Midday Xylem Water Potential Research Articles

Microclimatic conditions and plant morpho-physiological development within a tree shelter environment during establishment of Quercus ilex seedlings

Tree shelters are used commonly under a wide range of agriculture and forestry applications, and the presence of the shelter is known to influence plant development through shelter–plant interactions that affect microclimatic conditions. However, effects of tree shelter microclimates on development of relatively slow-growing forest tree species characteristic of semi-arid Mediterranean climates have yet to be examined. Under a controlled environment using mesic and xeric watering regimes, we examined microclimatic conditions within light and dark tree shelters relative to non-sheltered conditions and corresponding influences on morpho-physiological development of holm oak ( Quercus ilex L.) seedlings during initial establishment. Despite relatively low photosynthetic rates (<1 μmol CO 2 m −2 s −1), CO 2 concentrations within shelters oscillated widely during the day, reflecting respiration from late afternoon through night and rapid assimilation during the first 2–3 h after sunrise that dropped sharply around noon. In dark shelters within the mesic watering regime, reduced vapor pressure deficit (VPD) was associated with high plant transpiration. Higher irradiance inside light shelters stimulated photosynthesis, although higher VPD under xeric conditions led to decreased mid-day xylem water potential within light shelters. Additionally, decreased light transmittance among shelter treatments (control > light > dark) did not affect plant N or starch concentrations nor total plant biomass, but resulted in increased height, as well as leaf area production and shoot:root ratio under mesic conditions, morphological adaptations likely to increase drought susceptibility under hot, dry conditions characteristic of late summer in this region. We conclude that microclimatic conditions within tree shelters and corresponding influences on plant morpho-physiological development are interrelated through complex phenomena dependent upon environmental conditions and phenotypic characteristics of a given plant species. Consequentially, shelter configurations must be adapted to match climatic conditions of the outplanting site with species plasticity; we recommend light shelters with high light transmittance for planting holm oak in Mediterranean areas.

Influence of soil texture on hydraulic properties and water relations of a dominant warm-desert phreatophyte

We investigated hydraulic constraints on water uptake by velvet mesquite (Prosopis velutina Woot.) at a site with sandy-loam soil and at a site with loamy-clay soil in southeastern Arizona, USA. We predicted that trees on sandy-loam soil have less negative xylem and soil water potentials during drought and a lower resistance to xylem cavitation, and reach E(crit) (the maximum steady-state transpiration rate without hydraulic failure) at higher soil water potentials than trees on loamy-clay soil. However, minimum predawn leaf xylem water potentials measured during the height of summer drought were significantly lower at the sandy-loam site (-3.5 +/- 0.1 MPa; all errors are 95% confidence limits) than at the loamy-clay site (-2.9 +/- 0.1 MPa). Minimum midday xylem water potentials also were lower at the sandy-loam site (-4.5 +/- 0.1 MPa) than at the loamy-clay site (-4.0 +/- 0.1 MPa). Despite the differences in leaf water potentials, there were no significant differences in either root or stem xylem embolism, mean cavitation pressure or Psi(95) (xylem water potential causing 95% cavitation) between trees at the two sites. A soil-plant hydraulic model parameterized with the field data predicted that E(crit) approaches zero at a substantially higher bulk soil water potential (Psi(s)) on sandy-loam soil than on loamy-clay soil, because of limiting rhizosphere conductance. The model predicted that transpiration at the sandy-loam site is limited by E(crit) and is tightly coupled to Psi(s) over much of the growing season, suggesting that seasonal transpiration fluxes at the sandy-loam site are strongly linked to intra-annual precipitation pulses. Conversely, the model predicted that trees on loamy-clay soil operate below E(crit) throughout the growing season, suggesting that fluxes on fine-textured soils are closely coupled to inter-annual changes in precipitation. Information on the combined importance of xylem and rhizosphere constraints to leaf water supply across soil texture gradients provides insight into processes controlling plant water balance and larger scale hydrologic processes.

Effects of soil temperature on ecophysiological traits in seedlings of four boreal tree species

One-year-old seedlings of black spruce (Picea Mariana (Mill.) B.S.P.), white spruce (Picea glauca (Moench) Voss.), jack pine (Pinus banksiana Lamb.) and aspen (Populus tremuloides Michx.) were exposed to 5, 10, 15, 20, 25, 30 and 35 °C soil temperatures for 4 months. The rate of net photosynthesis (A), stomatal conductance, mid-day xylem water potential, the internal to ambient CO2 concentration ratio (Ci/Ca), and specific leaf area (SLA) were evaluated 3 months after the initiation of the treatments. The responses of the above variables generally showed a bell-shaped curve except the Ci/Ca ratio. The relationships between soil temperature and the ecophysiological variables (except Ci/Ca) were modeled using third-order polynomials. The models suggest that jack pine generally had the highest optimal soil temperature among the four species, followed sequentially by black spruce, trembling aspen and white spruce. Aspen was generally more sensitive to low soil temperatures than the conifers while black spruce was more sensitive to high soil temperatures than other species. Jack pine and trembling aspen generally showed different response patterns than black and white spruce. The photosynthesis in aspen and jack pine was progressively less limited by stomatal conductance (relative to mesophyll limitation) as soil temperature increased from 5 to 35 °C whereas in the spruces, stomatal conductance was the least limiting to photosynthesis at moderate soil temperatures (10–15 °C for white spruce, 15–20 °C for black spruce). The xylem water potential of jack pine and aspen was more sensitive to low soil temperatures while that of the spruces was more sensitive to high soil temperatures. The specific leaf area of jack pine and aspen showed large variations with changes in soil temperature while that of the spruces was relatively constant throughout the range of soil temperatures. Most of the conifer seedlings in the 35 °C soil temperature treatment died at the end of the experiment while all aspen seedlings survived.

Effects of soil temperature on ecophysiological traits in seedlings of four boreal tree species

One-year-old seedlings of black spruce ( Picea Mariana (Mill.) B.S.P.), white spruce ( Picea glauca (Moench) Voss.), jack pine ( Pinus banksiana Lamb.) and aspen ( Populus tremuloides Michx.) were exposed to 5, 10, 15, 20, 25, 30 and 35 °C soil temperatures for 4 months. The rate of net photosynthesis ( A), stomatal conductance, mid-day xylem water potential, the internal to ambient CO 2 concentration ratio ( C i/ C a), and specific leaf area (SLA) were evaluated 3 months after the initiation of the treatments. The responses of the above variables generally showed a bell-shaped curve except the C i/ C a ratio. The relationships between soil temperature and the ecophysiological variables (except C i/ C a) were modeled using third-order polynomials. The models suggest that jack pine generally had the highest optimal soil temperature among the four species, followed sequentially by black spruce, trembling aspen and white spruce. Aspen was generally more sensitive to low soil temperatures than the conifers while black spruce was more sensitive to high soil temperatures than other species. Jack pine and trembling aspen generally showed different response patterns than black and white spruce. The photosynthesis in aspen and jack pine was progressively less limited by stomatal conductance (relative to mesophyll limitation) as soil temperature increased from 5 to 35 °C whereas in the spruces, stomatal conductance was the least limiting to photosynthesis at moderate soil temperatures (10–15 °C for white spruce, 15–20 °C for black spruce). The xylem water potential of jack pine and aspen was more sensitive to low soil temperatures while that of the spruces was more sensitive to high soil temperatures. The specific leaf area of jack pine and aspen showed large variations with changes in soil temperature while that of the spruces was relatively constant throughout the range of soil temperatures. Most of the conifer seedlings in the 35 °C soil temperature treatment died at the end of the experiment while all aspen seedlings survived.

Patterns of tree dieback in Queensland, Australia: the importance of drought stress and the role of resistance to cavitation.

During the extreme 1992-1997 El Niño drought event, widespread stem mortality, or tree "dieback", of both mature and juvenile eucalypts occurred within the tropical savannas of northeast Australia. Most of the dieback occurred in individuals of the ironbark species complex ( Eucalyptus crebra- E. xanthoclada) while individuals of the bloodwood species Corymbia erythrophloia, exhibited significantly less stem mortality. Indicative of greater water stress, predawn and midday xylem water potentials of ironbark adults and saplings were significantly more negative than predawn values of bloodwoods. The very negative xylem water potentials in ironbarks suggest that stem mortality in both adult and juvenile ironbarks results from drought-induced embolism and that ironbarks perhaps have a shallower and less extensive root system than bloodwoods. Although predawn and midday water potentials for ironbark adults and saplings were similar, a census of mature and juvenile ironbark trees indicated that mortality was higher in adult trees. Cavitation vulnerability curves indicated that ironbark saplings may be better buffered against cavitation than adult trees. If they possess smaller root systems, saplings are more likely than adults to experience low xylem water potentials, even in non-drought years. Xylem conduits produced in adult trees during periods of normal rainfall, although perhaps more efficient in water conduction, may be more vulnerable to cavitation during infrequent severe droughts.

Yield and quality of two rainfed olive cultivars following shifting to irrigation

SummarySix year old ‘Frantoio’ and ‘Leccino’ olive plants were subjected to different water regimes for three years to assess yield and quality performance in response to the onset of irrigation. Irrigated plots received 33, 66 and 100% of crop evapotranspiration rate (ETc), accounting for 173, 212 and 278.mm, in 1999, 2000 and 2001 respectively – while no water was applied to treatment 0. Little rain occurred throughout the summer of 2000 and 2001 seasons and mean air temperature was in both years higher than in 1999. Midday xylem water potential of non-irrigated plants was only slightly decreased, however. Stem diameter and canopy volume of ‘Frantoio’ were enhanced by irrigation, while ‘Leccino’ showed a response only in terms of the latter variable. The response of both vegetative and reproductive variables grouped in two classes, with the rain-fed control not different from 33 and treatment 66 and 100 being almost identical. Yield to water supply relationship was curvilinear in the first year, with little yield increase in response to 100% ETc. In 2000, a non-bearing year, yields were lower and the trends were linear, with a gentle slope. In 2001, much higher yield were achieved overall and ‘Frantoio’ still responded in a linear fashion while ‘Leccino’ reached a plateau under 66. Water use efficiency reached top values in excess of 4.kg l–1 in 2001 featuring a typical decreasing trend from rainfed to 100 for both cultivars. Irrigation efficiency peaked at the level of 66 for ‘Frantoio’ in all years and for ‘Leccino’ in 2001. The latter however was more efficient under 33 ETc during the first two years. A complete replacement of water loss by plant is to be recommended only in situations of unrestricted water supplies, and ‘Leccino’ should be preferred when water is costly or scarce. Oil quality was little affected and only total polyphenolic content was modified by irrigation, to an extent not capable of influencing oil storage capacity.

Field assessment of Douglas-fir somatic and zygotic seedlings with respect to gas exchange, water relations, and frost hardiness

Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) zygotic seedlings and seedlings produced through somatic embryogenesis were grown in a field test on southern Vancouver Island, British Columbia. The two stock types were compared in a number of adaptive attributes evaluated during two growing seasons (1999 and 2000). The attributes were related to gas exchange, water relations, phenology, and fall frost hardiness. In both years, somatic and zygotic seedlings had similar rates of net photosynthesis in optimum and reduced light conditions, similar mesophyll conductance, and dark respiration rates. Small differences (P [Formula: see text] 0.05) were found for water relation attributes measured on irrigated plants: intrinsic water use efficiency (WUEi), transpiration (E), stomatal conductance (gwv) and midday xylem water potential (Ψ). Somatic seedlings had marginally higher E and gwv and lower Ψ in 2000 and lower WUEi in 1999 and 2000. Zygotic seedlings had higher WUEi because of their lower gwv while maintaining the same rates of net photosynthesis as somatic seedlings. There were no differences between somatic and zygotic seedlings in frost hardiness throughout the fall. Zygotic and somatic seedlings had similar timing of spring bud break pointing to a comparable level of spring frost hardiness in both stock types. Findings from this study indicate that somatic and zygotic seedlings had a similar pattern of physiological performance throughout 2 years of assessment.

Soil water content and water relations in planted and naturally regenerated Pinus halepensis Mill. seedlings during the first year in semiarid conditions

The capacity of Aleppo pine (Pinus halpensis Mill.) seedlings to overcome the planting shock in dry conditions was assessed by firstly studying the survival and water status during the first year after planting in relation to soil water content. In spite of receiving only 177 mm rainfall during the year studied, survival of planted Aleppo pine was very high (88.5%). Soil water during summer months (after receiving 67 mm rainfall in winter and spring) was only available at 30–60 cm depth, with tension values of −1.1 and −1.3 MPa in July and August respectively; in these conditions, July predawn xylem water potential measured was −2.5 MPa, and midday potential was −3.6 MPa. According to different authors, these values don't jeopardize the survival of Aleppo pine. In addition, acclimation of outplanted seedlings to environmental conditions was followed by comparing their water relations with those of naturally regenerated seedlings on the site. Predawn and midday xylem water potential showed differences in favour of outplanted seedlings since June, indicating an adjustment to this dry site. Compared to naturally regenerated trees, nursery grown stock of the same age before field planting had much more biomass and higher N and P concentrations and contents; although shoot:root balance and Dickson quality index were not significantly different. Finally, planted seedlings acclimation level during first year was also evaluated by Transplant Stress Index, which value (−0.1278) indicated a slight planting impact.

TRUNK DIAMETER VARIATIONS IN RELATION TO WALNUT WATER POTENTIAL

Diurnal changes in trunk diameter depend mostly upon variations in water content. The admitted interpretation of this process is based on a reverse flux of water from the trunk in response to the transpirational pull from the foliage. A linear relation between water content and water potential is assumed. The aim of this study is to calculate xylem water potential using trunk diameter changes. Measurements of stem diameter variations (with LVDT sensors) and xylem water potential (with pressure chamber on covered leaves) were made in Tarragona (Spain) on irrigated and non-irrigated walnut trees in an orchard. The relation between these two variables during the day is loop-shaped. A simple model is presented, assuming the existence of a water reservoir (representing elastic tissues) and thus the loop-shaped curve. After calibration for one or few days, the variations of xylem water potential with a fine time scale (few minutes) and for a long period could be monitored from the trunk diameter measurements. Such predicted values, especially predawn and midday xylem water potential, could be very useful for irrigation scheduling. Moreover, this kinetics could improve the understanding of tree water physiology.

THE WATER RELATIONS OF MATURE `SUNDROP' APRICOT TREES IN RESPONSE TO DIFFERENT VIGOUR CONTROL TECHNIQUES

In the absence of dwarfing rootstocks for apricot, techniques which reduce vegetative growth are important in the orchard management system. A number of techniques may be employed to moderate vegetative vigour of fruit trees. In the orchard in the humid climate of Palmerston North, New Zealand, five-year-old vigorousSundrop' apricot trees on `Golden Queen' peach seedlings trained on Tatura trellis at 2000 tree ha -1 were used. The treatments were regulated deficit irrigation (RDI), dormant root-pruning, soil applied Paclobutrazol (PBZ) and untreated control. The objectives were to examine the effects of these treatments on the internal water relations of apricot. Also, to determine whether the mechanism of response to root pruning appeared similar to the mechanism of response to water stress. Throughout the season treatment effects on vegetative, reproductive growth and leaf physiology of the trees were monitored. Predawn and midday xylem water potential (Ψ xylem) in root pruned and water stressed trees were lower than in control trees, but Cultar treatments did not significantly affect this. PBZ treated trees had the same water status as controls. Root-pruned trees developed an increased internal water deficit in the leaves and fruits especially at the time of highest water demand during fruit stage III.

Facilitative effects of a sand dune shrub on species growing beneath the shrub canopy.

Only recently has the importance of positive interactions among plant species in structuring natural communities been supported by experimental evidence. Most studies have focused on interactions between a pair of species at a single life-history stage. In this study positive interactions between a woody nitrogen-fixing shrub (Myrica pensylvanica) and two herbaceous sand dune species (Solidago sempervirens, Ammophila breviligulata) which frequently grow beneath shrub canopies are examined throughout the life cycles of the herbaceous species. Comparisons of S. sempervirens and A. breviligulata growing beneath and outside M. pensylvanica shrubs show that plants growing in association with shrubs are larger, are more likely to flower, produce greater numbers of flowers and seeds, have higher midday xylem water potentials, have higher tissue nitrogen concentrations, and have higher photosynthetic efficiencies. Measurements of environmental conditions show that areas beneath shrubs are more shaded, have lower soil temperatures, and have higher soil nitrogen levels. The results from experimental manipulations designed to test the effects of Myrica shrubs on understory species suggest that the observed differences in plant performance are strongly influenced by canopy shading and soil nutrient enrichment associated with the shrubs. The results demonstrate that M. pensylvanica facilitates growth, reproduction, and recruitment of S. sempervirens and A. breviligulata growing beneath it. This study, one of the few to examine positive interactions at different life-history stages, supports previous predictions that positive interactions may be particularly important in plant communities characterized by physiologically stressful conditions.

Effects of Restoration Thinning on Presettlement Pinus ponderosa in Northern Arizona

AbstractIn the 100 years following the arrival of Euro‐American settlers in northern Arizona, Pinus ponderosa (ponderosa pine) forests changed from open, low‐density stands to closed, high‐density stands. The increase in tree density has been detrimental to the vigor of old‐growth trees that established before settlement (presettlement trees). In this study, we examined whether the vigor of presettlement trees could be improved by restoring the original stand structure by thinning the ponderosa pines that established after settlement (postsettlement trees). The restoration treatment caused the following changes in the presettlement trees and their environment in the first year following thinning: an increase in volumetric soil water content between May and August, an increase in predawn xylem water potential in July and August, a decrease in midday xylem water potential in June and August, an increase in net photosynthetic rate in August, an increase in foliar nitrogen concentration in July and August, and an increase in bud and needle size. The results show that the thinning restoration treatment improved the condition of presettlement ponderosa pines by increasing canopy growth and the uptake of water, nitrogen, and carbon.

The effects of acclimation to sunlight on the xylem vulnerability to embolism in Fagus sylvatica L.

We assessed the effects of irradiance received during growth on the vulnerability of Fagus sylvatica L. xylem vessels to water‐stress‐induced embolism. The measurements were conducted on (1) potted saplings acclimated for 2 years under 100% and 12% incident global radiation and (2) branches collected from sun‐exposed and shaded sides of adult trees. Both experiments yielded similar results. Light‐acclimated shoots were less vulnerable to embolism. Xylem water potential levels producing 50% loss of hydraulic conductivity were lower in sun‐exposed branches and seedlings than in shade‐grown ones (–3·0 versus –2·3 MPa on average). The differences in vulnerability were not correlated with differences in xylem hydraulic conductivity nor vessel diameter. Resistance to cavitation was correlated with transpiration rates, midday xylem and leaf water potentials in adult trees. We concluded that vulnerability to cavitation in Fagus sylvatica may acclimate to contrasting ambient light conditions.

Atmospheric CO 2 enrichment and soil N fertility effects on juvenile ponderosa pine: Growth, ectomycorrhizal development, and xylem water potential

Interactive effects of elevated atmospheric CO 2 and soil N fertility on above- and below-ground growth, mycorrhizal colonization, and water relations of juvenile ponderosa pine ( Pinus ponderosa Dougl. ex Laws.) were investigated. One-year-old seedlings were planted in undisturbed field soil within open-top chambers which permitted creation of atmospheres with 700 μl l −1, 525 μl l −1, or ambient CO 2 concentrations. High and medium soil N treatments were imposed by incorporating sufficient (NH 4) 2SO 4 to increase total N by 200 μg g −1 and 100 μg g −1, respectively, while unamended soil, which had a total N concentration of approximately 900 μg g −1, constituted the low N treatment. Following each of two consecutive field growing seasons, whole seedlings of every combination of CO 2 and N treatment were harvested to permit assessment of shoot and root growth and quantification of ectomycorrhizal development. Late in the second growing season, a simulated drought episode was imposed by withholding irrigation during which predawn and midday xylem water potential and soil water potential were measured. The initial harvest revealed that coarse and fine root weights were increased by CO 2 enrichment during the first growing season. This result was most apparent in the 525 μl l −1 CO 2 treatment and high soil N, which produced the greatest root volume as well. Shoot/root ratio decreased with increasing CO 2 at the first harvest. After two growing seasons, elevated CO 2 increased seedling diameter, shoot and root volume, and shoot and coarse root weight, again most prominently in high N. Unlike the initial results, however, stimulation of seedling growth by the 700 μl l −1 CO 2 atmosphere exceeded that in 525 μl l −1 CO 2 after two growing seasons, and shoot/root ratio was unaffected by either CO 2 or N. At both harvests, seedlings grown in the enriched atmospheres generally had higher mycorrhizal counts and greater percentages of colonized root length, but differences among treatments in ectomycorrhizal development were nonsignficant regardless of quantification method. During the imposed drought episode, xylem water potential of seedlings grown in elevated CO 2 descended below that of seedlings grown in the ambient atmosphere as soil water potential decreased, most notably in the predawn measurements. These results suggest that CO 2 enrichment stimulates shoot and root growth of juvenile ponderosa pine under field conditions, a response somewhat dependent on soil N availability. However, below-ground growth is not increased proportionally more than that above ground, which may predispose this species to greater stress when soil water is limited.

Physiological Responses of Switchgrass (Panicum virgatum L.) to Organic and Inorganic Amended Heavy-Metal Contaminated Chat Tailings

Study plots established at the Galena subsite of the Cherokee County Superfund Site in southeastern Kansas by the U.S. Bureau of Mines in 1990 were examined during the summer of 1996 to determine whether physiological criteria could be used to determine suitability of switchgrass for remediation of heavy-metal contaminated substrates. Switchgrass was chosen because it was the most frequently encountered species on these plots. Treatment plots included a treatment control, an organic residue treatment of 89.6 Mg ha-1 composted cattle manure, and two inorganic fertilizer treatments recommended for either native grass or grass/legume mixtures. Plant response variables were photosynthetic rate, leaf conductance to water vapor, internal concentration of carbon dioxide in leaves, foliar transpiration rate, leaf water-use efficiency, predawn leaf xylem water potential, and midday leaf xylem water potential. Predawn and midday xylem water potentials were higher for grass/legume inorganic treatment than for the other inorganic treatments. Leaf conductances were lower for organically treated plots than those plots not organically amended and both photosynthesis and transpiration were lower for organically treated plots. Leaf conductances and transpiration were higher for grass/legume treated plots than for plots lacking inorganic treatment. Water-use-efficiency was higher for native grass-treated plots than for other inorganic treatments. Grass/legume inorganic treatment in absence of organic treatment increased predawn and midday xylem water potential, leaf conductance, photosynthesis, and transpiration. Organic amendment in absence of inorganic amendment increased predawn and midday xylem water potential.

Elevated atmospheric CO2 and soil N fertility effects on growth, mycorrhizal colonization, and xylem water potential of juvenile ponderosa pine in a field soil

Interactive effects of atmospheric CO2 enrichment and soil N fertility on above- and below-ground development and water relations of juvenile ponderosa pine (Pinus ponderosa Dougl. ex Laws.) were examined. Open-top field chambers permitted creation of atmospheres with 700 µL L-1, 525 µL L-1, or ambient CO2 concentrations. Seedlings were reared from seed in field soil with a total N concentration of approximately 900 µg g-1 or in soil amended with sufficient (NH4)2SO4 to increase total N by 100 µg g-1 or 200 µg g-1. The 525 µL L-1 CO2 treatment within the intermediate N treatment was excluded from the study. Following each of three consecutive growing seasons, whole seedlings of each combination of CO2 and N treatment were harvested to permit assessment of shoot and root growth and ectomycorrhizal colonization. In the second and third growing seasons, drought cycles were imposed by withholding irrigation during which predawn and midday xylem water potential and soil water potential were measured. The first harvest revealed that shoot weight and coarse and fine root weights were increased by growth in elevated CO2. Shoot and root volume and weights were increased by CO2 enrichment at the second harvest, but growth stimulation by the 525 µL L-1 CO2 concentration exceeded that in 700 µL L-1 CO2 during the first two growing seasons. At the third harvest, above- and below-ground growth increases were largely confined to the 700 µL L-1 CO2 treatment, an effect accentuated by high soil N but evident in all N treatments. Ectomycorrhizal formation was reduced by elevated CO2 after one growing season, but thereafter was not significantly affected by CO2 and was unaffected by soil N throughout the study. Results of the xylem water potential measurements were variable, as water potentials in seedlings grown in elevated CO2 were intermittently higher on some measurement days but lower on others than that of seedlings grown in the ambient atmosphere. These results suggest that elevated CO2 exerts stimulatory effects on shoot and root growth of juvenile ponderosa pine under field conditions which are somewhat dependent on N availability, but that temporal variation may periodically result in a greater response to a moderate rise in atmospheric CO2 than to a doubling of the current ambient concentration.

Root-zone Stress Effects on Water Relations and Growth of Silver, Red, and Freeman Maples

Freeman maples (Acer ×freemanii E. Murray) are suspected to be more resistant to environmental stress than red maples (A. rubrum L.) because the lineage of Freeman maple includes silver maple (A. saccharinum L.). Little is known, however, about stress resistance of silver maple, and few data from direct comparisons of red and Freeman maples are available. Our objectives were to determine effects of root-zone heat on silver maples from northern and southern provenances, and to compare red and Freeman maple cultivars for resistance to rootzone heat stress and drought. There were no provenance-by-temperature interactions when silver maples from 33.3°N (Mississippi) and 44.4°N (Minnesota) latitude were grown with root zones at 29 and 35°C. Plants from 44.4°N latitude had 36% higher fresh mass, 43% more leaf surface area, and 35% and 59% higher, respectively, root and shoot dry masses than plants from 33.3°N latitude. Midday xylem water potential was 68% more negative for plants at 35°C than for plants at 29°C, and transpiration rate was 129% less for plants with root zones at 35°C than for those with root zones at 29°C. During preliminary work with Autumn Flame and Franksred red maple and Indian Summer and Jeffersred Freeman maples, rooted cuttings were grown in 25 and 37°C root zones under both drought and nondrought conditions. Reductions in growth at 37°C were similar for all cultivars. Results of this work could influence development, marketing, and use of Freeman maples.

Diel and Seasonal Patterns of Leaf Gas Exchange and Xylem Water Potentials of Different-Sized Prunus serotina Ehrh. Trees

Abstract Leaf gas exchange and xylem water potentials were measured in the field throughout the 1994 growing season on leaves in the upper crown of seedling, sapling, and forest canopy black cherry trees (Prunus serotina Ehrh.) in northcentral Pennsylvania. Rates of gas exchange and xylem water potentials generally decreased with increasing tree size. Rates of dark respiration also decreased with increasing tree size. Differences among tree size classes were consistent throughout the growing season for xylem water potentials, but not for leaf gas exchange measurements. In May and June, seedling net photosynthesis and stomatal conductance were approximately 2 x that of larger trees, but their values tended to be similar to or lower than those of larger trees in July and August. Averaged over the entire season, seedlings had higher leaf gas exchange rates than saplings, which had higher rates than canopy trees. Regardless of tree size, stomatal conductance and net photosynthetic rates reached a maximum near mid to late morning. Stomatal conductance and net photosynthesis decreased steadily during the afternoon for larger trees, but seedling rates remained high until late afternoon. Seedlings consistently had the highest predawn and midday xylem water potentials and leaf-to-air water vapor pressure deficits, while canopy trees had the lowest. The results of this study indicate that tree size is an important factor influencing foliar gas exchange and water relations. For. Sci. 42(3):359-365.

Monosoonal precipitation responses of shrubs in a cold desert community on the Colorado Plateau.

South-eastern Utah forms a northern border for the region currently influenced by the Arizona monosoonal system, which feeds moisture and summer precipitation into western North America. One major consequence predicted by global climate change scenarios is an intensification of monosoonal (summer) precipitation in the aridland areas of the western United States. We examined the capacity of dominant perennial shrubs in a Colorado Plateau cold desert ecosystem of southern Utah, United States, to use summer moisture inputs. We simulated increases of 25 and 50 mm summer rain events on Atriplex canescens, Artemisia filifolia, Chrysothamnus nauseosus, Coleogyne ramosissima, and Vanclevea stylosa, in July and September with an isotopically enriched water (enriched in deuterium but not 18O). The uptake of this artificial water source was estimated by analyzing hydrogen and oxygen isotope ratios of stem water. The predawn and midday xylem water potentials and foliar carbon isotope discrimination were measured to estimate changes in water status and water-use efficiency. At. canescens and Ch. nauseosus showed little if any uptake of summer rains in either July or September. The predawn and midday xylem water potentials for control and treatment plants of these two species were not significantly different from each other. For A. filifolia and V. stylosa, up to 50% of xylem water was from the simulated summer rain, but the predawn and midday xylem water potentials were not significantly affected by the additional summer moisture input. In contrast, C. ramosissima showed significant uptake of the simulated summer rain (>50% of xylem water was from the artificial summer rain) and an increase in both predawn and midday water potentials. The percent uptake of simulated summer rain was greater when those rains were applied in September than in July, implying that high soil temperature in midsummer may in some way inhibit water uptake. Foliar carbon isotope discrimination increased significantly in the three shrubs taking up simulated summer rain, but pre-treatment differences in the absolute discrimination values were maintained among species. The ecological implications of our results are discussed in terms of the dynamics of this desert community in response to changes in the frequency and dependability of summer rains that might be associated with a northward shift in the Arizona monsoon boundary.

Genetic variation of ecophysiological traits in red alder (Alnusrubra Bong.)

We examined the genetic variation of ecophysiological traits within and among 40 red alder (Alnusrubra Bong.) provenances (two families per provenance) in a common-garden experiment in the summer of 1993. The provenances were representative of the entire species range in British Columbia, Canada. We found significant genetic variation among provenances (P &lt; 0.001) in photosynthetic rate (A), mesophyll conductance (gm), transpiration rate (E), stomatal conductance (gsw), stomatal sensitivity to water vapour pressure deficit (SENSVPD), intercellular to ambient CO2 concentration ratio (Ci/Ca), and midday xylem water potential (ψ). Photosynthetic water-use efficiency, however, did not differ significantly among provenances. There were no significant differences between families within provenance for any of these variables. A weak but significant geographic trend was detected in ecophysiological traits: ψ, A, gm, and E increased, and SENSVPD decreased, from southeast to northwest. Photosynthetic rate, E, gm, gsw and ψ were positively related to each other, but negatively correlated with SENSVPD. Ci/Ca was negatively correlated with gsw. These correlations indicate that red alder might have undergone genetic differentiation in drought resistance.