Effects Of Partial Defoliation Research Articles

Compensatory growth mechanisms in lettuce plants after partial defoliation

Leaf area loss is a frequent problem in crops, and it can be caused by biotic or abiotic factors. Reduced leaf area can produce alterations in plants, affecting their metabolism, growth, and yield. The leaf area in lettuce plants (Lactuca sativa L.) is often affected by herbivores such as slugs. The effects of partial defoliation on the growth of lettuce plants were evaluated under greenhouse conditions in Tunja, Colombia. Some plants had half of their leaves removed, while others were left intact as a control. The variables normally used in the basic analysis of plant growth were evaluated. There was nonsignificant difference between the two treatments; however, lettuce plants showed a remarkable ability to reduce the negative effect caused by partial defoliation, and they managed to maintain a balance in the root to shoot ratio, leaf area ratio, specific leaf area, leaf weight ratio, DM partitioning, and harvestable DM. Partial defoliation decreased the absolute growth rate by 17.8% and the relative growth rate by 13.8%. Additionally, the chlorophyll content index and the number of leaves increased by 16.0% and 15.4%, respectively, in plants subjected to partial defoliation compared with the control plants. These results indicate the regeneration capacity of the plants after partial defoliation.

The Effect of Partial Defoliation, Leaf Position and Developmental Stage of the Vine on Leaf Chlorophyll Concentration in Relation to the Photosynthetic Activity and Light Intensity in the Canopy of Vitis vinif era L. cv. Cabernet Sauvignon

The effect of partial defoliation and leaf position on leaf chlorophyll concentration in relation to the photosynthetic activity and light intensity in the canopy of Vitis vinifera L. cv. Cabernet Sauvignon was investigated at berry set, pea size, veraison and ripeness stages. The leaves of the severely defoliated vines appeared to contain the highest chlorophyll concentration. In general, chlorophyll a decreased as the leaves were situated progressively deeper into the canopy. No consistent relationship between chlorophyll concentration, light intensity and photosynthetic activity could be found for the different leaf positions. However, to obtain leaves that photosynthesize optimally, the amount and time of leaf removal in the grapevine canopy must be carefully planned.

The Effect of Partial Defoliation, Leaf Position and Developmental Stage of the Vine on the Photosynthetic Activity of Vitis vinifera L. cv Cabernet Sauvignon

The effect of partial defoliation, :eaf position and developmental stage of the vine on the photosynthesis, stomatal resistance and transpiration of Vitis vinifera L. cv Cabernet Sauvignon was investigated. Partially defoliated vines displayed a higher rate of photosynthesis, generally increasing with degree of defoliation. The highest photosynthetic rates were found for the apical leaves, while those of the leaves opposite and below the bunches were restricted. Generally, rate of photosynthesis declined as the season progressed. The course of transpiration rate and stomata! resistance correlated with that of the rate of photosynthesis. However, transpiration and photosynthesis correlated poorly in the case of the apical leaves. In general, photon flux density and relative humidity at the leaf surface increased with an increase in defoliation percentage for all leaf positions. Leaf temperature was not significantly affected by partial defoliation. The results of the investigation suggested that excess vegetative growth is detrimental to interior-canopy microclimate as well as the photosynthetic rate of the entire vine. Partial defoliation seemed to provide a means to reduce some of the deleterious effects of vigorous growth.

The Effect of Partial Defoliation on Growth Characteristics of Vitis vinif era L. cv. Cabernet Sauvignon IL Reproductive Growth

The effect of partial defoliation over the whole canopy on the reproductive growth of Vitis vinifera L. cv. Cabernet Sauvignon was investigated. The 33% defoliation treatment prior to pea size and the 66% defoliation treatment prior to veraison adversely affected fresh mass per berry and yield at harvest. The 33% defoliation treatment from veraison increased fresh berry mass. Partial defoliation had no effect on berry water content. Dry matter started to accumulate rapidly only from after pea size stage. The fresh berry mass:cane mass ratio increased with partial defoliation from veraison. Leaf area/g fresh mass results indicated that control vines carried excess foliage which prevented maximum photosynthetic activity. Partial defoliation of the canopy improved budding percentage, generally increasing with increasing defoliation, whereas bud fertility was improved only by 33% defoliation. In general, leaf removal from bud break and berry set was more effective in improving budding, whereas bud fertility was favoured by partial defoliation from bud break.

The Effect of Partial Defoliation on Growth Characteristics of Vitis vinifera L. cv. Cabernet Sauvignon I. Vegetative Growth

The effect of partial defoliation over the whole canopy on the reproductive growth of Vitis vinifera L. cv. Cabernet Sauvignon was investigated. The 33% defoliation treatment prior to pea size and the 66% defoliation treatment prior to veraison adversely affected fresh mass per berry and yield at harvest. The 33% defoliation treatment from veraison increased fresh berry mass. Partial defoliation had no effect on berry water content. Dry matter started to accumulate rapidly only from after pea size stage. The fresh berry mass:cane mass ratio increased with partial defoliation from veraison. Leaf area/g fresh mass results indicated that control vines carried excess foliage which prevented maximum photosynthetic activity. Partial defoliation of the canopy improved budding percentage, generally increasing with increasing defoliation, whereas bud fertility was improved only by 33% defoliation. In general, leaf removal from bud break and berry set was more effective in improving budding, whereas bud fertility was favoured by partial defoliation from bud break.

Effects of partial defoliation on the growth, ion relations and photosynthesis of Lycium chinense Mill. under salt stress

In this study, we investigated the effects of artificial defoliation on the growth and physiological response of Lycium chinense Mill. to salt stress. Our results show that partial defoliation increases the plant relative growth rate, leaf water content and dry weight-based leaf Na+ content, and reduces the fresh weight-based leaf Na+ content under salt stress. In response to defoliation, the leaf Na+/Ca2+ and Na+/Mg2+ ratios were decreased, but the K+ content remained unchanged. The contents of ROS and MDA were decreased in defoliated plants. Net The photosynthetic rate (PN), stomatal conductance (gs), electron transport rate (ETR), actual photochemical quenching (?PSII) and photochemical quenching (qp) were enhanced by defoliation. Together, these findings indicate that partial defoliation mitigates the salt-induced growth inhibition and physiological damage in L. chinense.

Partial defoliation and runner removal affect runnering, fruiting, leaf photosynthesis and root growth in ‘Toyonoka’ strawberries for subtropical winter production

Removing runners and old leaves are two major routine and labor consuming tasks in winter strawberry (Fragaria × {ptananassa} Duch.) production in subtropics. However, the potential negative effects of defoliation has not been evaluated. We studied the effects of partial defoliation and runner removal on plant growth, leaf photosynthesis (Pn), and yield in field-grown or potted strawberry plants (‘Toyonoka’). The treatments were consisted of partial defoliation by removing leaves older than 45 days (PD), removing all runners (DR), PD + DR, and the control (CK). Treatments were applied weekly from mid-November until early March. DR promoted yield and number of fruits for the first harvest cycle but not for the second harvest cycle. Multiple linear regressions indicated that leaf area had greater overall effects on runnering and fruit traits than the existence of runners. The leaf Pn was not responsive to DR but a transient increase in Pn was consistently detected on the remaining leaf after each PD treatment. The compensatory increase in Pn was only detectable within 1 days after each PD treatment, indicating that the actual compensation for partial loss of functioning leaf area may be negligible. Crown dry weight was less affected by canopy manipulation than growth and dry weight of roots. Our results indicated that yield of strawberry in Taiwan’s subtropical climate can be improved by removing runners while maintaining a greater leaf area with less severe defoliation.

Effect of partial defoliation after silking stage on yield components of three grain maize hybrids under semi-arid conditions

The effect of source reduction on yield and yield components of three maize hybrids at three plant densities was studied under agro-climatic conditions in southern Iran. Field experiments were conducted at the research farm of the College of Agriculture, Shiraz University, Shiraz, Iran, located at Bajgah (52° 35′ N and 39° 4′ E, 1810 masl) during the 2008 and 2009 growing seasons. The treatments included three hybrids, three plant densities and defoliation, arranged in the main, subplots and sub-subplots, respectively. Defoliation treatments, which consisted of removing all the leaves from one side of the maize plants, were imposed when plants were at the silking stage. Silking was taken as the time when 50% of the plants in a row presented visible silks. Partial defoliations included control, and 50% defoliation at 25 and 35 days after silking (defoliation treatments were applied to all plants in each plot). The experiments were conducted in a randomized complete block (RCB) design with three replications. Dry matter accumulation was assessed by sampling ears at 7-day intervals from the mid-silking stage to black layer formation. Defoliation treatments decreased grain yields significantly in both years. The highest grain yield in 2008 (19 t ha−1) was obtained from hybrid Maxima ‘524’ and in 2009 (14 t ha−1) from hybrid 704 at 95,000 plants ha−1 density. Defoliation treatments decreased grain yields due to a reduction in the number of kernels per ear, as well as mean kernel weight. Some other measured parameters including stalk, shank, husk and cob dry weights, and cob and ear lengths were also decreased under defoliation treatments. If 50% of the photosynthetic area after silking was removed, the quantity of retransferred assimilates from stalk to kernel was increased. Finally, partial defoliation, 25 days after silking, reduced all the yield components more than any other treatments.

Effects of partial defoliation on closed canopy Eucalyptus globulus Labilladière: Growth, biomass allocation and carbohydrates

Herbivory caused by leaf-eating insects continues to be a severe risk to forest trees and forest stands. Besides quantifying the extent of defoliation, the quantification of the trees’ response to the loss of biomass is a challenge to plant ecologists and foresters alike, and an important precondition for the application of appropriate silvicultural measures. While many defoliation studies target small trees as model systems, little is known about the effect of defoliation on larger trees. In the present study, we investigated the effects of 45% removal of leaf area on growth, biomass allocation and carbohydrates of 13m tall, four-year-old, plantation Eucalyptus globulus Labill. in southern Tasmania. Responses were measured in three crown zones (lower, middle, upper) over a period of 11 months. Height increment was unaffected by defoliation, but diameter increment was significantly reduced 155 days after treatment. Defoliation treatment had no effect on stem volume and biomass partitioning compared with the control treatment. Trees responded to defoliation by decreased branch senescence in the lower crown, greater leaf area development in the mid crown and increased specific leaf area. Defoliation reduced concentration of soluble sugars (SS) in foliage by 22% and the pools of SS in the coarse roots by 34%. Decrease in root SS was only observed in 10–15mm diameter class and the rootball. We concluded that this four-year-old E. globulus stands with a closed canopy was able to tolerate a single, partial artificial defoliation event, which is similarly observed with younger trees.

Effect of partial defoliation on the dry-matter production in mulberry trees

Effect of partial defoliation on the dry-matter production in mulberry trees

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.

The long‐term effect of partial defoliation on the yield of short‐rotation coppice willow

AbstractFive varieties of willow were planted in a randomised block design at the Northern Ireland Horticulture and Plant Breeding Station, Loughgall, County Armagh in 1997. Three treatments were applied: control (no treatment), manual defoliation and routine control (spraying) of willow beetles. The defoliation was carried out at 75% for the first 2 years and thereafter 25% up to the first harvest in January 2001. During the second production cycle, no manual defoliation was applied in order to observe the ability of the different varieties to recover from earlier damage. The variety 78112 exhibited the highest yield loss in the first cycle as a result of defoliation (∼70%), while the vigorous variety Tora suffered least yield loss (35–43%). In the recovery phase (second production cycle 2001–2003), all the varieties showed little improvement in yields in plots that had been defoliated previously, indicating a long‐term legacy of yield loss as a result of defoliation. The possible reasons for this inability to recover are discussed.

Effects of Partial Defoliation on Sucrose Accumulation, Enzyme Activity and Agronomic Parameters in Sugar cane (Saccharum spp.)

AbstractMechanical defoliation of sugar cane plants (Saccharum spp.) will provide leaves that can be used as fodder. The effect of partial mechanical defoliation on sucrose content, enzyme activities and agronomic parameters of sugar cane is still unknown. We investigated how sucrose accumulation, activities of sucrose phosphate synthase, soluble acid invertase, sucrose synthase, neutral invertase, brix grades, purity grade, moisture content, fibre content, maturity index and reduced sugars of two commercial sugar cane plants (Mex 69‐290 and Mex 57‐473) were affected in a field experiment. The concentration of sucrose in stems of partial defoliated plants was not significantly different from that found in intact plants. Agronomic parameters and enzyme activities were not different in defoliated plants compared with intact plants except for the moisture content which was higher in defoliated plants than in intact ones. These results indicated that sugar cane plants could be partially defoliated without changing sucrose production and agronomic parameters while providing leaves that could be used as fodder.

Effects of partial defoliation on carbon and nitrogen partitioning and photosynthetic carbon uptake by two-year-old cork oak (Quercus suber) saplings.

At the end of the growing season in late July, 20-month-old cork oak (Quercus suber L.) saplings were partially defoliated (63% of leaf area) to evaluate their ability to recover leaf area after defoliation. At 18 and 127 days after defoliation, changes in starch and nitrogen pools were determined in leaves and perennial organs, and variations in photosynthetic carbon uptake were investigated. To determine the role of stored nitrogen in regrowth after defoliation, plant nitrogen was labeled in the previous winter by enriching the nutrient solution with 15N. Plants recovered the lost leaf area in 127 days. Although there was remobilization of starch and nitrogen from leaves and perennial organs, the availability of resources for growth in the following spring was not decreased by defoliation. On the contrary, starch concentration in coarse roots was higher in defoliated saplings than in control saplings, presumably as a result of the higher net CO2 exchange rate in newly developed leaves compared with pre-existing leaves.

Growth, seed production and effect of defoliation in an early flowering perennial grass, Alloteropsis semialata (Poaceae), on Cape York Peninsula, Australia

Alloteropsis semialata (R.Br.) A.Hitchc. is one of the first perennial grasses in monsoonal Australia to produce seed at the start of the wet season. Patterns of growth and seed production and seed dynamics of Alloteropsis semialata were examined in this study, along with the effects of partial defoliation. Growth of Alloteropsis semialata tussocks started with the first pre-wet-season rains, and was then interrupted during a period with little rain. Growth ceased before the end of the wet season, indicating that factors other than moisture availability were limiting. Seeds of Alloteropsis semialata were germinable on production, but did not remain viable or persist on the soil surface through the dry season. Most seeds and young seedlings were harvested and no seedlings were recruited. Inflorescence production increased with plant size. Moderate defoliation in the early wet season had no impact on plant growth, but reduced inflorescence and seed production for at least 2 years. Absence of a seed bank and early wet-season flowering mean that Alloteropsis semialata is likely to be sensitive to long-term over-grazing.

Effect of nitrogen supply and defoliation on loss of organic compounds from roots of Festuca rubra

The aim of this study was to determine the effects of N‐supply and defoliation on rhizodeposition from Festuca rubra , in the context of whole‐plant C‐ partitioning and root morphology. Plants were grown for 36 d in axenic sand microcosms continuously percolated with nutrient solutions of either high or low N concentration (2 mM or 0.01 mM NH 4 NO 3 , respectively). The effects of partial defoliation at weekly intervals were determined at high and low N. At low N, dry matter accumulation in roots and shoots was reduced significantly ( P <0.001), with proportionately increased partitioning to roots, in comparison with the high N treatment. Root morphology was also affected by N‐treatment; at low N, lower biomass production was offset by increased specific root length ( P <0.001), reducing the magnitude of the significant ( P =0.002) increase in total root length at high N. Cumulative release of organic C from roots of F . rubra over the experimental period was not altered significantly by N‐treatment. However, as a proportion of net C‐assimilation, rhizodeposition was significantly ( P <0.001) greater at low N than at high N. Defoliation transiently (3–5 d) increased the release of soluble organic compounds from roots at each N‐supply rate, and increased significantly ( P <0.001) cumulative rhizodeposition over the experimental period. These effects of N‐supply and defoliation on rhizodeposition are of importance in understanding interactions between plant and microbial productivity in grazed grasslands, and in interpretation of concurrent effects on microbially driven nutrient cycling processes in these systems.

Effect of nitrogen supply and defoliation on loss of organic compounds from roots of Festuca rubra

The aim of this study was to determine the effects of N-supply and defoliation on rhizodeposition from Festuca rubra, in the context of whole-plant C- partitioning and root morphology. Plants were grown for 36 d in axenic sand microcosms continuously percolated with nutrient solutions of either high or low N concentration (2 mM or 0.01 mM NH(4)NO(3), respectively). The effects of partial defoliation at weekly intervals were determined at high and low N. At low N, dry matter accumulation in roots and shoots was reduced significantly (P<0.001), with proportionately increased partitioning to roots, in comparison with the high N treatment. Root morphology was also affected by N-treatment; at low N, lower biomass production was offset by increased specific root length (P<0.001), reducing the magnitude of the significant (P=0.002) increase in total root length at high N. Cumulative release of organic C from roots of F: rubra over the experimental period was not altered significantly by N-treatment. However, as a proportion of net C-assimilation, rhizodeposition was significantly (P<0.001) greater at low N than at high N. Defoliation transiently (3-5 d) increased the release of soluble organic compounds from roots at each N-supply rate, and increased significantly (P<0.001) cumulative rhizodeposition over the experimental period. These effects of N-supply and defoliation on rhizodeposition are of importance in understanding interactions between plant and microbial productivity in grazed grasslands, and in interpretation of concurrent effects on microbially driven nutrient cycling processes in these systems.

The effect of defoliation intensity and history on photosynthesis, growth and carbon reserves of two conifers with contrasting leaf lifespans and growth habits

The effects of partial defoliation on photosynthesis, whole‐seedling carbon allocation, partitioning and growth were studied for two species with contrasting foliar traits. Field‐grown seedlings of deciduous Japanese larch (Larix leptolepis) and evergreen red pine (Pinus resinosa) were defoliated by hand in early summer for 2 consecutive years. In the first year (1990), seedlings were defoliated by removing the distal 0, 25, 50 or 75% of each needle. In the second year (1991), seedlings were defoliated either 0 or 50%, regardless of previous defoliation treatments. Defoliation had little effect on photosynthesis and starch concentration in whole seedlings of either species in the first year. In the second year, photosynthesis increased in both species in response to the 1991 defoliation treatment, and in red pine also increased in response to the 1990 defoliation treatment. Further, in 1991 both larch and pine had decreased whole‐seedling total non‐structural carbohydrate concentrations in all seedlings that were defoliated at least once over the 2‐yr period. This decrease was noted mostly in the starch component of the non‐structural carbohydrates, and was similar in both species. In 1991, biomass was similarly decreased in both species in response to 1991 defoliation. Both species showed overcompensation in total and component biomass in seedlings defoliated by 25% in 1990. Overall, the results do not support the widely held belief that evergreen trees are substantially more affected than deciduous trees by defoliation.

Partial Defoliation ofVitis viniferaL. cv. Cabernet Sauvignon/99 Richter: Effect on Root Growth, Canopy Efficiency; Grape Composition, and Wine Quality

<i>Vitis vinifera</i> L. cv. Cabernet Sauvignon/99 Richter was grown under field conditions. The effect of partial defoliation (33%) in the lower half of the canopy at berry set stage, and thereafter at pea-size and veraison, respectively, on root development, distribution, and composition as well as on canopy efficiency, yield, grape composition, and wine quality was investigated. Defoliation evidently stimulated occurrence of fine and extension roots, which may have increased the absorptive capacity of the root system. Root number decreased with increasing depth and roots occurred predominantly in the top 800 mm of the soil profile. Starch was the principal carbohydrate storage form in the roots, irrespective of root size. Starch synthesis appeared not affected by root age. Sucrose and organic acid patterns were similar. Citric and tartaric acids were the main organic acids in roots, followed by malic acid. Elevated sugar and organic acid levels were found in roots of treated vines. The results demonstrate that the remaining leaves of partially defoliated vines were able to sustain normal metabolic functions in the roots. Canopy density was efficiently reduced by partial defoliation, leading to increased light penetration, fruit exposure, and photosynthetic activity of mature and old leaves. Although partially defoliated vines had much less leaf area per gram fresh berry mass at ripeness, yield increased considerably with defoliation at pea-size and veraison. Root density, yield, and cane mass were related. Grape total soluble sugar content was unaffected, but titratable acidity increased and the pH of the must decreased with partial defoliation. Ostensible increases in wine constituents (anthocyanins, phenolics), color density, cultivar character intensity, and overall wine quality were found in wines from treated vines.

Effects of defoliation, nitrogen nutrition, and temperature on leafing and root carbohydrates of birch seedlings

Difficulties were observed in the leafing of mature birch, alder, and willow species in southern Finland in the spring 1989, especially at lush growing sites. The suspected reason was freezing of the buds in the preceding autumn caused by disturbed bud dormancy. The hypothesis was tested experimentally with 1-year-old Betulapendula Roth seedlings, investigating the effects of partial defoliation, nitrogen nutrition, and temperature. Defoliation clearly weakened both the growth and overwintering of the seedlings, altered the carbohydrate relations in their roots, and markedly delayed leafing in the spring. The earlier in the summer the defoliation was performed, the more conspicuous were its effects, which were also emphasized by the fertilization. A short greenhouse treatment in autumn had no significant effect, however, and it is thought that the partial death of the defoliated top shoots may have been caused by frost drying. The main reason for the late leafing seems to be the delayed development of the buds as a consequence of early defoliation. On the other hand, the growth-promoting effect of nitrogen fertilization and the premature branching of the buds evidently disturbed the carbohydrate balance in the roots and thus the development of the whole seedlings.