Hemiparasitic plants obtain water and solutes from their hosts, but much remains to be learned about these transfers. We used a forest girdling experiment to investigate how leaf gas exchange, carbon and nitrogen cycling in the root hemiparasite Melampyrum lineare Desr. responded to disturbance and changes in physiology of potential host trees. By preventing belowground C allocation by 35% of the canopy, girdling decreased the starch and soluble sugar contents of bulk forest floor fine roots. Photosynthetic rates of M. lineare were statistically significantly lower in the girdled plot, but their hypothesized drivers (foliar N, stomatal conductance and transpiration) had no statistically significant differences between girdled and non-girdled plots. However, M. lineare in the girdled plot had higher foliar C concentrations and Δ14C than in the control plot, suggesting possible photosynthetic down-regulation in the girdled plot due to influx of older (e.g., host-derived) C into the leaves of M. lineare. Within the girdled plot (but not the control plot), M. lineare foliar C concentrations were positively correlated with foliar Δ14C and δ15N, suggesting that M. lineare may respond to changes in both C and N biogeochemistry during the decline of dominant canopy species.

Scanning electron microscopy (SEM) showed that EPTC (S-ethyl dipropylthiocarbamate) caused an aggregation of the epicuticular wax layer of corn (Zea mays L.). R-25788 (2,2-dichloro-N,N-diallylacetamide) prevented this aggregation when applied in combination with EPTC. Neither EPTC, metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], nor R-25788 changed the weight of chloroform extractable epicuticular wax on corn leaves. EPTC apparently does not block lipid synthesis in corn as it does in other plant species. Thus R-25788 does not protect corn from EPTC or metolachlor by overcoming such a block. EPTC did affect wax arrangement on the leaf surface and caused an increase in the cuticular transpiration of corn and predisposed corn to injury from subsequent postemergence applications of paraquat (1,1′-dimethyl-4,4′-bipyridinium ion). R-25788 protected corn against these deleterious effect.

Growth, development, and germination among jointed goatgrass (Aegilops cylindrica Host. # AEGCY) accessions collected from nine western states were not consistently different in field plots near Pullman, WA, or in the greenhouse. Germination percentage and rate of spikelet germination of all accessions produced in the field and greenhouse were consistently high, averaging about 64% and 5.2 (on a unitless scale of 0 to 7), respectively. The Montana accession germinated consistently less than the others. In a separate greenhouse study comparing only the accessions from Colorado and Nebraska, the accession from Colorado averaged 18, 16, and 15% greater net photosynthesis rate (Pn), transpiration rate (E), and stomatal density, respectively, and 21% lower diffusive resistance (rl) than did the accession from Nebraska. However, growth parameters of the Nebraska accession averaged 7 to 35% greater than for the Colorado accession. Overall, the germination, growth, CO2 fixation, and water use among accessions appeared to be similar when jointed goatgrass was grown under Pacific Northwest conditions.

The effect of calcium and nitrogen level on the uptake of linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] from nutrient solution by soybean [Glycine max (L.) Merr.] seedlings was determined and related to root membrane fatty acid composition. Calcium levels in the nutrient solution were 0.4, 4.0, or 8.0 mM and nitrogen levels were 4.0, 16.0, or 32.0 mM with the pH adjusted to 6.5. As calcium concentration increased, linuron uptake decreased. The reverse was true for nitrogen. These changes were not related to transpiration. Increasing calcium concentration increased palmitic acid and decreased linolenic acid in the plasmalemma of the soybean roots resulting in a greater degree of saturation. Nitrogen likewise increased the degree of saturation in the plasmalemma, but the effect was mainly seen in the balance between stearic and linoleic acids. In the mitochondria, however, the trends were inconclusive. High levels of linolenic acid were observed in the mitochondria regardless of treatment.

Two field experiments were conducted in 1984 and 1985 to determine the effects of fluazifop, haloxyfop, and sethoxydim on the suppression of water uptake and competition of wheat to seedling alfalfa. In all cases, suppression of wheat growth and stand led to significant reduction in soil water use. The amounts of conserved soil water significantly correlated with increased numbers of alfalfa plants; the correlation coefficients, respectively, for mid- and late-summer plantings were 0.47 and 0.41 in 1984 and 0.90 and 0.86 in 1985. Conservation of soil water was attributed to growth reduction or cessation of wheat growth by the herbicides and, to some extent, suppression of wheat leaf transpiration. All of the three herbicides would be effective in controlling volunteer wheat in a new alfalfa planting.

Redroot pigweed is a major weed worldwide. Increasing emphasis on modeling physiological processes of weeds for use in weed control decision support systems requires a knowledge of the response of weeds to resource levels and environmental conditions. The purpose of this study was to determine functional relationships for carbon exchange rate (CER) and transpiration based on photosynthetic photon flux density (PPFD) and temperature from measurements made on field-grown redroot pigweed. Measurements were made using a portable photosynthesis system on four dates. An equation that had the form of a power function on PPFD and a quadratic polynomial on temperature was fit to the data. The equation fit the measured CER data better than the measured transpiration data. The equations should be useful in modeling the physiological processes of pigweed within crop canopies.

The productivity of riparian sites in managed forests can be focused to provide productive fish and wildlife habitat while yielding most of its productive capacity for other than amenity values. Establishment of habitat protection goals and measures of achievement permit flexible approaches for meeting them. Once the protection standards are set, intensive management of the woody cover is logically dependent on minimum disturbance methods, in general, for both vegetation management and harvest. Several currently registered chemical products and non-chemical methods are helpful and safe in achieving both yield and protection goals.

Field tests in 1980 and 1981 indicated that smooth pigweed (Amaranthus hybridus L.) competition affected cotton (Gossypium hirsutum L. ‘GSA 71′) water relations by reducing plant water status early in the season and by shading late in the season. Early in the growing season, cotton leaf water potential and turgor pressure reductions as great as 0.53 and 0.21 MPa, respectively, were measured at a smooth pigweed density of 2.5 plants m-2. Late in the 1981 growing season, smooth pigweed reduced the photon flux density reaching the cotton canopy by 90% at midday. The shaded conditions resulted in increased cotton water potential under low soil water conditions, but the inability to reduce solute potential lowered the turgor pressure of cotton, irrespective of soil water level. Comparisons of smooth pigweed and cotton water relations indicated that smooth pigweed had the capacity to maintain higher water potential and turgor pressure than cotton. The more favorable water status of smooth pigweed resulted in part from increased water extraction at lower depths in the soil profile and higher diffusive resistance, thereby reducing transpirational water loss.

Greenhouse experiments were conducted to elucidate the effects of water stress on photosynthetic parameters of soybean [Glycine max (L.) Merr. ‘Hutton′] and velvetleaf (Abutilon theophrasti Medik. # ABUTH). Stomatal conductance of both species responded curvilinearly to reductions in leaf water potential. At leaf water potentials less negative than −2.5 MPa, stomatal conductance, net photosynthetic rate, and transpiration rate were greater in velvetleaf than in soybean. Soybean photosynthetic rate was linearly related to stomatal conductance. Velvetleaf photosynthetic rate increased linearly with stomatal conductances up to 1.5 cm s–1; however, no increase in photosynthetic rate was observed at stomatal conductances greater than 1.5 cm s–1, indicating nonstomatal limitations to photosynthesis. As water stress intensified, stomatal conductance, photosynthetic rate, and transpiration of velvetleaf declined more rapidly than in soybean.

Intraspecific and interspecific interference effects on growth, gas exchange, and water potential of wild oat and spring barley were measured under greenhouse conditions using a 1:1.06 barley to wild oat replacement series. Intraspecific barley interference affected barley growth more than interspecific wild oat interference. Interspecific wild oat interference with barley reduced wild oat growth more than intraspecific interference. Wild oat plant height surpassed barley plant height near barley anthesis. Growth and gas exchange of barley and wild oat responded the same to short-term water stress.

Soybean and ivyleaf morningglory were grown alone and together to quantify water use and growth after treatment with soil-applied chlorimuron plus metribuzin, imazaquin, or no herbicide. Soybean water consumption was 22 ml pot−1 day−1 or more when grown alone or with another soybean, regardless of herbicide treatment. Ivyleaf morningglory grown alone or with another ivyleaf morningglory consumed ≥ 32 ml water pot−1 day−1 when no herbicide was applied. Treatment with chlorimuron plus metribuzin or imazaquin reduced ivyleaf morningglory water consumption to ≤ 4 ml pot−1 day−1. Water use was reduced with either herbicide when soybean and ivyleaf morningglory were grown together, indicating little or no water consumption by ivyleaf morningglory. Ivyleaf morningglory height, root length, leaf area, and dry matter were reduced by imazaquin or chlorimuron plus metribuzin. Soybean leaf area was also reduced by herbicide treatment or the presence of another plant. Soybean biomass was not reduced in any planting combination, except when two soybean were grown together and treated with imazaquin. Nontreated ivyleaf morningglory partitioned more biomass into the shoots than roots. Ivyleaf morningglory responded to herbicide treatment by partitioning more biomass into roots.

Photosynthetic productivity parameters were determined for mayweed chamomile, a troublesome annual weed of the cropping systems in the Pacific Northwest. At a photosynthetic photon flux density of 1800 μE m−2 s–1, maximum net photosynthetic rate of greenhouse-grown plants was 35 mg CO2 dm−2 h–1 and maximum transpiration rate was 6.7 μg H2O cm−2 s–1. Dark respiration rate was 1.4 mg CO2 dm−2 h–1 and the light compensation point was 17.5 μE m−2 s–1. Carbon dioxide compensation point increased from 25 ppm at 15 C to 43 ppm at 30 C. At saturating photosynthetic photon flux densities, optimum leaf temperature for net photosynthesis was about 25 C. Maximum net photosynthesis of leaves of field-grown plants averaged 15.8 mg CO2 dm−2 h–1. After a 24-h exposure to 0.075 kg ha–1 metribuzin, maximum net photosynthesis and transpiration were reduced 85 and 40%, respectively. Soil water deficits reduced maximum net photosynthesis about 50%.

Gas exchange of jointed goatgrass leaves was affected by temperature, irradiance level, and soil matric potential. Net photosynthesis of leaves under saturating irradiance (PPFD3 = 1850 (μE·m–2·s−1) was optimum at about 20 C. At 25 C, net photosynthesis was nearly 90% of maximum at a PPFD of 800 μE·m–2·−1. Transpiration, and presumably water use, increased steadily with temperature from 10 to 40 C. Dark respiration rate and compensation points for light and for CO2 increased exponentially, or nearly so, from 10 to 40 C. Soil moisture deficits of −130 kPa reduced net photosynthesis and transpiration by about 30 and 55%, respectively, compared to well-watered plants.

‘Forrest’ soybean [Glycine max (L.) Merr.] infested with entireleaf morningglory [Ipomoea hederacea (L.) Jacq. var. integriusula Gray] were treated in the field with three postemergence herbicides, dinoseb (2-sec-butyl-4,6-dinitrophenol), sodium salt of acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}, and 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid]. Foliar nitrogen (N) loss, transpiration, and CO2 equilibrium concentrations were measured from 4 to 148 h after treatment. In morningglory foliar N loss was increased by dinoseb, decreased by acifluorfen, and first increased and then decreased by 2,4-DB treatments. Transpiration in this weed species was decreased by all three herbicides. In soybean, N loss was increased and transpiration decreased with dinoseb; acifluorfen did not affect either activity; and 2,4-DB decreased both processes during one sampling period. In both plant species dinoseb increased the CO2 equilibrium concentration within 4 h after treatment. Treatments with acifluorfen and 2,4-DB initially increased the CO2 concentration in morningglory with major increases noted at the onset of chlorosis 52 h after treatment. In soybean, some significant decreases in CO2 equilibrium concentrations occurred with the lowest rate of all three herbicides.

The effect of invasive species might be lessened if herbivores reduced transpiration and growth rates; however, simply removing photosynthetic material might not ensure that the transpiration rate of active leaf tissue decreases. We assessed whether biological control has an injurious effect on the target plant species, giant reed (Arundo donax), by quantifying leaf photosynthetic and transpiration responses to two herbivores: an armored scale, Rhizaspidiotus donacis, and a stem-galling wasp, Tetramesa romana. Herbivory by a sap-feeding scale and a stem-galling wasp both separately and together, reduces the rates of leaf level physiological processes in A. donax. The effect of the wasp increases with density and reduces photosynthesis by reducing the carboxylation rate of ribulose-1,5-bisphosphate carboxylase oxygenase, which controls CO2 fixation in photosynthesis. The scale insect reduces photosynthesis by decreasing the maximum rate of electron transport, which determines how much light energy can be captured in photosynthesis. The effect of the armored scale takes approximately 5 mo after infestation, which coincides with generation time. When both insects are present at the same time, the effect of their herbivory appears additive after time for the scale to reproduce. We conclude that a combination of two herbivores can have a stronger physiological effect than one type of herbivore, likely because of their different effects on leaf function.

Three herbicides were compared for their ability to reduce both carbon fixation and soil water depletion by yellow nutsedge in a growth chamber study. Whole-plant CO2 exchange and water use were measured for 11 d after herbicide application. MSMA reduced carbon assimilation relative to the untreated control 1 d after treatment, and by 5 d after treatment respiration exceeded carbon assimilation during the photoperiod; however, MSMA had no significant effect on whole-plant water use during the measurement period. Halosulfuron reduced gross carbon assimilation to 30% of the pretreatment rate by the end of the experiment, but in contrast to MSMA it also strongly suppressed water use. Mesotrione never reduced carbon assimilation below 59% of the pretreatment rate and had no measurable effect on water use. Halosulfuron and MSMA reduced shoot regrowth to between 0 and 5% of the control, whereas mesotrione treatment allowed some 58% regrowth. These results indicate that whereas both MSMA and halosulfuron should provide effective control of yellow nutsedge, halosulfuron may be better able to rapidly suppress the weed's ability to compete for available soil water.

Tropical montane cloud forests (TMCFs) are dynamic ecosystems defined by frequent, but intermittent, contact with fog. The resultant microclimate can vary considerably over short spatial and temporal scales, affecting the ecophysiology of TMCF plants. We synthesized research to date on TMCF carbon and water fluxes at the scale of the leaf, plant and ecosystem and then contextualized this synthesis with tropical lowland forest ecosystems. Mean light-saturated photosynthesis was lower than that of lowland forests, probably due to the effects of persistent reduced radiation leading to shade acclimation. Scaled to the ecosystem, measures of annual net primary productivity were also lower. Mean rates of transpiration, from the scale of the leaf to the ecosystem, were also lower than in lowland sites, likely due to lower atmospheric water demand, although there was considerable overlap in range. Lastly, although carbon use efficiency appears relatively invariant, limited evidence indicates that water use efficiency generally increases with altitude, perhaps due to increased cloudiness exerting a stronger effect on vapour pressure deficit than photosynthesis. The results reveal clear differences in carbon and water balance between TMCFs and their lowland counterparts and suggest many outstanding questions for understanding TMCF ecophysiology now and in the future.

The aim of the present study was to examine the micromorphology of the cork-oak (Quercus suber) acorn and to evaluate the efficiency of the pericarp as a barrier to water loss. When the desiccation curve obtained at 25 ± 1°C and 62% RH for physiologically mature acorns collected from the tree was compared with that corresponding to fully ripe acorns which had been shed, the latter showed a slightly lower rate of water loss. A marked reduction in the mean rate of water loss was recorded for intact acorns compared with those from which the pericarp had been removed. The external surface and transverse sections of the pericarp from both mature and fully ripe acorns were examined by scanning electron microscopy. Two zones presenting morphological and micromorphological differences were identified: an area including the point of attachment to the cupule and an apical zone covering the embryo. The microstructure of the pericarp showed an external thick cuticle and a single external palisade layer of closely packed cells with no intercellular spaces. Underlying this layer, there was a further parenchymatous layer of poorly differentiated, roughly isodiametric cells. The pericarp in the cupular zone consisted of only this undifferentiated layer between the two epidermal cell layers and contained vascular bundles with many xylem elements.