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PubMed2002

Effects of branch height on leaf gas exchange, branch hydraulic conductance and branch sap flux in open-grown ponderosa pine.

Recent studies have shown that stomata respond to changes in hydraulic conductance of the flow path from soil to leaf. In open-grown tall trees, branches of different heights may have different hydraulic conductances because of differences in path length and growth. We determined if leaf gas exchange, branch sap flux, leaf specific hydraulic conductance, foliar carbon isotope composition (delta13C) and ratios of leaf area to sapwood area within branches were dependent on branch height (10 and 25 m) within the crowns of four open-grown ponderosa pine (Pinus ponderosa Laws.) trees. We found no difference in leaf gas exchange or leaf specific hydraulic conductance from soil to leaf between the upper and lower canopy of our study trees. Branch sap flux per unit leaf area and per unit sapwood area did not differ between the 10- and 25-m canopy positions; however, branch sap flux per unit sapwood area at the 25-m position had consistently lower values. Branches at the 25-m canopy position had lower leaf to sapwood area ratios (0.17 m2 cm-2) compared with branches at the 10-m position (0.27 m2 cm-2) (P = 0.03). Leaf specific conductance of branches in the upper crown did not differ from that in the lower crown. Other studies at our site indicate lower hydraulic conductance, sap flux, whole-tree canopy conductance and photosynthesis in old trees compared with young trees. This study suggests that height alone may not explain these differences.

Photosynthesis↗
PubMed2005

Regeneration patterns in boreal Scots pine glades linked to cold-induced photoinhibition.

Regeneration patterns of Pinus sylvestris L. juveniles in central Siberian glades were studied in relation to cold-induced photoinhibition. Spatial distribution of seedlings in different height classes revealed higher seedling densities beneath the canopy than beyond the canopy, and significantly higher densities of seedlings < 50 cm tall on the north side of the trees. These patterns coincided with differences in light conditions. Compared with plants on the north side of canopy trees (north-exposed), photosynthetic photon flux (PPF) received by plants on the south side of canopy trees (south-exposed) was always higher, making south-exposed plants more susceptible to photoinhibition, especially on cool mornings. Chlorophyll fluorescence data revealed lower photochemical efficiency and increased non-photochemical quenching of small (20-50 cm in height), south-exposed seedlings from spring to early autumn, indicating increased excitation pressure on photosynthesis. Maximum rate of oxygen evolution was less in south-exposed plants than in north-exposed plants. Increased pools of xanthophyll cycle pigments and formation of the photoprotective zeaxanthin provided further evidence for the higher susceptibility to photoinhibition of south-exposed seedlings. A linear mixed model analysis explained many of the physiological differences observed in seedlings according to height class and aspect with early morning temperature and PPF as predictors. The link between photoinhibition and differential distribution of seedlings by height class suggests that photoinhibition, together with other environmental stresses, decreases the survival of small, south-exposed P. sylvestris seedlings, thereby significantly affecting the regeneration pattern of central Siberian pine glades.

Chlorophyll↗
PubMed2006

Relationship of water status to vegetative growth and leaf gas exchange of peach (Prunus persica) trees on different rootstocks.

We investigated relationships between tree water status, vegetative growth and leaf gas exchange of peach trees growing on different rootstocks under field conditions. Tree water status was manipulated by partially covering (0, approximately 30 and approximately 60%) the tree canopies on individual days and then evaluating the effects of tree water status on vegetative growth and leaf gas exchange. Early morning stem water potentials were approximately -0.4 MPa for trees in all treatments, but mean midday values ranged from -1.1 to -1.7 MPa depending on rootstock and canopy coverage treatment. Relative shoot extension growth rate, leaf conductance, transpiration rate and net CO2 exchange rate differed significantly among trees in the different rootstocks and canopy coverage treatments. Shoot extension growth rate, leaf conductance, leaf transpiration rate and leaf net CO2 exchange rate were linearly correlated with midday stem water potential. These relationships were independent of the rootstock and canopy coverage treatments, indicating that tree water relations are probably directly involved in the mechanism that imparts vegetative growth control by selected peach rootstocks.

Carbon Dioxide↗
PubMed1987

Ecophysiological characteristics of the seed of the tropical forest pioneer Urera caracasana (Urticaceae).

Urera caracasana (Jacq.) Griseb is a small, fast-growing evergreen pioneer tree which colonizes openings in the tropical rain forest of 'Los Tuxtlas', Veracruz, Mèxico. Annual seed production by 10 trees was estimated to range from 0.4 x 10(5) to 1.6 x 10(6) seeds per tree. Fifteen species of resident and migratory birds were observed to visit the plants and disperse the seeds. Most seeds imbibed in petri dishes placed on the forest floor beneath a small opening in the canopy, where the red/far-red ratio of the light was around 1.0, germinated within 2 weeks. Germination beneath the forest canopy, where the red/far-red ratio of the light was approximately 0.2, was much slower and did not exceed 40%. A minimum of 4 h daily exposure to unfiltered natural light was required for rapid germination in the forest. In the laboratory rapid germination at 25 degrees C required a minimum of 4 h white light. However, if temperature during the light period was 35 degrees C, 30 min exposure to white light daily was sufficient to induce germination. Seeds that failed to germinate when imbibed for 60-360 days in petri dishes placed on the forest floor beneath the forest canopy, germinated rapidly in the laboratory when held at 25 degrees C and exposed daily to 12 h white or red light. Seeds imbibed for 120 days or more beneath the forest canopy were also induced to germinate by 12 h daily exposure to far-red light when this was combined with a 35/25 degrees C day/night temperature regime. Seeds buried in vermiculite-filled nylon mesh bags disappeared rapidly with few remaining after 2 months. Seeds that survived remained viable and germinated when incubated in petri dishes at 25 degrees C. Initially, buried seeds required light for germination. However, after 17 months' burial, seeds germinated in darkness when transferred to the laboratory and incubated on agar at 25 degrees C.

Journal Article↗
PubMedDate not supplied

Modeling the water balance of a small Pinus radiata catchment.

An hourly biophysical model was used to calculate the water balance over a period of one year for an 8.7-ha catchment with a closed-canopy, 13-year-old Pinus radiata D. Don forest in the central North Island, New Zealand. Components of the model are transpiration from the dry tree canopy, evaporation from the partially wet tree canopy and stems, evaporation from the understory and soil, and drainage from a single-layer root zone. The model requires input of hourly weather data (net radiation, air and wet bulb temperatures, windspeed, and rainfall), tree stand characteristics (average height, tree number, leaf area index), physical characteristics of the site (root zone depth, relationship between root zone matric potential and volumetric water content, the relationship between the rate of drainage from the root zone and volumetric water content, and the area of open-stream channels). A submodel of the response of stomatal conductance to air saturation deficit and root zone matric potential is also required. Tree transpiration (704 mm year(-1) or 50% of annual rainfall) was a dominant component of the catchment water balance. Estimated evaporation from the wet tree canopy was 203 mm year(-1) (15%). Evaporation from the understory was much less, amounting to 94 mm year(-1) (7%) and an increase in water storage for the 3.5 m root zone depth was estimated to be 53 mm year(-1) (4%). Estimated daily rates of drainage generally agreed well with measurements of streamflow, although estimated annual drainage (349 mm year(-1), 24%) exceeded measured streamflow (234 mm year(-1)). The significance of the results is discussed in relation to closure of the hydrologic balance.

Journal Article↗
PubMed2006

Decreases in stomatal conductance of soybean under open-air elevation of [CO2] are closely coupled with decreases in ecosystem evapotranspiration.

Stomatal responses to atmospheric change have been well documented through a range of laboratory- and field-based experiments. Increases in atmospheric concentration of CO(2) ([CO(2)]) have been shown to decrease stomatal conductance (g(s)) for a wide range of species under numerous conditions. Less well understood, however, is the extent to which leaf-level responses translate to changes in ecosystem evapotranspiration (ET). Since many changes at the soil, plant, and canopy microclimate levels may feed back on ET, it is not certain that a decrease in g(s) will decrease ET in rain-fed crops. To examine the scaling of the effect of elevated [CO(2)] on g(s) at the leaf to ecosystem ET, soybean (Glycine max) was grown in field conditions under control (approximately 375 micromol CO(2) mol(-1) air) and elevated [CO(2)] (approximately 550 micromol mol(-1)) using free air CO(2) enrichment. ET was determined from the time of canopy closure to crop senescence using a residual energy balance approach over four growing seasons. Elevated [CO(2)] caused ET to decrease between 9% and 16% depending on year and despite large increases in photosynthesis and seed yield. Ecosystem ET was linked with g(s) of the upper canopy leaves when averaged across the growing seasons, such that a 10% decrease in g(s) results in a 8.6% decrease in ET; this relationship was not altered by growth at elevated [CO(2)]. The findings are consistent with model and historical analyses that suggest that, despite system feedbacks, decreased g(s) of upper canopy leaves at elevated [CO(2)] results in decreased transfer of water vapor to the atmosphere.

Carbon Dioxide↗
PubMed2004

Effect of plant interaction on wind-induced crop motion.

Plant motion due to wind affects plant growth, a phenomenon called thigmomorphogenesis. Despite intensive studies of the turbulence over plant canopies, the study of plant motion induced by wind has often been limited to individual trees or cereal plants. Few models of global canopy motions are available. Moreover the numerical analysis of models that are based on individual stems becomes time consuming when dealing with crops. A model of motion within the canopies is proposed here using a wave propagation equation within a homogenized continuous medium, and a forcing function representing turbulent gusts advected over the canopy. This model is derived from a discrete model of a set of plant shoots represented as individual oscillators, including elastic contacts between shoots. Such contacts induce nonlinearities into the wave equation. A new experimental method to measure stem dynamical properties and elastic collision properties is presented with an illustration on alfalfa stems. Results obtained modeling plant motions in an alfalfa crop are presented.

Biological Clocks↗
PubMed2003

Calculating the micrometeorological influences on the speed of sound through the atmosphere in forests.

A key element in determining point-to-point acoustic transmission within and above forests is modeling the variation (with height above ground) of the effective speed of sound. Effective speed of sound is readily derived from estimates of air temperature, relative humidity, and wind velocity. However, meteorological models for the forest canopy vary from comparatively simple to academically complex, requiring different amounts and numbers of inputs and computer capabilities. In addition, not all canopy profile models are suitable for acoustic applications. In this paper, a meteorological computer model for the forest canopy is developed to derive continuous profiles of effective sound speed from the ground to 3 h, where h is the height of the canopy. In turn, these profiles are used to make some initial approximations of short-range acoustic transmission loss through a uniform forest stand for typical clear sky, midday atmospheric conditions. Also, a radiative transfer and energy budget algorithm is incorporated into the model to obtain the appropriate heat source profile for any time of day. Thus, physics-based micrometeorology is coupled to acoustics for future applications of acoustic information in forest environments.

Journal Article↗
PubMed1982

Plants as sources of airborne bacteria, including ice nucleation-active bacteria.

Vertical wind shear and concentration gradients of viable, airborne bacteria were used to calculate the upward flux of viable cells above bare soil and canopies of several crops. Concentrations at soil or canopy height varied from 46 colony-forming units per m over young corn and wet soil to 663 colony-forming units per m over dry soil and 6,500 colony-forming units per m over a closed wheat canopy. In simultaneous samples, concentrations of viable bacteria in the air 10 m inside an alfalfa field were fourfold higher than those over a field with dry, bare soil immediately upwind. The upward flux of viable bacteria over alfalfa was three- to fourfold greater than over dry soil. Concentrations of ice nucleation-active bacteria were higher over plants than over soil. Thus, plant canopies may constitute a major source of bacteria, including ice nucleation-active bacteria, in the air.

Journal Article↗
PubMed1992

Validation of a portable indirect calorimetry system for measurement of energy expenditure in sick preterm infants.

A portable indirect calorimeter adapted from adult use was validated for use in preterm infants. Oxygen consumption (VO2) and carbon dioxide production (VCO2) were subsequently measured in 16 preterm infants breathing spontaneously in room air (canopy mode) and in nine preterm infants receiving intermittent positive pressure ventilation (ventilator mode). Validation of the system was performed using a gas injection technique with nitrogen to simulate VO2 and carbon dioxide for VCO2. Mean errors in validation of the canopy mode were 1.4% and 0.2% for VO2 and VCO2 with limits of agreement of 0.6 (+2SD) ml/min and -1.3 (-2SD) ml/min, and 0.9 (+2SD) ml/min and -2.3 (-2SD) ml/min respectively. In validation of the ventilator mode mean errors were -1.8% and -5.05% for VO2 and VCO2 with limits of agreement of 1.02 (+2SD) ml/min and -0.74 (-2SD) ml/min, and 0.93 (+2SD) ml/min and -1.45 (-2SD) ml/min respectively. Values of VO2 and VCO2 in 16 preterm infants in the canopy mode were 6.2 ml/kg/min (0.5 1SD) and 6.7 ml/kg/min (0.6 1SD) and in nine preterm infants in the ventilator mode 4.98 ml/kg/min (1.09 1SD) and 4.74 ml/min/kg (1.08 1SD) respectively. Mean energy expenditure was 45.5 kcal (191 kJ)kg/day for infants measured in the canopy mode and 35.5 kcal (149 kJ)/kg/day for ventilated infants. This metabolic system can be adapted for use in the newborn but accuracy is reduced when it is used in those weighing less than 1000 g.

Calorimetry, Indirect↗
PubMed1981

Preliminary observations on habitat utilization and diet in eight Surinam Monkeys.

The eight monkey species occurring in Surinam were studied in the Raleigh-vallen-Voltzberg Nature Reserve along the Coppename River. Special emphasis was placed on determining how these eight species divide up available habitat and food resources within a 300-ha study area. Cebus apella apella is probably the most adaptable of the Surinam monkeys. It was found mainly in the understory and lower to middle parts of the canopy of all five forest types (high rain forest, low rain forest, mountain savanna forest, liane forest, pina swamp forest) in the study area, and entered a variety of edge habitats. Saguinus midas midas, the only callitrichid in Surinam, also occurred mainly in the understory and lower to middle parts of the canopy of all five forest types, but was the only species to spend more time in edges than in non-edge habitats. Alouatta seniculus was most often seen in the middle to upper strata of high forest, but occasionally entered the four other forest types and a variety of edges. Cebus nigrivittatus is apparently less adaptable than its congener and was largely restricted to the understory and lower to middle strata of high forest. It occasionally entered two other forest types as well, but was rarely seen in edges. Chiropotes and Pithecia were both found almost exclusively in high forest and mountain savanna forest, but Chiropotes was mainly in the upper part of the canopy and in emergents, whereas Pithecia occupied the lower to middle parts of the canopy and the understory. Neither species made much use of edges. Ateles paniscus paniscus and Saimiri sciureus represent the extremes of primate adaptation in the Voltzberg area. Ateles was the most restricted species, and was found almost exclusively in high forest. It very rarely entered edges and was most often seen in the uppermost forest strata. In contrast, Saimiri was the only species that was not found most often in high forest, and it occurred consistently lower than any other monkey in the area. More than 50% of all Saimiri observations were in liane forest, a habitat rarely or never entered by most of the other species, and more than 60% were in the understory stratum. Saguinus, Saimiri, Cebus apella and C. nigrivittatus were omnivorous, with Saimiri apparently eating the most arthropods. The four remaining species were not seen feeding on insects or other animals. All eight species included a high proportion of fruit in their diet, with flowers and sometimes leaves usually playing a minor role. The two largest species, Alouatta and Ateles, were the most folivorous, but Alouatta was the only one that ate mature leaves and its leaf intake far exceeded that of Ateles. The three smallest species (Saguinus, Saimiri, Pithecia) did not eat leaves at all. Chiropotes was an important seed predator; Pithecia and C. Nigrivittatus may also depend heavily on seeds. Alouatta and Saimiri were never seen acting as seed predators. Alouatta and Ateles were major seed dispersers. The other six species occasionally dispersed seeds, but to a much lesser extent.

Alouatta↗
PubMed2001

Azalea growth in response to azalea lace bug (Heteroptera: Tingidae) feeding.

The effects of azalea lace bug, Stephanitis pyrioides (Scott), feeding injury on azalea growth and development were investigated using 'Girard's Rose' azaleas during a 2-yr field study in Georgia Low, medium, and high injury treatments, which corresponded to 6, 8, and 14% maximum canopy area injury, were compared with control azaleas that received no lace bug infestation. Flower number, whole-shrub leaf and stem dry mass, and dry mass and size of new growth tissues were unaffected by treatments. In contrast, growth index measurements, a general measure of variability frequently used for horticultural differentiation, showed significant reductions for all treatments in comparison to control azaleas after 20 wk. Though not directly quantified, this apparent discrepancy may be explained as an artifact of lace bug feeding-induced leaf abscission. Growth index measurements had considerable variability and may not be the most reliable measurement of size. In July 1998, plant canopy densities among azaleas maintained in the high injury treatments were approximately 15% less full than the canopies of control shrubs. Predaceous insects had a significant negative association with azalea lace bug number during the 2-yr study. Flower and new tissue production, measured destructively during two growing seasons, revealed azalea tolerance to 14% of maximum canopy area lace bug feeding-injury levels.

Animals↗
PubMed2006

Hyperspectral spectrometry as a means to differentiate uninfested and infested winter wheat by greenbug (Hemiptera: Aphididae).

Although spectral remote sensing techniques have been used to study many ecological variables and biotic and abiotic stresses to agricultural crops over decades, the potential use of these techniques for greenbug, Schizaphis graminum (Rondani) (Hemiptera: Aphididae) infestations and damage to wheat, Triticum aestivum L., under field conditions is unknown. Hence, this research was conducted to investigate: 1) the applicability and feasibility of using a portable narrow-banded (hyperspectral) remote sensing instrument to identify and discern differences in spectral reflection patterns (spectral signatures) of winter wheat canopies with and without greenbug damage; and 2) the relationship between miscellaneous spectral vegetation indices and greenbug density in wheat canopies growing in two fields and under greenhouse conditions. Both greenbug and reflectance data were collected from 0.25-, 0.37-, and 1-m2 plots in one of the fields, greenhouse, and the other field, respectively. Regardless of the growth conditions, greenbug-damaged wheat canopies had higher reflectance in the visible range and less in the near infrared regions of the spectrum when compared with undamaged canopies. In addition to percentage of reflectance comparison, a large number of spectral vegetation indices drawn from the literature were calculated and correlated with greenbug density. Linear regression analyses revealed high relationships (R2 ranged from 0.62 to 0.85) between greenbug density and spectral vegetation indices. These results indicate that hyperspectral remotely sensed data with an appropriate pixel size have the potential to portray greenbug density and discriminate its damage to wheat with repeated accuracy and precision.

Animals↗
PubMed2006

Modeling the effect of photosynthetic vegetation properties on the NDVI--LAI relationship.

Developing a relationship between the normalized difference vegetation index (NDVI) and the leaf area index (LAI) is essential to describe the pattern of spatial or temporal variation in LAI that controls carbon, water, and energy exchange in many ecosystem process models. Photosynthetic vegetation (PV) properties can affect the estimation of LAI, but no models integrate the effects of multiple species. We developed four alternative NDVI-LAI models, three of which integrate PV effects: no PV effects, leaf-level effects, canopy-level effects, and effects at both levels. The models were fit to data across the natural range of variation in NDVI for a widespread High Arctic ecosystem. The weight of evidence supported the canopy-level model (Akaike weight, wr = 0.98), which includes species-specific canopy coefficients that primarily scale fractional PV cover to LAI by accounting for the area of unexposed PV. Modeling the canopy-level effects improved prediction of LAI (R2 = 0.82) over the model with no PV effect (R2 = 0.71) across the natural range of variation in NDVI but did not affect the site-level estimate of LAI. Satellite-based methods to estimate species composition, a variable in the model, will need to be developed. We expect that including the effects of PV properties in NDVI-LAI models will improve prediction of LAI where species composition varies across space or changes over time.

Arctic Regions↗
PubMedDate not supplied

Narrow-waveband reflectance ratios for remote estimation of nitrogen status in cotton.

Tailoring nitrogen (N) fertilizer applications to cotton (Gossypium hirsutum L.) in response to leaf N status may optimize N use efficiency and reduce off-site effects of excessive fertilizer use. This study compared leaf and canopy reflectance within the 350 to 950 nm range in order to identify reflectance ratios sensitive to leaf chlorophyll (Chl), and hence N status, in cotton. Plants were grown outdoors in large pots using half-strength Hoagland's (control) solution until some three-row plots received a restricted supply of N. Treatments comprised control, 20% of control N at first flower bud (square) onward; 0 and 20% of control N at first flower onward; and 0% of control N at fruit-filling onward. Despite leaf N values ranging from 51 to 19 g kg-1 across treatments and sampling dates, a weak correlation was obtained between Chl and N (r2 = 0.32, df = 70). In general, N stress led to increased reflectance at 695 +/- 2.5 nm (R695) and decreased reflectance at R410, and changes in leaf N were best correlated with either R695 or R755 in leaves and either R410 or R700 in canopies. The strongest associations between leaf constituent and canopy reflectance ratio were Chl vs. R415/R695 (r2 = 0.72), carotenoids vs. R415/R685 (r2 = 0.79), and N vs. R415/R710 (r2 = 0.70). The R415 measure appears to be a more stable spectral feature under N stress, as compared with more pronounced changes along the reflectance red edge (690-730 nm). Multiple regression identified a three-waveband canopy reflectance model that explained 80% of the variability in leaf N. Results indicate that remote sensing of N status in cotton is feasible using narrow-waveband reflectance ratios that involve the violet or blue region of the spectrum (400 to 450 nm) and the more commonly featured red-edge region.

Chlorophyll↗
PubMedDate not supplied

Gas exchange characteristics of wheat stands grown in a closed, controlled environment.

Information on gas exchange of crop stands grown in controlled environments is limited, but is vital for assessing the use of crops for human life-support in closed habitats envisioned for space. Two studies were conducted to measure gas exchange of wheat stands (Triticum aestivum L. cv. Yecora Rojo) grown from planting to maturity in a large (20 m2 canopy area), closed growth chamber. Daily rates of dark-period respiration and net photosynthesis of the stand were calculated from rates of CO2 build-up during dark cycles and subsequent CO2 drawdown in the light (i.e., a closed-system approach). Lighting was provided as a 20-h photoperiod by high-pressure sodium lamps, with canopy-level photosynthetic photon flux density (PPFD) ranging from 500 to 800 micromoles m-2 s-1 as canopy height increased. Net photosynthesis rates peaked near 27 micromoles CO2 m-2 s-1 at 25 d after planting, which corresponded closely with stand closure, and then declined slowly with age. Similarly, dark-period respiration rates peaked near 14 micromoles CO2 m-2 s-1 at 25 d and then gradually declined with age. Responses to short-term changes in irradiance after canopy closure indicated the stand light compensation point for photosynthesis to be near 200 micromoles m-2 s-1 PPFD. Tests in which CO2 concentration was raised to approximately 2000 micromoles mol-1 and then allowed to draw down to a compensation point showed that net photosynthesis was nearly saturated at > 1000 micromoles mol-1; below approximately 500 micromoles mol-1, net photosynthesis rates dropped sharply with decreasing CO2. The CO2 compensation point for photosynthesis occurred near 50 micromoles mol-1. Short-term (24 h) temperature tests showed net photosynthesis at 20 degrees C > or = 16 degrees C > 24 degrees C, while dark-period respiration at 24 degrees C > 20 degrees C > 16 degrees C. Rates of stand evapotranspiration peaked near Day 25 and remained relatively constant until about Day 75, after which rates declined slowly. Results from these tests will be used to model the use of plants for CO2 removal, O2 production, and water evaporation for controlled ecological life support systems proposed for extraterrestrial environments.

Carbon Dioxide↗
PubMed1991

Effects of grass species on grazing steers: I. Diet composition and ingestive mastication.

In traditional grazing trials, per animal and per hectare productivity are determined, but pasture and animal measurements are generally inadequate to address reasons for different treatment responses. This 2-yr study examined the diet and diet characteristics of steers grazing tall fescue (Festuca arundinacea Schreb.), switchgrass (Panicum virgatum L.), flaccidgrass (Pennisetum flaccidum Griseb.), and bermudagrass (Cynodon dactylon [L.] Pers.) pastures. A randomized complete block design was used with two agronomic replicates. In vitro DM disappearance (IVDMD) of masticates from tall fescue (TF), switchgrass (SG), and flaccidgrass (FG) generally were similar; all exceeded 70% (70.3 to 79.9%), except for bermudagrass (BG), which was lowest (63.5 to 65.0%). Sieving the masticate DM showed BG to contain the highest proportion (20 to 29%) of particles passing a .5-mm sieve and the lowest proportion (6 to 8%) of particles retained on a 2.8-mm sieve. This resulted in BG having the smallest mean (1.29 mm) and median (1.08 mm) particle sizes in yr 1 and a mean (1.10 mm) and median (.91 mm) particle size smaller than SG in yr 2. Except for BG, the IVDMD of the masticate DM was lowest for small particles. Canopies showed BG and SG to have the highest proportion of stem (47 and 52%, respectively); the BG canopy was composed of fractions that were consistently lowest in IVDMD. In general, BG offered the grazing animal a canopy inferior in IVDMD concentration and had canopy characteristics that limited the animals' selection of a diet with quality as high as that of TF, SG, or FG.

Animal Feed↗
PubMed2000

A simple method to determine leaf angles of grass species.

There are several very accurate methods to determine leaf angles in closed canopies. However, these are generally very time-consuming or require special equipment. Average canopy leaf angles were derived from simple height and blade length measurements. An exponential relationship between the height/length ratio and the average blade leaf angle was used. The method was tested for two grass species, Dactylis glomerata and Festuca arundinacea, grown under different UV-B levels. The results clearly show that the method is reasonably accurate and able to identify UV-B induced changes in leaf angle. To get these results only 50 measurements of leaf blade height and length were necessary to calculate the allometric relationship, after which 10 length and height measurements from a canopy were used to calculate the average canopy leaf angle.

Plant Leaves↗