Non-structural Carbohydrate Storage Research Articles

Non-Structural Carbohydrate Storage Strategy Explains the Spatial Distribution of Treeline Species.

Environmental factors that drive carbon storage are often used as an explanation for alpine treeline formation. However, different tree species respond differently to environmental changes, which challenges our understanding of treeline formation and shifts. Therefore, we selected Picea jezoensis and Betula ermanii, the two treeline species naturally occurring in Changbai Mountain in China, and measured the concentration of non-structural carbohydrates (NSC), soluble sugars and starch in one-year-old leaves, shoots, stems and fine roots at different elevations. We found that compared with P. jezoensis, the NSC and soluble sugars concentrations of leaves and shoots of B. ermanii were higher than those of P. jezoensis, while the starch concentration of all the tissues were lower. Moreover, the concentration of NSC, soluble sugars and starch in the leaves of B. ermanii decreased with elevation. In addition, the starch concentration of B. ermanii shoots, stems and fine roots remained at a high level regardless of whether the soluble sugars concentration decreased. Whereas the concentrations of soluble sugars and starch in one-year-old leaves, shoots and stems of P. jezoensis responded similarly changes with elevation. These findings demonstrate that compared with P. jezoensis, B. ermanii has a higher soluble sugars/starch ratio, and its shoots, stems and fine roots actively store NSC to adapt to the harsh environment, which is one of the reasons that B. ermanii can be distributed at higher altitudes.

Death, sex, and sugars: variations in nonstructural carbohydrate concentrations in a sexually plastic tree.

Environmental sex determination (ESD) is a rare sex determination system in which individuals may switch sex expression throughout their lifetimes in response to environmental factors. In sexually stable species, individuals usually bear more female flowers if the plants are larger, have greater access to limiting resources, or are in better condition. Research regarding sexually plastic species with ESD and how resources correlate with sex expression is limited. Furthermore, most research investigates resources at the population level, failing to account for resources available to individuals for growth, maintenance, or reproduction. Acer pensylvanicum is a species that is known to switch sex. Using twig samples collected during 2014-2016 in December and May, we analyzed resource status in the form of stored nonstructural carbohydrates (NSCs) and compared this with expressed sex. We found that females had higher sugar concentrations than males. Furthermore, males changing expression to female had higher sugar concentrations during the prior winter than did males remaining male. We found that size was not a key predictor: neither male nor female-flowering individuals increased NSC concentrations with size. Dying female trees had high concentrations of NSCs throughout the dying process and only manifested reduced NSCs once dead. This is the first study showing significant correlations between NSCs and sex expression in a plant species with ESD. These findings support the hypothesis that sex switching could be a consequence of increased resource availability and that the high female mortality of A. pensylvanicum populations is likely not a direct result of carbon starvation.

Ray fractions and carbohydrate dynamics of tree species along a 2750m elevation gradient indicate climate response, not spatial storage limitation.

Parenchyma cells in the xylem store nonstructural carbohydrates (NSC), providing reserves of energy that fuel woody perennials through periods of stress and/or limitations to photosynthesis. If the capacity for storage is subject to selection, then the fraction of wood occupied by living parenchyma should increase towards stressful environments. Ray parenchyma fraction (RPF) and seasonal NSC dynamics were quantified for 12 conifers and three oaks along a transect spanning warm dry foothills (500m above sea level) to cold wet treeline (3250m asl) in California's central Sierra Nevada. Mean RPF was lower for both conifer and oak species with warmer dryer ranges. RPF variability increased with elevation or in relation to associated climatic variables in conifers-treeline-dominant Pinus albicaulis had the lowest mean RPF measured (c. 3.7%), but the highest environmentally standardized variability index. Conifer RPF variability was explained by environment, increasing predominantly towards cooler wetter range edges. In oaks, NSC was explained by environment-values increasing for evergreen and decreasing for deciduous oaks with elevation. Lastly, all species surveyed appear to prioritize filling available RPF with sugar to achieve molarities that balance reasonable tensions over starch to maximize stored carbon. RPF responds to environment but is unlikely to spatially constrain NSC storage.

Comparison of phenological traits, growth patterns, and seasonal dynamics of non-structural carbohydrate in Mediterranean tree crop species

Despite non-structural carbohydrate (NSC) importance for tree productivity and resilience, little is known about their seasonal regulations and trade-off with growth and reproduction. We characterize the seasonal dynamics of NSC in relation to the aboveground phenology and temporal growth patterns of three deciduous Mediterranean species: almond (Prunus dulcis (Mill.) D. A. Webb), walnut (Juglans regia L.) and pistachio (Pistacia vera L.). Seasonal dynamics of NSC were synchronous between wood tissues from trunk, branches and twigs. Almond had almost identical levels and patterns of NSC variation in twigs, branches and trunks whereas pistachio and walnut exhibited clear concentration differences among plant parts whereby twigs had the highest and most variable NSC concentration, followed by branches and then trunk. While phenology had a significant influence on NSC seasonal trends, there was no clear trade-off between NSC storage and growth suggesting that both were similarly strong sinks for NSC. A temporal trade-off observed at the seasonal scale was influenced by the phenology of the species. We propose that late senescing species experience C allocation trade-off at the end of the growing season because of C-limiting thermal conditions and priority allocation to storage in order to survive winter.

Effects of pruning intensity on nonstructural carbohydrates of Populus alba × P. talassica in the arid desert region of Northwest China

Although pruning is important to obtain high-quality, large-diameter timber, the effects of pruning on nonstructural carbohydrates (NSC) in aboveground organs of many timber species are not well understood. Three intensities of pruning (none, moderate and severe) were tested on poplars (Populus alba × P. talassica) in the arid desert region of northwest China to compare the concentrations of soluble sugar (SS), starch (ST) and total nonstructural carbohydrate (TNC) in leaves, branches and trunks during the growing season. The concentration of NSC components after different pruning intensities varied similarly in seasonal patterns, increasing slowly at the beginning of the growing season, continuously declining in the middle, then gradually recovering by the end of the growing season. The monthly mean NSC concentration in poplar differed significantly among the three pruning intensities (p branch > trunk, while the order of ST concentration was trunk > leaf > branch, which was related to functional differences of plant organs. The annual average growth in height of unpruned, moderately pruned, and severely pruned poplars was 0.21 ± 0.06, 0.45 ± 0.09 and 0.24 ± 0.05 m, respectively, and the annual average growth in DBH were 0.92 ± 0.04, 1.27 ± 0.06 and 1.02 ± 0.05 cm, respectively. Our results demonstrate that moderate pruning may effectively increase the annual growth in tree height and DBH while avoiding damage caused by excessive pruning to the tree body. Therefore, moderate pruning may increase the NSC storage and improve the growth of timber species.

Combined Effects of Drought and Shading on Growth and Non-Structural Carbohydrates in Pinus massoniana Lamb. Seedlings

Carbon assimilation is reduced by stress. Under such conditions, the trade-off between growth and non-structural carbohydrate (NSC) storage becomes crucial for plant survival and continued growth. However, growth and NSC responses to drought and shading in Pinus massoniana Lamb. remain unclear. Here, we investigated the effects of drought, shading, and combined drought and shading on leaf gas exchange parameters, stem basal diameter, plant height, biomass accumulation, and NSC concentration in 2-year old seedlings after a 2 month treatment. The results showed that (1) both drought and shading significantly reduced photosynthetic rate, increment of stem basal diameter and plant height, and biomass accumulation, while NSC concentration increased under drought but decreased under shading; (2) the combined drought-shading treatment had a stronger effect on photosynthetic rate and growth than either stress factor individually, whereas the concentration of NSC did not change significantly; and (3) drought, shading, and their combination had a lower effect on biomass than on NSC partitioning, in which case clear effects were observed. Drought increased NSC proportion in roots by 5.4%; conversely, shading increased NSC proportion in leaves by 3.7%, while the combined treatment increased NSC proportion in roots by 5.1% but decreased it in the leaves by 5.4%. These results suggest that the mechanism inhibiting P. massoniana growth is different under drought and shading conditions according to carbon partitioning. Furthermore, complex environmental stress may lead to different mechanisms of carbon partitioning compared with either dry or shaded environments. Our findings will be helpful in predicting the impact of climate change on P. massoniana growth.

How can the shade intolerant Korean pine survive under dense deciduous canopy?

The regeneration of Korean pine (Pinus koraiensis Sieb. et Zucc) is a core issue for restoration from secondary to primary forests. There is a lack of Korean pine regeneration in primary forests, compared to an abundance of regeneration in secondary forests. However, the mechanisms behind this mysterious phenomenon have not been studied. This study investigated seasonal understory light availability in addition to carbon (C) gain of understory Korean pine, nonstructural carbohydrate (NSC) storage of Korean pine in secondary forests, and the growth and survival of seedlings under manipulated light regimes. Understory light intensities in early spring and late autumn in secondary forests were significantly higher than in primary forests. The C gain of understory Korean pine occurred mostly in early spring and late autumn, whereas it was negative in the growing season (summer). Total NSC concentrations of Korean pine saplings increased between growing seasons, and decreased during the growing season. In particular, the NSC was dominated by a progressive increase in starch in early spring and by a peak in soluble sugar in late autumn. In this study, the biomass, NSC concentration and pool sizes, as well as survival rates, were positively correlated with light availability, revealing that the species is shade intolerant. The accumulated survival rate, examined in the autumn, was less correlated with biomass, but positively correlated with the carbohydrate storage in autumn. High light availability and positive C gain in early spring and late autumn are key factors affecting the growth and survival of understory seedlings. These two periods in secondary forests are crucial for the survival of seedlings by ensuring sufficient energy to live through the long-lasting dark summer. In primary forests, however, light availability was relatively stable across all seasons, especially in the leafless period, and insufficient through-canopy radiation, along with dense lateral closure, caused seedlings mortality.

Effects of nitrogen enrichment on tree carbon allocation: A global synthesis

AbstractAimIncreased atmospheric nitrogen deposition may have profound effects on tree carbon allocation dynamics. However, a comprehensive understanding of how nitrogen (N) enrichment influences carbon (C) allocation across plant functional processes and tree organs in individual trees remains elusive.LocationGlobal forest ecosystems.Time period1990–2018.Major taxa studiedTrees.MethodsWe compiled data from 75 N addition experiments and conducted a meta‐analysis to evaluate the responses of C source (photosynthesis), sinks (growth and respiration) and storage (non‐structural carbohydrate concentrations) in different tree organs (foliage, above‐ground wood and roots) to N enrichment.ResultsN enrichment significantly enhanced C supply via photosynthesis (+39.6%, n = 128). C allocation to growth (biomass increment/production) significantly increased in foliage (+15.9%, n = 68) and above‐ground wood (+31.8%, n = 64; bole, branch, stem and/or twig) with increasing N availability, but not in roots, whereas allocation increased in roots via increasing fine root turnover rate (+22.6%, n = 11). N fertilization significantly increased C allocation to respiration in above‐ground wood (+46.6%, n = 12) and roots (+5.5%, n = 57), but not in foliage. N addition decreased non‐structural carbohydrate (NSC) concentrations in foliage (−5.4%, n = 16) and roots (−5.0%, n = 21), but increased NSC in above‐ground wood (+6.1%, n = 22). In addition, N enrichment effects were strongly affected by moderator variables.Main conclusionsOur results demonstrate that N addition increased C allocation to growth and respiration more strongly than C allocation to NSC storage, and increased C allocation to above‐ground parts more strongly than to below‐ground parts. Our results are useful for better understanding the response of tree functional processes at organ level to N enrichment. The existing data also reveal that more long‐term experimental studies on mature trees in tropical and boreal forests are urgently needed to provide a basis for forecasting tree responses to N enrichment at the global scale.

Non-structural Carbohydrates in Dormant Woody Perennials; The Tale of Winter Survival and Spring Arrival

Woody perennials’ reliance on nonstructural carbohydrates (NSC) reserves for the resumption of spring growth necessitates an accumulation of NSC prior to dormancy. It is assumed that during dormancy temperature-regulated biological activities gauge the progression of winter and affect the metabolic rates and physiology of NSC reserves. Thus, changes in temperature signal the arrival of spring and determine the amount of reserves available for growth resumption. As woody perennials are dependent on dispersed storage of NSC during spring, they need an integrated remobilization and redistribution for synchronous and effective development of photosynthetic and reproductive organs. However, it is not known how storage compartments interact at the whole plant level, when NSC reserves are mobilized, or how local and distal storage compartments influence the biology of spring growth resumption. The goal of this mini-review is to shift the focus of winter biology from bud-centric to the whole plant. We discuss winter NSC management in the context of climate change with a special emphasis on how projected mild winters may affect the carbon budget, transport, and allocation during winter. We look at three aspects of NSC regulation underlying dormancy (I) the molecular regulation of dormancy (II) temperature dependent winter NSC metabolism, and (III) spring NSC remobilization and redistribution processes.

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.

Response of Taxodium distichum to winter submergence in the water-level-fluctuating zone of the Three Gorges Reservoir region

This study investigated the physiological and ecological processes of Taxodium distichum in the water-level-fluctuating zone (WLFZ) of the Three Gorges Reservoir (TGR). We determined the contents of non-structural carbohydrates (NSCs), N and P in the aboveground parts and root systems of T. distichum individuals that had experienced 3 yearly flooding cycles. These flooding cycles were driven by the operation of the reservoir in the Zhong County vegetation restoration demonstration area. This flooding inhibited the growth of T. distichum. The plant heights and canopy diameters of the flooded groups were significantly smaller than those of the control group. The flooding facilitated the synthesis of NSCs, and the soluble sugar content in the NSCs increased. The flooding inhibited the uptake of N and P, but the N/P ratios remained stable. The ratios of NSCs to N or P increased. T. distichum adapts well to submergence because of its regulation of NSC synthesis and storage, its balancing of the inputs of photosynthetic products to growth and storage, and its storage of material during exposure to maintain physiological activities during winter submergence and the energy sources required for growth during exposure. This study may provide a useful reference for use in vegetation reconstructions in areas with hydrological characteristics similar to those of the TGR.

Summer drought stress: differential effects on cane anatomy and non-structural carbohydrate content in overwintering Cabernet Sauvignon and Syrah vines

Grapevines store non-structural carbohydrates (NSC) during late summer to sustain plant development at the onset of the following spring’s growth. Starch is the main stored carbohydrate, found in the wood-ray parenchyma of roots and canes. Although the relationship between hydraulic and plant photosynthetic performance is well-recognized, little research has been done on the long-term effects of drought in grapevines adopting different strategies to cope with water stress (i.e. isohydric and anisohydric). We performed our study by exposing two different grape cultivars (Syrah and Cabernet Sauvignon) to a short but severe drought stress, at two stages of the growing season (July and September). No marked differences in the physiological and hydraulic responses of the two varieties were found, probably due to our experimental conditions. However, anatomical and biochemical characterization of overwintering canes pointed out several interesting outcomes. We found a significant and parallel increase of starch and medullar ray number in both cultivars exposed to early water stress. We hypothesize that stressed vines limited their carbon allocation to growth, while shifting it to starch accumulation, with a most evident effect in the period of intense photosynthetic activity. We also speculate that a different aptitude to osmotic adjustment may underlay variation in starch increase and the specific involvement of bark NSC in the two cultivars.

Physiological responses of orchid pseudobulbs to drought stress are related to their age and plant life form

As storage organs for water and nutrients, pseudobulbs play an important role in the survival of orchids. However, the differences in morphological and physiological responses of pseudobulbs to drought stress between epiphytic and terrestrial orchids remain undefined, and little is known about the physiological imparity of different-aged pseudobulbs. We investigated the anatomy and changes in physiology of pseudobulbs in an epiphytic orchid (Cymbidium tracyanum) and a terrestrial orchid (C. sinense) and compared their responses and recovery during and after periods of drought stress. In particular, “ramets severance treatment” and “multiple leafless pseudobulbs treatment” were applied for C. tracyanum to verify the utilization strategy for the stored water. When compared with C. sinense, the pseudobulbs of C. tracyanum have larger water-storage cells and higher water content, and the enhanced water storage of C. tracyanum can be used and recovered more rapidly. And they had more flexibility in shifting stored nonstructural carbohydrates. The remarkably high concentration and different change trends of abscisic acid (ABA) between different-aged pseudobulbs under drought stress were only found in C. tracyanum. When pseudobulb age was considered, the stored water and carbohydrate changed more rapidly in the youngest pseudobulbs of both species in response to stress. Our results indicated that the pseudobulbs differ in their means for coping with drought conditions according to their life form and age. These findings contribute to our understanding about the functional diversification of pseudobulbs and their strategies for ecological adaptations.

Heartwood formation process in teak (<i>Tectona grandis</i> L. f): fate of non-structural carbohydrates and characterization of forsythoside B

Heartwood formation is an important process in perennial plants as trees. Non-structural carbohydrates (NSC) storage in wood is an important feature of heartwood formation properties before and after wood drying. To better understand how NSC are stored and transformed in teak wood, their radial distribution was studied before and after chemical hydrolysis by using a spectrophotometric method coupled to enzymatic assays. In sapwood, NSC (starch, glucose, fructose and sucrose) and condensed NSC (mainly phenolic glucosides) were strongly accumulated respectively 100.9  5.9 and 30.2  5.5 mol.g.dw-1. They decreased abruptly (5-10 folds lower) from sapwood to heartwood. However, if the proportion of condensed glucose was 3 folds higher than that of non-condensed glucose in the sapwood, this ratio increases 20 folds in the heartwood indicating that glucosylation process could occur. The forsythoside B, a trisaccharide of caffeic acid present in sapwood, was likely hydrolyzed during heartwood formation. Our results show that high proportions of starch and soluble NSC (glucose, fructose and sucrose; 80%) and condensed NCS (essentially glucose after chemical hydrolysis of the extract; 20%) were mobilized in the sapwood and used in the transition zone leading to their abrupt depletion in the heartwood where condensed NSC dominated (75-90%). The unmetabolized glucose was likely stored mainly by etherification. Significant correlations between glucose contents (before and after hydrolysis) and natural durability (-0.43≤ R≤ -0.67) were found. These results indicate that high levels of NSC mobilization in the stem could be a relative efficient strategy of teak for enhancing its heartwood natural durability. Keywords : Teak, sapwood, non-structural carbohydrate, hydrolysis, natural durability.

Diurnal Variation in Nonstructural Carbohydrate Storage in Trees: Remobilization and Vertical Mixing.

Nonstructural carbohydrate (NSC) storage plays a critical role in tree function and survival, but understanding and predicting local NSC storage dynamics is challenging because NSC storage pools are dispersed throughout the complex architecture of trees and continuously exchange carbon between source and sink organs at different time scales. To address these knowledge gaps, characterization and understanding of NSC diel variation are necessary. Here, we analyzed diurnal NSC dynamics in the overall architecture of almond (Prunus dulcis) trees. We also analyzed the allocation of newly assimilated carbon using isotopic labeling. We show that both components of NSC (i.e. soluble carbohydrates and starch) are highly dynamic at the diurnal time scale and that these trends are influenced by tissue type, age, and/or position within the canopy. In leaves, starch reserves can be depleted completely during the night, while woody tissue starch levels may vary by more than 50% over a daily cycle. Recently assimilated carbon showed a dispersed downward allocation across the entire tree. NSC diurnal fluctuations within the tree's structure in combination with dispersed carbon allocation patterns provide evidence for the presence of vertical mixing and suggest that the xylem acts as a secondary NSC redistribution pathway.

Whole-tree nonstructural carbohydrate storage and seasonal dynamics in five temperate species.

Summary Despite the importance of nonstructural carbohydrates (NSC) for growth and survival in woody plants, we know little about whole‐tree NSC storage. The conventional theory suggests that NSC reserves will increase over the growing season and decrease over the dormant season. Here, we compare storage in five temperate tree species to determine the size and seasonal fluctuation of whole‐tree total NSC pools as well as the contribution of individual organs. NSC concentrations in the branches, stemwood, and roots of 24 trees were measured across 12 months. We then scaled up concentrations to the whole‐tree and ecosystem levels using allometric equations and forest stand inventory data.While whole‐tree total NSC pools followed the conventional theory, sugar pools peaked in the dormant season and starch pools in the growing season. Seasonal depletion of total NSCs was minimal at the whole‐tree level, but substantial at the organ level, particularly in branches. Surprisingly, roots were not the major storage organ as branches stored comparable amounts of starch throughout the year, and root reserves were not used to support springtime growth.Scaling up NSC concentrations to the ecosystem level, we find that commonly used, process‐based ecosystem and land surface models all overpredict NSC storage.

Rapid evaluation method for rice (Oryza sativa L.) straw feeding quality

Since conventional methods to evaluate the feeding quality of rice (Oryza sativa L.) straw were time consuming, this study was conducted to investigate the potential of a rapid evaluation method for rice straw feeding quality. Nine rice cultivars in 2011 and ten rice cultivars in 2012 were used in this experiment. The feeding quality related traits (such as nonstructural carbohydrates (NSC), crude protein (CP) and acid detergent fiber (ADF) content, in vitro dry matter digestibility (IVDMD), and the fermentation quality related traits (pH, lactic acid (LA) and NH3-N concentration) of rice straw were analyzed. The fresh top 3rd inter-nodes of stem were used to make freehand sections. The results indicated that the NSC content in the whole plant of rice straw was positively correlated with its IVDMD and the fermentation quality (p < 0.01); the top 3rd node of stem was the main NSC storage organ of rice straw, and the main composition of NSC-starch in this part was also positively correlated with IVDMD and the fermentation quality of the whole plant of rice straw (p < 0.01); the starch particle quantity in the parenchyma area of the top 3rd inter-node was significantly consistent with the starch content in this part. According to the results above, observing the starch particle quantity in the top 3rd inter-node of stem by free hand sections would be a rapid evaluation method for rice straw feeding quality.

Inferring the effects of sink strength on plant carbon balance processes from experimental measurements

Abstract. The lack of correlation between photosynthesis and plant growth under sink-limited conditions is a long-standing puzzle in plant ecophysiology that currently severely compromises our models of vegetation responses to global change. To address this puzzle, we applied data assimilation to an experiment in which the sink strength of Eucalyptus tereticornis seedlings was manipulated by restricting root volume. Our goals were to infer which processes were affected by sink limitation and to attribute the overall reduction in growth observed in the experiment to the effects on various carbon (C) component processes. Our analysis was able to infer that, in addition to a reduction in photosynthetic rates, sink limitation reduced the rate of utilization of nonstructural carbohydrate (NSC), enhanced respiratory losses, modified C allocation and increased foliage turnover. Each of these effects was found to have a significant impact on final plant biomass accumulation. We also found that inclusion of an NSC storage pool was necessary to capture seedling growth over time, particularly for sink-limited seedlings. Our approach of applying data assimilation to infer C balance processes in a manipulative experiment enabled us to extract new information on the timing, magnitude and direction of the internal C fluxes from an existing dataset. We suggest that this approach could, if used more widely, be an invaluable tool to develop appropriate representations of sink-limited growth in terrestrial biosphere models.

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.

Active summer carbon storage for winter persistence in trees at the cold alpine treeline.

The low-temperature limited alpine treeline is one of the most obvious boundaries in mountain landscapes. The question of whether resource limitation is the physiological mechanism for the formation of the alpine treeline is still waiting for conclusive evidence and answers. We therefore examined non-structural carbohydrates (NSC) and nitrogen (N) in treeline trees (TATs) and low-elevation trees (LETs) in both summer and winter in 11 alpine treeline cases ranging from subtropical monsoon to temperate continental climates across Eurasia. We found that tissue N concentration did not decrease with increasing elevation at the individual treeline level, but the mean root N concentration was lower in TATs than in LETs across treelines in summer. The TATs did not have lower tissue NSC concentrations than LETs in summer. However, the present study with multiple tree species across a large geographical scale, for the first time, revealed a common phenomenon that TATs had significantly lower NSC concentration in roots but not in the aboveground tissues than LETs in winter. Compared with LETs, TATs exhibited both a passive NSC storage in aboveground tissues in excess of carbon demand and an active starch storage in roots at the expense of growth reduction during the growing season. This starch accumulation disappeared in winter. Our results highlight some important aspects of the N and carbon physiology in relation to season in trees at their upper limits. Whether or to what extent the disadvantages of winter root NSC and summer root N level of TATs affect the growth of treeline trees and the alpine treeline formation needs to be further studied.