf life span and/or stem longevity are long. The model's predictions are consistent with leaf size variation among habitats, in which leaf size tends to be small in poor habitats with a low primary productivity. The model also explains large variations in leaf size within habitats for which leaf longevity and stem longevity serve as important determinants.<h4>Conclusions</h4>The diminishing returns in the scaling of total leaf area with twig size can be explained in terms of a very simple model on twig siz
Project description:Metabolic scaling theory (MST) posits that the scaling exponents among plant height H, diameter D, and biomass M will covary across phyletically diverse species. However, the relationships between scaling exponents and normalization constants remain unclear. Therefore, we developed a predictive model for the covariation of H, D, and stem volume V scaling relationships and used data from Chinese fir (Cunninghamia lanceolata) in Jiangxi province, China to test it. As predicted by the model and supported by the data, normalization constants are positively correlated with their associated scaling exponents for D vs. V and H vs. V, whereas normalization constants are negatively correlated with the scaling exponents of H vs. D. The prediction model also yielded reliable estimations of V (mean absolute percentage error?=?10.5?±?0.32 SE across 12 model calibrated sites). These results (1) support a totally new covariation scaling model, (2) indicate that differences in stem volume scaling relationships at the intra-specific level are driven by anatomical or ecophysiological responses to site quality and/or management practices, and (3) provide an accurate non-destructive method for predicting Chinese fir stem volume.
Project description:There have been a number of studies on biogeographic patterns of plant leaf functional traits; however, the variations in traits of other plant organs such as twigs are rarely investigated. In this study, we sampled current-year twigs of 335 tree species from 12 forest sites across a latitudinal span of 32 degrees in China, and measured twig specific density (TSD), twig dry matter content (TDMC), and carbon (C), nitrogen (N) and phosphorous (P) contents, to explore the latitudinal and environmental patterns of these twig traits. The overall mean of TSD and TDMC was 0.37 g cm(-3) and 41%, respectively; mean twig C, N and P was 472 mg g(-1), 9.8 mg g-1 and 1.15 mg g(-1), respectively, and mean N:P mass ratio was 10.6. TSD was positively correlated with TDMC which was positively associated with twig C but negatively with twig N and P. There were no significant differences in TSD between conifer, deciduous-broadleaf and evergreen-broadleaf plants, but evergreen-broadleaf plants had the lowest and conifers the highest TDMC. Conifer twigs were lowest in C, N, P and N:P, whereas deciduous-plant twigs were highest in N and P and evergreen-plant twigs were highest in C and N:P. As latitude increased or temperature/precipitation dropped, TDMC and P increased, but N:P ratio decreased. Our results also showed that the patterns of twig P and N:P stoichiometry were consistent with those reported for leaves, but no significant trends in twig N were observed along the gradient of latitude, climate and soils. This study provides the first large-scale patterns of the twig traits and will improve our understanding of the biogeochemistry of carbon and other key nutrients in forest ecosystems.
Project description:Allocation of biomass to different organs is a fundamental aspect of plant responses and adaptations to changing environmental conditions, but how it responds to nitrogen (N) and phosphorus (P) availability remains poorly addressed. Here we conducted greenhouse fertilization experiments using <i>Arabidopsis thaliana</i>, with five levels of N and P additions and eight repeat experiments, to ascertain the effects of N and P availability on biomass allocation patterns. N addition increased leaf and stem allocation, but decreased root and fruit allocation. P addition increased stem and fruit allocation, but decreased root and leaf allocation. Pooled data of the five levels of N addition relative to P addition resulted in lower scaling exponents of stem mass against leaf mass (0.983 vs. 1.226; <i>p</i> = 0.000), fruit mass against vegetative mass (0.875 vs. 1.028; <i>p</i> = 0.000), and shoot mass against root mass (1.069 vs. 1.324; <i>p</i> = 0.001). This suggested that N addition relative to P addition induced slower increase in stem mass with increasing leaf mass, slower increase in reproductive mass with increasing vegetative mass, and slower increase in shoot mass with increasing root mass. Further, the levels of N or P addition did not significantly affect the allometric relationships of stem mass vs. leaf mass, and fruit mass vs. vegetative mass. In contrast, increasing levels of N addition increased the scaling exponent of shoot to root mass, whereas increasing levels of P addition exerted the opposite influence on the scaling exponent. This result suggests that increasing levels of N addition promote allocation to shoot mass, whereas the increasing levels of P addition promote allocation to root mass. Our findings highlight that biomass allocation of <i>A. thaliana</i> exhibits a contrasting response to N and P availability, which has profound implications for forecasting the biomass allocation strategies in plants to human-induced nutrient enrichment.
Project description:Empirical studies indicate that the exponents governing the scaling of plant respiration rates (<i>R</i>) with respect to biomass (<i>M</i>) numerically vary between three-fourth for adult plants and 1.0 for seedlings and saplings and are affected by nitrogen (N) and phosphorus (P) content. However, whether the scaling of <i>R</i> with respect to <i>M</i> (or N and P) varies among different phylogenetic groups (e.g., gymnosperms vs. angiosperms) or during the growing and dormant seasons remains unclear. We measured the whole-plant <i>R</i> and <i>M</i>, and N and P content of the seedlings of four woody species during the growing season (early October) and the dormant season (January). The data show that (i) the scaling exponents of <i>R</i> versus <i>M</i>, <i>R</i> versus N, and <i>R</i> versus P differed significantly among the four species, but (ii), not between the growing and dormant seasons for each of the four species, although (iii) the normalization constants governing the scaling relationships were numerically greater for the growing season compared to the dormant season. In addition, (iv) the scaling exponents of <i>R</i> versus <i>M</i>, <i>R</i> versus N, and <i>R</i> versus P were numerically larger for the two angiosperm species compared to those of the two gymnosperm species, (v) the interspecific scaling exponents for the four species were greater during the growing season than in the dormant season, and (vi), interspecifically, P scaled nearly isometric with N content. Those findings indicate that the metabolic scaling relationships among <i>R</i>, <i>M</i>, N, and P manifest seasonal variation and differ between angiosperm and gymnosperm species, that is, there is no single, canonical scaling exponent for the seedlings of woody species.