Increase In Specific Leaf Weight Research Articles

Specific Leaf Area and Specific Leaf Weight in Small Grain Crops Wheat, Rye, Barley, and Oats Differ at Various Growth Stages and NPK Source

Leaf thickness plays an important role in leaf and plant functioning and is related to species’ strategies of resource acquisition and use. Leaf thickness in small grains crops was measured as specific leaf area (SLA) (leaf area in cm2 produced g−1 leaf dry weight plant−1) and specific leaf weight (SLW) (leaf dry weight in mg produced cm−2 leaf area plant−1). The four small grains crops (cool season C3 cereals) studied were wheat (Triticum aestivum L.), rye (Secale cereale L.), barley (Hordeum vulgare L.) and oats (Avena sativa L.). The null hypothesis tested was that SLA and SLW in small grain crops do not differ at different growth stages and nitrogen, phosphorus, and potassium (NPK) source. Eight NPK sources used in the experiment were: S1 = 20-20-20, S2 = 20-27-5, S3 = 7-22-8, S4 = 10-10-10-20S, S5 = 11-15-11, S6 = 31-11-11, S7 = 24-8-16, and S8 = 19-6-12, and each was applied at the rate of 300 mg pot−1 at the time of sowing to each crop species. The experiment was performed in completely randomized design with three repeats at the Green House of Dryland Agriculture Institute, West Texas A&M University, Texas, during winter 2009-10. Based on the results, it was observed that both SLA and SLW differed with change in crop species, growth stage and NPK source. Among the crop species, SLA was greater in oats > barley > rye > wheat at different growth stages; while SLW of wheat and rye > barley and oats. The differences in the SLW between wheat vs. rye; and between oats vs. barley at different growth stages were not significant (P ≤ 0.05). Among the NPK sources, application of S7 (24: 8: 16) had higher SLA at 60 and 90 DAE (days after emergence). Application of S6 (31: 11: 11) had higher SLW at 60 DAE due to the production of the lowest leaf area plant−1, but the increase in SLW at 90 DAE with S5 and S4 was due to the higher leaf dry weight plant−1produced. Leaf dry weight and leaf area plant−1 were considered the two most important leaf characteristics that influenced SLA and SLW. On the average, SLA increased with passage of time i.e. 0.70 < 520 < 600 cm2 g−1 at 30, 60 and 90 DAE, respectively; but SLW on the other hand, was highest 3.5 at 60 DAE > 2.2 at 90 DAE > 1.5 mg cm−2 at 30 DAE. The increase in leaf area plant−1 and decline in the leaf dry weight plant−1 increased SLA; in contrast, increase in leaf dry weight plant−1 and reduction in leaf area plant−1 increased SLW indicated reciprocal relationship between SLA and SLW in the crop species.

English

Seven species of oat (Avena) were evaluated for their relative drought tolerance under soil moisture stress. The plant height, leaf area production and biomass yield reduced under soil moisture stress. Among the species tested, minimum reduction in height was recorded in Avena vaviloviana, Avena abyssinica and Avena sterilis at vegetative and flowering stages. Significant decrease in leaf area production was recorded at vegetative stage, whereas at flowering stage, the decrease in leaf area production was marginal in A. sterilis followed by A. abyssinica predicting their more adaption to stress environment. The increase in specific leaf weight (SLW) of all the species of Avena showed increase in leaf thickness, exhibiting high water retention capacity under soil moisture stress condition which is a requisite trait for drought tolerance. Soil moisture stress imposed at vegetative and flowering stages reduced fresh biomass yield in all the species. Minimum reduction in dry biomass accumulation under stress environment at vegetative stage was recorded in A. sterilis followed by A. strigosa and A. sativa, exhibiting their tolerance to drought at early stages of growth. However, at flowering stage, minimum decrease in dry biomass production was recorded in A. sterilis (3.47%) followed by A. marocana (12.56%) indicating their relative drought tolerance at flowering stage of crop growth. A significant positive correlation between total leaf area and dry biomass (r2=0.738) under stress environment indicates that dry biomass accumulation was governed by total leaf area production. A. sterilis accumulated maximum fresh and dry biomass under soil moisture stress with minimum reduction over the non stress environment, indicating its drought tolerance potential as compared to other genotypes tested. &nbsp; Key words: Avena, biomass, flowering stage, leaf area, soil moisture stress, vegetative stage.

Physiological effects of prohexadione-calcium in apple trees: effects on parameters related to photoproductivity

SummaryDifferent prohexadione-Ca (RegalisTM, Pro-Ca) treatments were applied as foliar sprays to ‘Royal Gala’ and ‘Smoothee Golden Delicious’ apple trees to asses its effects on different physiological traits, under the growing condition of the Middle Ebro Valley (Spain). The application of Pro-Ca resulted in a decrease in leaf area, as well as fresh and dry leaf weights, and an increase in specific leaf weight. Greater light penetration through the canopy was recorded, indicative of a lower canopy density, resulting both from the inhibition of shoot growth and leaf extension growth. In addition, increases in leaf chlorophyll concentrations, and photosynthetic rates were found, which could account for the lack of effect of Pro-Ca on overall tree growth.

Fluorescent Pseudomonas influences palisade mesophyll development and spatial root development in Phaseolus vulgaris

Three strains of plant growth promoting fluorescent Pseudomonads (HPR6, RRLJ008 and RRLJ134) were studied for their effect on growth and yield of French bean (Phaseolus vulgaris L.) under field conditions. The effect of these strains on nature of root development and leaf palisade tube length were also examined. The strains induced positive response on growth and physiological parameters resulting in higher yield in P. vulgaris. Strain HPR6 produced the most promising results in thickening of leaf palisade layer, spreading of lateral roots and production of root hairs. The increase in specific leaf weight (SLW), net assimilation rate (NAR) and relative growth rate (RGR) by these strains were 68%, 152% and 167%, respectively. The growth and yield parameters were also significantly improved compared to the uninoculated control. Antibiotic resistant mutant strains demonstrated that these bacteria effectively colonized the rhizosphere of French bean. The results suggest that the strains could be developed for field application on a large scale.

Secondary cell wall deposition causes radial growth of fibre cells in the maturation zone of elongating tall fescue leaf blades.

A gradient of development consisting of successive zones of cell division, cell elongation and cell maturation occurs along the longitudinal axis of elongating leaf blades of tall fescue (Festuca arundinacea Schreb.), a C3 grass. An increase in specific leaf weight (SLW; dry weight per unit leaf area) in the maturation region has been hypothesized to result from deposition of secondary cell walls in structural tissues. Our objective was to measure the transverse cell wall area (CWA) associated with the increase in SLW, which occurs following the cessation of leaf blade elongation at about 25 mm distal to the ligule. Digital image analysis of transverse sections at 5, 15, 45, 75 and 105 mm distal to the ligule was used to determine cell number, cell area and protoplast area of structural tissues, namely fibre bundles, mestome sheaths and xylem vessel elements, along the developmental gradient. Cell diameter, protoplast diameter and area, and cell wall thickness and area of fibre bundle cells were calculated from these data. CWA of structural tissues increased in sections up to 75 mm distal to the ligule, confirming the role of cell wall deposition in the increase in SLW (r2 = 0.924; P < or = 0.01). However, protoplast diameter of fibre cells did not decrease significantly as CWA increased, although mean thickness of fibre cell walls increased by 95 % between 15 and 105 mm distal to the ligule. Therefore, secondary cell wall deposition in fibre bundles of tall fescue leaf blades resulted in continued radial expansion of fibre cells rather than in a decrease in protoplast diameter.

微気象調節による減農薬・多収型水稲栽培の検討

A possibility of paddy rice (Oryza sativa) cultivation with reflective mulching materials as a tool of low input and high-yielding culture was examined. The albedo increased and water temperature in the daytime decreased by mulching of white styrofoam board or reflective film over the interrow space. Leaf area indexes in the mulching plots decreased as compared to the control plot due to the decline in leaf weight ratio and the increase in specific leaf weight. By mulching, the dry matter production at early growth stage increased in a year 1999 under relatively low sunshine but it tended to decrease in another year 2000 under intense sunshine, high temperature and low humidity. Furthermore, dry matter production in the latter half of growth tended to increase in both years, and the percentage of ripened grains elevated as well as the number of ripened grains. In both years, the grain yield increased about 10% and the damage due to grass leaf roller (Cnaphalocrocis medinalis) reduced, by mulching.

Evaluation of a Rapid Method for Screening the Capacity of Leaves to Export Photosynthate

A method was developed to rapidly screen genotypes for capacity of leaves to export photosynthate, with the expectation that rapid export should promote growth. Vegetative plants of 13 cultivars of Pisum sativum L. (pea) were screened based on changes in specific leaf weight (SLW) at dawn before and after exposing plants to CO2-enriched air (1200 ppm) for one diurnal cycle. Three cultivars (Nofila, Little Marvel, Sugar Daddy) had relatively little increase in SLW and were designated rapid exporters; based on this criterion `Alaska', `Oregon Sugar Pod II', and `Manoa' were slow exporters. The increase in SLW was due to starch and sugars. Neither single leaf net photosynthetic nor dark respiration rates consistently differed among cultivars when measured at 1200 or 350 ppm CO2 (normal air). The difference between rapid and slow exporters persisted after plants were grown for 2 weeks at 1200 vs. 350 ppm CO2. However, the relative growth rate (RGR) of whole-plant dry mass did not differ consistently among cultivars at either CO2 level, except it was high for `Alaska', a slow exporter. The high RGR for `Alaska' was due in part to a high ratio of whole plant leaf area to dry mass early in the growth period. Thus, although the rapid exporters accumulated relatively low levels of starch and sugars, this trait did not dominate other growth determining traits.

Relationships among Specific Leaf Weight, Photosynthetic Rate, and Seed Yield in Soybean

Increasing leaf apparent photosynthesis (AP) may improve seed yield in soybean [Glycine max (L.) Merr.]. Selection for high specific leaf weight (SLW) may increase AP. The objectives of this study were to (i) incorporate extremes in SLW from exotic germplasm into adapted soybean lines with high agronomic potential, (ii) compare the time course of SLW in lines known to vary in SLW, and (iii) evaluate the relationships among SLW, AP, and seed yield. In 1991 and 1992, 16 genotypes representing extremes in SLW were grown at Urbana, IL, and West Lafayette, IN. The SLW and AP were measured at the R2, R4, and R5 growth stages. At the R5 growth stage in 1992, AP was also measured at approximately twice ambient CO2 concentrations. A subset of lines was sampled weekly for SLW from R1 until R7. High SLW lines displayed a greater rate of increase in SLW than low SLW lines beginning after R2 and continuing until R6. Significant class mean differences (P &lt; 0.01) in SLW were observed on all sample dates across locations. Class mean differences in AP at ambient and twice ambient CO2 concentrations were observed at Urbana, although ranking of SLW classes was inconsistent across years. Leaf rugosity was negatively correlated with AP and seed yield. A high SLW line with low rugosity, LG89‐1917, expressed high AP and produced yields very similar to the adapted cultivars Chapman and Elgin 87. Lines with high SLW and low leaf rugosity may hold the greatest potential for high AP and yield improvement.

UV‐B‐INDUCED INCREASE IN SPECIFIC LEAF WEIGHT OF CUCUMBER AS A CONSEQUENCE OF INCREASED STARCH CONTENT

Abstract Specific leaf weight (SLW), the ratio of leaf dry matter to area, often increases in plants exposed to elevated UV‐B radiation (280–315 nm). Increased SLW can result from greater leaf thickness or increased leaf density (e.g. accumulation of high density substances in cells). The basis for large increases in SLW was examined in the first and third leaves of cucumber differing in developmental stage at the start of UV treatment. Leaf 1 was approximately 50% fully expanded, while leaf 3 had just unfolded. It is shown here that up to 80% of the UV‐generated change in SLW in leaf 1 was caused by accumulation of nonstructural carbohydrates, especially starch (increasing from 13 to 23% of total dry weight). Leaf 3 contained a much smaller proportion of nonstructural carbohydrates (less than 8%) and the effect on SLW was correspondingly less. As shown in the previous paper, UV‐B inhibition of growth in leaf 3 was reversed by supplemental blue light (BL) in a fluence‐dependent manner between 0.23 to 2.68 mol m 2 perday. Fluence‐response curves revealed that supplemental BL reversed both the UV‐induced accumulation of starch and increase in SLW in leaf 1 over the same range. The data are consistent with a back‐up of photosynthate into leaf 1 as a result of UV‐B inhibition of growth in leaf 3. The data also demonstrate that increases in SLW cannot be assumed to represent increases in leaf thickness.

Nitrogen Source Regulation of Growth and Photosynthesis in Beta vulgaris L.

Sugar beets (Beta vulgaris L. cv F58-554H1) were grown hydroponically in a 16-h light, 8-h dark period at a photosynthetic photon flux density of 0.5 mmol m-2 s-1 for 4 weeks in half-Hoagland culture solution containing only nitrate-nitrogen. Half of the plants were then transferred to half-Hoagland solution with ammonium-nitrogen (7.35mM), while the other half continued on 7.5 mM nitrate. Growth analysis was carried out by sampling the plants at 3-d intervals over a period of 21 d. Compared to plants supplied with nitrate, ammonium initially slowed the growth of shoots more than roots. Ammonium reduced both the area expansion of individual leaves and the relative water content of these leaves, but increased the amount of dry matter/area. The increase in specific leaf weight in ammonium-grown leaves was associated with a doubling of chloroplast volume, as much as a 62% rise in chlorophyll content, and a 4.3-fold higher accumulation of soluble protein. Ammonium nutrition substantially decreased the rate of expansion of photosynthetic (leaf) surface but did not decrease the rate of photosynthesis per area; in fact, net photosynthetic CO2 exchange rates were slightly higher than in nitrate plants, due to the build-up in stromal enzymes of the Calvin cycle, several of which increased in total extractable activity on a leaf area basis, e.g. ribulose-1,5- biphosphate carboxylase oxygenase, sedoheptulose-1,7-biphosphatase. Nitrogen source had no effect on stomatal conductance. Rates of photosynthesis per chlorophyll were decreased slightly in ammonium-grown leaves, possibly due to an increased CO2-diffusion resistance associated with the enlarged chloroplasts.

Starch accumulation during hydroponic growth of spinach and basil plants under carbon dioxide enrichment

The effects of CO 2 enrichment, photoperiod duration, and inorganic phosphate levels on growth and starch accumulation by spinach and basil plants were studied in a commercial hydroponic facility. During a 3-week growth period, both species exhibited increased whole-plant fresh weight as a result of an increase in atmospheric CO 2 concentration from 400 to 1500 μl/l. However, basil leaves exhibited a 1.5- to 2-fold greater increase in specific leaf weight ( SLW), and accumulated starch to much greater levels than did leaves of spinach. At 1500 μl CO 2/l, starch accounted for up to 38% of SLW with basil compared to <10% of SLW with spinach. The maximum ratio of starch/chlorophyll was 55.0 in basil leaves vs 8.0 in spinach leaves. High ratio values were associated with the appearance of chlorotic symptoms in leaves of basil grown under CO 2 enrichment ( Wallick and Zinnen (1990) Plant Disease 74, 171–173), whereas spinach did not exhibit chlorosis. Increasing inorganic phosphate concentrations from 0.7 to 1.8 mM in the hydroponic medium did not appreciably affect leaf starch accumulation in either species. Starch accumulation in basil leaves was not consistently related to the duration of the photoperiod. However, photoperiod-induced changes in leaf starch levels were much greater in basil than spinach. The results clearly indicate that different horticultural crops can show diverse responses to CO 2 enrichment, and this highlight the need to develop individual growth strategies to optimize production quality of each species.

Effects of Abscisic Acid on Morphological and Physiological Responses to Water Stress in Eucalyptus camaldulensis Seedlings

The effects of abscisic acid (ABA) and a subsequent water stress on the physiological and morphological characteristics of seedlings of three provenances of Eucalyptus camaldulensis Dehnh. grown in pots in a glasshouse were compared 56 days after application of ABA. Seedlings from a high rainfall monsoon provenance in the dry tropics (Katherine, Northern Territory, Australia) were largely unaffected by ABA or by water strees in either physiological or morphological characteristics. Seedlings from a lower rainfall monsoon provenance in the humid tropics (Petford, Queensland) responded to water stress by reducing gas exhange while increasing photosynthetic capacity, indicated by increased leaf nitrogen and chlorophyll concentrations, and both short- and long-term leaf transpiration efficiency, indicated by changes in carbon-isotope discrimination. The changes were largest when ABA was also applied. Seedlings from semi-arid Tennant Creek (Northern Territory), which had the highest assimilation rates overall, responded to both ABA and water stress primarily by morphological changes including suppression of apical growth and increase in specific leaf weight. The results are discussed in terms of specific adaptations for establishment in increasingly dry environments and the possible role of ABA in mediating stress responses.

Leaf morphology and water status changes in Triticum durum under water stress

Water relations, leaf morphology and the chemical composition of cell walls in irrigated and unirrigated plants of three durum wheat eultivars were measured at two growth stages (booting and flowering). Plant response to water stress differed at the two stages: cell wall elasticity increased at booting and osmotic potential values decreased at flowering; this may be due to the changes in stress history, leaf development and plant growth stage between the two harvests. Leaf tissue characteristics were modified by water stress only at flowering: accumulation of fibrous constituents and hemicellulose in the cell walls, reduction of acid detergent fiber (ADF) per unit of leaf area, increase in specific leaf weight (SLW), decrease in turgid weight/dry weight ratio (TW/DW) and alteration in mesophyll cell morphology (cell area / ceil perimeter ratio) were observed.Generally, cv. Valforte (the less drought‐resistant cultivar) had the greatest mesophyll cell area and perimeter and it had greater values of neutral detergent fiber (NDF) at the booting stage than cv. Appulo. Reactivity to water stress differed in the eultivars: Valforte showed the greatest increase in hemicellulose content and decrease in cell dimensions under drought at flowering.No significant relationships between osmotic potential and mesophyll cell characters were observed; there were no correlations among cell wall elasticity, cell morphology and the chemical components of leaf tissue. The total fiber content and the hemicellulose per unit of leaf area were correlated with the TW/DW ratio at flowering. This parameter decreased more in plants subjected to water stress owing to accumulation of hemicellulose. Correlations between leaf structural constituents and $$ suggest that the absorptive capacity of the cell wall may significally affect the osmotic volume of the cell.

Effect of UV‐B (290–320 nm) irradiation on growth and metabolism of cucumber cotyledons

Cucumber (Cucumis sativus L. cv. Natsusairaku 3) seedlings were grown in a growth cabinet under UV‐B (290–320 nm) irradiation (equivalent to the UV‐B radiation normally incident at Tokyo, 36°N latitude, during clear sky conditions in mid‐april on a weighted daily fluence basis) and a UV‐B‐free control condition. UV‐B irradiation inhibited the growth of the cotyledons, i.e. the increase in area, and increase in fresh and dry weights of the cotyledons. The greatest inhibition rate was observed in the increase in area, causing a significant increase in specific leaf weight (the ratio of weight to area). UV‐B irradiation had no significant effect on DNA and RNA contents in the cotyledons, but decreased protein content slightly. In contrast, the irradiation reduced the amounts of organic acids and soluble sugars, indicating that primary carbon metabolism was very sensitive to UV‐B radiation. UV‐B irradiation lowered the photosynthetic activity in the cotyledons without any effect on chlorophyll content and respiratory activity. These results indicate that UV‐B radiation at the ambient level may act as a physiological stress in some UV‐sensitive plants.

The nitrogen balance of Raphanus sativus x raphanistrum plants. II. Growth, nitrogen redistribution and photosynthesis under NO3− deprivation

Abstract. Wild radish plants deprived of, and continuously supplied with solution NO−3 for 7 d following 3 weeks growth at high NO−3 supply were compared in terms of changes in dry weight, leaf area, photosynthesis and the partitioning of carbon and nitrogen (NH2‐N and NO−3‐N) among individual organs. Initial levels of NO−3‐N accounted for 25% of total plant N. Following termination of NO−3 supply, whole plant dry weight growth was not significantly reduced for 3 d, during which time plant NH2‐N concentration declined by about 25% relative to NO−3‐supplied plants, and endogenous NO−3‐N content was reduced to nearly zero. Older leaves lost NO−3 and NH2‐N, and roots and young leaves gained NH2‐N in response to N stress. Relative growth rate declined due both to decreased net assimilation rate and a decrease in leaf area ratio. A rapid increase in specific leaf weight was indicative of a greater sensitivity to N stress of leaf expansion compared to carbon gain. In response to N stress, photosynthesis per unit leaf area was more severely inhibited in older leaves, whereas weight‐based rates were equally inhibited among all leaf ages. Net photosynthesis was strongly correlated with leaf NH2‐N concentration, and the relationship was not significantly different for leaves of NO3−‐supplied compared to NO−3‐deprived plants. Simulations of the time course of NO−3 depletion for plants of various NH2‐N and NO−3 compositions and relative growth rates indicated that environmental conditions may influence the importance of NO−3 accumulation as a buffer against fluctuations in the N supply to demand ratio.

Assimilate Movement in Lolium and Sorghum Leaves. IV. Photosynthetic Responses to Reduced Translocation and Leaf Storage

The net CO2 exchange (NCE) rates of the last fully expanded leaves of Lolium temulentum L. and Sorghum bicolor Moench were examined in relation to the accumulation of photosynthate that occurred with time in continuous light (1100 μmol m-2 s-1 PAR). On a leaf area basis Lolium, although having a lower NCE, accumulated current photosynthate at a faster rate than Sorghum and had a greater capacity for storage. In Lolium there was an initial rapid rise in leaf solute, followed by a steady increase in the accumulation of starch, while in contrast in Sorghum there was an initial rapid rise in starch followed by a change to the accumulation of soluble photosynthate. After 4-6 h in continuous light there was a fall in NCE in both species, with the response depending on the balance between source and sink tissue. The decrease' in NCE coincided with an increase in specific leaf weight (SLW) of about 40% and SLW showed a closer negative correlation with NCE than leaf solute potential (Ψs). The fall in NCE, associated with an accumulation of photosynthate, was primarily related to factors within the leaf and not to stomatal conductance. The fall in NCE could not be accounted for by a rise in photorespiration and did not appear to be associated directly with an increase in the partitioning of photosynthate into starch. In both Lolium and Sorghum a fall in apparent quantum yield coincided with the fall in NCE.

Morphology and Growth in Seedlings of Several C4, Perennial Grasses

Morphology and Growth in Seedlings of Several C4, Perennial Grasses

Influence of deflowering on dry matter production of soybeans

Abstract Soybeans ( Glycine max (L.) Merr.) of maturity group 00 were grown in a greenhouse to investigate the effect of continuous flower removal on growth and dry matter partitioning. After growth stage R1 (initial bloom) one-half of the plants were deflowered daily for 50 days. Plants were harvested at 10-day intervals, beginning at R1, and continuing until control plants reached maturity. Total dry matter (all vegetative plant parts plus fruits, where present) was similar for both treatments at 30 days after R1; however, the total dry matter of the deflowered plants was greater than the controls at 40 and 50 days after R1. There was no difference in the photosynthetic rate of single leaves for 30 days after R1. Deflowering had only a minimal effect on the leaf area, number of branches, number of branch nodes, and plant height. Thus, the increase in the mass of the vegetative plant parts in the deflowered plants resulted primarily from an increase in specific leaf weight and thicker stems and branches. The relative proportion of the total vegetative weight represented by a given vegetative component was not greatly altered by flower removal. The results suggest that the vegetative plant parts in soybeans can serve as strong sinks for photosynthate when reproductive structures are not allowed to develop.

Diurnal Changes in Volume and Specific Tissue Weight of Crassulacean Acid Metabolism Plants

The diurnal variations in volume and in specific weight were determined for green stems and leaves of Crassulacen acid metabolism (CAM) plants. Volume changes were measured by a water displacement method. Diurnal variations occurred in the volume of green CAM tissues. Their volume increased early in the light period reaching a maximum about mid-day, then the volume decreased to a minimum near midnight. The maximum volume increase each day was about 2.7% of the total volume. Control leaves of C(3) and C(4) plants exhibited reverse diurnal volume changes of 0.2 to 0.4%. The hypothesis is presented and supported that green CAM tissues should exhibit a diurnal increase in volume due to the increase of internal gas pressure from CO(2) and O(2) when their stomata are closed. Conversely, the volume should decrease when the gas pressure is decreased.The second hypothesis presented and supported was that the specific weight (milligrams of dry weight per square centimeter of green surface area) of green CAM tissues should increase at night due to the net fixation of CO(2). Green CAM tissues increased their specific weight at night in contrast to control C(3) and C(4) leaves which decreased their specific weight at night. With Kalanchoë daigremontiana leaves, the calculated increase in specific leaf weight at night based on estimates of carbohydrate available for net CO(2) fixation was near 6% and the measured increase in specific leaf weight was 6%.Diurnal measurements of CAM tissue water content were neither coincident nor reciprocal with their diurnal patterns of either volume or specific weight changes.

Carbohydrate Levels in Soybean Leaves During Reproductive Growth1

The carbohydrate status of a soybean [Glycine max (L.) Merrill] leaf during reproductive growth is related to the interaction between the production of carbohydrate by photosynthesis and its utilltation by the developing seeds and other active sinks. This interaction between source and sink plays an important role in the production of yield. Leaf samples were collected from field grown soybeans, ‘Cutler 71,’for 3 years to investigate changes in levels of free sugars and starch during reproductive growth. Shade cloth that reduced the incident solar radiation by 60% was installed over plants at the beginning of the seed filling period for 2 years and leaf samples were collected from the 6th and/or 12th leaf position at weekly intervals. Changes in free sugar levels in the leaves during seed filling varied from an increase to no change to a decrease across the $ years. Starch leveis increased to a maximum and, in 2 of the 3 years, declined as the plant approached maturity. The increase in starch was associated with an increase in specific leaf weight. Leaves that were ready to abscise contained up to 8.5% starch. Shading reduced yield (19 to 32%) but had no effect the level of free sugars in the leaves. However, the shade caused an immediate reduction (within 5 to 8 days) the concentration of starch, to 13 to 28% below the control, and this difference in concentration was maintained throughout the remainder of the filling period. Although soybean leaves accumulate starch during the seed filling period, some of the starch is remobili~ed prior to leaf abscission and the amount in the abseised leaves does not represent a significant quantity relative to the seed yield.