Open Plots Research Articles

Animal protein as a reproductive constraint in spring reproduction of the bank vole

Survival conditions over the winter and determinants of variability in the onset of reproduction are major factors shaping the life history of most organisms in strongly seasonal environments. During the long non-breeding season availability and quality of food may be major constraints determining the onset of reproduction. We studied the effects of supplemental animal protein over winter on the onset of reproduction in the bank vole, Clethrionomys glareolus, an iteroparous seasonal breeder, granivorous-herbivorous, with small amounts of animal food in its diet. We predicted that animal protein would be especially important during spring, when energy demands are increasing due to the onset of reproduction and availability of new plant food is still limited. Field experiments were conducted in 6 open forest plots (2.25 ha each), and bank voles were fed supplemental whey protein during the winter and spring. Supplemented males were heavier at the onset of reproduction than non-supplemented males. Maturation and parturition of first litter occurred significantly earlier in females fed supplemental animal protein. No differences in litter size and litter mass were detected between treatments. We conclude that animal protein in the form of whey may play an important role in the timing of spring reproduction. Therefore, natural animal protein food sources like insects, pupae, and possibly carcasses of mammals and birds gain importance for the onset of breeding even in an granivorous-herbivorous species like the bank vole.

Visible leaf injury in young trees of Fagus sylvatica L. and Quercus robur L. in relation to ozone uptake and ozone exposure. An Open-Top Chambers experiment in South Alpine environmental conditions

An Open-Top Chambers experiment on Fagus sylvatica and Quercus robur seedlings was conducted in order to compare the performance of an exposure-based (AOT40) and a flux-based approaches in predicting the appearance of ozone visible injuries on leaves. Three different ozone treatments (charcoal-filtered; non-filtered; and open plots) and two soil moisture treatments (watered and non-watered plots) were performed. A Jarvisian stomatal conductance model was drawn up and parameterised for both species and typical South Alpine environmental conditions, thus allowing the calculation of ozone stomatal fluxes for every treatment. A critical ozone flux level for the onset of leaf visible injury in beech was clearly identified between 32.6 and 33.6 mmol O 3m −2. In contrast, it was not possible to identify an exposure critical level using the AOT40 index. Water stress delayed the onset of the leaf visible injuries, but the flux-based approach was able to take it into account accurately.

An experimental study of translocation success and habitat improvement in wild rabbits

AbstractThe translocation of wild animals is a strategy frequently used in the conservation and management of natural populations. The aim of this study was to evaluate the impact of translocation (population supplementation) and habitat improvement on the abundance of European wild rabbitOryctolagus cuniculus. We used eight open plots with different habitat treatments: two with increased shelter, two with increased food, two with increased shelter and food and two without habitat treatment (control plots). We translocated wild rabbits during 3 consecutive years, each year in four of the eight plots, with the remaining plots serving as control for the translocation treatment. Rabbit abundance (translocated plus native rabbits) was calculated by means of pellet counts, and the results were evaluated mainly by generalized linear mixed models. We found that rabbit abundance was determined primarily by habitat improvement. Rabbits were more abundant in treated than in control plots, and most abundant in the plots where food availability was increased. This effect persisted throughout the year. Translocation also increased abundance, but this effect was the strongest where shelter and food had also been improved and declined and disappeared after breeding. These findings suggest that the habitat is an important factor for rabbit abundance, with food availability being the prime factor regulating densities. Moreover, translocations on their own are only effective in the short term in situations in which factors limiting population growth (e.g. disease and predation) have not been corrected. Translocations should be carried out in conjunction with improvements in release habitat as rabbit densities will depend on the maximum carrying capacity of the habitat.

Changes in the spatial distribution of subtidal macrobenthos due to predation by white shrimp (Litopenaeus setiferus)

Manipulative caging experiments were conducted in North Inlet, South Carolina, to measure the predatory effect of juvenile penaeid white shrimp,Litopenaeus setiferus, on their subtidal macrobenthic prey. We used the natural neighbor interpolation procedure within a Geographic Information System (GIS) to map macrobenthos distributions at both the start and end of the cage deployments. Moran’s I, a commonly used index of spatial autocorrelation, provided a quantitative metric for evaluating the statistical significance of the observed changes. We tested the hypothesis that juvenile white shrimp are optimal foragers by assessing whether their predatory behavior was targeted at higher density macrobenthos patches inside the enclosures, resulting in a more homogeneous distribution of prey after seven days. Since large changes in patchiness could occur over seven days without incurring a significant change in index value, we treated each index as a continuous measure of patchiness, and examined whether the value increased or decreased consistently among treatment replicates. Using Moran’s I, the abundance and spatial distribution of macrobenthos inside control, partial, open, and shrimp inclusion treatments varied in their response. After seven days, decreased patchiness was consistently observed in the high density shrimp treatment replicates, and increased patchiness in the open plots. The GIS natural neighbor interpolation created a succinct visual representation of dramatic changes in prey spatial distribution and prey densities throughout each cage. The GIS interpolation conveyed the dynamic nature of the spatial variability that would not have been evident by calculation of Moran’s I alone. Although we could only weakly support our hypothesis, the combination of visual interpolation methods with index calculations has great potential for gaining further insights into the role of different factors as they affect changes in spatial distribution of benthic infauna.

Ozone air pollution effects on tree-ring growth, 13C, visible foliar injury and leaf gas exchange in three ozone-sensitive woody plant species

We assessed the effects of ambient tropospheric ozone on annual tree-ring growth, delta(13)C in the rings, leaf gas exchange and visible injury in three ozone-sensitive woody plant species in southern Switzerland. Seedlings of Populus nigra L., Viburnum lantana L. and Fraxinus excelsior L. were exposed to charcoal-filtered air (CF) and non-filtered air (NF) in open-top chambers, and to ambient air (AA) in open plots during the 2001 and 2002 growing seasons. Ambient ozone exposures in the region were sufficient to cause visible foliar injury, early leaf senescence and premature leaf loss in all species. Ozone had significant negative effects on net photosynthesis and stomatal conductance in all species in 2002 and in V. lantana and F. excelsior in 2001. Water-use efficiency decreased and intercellular CO(2) concentrations increased in all species in response to ozone in 2002 only. The width and delta(13)C of the 2001 and 2002 growth rings were measured for all species at the end of the 2002 growing season. Compared with CF seedlings, mean ring width in the AA and NF P. nigra seedlings was reduced by 52 and 46%, respectively, in 2002, whereas in V. lantana and F. excelsior, ring width showed no significant reductions in either year. Although delta(13)C was usually more negative in CF seedlings than in AA and NF seedlings, with the exception of F. excelsior in 2001, ozone effects on delta(13)C were significant only for V. lantana and P. nigra in 2001. Among species, P. nigra exhibited the greatest response to ozone for the measured parameters as well as the most severe foliar injury and was the only species to show a significant reduction in ring width in response to ozone exposure, despite significant negative ozone effects on leaf gas exchange and the development of visible foliar injury in V. lantana and F. excelsior. Thus, significant ozone-induced effects at the leaf level did not correspond to reduced tree-ring growth or increased delta(13)C in all species, indicating that the timing of ozone exposure and severity of leaf-level responses may be important in determining the sensitivity of tree productivity to ozone exposure.

DIRECT AND INDIRECT EFFECTS OF ANTS ON A FOREST-FLOOR FOOD WEB

Interactions among predators that prey on each other and are potential competitors for shared prey (intraguild [IG] predators) are widespread in terrestrial ecosystems and have the potential to strongly influence the dynamics of terrestrial food webs. Ants and spiders are abundant and ubiquitous terrestrial IG predators, yet the strength and consequences of interactions between them are largely unknown. In the leaf-litter food web of a deciduous forest in Kentucky (USA), we tested the direct and indirect effects of ants on spiders and a category of shared prey (Collembola) by experimentally subsidizing ants in open plots in two field experiments. In the first experiment, ant activity was increased, and the density of ants in the litter was doubled, by placing carbohydrate and protein baits in the center of each plot. Gnaphosa spiders were almost twice as abundant and Schizocosa spiders were half as abundant in baited plots relative to controls. There were more tomocerid Collembola in baited plots, suggesting possible indirect effects on Collembola caused by ant-spider interactions. The second experiment, in which screening of two mesh sizes selectively excluded large and small worker ants from a sugar bait, revealed that the large ants, primarily Camponotus, could alone induce similar effects on spiders. Gnaphosa biomass density was almost twice as high in the plots where large ants were more active, whereas Schizocosa biomass density was reduced by half in these plots. Although tomocerid densities did not differ between treatments, tomocerid numbers were negatively correlated with the activity of Formica, another large ant species. Path analysis failed to support the hypothesis that the ant Camponotus indirectly affected tomocerid Collembola through effects on densities of spiders. However, path analysis also revealed other indirect effects of Camponotus affecting tomocerids. These results illustrate the complexity of interactions between and within two major IG predator groups with disparate predatory behaviors, complexities that will have consequences for functioning of the forest-floor food web.

Chemical composition and net energy content of alpine pasture species during the grazing season

The aim of this study was to investigate changes over time in chemical composition, digestibility and net energy for lactation (NEl) contents of 12 species of alpine pastures during the vegetative season ( i.e., Agrostis tenuis, Anthoxanthum alpinum, Carex sempervirens, Festuca rubra, Nardus stricta, Phleum alpinum, Poa alpina, Poa violacea, Alchemilla vulgaris, Leontodon hispidus, Potentilla aurea, Trifolium repens). Wild seeds were collected from plants spontaneously occurring in mountain pastures in North-East Italy and sown in a greenhouse. Plants were transplanted in open main field plots. Each main plot was divided into sub-plots, which were cut (first cut) in succession every 10 days in two consecutive years. Herbage regrowth (second cut) was evaluated at 45, 60 and 75 days after first cut. Herbage samples were analysed for chemical composition, for in vitro organic matter digestibility (OMD), and the NEl content was estimated. During the pasture utilisation period ( i.e., thermic sum between 500 and 1200 °C) the species had limited variation in their average CP contents (81–109 g/kg DM) excluding the lowest values of F. rubra and P. violacea (74 and 71 g/kg DM, respectively; P<0.05) and the highest value of T. repens (202 g/kg DM; P<0.05). Within grasses, there were very fibrous species (>700 g NDF/kg DM, such as F. rubra, N. stricta and P. violacea) and species with medium contents (573–664 g NDF/kg DM), while forbs and the legume specie had a low content (≤403 g NDF/kg DM). The OMD ranged from P. violacea (256 g/kg DM; P<0.05) to T. repens (730 g/kg DM; P<0.05). The highest NEl content was for T. repens (6.3 MJ/kg DM; P<0.05), while low NEl values were calculated for N. stricta and C. sempervirens (2.9 and 2.5 MJ/kg DM, respectively). The lowest (P<0.05) NEl content was estimated for P. violacea (1.9 MJ/kg DM). Most species investigated (in particular, Agrostis tenuis, F. rubra, L. hispidus, Potentilla aurea), had an initial intense decrease in the CP content with advancing season, reaching minimum levels at the thermic sum of 800–1000 °C. During season advancement, all species had increased NDF content, with marked increments for F. rubra and Poa species, and all species had decreased NEl contents. Regrowth samples collected at 75 days after first cut had lower CP and NEl contents relative to those collected after 45 days from the first cut (140 g/kg versus 160 g/kg DM and 4.4 MJ/kg versus 4.8 MJ/kg DM, respectively; P<0.05). This study provides nutritional information on individual herbage species of alpine pastures at different vegetative phases which can be used to obtain average nutritional values of use in pasture management work.

Herbivory effects on the morphology of the brown alga Padina boergesenii (Phaeophyta)

G. Diaz-Pulido, L. Villamil, and V. Almanza. 2007. Herbivory effects on the morphology of the brown alga Padina boergesenii (Phaeophyta). Phycologia 46: 131–136. DOI: 10.2216/05-60.1Many coral reef benthic algae exhibit morphological plasticity enabling them to persist in diverse habitats under different environmental pressures. Morphological plasticity has been previously observed in the brown alga Padina jamaicensis, which displays a foliose morphology under low grazing pressure and a turf morphology in habitats with medium to high herbivory levels. To determine whether a different species of Padina, P. boergesenii, exhibits morphological plasticity regulated by herbivory, we excluded macroherbivores from experimental plots containing P. boergesenii thalli on a rocky reef off Santa Marta in the Colombian Caribbean. The experiment used exclusion cages to test for effects of herbivores and was carried out in two contrasting oceanographic seasons: upwelling (low water temperature and high water transparency) and rainy (higher temperature and low water transparency). The morphology of P. boergesenii was significantly affected by herbivory but only during the upwelling season. Padina boergesenii rapidly changed from a turf morphology to a fan-shaped form and increased in size when protected from herbivores in full cages in a period of less than a week. Thalli exposed to macroherbivores in open plots did not shift to a foliose morphology, and neither did thalli investigated during the rainy season, independent of herbivore treatment. Our results show that herbivory plays an important role in controlling the morphology and may affect life history processes of the alga P. boergesenii but suggest that plant response to herbivory may be a seasonal process. This suggests that there are important climatic (e.g. trade winds inducing upwelling) and oceanographic factors (e.g. water temperature) limiting algal abundance and that these factors may mediate morphological plasticity of algae. Therefore, reductions of grazing are not enough to promote morphological plasticity during the rainy season.

Pigment apparatus in Ajuga reptans plants as affected by adaptation to light growth conditions

Mechanisms of adaptation of the photosynthetic apparatus at the level of pigment complex in a shade-tolerant bugle plant (Ajuga reptans L.) grown at full solar irradiation in an open plot were studied. In “sun” plants, the content of photosynthetic pigments decreased markedly as compared to “shade” plants grown under a forest canopy at 5–10% of the full solar irradiation. In leaves of sun plants, the portion of β-carotene and lutein in the carotenoid spectrum was higher than in shade plant leaves, antheraxanthin and zeaxanthin were present, and de-epoxidation of violaxanthin was by an order of magnitude higher in sun plant leaves reaching 40%. The data obtained indicate the role of the violaxanthin cycle in the protection of photosynthetic apparatus in a shade-tolerant plant against destruction under excessive irradiation.

Field electroantennogram and trap assessments of aerosol pheromone dispensers for disrupting mating in Epiphyas postvittana

An electronically controlled aerosol system for mating disruption was evaluated against Epiphyas postvittana Walker in apple orchards in New Zealand. The area in which male moths were affected by the aerosol system was examined using catches in traps radiating from a central single-point source of either one aerosol can dispenser or 100 polyethylene tubing dispensers, compared with catches in orchard plots without pheromone dispensers. Both pheromone dispensing systems decreased moth catch to similar levels at 5-10 m from the central release point, but there was 5.5-fold more pheromone released from aerosol cans than from polyethylene dispensers over a 24 h period. Trap catches were reduced by about 90% in plots treated with either five aerosol cans per hectare or uniform deployment of polyethylene dispensers. Recordings of electroantennograms in open grassed plots and orchards indicated that the treated cotton pad of an aerosol dispenser and a point source of 100 polyethylene tubing dispensers produced similar electroantennogram recordings. Electroantennogram recordings provided evidence that pheromone plume detection from a single-point source was maintained over a range of 5-40 m downwind in the orchard. On present evidence, aerosol pheromone dispensers could not be recommended for further testing towards control of E. postvittana under New Zealand conditions owing to their higher cost of purchase and operation.

Impacts of endangered Key deer hervivory on imperiled pine rocklands: a conservation dilemma?

In the lower Florida Keys, endangered Key deer (Odocoileus virginianus clavium) herbivory, along with fire, can affect pine rocklands, an endangered plant community. We compared pineland vegetation from three studies over approximately 50 years on four islands with either high or low deer density (historical analysis). We also compared extant vegetation samples between two islands with high or low deer density, which contained pinelands burned 10 years and 14 years prior to sampling and control areas (unburned for &gt; 50yr). In addition, experimental deer exclosures and control plots established in pineland were prescribe burned and analyzed for deer effects on an island with high density of Key deer. The historical analysis suggests that, over time, deer-preferred plant species declined while less-preferred species increased, regardless of fire history on islands. The extant vegetation analysis suggests that fire and Key deer herbivory both reduce hardwood plant density and growth. Densities of deer-preferred woody species were higher on an island with low deer density than on an island with high deer density in burn treatments, but relatively similar in control areas. On the high deer density island, a fire effect was evident in that the control area had higher densities of woody species than burned areas, and herbaceous species richness was higher in the control area, indicating a possible refuge from deer herbivory. In deer exclosures, preferred woody species and herbaceous species tended to increase after fire, but decrease in adjacent open plots. Results suggest that Key deer herbivory, along with fire, shapes pine rockland plant communities, and that overbrowsing might have substantial impacts on preferred herbaceous and woody species in pinelands. Therefore, efforts could be confounded in managing both the endangered Key deer and the endangered pine rocklands that they affect.

Impact of changes in rainfall amounts predicted by climate-change models on decomposition in a deciduous forest

Climate-change models predict a more intense hydrological cycle, with both increased and decreased amounts of rainfall in areas covered with temperate deciduous forests. These changes could alter rates of litter decomposition, with consequences for rates of nutrient cycling in the forest ecosystem. To examine impacts of predicted changes in precipitation on the rate of decay of canopy leaves, we placed litterbags in replicated, fenced 14 m 2 low-rainfall and high-rainfall plots located under individual rainout shelters. Unfenced, open plots served as an ambient treatment. Litter in the high-rainfall and ambient plots decayed 50% and 78% faster, respectively, than litter in the low-rainfall plots. Litter in the ambient plots disappeared 20% faster than in the high-rainfall treatment, perhaps via greater leaching during heavy rainfall events. Ambient rainfall during the experiment was similar in total amount to the high-rainfall treatment, but was more variable in intensity and timing. We used litterbags of different mesh sizes to examine whether changes in rainfall might alter the impacts of major categories of the fauna on litter decay. However, we found no consistent evidence that excluding arthropods of different sizes affected litter decay rate within any of the three rainfall treatments. This research reveals that changes in rainfall predicted to occur with global climate change will likely strongly alter rates of litter decay in deciduous forests.

Influence of hydrologic pulses, flooding frequency, and vegetation on nitrous oxide emissions from created riparian marshes

The effects of hydrologic conditions, water quality gradients, and vegetation on nitrous oxide gaseous emissions were investigated in two identical 1-ha surface-flow created riverine wetlands in Columbus, Ohio, USA. For two years, both wetlands experienced seasonal (winter-spring) controlled hydrologic flood pulses followed by one year in which they received a steady flow rate of water. Nitrous oxide fluxes were quantified in a transverse gradient at different elevations (edge plots and high marsh plots with alternate wet and dry conditions, and low marsh plots and open water plots that were permanently flooded). The highest average of N2O fluxes was observed in high marsh plots (21.8 ± 2.5 μg-N m−2 h−1), followed by edge plots (12.6 ± 2.5 μg-N m−2 h−1), open water plots (9.9 ± 2.1 μg-N m−2 h−1), and low marsh plots (7.0 ± 4.8 μg-N m−2 h−1). Highest nitrous oxide fluxes were consistently observed in high marsh plots during summer when soil temperatures were ≥ 20°C. In permanently flooded plots without vegetation, nitrous oxide fluxes were low, regardless of flood-pulse conditions. In high marsh plots, water table remained near the soil surface one week after flooding, causing an increase in N2O fluxes (25.9 ± 13.9 μg-N m−2 h−1) compared with fluxes before (2.4 ± 6.4 2.2 μg-N m−2 h−1) and during (6.9 ± 2.2 μg-N m−2 h−1) flooding. In edge plots, nitrous oxide emissions increased during and after the flooding (11.3 ± 3.2 and 7.3 ± 3.3 μg-N m−2 h−1) compared with fluxes before the flood pulse (4.1 ±1.8 μg-N m−2 h−1). In low marsh and edge zones, no significant (P> 0.05) differences were observed in the seasonal N2O fluxes in the pulsing year versus steady-flow year. Spring N2O fluxes from high marsh plots were significantly (P=0.04) higher under steady-flow conditions (26.2 ± 5.5 μg-N m−2 h−1) than under pulsing conditions (9.6 ± 3.6 μg-N m−2 h−1), probably due to the water table near the surface that prevailed in those plots under steady flow condition. N2O fluxes were higher in plots with vegetation (39.6 ± 13.7 μg-N m−2 h−1) than in plots without vegetation (−3.6 ± 13.7 μg-N m−2 h−1) when plots were inundated; however, when no surface water was present, N2O fluxes were similar in plots with and without vegetation. Implications for large-scale wetland creation and restoration in the Mississippi River Basin and elsewhere for controlling nitrogen are discussed.

RAPD markers utilization and other parameters in the determination of mango hybrids genitors

Actually mango (Mangifera indica, L.) is considered one of the largest Brazilian fruitbusiness for the export market. Cultivar selection having high fruit quality is a fundamental step to obtain excellent results in this business. A mango breeding program based on intervarietal hybridization may produce new improved cultivars for mango growers. Mango hybrids have been obtained by controlled or open crosses. In the last one, it is important to identify the male parent because it is useful for the genetic cultivar history, thus it is important for planning further improvements. This work presents a parentage test using among others parameters RAPD (Random amplified Polymorphic DNA) markers to estimate the male parent of the selected hybrids in an open cross plot by using five mango cultivars densely planted in a latin square design.

(144) Landscape Growth and Aesthetic Quality of Coleus Managed with Irrigation Deficits

Previous research indicated that bedding plants can be maintained in landscape soils allowed to dry to substantially less than field capacity before irrigation; however, canopy size and aesthetic quality were compromised. Continuing this research, Solenostemon scutellarioides (coleus) were grown in drainage lysimeters in an open-sided clear polyethylene-covered shelter to assess growth characteristics and landscape quality when irrigated at various managed allowable deficits. Using tensiometers, plants were irrigated back to field capacity when 30%, 40%, or 50% of plant available water within a soil was depleted. Deficits were evaluated against a control treatment of 1.25 cm daily irrigation. Additional plants were grown in a companion open field plot. Growth indices, biomass, irrigation volumes, and landscape quality ratings were recorded. No differences in final height, growth index, shoot or root dry weights, total biomass, or shoot-to-root ratios were found among treatments for either lysimeter or companion field plots. Landscape quality was comparable among treatments. However, total irrigation volume applied was significantly greater for the control treatments than deficit irrigation treatments. On average, irrigation volumes were 4.75-fold greater for daily irrigation in comparison to other treatments.

Fertilizer Source and High Tunnel Production Environment Affect Antioxidant Levels of Pac Choi

An experiment was conducted at Olathe, Kan., in Spring 2004 to investigate the influence of organic and conventional fertilizer sources and application rates on antioxidant levels of pac choi (Brassica rapa L. cv. Mei Qing) in open fields and poly-covered high-tunnel plots. Organic plots received pre-plant application of composted cattle manure and alfalfa (Hu-More 1–1–1) at 0 kg/ha N, 156 kg/ha N, or 314 kg/ha N, and conventional plots received preplant application of 13N–13P–13K at 0 kg/ha N, 78 kg/ha N, or 156 kg/ha N. Antioxidant levels were measured using the oxygen radical absorbance capacity (ORAC) assay. There were significant effects of fertilizer source and high-tunnel environment on the antioxidant capacity of pac choi. Organic fertilization significantly increased hydrophilic ORAC of pac choi in open field plots, but not in high tunnels. Regardless of the fertilizer source, pac choi grown in the open field had significantly higher hydrophilic ORAC than that grown in tunnels. Lipophilic ORAC was significantly increased by organic fertilization but was not affected by high-tunnel production. Total ORAC (hydrophilic + lipophilic) was significantly higher in pac choi from organic or open-field plots, compared to conventional and high-tunnel plots, respectively. Although fertilizer rate did not show significant impact on antioxidant level of pac choi, hydrophilic and total ORAC seemed to decrease as the fertilizer rate increased, especially under conventional fertilization, while lipophilic ORAC reached the highest level at the medium fertilizer rate. Differences in antioxidant levels were likely associated with the enhanced phytochemical content of pac choi from organically fertilized and open-field plots.

Herbicide Drift Study on White Oak Seedlings

In 2004 and 2005, potted white oak seedlings 0.6 m in height were treated with six herbicide treatments at three concentrations, 1/4, 1/10, and 1/100× of the standard field use rate. These herbicides and their standard field use rate of active ingredient (a.i.) included 2,4-D at 1.5 kg/ha, 2,4-D + glyphosate at 0.8 kg/ha + 1 kg/ha, acetochlor + atrazine at 3.5 kg/ha, dicamba at 0.7 kg/ha, glyphosate at 1.1 kg/ha and metolachlor at 2.0 kg/ha. The seedlings were treated at three growth stages: swollen buds, leaves unfolding, and expanded leaves. A compressed air spraying chamber delivering 187 L/ha was used to apply the herbicides. After treatment, the containers were placed in an open field plot in a completely randomized design. Oak seedlings were most susceptible to herbicide injury at all concentrations, at the leaves unfolding stage. Symptoms on seedlings treated with 2,4-D and dicamba at the leaves unfolding stage included leaf cupping and rolling, leaf curling, leaf rolling downward from leaf margin, and unusual elongation at leaf tip. Glyphosate + 2,4-D applications resulted in leaf cupping, yellowing, leaf rolling downward from leaf margin and abnormal leaf tips. Glyphosate symptoms ranged from leaf yellowing and browning, to slight browning of interveinal leaf tissues. Acetochlor + atrazine, or metolachlor alone caused the abnormality referred to as “leaf tatters” where in severe cases, only the main veins are present with limited amounts of interveinal tissues. Detailed description of the injury symptoms, supplemented with photographs are posted on a web site: http://www.nres.uiuc.edu/research/herbicide_research/index.htm

Host-Plant-Mediated Competition Via Induced Resistance: Interactions Between Pest Herbivores On Potatoes

Plant-mediated competition among insect herbivores occurs when one species induces changes in plant chemistry, nutrition, or morphology that render plants resistant to attack by others. We explored plant-mediated interspecific interactions between the potato leafhopper (Empoasca fabae) and the Colorado potato beetle (Leptinotarsa decemlineata), two important pests on potatoes. Leafhoppers colonize fields in advance of beetles, and thus the possibility exists that previous feeding by leafhoppers induces changes in potato plants that have adverse consequences for beetles. The consequences of leafhopper-induced resistance for beetle performance were studied in the greenhouse, field cages, and in large open-field plots. Potato plants were exposed to four densities of leafhoppers (none, low, moderate, and high), and visible feeding symptoms were measured as percentage leaf curling, chlorosis, and necrosis. The oviposition preference, performance, and survivorship of Colorado potato beetles were then measured on the four categories of induced plants in field-cage and greenhouse settings. In open field plots, survival on the four categories of induced plants was determined by placing cohorts of beetle adults onto plants and measuring the densities of resulting eggs, larvae, and emerging Fl adults. Leafhopper-induced symptoms on potato plants were density dependent, with the percentage of curled, chlorotic, and necrotic leaves increasing with leafhopper density. Previous feeding by leafhoppers adversely affected oviposition and larval performance of beetles. Fewer egg masses were deposited on plants that incurred high levels of leafhopper feeding. Similarly, larval development was delayed and emerging adult beetles weighed less when fed induced foliage from the high leafhopper-density treatment. Beetles survived less well in the field on plants experiencing moderate and high levels of leafhopper feeding as evidenced by lower densities of eggs, larvae, and emerging F1 adults. Overall, leafhoppers and beetles competed through feeding-induced changes in plant quality. Notably, the asymmetric interaction took place at a large spatial scale in open field plots and had negative consequences that persisted to the next beetle generation. Ultimately, to establish an effective management strategy for crop pests such as leafhoppers, it is essential to consider the positive indirect effects of induced resistance along with the negative direct effects on crop yield.

Response of vegetation and net ecosystem carbon dioxide exchange at different peatland microforms following water table drawdown

Northern peatlands are significant stocks of terrestrial soil carbon, and it has been predicted that warmer temperatures and lower water tables resulting from climate change will convert these ecosystems into sources for atmospheric carbon dioxide (CO2). However, these predictions do not consider the potential for hydrologically induced ecological succession or the spatial variability of carbon accumulation rates between different microforms in peatlands. To address these issues, the vegetation community was described, and the rates of gross ecosystem photosynthesis (GEP), ecosystem respiration (Rtot) and net ecosystem CO2 exchange were determined along poor fen microtopographic gradients at a control site and at a site which experienced a water table drawdown of ∼20 cm 8 years prior to the study (drained). Sampling plots within these sites were classified as microforms of hummocks, lawns, or hollows. The coverage of Sphagnum moss declined on drained hummocks, drained lawns were invaded by sedges, and hollows shifted from open water plots at the control site to Sphagnum‐dominated plots with sparse vascular plant cover at the drained site. As a result, Rtot was significantly greater at the drained site at all microforms while maximum rates of GEP declined at drained hummocks and were enhanced at drained lawns and hollows compared to similar control microforms. These results suggest that predictions about the response of northern peatland carbon exchange to climate change must consider the interaction between ecology and hydrology and the differential responses of microforms related to their initial ecohydrological conditions.

Forest encroachment into a Californian grassland: examining the simultaneous effects of facilitation and competition on tree seedling recruitment

Competition and facilitation are both considered major factors affecting the structure of plant assemblages, yet few studies have quantified positive, negative, and net effects simultaneously. In this study, we investigated the positive, negative, and net effects of tree saplings on the encroachment of two tree species, Douglas fir (Pseudotsuga menziesii) and tanoak (Lithocarpus densiflora), into a coastal California grassland. The study involved three components: sampling the spatial distributions of P. menziesii and L. densiflora in the grasslands, a field experiment examining seedling survival in different grassland environments, and a greenhouse experiment examining the effects of soil moisture on early seedling performance. The field experiment was conducted over a 2-year period, using Pseudotsuga in 2002 and both species in 2003. Seedlings were separated into four treatment groups: those planted in open grassland, in shaded grassland, under artificial (plastic) conifer saplings, and under natural Pseudotsuga saplings. Air temperature, relative humidity, soil moisture, incident radiation levels and fog water inputs were measured for each treatment group in 2003. In the greenhouse experiment, Pseudotsuga and Lithocarpus seedlings were grown for 13 weeks in watering treatments simulating the summer soil moisture conditions of the open grasslands and under Pseudotsuga saplings. Surveys of naturally established seedlings found that Lithocarpus occurred only under Pseudotsuga saplings, while most Pseudotsuga seedlings were located near but not directly under conspecific saplings. In the field experiment, positive effects of tree saplings were much larger than negative effects, resulting in strong net facilitation of seedling establishment. Survival for both species was always higher under the plastic and live trees than in the open or shade plots. The primary mechanism facilitating seedling survival appeared to be increased soil moisture caused by input of fog precipitation coupled with reduced microsite evaporation. The greenhouse experiment further showed that soil moisture strongly affected seedling performance, with both species having much higher photosynthetic rates in the higher moisture treatment. In the lower moisture treatment, Pseudotsuga seedlings had higher photosynthetic rates and stomatal conductance than Lithocarpus, suggesting they may be able to better tolerate the environmental conditions found in the open grasslands. Our combined results suggest that rate and patterning of woody plant encroachment can be strongly influenced by facilitation and that fog precipitation may play a key role in plant interactions.