Total Nonstructural Carbohydrate Concentration Research Articles

Effect of Time of Harvest on Postharvest Leaf Abscission in Lantana (Lantana camara L. ‘Dallas Red’) Unrooted Cuttings

This study investigated the preharvest carbohydrate status and postharvest ethylene action of unrooted shoot-tip cuttings of lantana ‘Dallas Red’ harvested at three times during the day (0800, 1200, and 1600 hr) in relation to subsequent leaf abscission, shoot apices blackening, and adventitious root formation. The cuttings harvested at various times during the day were stored in darkness at 20 ± 1 °C for 4 days in sealed polyethylene bags. The cuttings harvested at 0800 hr had lowest total nonstructural carbohydrate concentrations; however, the amount of ethylene production during postharvest storage was similar among harvest times and increased during the storage period. After 4 days of storage, 69% of the leaves of cuttings harvested at 0800 hr abscised, but only 22% and 8% of the leaves abscised in cuttings harvested at 1200 and 1600 hr, respectively. Application of 1-methylcyclopropene (1-MCP) increased ethylene production and suppressed leaf abscission regardless of the harvest time, but cuttings harvested at 0800 hr developed blackened shoot apices. Leaf abscission was negatively correlated with total nonstructural carbohydrate concentration in the leaves, but no relationship was found with ethylene production. These results indicate that a high endogenous carbohydrate status decreases the postharvest ethylene sensitivity in unrooted shoot-tip cuttings of lantana. Time of harvest influenced subsequent rooting response; however, 1-MCP application did not inhibit rooting. Among various storage treatments, the best rooting response was observed in cuttings harvested at 1600 hr and treated with 1-MCP. Therefore, significant improvement of postharvest storage quality in vegetative lantana cuttings could be achieved by harvesting cuttings late in the day and treating with 1-MCP.

Carbohydrate storage enhances seedling shade and stress tolerance in a neotropical forest

SummaryTo survive in forest understoreys, seedlings must depend on carbohydrate reserves when they experience negative carbon balance imposed by occasional light reduction and tissue loss to herbivores and diseases. We present the first experimental evidence in support of this hypothesis, using seven woody neotropical species.We transplanted seedlings that had recently expanded their first photosynthetic cotyledon or leaf to the forest understorey (1% of full sun) and quantified initial biomass and total non‐structural carbohydrate (TNC) in stems, roots and storage cotyledons. We then randomly assigned seedlings to control and two stress treatments: light reduction (0.08% of full sun for 8 weeks) and complete defoliation.First‐year survival of control seedlings, a comparative measure of shade tolerance, differed widely among species. The two stress treatments reduced survival and relative growth rates (RGR) of all species. Shade‐tolerant species were little impacted by the stress treatments, whereas the two least shade‐tolerant species experienced 100% mortality.In all treatments, 8‐week and first‐year survival was positively correlated with initial TNC pool size in stems and roots. By contrast, survival was generally not correlated with initial TNC concentration in any organ, TNC pools in cotyledons, seed mass or seedling biomass.TNC in stems and roots, but not in cotyledons, decreased in response to light reduction and defoliation over 8 weeks. Leaf area recovery of defoliated seedlings was positively correlated with initial TNC pools in stems and roots.First‐year survival in each treatment was negatively correlated with 0–8 week RGR of control seedlings, suggesting higher stress tolerance of species with inherently slow growth rates in shade. RGR of control seedlings from 0 to 8 weeks was negatively correlated with initial TNC pools, but not concentrations, in stems and roots. After 8 weeks, RGR was positive for all species, without clear relationships with survival or TNC.We conclude that carbohydrate storage in stems and roots enhances long‐term survival in shade by enabling seedlings to cope with periods of biotic and abiotic stress. Carbohydrate storage is a key functional trait that can explain species differences in growth and survival that lead to species coexistence through niche assembly processes and life‐history trade‐offs.

Nitrogen availability, growth, carbon partition and resin content in Grindelia chiloensis

Grindelia chiloensis (Asteraceae) is a shrub native to the Patagonia and Monte regions of Argentina and is presently under study as a resin crop. The production rate of diterpene resin acids is, partly, determined by environmental conditions and can be controlled by changing water and radiation availability or temperature. Although theory predicts that resin content should increase with low nitrogen availability, the responses reported in the literature are few, mainly in conifers and are not always consistent with predictions by the carbon nutrient balance hypothesis (CNBH). The objective of this work was to test whether resin production is linked to nitrogen availability as predicted by the CNBH. Plants of G. chiloensis were grown in a greenhouse under four nitrogen availability conditions (0, 1.5, 3.0, and 6.0 mM of N) generated using a modified Hoagland solution. Structural and functional characters were measured. Leaf resin and root total non-structural carbohydrate content (TNC) were higher in plants grown with low nitrogen availability, whereas assimilation rate was slightly affected, in accordance with predictions. Under low nitrogen availability, shoot biomass, and leaf–stem ratio were lower. Resin composition was only slightly affected by nitrogen availability, suggesting that this character is under strong genetic control.

Daily carbohydrate accumulation in eight tall fescue cultivars

AbstractEight cultivars of tall fescue (Loliumarundinaceum Schreb., S.J. Darbyshire = Festuca arundinacea Schreb.), Barcel, Kenhy, Kentucky‐31, Missouri‐96, Mozark, Stargrazer, C‐1 (an experimental selection), and HiMag, were sampled at 2‐h intervals during daylight on four cutting dates. Cultivars varied in concentrations of carbohydrate fractions but accumulation rates were not different. Daily mean total non‐structural carbohydrate (TNC) concentrations for cutting dates in May, July, August and September declined from 239 to 231, 143 and 120 g TNC kg−1 adjusted dry weight (ADW) respectively. Concentrations of fructans were highest in July but sucrose, glucose and starch concentrations were highest in May. Sucrose was the largest contributor proportionately to TNC daily means across accessions in May (0·33), August (0·30) and September (0·38). Glucose composed an equivalent proportion of TNC in the August harvest. Starch concentration was highest in May at 53 g kg−1 ADW and lowest in August at 23 g kg−1 ADW. The TNC concentration increased by 22·4 (May), 16·8 (July), 21·0 (August) and 30·8 g kg−1 ADW (September) from dawn to dusk. Forage samples taken to estimate preference by ruminants or for TNC analyses should be cut and preserved within 1 h to control the diurnal variation of TNC proportionately within 0·05. Tall fescue should generally be cut between noon and sunset for TNC concentrations to be greater than the daily mean.

Growth and Carbon Partitioning in Cranberry Uprights as Influenced by Nitrogen Supply

Information on growth and carbon partitioning of cranberry uprights in response to soil N application is lacking. Therefore, two experiments were initiated on `Stevens' uprights to determine the effect of soil-applied N on tissue N, growth, net carbon exchange (NCER), and nonstructural carbohydrate production of uprights of `Stevens' cranberry. Tissue N concentration increased linearly with increasing soil N but was greater in vegetative uprights than in fruiting uprights. Current season growth on vegetative uprights was more responsive to tissue N than on fruiting uprights. Although chlorophyll concentration and NCER increased with increased soil N, upright starch concentration and often total nonstructural carbohydrate concentration decreased with increased soil N at midfruit development and preharvest, especially in vegetative uprights.

Activities of starch hydrolytic enzymes and starch mobilization in roots of Caragana korshinskii following above-ground partial shoot removal

In many resprouting plants, carbohydrates are stored as starch in roots and will be mobilized to support above-ground tissue regrowth after shoot damage. Our objective was to determine how activities of starch hydrolytic enzymes change damage-induced starch mobilization in Caragana korshinskii roots after above-ground tissue loss. Zero percent (control), 30% (30% RSL), 60% (60% RSL) of main shoot length, and 25% (25% RSN), 50% (50% RSN), and 100% (100% RSN) of main shoot number were removed. Compared with control plants, clipping accelerated the reduction of starch in the roots, increased sucrose flux per flower per hour and nectar production per flower per day in 30% RSL, 60% RSL, 25% RSN, and 50% RSN treatments, and improved vegetative growth in 100% RSN treatment. All treatments had similar total nonstructural carbohydrate (TNC) concentrations in leaves, shoots, and stems with the exception of 100% RSN with higher TNC concentration in shoots. Both α-, and β-amylase activities were enhanced by clipping, the former being more strongly correlated with starch degradation in the roots than the latter. The other two possible starch-breaking enzymes, α-glucosidase, and starch phosphorylase showed no significant differences in the activities between treatments. The results suggest that starch degradation in the roots of C. korshinskii was regulated by α-amylase activity and more mobilized starch was used to support vegetative growth in 100% RSN treatment and support sexual reproduction followed by other clipping treatments.

Seedling size influences relationships of shade tolerance with carbohydrate‐storage patterns in a temperate rainforest

1 Carbohydrate storage has been attributed an important role in the ability to tolerate shade, yet empirical support for this idea has been patchy. We asked if carbohydrate-storage patterns of seedling evergreens in low light are correlated with variation in shade tolerance, and how these patterns change with seedling size. 2 We measured biomass distribution and total non-structural carbohydrate (NSC) concentrations of leaves, stems and roots of two seedling size classes of six evergreens growing in a temperate rainforest understorey. Light requirements of the six species were quantified by calculating the 10th percentile of the distribution of established seedlings in relation to canopy openness. 3 NSC averaged 14% of the dry mass of small seedlings (40–60 mm tall), and 22% of that of large seedlings (400–600 mm tall). This difference was entirely due to variation in starch reserves, which on average accounted for 60% of NSC in small seedlings and 84% in large seedlings. 4 NSC concentrations of leaves and roots (but not stems) of large seedlings were negatively correlated with species’ shade tolerance, but no such pattern was found in small seedlings. Leaf NSC on an area basis was not related to species’ shade tolerance in either size class. 5 Partitioning of the NSC pool between leaves, stems and roots of small seedlings was closely related to variation in shade tolerance. Small seedlings of shade-tolerant species had a relatively low proportion of their NSC pool in leaves and a high proportion in roots. This is likely to ensure the retention of the greater part of the NSC pool even in the event of extensive defoliation, and the availability of reserves to replace lost leaves. In contrast, the large leaf-mass fraction of large seedlings of shade-tolerant species (46–47% of biomass) meant that these plants had a large proportion of their NSC pool in foliage. 6 Results suggest that, in Chilean rainforest evergreens, any adaptive relationship of carbohydrate storage with shade tolerance may be confined to young seedlings, involving interspecific variation in the partitioning of reserves between leaves and other organs, rather than especially high NSC concentrations in shade-tolerant species.

Effects of shoot excision on in situ soil and root respiration of wheat and soybean under drought stress

Little information is available about the variability of root-derived respiration rate in relation to biotic factors such as photosynthesis and substrate availability in roots. Here we examine the role of decreased carbohydrates availability on root-derived respiration through removal of above ground biomass. Spring wheat (Triticum aestivum L. cv. Longchun 8139) and soybean (Glycina max L. cv. Tianchan 2) were grown in the field under a moveable rain shelter, and subjected to three different water regimes: (1) well-watered control; (2) moderate drought stress, and (3) severe drought stress. Root-derived respiration before and after shoot clipping, and the concentration of total nonstructural carbohydrate, malic and citric acid were measured for spring wheat and soybean. Root-derived CO2 flux and total nonstructural carbohydrate concentration of clipped wheat decreased by 38% and 31%, respectively. However, for soybean the root- derived CO2 flux and total nonstructural carbohydrate concentrations were only 58% and 62% of control, respectively, indicating the root respiration rate was controlled by the availability of carbon in the root. A significant positive correlation between total nonstructural carbohydrate concentration of the root and soil water content was observed in unclipped plants. Total nonstructural carbohydrate contributed 93% of the variance in root-derived respiration. Our results clearly show, that in the field, the availability of carbon substrate in roots determines root-derived respiration and plays a key link between soil moisture and root-derived respiration. A period of time is needed for root respiration to return to “steady-state” after shoot removal and this period needed is strongly dependent on species and soil water content.

Impact of eastern dwarf mistletoe (Arceuthobium pusillum) infection on the needles of red spruce (Picea rubens) and white spruce (Picea glauca): oxygen exchange, morphology and composition

Eastern dwarf mistletoe (Arceuthobium pusillum Peck) is a hemiparasitic angiosperm that infects white spruce (Picea glauca (Moench) Voss) and red spruce (P. rubens Sarg.) in northeastern North America. The effects of mistletoe infection differ substantially between white and red spruce, with white spruce suffering greater infection-induced mortality. In the present study, we sought to determine the role that species-specific differences in needle-scale responses to parasitism may play in the observed differences in the effect of infection on host tree health. Based on the measurements made, the most apparent effect of parasitism was a reduction in needle size distal to infections. The magnitude of this reduction was greater in white spruce than in red spruce. Eastern dwarf mistletoe was a sink for host photosynthate in red spruce and white spruce; however, there were no adjustments in needle photosynthetic capacities in either host to accommodate the added sink demands of the parasite. Needle total nonstructural carbohydrate concentrations (TNC) were also unaltered by infection. Red spruce needles had higher TNC concentrations despite having lower overall photosynthetic capacities, suggesting that red spruce may be more sink limited and therefore better able to satisfy the added sink demands of parasitic infection. However, if carbon availability limits the growth of the mistletoe, one may expect that the extent of the parasitic infection would be greater in red spruce. Yet in the field, the extent of infection is generally greater in white spruce. Taken together, these results suggest that dwarf mistletoe may not substantially perturb the carbon balance of either host spruce species and that species-specific differences in needle-scale responses to the parasite cannot explain the contrasting effects of infection on white spruce and red spruce.

Forage Nutritive Value in an Emulated Silvopasture

Incorporating trees into pastures may alter forage nutritive value. The objective of this study was to determine nutritive value in response to trees and slope position in an emulated (no animals) silvopasture. In 1995, black walnut (Juglans nigra L.) and honey locust (Gleditsia triacanthos L.) trees were planted within three block plots of predominantly tall fescue (Lolium arundinaceum (Schreb.) Darbysh.) pasture. Soils on the site, (Unison and Braddock) are fine, mixed mesic Typic Hapludults, well drained, with moderately steep slopes (10–25%). Trees were planted down slopes in rows to create low‐, medium‐, and high‐tree densities at shoulder‐, mid‐, and toe‐slope positions. Forage from sampling sites (n = 54) under field treatment combinations was harvested May, June, and July in 2002 and 2003. Concentrations of neutral and acid detergent fiber (NDF, ADF), acid detergent lignin (ADL), crude protein (CP), total nonstructural carbohydrate (TNC) and Ca, P, Mg, and K were determined. Few differences due to treatment were observed for NDF and ADF concentrations. Concentrations of TNC decreased with greater tree density and appeared to follow tree leaf growth. Crude protein concentrations were typically greater under honey locust trees. Forage mineral concentrations frequently were greater with increased tree density. Trees appear to have both positive and negative effects on forage nutritive value, and their effects on animal performance warrants further research.

Carbohydrate transfer through root grafts to support shaded trees

We investigated whether root grafts between lodgepole pine (Pinus contorta var. latifolia Dougl. ex. Loud.) trees can transfer sufficient carbohydrate reserves from a source tree to a grafted sink tree to affect the vigor of trees growing in a light-limited environment. Eleven plots were established in early spring and two grafted tree pairs and two independent non-grafted trees were selected at each plot. One tree in a grafted pair and one non-grafted tree were shaded at each plot, whereas the remaining trees were non-shaded during the experimental period. Shaded trees had significantly lower carbohydrate reserves and smaller crowns than non-shaded trees following one growing season. Grafted shaded trees had significantly higher root total nonstructural carbohydrate concentrations than non-grafted shaded trees, indicating that root grafts partially offset the effects of shading. Also, large root grafts transferred proportionately more carbohydrates to the shaded trees than small root grafts. Carbohydrates transferred through root grafts could allow grafted trees to persist under conditions where non-grafted trees would be removed by competition.

Dark respiration rate increases with plant size in saplings of three temperate tree species despite decreasing tissue nitrogen and nonstructural carbohydrates

In shaded environments, minimizing dark respiration during growth could be an important aspect of maintaining a positive whole-plant net carbon balance. Changes with plant size in both biomass distribution to different tissue types and mass-specific respiration rates (R(d)) of those tissues would have an impact on whole-plant respiration. In this paper, we evaluated size-related variation in R(d), biomass distribution, and nitrogen (N) and total nonstructural carbohydrate (TNC) concentrations of leaves, stems and roots of three cold-temperate tree species (Abies balsamea (L.) Mill, Acer rubrum L. and Pinus strobus L.) in a forest understory. We sampled individuals varying in age (6 to 24 years old) and in size (from 2 to 500 g dry mass), and growing across a range of irradiances (from 1 to 13% of full sun) in northern Minnesota, USA. Within each species, we found small changes in R(d), N and TNC when comparing plants growing across this range of light availability. Consistent with our hypotheses, as plants grew larger, whole-plant N and TNC concentrations in all species declined as a result of a combination of changes in tissue N and shifts in biomass distribution patterns. However, contrary to our hypotheses, whole-plant and tissue R(d) increased with plant size in the three species.

(124) The Impact of Nitrogen Application on Nonstructural Carbohydrate Production in Cranberry Leaves

Five fertilizer treatments were applied to a `Stevens' cranberry bed in a 3-way split application (roughneck, 75% bloom, and 3 weeks after bloom) in Spring 2004 at State Bog in E. Wareham, Mass. Nitrogen rates were 0, 22, 45, 67, and 90 kg/ha; P was applied at 22 kg/ha, and K at 44 kg/ha. At mid-fruit development and again at preharvest, 20 vegetative and 20 fruiting uprights were collected from each plot in mid-morning. The N concentration per upright increased linearly with increased N application. Increased upright N concentration had no effect on soluble carbohydrate (sucrose + glucose + fructose) concentration, but decreased starch concentration, more so in vegetative uprights than in fruiting uprights on both sampling dates. Total nonstructural carbohydrate concentration (TNSC) was negatively impacted by increased N in vegetative and fruiting uprights at mid-fruit development, but N did not impact TNSC in either type of upright by harvest. Vegetative uprights contained greater concentrations of N, soluble carbohydrates, starch, and TNSC at both sampling dates, but contained lower concentrations of chlorophyll A and chlorophyll B.

Changes in Carbon Partitioning and Accumulation Patterns during Drought and Recovery for Colonial Bentgrass, Creeping Bentgrass, and Velvet Bentgrass

Efficient carbon distribution and utilization may enhance drought survival and recovery ability for perennial grasses. The objectives of this study were to examine changes in carbon partitioning and carbohydrate accumulation patterns in shoots and roots of colonial bentgrass (Agrostis capillaris L.), creeping bentgrass (A. stolonifera L.), and velvet bentgrass (A. canina L.) in response to drought and re-watering following drought, and to determine whether species variation in drought tolerance and recuperative potential is related to differences in the patterns of carbon partitioning and accumulation. The experiment consisted of three treatments: 1) well-watered control; 2) drought, irrigation completely withheld for 18 days; and 3) drought recovery, a group of drought-stressed plants were re-watered at the end of the drought treatment (18 days). Drought tolerance and recuperative ability of three species was evaluated by measuring turf quality and leaf relative water content. These parameters indicated that velvet bentgrass was most drought tolerant while colonial bentgrass had highest recuperative ability among the three species. Plants were labeled with 14CO2 to determine carbon partitioning to shoots and roots. Carbohydrate accumulation was assessed by total nonstructural carbohydrate (TNC) content. The proportion of newly photosynthesized 14C partitioned to roots increased at 12 days of drought compared to the pre-stress level, to a greater extent for velvet bentgrass (45%) than for colonial bentgrass (35%) and creeping bentgrass (30%). In general, the proportion of 14C was highest in roots, intermediate in stems, and lowest in leaves at 12 days of drought treatment for all three bentgrass species. As drought duration and severity increased (18 days), 14C partitioning increased more in leaves and stems relative to that in roots for all three species. Stem TNC content was significantly greater for drought-stressed plants of colonial bentgrass and velvet bentgrass compared to their respective well-watered control plants, whereas no differences in stem TNC content were observed between drought-stressed and well-watered creeping bentgrass. Our results suggest that increased carbon partitioning to roots during initial drought stress represented an adaptive response of bentgrass species to short-term drought stress, and increased carbon partitioning and carbohydrate accumulation in stems during prolonged period of drought stress could be beneficial for rapid recovery of turf growth and water status upon re-watering.

Nitrogen Rate and Mowing Height Effects on TifEagle Bermudagrass Establishment

In the southeastern United States, ‘TifEagle’ hybrid bermudagrass [Cynodon dactylon (L). Pers. × C. transvaalensis Burtt Davy] has become a selected cultivar for renovated or new bermudagrass putting greens, and its use has increased in popularity. However, there is limited research which examines TifEagle establishment, especially when cultural practices such as mowing height are included in the experimental design. The objective of this research was to evaluate the impact of N rate and mowing height on the percentage ground cover, shoot density, color, total nonstructural carbohydrate (TNC) content, and soil nitrate (NO3–N) and ammonium (NH4–N) content of TifEagle hybrid bermudagrass putting greens throughout three establishment years (2002, 2003, and 2004). Weekly applications of N were applied at 0.3, 0.6, 1.2, 2.4, and 4.8 g N m−2 wk−1, and mowing height applied at 3.2, 3.9, and 4.8 mm. Almost every agronomic measure (percentage ground cover, shoot density, root or rhizome and stolon mass, color) responded to increased applications of N, with maximum ground cover and shoot density reached at N rates from 3.4 to 4.3 g N m−2 wk−1 Turf mowed under the lowest mowing height often had reduced turfgrass color and rhizome and stolon mass, compared with that mowed at 3.9 or 4.8 mm. Soil pH and residual NO3−N and NH4–N were almost always affected by N rate, but not by mowing height. For rapid establishment without significant reductions in shoot density, rhizome and stolon mass, and TNC, the highest N rate of 4.8 g N m−2 wk−1, as used in this study, was not needed.

THE EFFECT OF FLOOD WATER TEMPERATURE ON CRANBERRY UPRIGHTS AND ROOTS DURING SPRING AND FALL FLOODS

Cranberry bogs are flooded for several purposes during the growing season, including pest control and harvest. A spring `late water' and a fall `harvest' flood were simulated on potted cranberry uprights (`Stevens'). The `late water' flood is a 1-month flood held on some Massachusetts bogs from mid-April to mid-May. The flood was simulated at 11 and 21 °C. Over the course of the 1-month flood, total non-structural carbohydrate concentration (TNSC) of the upright tissue decreased by 13% and 46% in the 11 and 21 °C treatments, respectively. Root TNSC was not affected by flooding in the 11 °C treatment, but was reduced by 39% in the 21 °C treatment. In the 1-week `harvest' flood simulated at 12 and 20 °C, TNSC of the upright tissue decreased by 47% and 59% in the 12 and 20 °C treatments, respectively. Root TNSC was reduced by 22% in the 12 °C flood, and by 41% in the 20 °C flood. Two weeks following removal from the 1-month `late water' flood, uprights in the 11 °C treatment contained 9% more TNSC than uprights in the 21 °C treatment, while root TNSC from the two treatments was similar. No treatment differences were evident in the uprights or roots of the vines subjected to the `late water' flood by harvest. Two weeks following removal from the 1-week `harvest' flood, uprights in the 12 °C treatment contained 20% more TNSC than uprights in the 20 °C treatment, while roots of vines in the 12 °C flood contained 17% more TNSC compared to vines in the 20 °C flood. Vines which were negatively impacted by the warmer `harvest' flood treatment likely had reduced energy available for winter survival, spring growth and fruit production.

The Effect of Partial Defoliation on Vine Carbohydrate Concentration and Flavonoid Production in Cranberries

The effect of partial defoliation (rate and timing) on vine carbohydrate concentration and the development of phenolic compounds in field-grown `Stevens' cranberry fruit was investigated in two experiments. In Expt. 1, partial defoliation rates of 0%, 18%, 39%, and 53% of total leaf area were applied before new growth, at fruit set, at midfruit development, and preharvest. In Expt. 2, treatments of 0% and 34% removal of new leaves were applied at postfruit set, and at midfruit development. In both experiments, upright samples were harvested for carbohydrate analysis 10d after defoliation, and fruit were removed for analysis before commercial harvest of the site. While total berry phenolic concentration was unaffected by partial defoliation in both studies, the separate pools of flavonoid compounds were affected differently by treatment. In Expt. 1, total flavonol concentration at harvest was improved by the highest rate of partial defoliation (53% of total leaf area) at both fruit set and midfruit development. Total anthocyanin concentration was improved by partial defoliation rates of 39% and 53% of total leaf area compared to the 18% defoliation treatment, but was not affected by timing of defoliation. Pearson correlation coefficients indicated that total flavonol concentration was positively correlated with vine total nonstructural carbohydrate concentration at preharvest, while total anthocyanin concentration was negatively correlated with vine soluble carbohydrates, starch, and total nonstructural carbohydrate concentration at midfruit development. In Expt. 2, total phenolics, flavonols, and anthocyanins were unaffected by partial defoliation; however there was a negative correlation between total anthocyanin concentration in the fruit and soluble carbohydrate concentration in the vine at midfruit development. In these experiments, partial defoliation early in the growing season improved total flavonols and total anthocyanins. Production of flavonols and anthocyanins appeared to be regulated independently of each other.

Long-term Dynamics of Nitrogen and Carbohydrate Reserves in Woody Parts of Minimally and Severely Pruned Riesling Vines in a Cool Climate

Seasonal dynamics of reserve nitrogen (N) over five years and nonstructural carbohydrates over three years were monitored at six vine phenological stages in one-, two-, or older than two-year-old wood fractions of minimally (MP) and severely pruned (VSP) Riesling (<i>Vitis vinifera</i> L.) under cool-climate conditions. Levels of reserve nitrogen were highest in all woody fractions and both pruning systems at leaf fall, dormancy, and budbreak and lowest at bloom, bunch closure, and veraison. In general, N-concentrations were lower in older wood fractions. The magnitude of N-mobilization between budbreak and bunch closure and N-replenishment after veraison was higher for MP vines than for VSP vines and correlated with leaf area formation and leaf area loss, respectively. During the observation period, MP attained higher concentrations of N at most sampling dates in all wood fractions as compared with the VSP system, with the greatest differences in 2002 and 2003. Over a five-year period, N-concentration at veraison declined in both systems, which may have been related to the long-term trend in seasonal plant water status. Changes in dry matter and total nonstructural carbohydrates (TNC) in different wood fractions followed a similar general pattern as changes in N, but mobilization and replenishment occurred at earlier phenological stages. Concentrations in glucose, fructose, and sucrose decreased to almost the lowest values during the season at budbreak and increased again before leaf fall, whereas starch degradation occurred after budbreak and its re-formation between bunch closure and veraison. Minimum TNC concentration, usually observed between full bloom and bunch closure, increased with age of the woody fraction but decreased over the three seasons for all fractions and both systems. With the exception of 2001, MP had slightly lower concentrations in TNC and its component sugars for most sampling dates.

Whole-plant carbon relations and root respiration associated with root tolerance to high soil temperature for Agrostis grasses

Plant tolerance to high soil temperature may be related to the adjustment in carbon production and utilization. The objective of this study was to determine changes in whole-plant carbon balance and root respiration rate in relation to root tolerance to high soil temperature for two Agrostis grass species varying in heat tolerance. Plant tolerance to high soil temperature was compared between Agrostis scabra, a thermal grass species adapted to chronic high-temperature soils in the geothermal areas in Yellowstone National Park, and creeping bentgrass ( Agrostis stolonifera), a cultivated grass species adapted to cool climatic regions. Plant roots were exposed to low soil temperature (20 °C) or high soil temperature (37 °C) for 17 days in water baths placed in a controlled-environment growth chamber. Root biomass and cell membrane stability were determined to evaluate root thermotolerance of both species. Canopy photosynthetic rate (Pn), whole-plant respiration rate, root respiration rate, and total non-structural carbohydrate (TNC) content were measured to assess changes in carbon production and utilization in response to high soil temperature. Root biomass and cell membrane stability declined with increasing soil temperature, but the decline was much less for A. scabra than A. stolonifera, suggesting that roots of A. scabra were more tolerant to heat stress. Canopy Pn decreased and whole-plant respiration rate increased for A. stolonifera, but canopy Pn and respiration rate were unchanged for A. scabra in response to increasing soil temperature. After 17 days of high soil temperature treatment, A. stolonifera exhibited carbon deficit at the whole-plant level, whereas A. scabra maintained positive carbon gain. Root respiration of plants previously grown at 20 °C increased after a short-term treatment (24 h) at 37 °C, but the increase was significantly lower for A. scabra than for A. stolonifera. TNC content in roots did not show response to short-term (24 h) changes in temperature and did not exhibit species variations. Leaves of A. scabra, however, maintained TNC content under both low and high temperature regimes. Our results suggest that root thermotolerance of cool-season grasses could be related to the maintenance of positive whole-plant carbon balance, and down-regulation of whole-plant and root respiration rates in response to increasing soil temperature.

Infertile times: response to damage in genets of the clonal sedge Carex bigelowii

Tolerance to grazing is a plant trait that can be adaptive in systems where plants are subjected to a diversity of herbivore attack types. To test the tolerance ability of the clonal sedge Carex bigelowii, which is food plant to several herbivores in alpine and arctic areas, and the potential fitness costs of this tolerance, replicated units of genets were subjected to three levels of damage throughout three consecutive seasons. The three levels of treatment were no damage, light damage and heavy damage, and the damage was conducted by tearing off all plant material at 3 and 0 cm above-ground respectively. The genets had no tolerance under damage in terms of sexual reproduction. In terms of clonal reproduction the genets showed tolerance under light damage but not under heavy damage. However, no fitness cost was found for this tolerance ability, i.e. genets had higher reproduction and growth under no damage. The average ramet weight had a similar decrease under both a low and high damage treatment. Changed partitioning of biomass between plant parts and reduced concentration of total non-structural carbohydrates (TNC) in storage organs are possible mechanisms for the ability to uphold clonal reproduction in response to damage. There were no significant indications that tolerance ability or its fitness cost differed between genets. Our results suggest that when subjected to heavy damage genets will only reproduce vegetatively. Consequently, it seems C. bigelowii has evolved to allocate resources to the survival of an already successful genet rather than to a potential new genet of unknown success.