Ambient Field Conditions Research Articles

Leaf Gas Exchange Response of 'Arapaho' Blackberry and Six Red Raspberry Cultivars to Moderate and High Temperatures

Leaf gas exchange of six red raspberry (Rubus idaeus L.) and one blackberry (Rubus L. subgenus Rubus Watson) genotypes growing in 12-L containers was measured at four temperatures (20, 25, 30, and 35 °C) once a month for 3 months in growth chambers by infrared gas analysis. Measurements were taken on three successive leaves on the same primocane between the third and seventh nodes (≈75% to 85% of full leaf expansion). The plants were grown in ambient (field) conditions except when measurements were taken. Maximum daily ambient temperatures rose as high as ≈37 °C during this period. Net CO2 assimilation (A), evapotranspiration (ET), and stomatal conductance (gs) were measured during June, July, and August. Significant differences (P ≤ 0.01) in A were found among the seven genotypes. 'Arapaho' blackberry displayed the highest mean A rate at all temperatures. Only in the raspberry cultivars Nova and Reveille did the rate of A drop significantly when temperature increased from 20 to 30 °C. 'Reveille' was also the only cultivar in which A significantly declined between 30 and 35 °C. The ET increased significantly over the four temperatures in four cultivars ('Arapaho', 'Heritage', 'Nova', and 'Southland'). The ET rate at 35 °C was higher for 'Arapaho' than for all other cultivars. 'Autumn Bliss', 'Dormanred', and 'Reveille' did not change significantly as the temperature rose from 20 to 35 °C. Stomatal conductance of 'Heritage' and 'Arapaho' did not change significantly between 20 and 35 °C, whereas that of 'Autumn Bliss' and 'Reveille' declined almost 50% when temperature increased to 30 or 35 °C.

Annual CO2 Flux in Dry and Moist Arctic Tundra: Field Responses to Increases in Summer Temperatures and Winter Snow Depth

We examined the annual exchange of CO2 between the atmosphere and moist tussock and dry heath tundra ecosystems (which together account for over one-third of the low arctic land area) under ambient field conditions and under increased winter snow deposition, increased summer temperatures, or both. Our results indicate that these two arctic tundra ecosystems were net annual sources of CO2 to the atmosphere from September 1994 to September 1996 under ambient weather conditions and under our three climate change scenarios. Carbon was lost from these ecosystems in both winter and summer, although the majority of CO2 evolution took place during the short summer. Our results indicate that (1) warmer summer temperatures will increase annual CO2 efflux from both moist and dry tundra ecosystems by 45–55% compared to current ambient temperatures; (2) deeper winter snow cover will increase winter CO2 efflux in both moist and dry tundra ecosystems, but will decrease net summer CO2 efflux; and (3) deeper winter snow cover coupled with warmer summer temperatures will nearly double the annual amount of CO2 emitted from moist tundra and will result in a 24% increase in the annual CO2 efflux of dry tundra. If, as predicted, climate change alters both winter snow deposition and summer temperatures, then shifts in CO2 exchange between the biosphere and atmosphere will likely not be uniform across the Arctic tundra landscape. Increased snow deposition in dry tundra is likely to have a larger effect on annual CO2 flux than warmer summer temperatures alone or warmer temperatures coupled with increased winter snow depth. The combined effects of increased summer temperatures and winter snow deposition on annual CO2 flux in moist tundra will be much larger than the effects of either climate change scenario alone.

An experimental study of positive leaders initiating rocket-triggered lightning

Simultaneous, co-located measurements of ambient, electrostatic-field profiles and rocket-triggered lightning phenomenology beneath Florida thunderstorms are reported. Ambient-field conditions that are sufficient to initiate and sustain the propagation of positive lightning leaders are identified. It is found that lightning can be triggered with grounded triggering wires approximately 400 m long when the ambient fields aloft are as small as 13 kV/m (foul-weather polarity). Ambient potential differences between the height of the triggering wires and ground were as small as −3.6 MV (negative wrt. earth) when lightning occurred. `Precursors,' the first measurable current pulses from the triggering wires, were initiated at similar fields aloft but at wire heights only about half as large, where ambient potentials were as small as −1.3 MV. The mean speed of one `failed leader' is estimated at 1.9×10 4 m/s over 35 m of propagation. The lengths of `leader' extension and positive-streamer `fan' during individual impulses of multiple-pulse precursors are estimated to be 0.7 and 2.0 m, respectively.

Atmospheric CO2 enrichment increases growth and photosynthesis of Pinus taeda: a 4 year experiment in the field

ABSTRACTForest trees are major components of the terrestrial biome and their response to rising atmospheric CO2 plays a prominent role in the global carbon cycle. In this study, loblolly pine seedlings were planted in the field in recently disturbed soil of high fertility, and CO2 partial pressures were maintained at ambient CO2 (Amb) and elevated CO2 (Amb + 30 Pa) for 4 years. The objective of the study was to measure seasonal and long‐term responses in growth and photosynthesis of loblolly pine exposed to elevated CO2 under ambient field conditions of precipitation, light, temperature and nutrient availability. Loblolly pine trees grown in elevated CO2 produced 90% more biomass after four growing seasons than did trees grown in ambient CO2. This large increase in final biomass was primarily due to a 217% increase in leaf area in the first growing season which resulted in much higher relative growth rates for trees grown in elevated CO2. Although there was not a sustained effect of elevated CO2 on relative growth rate after the first growing season, absolute production of biomass continued to increase each year in trees grown in elevated CO2 as a consequence of the compound interest effect of increased leaf area on the production of more new leaf area and more biomass. Allometric analyses of biomass allocation patterns demonstrated size‐dependent shifts in allocation, but no direct effects of elevated CO2 on partitioning of biomass. Leaf photosynthetic rates were always higher in trees grown in elevated CO2, but these differences were greater in the summer (60–130% increase) than in the winter (14–44% increase), reflecting strong seasonal effects of temperature on photosynthesis. Our results suggest that seasonal variation in the relative photosynthetic response to elevated CO2 will occur in natural ecosystems, but total non‐structural carbohydrate (TNC) levels in leaves indicate that this variation may not always be related to sink activity. Despite indications of canopy‐level adjustments in carbon assimilation, enhanced levels of leaf photosynthesis coupled with increased total leaf area indicate that net carbon assimilation for the whole tree was greater for trees grown under elevated CO2 compared with ambient CO2. If the large growth enhancement observed in loblolly pine were maintained after canopy closure, then these trees could be a large sink for fossil carbon emitted to the atmosphere and produce a negative feedback on atmospheric CO2.

Comparative Plant Water Relations and Soil Water Depletion Patterns of Three Seral Shrub Species on Forest Sites in Southwestern Oregon

Abstract We compared stomatal conductance, transpiration, plant water potential, and soil moisture depletion patterns for three shrub species common on early seral forest sites in southwestern Oregon following logging or fire. Our goal was to determine which of these species were more likely to be the strongest competitors with regenerating conifers. The three species, Arctostaphylos patula Greene, Ceanothus sanguineus Pursh., and Holodiscus discolor (Pursh.) Maxim., were selected to represent a range in leaf morphology and expected water use patterns. Diurnal patterns of leaf conductance, plant water potential, and environmental parameters were measured throughout the growing season, along with seasonal patterns in soil moisture. As with any data obtained under ambient field conditions, environmental parameters and exact timing of measurements varied among shrubs. To better evaluate the response of individual species to common environmental parameters, we constructed models of leaf conductance based on field data and used these models to estimate responses of conductance and transpiration to averaged environmental conditions. This allowed us to better compare species responses to seasonal and diurnal trends in environmental variables. C. sanguineus typically had the highest transpiration rates per unit leaf area, and H. discolor the lowest; however, due to much higher leaf area indices of H. discolor, the two species depleted soil moisture at about the same rate. C. sanguineus and A. patula both had high predawn water potentials throughout the season, even when soil water potential at 1 m depth was less than -1.2 Mpa, suggesting that these species, but not H. discolor, had roots in deeper soil layers. We predict that the two deciduous species, C. sanguineus and H. discolor, will be stronger competitors for soil moisture than A. patula, at least in the top meter of soil. In contrast, A. patula and C. sanguineus are capable of depleting moisture from deeper in the soil and may therefore strongly compete even with deep-rooted conifers late in the season. Our use of empirical models allowed us to compare species responses to common environmental conditions, which facilitated ecological interpretation of species differences in water use patterns. By early August, soil water potentials under all species were low enough to significantly inhibit conifer transpiration, photosynthesis, and growth. For. Sci. 43(3):336-347.

Effects of Food Limitation and Sexual Cannibalism on Reproductive Output of the Nursery Web Spider Dolomedes triton (Araneae: Pisauridae)

Reproductive output of free-ranging females of Dolomedes triton was not constrained by natural food limits in relation to that of sated spiders held in field cages. A two-year study revealed both seasonal and annual variation in egg number and egg-sac development time that was driven by factors other than food availability. There was a strong, positive correlation between egg numbers in first and second egg-sacs; some females produced three egg sacs under field conditions. In an experiment using field cages, reproductive output was affected by food availability to adults, female body size measured as carapace width, and by interaction between these two variables. Under both ambient field conditions and experimentally maintained satiation, fecundity increased linearly with carapace width. However, larger females failed to achieve their full, reproductive potential when food was scarce, although reproductive output of smaller females was unaffected. Females of D. triton allowed to feed on their mates did not show increased reproductive output or rate and thus do not receive any special nutrient supplements through sexual cannibalism.

Responses of the Spring Ephemeral Claytonia virginica L. to Light and Nutrient Manipulations and Implications for the "Vernal-Dam" Hypothesis

EICKMEIER, W. G. AND E. E. SCHUSSLER (Department of Biology, Vanderbilt University, Nashville, TN 37235). Responses of the spring ephemeral Claytonia virginica L. to light and nutrient manipulations and implications for the vernal-dam hypothesis. Bull. Torrey Bot. Club 120: 157-165. 1993.-The effects of shading and fertilization on the ecophysiology of the spring ephemeral Claytonia virginica L. (Portulacaceae) were examined in the field. A two-way factorial design with main factors of light treatment (ambient control irradiance vs. 90% attenuation) and nutrient treatment (unfertilized control vs. 192 kg ha- i total N, P205, and K20 equivalents added) was employed at Radnor Lake, TN. Plant shading reduced biomass development, enhanced tissue nutrient concentration, and reduced both specific leaf weight and ribulose bisphosphate carboxylase/oxygenase (RUBISCO) activity relative to unshaded controls. Fertilization enhanced aboveground nonreproductive biomass, elevated tissue nutrient concentration for N and P but not K, and increased the leaf width/length index relative to controls. Of greatest ecophysiological importance were significant light by nutrient interactions where the stimulation of both aboveground productivity and RUBISCO activity in response to fertilization occurred only for plants in unshaded, high-irradiance conditions. These results suggest that C. virginica may be nutrient limited under ambient field conditions, is not capable of acclimation to low-irradiance, that irradiance and nutrient availability interact synergistically to affect the magnitude of short-term nutrient sequestering in C. virginica biomass, and imply that total nutrient capture by the vernal dam may adjust to variation in early-season nutrient conditions to affect forest-wide nutrient conservation.

The seasonal course of physiological processes in Juniperus occidentalis

The seasonal course of carbon dioxide assimilation, leaf conductance, transpiration, leaf temperature, xylem pressure potentials, growth, foliage macro- and micronutrient element concentrations, and water- and nitrogen-use efficiencies were measured in juvenile, small-adult, and large-adult western juniper ( Juniperus occidentalis) growing under ambient field conditions in eastern Oregon to explore the timing of, and seasonal limitations on, those processes. Highest daily total assimilation occurred during July and August; over the 15 month period juveniles had significantly higher daily total assimilation and transpiration per gram foliage than small adults or large adults. As soil water became limiting, total daily assimilation of juveniles and small adults declined to levels similar to those of large adults. Juveniles had the highest leaf conductance flux densities in all except three measurement periods, when leaf conductances in all three morphotypes were equally low. Juveniles also had the tightest stomatal control over water loss; however, during periods of low soil water, juveniles had the most negative xylem pressure potentials. Soil drought affected leaf conductance independent of plant water potentials or vapor pressure deficits. Juveniles had the capacity for higher carbon dioxide assimilation over a broader range of stomatal resistances and xylem pressure potentials than did small or large adults. Foliage nitrogen concentrations were usually highest in small adults and large adults. High rates of transpiration may be required to acquire an adequate supply of nitrogen, but nitrogen did not appear to be allocated preferentially to photosynthetic compounds. Potential photosynthetic nitrogen-use efficiences of J. occidentalis were very low compared with other growth forms. Branchlet elongation was greatest in June and July. Juveniles were more responsive to the changing environment than were small adults; large adults had the least seasonal variation in measured proceses.

Sulfate Mobility in an Acid Danish Forest Soil

ABSTRACTA key question in the acidification of soils due to atmospheric deposition of strong acids is the accumulation of SO2−4 in the soil. Sulfate leaching was studied in the laboratory in undisturbed soil cores taken in a Typic Udipsamment under spruce forest. The soil cores were watered with natural throughfall water (pH 3.6) or with throughfall acidified to pH 3.3 or 2.8 with a mixture of sulfuric and nitric acid (1:1, molar basis). A total of 660 mm of throughfall was applied during 11 months. The technique of using soil cores produced increased nitrification and mineralization in the soil, causing a continuous acid production in the soil cores and decrease in the leachate pH during the experiments. Soil solution concentrations of SO2−4 were in the range 0.4 to 1.5 mmol L−1, total Al 0.2 to 1.5 mmol L−1, and pH 3.5 to 4.1. Stability diagrams using Al and SO2−4 activities and pH indicate that precipitation of a solid phase with the composition of AlOHSO4 may control the Al and sulfate activities in the soil solutions in the Bw horizon but not in the Ap horizon. The equilibrium constant for this basic Al sulfate was estimated at 20°C, pKs = 17.36 and at 5°C, pKS = 17.05. The 35S labeled SO2−4 was added once to the same soil cores followed by 15 mm throughfall per day (Natural or adjusted to pH 2.8). After application of 75, 150, or 225 mm of throughfall water the distribution of 35S‐SO2−4 in the soil cores was determined. From 38 to 100% of the applied 35S‐SO2−4 was retained in the soil cores and of this amount 32 to 63% was found in the top of the Bw horizon, which was highest in free Al and Fe oxides. The studied soil did not accumulate SO2−4 under ambient field conditions. In the laboratory, however, SO2−4 accumulation was demonstrated when the soil was exposed to increased SO2−4 load and temperature as well as decreased pH, showing that SO2−4 sorption/desorption may buffer variations in SO2−4 concentrations in soil solutions, and thereby delay effects of acidification on cation leaching.

Temporal patterns in three-dimensional structure and activity of schools of the Atlantic silverside Menidia menidia

Temporal patterns in the structure and activity of schools of the Atlantic silverside Menidia menidia were investigated under laboratory conditions using a new computerized video technique for three-dimensional analysis. Fish were collected by seining at Middle Bridge, Pettaquamscutt River, South Kingstown, Rhode Island, USA. Approximately once a week from May to December, 1979, the behavior of a school was videotape-recorded in the laboratory at 30 min intervals from sunrise to sunset under a temperature and photoperiod regime simulating ambient field conditions. Four measurements of structure and activity were computed: (1) swimming speed (SPEED); (2) distance to nearest neighbor (NN); (3) mean direction of travel (DOT); (4) depth in the tank (DEPTH). Results demonstrated a strong seasonal rhythm in the behavior of schools, but were inconclusive in showing periodicities associated with daily, tidal or lunar cycles. NN and DEPTH were significantly different between spring, summer, fall and winter while SPEED changed significantly across 3 seasons (summer and winter were not significantly different). DOT was bimodally distributed, with peaks in spring and fall. Changes in these variables corresponded to shifts in the behavior of silversides from active, synchronized schools in spring and fall to inactive mills in summer and inactive non-schooling groups in winter. Changes in schooling behavior were only partly related to changes in temperature and photoperiod. Patterns of silverside schooling behavior correlated with their reproductive and migratory cycles and may represent an anti-predator strategy.

Bunchgrass architecture, light interception, and water-use efficiency: assessment by fiber optic point quadrats and gas exchange.

The bunchgrass growth form, which is very prominent in water-limited environments, can result in considerable self-shading of photosynthetically active foliage. The consequences of this growth form for light interception and water-use efficiency (photosynthesis/transpiration, P/T) were investigated for two Agropyron species which differ in tussock density and degree of self-shading. During the period of most active gas exchange, the tussocks were very compact and photosynthesis of shaded foliage was markedly light-limited. Stomatal control of older shaded foliage was poorly attuned for water-use efficiency. At low light, P/T decreased and intercellular CO2 concentrations increased. Despite differences in architecture and amount of shaded foliage, P/T of whole tussocks under ambient field conditions did not differ between these species. Partial defoliation decreased, rather than increased, P/T, primarily as a result of the poor photosynthetic light harvesting by the remaining foliage. Despite self-shading, the architecture of widely-spaced bunchgrasses provides for interception of as much direct beam solar radiation as is calculated for a rhizomatous grass occupying an area six-fold greater than the ground area underneath the canopy of these bunchgrasses.

The effects of acid rain on forest nutrient status

The effects of acidic atmospheric inputs on forest nutrient status must be assessed within the context of natural, internal acid production by carbonic and organic acids as well as the nutrient inputs and drains by management practices such as harvesting, fire, and fertilization. In all cases the anion associated with acid inputs must be mobile in the soil if leaching is to occur; immobilization of anions can effectively prevent cation leaching. Soil acidification will occur only if the often substantial buffering capacity of the soil in question is exceeded by acid inputs and if cation weathering from primary minerals is insufficient to offset cation losses by leaching. Such circumstances are rare but certainly could occur in theory, at least, given sufficiently large acid inputs on poorly buffered soils. Soils most sensitive to change are thought to be those of moderately acid pH and low cation exchange capacity. Neither very acid soils nor neutral, highly buffered soils are sensitive to acidification by acid rain. Given extremely high acid inputs, acid rain can cause temporary increases in nitrogen mineralization and nitritication as well as Al mobilization in soils. While temporary increases in N availability can cause increased forest growth in N‐deficient forests, increased Al availability can cause toxic reactions in tree roots. Little is known about tree Al toxicity levels as yet, however. It must be emphasized that assessment of acid rain effects is a problem of quantification. Given sufficiently high inputs on sensitive sites, negative effects of acid rain must occur, as is true of inputs of any substance, including H2O. Acid rain inputs of sufficient magnitude to cause acute effects, such as growth increase due to N mobilization or growth decrease due to Al mobilization, are apparently very rare under ambient field conditions. Long‐term effects on forest nutrient status can be either beneficial or adverse, depending on site nutrient status, silvicultural practices, and amount of atmospheric inputs.

Measurement of the responses of mussels to environmental stress and pollution in Sullom Voe: a base-line study

SynopsisThe base-line study consisted of three visits to Sullom Voe before the oil terminal became operational. General stress indices were used to measure the health and condition of four native and two transplanted populations of mussels (Mytilus edulis). A mobile laboratory was used to measure the physiological responses under ambient field conditions. These were then integrated into the stress indices, scope for growth and oxygen :nitrogen ratio. The general biochemical and cytological stress indices, namely taurine: glycine ratio, gametogenic development and latency of lysosomal β-hexosaminidase were also measured for each population. All these general stress indices indicated that the mussel populations were in a relatively healthy physiological condition. However, mussels from the Houb of Scatsta showed a transient stress response, probably caused by freshwater run-off from the surrounding peat beds.In addition to the general stress indices, specific cellular responses known to be induced by petroleum hydrocarbons were monitored. The activity of enzymes forming components of the mixed-function oxidase system (NADPH neotetrazolium reductase, G6PDH and NADP-ICDH, and aldrin epoxidation) were measured.The rationale for measuring these general and specific stress indices as part of a Sullom Voe environmental monitoring programme is discussed in the light of experiments with petroleum hydrocarbons in the laboratory and with reference to the future operation of the oil terminal.

Fire and the opening of Banksia ornata F. Muell. Follicles

Banksia ornata is a sclerophyll shrub, characteristic of the heaths of south-eastern Australia. Its follicles are almost entirely dependent on fire for rupture and release of seed, although a few open under ambient field conditions. At air-dry moisture content (10-12% oven-dry weight) temperatures in excess of about 75°C are required for the rupture of the abscission layer between the woody valves, the time of exposure necessary for rupture decreasing with increasing temperature. At higher moisture contents rupture is delayed. No rupture occurs when follicles are water-saturated and exposed to a temperature of 100° over long periods. Similarly, no rupture occurs at room temperature when follicles are dried under vacuum (to 1.4% oven-dry weight). After rupture, the extent of valve reflexion is greatest when follicle valves are driest. These results are interpreted as follows. Follicle rupture occurs when tension across the abscission zone exceeds its strength: moisture has a major role in affecting the tension, and temperature a major role in affecting the strength.