Non-structural Carbohydrate Content Research Articles

Infestations of Aulacaspis yasumatsui Reduce Asexual Propagation and Transplantation Success of Cycas revoluta Plants

Cycad transplantation and asexual propagation by stem cuttings are highly successful horticultural procedures because the manoxylic stems contain copious nonstructural carbohydrates. The success of these horticultural procedures may be impaired by antecedent abiotic or biotic stress that decreases stem nonstructural carbohydrate content. The armored scale Aulacaspis yasumatsui Takagi has emerged as a global threat to cycad conservation, and the direct influence of A. yasumatsui herbivory on cycad transplantation or asexual propagation outcomes has not been adequately determined. Cycas revoluta Thunb. plants were infested with A. yasumatsui for 0, 20, or 40 weeks to determine the influence of infestation duration on transplantation or asexual propagation success. Following 20 weeks of infestation in one study, 100% of the undisturbed replications but only 60% of the transplanted replications survived. Following 40 weeks, 80% of the undisturbed replications but only 40% of the transplanted replications survived. Following 20 weeks of infestation in a second study, 100% of the intact replications but only 43% of the cuttings survived. Following 40 weeks, 86% of the intact replications and none of the cuttings survived. Leaf number and root, stem, and leaf dry weights followed similar trends, with declines in these metrics occurring with longer infestation durations. These outcomes indicated that adding the stress of asexual propagation or transplantation to C. revoluta plants that were damaged by A. yasumatsui herbivory decreased subsequent plant health and increased mortality.

Responses of non-structural carbohydrate content to different stand densities and configurations in poplar plantations

Responses of non-structural carbohydrate content to different stand densities and configurations in poplar plantations

Physiological factors contribute to increased competitiveness of grass relative to sedge, forb and legume species under different N application levels

In alpine grasslands, increased N deposition is increasing the dominance of grasses relative to other functional types according to our previous study Shen et al. (2022). However, the mechanisms that drive this compositional change are not fully understood. We measured the effects of 4–6 years' N addition to simulate N deposition at rates of 0 (CK), 8 (N1), 24 (N2), 40 (N3), 56 (N4), and 72 (N5) kg N ha−1 year−1 on dominant representatives of four functional types, Leymus secalinus (grass), Carex capillifolia (sedge), Potentilla multifidi (non-leguminous forb), and Medicago ruthenica (legume), in the alpine grassland on the Qinghai-Tibetan Plateau (QTP). In-situ experiment showed that N addition increased aboveground biomass in L. secalinus but had negative or neutral effects on aboveground biomass in the other species. Consistent with this finding, N addition increased net photosynthesis, chlorophyll content, and rubisco activity in L. secalinus with less positive effects on the other species. Nitrogen addition increased leaf N content in L. secalinus and C. capillifolia and reduced leaf non-structural carbohydrate content in all four species. In L. secalinus, the highest N addition rate (N5) reduced MDA content, a marker of oxidative stress, by enhancing antioxidant enzyme activity. Overall, our findings suggested that physiological factors can contribute to increased competitiveness of grass relative to sedge, forb and legume species under high N application levels. The rapid growth of this grass species reduces resource availability to non-grass species, increasing its dominance in the alpine meadow.

Grain Yield, Biomass Accumulation, and Leaf Photosynthetic Characteristics of Rice under Combined Salinity-Drought Stress

Simultaneous stresses of salinity and drought often coincide during rice-growing seasons in saline lands, primarily due to insufficient water resources and inadequate irrigation facilities. Consequently, combined salinity-drought stress poses a major threat to rice production. In this study, two salinity levels (NS, non-salinity; HS, high salinity) along with three drought treatments (CC, control condition; DJ, drought stress imposed at jointing; DH, drought stress imposed at heading) were performed to investigate their combined influences on leaf photosynthetic characteristics, biomass accumulation, and rice yield formation. Salinity, drought, and their combination led to a shortened growth period from heading to maturity, resulting in a reduced overall growth duration. Grain yield was reduced under both salinity and drought stress, with a more substantial reduction under the combined salinity-drought stress. The combined stress imposed at heading caused greater yield losses in rice compared with the stress imposed at jointing. Additionally, the combined salinity-drought stress induced greater decreases in shoot biomass accumulation from heading to maturity, as well as in shoot biomass and nonstructural carbohydrate (NSC) content in the stem at heading and maturity. However, it increased the harvest index and NSC remobilization reserve. Salinity and drought reduced the leaf area index and SPAD value of flag leaves and weakened the leaf photosynthetic characteristics as indicated by lower photosynthetic rates, transpiration rates, and stomatal conductance. These reductions were more pronounced under the combined stress. Salinity, drought, and especially their combination, decreased the activities of ascorbate peroxidase, catalase, and superoxide dismutase, while increasing the contents of malondialdehyde, hydrogen peroxide, and superoxide radical. Our results indicated a more significant yield loss in rice when subjected to combined salinity-drought stress. The individual and combined stresses of salinity and drought diminished antioxidant enzyme activities, inhibited leaf photosynthetic functions, accelerated leaf senescence, and subsequently lowered assimilate accumulation and grain yield.

Juniperus virginiana sourced from colder climates maintain higher ratios of soluble sugars to starch during cold acclimation.

Non-structural carbohydrates (NSCs) are carbon compounds that serve a large variety of purposes, which makes it hard to disentangle how their concentrations change in response to environmental stress. Soluble sugars can accumulate in plants as metabolic demand decreases, e.g. in response to drought or as seasonal temperatures decrease. Alternatively, actively allocating to NSCs could be beneficial in cold acclimation or periods of increased aridity because soluble sugars serve non-metabolic functions as cryoprotectants and in osmoregulation. We used Juniperus virginiana, a woody plant currently expanding its range, to investigate whether plants sourced from colder and more arid locations maintained higher concentrations of NSCs. We sourced three populations of J. virginiana from across an environmental gradient, and we compared these with the closely related Juniperus scopulorum. We grew the plants in a common garden in northeast Ohio, part of J. virginiana's historic range. We exposed the plants to a drought treatment during the summer and then measured NSC concentrations and cold hardiness as the plants acclimated to colder temperatures and shorter days. We found that individuals originating from the warmer, more southern, range edge were initially not as cold hardy as plants from the other source populations and only reached similar hardiness after prolonged low temperatures. We did not find an effect of drought on NSCs, although this may be due to other traits conferring a high level of drought tolerance in J. virginiana. Across all plants, the NSCs concentration increased over the cold acclimation period, specifically as sugars. Although the highest concentrations of sugars were found in plants from southern populations, the plants from colder environments maintained higher ratios of sugars to starch. These results highlight the importance of NSCs in cold acclimation, and that plants sourced from different climates showed different physiological responses to shortening days and low temperatures.

Overexpression of OsSnRK1a through a green tissue-specific promoter improves rice yield by accelerating sheath-to-panicle transport of nonstructural carbohydrates and increasing leaf photosynthesis

The redistribution of nonstructural carbohydrates (NSCs) in rice (Oryza sativa) sheaths contributes greatly to grain filling. Sucrose nonfermenting-1-related protein kinase 1 (SnRK1) regulates sheath-to-panicle transport of NSCs during rice grain filling; however, it is unknown whether elevated activity of SnRK1 in sheaths improves NSC transport and grain filling. Expression of OsSnRK1a is mainly responsible for regulating SnRK1 activity in rice sheaths. Analysis of transgenic rice plants containing the OsSnRK1a promoter::GUS construct indicated that OsSnRK1a is widely expressed in rice. Notably, OsSnRK1a is highly expressed in mesophyll cells of sheaths. Therefore, a green tissue promoter specifically expressed in sheaths and leaf parenchyma cells and phloem tissue was used to over-express OsSnRK1a in japonica rice. The transgenic lines exhibited increased SnRK1a expression and SnRK1 activity in sheaths. The NSC and starch in the transgenic lines and WT all showed accumulation before heading and during the early-filling stage, and declining at the peak filling stage. But the starch and NSC content in transgenic lines was lower than that of WT. Moreover, the transgenic lines showed lower sucrose contents and higher sucrose efflux rates. The accelerated sheath NSC transport improved grain filling, and stimulated panicle development in transgenic lines. SnRK1a expression and SnRK1 activity were also increased in the leaves of transgenic lines, which improved leaf photosynthetic activity and contributed to optimal grain filling and panicle development. These results verify the promotion of high SnRK1 activity in sheath NSC transport, and also provide a new approach to improving sheath NSC transport and rice yield.

Maintenance of xylem hydraulic function during winter in the woody bamboo Phyllostachys propinqua McClure.

Frost is a common environmental stress for temperate plants. Xylem embolism occurs in many overwintering plants due to freeze-thaw cycles, so coping with freeze-thaw-induced embolisms is essential for the survival of temperate plants. This study was conducted on Phyllostachys propinqua McClure, a woody bamboo species that was grown under natural frost conditions to explore its responses to winter embolisms. From autumn to the following spring, the following measurements were recorded: predawn branch and leaf embolism, branch and leaf relative water content (RWC), root pressure and soil temperature, xylem sap osmotic potential, branch and leaf electrolyte leakage (EL), branch nonstructural carbohydrate (NSC) content and leaf net photosynthetic rate. P. propinqua had a mean vessel diameter of 68.95 ±1.27 µm but did not suffer severe winter embolism, peaking around 60% in winter (January), with a distinct reduction in March when root pressure returned. Leaves had a more severe winter embolism, up to 90%. Leaf RWC was much lower in winter, and leaf EL was significantly higher than branch EL in all seasons. Root pressure remained until November when soil temperature reached 9°C, then appeared again in March when soil temperatures increased from -6°C (January) to 11°C. Xylem sap osmotic potential decreased from autumn to winter, reaching a minimum in March, and then increasing again. Soluble sugar (SS) concentration increased throughout the winter, peaked in March, and then decreased. These results suggest that (1) there is a hydraulic segmentation between the stem and leaf, which could prevent stem water loss and further embolization in winter; (2) maintenance of root pressure in early winter played an important role in reducing the effect of freeze-thaw cycles on the winter embolism; (3) the physiological process that resulted in a decrease in xylem sap osmotic potential and tissue water content, and an accumulation of SS associated with cold acclimation also aided in reducing the extent of freeze-thaw-induced embolism. All these strategies could be helpful for the maintenance of xylem hydraulic function of this bamboo species during winter.

Quantifying the effects of precipitation exclusion and groundwater drawdown on functional traits of Haloxylon ammodendron — How does this xeric shrub survive the drought?

The increasing frequency of drought and decline in groundwater levels are causing ecophysiological changes in woody plants, particularly in desert ecosystems in arid regions. However, the combined effects of meteorological and hydrological droughts on perennial desert plants, especially phreatophytes, remain poorly understood. To address this knowledge gap, we conducted a 5-year precipitation exclusion experiment at two sites with contrasting groundwater depths in the Gurbantunggut Desert located in northwest China. Our study aimed to investigate the impacts of precipitation exclusion and groundwater depth decline on multiple traits of H. ammodendron. We found that long-term precipitation exclusion enhanced midday leaf water potential, stomatal conductance, chlorophyll content, root nonstructural carbohydrates concentration, leaf starch concentration, but decreased water use efficiency. Groundwater drawdown decreased predawn and midday leaf water potentials, maximum net photosynthetic rate, stomatal conductance, Huber value, stem water δ18O, but enhanced water use efficiency and branch nonstructural carbohydrates concentration. A combination of precipitation exclusion and groundwater depth decline reduced Huber value, but did not show exacerbated effects. The findings demonstrate that hydrological drought induced by groundwater depth decline poses a greater threat to the survival of H. ammodendron than future changes in precipitation.

Divergent role of nutrient availability in determining drought responses of sessile oak and Scots pine seedlings: evidence from 13C and 15N dual labeling.

Increased soil nutrient availability can promote tree growth while drought impairs metabolic functioning and induces tree mortality. However, limited information is available about the role of nutrients in the drought responses of trees. A greenhouse experiment was conducted with sessile oak (Quercus petraea (Matt.) Liebl) and Scots pine (Pinus sylvestris L.) seedlings, which were subjected to three fertilization treatments in the first year and two water regimes in the second year. Old and newly fixed carbon (C) and nitrogen (N) allocation were traced by dual labeling with 13C and 15N tracers, respectively, at two time points. Leaf gas exchange, biomass, as well as N and nonstructural carbohydrate (NSC) concentrations of all organs were measured. Fertilization predisposed sessile oak to drought-induced mortality, mainly by prioritizing aboveground growth, C and N allocation, reducing root NSC concentrations and decreasing old C contribution to new growth of leaves. In contrast, fertilization did not additionally predispose Scots pine to drought, with minor effects of fertilization and drought on newly fixed and old C allocation, tissues N and NSC concentrations. The role of nutrients for drought responses of trees seems to be species-specific. Therefore, we suggest nutrient availability and species identity to be considered in the framework of physiological mechanisms affecting drought-induced mortality.

Close relationship between potassium accumulation in internodes and translocation of non-structural carbohydrate to grains in rice cultivars with different yields

Potassium (K) is an important macronutrient together with nitrogen and phosphorous. Potassium mostly accumulates in the internodes of rice plants during ripening stage. Since internodes are responsible for translocation of carbohydrates to the grains during ripening, the involvement of internode K in grain yield has been suggested, however, the precise mechanism remains unclear. This study aims to examine the relationship between rice grain yield in different cultivars and the dynamics of K and non-structural carbohydrates (NSC) in the internodes during the ripening period. Field experiments were conducted to investigate the differences in the dynamics of K and NSCs in internodes from heading to maturation in 10 cultivars with different yields and three mutants with different grain numbers. To reveal the localization of K in internode tissues, we conducted laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis. During the early ripening period from heading to 14 days after heading (14 DAH), the decrease in NSC contents in lower internodes was higher in the high-yielding indica cultivars than in japonica cultivars. In the late ripening period from 14 DAH to maturing, re-accumulation of NSC in lower internodes was higher in the japonica than in the indica. In contrast, the increase in K contents in the internodes was larger in the indica than in the japonica throughout the ripening stage. In the internodes of low-yielding whole crop silage (WCS) cultivar, the NSC contents were maintained at high levels during ripening, while K contents were consistently low. Similar results were observed in the mutant with low grain numbers. The mutant had lower K contents and higher NSC contents than the wild type (WT). Correlation analysis of different cultivars indicated that the change in K content in whole internodes from heading to maturing was negatively correlated with the change in NSC content. LA-ICP-MS analysis of internode tissues of the indica cultivar revealed that K accumulated more in the parenchyma cells than in large vascular bundles. These results suggest that K accumulation in the internodes is positively correlated with NSC translocation from internodes to grains, which could be through indirect effect of K accumulation in parenchyma on enhancement of long distance transport of NSC from internodes to the grains. This study provides new insights into the mechanism underlying the role of K in grain filling, which would help improving usage of K fertilizer for optimum plant growth and yields.

Estimation of the Total Nonstructural Carbohydrate Concentration in Apple Trees Using Hyperspectral Imaging

The total nonstructural carbohydrate (TNC) concentration is an important indicator of the growth period and health of fruit trees. Remote sensing can be applied to monitor the TNC concentration in crops in a non-destructive manner. In this study, hyperspectral imaging from an unmanned aerial vehicle was applied to estimate the TNC concentration in apple trees. Partial least-squares regression, ridge regression, and Gaussian process regression (GP) were used to develop estimation models, and their effectiveness using selected key bands as opposed to full bands was evaluated in an effort to reduce computational costs and improve reproducibility. Nine key bands were identified, and the GP-based model using these key bands performed almost as well as the models using full bands. These results can be combined with previous studies on estimating the nitrogen concentration to provide useful information for more precise nutrient management to improve the yield and quality of apple trees.

Nutrient Composition and Antioxidant Activity of Cercis chinensis Flower in Response to Different Development Stages

Cercis chinensis Bunge (C. chinensis), well known as an ornamental plant widely distributed in China, and its flowers, bark, fruit, etc., have multiple bioactivities. However, reports on the changes in mineral elements, nutrient composition and antioxidant activity in C. chinensis flower at different development stages are rare. In this study, the flower samples were collected every 20 days from March 2023 to May 2023. The changes in carbon (C), nitrogen (N), phosphorous (P), soluble protein (SP), amino acid (AA), non-structural carbohydrate (NSC), total phenol (TP) and total flavonoids (TF) content as well as antioxidant activity in C. chinensis flower at different development stages were investigated. The results suggested that C, N, and P content, the C:N:P stoichiometric ratio, NSC contents, SP, AA, TP, TF and antioxidant activity of flower showed large variations at three development stages. This study found that C and P contents showed a significant decrease with the development and opening of flowers, while N content showed an opposite trend. The soluble protein content first decreased and then increased. The amino acid content, total polyphenol content, and total flavonoid content all showed a significant downward trend, while the content of NSC increased. Both ABTS and ferric-reducing antioxidant power (FRAP) showed significant decreases at various developmental stages, but DPPH was completely opposite. The highest NSC content and DPPH activity were observed at stage III, but the highest AA, TP, TF, as well ABTS and FRAP activity wereobserved at stage I. These findings will improve understanding of the requirements and dynamic balance among C, N, and P, NSC and nutrient contents as well as antioxidant activity of C. chinensis flowers in response to development stages.

Tropical forest lianas have greater non-structural carbohydrate concentrations in the stem xylem than trees.

Lianas (woody vines) are important components of tropical forests and are known to compete with host trees for resources, decrease tree growth and increase tree mortality. Given the observed increases in liana abundance in some forests and their impacts on forest function, an integrated understanding of carbon dynamics of lianas and liana-infested host trees is critical for improved prediction of tropical forest responses to climate change. Non-structural carbohydrates (NSC) are the main substrate for plant metabolism (e.g., growth, respiration), and have been implicated in enabling tree survival under environmental stress, but little is known of how they vary among life-forms or of how liana infestation impacts host tree NSC. We quantified stem total NSC (NSC) concentrations and its fractions (starch and soluble sugars) in trees without liana infestation, trees with more than 50% of the canopy covered by lianas, and the lianas infesting those trees. We hypothesized that i) liana infestation depletes NSC storage in host trees by reducing carbon assimilation due to competition for resources; ii) trees and lianas, which greatly differ in functional traits related to water transport and carbon uptake, would also have large differences in NSC storage, and that As water availability has a significant role in NSC dynamics of Amazonian tree species, we tested these hypotheses within a moist site in western Amazonia and a drier forest site in southern Amazonia. We did not find any difference in NSC, starch or soluble sugar concentrations between infested and non-infested trees, in either site. This result suggests that negative liana impact on trees may be mediated through mechanisms other than depletion of host tree NSC concentrations. We found lianas have higher stem NSC and starch than trees in both sites. The consistent differences in starch concentrations, a long term NSC reserve, between life forms across sites reflect differences in carbon gain and use of lianas and trees. Soluble sugar concentrations were higher in lianas than in trees in the moist site but indistinguishable between life forms in the dry site. The lack of difference in soluble sugars between trees and lianas in the dry site emphasize the importance of this NSC fraction for plant metabolism of plants occurring in water limited environments. Abstract in Portuguese and Spanish are available in the supplementary material.

Soil phosphorus availability alters the correlations between root phosphorus-uptake rates and net photosynthesis of dominant C3 and C4 species in a typical temperate grassland of Northern China.

Phosphorus (P) fertilization can alleviate a soil P deficiency in grassland ecosystems. Understanding plant functional traits that enhance P uptake can improve grassland management. We measured impacts of P addition on soil chemical and microbial properties, net photosynthetic rate (Pn ) and nonstructural carbohydrate concentrations ([NSC]), and root P-uptake rate (PUR), morphology, anatomy, and exudation of two dominant grass species: Leymus chinensis (C3 ) and Cleistogenes squarrosa (C4 ). For L. chinensis, PUR and Pn showed a nonlinear correlation. Growing more adventitious roots compensated for the decrease in P transport per unit root length, so that it maintained a high PUR. For C. squarrosa, PUR and Pn presented a linear correlation. Increased Pn was associated with modifications in root morphology, which further enhanced its PUR and a greater surplus of photosynthate and significantly stimulated root exudation (proxied by leaf [Mn]), which had a greater impact on rhizosheath micro-environment and microbial PLFAs. Our results present correlations between the PUR and the Pn of L. chinensis and C. squarrosa and reveal that NSC appeared to drive the modifications of root morphology and exudation; they provide more objective basis for more efficient P-input in grasslands to address the urgent problem of P deficiency.

Growth, nutritional status, and nonstructural carbohydrates of Armand pine (Pinus armandii) seedlings in response to fertilization regimes and levels

ABSTRACT Exponential fertilization has been regarded as an important technique for improving seedling growth and enlarging internal nutrients reserve. However, the effects of exponential fertilization under varying fertilization levels on seedlings’ growth, nutritional status, and nonstructural carbohydrates (NSC) are poorly understood. We employed Armand pine (Pinus armandii) seedlings to investigate the responses of growth, nutrients (nitrogen, phosphorus, and potassium) in seedlings, and NSC in organs to varying exponential and conventional fertilization levels. Shoot height, root collar diameter, and biomass increased and then declined with the increased fertilization levels. At high fertilization levels (≥300 mg seedling−1), the seedings accumulated more biomass in exponential fertilization than in conventional fertilization. The exponentially fertilized seedlings contained more concentrated nitrogen, starch, and NSC than the conventionally fertilized ones. Vector analysis revealed that conventional fertilization of 200 mg seedling−1 or exponential fertilization of 300 mg seedling−1 could induce luxury consumption. NSC was closely related to the nutrient states. With the increased fertilization level, regardless of the regime, soluble sugar concentrations in roots and needles trended toward declining with changes in the nutrient supply from deficiency to sufficiency and then increased with the changes from sufficiency to toxicity. Meanwhile, starch and NSC concentrations in roots and needles increased with the changes in the nutrient supply from deficiency to sufficiency; the concentrations in roots decreased with the changes from sufficiency to excess. Exponential fertilization at high levels did not only promote seedling growth but also induced seedlings to reserve more nutrients and NSC, which could improve afforestation success.

Modeling of non-structural carbohydrate dynamics by the spatially explicit individual-based dynamic global vegetation model SEIB-DGVM (SEIB-DGVM-NSC version 1.0)

Abstract. Forest dynamics need to be considered when estimating the global carbon budget. The alteration of forest structure and function under a changing climate and expanding human activity could lead to a reduction of forest canopy cover and a spread of lower-biomass ecosystems in warm and dry regions. A non-structural carbohydrate (NSC) acts as a storage buffer between carbon supplied by assimilation and carbon consumed by, inter alia, respiration, reproduction, and pests. Estimation of NSC concentrations in a tree is very important for accurate projection of future forest dynamics. We developed a new NSC module for incorporation into a spatially explicit individual-based dynamic global vegetation model (SEIB-DGVM) to validate the simulated NSC dynamics with observations. NSC pools were simulated in three plant organs: leaves, trunk, and roots. The seasonal dynamics of the NSCs varied among plant species, and the sizes of the NSC pools inferred from observations differed between the boreal, temperate, and tropical climates. The NSC models were therefore validated for each of the three climatic regions at both point and global scales to assess the performance of the models. The modeled NSCs showed good agreement in seasonality with the observed NSCs at four sites – Canada (boreal), Austria and Switzerland (temperate), and Panama (tropical) – and in mean values for three climate zones derived from the global NSC dataset. The SEIB-DGVM-NSC version 1.0 is expected to enable simulation of biome shifts caused by the changes in NSC dynamics worldwide. These dynamics will contribute to changes in not only the global carbon cycle but also in forest structure and demography at a global scale.

Non-structural carbohydrate concentrations in contrasting dry and wet years in early- and late-successional boreal forest trees

Key messagePatterns of non-structural carbohydrate allocation in dry and wet differ between birch and larch in southern boreal forest.An increasing area of boreal forests is currently switching from temperature to drought limitation. It is not sufficiently known how the trees’ non-structural carbohydrate (NSC) pools are affected by alternating dry and wet phases in drought-prone boreal forests and how NSC concentrations are related to growth responses. In the southern boreal forests of Mongolia, NSC concentrations (including soluble sugars and starch) were determined enzymatically in the stemwood of two tree species during a drought year (2017) that was preceded by another drought in 2015 and two subsequent wet years (2018/19). Betula platyphylla as a broadleaved pioneer tree showed reduced radial stem increment in the drought year and rapidly increasing growth in the following wet years. It had low concentrations of NSC and of soluble sugars in particular, suggesting that most assimilate were invested into growth in this early successional tree. Larix sibirica as a late-successional conifer also showed reduced growth in the drought year, but lagged reductions in NSC concentrations and less pronounced growth releases than birch in 2018/19, suggesting a longer aftereffect of the drought than in birch. Larch maintained much higher NSC concentrations throughout the three studied growing seasons, including the drought episode in 2017. The NSC pool in larch was primarily formed by soluble sugars in sapwood and heartwood. In contrast to birch, larch showed a high allocation priority for assimilates in soluble sugars before investment in biomass, which explains the aftereffect of the drought on both growth and NSC. We conclude that the high soluble sugar concentrations in larch are a key determinant of the extreme drought and cold tolerance of L. sibirica and, therefore, growth has lower allocation priority for carbon compared to birch.

Thinning effectively mitigates the decline of aging Mongolian pine plantations by alleviating drought stress and enhancing plant carbon balance

Intensifying drought around the globe poses strong challenges to the growth and survival of trees, emphasizing the urgency of understanding the physiological mechanisms of drought-induced tree decline and mortality and the necessity of using silvicultural approaches to mitigate drought effects on tree growth. We experimentally explored whether thinning enhances tree growth vigor and drought resilience in early aging Mongolian pine (Pinus sylvestris var. mongolica Litv.) plantations in a water-limited area of Northeast China using dendrochronological methods. Meanwhile, we compared plant hydraulic traits, water relations, and non-structural carbohydrate concentrations between trees growing in the thinned and un-thinned stands with the aim of unraveling the physiological mechanisms underlying the density effects on tree growth performance. The results showed that basal area increments of Mongolian pine trees in the high-density plantations started to decline continuously at tree cambium age of around 15 years over about a decade, while thinning effectively reversed their growth decline. Trees in thinned stands exhibited significantly higher predawn leaf water potentials, higher stem hydraulic conductivities, and larger carbon reserves than trees in un-thinned stands. Although trees growing in high-density stands maintained as low risks of xylem hydraulic dysfunction as trees growing in low-density stands, that was at the cost of substantially reducing tree crown size through branch mortality that unavoidably undermined their carbon balance at the whole-plant level. Consistently, trees growing in the thinned low-density stands showed significantly higher levels of non-structural carbohydrate reserve in stems and enhanced growth resilience to extreme drought than trees growing in the high-density reference stands. Our results suggest that thinning can effectively enhance xylem hydraulic transport efficiency and reduce the risk of carbon imbalance by increasing soil water availability and hence mitigates the early aging of Mongolian pine plantations in water-limited environments.

Moisture stress limits radial mixing of non-structural carbohydrates in sapwood of trembling aspen.

Dynamics in non-structural carbohydrate (NSC) pools may underlie observed drought legacies in tree growth. We assessed how aridity influences the dynamics of different-aged NSC pools in tree sapwood at two sites with differing climate conditions ('wet' vs. 'dry') that also experienced widespread regional drought five years earlier. We used an incubation method to measure radiocarbon (Δ14C) in CO2 respired from Populus tremuloides (aspen) tree rings to evaluate NSC storage and mixing patterns, coupled with measurements of NSC (soluble sugars, starch) concentrations and respired δ13C-CO2. At a wet site, CO2 respired from rings formed during 1962-1967 was only ~ 11years old, suggesting deep sapwood mixing of NSCs as starch. At a dry site, total NSC was about one-third of wet site totals, maximum ages in deep rings were lower, and ages more rapidly increased in shallow rings then plateaued. These results suggest historically shallower mixing and/or relatively higher consumption of NSCs under dry conditions. Both sites, however, had similar aged NSC (<1yr) in the most recent six rings, indicative of deep radial mixing following relatively wet conditions during the sampling year. We suggest significant differences in NSC mixing among sites are driven by moisture stress, where aridity reduces NSC reserves and restricts the depth of radial mixing. However, dynamic climate conditions in the southwestern US resulted in more complex radial patterns of sapwood NSC age than previously described. We suggest a novel conceptual framework to understand how moisture variability might influence the dynamics of NSC mixing in the sapwood.

Contrasting Responses ofTwo Grapevine Cultivars to Drought: The Role ofNon-structural Carbohydrates inXylem Hydraulic Recovery.

Xylem embolism is one of the possible outcomes of decreasing xylem pressure when plants face drought. Recent studies have proposed a role for non-structural carbohydrates (NSCs) in osmotic pressure generation, required for refilling embolized conduits. Potted cuttings of grapevine Grenache and Barbera, selected for their adaptation to different climatic conditions, were subjected to a drought stress followed by re-irrigation. Stem embolism rate and its recovery were monitored in vivo by X-ray micro-computed tomography (micro-CT). The same plants were further analyzed for xylem conduit dimension and NSC content. Both cultivars significantly decreased Ψpd in response to drought and recovered from xylem embolism after re-irrigation. However, although the mean vessel diameter was similar between the cultivars, Barbera was more prone to embolism. Surprisingly, vessel diameter was apparently reduced during recovery in this cultivar. Hydraulic recovery was linked to sugar content in both cultivars, showing a positive relationship between soluble NSCs and the degree of xylem embolism. However, when starch and sucrose concentrations were considered separately, the relationships showed cultivar-specific and contrasting trends. We showed that the two cultivars adopted different NSC-use strategies in response to drought, suggesting two possible scenarios driving conduit refilling. In Grenache, sucrose accumulation seems to be directly linked to embolism formation and possibly sustains refilling. In Barbera, maltose/maltodextrins could be involved in a conduit recovery strategy via the formation of cell-wall hydrogels, likely responsible for the reduction of conduit lumen detected by micro-CT.