Non-structural Carbohydrates Allocation Research Articles

Allocation of non-structural carbohydrates (NSC) contents in leaves and branches of Quercus variabilis during its growth process

Allocation of non-structural carbohydrates (NSC) contents in leaves and branches of Quercus variabilis during its growth process

Non-structural carbohydrates coordinate tree peony flowering both as energy substrates and as sugar signaling triggers, with the bracts playing an essential role

The natural fluorescence of tree peony is short. Forcing culture, mainly by defoliation and gibberellin (GA) treatment, is frequently used for its industrial production. We previously found forcing culture to be coordinated by non-structural carbohydrates (NSCs). Herein, we further revealed the specific role of NSCs during this process. We observed that both defoliation and GA treatment increased the photosynthesis in the bracts, and defoliation had a greater effect on NSC assimilation. We further determined the NSC content and PsSWEETs expression in the bracts, and the results indicated that GA may contribute more to NSC allocation by inducing PsSWEET7. Furthermore, we determined the trehalose-6-phosphate (T6P) content and sugar signaling-related gene (PsTPS1, PsSnRK1, and PsHXK1) expression in both the petals and bracts and found that both defoliation and GA treatment induced T6P levels as well as PsTPS1 expression in both tissues. This indicated that the sugar signaling pathway may also be involved in NSC-coordinated tree peony flowering. In particular, PsSnRK1 was more rapidly induced in the bracts (as an energy shortage response) in the control plants and was completely prohibited by defoliation and GA treatment, indicating the key role of the bracts in sugar signaling. In conclusion, NSCs induced tree peony flowering both as an energy substrate and sugar signaling trigger, with the bracts playing an essential role. These results may provide further evidence on the mechanism of NSC-coordinated flower opening in tree peony under forcing culture conditions, which may also provide a foundation for improving this technology.

Pathogen-induced defoliation impacts on transpiration, leaf gas exchange, and non-structural carbohydrate allocation in eastern white pine (Pinus strobus)

Pathogen-induced defoliation resulted in a reduction in transpiration, an upregulation of photosynthesis in the early growing season, and no change in NSC reserves across stem, root, and foliar tissues. The defoliation of eastern white pine (Pinus strobus L.) by native fungi associated with white pine needle damage (WPND) can substantially reduce foliar area for much of the growing season in the northeastern United States. Chronic defoliations in the region are known to have slowed growth rates in symptomatic stands, but the physiological impacts of WPND as it relates to tree water use and carbon assimilation are largely unresolved. We investigated how the severity of WPND defoliation influences transpiration throughout the course of a growing season. We also assessed leaf-level gas exchange between defoliation severity classes and needle age over time. Finally, we compared concentrations of non-structural carbohydrates (NSC) between defoliation severity classes in five different tissue types over time. We found that trees experiencing a high-severity defoliation had 20% lower sap flux density compared to low-severity individuals. We found that rates of photosynthesis were significantly influenced by the needle age class and time of year, while instantaneous water use efficiency was higher across all needle age classes late in the growing season. Our findings suggest that the residual current-year foliage of high-severity defoliated trees compensated for the loss of mature second- and third-year foliage in the early portion of the growing season. This study found that soluble sugars and starch varied significantly over time and by tissue type, but defoliation severity had little effect on NSC concentrations. Together with reduced basal area increment in high-severity trees relative to low-severity trees, this indicates that WPND-affected trees are prioritizing NSC storage over secondary growth.

Xeric Tree Populations Exhibit Delayed Summer Depletion of Root Starch Relative to Mesic Counterparts

Research linking soil moisture availability to nonstructural carbohydrate (NSC) storage suggests greater NSC reserves promote survival under acute water stress, but little is known about how NSC allocation responds to long-term differences in water availabilty. We hypothesized populations experiencing chronic or frequent water stress shift carbon allocation to build greater NSC reserves for increased survival probability during drought relative to populations rarely experiencing water stress. Over a year, we measured soluble sugar and starch concentrations from branches, stems, and coarse roots of mature Pinus palustris trees at two sites differing in long-term soil moisture availability. Xeric and mesic populations exhibited a cycle of summer depletion-winter accumulation in root starch. Xeric populations reached a maximum root starch concentration approximately 1–2 months later than mesic populations, indicating delayed summer depletion. Xeric and mesic populations reached the same minimum root starch at similar times, suggesting extended winter accumulation for xeric populations. These results suggest seasonal mobilization from root starch is compressed into a shorter interval for xeric populations instead of consistently greater reserves as hypothesized. Seasonal trends differed little between xeric and mesic populations for starch and sugars, suggesting the importance of roots in seasonal carbon dynamics and the primacy of starch for storage. If roots are the primary organ for longterm storage, then our results suggest that whole-plant mobilization and allocation respond to chronic differences in water availability.

Analysis of the NSC Storage Dynamics in Tree Organs Reveals the Allocation to Belowground Symbionts in the Framework of Whole Tree Carbon Balance

Photosynthesis is not entirely synchronized with carbon sinks, implying that trees are capable of storing non-structural carbohydrates (NSC) such as soluble sugars and starch. These storages provide a buffer between carbohydrate supply and demand and also allow trees to resist drought through osmoregulation. However, estimates of the total pool size and seasonal dynamics of the NSC storage of mature trees are still rare. Part of NSC is allocated outside roots, mainly to symbiotic, root-associated mycorrhizal fungi. The quantity and dynamics of this allocation are difficult to estimate in field conditions due to the close interaction between the symbionts. The aims of this study were to (1) determine the temporal development of NSC concentrations in tree organs, (2) upscale the storage compounds to whole-tree level and (3) analyse the significance of NSC allocation to belowground symbionts as part of the carbon balance in mature pines in a boreal Scots pine stand in southern Finland. We took samples every 2–4 weeks of needles, fine roots, stem wood, shoot wood and phloem from 1–3 trees in 2015. Concentrations of soluble sugars and starch were analyzed from the samples and upscaled to tree level. For quantifying the third aim, we used a whole-tree carbon balance model CASSIA that incorporates daily photosynthesis, respiration and organ-specific growth as functions of environmental factors. In this study, we included the allocation to belowground symbionts as an additional carbon sink and scaled the flux using the NSC pool over the whole tree. We observed that organ-specific NSC concentrations were highest in phloem, needles and fine roots. Total NSC increased in spring, peaked during mid-summer and decreased again in autumn without any notable decrease during the most intensive growth period at midsummer. In the model analysis, 6 % of yearly photosynthesis was allocated to the root-associated symbionts. The study highlights the applicability of the carbon balance approach in evaluating the importance of processes that cannot yet be directly measured.

Differentiated responses of nonstructural carbohydrate allocation to climatic dryness and drought events in the Inner Asian arid timberline

Isolated patchy forests in the arid timberline of Inner Asia are facing increasing risk of forest mortality with increasing drought frequency. The allocation of nonstructural carbohydrates (NSC) helps forests adapt to increasing drought. Previous studies that focused on site-level observations of NSC responses to changes in seasonal rainfall suggested that NSC in branches and stems showed no difference under different levels of drought stress. We conducted large-scale sampling of Larix sibirica-dominated forest patches of different sizes at 7 sites with different mean annual precipitation (MAP) in northern Mongolia in August 2017. Results showed that MAP determines the leaf and stem soluble sugar (SS), leaf and branch starch concentrations of Larix sibirica. The branch stores more starch at lower MAP. A comparison of seasonal NSC dynamics between wetter and dryer sites in the arid timberline of northern China shows that starch in stems is significantly higher for both Pinus sylvestris var. mongolica and Betula platyphylla at drier sites in the dry year 2017 than the normal year 2016. Our two lines of evidence suggest that the enhanced shoot starch allocation is an immediate response of trees to drought, rather than an adaptation strategy to regional climate dryness, although a spatial pattern may exist.

Short-term effects of combined elevated ozone and limited irrigation on accumulation and allocation of non-structural carbohydrates in leaves and roots of poplar sapling

Short-term effects of combined elevated ozone and limited irrigation on accumulation and allocation of non-structural carbohydrates in leaves and roots of poplar sapling

Allocation Mechanisms of Non-Structural Carbohydrates of Robinia pseudoacacia L. Seedlings in Response to Drought and Waterlogging

Climate change is likely to lead to an increased frequency of droughts and floods, both of which are implicated in large-scale carbon allocation and tree mortality worldwide. Non-structural carbohydrates (NSCs) play an important role in tree survival under stress, but how NSC allocation changes in response to drought or waterlogging is still unclear. We measured soluble sugars (SS) and starch in leaves, twigs, stems and roots of Robinia pseudoacacia L. seedlings that had been subjected to a gradient in soil water availability from extreme drought to waterlogged conditions for a period of 30 days. Starch concentrations decreased and SS concentrations increased in tissues of R. pseudoacacia seedlings, such that the ratio of SS to starch showed a progressive increase under both drought and waterlogging stress. The strength of the response is asymmetric, with the largest increase occurring under extreme drought. While the increase in SS concentration in response to extreme drought is the largest in roots, the increase in the ratio of SS to starch is the largest in leaves. Individual components of SS showed different responses to drought and waterlogging across tissues: glucose concentrations increased significantly with drought in all tissues but showed little response to waterlogging in twigs and stems; sucrose and fructose concentrations showed marked increases in leaves and roots in response to drought but a greater response to drought and waterlogging in stems and twigs. These changes are broadly compatible with the roles of individual SS under conditions of water stress. While it is important to consider the role of NSC in buffering trees against mortality under stress, modelling this behaviour is unlikely to be successful unless it accounts for different responses within organs and the type of stress involved.

Effects of defoliation on the allocation of non-structural carbohydrates in roots of Fraxinus mandshurica seedlings.

Global climate changes would lead to outbreaks of leaf-feeding insects. Leaf loss could reduce photosynthate production, with consequences on non-structural carbohydrates (NSC) storage and allocation in trees. In this study, the responses of NSC and its compartment concentrations in tap-, coarse- and the first to fifth order fine roots of 2-year-old seedlings of Fraxinus mandshurica to defoliation (40% loss of leaf area) were measured from June to October. The results showed that NSC and its compartment concentrations in roots exhibited distinct seasonal dynamics in both control and defoliation treatments. Following defoliation, NSC concentration decreased in tap- and coarse roots by 3.8% and 30.7%, respectively, while increased in the first five order roots by 1.2%-23.5%, to which starch contributed majorly for each root compartment. Soluble sugar concentration was enhanced by defoliation in tap- and coarse roots by 7.1% and 62.3%, respectively, but decreased in the first to fifth order roots by 2.7%-42.8%. Defoliation had different influences on starch and soluble sugar, with positive effects on the ratio of soluble sugar to starch concentrations in tap- and coarse roots but negative effects on the first to fifth order roots. Overall, defoliation decreased photosynthate production in leaves, leading to the remobilization of starch in tap- and coarse roots and the transportation as soluble sugar to fine roots, as well as the following storage in these roots, which would facilitate the resistance of fine roots to the low temperature in winter.

Leaf non-structural carbohydrate allocation and C:N:P stoichiometry in response to light acclimation in seedlings of two subtropical shade-tolerant tree species

Light availability greatly affects plant growth and development. In shaded environments, plants must respond to reduced light intensity to ensure a regular rate of photosynthesis to maintain the dynamic balance of nutrients, such as leaf non-structural carbohydrates (NSCs), carbon (C), nitrogen (N) and phosphorus (P). To improve our understanding of the nutrient utilization strategies of understory shade-tolerant plants, we compared the variations in leaf NSCs, C, N and P in response to heterogeneous controlled light conditions between two subtropical evergreen broadleaf shade-tolerant species, Elaeocarpus sylvestris (E. sylvestris) and Illicium henryi (I. henryi). Light intensity treatments were applied at five levels (100%, 52%, 33%, 15% and 6% full sunlight) for 30 weeks to identify the effects of reduced light intensity on leaf NSC allocation patterns and leaf C:N:P stoichiometry characteristics. We found that leaf soluble sugar, starch and NSC concentrations in E. sylvestris showed decreasing trends with reduced light intensity, whereas I. henryi presented slightly increasing trends from 100% to 15% full sunlight and then significant decreases at extremely low light intensity (6% full sunlight). The soluble sugar/starch ratio of E. sylvestris decreased with decreasing light intensity, whereas that of I. henryi remained stable. Moreover, both species exhibited increasing trends in leaf N and P concentrations but limited leaf N:P and C:P ratio fluctuations with decreasing light intensity, revealing their adaptive strategies for poor light environments and their growth strategies under ideal light environments. There were highly significant correlations between leaf NSC variables and C:N:P stoichiometric variables in both species, revealing a trade-off in photosynthesis production between leaf NSC and carbon allocation. Thus, shade-tolerant plants readjusted their allocation of leaf NSCs, C, N and P in response to light acclimation. Redundancy analysis showed that leaf morphological features of both E. sylvestris and I. henryi affected their corresponding leaf nutrient traits. These results improve our understanding of the dynamic balance between leaf NSCs and leaf C, N and P components in the nutritional metabolism of shade-tolerant plants. Key messageTwo species of understory shade-tolerant plants responded differently to varying light intensities in terms of leaf non-structural carbohydrate allocation and the utilization of carbon, nitrogen and phosphorus to balance nutritional metabolism and adapt to environmental stress.

Seasonal patterns of nonstructural carbohydrate reserves in four woody boreal species1

Plants store nonstructural carbohydrates (NSCs), such as sugars and starch, to use as carbon and energy sources for daily maintenance and growth needs as well as during times of stress. Allocation of NSCs to storage provides an important physiological strategy associated with future growth and survival, and thus understanding the seasonal patterns of NSC reserves provides insight into how species with different traits (e.g., growth form, leaf habit, wood anatomy) may respond to stress. We characterized the seasonal patterns of NSCs in four woody boreal plant species in Minnesota, USA. Sugar and starch concentrations were measured across the year in the roots and branches of two conifer trees, black spruce (Picea mariana (Mill.) B.S.P.) and eastern tamarack (Larix laricina (Du Roi) K. Koch), as well as in the leaves and branches of two evergreen broadleaf shrubs, bog Labrador tea (Rhododendron groenlandicum (Oeder) Kron & Judd) and leatherleaf (Chamaedaphne calyculata (L.) Moench). In general, seasonal variation was dominated by changes in starch across all organs and species. While similar seasonal patterns of NSCs were observed in the shrubs, different seasonal patterns were observed between the trees, particularly in the roots. Our results suggest that species-specific traits likely have consequences for organ-level storage dynamics, which may influence whole-plant growth and survival under global change.

Unfolding Non-structural Carbohydrates from Sapling to Dying Black Locust on China’s Loess Plateau

Non-structural carbohydrates (NSC) play important roles in metabolic processes of plants and represent important functional traits in plant adaptation to the external environment. However, there are few reports concerning intra-annual NSC distribution in temperate deciduous forests, especially for the purpose of comparison among different stand ages on China’s Loess Plateau. Here, NSC allocation dynamics with age ring-porous black locust tree was determined for the growing (May) and dormant (November) seasons over the period from sapling to dying trees—defined as a completely defoliated tree with dried branches in the growing season. It was noted that regardless of tree age, NSC concentration was highest in coarse roots [16.4 g per 100 g of dry mass (16.4% DM)] and stems (15.1% DM). At the tree level, NSC concentration was highest (14.3% DM) in a 30-year-old stand in November and lowest (4.1% DM) in dying stands in May. The pool of NSC at tree level was highest (25.2 kg DM per tree) in 30-year-old stands in November and lowest (0.13 kg DM per tree) in sapling stands in May. The concentration of NSC was significantly lower in May than in November for all tree ages, organs, and biochemical components. The results underscored the importance of NSC in plant growth on China’s Loess Plateau. It also provided a useful insight into the dynamics of NSC from sapling to dying broadleaved tree species.

Whole-tree distribution and temporal variation of non-structural carbohydrates in broadleaf evergreen trees.

Non-structural carbohydrates (NSCs) form a fundamental yet poorly quantified carbon pool in trees. Studies of NSC seasonality in forest trees have seldom measured whole-tree NSC stocks and allocation among organs, and are not representative of all tree functional types. Non-structural carbohydrate research has primarily focussed on broadleaf deciduous and coniferous evergreen trees with distinct growing seasons, while broadleaf evergreen trees remain under-studied despite their different growth phenology. We measured whole-tree NSC allocation and temporal variation in Eucalyptus obliqua L'Hér., a broadleaf evergreen tree species typically occurring in mixed-age temperate forests, which has year-round growth and the capacity to resprout after fire. Our overarching objective was to improve the empirical basis for understanding the functional importance of NSC allocation and stock changes at the tree- and organ-level in this tree functional type. Starch was the principal storage carbohydrate and was primarily stored in the stem and roots of young (14-year-old) trees rather than the lignotuber, which did not appear to be a specialized starch storage organ. Whole-tree NSC stocks were depleted during spring and summer due to significant decreases in starch mass in the roots and stem, seemingly to support root and crown growth but potentially exacerbated by water stress in summer. Seasonality of stem NSCs differed between young and mature trees, and was not synchronized with stem basal area increments in mature trees. Our results suggest that the relative magnitude of seasonal NSC stock changes could vary with tree growth stage, and that the main drivers of NSC fluctuations in broadleaf evergreen trees in temperate biomes could be periodic disturbances such as summer drought and fire, rather than growth phenology. These results have implications for understanding post-fire tree recovery via resprouting, and for incorporating NSC pools into carbon models of mixed-age forests.

Recovery following defoliation involves shifts in allocation that favour storage and reproduction over radial growth in black oak

SummaryCarbon allocation to growth, storage, reproduction and the effects of stress and disturbances on these processes remain poorly understood in trees. Non‐structural carbohydrates (NSC) are an important component of the carbon storage pool and are commonly used to assess whether tree growth under various conditions is carbon limited. Carbon limitation is generally assumed to result in reducedNSClevels and allocation, but changes in allocation priorities that favourNSCstorage could also limit carbon available for growth.We defoliated six mature oak trees in June 2010 and explored how defoliation affects the relationship between radial growth and netNSCstorage, estimated by the seasonal increase inNSCconcentration, for several years. We interpret our results in the context of a conceptual model of allocation – developed here – to help understand how allocation changed following defoliation. We also monitored flower and acorn production in 2011, as changes in reproduction could also affect allocation to growth and storage.Defoliation reduced radial growth for 3 years. Stemwood starch levels and storage were also generally reduced, although not as consistently as growth. In contrast, root collarNSCstorage was significantly greater in defoliated trees, allowing below‐ground stores to recover to control levels by November 2011. Defoliation had mixed effects on reproduction in 2011: production of second‐year acorns (initiated before defoliation) was not significantly affected, but there was complete cessation of flower production. Defoliation also changed the relationship betweenNSCallocation and growth in the 2 years following defoliation, indicating a shift in allocation favouring storage.According to our conceptual model, the positive relationship between growth andNSCallocation indicates that the allocation shifts occurred under carbon‐limiting conditions. We, therefore, propose that growth can be carbon limited by two different means: (i) a decrease in plant carbon availability and (ii) allocation shifts that reduce the priority of growth relative to other processes such as storage. Prioritizing storage over both growth and reproduction may be a strategy to protect against further disturbance or stress following storage depletion.Synthesis. Recovery following defoliation can involve substantial shifts in how trees allocate carbon between different functions, with carbohydrate storage and already initiated reproduction cycles being favoured relative to growth and new reproductive cycles.

Drought and shade deplete nonstructural carbohydrate reserves in seedlings of five temperate tree species.

Plants that store nonstructural carbohydrates (NSC) may rely on carbon reserves to survive carbon‐limiting stress, assuming that reserves can be mobilized. We asked whether carbon reserves decrease in resource stressed seedlings, and if NSC allocation is related to species' relative stress tolerances. We tested the effects of stress (shade, drought, and defoliation) on NSC in seedlings of five temperate tree species (Acer rubrum Marsh., Betula papyrifera Marsh., Fraxinus americana L ., Quercus rubra L., and Quercus velutina Lam.). In a greenhouse experiment, seedlings were subjected to combinations of shade, drought, and defoliation. We harvested seedlings over 32–97 days and measured biomass and NSC concentrations in stems and roots to estimate depletion rates. For all species and treatments, except for defoliation, seedling growth and NSC accumulation ceased. Shade and drought combined caused total NSC decreases in all species. For shade or drought alone, only some species experienced decreases. Starch followed similar patterns as total NSC, but soluble sugars increased under drought for drought‐tolerant species. These results provide evidence that species deplete stored carbon in response to carbon limiting stress and that species differences in NSC response may be important for understanding carbon depletion as a buffer against shade‐ and drought‐induced mortality.

Allocation to carbon storage pools in Norway spruce saplings under drought and low CO2.

Non-structural carbohydrates (NSCs) are critical to maintain plant metabolism under stressful environmental conditions, but we do not fully understand how NSC allocation and utilization from storage varies with stress. While it has become established that storage allocation is unlikely to be a mere overflow process, very little empirical evidence has been produced to support this view, at least not for trees. Here we present the results of an intensively monitored experimental manipulation of whole-tree carbon (C) balance (young Picea abies (L.) H Karst.) using reduced atmospheric [CO2] and drought to reduce C sources. We measured specific C storage pools (glucose, fructose, sucrose, starch) over 21 weeks and converted concentration measurement into fluxes into and out of the storage pool. Continuous labeling ((13)C) allowed us to track C allocation to biomass and non-structural C pools. Net C fluxes into the storage pool occurred mainly when the C balance was positive. Storage pools increased during periods of positive C gain and were reduced under negative C gain. (13)C data showed that C was allocated to storage pools independent of the net flux and even under severe C limitation. Allocation to below-ground tissues was strongest in control trees followed by trees experiencing drought followed by those grown under low [CO2]. Our data suggest that NSC storage has, under the conditions of our experimental manipulation (e.g., strong progressive drought, no above-ground growth), a high allocation priority and cannot be considered an overflow process. While these results also suggest active storage allocation, definitive proof of active plant control of storage in woody plants requires studies involving molecular tools.

Different light acclimation strategies of two coexisting tree species seedlings in a temperate secondary forest along five natural light levels

To understand how temperate coexisting tree species acclimate to natural light levels, seedlings of two coexisting species, Pinus koraiensis Sieb. et Zucc. and Quercus mongolica Fisch., were transplanted to five light levels (100%, 20%, 10%, 5%, and 1%) under natural forest stands. The survival/growth rates, nonstructural carbohydrate (NSC) concentrations and pools in each plant organ of the two species seedlings were monitored in two consecutive years. The survival rate and relative growth rate (RGR) of both species peaked at the 100% light level. No seedlings of both species survived at the 1% light level. The NSC concentration varied insignificantly with light levels in the roots of Q. mongolica and the stems of both species in 2010, while the NSC concentration and pool decreased with light reduction for both species in 2011. With a light level decrease from 20% to 5%, Q. mongolica showed insignificant differences, but P. koraiensis exhibited a significant decrease in survival rate and NSC levels. The survival rates of P. koraiensis and Q. mongolica seedlings were positively and significantly related to the NSC concentration in leaves (r1=0.9898) and NSC concentration in roots (r2=0.9976), respectively. These results suggested that: (1) full sunlight was the optimum light environment for the initial survival and growth of both tree species; (2) low light induced carbohydrate deficiency, which might be the key factor resulting in seedling mortality in forest understory; (3) different NSC allocation patterns in response to light alteration might promote the coexistence of P. koraiensis and Q. mongolica in the early stage of regeneration in the forest stands.

Allocation of nonstructural carbohydrates for three temperate tree species in Northeast China

Aims The content and allocation of nonstructural carbohydrates(NSC) in trees reflect whole-tree carbon balance regimes,and are crucial to determine growth / survivorship trade-off of trees and model tree carbon balance between uptake and investments in structure or loss.Our objective was to examine the concentration and allocation patterns of NSC for three temperate tree species,i.e.,Korean pine(Pinus koraiensis),Dahurian larch(Larix gmelinii) and Mongolian oak(Quercus mongolica).Methods During the mid-growing season(July of 2010),all biomass tissues,including foliage,branch,stem and root,were randomly sampled from three dominant trees for each species.The stem samples were taken from mid-canopy and breast height,and divided into sapwood and heartwood,while the root samples were divided into fine(diameter 2 mm),medium(2–5 mm) and coarse roots(5 mm).All samples were dried,ground,and analyzed for NSC concentrations(including soluble sugar and starch) with a modified phenol-sulfuric acid method.Important findings The concentrations of NSC and its component differed significantly among species and tissues.Concentration ranges were 0.65–8.45,1.96–5.95 and 3.00–13.90 g.100 g –1 DM for soluble sugar,starch,and NSC,respectively.On average,the contents of NSC and its components followed the order of: larch oak pine.Concentrations in the foliage and roots were higher than those in other tissues.Within the stems,the longitudinal variations in the concentrations of NSC and its components were insignificant,whereas the differences between sapwood and heartwood varied with species and NSC components.There was no significant difference in soluble sugar concentration between sapwood and heartwood,but significant differences in starch and total NSC concentration.The concentrations of NSC and its components varied insignificantly with root diameters for larch and pine,but significantly for oak.Oak invested more soluble sugar to aboveground growth,whereas the two conifers did more to roots.Nevertheless,starch was mainly reserved in stems,and the intra-tree allocation pattern of starch exhibited an opposite trend to soluble sugar,leading the total NSC to be relatively balanced between roots and branches.In the stems,heartwood was the major reserve of NSC and starch,while sapwood was the major reserve of soluble sugar for the two conifers.In the roots,coarse root was the dominant reserves of NSC and its components.We concluded that the inter-and intra-specific variations in the NSC and its components in this study reflect differences in growth strategies and within-tree carbon source / sink strength for the three temperate tree species.

Nonstructural carbohydrate allocation following different frequencies of simulated browsing in three semi-arid shrubs.

Nonstructural carbohydrate allocation patterns in response to different frequencies of simulated browsing (leaf and twig removal) were studied in the following semi-arid shrubs: Osteospermum sinuatum, a dwarf deciduous shrub, Pteronia pallens, a dwarf evergreen shrub, and Ruschia spinosa, a dwarf leaf-succulent shrub. Simulated browsing at all frequencies resulted in the elevation, or had no effect, on total nonstructural carbohydrate (TNC) concentrations of O. sinuatum plant parts, and resulted in the decrease in TNC concentrations of R. spinosa plant parts. The responses of P. pallens were intermediate with elevations as well as declines in TNC concentrations of plant parts measured in response to various clipping frequencies. At the low frequency of simulated browsing (every 26 weeks) elevations in plant TNC content were measured in the two non-succulent shrubs O. sinuatum and P. pallens. It was concluded that the overcompensation with respect to TNC accumulation observed in the two non-succulent species represents one of the ways in which excess photosynthate is utilized by browsed shrubs with a limited regiowth potential. Simulated browsing was the least detrimental with respect to biomass production to the non-succulent O. sinuatum and P. pallens, and most injurious to the leaf-succulent shrub, R. spinosa. The observed TNC allocation patterns could not adequately explain the variation among species in the production of new growth and it was concluded that some factor(s) other than the carbon resource was limiting regrowth.

Effect of artificial defoliation of mid-ribbed snow tussock,Chionochloa pallens, in the Murchison Mountains, Fiordland, New Zealand

Abstract Biomass, tillering, and plant chemistry were measured in tussocks of Chionochloa pallens in low-alpine snow tussock grassland in Fiordland in April 1986, eight years after severe clipping in spring, 1977. Clipping increased tiller density, but depressed tiller size and total tussock biomass. Defoliated tussocks responded by decreasing the proportion of total biomass and mineral nutrients allocated to roots, and losing a greater percentage of these resources in leaf senescence. Total non-structural carbohydrate allocation, primarily sucrose and starch, is also significantly reduced in the stems of clipped tussocks. The many severe effects of a single defoliation on Chionochloa pallens tussocks and their slow rate of recovery suggests that it will be two decades, even in the absence of grazing, before they recover fully.