Non-structural Carbohydrate Content Research Articles

Effects of Polyploidization on Morphology, Photosynthetic Parameters and Sucrose Metabolism in Lily.

Polyploidization is widely used in ornamental plant breeding. The polyploids usually produce greater amounts of biomass. However, the alternations to sucrose metabolism that occur in lily during development after polyploidization induced using colchicine are poorly understood. In this study, compared with their allodiploid counterparts, allotetraploid lilies presented a larger total leaf area per plant and slightly delayed flowering time. Moreover, photosynthetic parameter measurements revealed a higher net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and maximum Pn for allotetraploids than for allodiploids. Compared with allodiploids, allotetraploids also showed higher nonstructural carbohydrate (NSC) contents during development according to HILIC-CAD results. The expression levels of sucrose metabolism-related genes were higher in allotetraploids than in allodiploids at the same time points. The expression profiles of several target genes in allotetraploids were distinctly different from those in allodiploids. Susy2/3 exhibited opposite expression profiles in allotetraploids and allodiploids, and the expression profiles of SPS3 and Susy2 were significantly correlated with sucrose content change trends in allodiploids and allotetraploids, respectively.

Decreased panicle N application alleviates the negative effects of shading on rice grain yield and grain quality

Light deficiency is a growing abiotic stress in rice production. However, few studies focus on shading effects on grain yield and quality of rice in East China. It is also essential to investigate proper nitrogen (N) application strategies that can effectively alleviate the negative impacts of light deficiency on grain yield and quality in rice. A two-year field experiment was conducted to explore the effects of shading (non-shading and shading from heading to maturity) and panicle N application (NDP, decreased panicle N rate; NMP, medium panicle N rate; NIP, increased panicle N rate) treatments on rice yield- and quality-related characteristics. Compared with non-shading, shading resulted in a 9.5–14.8% yield loss (P<0.05), mainly due to lower filled-grain percentage and grain weight. NMP and NIP had higher (P<0.05) grain yield than NDP under non-shading, and no significant difference was observed in rice grain yield among NDP, NMP, and NIP under shading. Compared with NMP and NIP, NDP achieved less yield loss under shading because of the increased filled-grain percentage and grain weight. Shading reduced leaf photosynthetic rate after heading, as well as shoot biomass weight at maturity, shoot biomass accumulation from heading to maturity, and nonstructural carbohydrate (NSC) content in the stem at maturity (P<0.05). The harvest index and NSC remobilization reserve of NDP were increased under shading. Shading decreased (P<0.05) percentages of brown rice, milled rice, head rice, and amylose content while increasing (P<0.05) chalky rice percentage, chalky area, chalky degree, and grain protein. NMP demonstrated a better milling quality under non-shading, while NDP demonstrated under shading. NDP exhibited both lower chalky rice percentage, chalky area, and chalky degree under non-shading and shading, compared with NMP and NIP. NDP under shading decreased amylose content and breakdown but increased grain protein content and setback, contributing to similar overall palatability to non-shading. Our results suggested severe grain yield and quality penalty of rice when subjected to shading after heading. NDP improved NSC remobilization, harvest index, and sink-filling efficiency and alleviated yield loss under shading. Besides, NDP would maintain rice’s milling, appearance, and cooking and eating qualities under shading. Proper N management with a decreased panicle N rate could be adopted to mitigate the negative effects of shading on rice grain yield and quality.

Gibberellin Increased Yield of Sesbania pea Grown under Saline Soils by Improving Antioxidant Enzyme Activities and Photosynthesis

Crop yield is the ultimate manifestation of all physiological changes of crops and external environmental influence. A controlled study was conducted to investigate the effects of exogenous gibberellin on the morphological and physiological characteristics and yield formation of sesbania pea grown in saline soils. Seeds were presoaked with four levels of Gibberellin (GA3) solutions (0, 202.1, 404.2 and 606.3 µM) for 6 h, and then manually direct-sown with a seeding rate of 45 kg ha−1. The morphological parameters (plant height, root length, dry weight), photosynthesis (chlorophyll a and b content), the activities of antioxidant enzymes (superoxide dismutase (SOD); peroxidase (POD); catalase (CAT)), the contents of soluble protein and NSC (non-structural carbohydrates), and seed yield increased with the application of exogenous gibberellin, especially at the level of 404.2 µM GA3. But GA3 had no significant effects on 1000-seed weight. Our study suggested that the appropriate application of exogenous gibberellin could improve the yield of sesbania pea grown in saline soils by increasing photosynthesis and antioxidative defense.

The Dynamics of Non-Structural Carbohydrates in Different Types of Bamboo in Response to Their Phenological Variations: Implications for Managing Bamboo Plantations

Non-structural carbohydrate (NSC) dynamics in different bamboo types underlie the different management practices of bamboo plantations. The changes in moisture, soluble sugars, and starch content in response to phenological variations in different types of bamboo were measured to reveal the NSC dynamics in different bamboo forests for high yield. It was reported for the first time that new leaves of monopodial bamboo started sprouting after the completion of branching, while sympodial bamboo extended new leaves and branches simultaneously. NSC accumulation for shooting lasted about eight months for monopodial bamboo but only a short interval of two to three months for sympodial bamboo. The moisture content in different types of bamboo showed a similar trend of increasing from March to July and then decreasing until the coming January. From March to May, particularly in March, irrigation was required for the shooting of monopodial bamboo, whereas the shoot buds in sympodial bamboo showed sprouting, branching, and leafing. Total NSCs in different bamboo types remained relatively high in March, gradually decreased to the lowest in July, and then increased continuously until the coming January. Average soluble sugar and starch contents showed the same trend as the total NSCs in different types of bamboo. During the period from March to July, large amount of photoassimilates were required for shooting and height growth and then for branching and leafing in monopodial bamboo. Abundant photoassimilates were also required for branching, leafing, and shoot bud differentiation, as well as for subsequent shoot germination in sympodial bamboo. Thus, fertilizer application to both monopodial and sympodial bamboo plantations should be scheduled in early May and late July. Given the moisture, soluble sugar, starch, and total NSC content, January was the best season for harvesting monopodial bamboo for high production and future growth, whereas for sympodial bamboo, November was the best season.

Responses of chlorophyll fluorescence and non-structural carbohydrate accumulation of Castanopsis kawakamii seedlings to seed dispersal positions

When seeds fallen from the mother trees, their initial contact physical environment was litter or soil. The dispersal positions of seeds (seeds positioned on top of the litter, the soil surface and beneath the litter) determine the process of their natural regeneration. We simulated three different dispersal positions of Castanopsis kawakamii, including seeds positioned on top of the litter (2 and 4 cm litter was placed below the seed layer), soil surface (without litter), and seeds beneath the litter (2, 4, 6 and 8 cm litter covers in the upper layer of seeds). We examined the effects of seed dispersal position on the chlorophyll fluorescence characteristics, non-structural carbohydrate, specific leaf area, leaf dry matter content and nutrient content of seedlings. The results showed that leaf nitrogen content per area of seedlings had significantly positive correlation with soluble sugar content, non-structural carbohydrate content, and negative correlation with specific leaf area across different dispersal positions. Seedlings of the moderate litter cover (2 and 4 cm) adopted resource acquisitive strategies by increasing relative chlorophyll content, soluble sugar content, non-structural carbohydrate content, leaf dry matter content, leaf nitrogen content and phosphorus contents per area, and decreasing specific leaf area to achieve their demands for rapid growth. Seedlings grew on soil surface and beneath the deep litter (6 and 8 cm) adopted the resource conservative strategies with higher leaf nitrogen content per mass and specific leaf area, lower leaf dry matter content, and non-structural carbohydrate content to intercept more effective light resources to compensate for the shady environment brought by deep litter. This would further decrease the probability of seedling mortality due to 'carbon starvation'. Seedlings under litter layer stored starch in leaf, and reduced the energy consumption of photosynthetic tissues (low PSⅡ maximum photochemical efficiency) to maintain seedling growth. Comprehensive analysis of entropy method indicated that low amount of litter cover (2 cm) significantly promoted seedling growth of C. kawakamii. In the future, we could regulate the thickness of litter layer to promote the growth and regeneration of C. kawakamii seedlings in natural forest.

Effects of variable temperature and moisture conditions on respiration and nonstructural carbohydrate dynamics of tree roots

• Low soil moisture lowered the root respiration rate of boreal Scots pines. Root respiration was clearly higher in warm and dry than cool and moist year. • Root respiration peaked after the aboveground growth began to decrease. • The root fructose and glucose contents correlated negatively with soil moisture. The method used to determine root respiration should be selected carefully. In warming climates, soil water content (SWC) may act as an important factor in determining belowground carbon dynamics in boreal forests. Here, we estimated the respiration and nonstructural carbohydrate (NSC) concentrations of tree roots in a mature Scots pine ( Pinus sylvestris L.) stand in southern Finland during two growing seasons with contrasting weather conditions. Root respiration was estimated with four different methods: 1) incubating excised roots, 2) partitioning forest floor respirations with root exclusion, or 3) based on temperature response functions and 4) modelling with the whole-tree carbon model ‘CASSIA’. In addition, we conducted a drought experiment in a greenhouse to determine the effect of reduced soil-water availability on respiration by incubating soil and roots of Scots pine saplings. We observed that the respiration of incubated roots of Scots pine saplings and soil decreased with drying after excluding the effect of temperature on respiration (R RES ), soil being more sensitive to drought than roots. Similarly, R RES of incubated roots in the field was significantly decreased by lowered SWC, whereas respiration of the entire root system estimated with other methods was clearly higher in dryer and warmer than moister and cooler year. Nevertheless, incubated roots excavated from the topsoil are most affected by drying soil, which might not reflect the response of the entire root system. R RES of incubated roots was negatively associated with root fructose and glucose concentrations. At the same time, root fructose, glucose and sucrose concentrations were negatively associated with SWC due to their role in osmoregulation. Thereby it seems that R RES does not directly follow the changes in NSCs despite the apparent correlation. Our study highlights the responsive nature of root carbon dynamics in varying weather events that should be taken into account in estimating and modelling the impacts of warming climate.

The effect of hydrological regimes on the concentrations of nonstructural carbohydrates and organic acids in the roots of Salix matsudana in the Three Gorges Reservoir, China

Hydrological fluctuations accelerate biodiversity loss and damage riparian ecosystems surrounding dams and reservoirs. Restoration of vegetation is urgently required in such highly impacted buffer zones. However, it is not known how the nonstructural carbohydrate (NSC) and organic acid concentrations of prominent woody plants such as Salix matsudana would alter under the hydrological regime described in the literature. The study aims to investigate the tap and lateral roots of S. matsudana in the Three Gorges Reservoir, as well as the NSC and organic acid metabolism of these roots. Three groups of two-year-old S. matsudana saplings were planted in this experiment: control (SS), moderate submergence (MS), and deep submergence (DS) at altitudes of 175 m, 170 m, and 165 m, respectively. The results indicated that hydrological regimes restrained the height of S. matsudana with less impact on diameter at P < 0.05 compared with SS but showed a 100 % survival rate throughout the experiment. Meanwhile, root starch concentrations of 108.46 ± 9.18 mg/g (mean ± standard error) were higher than those of soluble sugars (86.81 ± 12.98 mg/g) after hydrological stress. Moreover, the levels of soluble sugar, starch, and NSC in MS were higher than those of SS1 (1stphase of control). However, soluble sugar, starch, and NSC content in DS were lower than in SS2 (2ndphase of control), where lateral root starch and NSC content were more significant than those in the taproot. After 205 days of submersion (DS), oxalic acid, tartaric acid, and malic acid content were higher than after 135 days (MS). They followed the pattern of malic acid > tartaric acid > oxalic acid. The tartaric acid content of the lateral roots and the total roots was significantly higher in MS than in SS1. Conversely, the oxalic acid and malic acid levels in tap roots, lateral roots, and total roots were higher in DS than in SS2. There were strong Pearson's correlations between root starch and NSC with tartaric and malic acids; these correlations ranged from −0.898 < r < 0.981. These data indicate that S. matsudana can maintain certain levels of starch, malic acid, and tartaric acid to enable it to better adapt to its environment under in-situ flooding stress.

Tree organ growth and carbon allocation dynamics impact the magnitude and δ13C signal of stem and soil CO2 fluxes.

Incomplete knowledge of carbon (C) allocation dynamics in trees hinders accurate modeling and future predictions of tree growth. We studied C allocation dynamics in a mature Pinus sylvestris L. dominated forest with a novel analytical approach, allowing the first comparison of: (i) magnitude and δ13C of shoot, stem and soil CO2 fluxes (Ashoot, Rstem and Rsoil), (ii) concentration and δ13C of compound-specific and/or bulk non-structural carbohydrates (NSCs) in phloem and roots and (iii) growth of stem and fine roots. Results showed a significant effect of phloem NSC concentrations on tracheid growth, and both variables significantly impacted Rstem. Also, concentrations of root NSCs, especially starch, had a significant effect on fine root growth, although no effect of root NSC concentrations or root growth was detected on Rsoil. Time series analysis between δ13C of Ashoot and δ13C of Rstem or δ13C of Rsoil revealed strengthened C allocation to stem or roots under high C demands. Furthermore, we detected a significant correlation between δ13C of Rstem and δ13C of phloem sucrose and glucose, but not for starch or water-soluble carbohydrates. Our results indicate the need to include C allocation dynamics into tree growth models. We recommend using compound-specific concentration and δ13C analysis to reveal C allocation processes that may not be detected by the conventional approach that utilizes bulk organic matter.

Effect of early cane pruning on yield components, grape composition, carbohydrates storage and phenology in &lt;i&gt;Vitis vinifera&lt;/i&gt; L. cv. Merlot

Dormant cane pruning has a great impact on vineyard management both in terms of labour costs and the time required to complete this field operation in the absence of mechanisation. In this study, we investigated over three seasons the influence of five pruning dates on yield components, grape composition, phenology and carbohydrate reserves in the variety Merlot, grown in a warm climate area. Pruning was conducted soon after harvest, at the end of leaf fall, two bud dormancy stages and vine bleeding. Early pruning, carried out a few days after the grape harvest, did not significantly affect vine productivity or grape composition in the next season compared to full winter pruning. Similarly, non-structural carbohydrate concentration in trunk and roots showed no difference just before budburst, no matter the timing of pruning. Late winter pruning at vine bleeding slightly postponed budburst and flowering; it also delayed veraison in one out of two years of observation without affecting grape maturity. Our findings suggested that, in a warm-climate area where leaf fall occurs within a ten-week period after harvest, early pruning had no detrimental effects on reserve accumulation in storage organs and, therefore, in vine yield and grape composition in the next harvest, thus allowing viticulturists to operate winter pruning over an extended interval of time.

Optimizing the use of protein in the young cattle body

The organization of complete feed rations for cattle meeting the needs of animals in energy, protein, amino acids, minerals and vitamins in terms of basic nutrients and biologically active substances represents the main condition to achieve the genetic potential of productivity. The purpose of the paper was to optimize the protein utilization in the body of young cattle by synchronizing the processes of fermentation of nitrogen-containing substances and carbohydrates in feed. Barothermal treatment of concentrated feed mixtures with high protein degradability and a high content of non-structural carbohydrates causes a more uniform fermentation of nutrients, intensification of microbial protein synthesis processes and an increase in the efficiency of energy use of carbohydrates and protein nitrogen by rumen microflora. This is evidenced by an increase in the number of ciliates by 4.4–8.1% and a decrease in the concentration of ammonia and volatile fatty acids in the rumen fluid by 5.2–.2% and 3.4–4.3 %, respectively. A decrease in nitrogen losses is indicated by a decrease in the content of urea in animals’ blood by 2.0–9.0%. Extrusion of concentrated feeds with high protein degradability and high content of non-structural carbohydrates improves animal productivity and feed efficiency. The average daily gain in live weight increases by 4.8-6.0% in the experimental group. As a result, feed consumption is reduced by 2.7-6.9%, while protein consumption is reduced by 2.6-5.7%.

Nonstructural carbohydrate content in the stubble per unit area regulates grain yield of the second crop in rice ratooning

AbstractRice (Oryza sativa L.) ratooning has attracted attention due to its higher yield potential. In the present study, a field experiment on rice ratooning using two rice genotypes, near isogenic line (NIL)‐GN1ATakanari and Koshihikari, was conducted in 2019 and 2020 in southwestern Japan to obtain direct evidence for the role of stubble nonstructural carbohydrate (NSC) concentration and/or content per unit area on grain yield of the second crop and to determine the effectiveness of a gene producing more spikelets. NIL‐GN1ATakanari is a near isogenic line carrying an allele of GN1A, which is a gene regulating the number of spikelets per unit area derived from an indica cultivar Takanari in the genetic background of a japonica cultivar Koshihikari, and it can produce more spikelets than Koshihikari. NIL‐GN1ATakanari did not produce a higher grain yield of the first crop than Koshihikari in both years because NIL‐GN1ATakanari had more spikelets m−2 but fewer filled spikelets and a lower grain weight. NIL‐GN1ATakanari produced a lower grain yield of the second crop than Koshihikari because NIL‐GN1ATakanari had fewer spikelets m−2 due to the fewer panicles. Also, NIL‐GN1ATakanari had a lower NSC content than Koshihikari due to the lower leaf sheath plus stem weight in the stubble in 2019. Thus, the lower grain yield in the second crop of NIL‐GN1ATakanari may result from the lower NSC content in the stubble. Additionally, the ability to produce more spikelets per unit area of NIL‐GN1ATakanari was not demonstrated in ratoon crop under the condition of low NSC content in the stubble.

ZMIANY WĘGLOWODANÓW W MIESZANKACH MOTYLKOWO-TRAWIASTYCH POD WPŁYWEM PODŁOŻA POPIECZARKOWEGO I GNOJOWICY BYDLĘCEJ

The aim of the research was to assess the effect of mushroom substrate and slurry on the content of structural and non-structural carbohydrates in hybrid alfalfa mixtures with grasses. The three-year research was conducted in an experimental field between 2013 and 2015, with the following variables: (1) spent mushroom substrate (SMS) and cow slurry (CS), applied in different combinations; (2) three legume grass mixtures: orchard grass, perennial ryegrass, hybrid alfalfa (M1); orchard grass, hybrid alfalfa (M2); perennial ryegrass, hybrid alfalfa (M3). In each growing season, the mixtures were harvested three times. Plant material was used to determine dry matter content and the content of neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent lignin (ADL), cellulose, hemicellulose, lignin, total protein, crude ash, and crude fat by near infrared spectroscopy (NIRS), using the NIRFlex N-500 spectrometer and ready-to-use INGOT® calibration applications. Generally, mushroom substrate applied on its own increased the amounts of cellulose and hemicellulose in legume grass mixtures more than slurry. The most cellulose, the least hemicelluloses, and the highest degree of lignification were recorded in the mixture of ryegrass with alfalfa, while the degree of lignification was the smallest in the forage of alfalfa and orchard grass, which also contained the least cellulose but the most hemicellulose. On average, the highest amount of cellulose was in the biomass of the first harvest and the least in the third.

The influence of increasing atmospheric CO2 , temperature, and vapor pressure deficit on seawater-induced tree mortality.

Increasing seawater exposure is killing coastal trees globally, with expectations of accelerating mortality with rising sea levels. However, the impact of concomitant changes in atmospheric CO2 concentration, temperature, and vapor pressure deficit (VPD) on seawater-induced tree mortality is uncertain. We examined the mechanisms of seawater-induced mortality under varying climate scenarios using a photosynthetic gain and hydraulic cost optimization model validated against observations in a mature stand of Sitka spruce (Picea sitchensis) trees in the Pacific Northwest, USA, that were dying from recent seawater exposure. The simulations matched well with observations of photosynthesis, transpiration, nonstructural carbohydrates concentrations, leaf water potential, the percentage loss of xylem conductivity, and stand-level mortality rates. The simulations suggest that seawater-induced mortality could decrease by c. 16.7% with increasing atmospheric CO2 levels due to reduced risk of carbon starvation. Conversely, rising VPD could increase mortality by c. 5.6% because of increasing risk of hydraulic failure. Across all scenarios, seawater-induced mortality was driven by hydraulic failure in the first 2 yr after seawater exposure began, with carbon starvation becoming more important in subsequent years. Changing CO2 and climate appear unlikely to have a significant impact on coastal tree mortality under rising sea levels.

Plant photosynthetic overcompensation under nocturnal warming: lack of evidence in subtropical evergreen trees.

Increased plant photosynthesis under nocturnal warming is a negative feedback mechanism to overcompensate for night-time carbon loss to mitigate climate warming. This photosynthetic overcompensation effect has been observed in dry deciduous ecosystems but whether it exists in subtropical wet forest trees is unclear. Two subtropical evergreen tree species (Schima superba and Castanopsis sclerophylla) were grown in a greenhouse and exposed to ambient and elevated night-time temperature. The occurrence of the photosynthetic overcompensation effect was determined by measuring daytime and night-time leaf gas exchange and non-structural carbohydrate (NSC) concentration. A reduction in leaf photosynthesis for both species and an absence of persistent photosynthetic overcompensation were observed. The photosynthetic overcompensation effect was transient in S. superba due to respiratory acclimation and stomatal limitation. For S. superba, nocturnal warming resulted in insufficient changes in night-time respiration and NSC concentration to stimulate overcompensation and inhibited leaf stomatal conductance by increasing the leaf-to-air vapour pressure deficit. The results indicate that leaf stomatal conductance is important for the photosynthetic overcompensation effect in different tree species. The photosynthetic overcompensation effect under nocturnal warming may be a transient occurrence rather than a persistent mechanism in subtropical forest ecosystems.

Root Carbon Resources Determine Survival and Growth of Young Trees Under Long Drought in Combination With Fertilization.

Current increases in not only the intensity and frequency but also the duration of drought events could affect the growth, physiology, and mortality of trees. We experimentally studied the effects of drought duration in combination with fertilization on leaf water potential, gas exchange, growth, tissue levels of non-structural carbohydrates (NSCs), tissue NSC consumption over-winter, and recovery after drought release in oak (Quercus petraea) and beech (Fagus sylvatica) saplings. Long drought duration (>1 month) decreased leaf water potential, photosynthesis, and NSC concentrations in both oak and beech saplings. Nitrogen fertilization did not mitigate the negative drought effects on both species. The photosynthesis and relative height increment recovered in the following rewetting year. Height growth in the rewetting year was significantly positively correlated with both pre- and post-winter root NSC levels. Root carbon reserve is critical for tree growth and survival under long-lasting drought. Our results indicate that beech is more sensitive to drought and fertilization than oak. The present study, in a physiological perspective, experimentally confirmed the view that the European beech, compared to oak, may be more strongly affected by future environmental changes.

Changes of non-structural carbohydrates and nitrogen contents of needles and twigs in Pinus sylvestris var. mongolica plantations along an aridity gradient

With six Pinus sylvestris var. mongolica plantations (Huinan, Xifeng, Fujia, Zhanggutai, Naiman and Wulanaodu) along an aridity gradient in the Horqin sandy land, we examined the changes in non-structural carbohydrates (NSCs) and nitrogen (N) contents of current and one-year-old needles and twigs, to explore the carbon supply and demand status as well as the nutrient accumulation strategies of P. sylvestris var. mongolica under drought. The results showed that the contents of NSCs and soluble sugars in needles and twigs of P. sylvestris var. mongolica plantations significantly decreased with increasing aridity. From the most humid site (Huinan) to the most aridity site (Wulanaodu), the soluble sugar contents in current and one-year old needles of P. sylvestris var. mongolica decreased from 12.8% and 12.5% to 9.0% and 9.5%, respectively. The soluble sugar contents in current-year old twigs decreased from 15.6% to 9.2%. With increasing aridity, the starch contents in needles and twigs remained relatively stable, soluble sugars/starch ratio in current and one-year old needles decreased, the N contents in current and one-year old twigs significantly increased. The P. sylvestris var. mongolica plantations in the Horqin sandy land consumed soluble sugar storage under drought, resulting in a risk of mortality from 'carbon starvation'. P. sylvestris var. mongolica tended to maintain stable starch storage and accumulate N in twigs to cope with long-term drought stress.

There Is No Carbon Transfer Between Scots Pine and Pine Mistletoe but the Assimilation Capacity of the Hemiparasite Is Constrained by Host Water Use Under Dry Conditions.

Pine mistletoe is a hemiparasitic shrub that can produce its own photosynthates. There is a lack of knowledge about the interaction of mistletoe and host under varying environmental condition that might influence carbon gain and allocation. In a 13C-pulse labeling experiment with mature Pinus sylvestris (pine) infected by mistletoes grown in naturally dry or irrigated conditions, (1) mistletoe clusters were shielded from 13CO2 added, and (2) mistletoes or host needles were removed to manipulate the local assimilate and water availability. No 13C signal was found in shielded mistletoes, indicating no carbon transfer from the host to the mistletoe. When the pine needles were removed from girdled branches, no 13C signal was found in the host tissues, implying no carbon transfer from mistletoe to the host. However, mistletoes on needle-removed pine trees accumulated more labeled assimilates and had higher non-structural carbohydrate (NSC) concentrations only under naturally dry conditions but not in irrigated plots. Our results suggest that mistletoes show full carbon autonomy, as they neither receive carbon from nor provide carbon resource to the host trees. Moreover, the high assimilation capacity of mistletoes seems to be constrained by the host water use under dry conditions, suggesting that drought stress is not only negatively impacting trees but also mistletoes. Therefore, we conclude that the hemiparasites live on their own in terms of carbon gain which, however, depends on the water provided by the host tree.

Non-Structural Carbohydrates, Foliar Nutrients, Yield Components and Oxidative Metabolism in Pecan Trees in Response to Foliar Applications of Growth Regulators

Foliar sprays of growth regulators have commercial potential for improving the performance of some of the parameters associated with alternate bearing in pecan trees. The objective was to evaluate the behaviour of alternate bearing through analysis of seasonal variations in buds and leaflets of non-structural carbohydrates (glucose, fructose, sucrose, and starch), mineral nutrients (N-total, P, K+, Ca2+, Mg2+, Fe2+, Cu2+, Mn2+ and Zn2+), yield components (nut weight per kilogram and kernel percentage) and oxidative metabolism (superoxide dismutase, hydrogen peroxide, catalase, guaiacol peroxidase and antioxidant capacity) in cv. Wichita pecan trees in response to foliar applications of gibberellic acid (50 mg L−1), calcium prohexadione (500 mg L−1) or thidiazuron (10 mg L−1). The experiment was of a completely randomized experimental design with five replicates. Foliar growth regulator (GRs) sprays help maintain the concentration of non-structural carbohydrates in the leaflets and buds between the evaluation years. With the exception of K+ (12.9 and 10.9 g kg−1) and Zn2+ (45.1 and 30.5 mg kg−1), the GRs did not show any effects on the concentrations of the foliar mineral nutrients. The results suggest foliar sprays of gibberellic acid improve the performance of parameters associated with alternate bearing, including oxidative metabolism.

In situ 13CO2 labeling reveals that alpine treeline trees allocate less photoassimilates to roots compared with low-elevation trees.

Carbon (C) allocation plays a crucial role for survival and growth of alpine treeline trees, however it is still poorly understood. Using in situ 13CO2 labeling, we investigated the leaf photosynthesis and the allocation of 13C labeled photoassimilates in various tissues (leaves, twigs and fine roots) in treeline trees and low-elevation trees. Non-structural carbohydrate concentrations were also determined. The alpine treeline trees (2000m. a.s.l.), compared with low-elevation trees (1700ma.s.l.), did not show any disadvantage in photosynthesis, but the former allocated proportionally less newly assimilated C belowground than the latter. Carbon residence time in leaves was longer in treeline trees (19 days) than that in low-elevation ones (10 days). We found an overall lower density of newly assimilated C in treeline trees. The alpine treeline trees may have a photosynthetic compensatory mechanism to counteract the negative effects of the harsh treeline environment (e.g., lower temperature and shorter growing season) on C gain. Lower temperature at treeline may limit the sink activity and C downward transport via phloem, and shorter treeline growing season may result in early cessation of root growth, decreases sink strength, which all together lead to lower density of new C in the sink tissues and finally limit the growth of the alpine treeline trees.

Seasonal Responses of Hydraulic Function and Carbon Dynamics in Spruce Seedlings to Continuous Drought.

Drought is expected to increase in the frequency and duration associated with climate change. Although hydraulic function and carbon (C) storage have been widely recognized as key components to plant survival under a single drought, the physiological responses to continuous drought remain largely unknown, particularly for high northern temperate and boreal forests which are sensitive to water stress. In this study, we quantified the survival, growth, gas exchange, water relations, and nonstructural carbohydrates (NSCs) in 3-year-old Jezo spruce (Picea jezoensis) seedlings responding to continuous drought stress. Seedlings were maintained in drought conditions for 392 days, covering two growing and one dormant winter season. Seedlings subjected to drought showed a significant decrease in net photosynthesis rate (Anet) and stomatal conductance (gs) in both growing seasons, and biomass in the second growing season. The seedling mortality continuously increased to 35.6% at the experimental end. Notably, responses of C storage and leaf water potential to drought varied greatly depending on seasons. Living seedlings exposed to drought and control treatments had similar NSC concentrations in both growing seasons. However, seedlings with concentrations of both the soluble sugars and starch less than 1% in root died in the winter dormant season. In the second growing season, compared with the control treatment, droughted seedlings had significantly lower leaf water potential and stem wood-specific hydraulic conductivity (Kw). Meanwhile, the leaf predawn water potential did not recover overnight. These suggest that C starvation might be an important reason for seedlings that died in the winter dormant season, while in the growing season drought may limit seedling survival and growth through inducing hydraulic failure. Such seasonal dependence in hydraulic dysfunction and C depletion may lead to higher mortality in spruce forests facing extended drought duration expected in the future.