Leaf Loss Research Articles

Growth of shredders on leaf litter biofilms: the effect of light intensity

Summary1. The effect of light intensity on the decomposition of poplar (Populus nigra) leaves and growth of the shredders, Asellus aquaticus and Gammarus pulex, was studied in a laboratory experiment. The response was studied along a gradient of six light intensities of 0, 5, 23, 54, 97 and 156 μmol m−2 s−1. It was hypothesised that an increase in light intensity would increase growth of shredders, because of an increase of algae (i.e. food quality) in the leaf‐biofilm.2. Light intensity affected both leaf‐biofilm quality and consumer behaviour and affected several aspects of the decomposition‐consumer interaction. In the absence of invertebrates, leaf mass loss was lower in the dark, while light intensity had no significant effect on mass loss of poplar leaf in the presence of invertebrates. Light intensity affected algal biomass, density and composition, and had a significant positive effect on the growth of both shredders.3. Our results suggest that algae can be an important component of the nutritional value of the leaf‐biofilm for benthic invertebrates, directly as an additional food source and indirectly through a link with bacteria and/or fungi.4. The River Continuum Concept mainly emphasises allochthonous inputs to headwater streams and autochthonous production further downstream. Our results suggest that light, by its effect on the biofilms on leaf surfaces, might be a more important factor in headwaters than is usually assumed.

Elevated CO2 protects poplar (Populus trichocarpa × P. deltoides) from damage induced by O3: identification of mechanisms.

CO2 concentrations in the Earth's atmosphere will rise to between 550 and 700 μL L-1 by 2100 (IPCC 2001). In much of the world, ozone (O3) is the air pollutant most likely to be having adverse effects on the growth of plants. Here we describe the impacts of CO2 and O3 episodes (rising to 100 nL L-1), singly and in mixtures on the growth and physiology of an interamerican hybrid poplar (Populus trichocarpa L. (Torr. & Gray ex Hook.) × P. deltoids Bartr. ex Marsh). 700 μL L-1 CO2 increased all growth variables relative to values in 350 μL L-1. Mainstem dry weight showed a 38% increase in year 1 and a 32% increase in year 2. Ozone episodes reduced mainstem dry mass by 45% in 350 μL L-1 CO2 and by 34% in 700 μL L-1 CO2. A / Ci analysis showed limited effects on photosynthetic efficiency of 700 μL L-1 CO2 but in contrast, Vcmax was reduced by O3 episodes. CO2 tended to increase leaf expansion but O3 episodes reduced expansion rates generally although a short period of increased leaf expansion in response to O3 was also observed. O3 reduced leaf solute potentials (Ψs) and increased turgor (P) in young leaves. Cell wall properties (elasticity and plasticity) were both stimulated by ozone and this was associated with increased leaf expansion. A new mechanism is proposed which suggests that O3 may act directly on the cell wall, attacking polysaccharides in the wall that result in altered cell wall properties and leaf growth. O3 episodes increased leaf loss, elevated CO2 delayed abscission and O3 was less effective at accelerating leaf loss in elevated CO2. Overall CO2 increased growth, O3 caused decreases and the treatment combination gave intermediate effects. Thus O3 episodes are less likely to be detrimental to P. trichocarpa × P. deltoides in the CO2 concentrations of the future.

Screening for Resistance to Pythium Root Rot among Twenty-three Caladium Cultivars

Caladiums (Caladium ×hortulanum) are widely grown as pot or landscape plants for their attractive leaves. Pythium root rot (Pythium myriotylum) is one of the most damaging diseases in caladium, severely reducing plant growth, aesthetic value, and tuber yield. Twenty-three commercial cultivars were inoculated with three aggressive isolates of P. myriotylum and evaluated for their resistance to root rot. Three cultivars, `Apple Blossom', `Blizzard', and `Etta Moore', were found to have a moderate level of resistance (partial resistance) to pythium root rot. The rest of these cultivars were susceptible or highly susceptible to Pythium infection, losing up to 94% of their root tissue to rotting within 10 days after inoculation. Data indicated a linear relationship between root rot severity and leaf loss severity on Pythium-inoculated plants and highlight the importance of controlling pythium root rot in caladium pot plant and tuber production. Comparison of some recent releases with their parents for pythium root rot resistance suggests the potential of developing new resistant caladium cultivars using the identified sources of resistance.

Survival Analysis of Time to Abscission of Blueberry Leaves Affected by Septoria Leaf Spot

ABSTRACT In the southeastern United States, Septoria leaf spot, caused by Septoria albopunctata, can result in premature defoliation of blueberry plants during summer and fall, thereby reducing yield potential for the following year. The effects of disease severity and leaf attributes (leaf age and leaf location in the canopy) on the dynamics (timing and extent) of defoliation were quantified in field plots of Premier rabbiteye blueberry (Vaccinium ashei) in 2002 and 2003. In each year, 50 shoots were selected for assessment in early spring, and all leaves on these shoots (n = 410 and 542 in 2002 and 2003, respectively) were monitored individually for disease progress and time of abscission at 3- to 10-day intervals throughout the season. In both years, disease progress was characterized by an exponential increase in disease severity up to late September, followed by a decline toward the end of the assessment period in late November. Defoliation was sporadic up to late August, followed by more rapid and sustained levels of leaf loss. Abscission of severely infected leaves could explain the decline in disease severity toward the end of the season. Final disease severity (i.e., disease severity on the last assessment date before leaf drop) was highest for leaves that abscised early and lowest for leaves that had not abscised by the end of the assessment period. Survival analysis revealed that older leaves (located on the lower halves of shoots) and leaves with high levels of disease (>/=5 spots/leaf at the time of fruit harvest in mid-June) abscised significantly (P < 0.0001) earlier than younger leaves and leaves with lower disease severity. Relative to their respective reference groups, mean times to abscission were approximately 2 weeks shorter for the older leaf group and approximately 3 weeks shorter in the leaf group afflicted by high disease severity. When an accelerated failure time model was fitted to the data, the resulting parameter estimates indicated that each additional leaf spot present at harvest accelerated time to leaf abscission (expressed using late August as a starting point) by 1.9 and 4.5% in 2002 and 2003, respectively. Leaf location in upper or lower portions of the canopy had no significant effect on time to abscission (P > 0.05).

Dikegulac Promotes Abscission in Citrus

Two formulations of the plant growth regulator dikegulac (2,3:4,6-di-O-isopro-pylidene-α-L-xylo-2-hexulofuranosoic acid), consisting of dikegulac-sodium (Atrimmec) or dikegulac:ascorbic acid (1:1) (DAA), as well as 5-chloro-3-methyl-4-nitro-pyrazole at 200 mg·L-1, were applied as foliar sprays to `Hamlin' and `Valencia' orange trees (Citrus sinensis L. Osbeck) at two dates during the harvest season for each cultivar (11 Nov. and 10 Jan. for `Hamlin', 22 Mar. and 25 May for `Valencia'). Fruit detachment force was evaluated 10 days after application, whereas cumulative leaf abscission was monitored up to 60 days after application. In both cultivars, Atrimmec and DAA at 3,000 mg·L-1 induced moderate fruit loosening when applied at the earlier application date, but fruit loosening improved when applied at the later application date. In `Hamlin', both formulations caused higher leaf abscission when applied at the later date. DAA applications resulted in low leaf loss in `Valencia' regardless of application time, whereas Atrimmec caused unacceptably high leaf loss at either application date. No differences in internal fruit quality were found as a result of any abscission material treatment. The results indicate that DAA could be a promising option to induce fruit loosening in late harvested `Valencia' orange trees with minimal undesirable side effects.

Bemisia tabaci

<i>Bemisia tabaci</i>

THE SPECIFICITY OF EAVESDROPPING ON SAGEBRUSH BY OTHER PLANTS

Wild tobacco growing in a field near experimentally clipped sagebrush became more resistant to herbivores than tobacco plants near unclipped sagebrush. Here, we asked whether eavesdropping on sagebrush is a common phenomenon. Do three other forb species that grow near sagebrush experience less herbivory when their sagebrush neighbors are clipped experimentally? Similarly, we asked if sagebrush becomes more resistant when conspecific neighbors are clipped. We found that levels of damage to leaves of lomatium, lupine, and valerian were unaffected by experimental clipping of neighboring sagebrush. These three forbs share many generalist herbivores with sagebrush, as does wild tobacco. Sagebrush individuals near clipped neighbors experienced approximately half the leaf loss to herbivores over the summer as plants with unclipped neighbors. Most of this herbivory was caused by generalist grasshoppers and mammals. Success of a chrysomelid beetle that specializes on sagebrush was unaffected by clipping neighboring sagebrush. These results indicate that communication between sagebrush and tobacco is not a unique phenomenon since sagebrush also responded when neighbors were clipped. In contrast, other plant species generally respond less strongly to cues than does tobacco, indicating that not all species respond to relatively high levels of jasmonate in their environments. Eavesdropping may be restricted to those species, like tobacco, that are strongly inducible and to those species, like sagebrush, that release high concentrations of cues.

Chrysanthemoides monilifera ssp. rotundata invasion alters decomposition rates in coastal areas of south-eastern Australia

Weed invasion can disrupt ecological processes and the structure of ecosystems. One process potentially affected by weed invasion is leaf litter decomposition, which is important for supplying nutrients and organic matter to the soil. Leaf litter decomposition of the environmental weed Chrysanthemoides monilifera spp. rotundata was compared to that of the native coastal shrubs Acacia longifolia var. longifolia, Banksia integrifolia and Leptospermum laevigatum. This was undertaken in sand dunes heavily infested with C. monilifera and in native un-infested dunes. Coarse and fine mesh litterbags were used to determine the importance of soil microflora and litter invertebrates. C. monilifera decomposition was fitted to a double exponential decay model, whereas the native leaf decomposition was best explained by a single exponential decay model. The succulent C. monilifera leaves decomposed at a significantly higher rate than the sclerophyllous native leaf mix. Time to 99% leaf loss was estimated to be 0.9–1.3 years for C. monilifera and 3.1–4.4 years for the native species. This reflects the physical properties of the leaves and the lower leaf mass area of C. monilifera. C. monilifera leaves decayed faster in the coarse mesh bags compared to the fine, indicating leaf litter invertebrates positively influenced their decomposition. Mesh size had little affect on the native leaf decomposition rate. C. monilifera leaves generally decomposed faster within the weed infestations, partly due to invasion creating a protected environment with an altered microclimate. Replacement of native species with C. monilifera will alter nutrient cycling through changes in litter quality and decomposition rates. This may have implications for ecosystem resilience and stability.

The Design and Testing of a Cutter and Feeder Mechanism for the Mechanical Harvesting of Lentils

Although lentil is a valuable source of protein for humans and its straw is a highly valued animal feed, its production in West Asia and North Africa (WANA) is limited due to harvesting difficulties, including uneven ripening, lodging, growing of pods close to the ground, and shattering of seeds and leaves at maturity. Existing mechanical harvesting systems cause excessive seed (up to 55%) and leaf losses. Harvesting is therefore still commonly done by hand, but manual labour is becoming increasingly scarce and expensive. The objective of this study was to design and test a cutter/feeder mechanism for mechanical harvesting of lentils. A self-propelled experimental harvester, which cuts and collects shoots without threshing, was developed for this purpose. Its performance was compared to hand harvesting, in rolled and unrolled fields, using a split plot design. Lentils with 22% moisture (wet basis) were harvested, and then threshed using a stationary thresher. The experimental harvester was operated at 5 km h −1 and a cutting height of 59 mm above the ground. Shattering losses of seed and straw were not significantly different from that which occurred in hand harvesting ( F-statistic F<1). Residue losses were those left in the stubble, representing 2% of the seed and 20% of the straw, which can be partially recovered by grazing.

Using Remote Sensing to Assess Stand Loss and Defoliation in Maize

Assessing hail and wind damage to crops is a difficult, laborintensive task. A quick and accurate method of determining losses could lead to better crop management decisions, more accurate insurance claim adjustment, and reduced expenses for the crop hail insurance industry. Radiometric data were collected in 1997, 1998, and 1999 in Indiana and Nebraska from field plots of maize, Zea mays L., subjected to varying levels of damage. Incremental differences in plant damage resulted in incremental differences in spectral responses. The red and near-infrared spectral bands provided the most discrimination among levels of damage. Classification of remotely sensed images by damage level was performed by extrapolating spectral information from areas where damage levels were known to adjacent unknown areas of damage. Depending on location, sensor, and date of data collection, it was possible to classify the degree of early-season stand loss at accuracies of 48 to 100 percent. For leaf loss during the late vegetative stages, it was possible to classify the degree of leaf loss at accuracies of 81 to 100 percent and, for leaf loss during the early reproductive stages, it was possible to classify damage at accuracies of 71 to 98 percent. These results indicate that remote sensing could be used to improve the accuracy of estimating crop damage as long as adequate ground reference for different levels of crop damage exists.

Bale Density and Moisture Effects on Alfalfa Round Bale Silage

Moisture concentration and crop density during fermentation affect preservation of chopped silage, but these variables have not been adequately assessed for round bale silage. The effects of these factors on retention of crop dry matter (DM), silage quality, and nutritive value of alfalfa (Medicago sativa L.) preserved as round bale silage or as dry round‐baled hay stored outside on the ground were determined in two field trials. Voluntary intake and in vivo digestibility were also assessed in beef cattle (Bos taurus). Silage bale weights were stable during storage but hay lost an average of 18% of its initial DM during 8 mo of storage. Prestorage alfalfa silage had lower concentrations of neutral detergent fiber (NDF) and acid detergent lignin (ADL) and higher crude protein (CP) and in vitro dry matter disappearance (IVDMD) than hay, probably because of leaf losses during hay harvest. Silage from the higher‐density treatment had a pH of 4.76 compared with a higher pH of 5.01 for lower‐density bales. Density did not affect lactic acid concentration in silage, but that from the higher‐density treatment had more propionic acid at the higher moisture level. Average DM intakes of steers were 17.5, 20.4, and 21.0 g kg−1 of body weight per day for hay, 594 g kg−1 moisture silage, and 512 g kg−1 moisture silage, respectively. In vivo DM digestibility of hay was 592 g kg−1, lower than the 629 g kg−1 average for two silages. Increasing bale density improved some aspects of silage quality, including a lower pH, but moisture effects on silage preservation were small. Results of two field trials indicate that the round bale silage preservation system saved a greater proportion of alfalfa crop DM and improved nutritive value and forage intake compared with hay.

Long‐term acclimation of leaf production, development, longevity and quality following 3 yr exposure to free‐air CO2 enrichment during canopy closure in Populus

Summary • The effects of elevated CO 2 on leaf development in three genotypes of Populus were investigated during canopy closure, following exposure to elevated CO 2 over 3 yr using free-air enrichment. • Leaf quality was altered such that nitrogen concentration per unit d. wt ( N mass ) declined on average by 22 and 13% for sun and shade leaves, respectively, in elevated CO 2 . There was little evidence that this was the result of ‘dilution’ following accumulation of nonstructural carbohydrates. Most likely, this was the result of increased leaf thickness. Specific leaf area declined in elevated CO 2 on average by 29 and 5% for sun and shade leaves, respectively. • Autumnal senescence was delayed in elevated CO 2 with a 10% increase in the number of days at which 50% leaf loss occurred in elevated as compared with ambient CO 2 . • These data suggest that changes in leaf quality may be predicted following longterm acclimation of fast-growing forest trees to elevated CO 2 , and that canopy longevity may increase, with important implications for forest productivity.

Effects of roadway crossings on leaf litter processing and invertebrate assemblages in small streams.

The effects of the Maine Turnpike (Interstate 95) on leaf litter processing were examined in five first- and second-order coastal plain streams in southern Maine, U.S.A. Invertebrate assemblages and red maple leaf softening and loss rates were compared at 53 stations arrayed upstream and downstream of the turnpike. Litter softening rate was not affected by the roadway. Litter loss rate was significantly faster at downstream stations (-0.0024 degree-day(-1)) than at upstream stations or at stations nearest the roadway, which were not different from each other (-0.0022 degree-day(-1)). Litter softening and loss rates were more strongly related to physical and chemical habitat variables than to shredder assemblage characteristics. Significant among-stream differences were observed in most community structural metrics and in biomass of important shredder taxa, but effects of the roadway were rarely consistent among streams. This is attributed in part to habitat variation, which was greater among streams than within streams. This study suggests that while the presence of the Maine Turnpike may influence stream water quality and habitat structure, the relatively subtle effects of roadway runoff and associated habitat modifications on stream ecosystem processes are masked by within- and among-stream variability in litter processing and leaf pack invertebrate assemblage structure.

Foliar blight of Roselle and its effect on yield in tropical forest region of southwestern Nigeria.

The etiology of foliar blight of roselle and its effect on yield in the tropical forest of southwestern Nigeria was investigated. More than 40% of leaves of roselle plants in fields under continuous cultivation (endemic plots) were blighted by Phyllosticta hibiscini. However, no infection was found on roselle plants in fields never previously planted with roselle. Over 20% leaf yield loss and over 34% edible leaf loss were due to leaf blight. The mean marketable and biological yield loss of calyces in 1999 and 2000 were 35% and 38% respectively, while seed yield loss was 30% and 32%.

Sex, secondary compounds and asymmetry. Effects on plant–herbivore interaction in a dioecious shrub

We analysed the links between herbivory, anthraquinone content and developmental instability of leaves in Rhamnus alpinus , taking into account possible effects of sexual dimorphism. The amount of leaf loss caused by herbivores averaged 3%, rarely exceeding 25%. Leaf losses were evenly distributed in the shrubs, with highest variability among leaves of the same shoot, thus hiding possible shrub, sex or population effects. This pattern of herbivory implies a shifting of caterpillars from one leaf to another before consuming all readily available material. We suggest that this behaviour might be triggered by a short-term change in leaf palatability by means of an increase in the production of secondary compounds. Supporting this hypothesis, we have found a higher anthraquinone content in damaged leaves compared with undamaged ones. The leaves of male plants exhibited a higher concentration of anthraquinones than those of females, which contrasts with classic hypotheses. We relate this to the lower rate of biomass increase in males, which should allow them to allocate more resources to defence. Leaves showed fluctuating asymmetry (FA), but we did not find any relationship between the degree of asymmetry and sex, herbivory or anthraquinone content at any level considered. Therefore, FA cannot be considered as an indicator of susceptibility to damage by herbivores or of the ability to induce the production of defensive compounds in R. alpinus .

Leafing, flowering and fruiting of Vitellaria paradoxa subsp. nilotica in savanna parklands in Uganda

Vitellaria paradoxa leafing, flowering and fruiting patterns were monitored in Otuke county (Lira district), northern Uganda, over a period of 25 months. The monitoring revealed that leaf shedding takes place in the middle of the dry season and the trees are in full leaf by the onset of the wet season. New leaves continue to appear on the new shoots while old leaves persist during the leaf-fall period. The pattern of leafing and leaf loss, flowering and fruiting are unimodal with major peaks in flowering and fruiting, although in the study area rainfall is bimodal. Flowering was concentrated in months when the atmospheric relative humidity begins to rise from an initially low value (around November), peaks three months later and usually ends when rainy conditions persist. Flowers produced during the rainy season usually abort. Fruiting starts at the end of the dry season (December/January) and peaks from February to April. Seed matures during the rainy season (March to May) and fruit harvesting occurs mainly from May to August, when the soil is well supplied with plant available water but coinciding with high pre-growing season famine risk in the community.

Enhanced Degradation of 2,4,6-Trinitrotoluene (TNT) in a Soil Column Planted with Indian Mallow (Abutilon avicennae)

Phytoremediation of soil contaminated with 2,4,6-trinitrotoluene (TNT) was studied by growing Indian mallow (Abutilon avicennae) in a soil column reactor with 2 kg of TNT contaminated soil (120 mgTNT/kg) in the top and 18 kg of uncontaminated soil in the bottom. After 50 d, TNT remaining in the column with Indian mallow was 23.2% of the initial TNT, while 48.1% of the initial TNT remained in the column without Indian mallow. In the TNT contaminated column, the growth of Indian mallow decreased by 32.4% in roots and 34.3% in shoots on a dry weight basis, respectively, compared to the uncontaminated column. However, critical symptoms such as chlorosis and leaf loss were not observed. Of the 76.8% of the TNT that disappeared in the planted column, less than 0.2% of initial TNT was recovered in the shoot and root extracts of Indian mallow. TNT transformation products in plants include unidentified polar intermediates and aminodinitrotoluenes. The results showed that planting Indian mallow in TNT contaminated soil enhanced TNT reduction both by stimulating microbial activity that enhances microbial TNT transformation, and by direct uptake and phytotransformation of TNT.

Bale Density and Moisture Effects on Alfalfa Round Bale Silage

Moisture concentration and crop density during fermentation affect preservation of chopped silage, but these variables have not been adequately assessed for round bale silage. The effects of these factors on retention of crop dry matter (DM), silage quality, and nutritive value of alfalfa (Medicago sativa L.) preserved as round bale silage or as dry round-baled hay stored outside on the ground were determined in two field trials. Voluntary intake and in vivo digestibility were also assessed in beef cattle (Bos taurus). Silage bale weights were stable during storage but hay lost an average of 18% of its initial DM during 8 mo of storage. Prestorage alfalfa silage had lower concentrations of neutral detergent fiber (NDF) and acid detergent lignin (ADL) and higher crude protein (CP) and in vitro dry matter disappearance (IVDMD) than hay, probably because of leaf losses during hay harvest. Silage from the higher-density treatment had a pH of 4.76 compared with a higher pH of 5.01 for lower-density bales. Density did not affect lactic acid concentration in silage, but that from the higher-density treatment had more propionic acid at the higher moisture level. Average DM intakes of steers were 17.5, 20.4, and 21.0 g kg−1 of body weight per day for hay, 594 g kg−1 moisture silage, and 512 g kg−1 moisture silage, respectively. In vivo DM digestibility of hay was 592 g kg−1, lower than the 629 g kg−1 average for two silages. Increasing bale density improved some aspects of silage quality, including a lower pH, but moisture effects on silage preservation were small. Results of two field trials indicate that the round bale silage preservation system saved a greater proportion of alfalfa crop DM and improved nutritive value and forage intake compared with hay.

Ornamental Cabbage Quality Improved by Continual Fertilization through Center-head Coloration

Current fertilizer recommendations for ornamental cabbage (Brassica oleracea var. acephala DC.) suggest applying 150 to 300 mg·L-1 N until the initiation of color development, after which fertilization should be reduced or discontinued. Because these plants are actively growing during cool weather when coloration is initiated, nutrient deficiencies may reduce overall plant quality. The objectives of this study were to investigate N to K ratios for plant growth of ornamental cabbage and the effects of continual and discontinued fertilization during the period of coloration. Fertilizing with 150 to 200 mg·L-1 N and 150 to 200 mg·L-1 K produced high-quality plants and provided sufficient tissue concentrations of N and K. Center-head coloration was not inhibited by N concentrations as high as 250 mg·L-1. Ceasing fertilization prior to center-head coloration resulted in the rapid depletion of N, P, and K concentrations in the lower foliage, leading to the appearance of deficiency symptoms and lower leaf loss. Plants were still actively growing as measured by increased shoot mass during the early stages of coloration; therefore, growers should continue to provide a complete analysis fertilizer at N concentrations ≥150 mg·L-1 until market date.

How to Succeed by Doing Nothing

Clarifying the amount of pest damage that can be tolerated without justifying insecticidal control will be useful in reducing insecticide use and in development of integrated pest management (IPM) systems. This study investigated the ability of irrigated, high‐yielding cotton (Gossypium hirsutum L.) to recover from artificially applied damage simulating that of early season insect pests. Six experiments were done across five cotton‐growing seasons. Damage included defoliation, terminal damage, and flower bud removal in a range of timings, combinations, and intensities. Crop yield was unaffected by defoliation applied before first flower buds appeared, even when 100% of true leaves were removed on three occasions (Nodes 2, 4, and 6). Crop maturity was affected by sustained high levels of leaf loss with a peak delay of 10 d after 100% defoliation three times. Up to three light tip damage events or one heavy damage event had no effect on yield and only a slight effect on crop maturity (&lt;5‐d delay to harvest). Heavy early fruit loss (100% fruit removal from the first four fruiting branches) did not affect yield but caused a delay in maturity of ≈7 d. Equations describing the relationship between damage type, intensity, and repetition and the yield and maturity of cotton were developed and used in sensitivity analysis to define tentative damage thresholds for IPM systems in cotton.