Total Nonstructural Carbohydrate Levels Research Articles

Dynamics of non-structural carbohydrates in two Ficus species after transfer to deep shade

The present study aims at assessing the role of stored carbohydrates of F. benjamina L. and F. binnendijkii (Miq.) Miq., two tropical trees of horticultural significance, during acclimation to very low light intensities. Plants were grown at an average photosynthetic photon flux density (PPFD) of 90 μmol m −2 s −1, and then transferred to a low-light treatment, with a PPFD of 5 μmol m −2 s −1. Plants of both species showed negative growth rates for approximately 1 week, coinciding with a substantial decrease in the levels of total non-structural carbohydrates (TNC; starch and soluble sugars) in leaves and stems. TNC reached much lower levels in developing leaves than in fully grown leaves, and some of these developing leaves were shed in F. benjamina. In stems and leaves combined, TNC levels were 142 mg g −1 (plant) in F. benjamina and 160 mg g −1 (plant) in F. binnendijkii at the time of transfer to low light. Thirty days later, in fully acclimated plants, these levels had stabilised at 116 and 112 mg g −1. The relatively minor damage to the plants and short duration of a negative carbon balance, despite the low mean PPFD 5 μmol m −2 s −1, illustrate the capacity of both F. benjamina and F. binnendijkii to tolerate deep shade. Stored carbohydrates are important in plants that grow in environments like forest understories or indoor environments, where carbon balance can be negative for several days.

Total Nonstructural Carbohydrate Assessment in Creeping Bentgrass at Different Mowing Heights

Any future precision turfgrass management system will benefit from the evaluation of turfgrass stress through indirect measurements of plant components. One such component might be the accumulation dynamics of total nonstructural carbohydrates (TNC). The effects of mowing height (MH) on TNC concentrations were measured in a field experiment. Clippings were collected from eight creeping bentgrass cultivars {Agrostis palustris Huds. [= A stolonifera var. palustris (Huds.) Farw.]} mowed at three different heights (0.64, 1.27, 1.90 cm) from 1998 through 2001. Clippings were evaluated 29 times by sampling early in the photoperiod before 1200 h. Collected clippings were instantly frozen in liquid nitrogen and freeze‐dried before TNC analyses. The TNC levels were predicted with near infrared reflectance spectroscopy (NIRS) after building a predictive equation for each carbohydrate fraction with conventional laboratory values. Seasonal trends in TNC concentrations and differences in TNC accumulation among creeping bentgrass cultivars were also evaluated. Mowing heights showed significant differences in TNC content, with 0.64‐cm mowed plots having higher TNC levels than 1.27‐ and 1.90‐cm mowed plots on 13 of the 29 dates of evaluation. No consistent differences were observed in TNC concentrations among different cultivars across different growing seasons. However, there were significant seasonal fluctuations in average TNC content at all MHs. The average TNC content of the clippings during 1999 and 2000 started decreasing in mid‐July, showing the lowest TNC content in August. The average TNC content showed an increasing trend in September, exhibiting the highest amount of TNC accumulation in October and November.

Total Nonstructural Carbohydrate Assessment in Creeping Bentgrass at Different Mowing Heights

Any future precision turfgrass management system will benefit from the evaluation of turfgrass stress through indirect measurements of plant components. One such component might be the accumulation dynamics of total nonstructural carbohydrates (TNC). The effects of mowing height (MH) on TNC concentrations were measured in a field experiment. Clippings were collected from eight creeping bentgrass cultivars {Agrostis palustris Huds. [= A stolonifera var. palustris (Huds.) Farw.]} mowed at three different heights (0.64, 1.27, 1.90 cm) from 1998 through 2001. Clippings were evaluated 29 times by sampling early in the photoperiod before 1200 h. Collected clippings were instantly frozen in liquid nitrogen and freeze-dried before TNC analyses. The TNC levels were predicted with near infrared reflectance spectroscopy (NIRS) after building a predictive equation for each carbohydrate fraction with conventional laboratory values. Seasonal trends in TNC concentrations and differences in TNC accumulation among creeping bentgrass cultivars were also evaluated. Mowing heights showed significant differences in TNC content, with 0.64-cm mowed plots having higher TNC levels than 1.27- and 1.90-cm mowed plots on 13 of the 29 dates of evaluation. No consistent differences were observed in TNC concentrations among different cultivars across different growing seasons. However, there were significant seasonal fluctuations in average TNC content at all MHs. The average TNC content of the clippings during 1999 and 2000 started decreasing in mid-July, showing the lowest TNC content in August. The average TNC content showed an increasing trend in September, exhibiting the highest amount of TNC accumulation in October and November.

Effects of fire severity and season of burn on Betula glandulosa growth dynamics

Betula glandulosa survives over a wide range of North American fire regimes by resprouting from the rhizome. Over-winter root carbohydrate reserves are important to sprout production and growth in the following spring. Nursery and field experiments were conducted to examine the effects of seasonal clipping and fire severity (lethal heat applied to different soil depths) on B. glandulosa sprouting and growth, and seasonal burning and clipping on over-winter root carbohydrate storage. Low fire severity increased sprout numbers, and low fire severity in spring caused a large increase in height growth and above-ground biomass production over a 2-year period. Mortality rates increased sharply with higher levels of fire severity. Over-winter total non-structural carbohydrate (TNC) concentrations in roots were significantly higher in plants burned immediately after leaf-flush than in mid-summer burned plants. None of the other seasonal burning or clipping treatments significantly influenced over-winter root TNC. Post-disturbance sprout growth reflected over-winter root TNC levels. B. glandulosa survives a wide range of fire frequencies by growing in plant communities that are most likely to burn in spring or autumn, and seldom burn in summer. This provides the greatest opportunity for maximum over-winter TNC storage. As well, high soil moisture after snowmelt ensures spring fires are almost always of low severity, which promotes increased sprout production, height growth and above-ground biomass.

Resprouting ability of Quercus crispula seedlings depends on the vegetation cover of their microhabitats.

To examine the effects of vegetation cover on the resprouting abilities of Quercus crispula seedlings, in each of three consecutive years, we artificially clipped seedlings growing in microhabitats with differing degrees of vegetation cover. We also investigated the relationship between the level of total nonstructural carbohydrate (TNC) and resprouting ability. Seedlings with clipped shoots in gaps produced larger resprouting shoots than those in the understory. Moreover, both the percentage of resprouting seedlings and the survival ratio in seedlings with clipped shoots were negatively correlated with the degree of vegetation cover. Seedlings stored high levels of TNC, especially in their roots, and their TNC levels were negatively correlated with the degree of vegetation cover. There were also positive relationships between the TNC levels in their roots and the degree of resprouting. Hence, we conclude that release from vegetation cover enhanced the resprouting ability of Q. crispula seedlings by increasing their levels of stored carbohydrate. The key variables affected were the resprouting ratio (the proportion of seedlings capable of producing new shoots) and the size of the resprouted shoots.

Johnsongrass Control, Total Nonstructural Carbohydrates in Rhizomes, and Regrowth After Application of Herbicides Used in Herbicide-Resistant Corn (Zea mays)1

Greenhouse and field experiments were conducted to evaluate the efficacy of nicosulfuron, primisulfuron, glyphosate, glufosinate, imazethapyr plus imazapyr, and quizalofop on johnsongrass biomass reduction, rhizome total nonstructural carbohydrate (TNC) content, and subsequent regrowth from rhizomes. In the greenhouse, johnsongrass plants originating from rhizome segments were controlled 88 to 97% with quizalofop, glyphosate, imazethapyr plus imazapyr, nicosulfuron, and primisulfuron and 56% with glufosinate 3 wk after treatment (WAT). Johnsongrass treated with quizalofop, glyphosate, and nicosulfuron did not regrow 6 WAT, whereas plants treated with primisulfuron, imazethapyr plus imazapyr, and glufosinate regrew from the rhizome of the treated plant. Rhizome TNC levels 3 WAT were not reduced by glufosinate or nicosulfuron, but they were reduced 64% by quizalofop, 32% by primisulfuron, 61% by glyphosate, and 29% by imazethapyr plus imazapyr. When rhizome TNC was reduced by 60% or more compared with nontreated plants, johnsongrass did not regrow from the treated rhizomes. In field experiments, nicosulfuron and glyphosate controlled johnsongrass 94 and 99%, respectively, whereas imazethapyr plus imazapyr (79%) and glufosinate (85%) provided less control 6 WAT.Nomenclature: Glufosinate; glyphosate; imazapyr; imazethapyr; nicosulfuron; primisulfuron; quizalofop; johnsongrass, Sorghum halepense (L.) Pers. #3 SORHA.Additional index words: Biomass reduction, carbohydrate analysis, corn yield, fresh weight.Abbreviations: DAT, days after treatment; POST, postemergence; TNC, total nonstructural carbohydrate; WAT, weeks after treatment.

Effects of Cadmium and Soil Type on Mineral Nutrition and Carbon Partitioning in Seedlings of Pinus Sylvestris

The responses of Pinus sylvestris seedlings grown in organic and mineral soils in the presence of Cd were compared inorder to evaluate the amelioration of Cd toxicity by soil organicmatter. Low levels of ammonium acetate-extractable Cd in organicsoil, compared with mineral soil, indicate a strong affinity ofCd for soil organic matter. Soil organic matter was notfound to ameliorate Cd toxicity in terms of shoot growth,however Cd levels in shoots were lower in seedlings grownin organic soil than those grown in mineral soil. Root Caand Mg concentrations were higher in organic soil. Improvednutrition of the seedlings in organic soil and organiccomplexing might be responsible for reduced Cd accumulationin shoots. Cd increased soluble carbohydrate concentrationand decreased starch concentration in the seedlings grownin organic soil. Lower levels of total non-structuralcarbohydrates in the seedlings grown in the organic soilappeared to be related to an increase in stem growth.

Evidence that carbon dioxide enrichment alleviates ureide-induced decline of nodule nitrogenase activity.

The hypothesis that elevated [CO(2)] alleviates ureide inhibition of N(2)-fixation was tested. Short-term responses of the acetylene reduction assay (ARA), ureide accumulation and total non-structural carbohydrate (TNC) levels were measured following addition of ureide to the nutrient solution of hydroponically grown soybean. The plants were exposed to ambient (360 micromol mol(-1)) or elevated (700 micromol mol(-1)) [CO(2)]. Addition of 5 and 10 mM ureide to the nutrient solution inhibited N(2)-fixation activity under both ambient and elevated [CO(2)] conditions. However, the percentage inhibition following ureide treatment was significantly greater under ambient [CO(2)] as compared with that under elevated [CO(2)]. Under ambient [CO(2)] conditions, ARA was less than that under elevated [CO(2)] 1 d after ureide treatment. Under ambient [CO(2)], the application of ureide resulted in a significant accumulation of ureide in all plant tissues, with the highest concentration increases in the leaves. However, application of exogenous ureide to plants subjected to elevated [CO(2)] did not result in increased ureide concentration in any tissues. TNC concentrations were consistently higher under elevated [CO(2)] compared with those under ambient [CO(2)]. For both [CO(2)] treatments, the application of ureide induced a significant decrease of TNC concentrations in the leaves and nodules. For both leaves and nodules, a negative correlation was observed between TNC and ureide levels. Results indicate that product(s) of ureide catabolism rather than tissue ureide concentration itself are critical in the regulation of N(2)-fixation.

Physiological Characteristics and Carbohydrate Contents of Spring-lifted Picea glauca Bareroot Seedlings Following Low-temperature Storage

This study examined the effects of low-temperature storage of white spruce [ Picea glauca (Moench) Voss] bareroot seedlings to determine whether the time between lifting and planting of spring-lifted seedlings could be extended. Seedlings were lifted from the nursery beds on May 4, 1994, and stored at- 2C (frozen storage) and 4C (cold storage) for 3, 5 and 7 weeks. Frozen storage of spring-lifted seedlings resulted in an increase in sugar levels in roots and needles that progressed with storage duration. Seedlings stored in cold storage maintained a relatively constant sugar content. Needle starch content decreased with storage duration in both frozen and cold storage. In the roots of cold-stored seedlings, starch content remained relatively constant during storage; however, in the frozen-stored seedlings, root starch levels sharply declined during the initial 3 weeks of storage. The levels of total non-structural carbohydrates (starch and sugars) decreased in both types of storage in needles, but not in roots. However, the decrease was more pronounced in the cold-stored than in the frozen-stored seedlings. Gas exchange, root growth potential and number of days to bud break were similar in frozen- and cold-stored seedlings planted in the greenhouse. However, following planting in the forest, cold-stored seedlings flushed buds earlier than did frozen-stored seedlings. The results indicate that tree nurseries could consider frozen storage of spring-lifted white spruce seedlings to facilitate lifting and planting schedules.

Growth, allocation of N and carbohydrates, and stomatal conductance of greenhouse grown apple treated with prohexadione-Ca and gibberellins

SummaryPotted M.26 apple (Mahis domestica) liners were treated with the gibberellin biosynthesis inhibitor prohexadione-Ca (Apogee®) at 0 to 500 mg l”1 as a foliar spray. Apogee inhibited stem elongation, leaf formation, total leaf area and shoot dry weight, while significantly increasing specific leaf weight, root dry weight and root: shoot ratio, regardless of rate. Foliar application of gibberellin A4+7 (GA4+7) at 200 mg l”1 to Apogee-treated plants one day later reversed these effects, especially stem elongation, root dry-matter production and root: shoot ratio. Apogee increased N concentration in stems but not in leaves and roots. There was no effect on the pattern of N allocation amongst organs. GA4+7 increased leaf N concentration but decreased stem and root N concentrations compared with untreated controls, with N allocation shifting from roots to stem. Total nonstructural carbohydrates (TNC), expressed either on a concentration or content basis, increased in all parts of the Apogee-treated plants, due to increased levels of starch rather than soluble sugars, without altering allocation pattern. Conversely, GA4+7 reduced TNC levels (mainly starch levels) in all parts, with the pattern of allocation slightly shifted from roots to stem. The afternoon decline in stomatal conductance occurred earlier in the Apogee treated plants, measured 10 d after stem elongation had ceased. Starch buildup in the Apogee-treated plants appeared to be associated with this effect, suggesting an involvement of a feedback inhibition of photosynthesis in the Apogee-induced stomatal control.

Mineral Nutrient and Carbohydrate Status of Loblolly Pine during Mist Propagation as Influenced by Stock Plant Nitrogen Fertility

Hedged stock plants of four full-sib families [27-2 × 27-5, 27-3 × 27-1, 27-2 × 27-1, and 27-6 × 27-1 (designated B, G, R, and W)] of loblolly pine (Pinus taeda L.) were fertilized daily with a complete nutrient solution containing N at 10, 25, 40, 55, or 70 mg·L–1. In May, terminal softwood stem cuttings were taken and placed under intermittent mist. Families were combined to form composite poor-rooting (BR) and good-rooting (GW) families. At 0, 3, 6, 9, and 12 weeks after sticking, cuttings were evaluated for rooting and analyzed for mineral nutrient and carbohydrate content. Percent rooting by week 12 for cuttings from stock plants receiving N between 25 to 70 mg·L–1 was 28% to 33%, whereas significantly fewer (17%) cuttings from plants receiving 10 mg·L–1 had rooted. By week 12, 98% of cuttings taken from stock plants receiving N at 10 mg·L–1 were alive, while significantly fewer (81% and 82%) of the more succulent cuttings receiving 55 and 70 mg·L–1, respectively, had survived. Nearly all increases in cutting height occurred within the first 3 weeks. In contrast, top dry weight increased steadily throughout the experiment. There were no significant differences in rooting between the two composite families until week 12, when 32% of cuttings from family GW had rooted compared with 24% for family BR. Survival of cuttings was greater for the poor-rooting family (BR) (94%) than for the good-rooting family (GW) (82%) after 12 weeks. Levels of total nonstructural carbohydrates (TNC) and individual soluble sugars were initially higher in cuttings taken from stock plants that received higher rates of N, whereas the reverse was true for starch content. With the exception of sucrose, content of TNC and soluble carbohydrates generally increased over time. Starch was nearly depleted by week 3, but had increased by weeks 6 and 9. No correlation was found between TNC: N ratios and rooting percentage. Family GW contained greater quantities of myo-inositol, glucose, fructose, sucrose, total soluble carbohydrates (TSC), and TNC than did family BR. Mineral nutrient content was generally greater in cuttings taken from stock plants that received higher rates of N; these cuttings also maintained higher levels throughout the 12-week rooting period. As with the soluble carbohydrates, the good-rooting composite family (GW) contained greater amounts of all mineral nutrients than did the poor-rooting family BR.

Protein Degradation and Fermentation Characteristics of Red Clover and Alfalfa Silage Harvested with Varying Levels of Total Nonstructural Carbohydrates

ABSTRACTExtensive degradation of protein during fermentation of high‐protein crops reduces efficiency of dietary N utilization in ruminants. Evidence suggests that enhanced levels of fermentable carbohydrates can reduce proteolysis. Our objective was to evaluate whether delaying daily cutting time, to allow total nonstructural carbohydrates (TNC) to accumulate, would inhibit protein degradation by way of greater acid production in the silo. Red clover (Trifolium pratense L.) and alfalfa (Medicago sativa L.) were harvested at 0600, 1000, 1400, and 1800 h in 1993, 1994, and 1995 and wilted to a dry matter (DM) content of 350 g kg−1 before ensiling. The level of TNC in fresh forage of both species increased throughout the day. Starch accounted for most of the daily change in TNC in fresh alfalfa, whereas in red clover, quantitative increases in sugar and starch impacted TNC similarly. Level of TNC at initiation of ensiling did not consistently affect protein degradation during fermentation as confirmed by generally insignificant correlation coefficients. The extent of proteolysis in the silo was consistently greater in alfalfa than red clover. Silage pH typically decreased and starch increased as cutting time was delayed from 0600 to 1800 h. While the extent of proteolysis was largely unaffected by inherent increases in TNC, lower silage pH and higher starch concentrations indicate that silage from the afternoon cuttings may be better preserved and higher in quality.

Effects of Light and Nutrient Availability on Aspen: Growth, Phytochemistry, and Insect Performance

This study explored the effect of resource availability on plant phytochemical composition within the framework of carbon–nutrient balance (CNB) theory. We grew quaking aspen (Populus tremuloides) under two levels of light and three levels of nutrient availability and measured photosynthesis, productivity, and foliar chemistry [water, total nonstructural carbohydrates (TNC), condensed tannins, and phenolic glycosides]. Gypsy moths (Lymantria dispar) and forest tent caterpillars (Malacosoma disstria) were reared on foliage from each of the treatments to determine effects on insect performance. Photosynthetic rates increased under high light, but were not influenced by nutrient availability. Tree growth increased in response to both the direct and interactive effects of light and nutrient availability. Increasing light reduced foliar nitrogen, while increasing nutrient availability increased foliar nitrogen. TNC levels were elevated under high light conditions, but were not influenced by nutrient availability. Starch and condensed tannins responded to changes in resource availability in a manner consistent with CNB theory; levels were highest under conditions where tree growth was limited more than photosynthesis (i.e., high light–low nutrient availability). Concentrations of phenolic glycosides, however, were only moderately influenced by resource availability. In general, insect performance varied relatively little among treatments. Both species performed most poorly on the high light–low nutrient availability treatment. Because phenolic glycosides are the primary factor determining aspen quality for these insects, and because levels of these compounds were minimally affected by the treatments, the limited response of the insects was not surprising. Thus, the ability of CNB theory to accurately predict allocation to defense compounds depends on the response of specific allelochemicals to changes in resource availability. Moreover, whether allelochemicals serve to defend the plant depends on the response of insects to specific allelochemicals. Finally, in contrast to predictions of CNB theory, we found substantial allocation to storage and defense compounds under conditions in which growth was carbon-limited (e.g., low light), suggesting a cost to defense in terms of reduced growth.

Growth Retardant Effects on Visual Quality and Nonstructural Carbohydrates of Creeping Bentgrass

Plant growth regulators are becoming important tools for managing high-quality turf. However, long-term suppression of growth might affect the potential of the turf to recuperate from summer stresses. This study was initiated to determine the impact of popular commercial turfgrass growth regulators (TGR) on the accumulation of total nonstructural carbohydrates (TNC), and their effect on turf quality. Three experiments, one each year from 1994 through 1996, were conducted on creeping bentgrass (Agrostis stolonifera Huds. `Penncross') in a greenhouse. Growth retardants evaluated included trinexapac-ethyl at 0.28 kg·ha-1, flurprimidol at 0.56 kg·ha-1, and paclobutrazol at 0.28 kg·ha-1. Each retardant was applied at three different intervals: a single initial application or multiple applications every 2 or 4 weeks, for the first 8 weeks of each experiment. The verdure and roots were harvested and analyzed for TNC. Trinexapac-ethyl, flurprimidol, and paclobutrazol significantly increased the TNC of creeping bentgrass 2 weeks after their initial application, but TNC levels began to decrease at week 4. The TNC content was strongly influenced by TGR application rate but not application intervals. A single trinexapac-ethyl application at 0.28 kg·ha-1 reduced TNC content more than did split applications, each at lower rates. Accordingly, TNC levels recovered more rapidly with lower, more frequent application rates; however, the retardation effect on vegetative growth diminished as the concentration was lowered. On the other hand, repeated low application rates of trinexapac-ethyl may have minimal effect on TNC accumulation. Chemical names used: [4(cyclopropyl-α-hydroxy-methylene)-3,5-dioxocyclohexanecarboxylic acid ethyl ester] (trinexapac-ethyl); {α-[1-methylethyl]-α-[4-(trifluoro-methoxy)phenyl]-5-pyrimidine-m ethanol}(flurprimidol);[(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-1,2,4,-t riazole-1-yl)penta-n-3--ol] (paclobutrazol).

Late-season Applications of Various Nitrogen Sources Affect Color and Carbohydrate Content of `Tiflawn' and Arizona Common Bermudagrass

Bermudagrass turfs in the southern United States often receive late growing season applications of nitrogen (N) in order to sustain turfgrass color prior to dormancy, even though such applications might increase winterkill potential. Yearly research trials were initiated in the last week of Sept. 1989 to 1991 at Mississippi State Univ. to evaluate fall and spring color responses and rhizome levels of total nonstructural carbohydrates (TNC) of `Tiflawn' and Arizona (AZ) Common bermudagrass [Cynodon dactylon L. (Pers.)] treated with various N sources delivering N at 98 kg·ha-1 in a single application. The fertilizers were ammonium nitrate (AN), sulfur-coated urea (SCU), a natural organic (`Milorganite', NO), isobutylidene diurea (IBDU), ureaformaldehyde (UF), and methylene urea (MU). Color responses from N fertilization were most prominent in the fall except when there was an early frost event in Oct. 1990. The most rapid greening response and highest color ratings were consistently observed for the water-soluble AN. Of the slow-release sources, SCU, MU, and IBDU provided color responses as long as temperatures remained warm enough to promote bermudagrass growth. The NO source provided an unexpected, significant greening response in Oct. 1989 and 1991 on `Tiflawn', but not on AZ Common. The UF consistently provided the lowest color ratings. There were virtually no differences in TNC levels between N treatments for either grass. At no time was there any indication that N fertilization increased bermudagrass winterkill potential; to the contrary, the predominant responses were better fall and spring color than the nontreated control.

Soybean nodulation and N2 fixation response to drought under carbon dioxide enrichment

The combined effects of carbon dioxide (CO2) enrichment and water deficits on nodulation and N2 fixation were analysed in soybean [Glycine max (L.) Merr.]. Two short‐term experiments were conducted in greenhouses with plants subjected to soil drying, while exposed to CO2 atmospheres of either 360 or 700 μmol CO2 mol–1. Under drought‐stressed conditions, elevated [CO2] resulted in a delay in the decrease in N2 fixation rates associated with drying of the soil used in these experiments. The elevated [CO2] also allowed the plants under drought to sustain significant increases in nodule number and mass relative to those under ambient [CO2]. The total non‐structural carbohydrate (TNC) concentration was lower in the shoots of the plants exposed to drought; however, plants under elevated CO2 had much higher TNC levels than those under ambient CO2. For both [CO2] treatments, drought stress induced a substantial accumulation of TNC in the nodules that paralleled N2 fixation decline, which indicates that nodule activity under drought may not be carbon limited. Under drought stress, ureide concentration increased in all plant tissues. However, exposure to elevated [CO2] resulted in substantially less drought‐induced ureide accumulation in leaf and petiole tissues. A strong negative correlation was found between ureide accumulation and TNC levels in the leaves. This relationship, together with the large effect of elevated [CO2] on the decrease of ureide accumulation in the leaves, indicated the importance of ureide breakdown in the response of N2 fixation to drought and of feedback inhibition by ureides on nodule activity. It is concluded that an important effect of CO2 enrichment on soybean under drought conditions is an enhancement of photoassimilation, an increased partitioning of carbon to nodules and a decrease of leaf ureide levels, which is associated with sustained nodule growth and N2 rates under soil water deficits. We suggest that future [CO2] increases are likely to benefit soybean production by increasing the drought tolerance of N2 fixation.

Postharvest sprouting of onion bulbs grown in different temperature and C02 environments in the UK

SummaryThe effects of different mean growing season temperatures and C02 concentrations during bulb production on postharvest bulb sprouting in a common storage environment at Reading, UK, was examined in two cultivars of the Rijnsburger type of onion (Allium cepa L.). Crops were grown in the field in temperature gradient tunnels maintained at either 374 or 532 ppm C02. At crop maturity, cohorts of bulbs were harvested, transferred to a constant temperature room (at an average of 11.6°C) and the subsequent duration to sprouting recorded. The duration to the onset of sprouting (expressed as days in storage until the first bulb sprouted) was not affected by cultivar, mean growing season temperature or CO2 concentration, and was 165 d. The subsequent rate of sprouting (expressed as bulbs per day) was a positive linear function of mean growing season temperature, but no effects of CO2 or cultivar were detected. Mean rate of sprouting increased from an average of 0.036 bulbs per day at 12.3°C to 0.093 bulbs per day at 18.6°C. Rapid sprouting in storage was associated with lower levels of total non-structural carbohydrate in the bulbs at the time of harvest. Thus, postharvest susceptibility of onion bulbs to sprouting in storage is expected to increase in warmer crop production temperatures.

Dietary Response of Chimpanzees and Cercopithecines to Seasonal Variation in Fruit Abundance. II. Macronutrients

In a continuation of our study of dietary differentiation among frugivorous primates with simple stomachs, we present the first comparison of differences in dietary macronutrient content between chimpanzees and cercopithecine monkeys. Previously we have shown that chimpanzee and monkey diets differ markedly in plant part and species content. We now examine whether this diet diversity is reflected in markedly different dietary macronutrient levels or the different feeding strategies yield the same macronutrient levels in their diets. For each primate group we calculated the total weighted mean dietary content of 4 macronutrients: crude lipid (lipid), crude protein (CP), water-soluble carbohydrates (WSC), and total nonstructural carbohydrates (TNC). We also calculated 4 fiber fractions: neutral-detergent fiber (NDF), which includes the subfractions hemicellulose (HC), cellulose (Cs), and sulfuric acid lignin (Ls). The HC and Cs are potentially fermentable fibers and would contribute to the energy provided by plant food, depending on the hind gut fermenting capacity of the individual primate species. The chimpanzee diet contained higher levels of WSC and TNC because during times of fruit abundance the chimpanzees took special advantage of ripe fruit, while the monkeys did not. The monkey diets contained higher levels of CP because the monkeys consumed a constant amount of leaf throughout the year. All four primate species consumed diets with similar NDF levels. However, the chimpanzees also took advantage of periods of ripe fruit abundance to decrease their Ls levels and to increase their HC levels. Conversely, the monkey diets maintained constant levels of the different fiber fractions thoughout the year. Nevertheless, despite these differences, the diets of the 4 frugivores were surprisingly similar, considering the substantial differences in body size. We conclude that the chimpanzee diet is of higher quality, particularly of lower fiber content, than expected on the basis of their body size.

Bermudagrass Growth, Total Nonstructural Carbohydrate Concentration, and Quality as Influenced by Nitrogen and Potassium

Hybrid bermudagrass cultivars (Cynodon dactylon L. × C. transvaalensis Burtt‐Davy) ditfer in their responses to N and K for growth, total nonstructural carbohydrate (TNC) concentration, and turf quality scores. This 1995 research was conducted in Florida to compare responses of two bermudagrass cultivars to N and K under long‐day (>13 h) and short‐day (<13 h) conditions in a glasshouse. Evaluations were made concerning shoot and root growth, TNC concentration, and quality scores of ‘FloraDwarf’ and ‘Tifdwarf’ bermudagrass during establishment in a coarse sand medium. Experimental design under each photoperiod was a randomized complete block with factorial treatments consisting of two cultivars, four rates of N, four rates of K, and four replications. Data were analyzed by fitting multiple regression equations starting with a second order polynomial model. Growth of FloraDwarf was highly responsive to photoperiod, in that decreased daylengths reduced growth. No growth differences were found in Tifdwarf due to daylength. Growth increased in response to N in both cultivars, while growth response to K varied by cultivar. Both cultivars accumulated higher levels of TNC under short day conditions, with higher levels in FloraDwarf. Nitrogen fertilization reduced TNC levels in FloraDwarf under short days and in Tifdwarf under long days, while K fertilization reduced TNC levels in Tifdwarf under short days. Quality scores in both cultivars increased in response to N under long days, and in response to both N and K under short days. Results of these studies indicated that growth, TNC accumulation, and quality differed due to cultivar, photoperiod, and rates of N and K.

Carbohydrate Allocation to Storage as a Basis of Interspecific Variation in Sapling Survivorship and Growth

Total nonstructural carbohydrates (TNC) of roots were sampled in early autumn from saplings of four species that differ in light-dependent growth and survivorship (shade tolerance). The two deciduous species (Acer saccharum and Fraxinus americana) had higher TNC concentrations than the evergreens (Tsuga canadensis and Pinus strobus), presumably because of autumn build-up of reserves for spring refoliation. In separate comparisons of deciduous and coniferous pairs, A. saccharum and T. canadensis had higher low-light TNC concentrations and survivorship than F. americana and P. strobus, respectively. In high light, TNC levels were not significantly different between A. saccharum and F. americana and both species had >98% survivorship. An analytical model of carbohydrate allocation demonstrates that variation in storage allocation can influence survivorship and growth and that the opportunity cost of storage is lower under low light. The model and empirical data are consistent with an observed correlation among species between growth determinancy and shade tolerance and a negative correlation between high-light growth rates and low-light survivorship. Allocation to storage may be an effective strategy of shade tolerance because it is relatively inexpensive under low light and provides a buffer against stresses.