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At least 127 records · Page 7Linked to original sources
PubMed1998

Increasing plant productivity in closed environments with inner canopy illumination.

Due to the high cost of habitable real estate associated with space travel and colonization, and the ultimate use of plants as the primary method of life support, it is necessary to develop cultivation methods whereby the highest sustainable level of productivity is achieved within the least amount of space. It is well known that in a dense plant canopy, lower leaves become shaded from above and eventually no longer contribute to carbon gain. In fact, they contribute to net respiratory carbon losses. One method of improving biomass production is to introduce light of suitable quantity and quality to the inner canopy, thereby utilizing unused photosynthetic capacity. By coupling microwave-powered lights to 100-mm-diameter glass tubes lined with 3M Optical Lighting Film, light with a spectral quality similar to that of sunlight was delivered to the inner canopy of a developing soybean crop. Results indicated that increases in productivity of 23-87%, as measured by CO2 assimilation, can be achieved in dense plant canopies (LAI approximately 6) when overhead lighting (40O-1200 micromoles m-2 s-1) is supplemented with inner canopy illumination.

Biomass↗
PubMed2004

Prevalence of West Nile virus in tree canopy-inhabiting Culex pipiens and associated mosquitoes.

Culex pipiens was the dominant mosquito captured in a West Nile virus (WNV) focus in Stratford, Connecticut. More Cx. pipiens were captured in Centers for Disease Control miniature light traps baited with CO(2), quail/hamster traps, and mosquito magnet experimental (MMX) traps placed in the tree canopy than in similar traps placed near the ground. Significantly more Cx. pipiens were captured in MMX traps placed in the canopy than in the other traps tested. Ninety-two percent and 85% of the 206 and 68 WNV isolations were from Cx. pipiens in 2002 and 2003, respectively; 5% and 12% were from Cx. salinarius. Eighty-five percent and 87% of the isolates were from mosquitoes captured in the canopy in each of the two years. The significantly larger numbers of WNV isolates from Cx. pipiens captured in the canopy are attributed to the significantly larger numbers of Cx. pipiens captured in the canopy in comparison to those captured in traps near the ground.

Animals↗
PubMed2004

Species composition of leaf beetle assemblages in the canopies of apple and pear orchards in Hungary and Great Britain (Coleoptera: Chrysomelidae).

The species richness and species composition of Coleoptera assemblages were investigated in the canopies of apple and pear orchards in Hungary and in the apple orchards in Great Britain. The investigations were carried out in Hungary (Nagykovácsi: 3 plots, Kecskemét: 5 plots, Sárospatak: 4 plots) between 1990-94, and in Great Britain in Kent (East Malling, Marden and Robertsbridge) in 2001 and 2002. Former investigations in Hungary revealed that the diversity of Coleoptera assemblages in the canopy of apple and pear orchard were surprisingly high. As a result of our investigations it was found that altogether 324 species, almost 3% of the Hungarian beetle fauna were represented: 253 species in apple orchards and 188 species in pear orchards. Similar results were obtained in the investigations carried out in Great Britain between 2001-2002. In Hungary, the majority of the species belonged to the families Curculionidae, Chrysomelidae and Coccinelidae. The proportion of leaf beetles varied between 15 and 20%. The most common leaf beetle species in the canopy of the commercial orchards were Phyllotreta vittula, Phyllotreta atra, Phyllotreta nigripes, Oulemta melanopus, and Aphthona euphorbiae. In the abandoned orchards the most common species were Luperus xanthopoda, Smaragdina salicina and Orsodacne liieola. In Great Britain 44 leaf beetle species were found in the canopies of the investigated orchards. The species with higher abundance were Aphthona euphorbiae. Chaetocnema concinna and Longitarsus parvulus. We concluded, that leaf beetles give high part of the orchard canopy biodiversity and sometimes occur with high species richness and abundance. However, the reasons of their occurrence and their potential role are poorly known.

Animals↗
PubMed2005

[Estimation models for vegetation water content at both leaf and canopy levels].

Based on spectral indices method, this paper utilized the water content (Cw) and reflectance data of 67 fresh different type leaves from LOPEX' 93 database to establish the statistical model between leaf Cw and spectral indices at leaf level through 47 samples, and to test the model with the other 20 samples. The results suggested that fuel moisture content (FMC) and equivalent water thickness (EWT) as Cw demonstrators were different in reflectance spectral curves. The difference between FMC and EWT was large when they were utilized to retrieve the leaf Cw. The correlation coefficient between EWT and each spectral index was higher than FMC, but the forecast precision of FMC was better than that of EWT. The 7 spectral indices could all retrieve the leaf FMC accurately, but only the Ratio975, II and SR were suitable to estimate the leaf EWT. Spectral indices linear model on the strength of optimal subset regressions had the highest precision to retrieve the leaf Cw. Ratio975 might be the universal spectral index to estimate the leaf Cw. At canopy level, the simulated canopy spectra under different leaf area index (LAI) and Cw were derived from the PROSPECT and SAILH coupling models. In order to eliminate background influence and to precisely retrieve the Cw, soil-adjusted water index (SAWI) was proposed at the first time to indicate the information of near-infrared and short-wave infrared canopy reflectance. The ratio of SAWI and other spectral indices could dramatically eliminate the soil background, and effectively retrieve the vegetation Cw at canopy level. Spectral index (Ratio975 - 0.96)/(SAWI + 0.2) as improved Ratio975 could be used to compute the canopy Cw more precisely when LAI was ranging from 0.3 to 8.0 and Cw from 0.0001 to 0. 07cm.

Ecosystem↗
PubMedDate not supplied

[Yeast diversity in Bulnesia retama and Larrea divaricata canopies and associated soils].

Bush like vegetation dominates arid environments, and there is nutrients accumulation under shrub canopies and relatively unfertile soils between vegetal patches areas. Plants are one of the most common habitats for yeasts. There are many reports about yeasts inhabiting different plant components. Nevertheless, there are no reports about yeasts associated with Zygophyllaceae, an important shrub family of the Argentinean Province of Monte. The objective of this work was to analyzed yeast biodiversity of Bulnesia retama and Larrea divaricata canopies and associated soils, at Medanos Grandes of Caucete, San Juan, Argentina. Eighty seven (87) isolated yeasts were identified. From B. retama canopy and associated soil was observed a larger taxonomical diversity respect to L. divaricata. Nine (9) and ten (10) species were isolated from canopy and associated soil of B. retama, respectively. From L. divaricata canopy were 4 species and 3 species from its associated soil isolated. Identified genera were: Candida, Debaryomyces, Dekkera, Saccharomyces, Torulaspora, Sporidiobolus and Pichia. Fourteen (14) species were found at all microenvironments.

Argentina↗
PubMed2004

The effect of different spray liquids on the foliar retention of agricultural sprays by wheat plants in a canopy.

The aim of this work was to examine the effect of liquid properties on spray retention in a range of situations representative of practical pesticide application. Liquids with different physical properties were sprayed with conventional flat-fan and air-induction nozzles onto outdoor-grown wheat plants (Triticum aestivum L cv Axona) at growth stages between GS 22 and GS 35. Since total retention is affected by leaf surface as well as plant growth stage and canopy density, the experiments included spraying both single leaves and groups of plants with different canopy densities. Retention on whole plants was strongly influenced by plant growth and canopy properties. Individual leaf surfaces were not as water-repellent as was found previously for younger indoor-grown plants, reducing the effect of dynamic surface tension on retention. This, combined with the increased probability of droplets hitting foliage in a denser canopy, gave reduced differences in retention between liquids when compared with similar measurements made previously on younger plants. With a leaf area index greater than 7, retention on whole plants was almost independent of liquid. Air-induction nozzles gave lower levels of retention than flat-fan nozzles, with this difference greatest when spraying high dynamic surface tension liquids and at low crop densities.

Agriculture↗
PubMed2002

Free-air fumigation of mature trees. A novel system for controlled ozone enrichment in grown-up beech and spruce canopies.

A novel system for continuous and controlled free-air fumigation of mature tree canopies with ozone is described. Ozone generated from oxygen is diluted with air in a pressurized tank and conducted into the canopies by a system of 100 PTFE tubes hanging down from a grid fixed above the crowns. With 45 calibrated outlets per tube providing a constant flow of 0.3 l/min each, a total volume of about 10*10*15 m3 comprising 5 beech and 5 spruce canopies is fumigated. The spatial ozone distribution in the fumigated volume as well as surrounding reference tree canopies is controlled by continuous measuring instruments installed at 4 levels and a dense array of passive samplers. The system will later be used for CO2 fumigation as well. Results of the first year of continuous operation, with 2 * ambient ozone levels having been achieved, are reported.

Forestry↗
PubMed2005

Microgravity effects on thylakoid, single leaf, and whole canopy photosynthesis of dwarf wheat.

The concept of using higher plants to maintain a sustainable life support system for humans during long-duration space missions is dependent upon photosynthesis. The effects of extended exposure to microgravity on the development and functioning of photosynthesis at the leaf and stand levels were examined onboard the International Space Station (ISS). The PESTO (Photosynthesis Experiment Systems Testing and Operations) experiment was the first long-term replicated test to obtain direct measurements of canopy photosynthesis from space under well-controlled conditions. The PESTO experiment consisted of a series of 21-24 day growth cycles of Triticum aestivum L. cv. USU Apogee onboard ISS. Single leaf measurements showed no differences in photosynthetic activity at the moderate (up to 600 micromol m(-2) s(-1)) light levels, but reductions in whole chain electron transport, PSII, and PSI activities were measured under saturating light (>2,000 micromol m(-2) s(-1)) and CO(2) (4000 micromol mol(-1)) conditions in the microgravity-grown plants. Canopy level photosynthetic rates of plants developing in microgravity at approximately 280 micromol m(-2) s(-1) were not different from ground controls. The wheat canopy had apparently adapted to the microgravity environment since the CO(2) compensation (121 vs. 118 micromol mol(-1)) and PPF compensation (85 vs. 81 micromol m(-2) s(-1)) of the flight and ground treatments were similar. The reduction in whole chain electron transport (13%), PSII (13%), and PSI (16%) activities observed under saturating light conditions suggests that microgravity-induced responses at the canopy level may occur at higher PPF intensity.

Carbon Dioxide↗
PubMed2004

Coordinated changes in photosynthesis, water relations and leaf nutritional traits of canopy trees along a precipitation gradient in lowland tropical forest.

We investigated leaf physiological traits of dominant canopy trees in four lowland Panamanian forests with contrasting mean annual precipitation (1,800, 2,300, 3,100 and 3,500 mm). There was near complete turn-over of dominant canopy tree species among sites, resulting in greater dominance of evergreen species with long-lived leaves as precipitation increased. Mean structural and physiological traits changed along this gradient as predicted by cost-benefit theories of leaf life span. Nitrogen content per unit mass (Nmass) and light- and CO2-saturated photosynthetic rates per unit mass (Pmass) of upper canopy leaves decreased with annual precipitation, and these changes were partially explained by increasing leaf thickness and decreasing specific leaf area (SLA). Comparison of 1,800 mm and 3,100 mm sites, where canopy access was available through the use of construction cranes, revealed an association among extended leaf longevity, greater structural defense, higher midday leaf water potential, and lower Pmass, Nmass, and SLA at wetter sites. Shorter leaf life spans and more enriched foliar delta15N values in drier sites suggest greater resorption and re-metabolism of leaf N in drier forest. Greater dominance of short-lived leaves with relatively high Pmass in drier sites reflects a strategy to maximize photosynthesis when water is available and to minimize water loss and respiration costs during rainless periods. Overall, our study links coordinated change in leaf functional traits that affect productivity and nutrient cycling to seasonality in lowland tropical forests.

Analysis of Variance↗
PubMed2005

Regional variation in canopy transpiration of Central European beech forests.

Forest hydrologists have hypothesised that canopy transpiration (E(c)) of European temperate forests occurs at rather similar rates in stands with different tree species and hydrologic regimes. We tested this hypothesis by synchronously measuring xylem sap flow in four mature stands of Fagus sylvatica along a precipitation gradient with the aim (1) of exploring the regional variability of annual canopy transpiration (E(c(t))) in this species, and (2) of analysing the relationship between precipitation (P) and E(c(t)). E(c(t)) rates of 216, 225, 272 and 303 mm year(-1) corresponded to precipitation averages of 520, 710, 801 and 1,040 mm year(-1) in the four stands. We explored the regional variability of E(c(t)) in Central European colline to sub-montane beech stands in two meta-analyses based on (1) existing sap flow data on beech (n=5 observations), or (2) all canopy transpiration data on beech obtained by different techniques (sap flow, micrometeorological or soil water budget approaches, n=25). With a coefficient of variation (CV) of 20%, the regional variability of E(c(t)) (213-421 mm year(-1)) was smaller than the variation in corresponding precipitation (550-1,480 mm year(-1)). The mean E(c(t)) for beech was 289 (+/-58) mm year(-1) (n=25). A humped-shaped relationship between E(c(t)) and P, with a broad transpiration maximum in the precipitation range from ca. 700 to 1,000 mm year(-1), was found which may indicate soil moisture limitation of transpiration for P 1,000 mm year(-1). Thus, the precipitation level significantly influences canopy transpiration of humid temperate forests; however, the size of the P influence on E(c(t)) and, in part, the direction of its effect differ from forests in semi-arid or arid climates. European beech has the capacity to maintain high E(c) rates in both humid and partly dry summer climates (P<550 mm year(-1)).

Biological Transport↗
PubMed2005

Dynamics of leaf area and nitrogen in the canopy of an annual herb, Xanthium canadense.

We studied leaf area and nitrogen dynamics in the canopy of stands of an annual herb Xanthium canadense, grown at a high (HN)- and a low-nitorgen (LN) availability. Standing leaf area increased continuously through the vegetative growth period in the LN stand, or leveled off in the later stage in the HN stand. When scaled against standing leaf area, both production and loss rates of leaf area increased but with different patterns: the production rate was retarded, while the loss rate was accelerated, implying an upper limit of standing leaf area of the canopy. The rate of leaf-area production was higher in the HN than in the LN stand, which was caused by the higher rate of leaf production per standing leaf area as well as the greater standing leaf area in the HN stand. Although the rate of leaf-area loss was higher in the HN than in the LN stand, it was not significantly different between the two stands when compared at a common standing leaf area, suggesting involvement of light climate in determination of the leaf-loss rate. On the other hand, the rate of leaf-area loss was positively correlated with nitrogen demand for leaf area development across the two stands, suggesting that leaf loss was caused by retranslocation of nitrogen for construction of new leaves. A simple simulation model of leaf and nitrogen dynamics in the canopy showed that, at steady state, where the rate of leaf-area loss becomes equal to the production rate, the standing leaf area was still greater in the HN than in the LN stand. Similarly, when the uptake and loss of nitrogen are equilibrated, the standing nitrogen was greater in the HN than in the LN stand. These results suggest that leaf-area production is strongly controlled by nitrogen availability, while both nitrogen and light climate determine leaf-loss rates in the canopy.

Analysis of Variance↗
PubMed1987

Measurement of dry deposition to surfaces in deciduous and pine canopies.

The importance of dry deposition was assessed at perimeter and interior locations in two vegetative canopies. Dry deposition was measured directly by washing particles from leaves. Ambient particles and gases were also collected at both locations within the canopies. Ambient concentrations on the canopy interior were decreased relative to perimeter concentrations due to dry deposition scavenging by the canopy. The least scavenging was found for SO(4)(2-) and NH(4)(+) and the highest scavenging was found for HNO(3). Dry deposition of all species was higher to perimeter vegetative and surrogate surfaces than to interior surfaces, due both to the lower concentrations and the lower wind speeds in the sheltered interior. Deposition velocities compared well with other experimental and theoretical values.

Journal Article↗
PubMed1996

Quantifying energy and mass transfer in crop canopies: sensors for measurement of temperature and air velocity.

Here we report on the in situ performance of inexpensive, miniature sensors that have increased our ability to measure mass and energy fluxes from plant canopies in controlled environments: 1. Surface temperature. Canopy temperature measurements indicate changes in stomatal aperture and thus latent and sensible heat fluxes. Infrared transducers from two manufacturers (Exergen Corporation, Newton, MA; and Everest Interscience, Tucson, AZ, USA) have recently become available. Transducer accuracy matched that of a more expensive hand-held infrared thermometer. 2. Air velocity varies above and within plant canopies and is an important component in mass and energy transfer models. We tested commercially-available needle, heat-transfer anemometers (1 x 50 mm cylinder) that consist of a fine-wire thermocouple and a heater inside a hypodermic needle. The needle is heated and wind speed determined from the temperature rise above ambient. These sensors are particularly useful in measuring the low wind speeds found within plant canopies. 3. Accurate measurements of air temperature adjacent to plant leaves facilitates transport phenomena modeling. We quantified the effect of radiation and air velocity on temperature rise in thermocouples from 10 to 500 micrometers. At high radiation loads and low wind speeds, temperature errors were as large as 7 degrees C above air temperature.

Air Conditioning↗
PubMed2004

Sub-canopy deposition of ozone in a stand of cutleaf coneflower.

Although there has been a great deal of research on ozone, interest in exposure of native, herbaceous species is relatively recent and it is still not clear what role the pollutant has in their ecological fitness. The ozone exposure of a plant is usually expressed in terms of the concentration above the canopy or as a time-weighted index. However, to understand the physiological effects of ozone it is necessary to quantify the ozone flux to individual leaves as they develop, which requires knowing the deposition velocity and concentration of the pollutant as a function of height throughout the plant canopy. We used a high-order closure model of sub-canopy turbulence to estimate ozone profiles in stands of cutleaf coneflower (Rudbeckia laciniata L.) located in the Great Smoky Mountains National Park, USA. The model was run for periods coinciding with a short field study, during which we measured vertical concentration profiles of ozone along with measurements of atmospheric turbulence and other meteorological and plant variables. Predictions of ozone profiles by the model are compared with observations throughout the canopy.

Air Pollutants↗
PubMed2001

The development of a test specification to determine the rollover protection of passengers in light commercial vehicles fitted with canopies.

In this paper, a basic test specification is proposed to assess the structural integrity of a canopy that covers the load-area of a light commercial vehicle (LCV) used to carry passengers in the rear. The proposed test specification is a first step towards improving the safety of these passengers during rollover accidents. Different test methods were evaluated for applicability, ease of use and financial implications. The mass and geometric characteristics of three different one-ton LCVs were experimentally obtained and used to determine the minimum lateral velocity that will result in a rollover should a tripping mechanism be encountered. These velocities, in conjunction with other published data, were used to determine the energy required for a pendulum qualification test. It was decided that 7.7 kJ of energy delivered by a pendulum travelling between 4 and 7 m/s just prior to impact would be the most representative load case. A finite element analysis (FEA) of the proposed impact test on a specimen canopy was completed. Thereafter, the actual pendulum impact test was conducted to demonstrate the applicability of the proposed test procedure as well as the correlation with the FEA. It was shown that both FEA and actual testing are viable qualification procedures and that they can in fact be used to reliably assess the strength of the canopy. Finally, the outline of a test specification was developed and proposed, which can be used by national regulatory institutions to assess the structural integrity of commercially manufactured canopies.

Accidents, Traffic↗
PubMed2003

Mercury in canopy leaves of French Guiana in remote areas.

A study of total Hg concentration in the foliage of the canopy was carried out in two remote areas in French Guiana. The sampled canopy is representative of the French Guiana canopy. The concentration in the foliage, 64+/-14 ngg(-1) (dry wt.), is used to estimate the annual input of total Hg to the soil through the litterfall, found to be 45+/-10 microgm(-2)y(-1). As translocation is negligible, mercury in the canopy originates mainly from atmospheric uptake by the leaves and this litterfall deposit represents a direct atmospheric input from the background atmospheric load into the soil.

Air Pollutants↗
PubMed2002

Atmospheric deposition and ionic interactions within a beech canopy in the Karkonosze Mountains.

A method, of artificial foliage placed above rain collectors, which enables to estimate total atmospheric inputs of elements, was employed to study processes related to ionic flow through a tree canopy. The investigations were conducted within a beech forest in the Karkonosze Mountains, in 1996-1997. An analysis of net canopy exchange (throughfall flux-atmospheric input) revealed that NH4+, NO3-, H+ had been retained in the canopy, Ca2+, Na+, Cl-, SO(2-)4, PO(3-)4 flowed passively, whereas K+ and Mg2- had been removed from the tree foliage. Ammonium absorption was more efficient than that of NO3- ions, because NH4+ was taken up from rain-waters and aerosol-gaseous fraction of the atmospheric input, whereas NO3- ions were captured primarily from the latter source. Retention of H+ was also related exclusively to the aerosol-gaseous input. Leaching losses of K+ and Mg2+ did not result from exchange reactions of these ions with retained H+, but from ionic exchange between NH4+ and K+ + Mg2+. At the same time, neutralisation of H+ in the canopy has been attributed to NO3- absorption, resulting most likely from HNO3 vapour penetration into the plants.

Acid Rain↗
PubMed2004

Throughfall chemistry and canopy interactions in a Sitka spruce plantation sprayed with six different simulated polluted mist treatments.

Throughfall chemistry was studied in a mature Sitka spruce plantation in order to investigate canopy interactions, such as nitrogen absorption, cation leaching, and neutralization of rainfall passing through the canopy. The plantation had been exposed to six different simulated mist treatments including N (NH(4)NO(3)) and S (H(2)SO(4) at pH 2.5) in four replicated blocks since 1996. Throughfall and rainfall were collected from May to September 2000. The results showed that 30-35% of the applied N was retained by the canopy. There were linear relationships between the loss of H(+) and increased K(+), Mg(2+) and Ca(2+) deposition through the canopy. However these increases in K(+), Mg(2+) and Ca(2+) deposition accounted for only about 50% of total neutralization of the acidity. The relationship between the anion deficits in throughfall and the loss of H(+) implied that weak organic acid anions were involved in the neutralization of the acidity in throughfall.

Acid Rain↗