Stem Mass Fraction Research Articles

Germination ecology and seedling growth of invasive Ageratum species and allied native Adenostemma lavenia

AbstractThe success of invasive plants can be better understood by comparing their traits with closely related native species. This study compared germination ecology and seedling growth of invasive Ageratum houstonianum and Ageratum conyzoides with co‐occurring and allied native Adenostemma lavenia. Seeds were germinated under a different light (12 h photoperiod/complete dark), temperatures (low: 25°C/15°C day/night, and high: 30°C/20°C), and different levels of water stress (−0.1, −0.25, −0.5, −0.75, and −1 MPa). Seedlings were grown to determine biomass allocation, relative growth rate (RGR), plant height, and number of leaves. The seed mass and size of native A. lavenia were higher than those of invasive species. Seeds of all species were positively photoblastic. At low temperature and in all levels of water stress, all measured parameters except mean germination time were the highest in A. houstonianum. However, at high temperature, there was no significant difference in germination percentage between A. houstonianum and A. lavenia. No germination of A. conyzoides and A. lavenia was recorded beyond −0.5 MPa water potential, but seeds of A. houstonianum germinated up to −0.75 MPa. A. houstonianum had higher root mass fraction, root‐to‐shoot ratio, and number of leaves than the other two species. Stem mass fraction and the height of seedling were highest in A. conyzoides. The RGR was 1.6 times higher in invasive Ageratum species than the native species; it was slightly higher in A. houstonianum than in A. conyzoides. Overall, the results suggest that germination traits and seedling growth performance can be used as predictors of a species' invasiveness.

Filler-induced heterogeneous nucleation of polymer crystals investigated by molecular dynamics simulations

Filler particles are known to act as nucleants for polymer crystallisation yet the connection between the filler surface properties and polymer crystallisation are not well understood. In this work, molecular dynamics simulations were used to investigate homogeneous and heterogeneous polymer nucleation and crystallisation using a generic linear bead–spring polymer model with a bond bending potential. The polymer systems were equilibrated at high temperature and then cooled at a constant rate. Without a surface present, polymers with stiff chains were found to crystallise more readily than more flexible polymers. The degree of crystallinity was estimated based on the mass fraction of straight chain segments which we equate to stem mass fraction. At a temperature Tc a sharp increase in density, radius of gyration and stem mass fraction occurred. After cooling, the systems were reheated and some systems showed hysteresis with a sharp decrease in these properties occurring upon melting at Tm>Tc. For slower heating rates, crystal growth occurred during heating from between the glass transition temperature, Tg, and Tc until just before melting at Tm. The presence of an isotropic surface was found to promote crystallisation in flexible systems that did not crystallise in the bulk, where the stem mass fraction and Tc increased with the interaction strength between the surface and the polymer beads. Changes in Tc and degree of crystallinity with cooling rate are consistent with experimental observations. This model captures polymer crystallisation phenomena and provides insight into heterogeneous nucleation, demonstrating that strong interfacial interactions promote crystallisation, thus aiding the choice or design of nucleants for control of polymer crystallisation and microstructure.

Nitrogen addition promotes terrestrial plants to allocate more biomass to aboveground organs: A global meta-analysis.

A significant increase in reactive nitrogen (Nr) added to terrestrial ecosystems through agricultural fertilization or atmospheric deposition is considered to be one of the most widespread drivers of global change. Modifying biomass allocation is one primary strategy for maximizing plant growth rate, survival, and adaptability to various biotic and abiotic stresses. However, there is much uncertainty as to whether and how plant biomass allocation strategies change in response to increased nitrogen inputs in terrestrial ecosystems. Here, we synthesized 3,516 paired observations of plant biomass and their components related to nitrogen additions across terrestrial ecosystems worldwide. Our meta-analysis reveals that N addition (ranging from 1.08 to 113.81 g m-2 yr-1 ) increased terrestrial plant biomass by 55.62% on average. Nitrogen addition has increased plant stem mass fraction, shoot mass fraction, and leaf mass fraction by 13.8%, 12.9%, and 13.4%, respectively, but with an associated decrease in plant reproductive mass (including flower and fruit biomass) fraction by 3.4%. We further documented a reduction in plant root-shoot ratio and root mass fraction by 27% (21.8-32.1%) and 14.7% (11.6-17.8%), respectively, in response to N addition. Meta-regression results showed that N addition effects on plant biomass were positively correlated with mean annual temperature, soil available phosphorus, soil total potassium, specific leaf area, and leaf area per plant. Nevertheless, they were negatively correlated with soil total nitrogen, leaf carbon/nitrogen ratio, leaf carbon and nitrogen content per leaf area, as well as the amount and duration of nitrogen addition. In summary, our meta-analysis suggests that N addition may alter terrestrial plant biomass allocation strategies, leading to more biomass being allocated to aboveground organs than belowground organs and growth vs reproductive trade-offs. At the global scale, leaf functional traits may dictate how plant species change their biomass allocation pattern in response to nitrogen addition.

Biomass allocation pattern of urban shrubs in the Yangtze River Delta region, China – A field observation of 13 shrub species

As a crucial part of urban green space, urban shrub biomass and biomass allocation play an important role in the urban carbon cycle. However, the current body of research mainly focuses on natural vegetation, and the biomass allocation patterns of urban shrubs remain poorly addressed. In this study, whole-plant harvests of 13 common urban shrubs in the Yangtze River Delta region were conducted to ascertain their biomass allocation patterns (i.e., leaf mass fraction (LMF), stem mass fraction (SMF), root mass fraction (RMF), and root/shoot ratio (R/S)) as well as the effects of ontogeny (i.e., plant height) and leaf traits (evergreen and deciduous). Our findings were as follows: (1) Among the 13 urban shrubs, the mean values of LMF, SMF, RMF and R/S were 0.22, 0.47, 0.31, and 0.46. Specifically, nine species had the most resources invested in stems, whereas four species exhibited similar proportion of roots and stems. (2) With increasing plant height, the changes in shrub biomass allocation to organs could be divided into three categories: 1) eight shrub species displayed increased partitioning of resources to stems (SMF) and decreased partitioning to leaves (LMF) and roots (RMF); 2) two shrub species shifted biomass from leaves to stems, with RMF remaining stable; and 3) three shrub species exhibited no response to increasing plant height. (3) Evergreen shrubs had higher LMF values (0.26 vs. 0.17) and lower SMF values (0.42 vs. 0.54) compared to deciduous species (P < 0.05), and their RMF and R/S values did not differ significantly (P> 0.05). We concluded that urban shrub biomass allocation was influenced by both plant ontogeny and leaf traits, and the data presented in this study could be made available for the precise estimation of regional urban shrub biomass and carbon storage.

Correlation of Leaf and Root Traits of Two Angiosperm Tree Species in Northeast China under Contrasting Light and Nitrogen Availabilities

Light and nitrogen availability are among the most important environmental factors influencing leaf and root morphological traits and forest ecosystems. Understanding the variation in leaf and root traits is pivotal to the adaptive plasticity and leaf-root-specific traits in response to low light and N availability. The effects of light and N availability on leaf and root traits and their interrelations are still not clear. We aimed to measure the response of leaf and root traits and their interrelations to light and N availability in a temperate region. Thus, a factorial experiment was conducted with two angiosperm tree species under two light (L+, L−) and two nitrogen (N−, N+) levels. Results showed that the leaf density (LD) and leaf mass per area (LMA) increased, while leaf thickness (LT) decreased under low light availability. Under N availability, the LD and LMA decreased, while LT increased in sun-exposed plots and remained stable under low light availability across two species. The root diameter, root length, specific root length (SRL), and specific root area (SRA) decreased, while the root tissue density (TD) increased under low light availability. Root diameter, root length, SRA, and SRL increased, while the TD decreased under N+ in L+ plots and remained stable under L− plots. LMA and LT were significantly positively correlated to root length and SRL while significantly negatively correlated to TD. However, LD was significantly positively correlated to TD. We observed that low light availability has significantly decreased the plant biomass and root mass fraction (RMF) and increased the leaf mass fraction (LMF), while the stem mass fraction (SMF) remained stable―indicating the shade in-tolerances in both species. Correlation analyses revealed that LMF is generally, and particularly under L− conditions, less related to leaf and root morphological traits, while RMF was frequently positively correlated to both leave and root traits under all environmental conditions. This illustrates a divergent regulation of morphological traits above and below ground under varying biomass allocation patterns.

Plant age affects intraspecific variation in functional traits

Functional traits are often used to examine ecological patterns and processes. Ontogeny—changes that occur over time as the result of development—generates variation in traits within individual organisms. We aimed to quantify the role of ontogeny in structuring functional trait variation across a range of co-existing herbaceous perennial species and hypothesized that ontogenetic variation in traits would be greater in younger vs. older plants. We grew eight herbaceous perennial forb species common in tallgrass prairies from seed in a greenhouse in Madison, Wisconsin, USA to determine how and when time-related variation in functional traits is large relative to other sources of variation, such as differences between leaves and species. We destructively measured common functional traits on four individuals of each species every two weeks for 19 weeks, including leaf mass fraction, root mass fraction, stem mass fraction, specific leaf area, leaf dry matter content, and leaf area. We found that most functional traits indeed change through time, that the direction of many changes are consistent between species but the magnitude of change is species specific, and most time-related variation occurred earlier in development. These results emphasize the importance of considering sampling timing and differences between young and old plants when measuring functional traits. Our results suggest that ontogenetic intraspecific variation can be substantial, especially early in life. It may be problematic to use traits measured from mature plants to interpret the importance of processes that occur at earlier life stages or vice versa; using seedling traits to understand adult plant responses may also be inappropriate.

Growth of yacon under artificial shading

ABSTRACT Yacon is a tuberous root cultivated in mild climate regions with high altitudes, but the crop shows the capacity to develop at low altitudes. The objective of this study was to evaluate growth rates and the partition of photoassimilates in yacon plants under different levels of artificial shading. The experiment was conducted in four shading levels (0%, 30%, 50% and 70%), and seven monthly harvests in a completely randomized design. We evaluated the accumulation of total dry mass on the whole plant and its parts; leaf area; leaf area ratio; leaf mass fraction; stem mass fraction; rhizophores mass fraction; tuberous roots mass fraction; estimates of relative growth rate, absolute growth, and net assimilation. The lower accumulation of total dry biomass and the lowest growth rates indicate that conditions of noticeable light restriction (70% shading) restrict the growth of yacon. Yacon plants grown under moderate shading levels (30 to 50%) showed greater capacity of accumulation of total biomass, directing part of this biomass to the tuberous roots, which directly reflects gains in the agronomic productivity of this crop, indicating that yacon has the potential to be associated with other crops, which promote a moderate shading.

Effects of two water regimes on morphological traits, nutritive value and physiology of three Bituminaria bituminosa varieties from the Canary Islands

AbstractMorphological traits, nutritive values and physiological responses to two different water regimes of three Bituminaria bituminosa varieties: var. albomarginata, var. crassiuscula and var. bituminosa were evaluated in a greenhouse experiment. Two water regimes were imposed for 63 days; well‐watered (WW) plants and deficit‐watered (DW) plants, both starting from a high soil water content (dripping point). The three varieties showed similar aerial biomass reduction under reduced watering, 50% for var. albomarginata, 51% for var. bituminosa and 43% for var. crassiuscula. Var. Albomarginata showed lower shoot biomass under both water regimes than var. bituminosa (56.2% in WW plants and 55.2% in DW plants) and var. crassiuscula (52% in WW plants and 57.8% in DW plants). This lower shoot biomass could be attributed to the high initial soil water content imposed in this experiment, affecting early development. This hypothesis is supported by the lower root biomass production of var. albomarginata and its distribution. The DW treatment of this experiment was not sufficiently restrictive to cause morphological modifications, whilst of the forage quality variables analysed, only ash was affected. Var. crassiuscula and var. albomarginata had a lower specific leaf area (239 cm2 g‐1 and 235 cm2 g‐1, respectively) than var. bituminosa (352 cm2 g‐1), which might represent an important adaptation to high light intensity and temperature conditions. The values of stem mass fraction (SMF) and leaf mass fraction (LMF) for var. crassiuscula (SMF = 0.36 and LMF = 0.28) and var. albomarginata (SMF = 0.35 and LMF = 0.36) indicated better forage aptitude of these varieties than var. bituminosa (SMF = 0.50 and LMF = 0.19). All varieties showed good values of crude protein and digestibility, although important differences were found between leaf and stem. According to the studied morphological, nutritional and physiological traits, var. albomarginata showed the best aptitude for being introduced as permanent grasslands in some Mediterranean farming systems. However, the possible susceptibility of var. albomarginata to high water content in the soil could limit its introduction. These results help to inform the potential use of these three Canarian B. bituminosa varieties to improve Mediterranean rainfed grasslands of extensive farming systems.

Nitrogen addition affects plant biomass allocation but not allometric relationships among different organs across the globe

Abstract Aims Biomass allocation to different organs is a fundamental plant ecophysiological process to better respond to changing environments; yet, it remains poorly understood how patterns of biomass allocation respond to nitrogen (N) additions across terrestrial ecosystems worldwide. Methods We conducted a meta-analysis using 5474 pairwise observations from 333 articles to assess how N addition affected plant biomass and biomass allocation among different organs. We also tested the ‘ratio-based optimal partitioning’ vs. the ‘isometric allocation’ hypotheses to explain potential N addition effects on biomass allocation. Important Findings We found that (i) N addition significantly increased whole plant biomass and the biomass of different organs, but decreased root:shoot ratio (RS) and root mass fraction (RMF) while no effects of N addition on leaf mass fraction and stem mass fraction at the global scale; (ii) the effects of N addition on ratio-based biomass allocation were mediated by individual or interactive effects of moderator variables such as experimental conditions, plant functional types, latitudes and rates of N addition and (iii) N addition did not affect allometric relationships among different organs, suggesting that decreases in RS and RMF may result from isometric allocation patterns following increases in whole plant biomass. Despite alteration of ratio-based biomass allocation between root and shoot by N addition, the unaffected allometric scaling relationships among different organs (including root vs. shoot) suggest that plant biomass allocation patterns are more appropriately explained by the isometric allocation hypothesis rather than the optimal partitioning hypothesis. Our findings contribute to better understand N-induced effects on allometric relationships of terrestrial plants, and suggest that these ecophysiological responses should be incorporated into models that aim to predict how terrestrial ecosystems may respond to enhanced N deposition under future global change scenarios.

Relationship of fertilizer and periodic drought on biomass allocation in greenhouse-grown sunflower

The objective was to analyze organ plasticity in biomass allocation in response to limited resources and its influence on commercial traits of potted sunflower production. Although drought dramatically increased net photosynthetic rate and water-use efficiency, total leaf area, leaf dry mass, and total dry mass with drought stress decreased at rates of 20.9, 21.8, 23.0, and 9.9%, respectively. Irrigation positively affected specific leaf area, stem mass fraction, and root mass fraction. Adversely, fertilizer had a negative effect on stem mass fraction, root mass fraction, and root/shoot ratio. Interestingly, leaf mass fraction was not affected by them. Drought and greater fertilizer amount promoted flower yield and maintained leaf mass fraction stability at the expense of stem and root production. This induced plants to produce a thin stem, poor root system, and weak lodging resistance despite high flower production. This could have significant economic consequences for commercial potted flower production.

Alterations in biomass allocation indicate the adaptation of submersed macrophytes to low-light stress

Abstract The decline in submersed macrophytes induced by low-light stress is ubiquitous in mid-lower Yangtze lakes in China. However, the trade-offs among the adaptation mechanisms used by submersed macrophytes to low-light stress remain unclear. Moreover, the experimental period used in most previous studies was relatively short, and plant traits were not monitored multiple throughout the experimental period. In the present study, we examined the growth of a representative submersed macrophyte, Potamogeton maackianus, under four light regimes (2.8%, 7.1%, 17.1% and 39.5% of ambient light) over a course of 12 months and assessed various plant traits at monthly and quarterly intervals. The results showed that P. maackianus exhibited a lower leaf moisture content and a higher stem moisture content under decreased light conditions. Under the lowest light regime, P. maackianus had low soluble carbohydrate (SC) contents in the leaves and low starch contents in the stems at all the seasons. P. maackianus showed different allometric relationships among different treatments reflected different adaption strategies resulting from different light environment. P. maackianus exhibited a relatively stable biomass allocation pattern characterized by a continual increase in the stem mass fraction of total biomass under relatively high light transmittance (17.1% and 39.5%), which is a response of P. maackianus that can ensure a high initial biomass in the next spring season. However, under low light transmittance, the biomass allocation pattern fluctuated early in the experiment, and the amplitude increased with decreases in the light transmittance (2.8% and 7.1%). P. maackianus exhibited trade-offs between the stem (plant height) and leaf mass (leaf area) fractions of the total biomass, which help improve the adaptation of the macrophyte to a low-light environment. Our results can be useful for estimating light-use conditions of P. maackianus according to regression relationships between the leaf/stem mass fractions of the total biomass and time.

The enhancement of root biomass increases the competitiveness of an invasive plant against a co-occurring native plant under elevated nitrogen deposition

Nitrogen (N) is one of the most important nutrition controlling plant functioning and ecological stability, which is predicted to increase rapidly in the future. Despite numerous attempts to clarify the effects of N deposition on the growth and physiological processes of plants, the difference in the effects of N deposition on biomass allocation between invasive and native species have not been fully understood. We conducted simulated N deposition experiments on a co-occurring species pair in a greenhouse to examine the plant invasion mechanisms from the patterns in plant biomass allocation. The results showed that the invasive Solidago canadensis and native Artemesia argyi have the similar response trend in N addition, where leaf mass fraction (LMF) significantly decreased and stem mass fraction (SMF) significantly increased. The root mass fraction (RMF) strongly increased in invasive S. canadensis but there was a decrease in native A. argyi respond to N addition. These findings indicated that increased nutrients, such as soil N, may shift the plant allocation structure due to unequal effects of N among different organs and species. And provided an invasion mechanism where a change in the environment leads to the potential exclusion of native competitors via a significant increase in root biomass fraction of invasive plants. We also found that the optimal partitioning theory rather than the allometric partitioning theory, better explains the N-induced changes in biomass allocation strategies in the poor-resource environment. These could lead to an increased competitive ability of invasive plants for resource acquisition and profit from neighboring species, coupled with greater biomass accumulation and higher competitiveness in its new habitat (N addition in poor resource environment) compared to A. argyi, could give S. canadensis a substantial advantage over its co-occurring native species.

Contribution of conspecific soil microorganisms to tree seedling light responses: Insights from two tropical species with contrasting shade tolerance

Light intensity drives whole-plant carbon gain, with consequences for biomass production and plant community dynamics in forest systems. Recent studies suggest that soil microbial communities may mediate the impacts of resource availability on plant performance, yet little is known about the net effect of conspecific soil microorganisms for tree seedling light responses. Here we examined the interactive effects of light availability and presence of conspecific soil microorganisms on tree seedling growth, morphology and nutrient content for two congeneric tropical tree species. The two Bauhinia tree species with contrasting shade tolerance were grown in sterilized or unsterilized soil medium, under either high (50%) or low (10%) light conditions in a greenhouse experiment. Plant light responses and soil feedback effects were determined after 12 weeks. Results showed that the light-demanding tree species was generally more responsive to both light and soil microbes compared with its shade-tolerant congener. Presence of soil microbes enhanced plant growth and biomass responses to increased light availability for the light-demanding species alone, driven by positive soil feedback effects in high light. Six plant traits (leaf mass fraction, stem mass fraction, specific stem length, leaf phosphorus concentration, leaf nitrogen: phosphorus ratio and root nitrogen: phosphorus ratio) showed significant interactive effects between light and soil treatment. Observed changes to leaf biomass allocation in response to light in the presence of conspecific soil microorganisms were consistent with optimality theory and adjustments to maximize resource acquisition under different light conditions. In addition, presence of soil microbes decreased the average plasticity of plant nutrient content and stoichiometry in response to light for the light-demanding Bauhinia species. Together these results highlight the importance of conspecific soil microbes for plant-light relations, with implications for plant-plant interactions and species coexistence.

Effects of oak root pruning in forest nurseries on potential pathogen infections

AbstractDespite the general practice of root pruning, little is known about the potential impact of reducing shoot/root systems of oak seedlings in this way on their future susceptibility to pathogens, for exampleCylindrocarponspp.,Fusariumspp.,Ilyonectriaspp., Pythiumspp.Phytophthoraspp. orRhizoctoniaspp. In this study, root‐pruned and non‐pruned seedlings ofQuercus roburgrown under controlled conditions were inoculated with aggressive and less‐aggressive pathogens. Results indicated, in contrast to our initial assumption, that pathogens significantly reduced lateral root biomass more in non‐pruned seedlings, the extent of the response depending on the pathogens species. In response to pathogen pressure, pruned seedlings tended to attain a higher dry stem mass fraction, but lower dry leaf mass fraction. Pathogens also suppressed leaf mass in total root dry mass fraction (dry leaf mass/total root dry mass ratio, in g × g−1) more in pruned than in non‐pruned seedlings. These results suggest differences in growth between non‐pruned and pruned seedlings in response to pathogen stress. In nurseries, root pruning of oak trees may enhance the reduction in leaf mass in lateral roots mass fraction resulting from pathogen infections, which may decrease seedling quality. It is therefore important to ensure a low level of inoculum of soil‐borne pathogens to minimize the risk of seedling infection.

Variation in Organ Biomass with Changing Climate and Forest Characteristics across Chinese Forests

Forest biomass allocation patterns are important for understanding global carbon cycling and climate change, which might change with environmental conditions and forest characteristics. However, the effects of climate and forest characteristics on biomass allocation fractions (the fraction of total forest biomass distributed in organs) remains unknown. The authors use a large Chinese biomass dataset (1081 forests encompassing 10 forest types) to analyse the responses of biomass allocation fractions to biogeography, climate, and forest characteristics. The authors found that the stem mass fraction significantly increased with age and precipitation and significantly decreased with latitude and temperature. The branch mass fraction significantly decreased with age and density, but significantly increased with temperature and latitude. The leaf mass fraction significantly decreased with age and precipitation and significantly increased with temperature. The root mass fraction significantly increased with latitude and density, and significantly decreased with precipitation. The results suggest that latitude, temperature, precipitation, stand age and density are good predictors of biomass partitioning. These findings support the hypotheses that variation in resource availability constrains organ allocation and provides biogeographically explicit relationships between biomass allocation and both environmental and forest characteristics, which might be used for assessing the impact of changing environmental and forest characteristics on forest carbon dynamics and fixation.

Elevated CO2 does not offset effects of competition and drought on growth of shea (Vitellaria paradoxa C.F. Gaertn.) seedlings

The shea tree (Vitellaria paradoxa C. F. Gaertn.) is a major parkland species occurring across Africa from East to West. Its fruits, butter, and further products from shea butter play key roles in the Sustainable Development Goals of poverty eradication, hunger elimination, and gender equity in many African regions. The inter-play of abiotic conditions (e.g. rainfall patterns, drought periods) and biotic interactions (grazing by large herbivores) shape parklands because they influence vital processes like photosynthesis, transpiration and biomass production of common plant species including shea. We measured gas exchange of shea seedlings grown under ambient and elevated atmospheric CO2 (eCO2), with and without competition of the C4 grass Cenchrus pedicellatus, and under different water availabilities in greenhouse chambers. We hypothesized that eCO2 will generally increase seedling growth in shea via increases in photosynthesis. When growing together with C4 grass at low water availability, we expect an improved competitiveness of shea under eCO2, beacuse eCO2 is reported to augment water use efficiency (WUEi) of C3 plants more than C4 plants. Increased CO2 caused a 10% (p < 0.001) increase in maximum light-saturated photosynthesis (Amax), 22% (p < 0.001) increase in WUEi and 13% (p < 0.001) increase in stem mass fraction (SMF) of shea. Grass competition significantly reduced Amax by 9% (p < 0.001), SMF (p < 0.001) by 19%, with a corresponding reduction in all biomass parameters, but also significantly increased the C/N ratio (by 3%, p < 0.001). Interactive effects of eCO2 and competition were recorded for maximum electron transport rate, dark respiration, stomatal conductance, CO2 compensation point and the leaf area ratio. The control of grasses in the early stages of shea development is therefore recommended.

Aboveground biomass partitioning and additive models for Combretum glutinosum and Terminalia laxiflora in West Africa

Accurate estimates of aboveground biomass (AGB) strongly depend on the suitability and precision of allometric models. Although additive allometric equations are expected to reduce uncertainties due to additivity property between biomass of tree components, methods for developing biomass equations do not comply with the additivity property. This study aimed to evaluate biomass allocation patterns within tree components, and to develop additive allometric equations for Combretum glutinosum and Terminalia laxiflora in West Africa. Sixty trees were destructively sampled and measured for stem, branch and leaf biomass in Sudanian savannas of Burkina Faso. Biomass allocation to stem, branch and leaf was assessed by calculating the biomass fractions for each component. Bivariate relationships between biomass fraction and diameter at beast height (dbh) were further examined. For each biomass component we tested three non-linear allometric equations based on dbh alone, and dbh in combination with height and/or crown diameter as independent variables. Seemingly Unrelated Regressions were used to fit a system of additive biomass allometric equations. Branch biomass accounted for between 60 and 70% of the AGB. Branch mass fraction increased with increasing stem diameter while a reverse trend was observed for leaf and stem mass fractions. The decline in the mass fraction was more pronounced for the leaf than the stem. Additive biomass models developed for the two species exhibited good model fit and performance, with explained variance of 68–89%. The models developed in this study provide a robust estimation of tree biomass components and can be used in Sudanian savannas of West Africa.

Photosynthesis and carbon allocation are both important predictors of genotype productivity responses to elevated CO2 in Eucalyptus camaldulensis.

Intraspecific variation in biomass production responses to elevated atmospheric carbon dioxide (eCO2) could influence tree species' ecological and evolutionary responses to climate change. However, the physiological mechanisms underlying genotypic variation in responsiveness to eCO2 remain poorly understood. In this study, we grew 17 Eucalyptus camaldulensis Dehnh. subsp. camaldulensis genotypes (representing provenances from four different climates) under ambient atmospheric CO2 and eCO2. We tested whether genotype leaf-scale photosynthetic and whole-tree carbon (C) allocation responses to eCO2 were predictive of genotype biomass production responses to eCO2. Averaged across genotypes, growth at eCO2 increased in situ leaf net photosynthesis (Anet) (29%) and leaf starch concentrations (37%). Growth at eCO2 reduced the maximum carboxylation capacity of Rubisco (-4%) and leaf nitrogen per unit area (Narea, -6%), but Narea calculated on a total non-structural carbohydrate-free basis was similar between treatments. Growth at eCO2 also increased biomass production and altered C allocation by reducing leaf area ratio (-11%) and stem mass fraction (SMF, -9%), and increasing leaf mass area (18%) and leaf mass fraction (5%). Overall, we found few significant CO2 × provenance or CO2 × genotype (within provenance) interactions. However, genotypes that showed the largest increases in total dry mass at eCO2 had larger increases in root mass fraction (with larger decreases in SMF) and photosynthetic nitrogen-use efficiency (PNUE) with CO2 enrichment. These results indicate that genetic differences in PNUE and carbon sink utilization (in roots) are both important predictors of tree productivity responsiveness to eCO2.

Functional response of Quercus robur L. to taproot pruning: a 5-year case study

Key messageQuercus roburseedling mass was affected more by planting density than by taproot pruning. Root pruning enhanced stem biomass at the expense of roots in later growth stages. Alteration of biomass allocation due to nursery practices may result in greater susceptibility to injury and death of the seedlings under unfavorable environmental conditions.ContextPlants adjust their growth and modulate the resource allocation in response to applied treatments and environmental conditions.AimsThe aim was to examine how taproot pruning in seedlings grown at different densities affected long-term growth of Quercus robur.MethodsSeedlings, sown as acorns at two planting densities, with or without pruned roots were harvested in the second, fourth, and fifth years of growth. The effect of root pruning on biomass allocation was determined by measuring leaf, stem, and root mass fractions; carbohydrate concentrations in the roots; and C/N ratios. Specific leaf area and root length were also determined to assess morphological adaptations to growth conditions.ResultsTotal seedling mass was affected more by planting density than by taproot pruning. After 4 years of growth, root mass fractions were lower and stem mass fractions were greater in seedlings planted at a higher density. Five-year old root-pruned seedlings also had a lower root mass fraction and higher stem mass fractions than unpruned seedlings. Specific root length was not affected by root pruning or planting density.ConclusionDecrease of relative root biomass with simultaneous increase of stem biomass may be a long-term consequence of taproot pruning of Q. robur, and the effects may manifest years after the seedling stage.

Auxin-to-Gibberellin Ratio as a Signal for Light Intensity and Quality in Regulating Soybean Growth and Matter Partitioning.

The intensity and quality (red to far-red (R/Fr) ratio) of light directly affect growth of plant under shading. Gibberellins (GAs) and auxin [indole-3-acetic acid (IAA)] play important roles in mediating the shading adaptive responses of plants. Thus, the intensity and quality of the uncoupling light from shading were assessed to identify the influence of each component on the morphology and matter distribution of the leaf, stem, and petiole. This assessment was based on the changes in endogenous Gibberellin 1 (GA1) and IAA levels. Soybean plants were grown in a growth chamber with four treatments [normal (N), N+Fr, low (L), and L+Fr light]. Results revealed that the reductions in photosynthetically active radiation (PAR) and R/Fr ratio equally increased height and stem mass fractions (SMFs) of the soybean seedling. The light intensity significantly influenced the dry mass per unit area and mass fraction of soybean leaves, whereas the light quality regulated the petiole elongation and mass fraction. Low R/Fr ratio (high Fr light) increased the soybean biomass by improving the photosynthetic assimilation rate and quantum yield of photosystem II. In addition, the IAA and GA1 levels in the leaf, stem, and petiole did not reflect the growth response trends of each tissue toward light intensity and quality; however, trends of the IAA-to-GA1 content ratios were similar to those of the growth and matter allocation of each soybean tissue under different light environments. Therefore, the response of growth and matter allocation of soybean to light intensity and quality may be regulated by the IAA-to-GA1 content ratio in the tissues of the soybean plant.