Days Of Shading Research Articles

Response of antioxidant enzymes to transfer from elevated carbon dioxide to air and ozone fumigation, in the leaves and roots of wild‐type and a catalase‐deficient mutant of barley

A catalase‐deficient mutant (RPr 79/4) and the wild‐type (cv. Maris Mink) barley (Hordeum vulgare L.) counterpart, were grown for 3 weeks in high CO2 (0.7%) and then transferred to air and ozone (120 nl 1−1) in the light and shade for a period of 4 days. Leaves and roots were analysed for catalase (CAT, EC 1.11.1.6), superoxide dismutase (SOD, EC 1.15.1.1) and glutathione reductase (GR, EC 1.6.4.2) activities. CAT activity in the leaves of the RPr 79/4 catalase‐deficient mutant was around 5‐10% of that determined in Maris Mink, but in the roots, both genotypes contained approximately the same levels of activity. CAT activity in Maris Mink increased in the leaves after transferring plants from 0.7% CO2 to air or ozone, reaching a maximum of 5‐fold, after 4 days in shade and ozone. For the catalase‐deficient mutant, only small increases in CAT activity were observed in light/air and light/ozone treatments. In the roots, CAT activity decreased consistently in both genotypes, after plants were transferred from 0.7% CO2. The total soluble SOD activity in the leaves and roots of both genotypes increased after plants were transferred from 0.7% CO2. The analysis of SOD isolated from leaves following non‐denaturing PAGE, revealed the presence of up to eight SOD isoenzymes classified as Mn‐SOD or Cu/Zn‐SODs; Fe‐SOD was not detected. Significant changes in Mn‐ and Cu/Zn‐SOD isoenzymes were observed; however, they could not account for the increase in total SOD activity.In leaves, GR activity also increased in Maris Mink and RPr 79/4, following transfer from 0.7% CO2; however, no constant pattern could be established, while in roots, GR activity was reduced after 4 days of the treatments.The data suggest that elevated CO2 decreases oxidative stress in barley leaves and that soluble CAT and SOD activities increased rapidly after plants were transferred from elevated CO2, irrespective of the treatment (light, shade, air or ozone).

Predominance of ecophysiological controls on soil CO2 flux in a Minnesota grassland

Ecosystem studies often study soil CO2 flux as a function of environmental factors, such as temperature, that affect respiration rates by changing the rate of utilization of carbon substrates. These studies tend not to include factors, such as photosynthesis, that affect the supply of carbon substrates to roots and root-associated processes. We examined the role of decreased carbohydrate source on soil CO2 flux and root respiration in an annually-burned grassland through manipulations of light intensity and removal of above ground biomass. We also quantified the contribution of root respiration to soil CO2 flux by measuring the respiration rates of excised roots. Two days of shading caused a 40% reduction in soil CO2 flux, while clipping was associated with a 19% reduction in soil CO2 flux. Both reductions were independent of soil and air temperature at the time of measurement. The relative decrease in soil CO2 flux observed in the clipping experiment was similar in magnitude to an observed decrease in root respiration per gram of root, linking decreased root activity and soil CO2 flux. From these experiments, we conclude that variation in factors that affect carbon availability to roots can be important determinants of soil CO2 flux and should be included explicitly in studies that measure or model soil CO2 flux.

The influence of low light on apple fruit abscission

SummaryRemoval of the stigma and half the style from flowers at the pink or early stages of bloom caused 98% of the fruits to drop by 15 days after full bloom (AFB). Two or three consecutive days of 92% artificial shade (92% polypropylene shade material) reduced fruit set to 83-93% when trees were shaded 14, 21 and 28 days AFB. However, two or three days of artificial shade applied 8, 35, or 42 days AFB did not influence fruit drop. After three days of artificial shade, fruit stopped growing on the last day of shading and up to six days after shading and dropped 7-12 days later. Naturally occurring fruit drop in the period from 15 to 40 days AFB appeared to be related to 2-4 days of cloudy weather. Low light from cloudy periods 3-4 days long were calculated to be equivalent to 2-3 days of 92% artificial shade. If 1-2 days of sunlight separated the two or three days of applied artificial shade, less thinning occurred. Two days of artificial shade induced more fruit drop than NAA, ethephon, or carbaryl + oil thinning sprays. When carbaryl + oil were applied on the first day of artificially shaded trees, more thinning occurred than if no shade was applied or if trees were exposed to one day of full sun before the thinner was applied. When fruit were 20 mm in diameter, shading the whole tree for three days caused 98% fruit abscission, but if a limb was left in the sun 70% of its fruit were retained on that limb whilst a shaded limb on the shaded part of the tree retained only 5% of its fruit. Shading only one limb for three days caused 45% fruit abscission on that limb without affecting the fruit set on the rest of the tree.

Net Photosynthesis, Specific Leaf Weight, and Flowering of Peach as Influenced by Shade

`Redhaven' peach [Prunus persica (L.) Batsch] trees were shaded to five light levels [100%, 45%, 23%, 17%, and 9% photosynthetic photon flux (PPF)] for four different periods. Net photosynthesis (Pn), measured under the various shade levels, increased nonlinearly with increasing percent PPF. After 18 days of shading, specific leaf weight (SLW) was positively and linearly related to percent PPF. After shade removal, Pn and SLW returned to control levels in 26 and 4 days, respectively. Flower density was positively related to percent PPF when trees were shaded from 16 June to 4 July or 4-31 July, but not from 31 July to 30 Sept. of the previous year.

Apple Thinning by Photosynthetic Inhibition

Shading (92%) of `Redchief Delicious' apple (Malus domestics Borkh.) trees for 10-day periods from 10 to 20, 15 to 25, 20 to 30, and 25 to 35 days after full bloom (DAFB) caused greater fruit abscission than shading from 5 to 15, 30 to 40, 35 to 45, or 47 to 57 DAFB. Fruit 8 to 33 mm in diameter (10 to 30 DAFB) were very sensitive to 10 days of shade, even though fruit sizes of 6 to 12 mm are considered the most sensitive to chemical thinners. In a second test, shading for 3 days caused fruit thinning; 5 days of shade in the periods 18 to 23, 23 to 28, and 28 to 33 DAFB caused greater thinning than 11 to 16 or 33 to 38 DAFB. Shading reduced photosynthesis (Pn) to about one-third that of noncovered trees. Terbacil (50 mg·liter-1) + X-77 surfactant (1250 mg·liter-1) applied with a hand-pump sprayer 5, 10, or 15 DAFB greatly reduced fruit set and caused some leaf yellowing, particularly in the earliest treatments. Terbacil reduced Pn by more than 90% at 72 hours after application. Shoot growth of trees defruited by shade or terbacil was equivalent to defruited or deblossomed trees; ethephon (1500 mg·liter-1) inhibited tree growth and defruited trees. No terbacil residues were dectected in fruit at harvest from applications made 5, 15, 20, 25, or 30 DAFB. Eleven of 12 photosynthesis-inhibiting herbicides were also found to thin `Redchief Delicious' apple trees. Shading caused more thinning than terbacil at the later applications, which may reflect poorer absorption and/or lesser photosynthetic inhibition than when terbacil was applied to older leaves.

Effect of Shading on Bud Necrosis and Bud Fruitfulness of Thompson Seedless Grapevines

Both localized shading of individual buds or shading entire shoots with neutral shade cloth resulted in a 60% to 500% increase in the number of buds showing necrosis in Thompson Seedless vines grown under field conditions in Chile. Primary buds showing necrosis usually did not burst, resulting in either `blind buds9 or `split buds9. The amount of bud necrosis and bud fruitfulness that developed at individual artificially shaded nodes were not influenced by the presence or absence of the primary leaf, cluster(s), or lateral shoot, provided these structures did not cause significant shading of the buds themselves. A period of 15 days of shading of individual buds or entire shoots at photosynthetic photon flux density (PPFD) less than 1% to 2% of full sunlight was sufficient to significantly raise bud necrosis above that of non-shaded control vines. Longer periods of shading did not significantly increase the amount of bud necrosis. Enhancement of light penetration within the canopy of grapevines by shoot positioning or by shoot thinning after berry set significantly reduced the amount of bud necrosis and increased bud fruitfulness.

Energy distribution in the focal region of an offsetfeed paraboloidal solar stove

A specific class of paraboloidal reflectors namely the offsetfeed paraboloidal reflectors which find application in space communications is utilized for concentration of solar energy at a fixed point (focus) maintained throughout the day in shade. The energy distributions on spherical receiver centered around the focus and on a flat sectorial receiver held in a plane perpendicular to the focal line have been studied for the case of perfect tracking in hour angle and declination axes. The spill-over of energy due to non-tracking in hour-angle or declination axis for specific periods in the case of a flat sectorial receiver has been studied and plotted. A summary of the results and suggested applications of this configuration are presented. A comparison of performance is made between wedge-type and circular aperture type offsetfeed reflectors.

Leaf Area, Nonstructural Carbohydrates, and Root Growth Characteristics of Blue Grama Seedlings

Leaf Area, Nonstructural Carbohydrates, and Root Growth Characteristics of Blue Grama Seedlings

Shade Effects on Growth, Partitioning, and Yield Components of Peanuts1

Peanut (Arachis hypogaea L.) may have one or more periods during development when low solar radiation intensity is particularly detrimental to high yield. The present studies were conducted in the field to determine the effect of shade on vegetative growth, partitioning of assimilates and yield components of peanut. In a 2‐year experiment, 75% shade was applied for 7, 10, 14, or 21 day periods during flowering, pegging, podding, and maturing phases. The objective was to determine which reproductive phase was most sensitive to low solar radiation intensity. Flower number, peg development, pod formation, and dry matter accumulation and partitioning were measured at regular sampling intervals. Shade during the peak flowering period reduced the number of flowers per plant and inhibited peg formation. Shade during the pegging and podding phases reduced total peg and pod number and reduced pod dry weight. Shade during the maturing phase reduced seed fill as shown by reduced shelling percentage and a lower number of fruits achieving mature pod status. On the average, over all stages, 75% reduction of light intensity decreased the growth rate of vegetative parts by 85%, the reproductive growth rate by 67%, and the total biomass growth rate by 67%. Shade prior to podding increased partitioning to vegetative growth, by 20%, whereas shade during the podding phase (83 to 104 days) increased dry matter partitioning to pods by 127%. Seventy‐five percent reduction in solar radiation intensity reduced yield of Florunner peanuts significantly only when the duration was for 14 or 21 day periods. Podding was the phase in which yield was most sensitive to shade with a 30% reduction in fruit yield from shade during 83 to 104 days of age. The maturing phase was next in sensitivity to shade, which decreased yield primarily by decreasing seed fill in existing fruits. Twenty‐one days of shade at flowering did not reduce final fruit yield, since the plants had time to recover from the loss of active flowers and subsequently bear flowers and produce a normal pod load.

Release od Soluble Protein and Nitrogen in Alfalfa. III. Influence of Shading1

Changes in leaf anatomy, morphology, and chemical composition due to different amounts of solar radiation could affect the apparent bloat potential of alfalfa (Medicago sativa L.) mediated via release of soluble protein into rumen fluid in the presence of ample available carbohydrates. Our objectives were to determine whether shading during growth would influence production characteristics as well as concentration of several N fractions and total nonstructural carbohydrates (TNC) released from alfalfa.Alfalfa was shaded with saran shades [0 (control), 47, and 73% shade] from 12 May to 1 June [Period (P)l], 30 June to 7 July (P2), and 9 to 16 August 1978 (P3). Total nitrogen (TN), total soluble N (TSN), soluble nonprotein N (SNPN), soluble protein N (SPN), total nonstructural carbohydrates (TNC) were determined.The 73% shade reduced yields 42% for P1, 30% for P2, and 24% for P3, while the 47% shade reduced yields 29% for P1, 22% for P2, and 10% for P3 compared to the respective control yields. In P1 (20 days of shade), concentration of SNPN in herbage was 10.1 mg/g dry wt for control, 10.5 mg for 47% shade, and 11.5 mg for 73% shade, while that of SPN was 14.8 mg for control, 13.8 mg for 47% shade, and 12.6 mg for 73% shade.In P2 (7 days of shade), concentrations of TN, TSN, and SNPN in herbage increased as shade increased. Shade did not significantly influence the herbage concentrations of SPN in P2. In P3 (7 days of shade), shade did not significantly affect herbage concentrations of any of the N fractions. Shade of 73% reduced the TNC concentrations in herbage 16% for P1, 44% for P2, and 19% for P3, while shade of 47% recuded TNC 8% for P1, 28% for P2, and 10% for P3, compared to that in control herbage.Reduced apparent bloat potential of alfalfa, as estimated by SPN release, occurred only in plants grown under low solar radiation for a continuous 20‐day period. However, both short and long periods of decreased solar radiation caused decreased TNC concentrations in herbage. Because an abundant supply of TNCis essential for the microbial activity that leads to gas production in the rumen, even relatively short periods of shade could be considered as potentially bloat suppressing. We conclude that the usual incidence of cloudy weather is not likely to be a major mediator of bloat incidence in ruminants that graze alfalfa, although periods of high solar radiation maybe considered bloat‐promoting rather than bloatsuppressing.

Effect of Light on the Response of Tomato (Lycopersicon esculentum) and Two Weed Species to Metribuzin

The response of tomato (Lycopersicon esculentumMill. ‘Chico III’), jimsonweed (Datura stramoniumL.), and velvetleaf (Abutilon theophrastiMedic.) to postemergence applications of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] applied after cloudy weather was determined by shading the plants artificially before field application of the herbicide. One day of 76% actual shade reduced the tolerance of tomato, jimsonweed, and velvetleaf to metribuzin, and 3 days of shade further reduced plant tolerance to the herbicide. The GR50values showed that tomato was about 30 times more tolerant than jimsonweed and about 40 times more tolerant than velvetleaf to metribuzin. After 3 days of shade, 2 or 3 days of sunshine were required to return tomato to its full tolerance to metribuzin. After 3 days of cloudy weather, metribuzin applied at about 55% of the normal dose should control jimsonweed and velvetleaf. Weather conditions before postemergence applications of metribuzin will determine the appropriate timing of application and the herbicide dose.