Showing papers in "Tree Physiology in 1994"
TL;DR: The LAI-2000 plant canopy analyzer was tested at six experimental plots of Scots pine in central Sweden at peak leaf area in August and after litterfall in October 1990 and it was shown that if shoots, instead of individual needles, are randomly distributed in the canopy, L(Li-Cor) corresponds to L multiplied by a factor (beta) characterizing the mutual shading of needles on the shoot.
Abstract: The LAI-2000 plant canopy analyzer (Li-Cor, Inc., Lincoln, NE) was tested at six experimental plots of Scots pine (Pinus sylvestris L.) in central Sweden at peak leaf area in August and after litterfall in October 1990. An independent estimate of leaf area index for August 1990 was obtained based on an empirically derived regression of needle area on stem sapwood area, and the decrease in leaf area between the two measurements was estimated from measurements of litterfall. A strong linear relationship was found between estimates by the LAI-2000 (L(Li-Cor)) and the indirect estimates of leaf area index (taken as half of total surface area) (L). The finding that L(Li-Cor) was considerably smaller than L was explained theoretically. It was shown that if shoots, instead of individual needles, are randomly distributed in the canopy, L(Li-Cor) corresponds to L multiplied by a factor (beta) characterizing the mutual shading of needles on the shoot. The shading factor, beta, was equal to the ratio of spherically projected shoot area to spherically projected needle area, where the spherically projected area is defined as the average projection (silhouette) area taken over all directions in space. The quantity betaL was defined as the shoot silhouette area index (SSAI), and an equation for the relationship between SSAI and the mean silhouette to total area ratio (mean STAR) of shoots was derived. Measured values of mean STAR for Scots pine indicated that L(Li-Cor) corresponds to SSAI rather than L. However, the decrease in leaf area index due to litterfall occurring between August and October was only partly detected by the LAI-2000, possibly because SSAI did not change to the same degree as L, i.e., there was an increase in the factor beta. This hypothesis is supported by data showing a large increase in mean STAR with shoot age.
240 citations
TL;DR: The fit between model predictions and field data supports the initial hypothesis that plants function as collections of semiautonomous, interacting organs that compete for resources based on their growth potentials.
Abstract: The hypothesis that carbohydrate partitioning is driven by competition among individual plant organs, based on each organ's growth potential, was used to develop a simulation model of the carbon supply and demand for reproductive and vegetative growth in peach trees. In the model, photosynthetic carbon assimilation is simulated using daily minimum and maximum temperature and solar radiation as inputs. Carbohydrate is first partitioned to maintenance respiration, then to leaves, fruits, stems and branches, then to the trunk. Root activity is supported by residual carbohydrate after aboveground growth. Verification of the model was carried out with field data from trees that were thinned at different times. In general, the model predictions corresponded to field data for fruit and vegetative growth. The model predicted that resource availability limited fruit and stem growth during two periods of fruit growth, periods that had been identified in earlier experimental studies as resource-limited growth periods. The model also predicted that there were two periods of high carbohydrate availability for root activity. The fit between model predictions and field data supports the initial hypothesis that plants function as collections of semiautonomous, interacting organs that compete for resources based on their growth potentials.
224 citations
TL;DR: Provenance tests of forest trees, which were originally intended to identify suitable seed sources for planting at different locations, provide valuable data for assessing the response of populations to environmental change, and can be used to predict the effects of climatic change on growth and survival.
Abstract: Provenance tests of forest trees, which were originally intended to identify suitable seed sources for planting at different locations, provide valuable data for assessing the response of populations to environmental change. Environmental differences between the location of origin and the planting (test) site have been calculated by principal component analysis and termed ecological distance. Based on ecological distance values, the growth response of tree populations can be modeled as a function of the test site macroclimate. These models can then be used to predict the effects of climatic change on growth and survival. The growth response model predicts that increasing annual mean temperatures will result in accelerated growth if precipitation is sufficient, but only within the limits characteristic of the species. At the southern limits of distribution, growth and competitive ability of the species will decline, leading to successional changes.
219 citations
TL;DR: Vulnerability of xylem to loss of hydraulic conductivity caused by drought-induced cavitation was determined for three riparian cottonwood species in Lethbridge, Alberta, making them the three most vulnerable tree species reported so far in North America.
Abstract: Vulnerability of xylem to loss of hydraulic conductivity caused by drought-induced cavitation was determined for three riparian cottonwood species in Lethbridge, Alberta: Populus deltoides Bartr., P. balsamifera L., and P. angustifolia James. These species suffered 50% loss of hydraulic conductivity in one-year-old stem segments when xylem pressure potential fell to -0.7 MPa for P. deltoides and -1.7 MPa for P. balsamifera and P. angustifolia, making them the three most vulnerable tree species reported so far in North America. The possible contribution of drought-induced xylem dysfunction to the decline of riparian ecosystems in dammed rivers is discussed.
189 citations
TL;DR: It was concluded from dye colorations, thermograms and axial profiles of sap flow and heat pulse velocity that, in intact trunks, most of the flow occurred in the current-year ring, where early-wood vessels in the outermost ring were still functional.
Abstract: Axial water flow in the trunks of mature oak trees (Quercus petraea (Matt.) Liebl. and Q. robur L.) was studied by four independent techniques: water absorption from a cut trunk, sap flowmeters, heat pulse velocity (HPV) and thermoimaging. Estimation of the total water flow with sap flowmeters, HPV and water absorption yielded comparable results. We concluded from dye colorations, thermograms and axial profiles of sap flow and heat pulse velocity that, in intact trunks, most of the flow occurred in the current-year ring, where early-wood vessels in the outermost ring were still functional. Nevertheless, there was significant flow in the older rings of the xylem. Total water flow through the trunk was only slightly reduced when air embolisms were artificially induced in early-wood vessels, probably because there was little change in hydraulic conductance in the root-leaf sap pathway. Embolization of the current-year vessels reactivated transport in the older rings.
165 citations
TL;DR: It is demonstrated that current photosynthate was the primary source of C for root growth and maintenance during the growing season and the suitability of the approach for studying long-term C fluxes is discussed.
Abstract: We studied whole-tree C allocation with special emphasis on the quantification of C allocation to roots and root respiration. To document seasonal patterns of C allocation, 2-year-old hybrid poplar trees greater than 3 m tall were labeled with (14)CO(2) in a large Plexiglas chamber in the field, in July and September. Climate and CO(2) concentration were controlled to track ambient conditions during labeling. Individual tree canopy CO(2) assimilation averaged 3.8 micromol CO(2) m(-2) s(-1) (12.9 g C day(-1) tree(-1)) in July and 6.2 micromol CO(2) m(-2) s(-1) (9.8 g C day(-1) tree(-1)) in September. Aboveground dark respiration was 12% of net daytime C fixation in July and 15% in September. Specific activity of root-soil respiration peaked 2 days after labeling and stabilized to less than 5% of maximum 2 weeks later. Low specific activity of root-soil respiration and a labeled pool of root C demonstrated that current photosynthate was the primary source of C for root growth and maintenance during the growing season. Root respiration averaged 20% of total soil respiration in both July and September based on the proportion of labeled C respired to labeled C fixed. In July, 80% of the recovered (14)C was found above ground and closely resembled the weight distribution of the growing shoot. By September, 51% of the recovered (14)C was in the root system and closely resembled the weight distribution of different size classes of roots. The finding that the distribution of biomass and (14)C were similar verified that the C introduced during labeling followed normal seasonal translocation pathways. Results are compared to smaller scale labeling studies and the suitability of the approach for studying long-term C fluxes is discussed.
163 citations
TL;DR: An analytical solution for coupled leaf photosynthesis and stomatal conductance equations that is based on established biochemical and physiological theory is presented.
Abstract: Iterative solutions of coupled leaf photosynthesis and stomatal conductance equations sometimes yield bifurcated or chaotic solutions. An analytical solution for coupled leaf photosynthesis-stomatal conductance equations is preferred because an analytical model has specific and known roots, and partial derivatives can be taken to perform sensitivity analyses. I present an analytical solution for coupled leaf photosynthesis and stomatal conductance equations that are based on established biochemical and physiological theory.
158 citations
TL;DR: Water flux in a four-year-old stand of hybrid Populus during midsummer 1992 suggested that both stomatal conductance and leaf specific hydraulic conductivity (LSHC) were linked with the ability to exploit the light resource.
Abstract: We studied water flux in a four-year-old stand of hybrid Populus during midsummer 1992. Study trees ranged in height from 11.0 to 15.1 m and in diameter from 8.3 to 15.1 cm. The large-leafed Populus hybrid was relatively poorly coupled to the atmosphere. The average value of the stomatal decoupling coefficient, Omega, was 0.66, indicating that, on average, a 10% change in stomatal conductance would result in only a 3 to 4% change in transpiration. During the middle of the summer, the smallest study tree used between 20 and 26 kg of water per day, whereas the largest tree used between 39 and 51 kg day(-1). The maximum observed rate of stand water loss was 4.8 mm day(-1) in this Populus clone. Maximum rates of sap velocity within the xylem were as high as 12.5 m h(-1); measured rates for exposed sunlit branches approached 90% of this maximum. Within-canopy patterns of stomatal conductance generally reflected patterns of incident radiation. Stomatal conductance of foliage grown in shade, even when exposed to non-limiting light and water source conditions, did not increase appreciably. Patterns of stomatal conductance under limiting and non-limiting conditions suggested that both stomatal conductance and leaf specific hydraulic conductivity (LSHC) were linked with the ability to exploit the light resource.
149 citations
TL;DR: It is concluded that there is justification for cautious optimism about the prospects for improving salt tolerance in forest tree species and the physiological and genetic mechanisms controlling salt tolerance are discussed briefly.
Abstract: Three major themes related to the improvement of salt tolerance in forest tree species are examined. First, evidence demonstrating that substantial intraspecific variation in salt tolerance exists in many species is presented. This evidence is important because it suggests that efforts to improve salt tolerance through conventional plant breeding techniques are justified. Second, the physiological and genetic mechanisms controlling salt tolerance are discussed briefly. Although salt tolerance involves the integration of numerous physiological processes, there is considerable evidence that differences in the ability to exclude Na(+) and Cl(-) from leaves are the most important factors underlying intraspecific differences in tolerance. It is also becoming apparent that, although salt tolerance is a multigenic trait, major genes play an important role. Third, progress to date in improving salt tolerance of forest tree species is assessed. Compared with agricultural crops, relatively little progress has been made with either conventional or biotechnological methods, but field trials designed to test clones identified as salt tolerant in screening trials are underway now in several countries. We conclude that there is justification for cautious optimism about the prospects for improving salt tolerance in forest tree species.
149 citations
TL;DR: This study was undertaken to determine whether provenance tests can be used to predict tree response to rapid climate changes in situ, and predicted a loss of about 5 to 10% in height growth below that expected for a genetically adapted seed source.
Abstract: Provenance tests are often used to determine genetic responses of seed sources to transfer to different climates. This study was undertaken to determine whether provenance tests can be used to predict tree response to rapid climate changes in situ. Data from provenance tests of loblolly pines (Pinus taeda L.), Norway spruce (Picea abies L. Karst) and other southern pines (subsect. AUSTRALES Loud.) were interpreted using regression models to relate growth to temperature variables. Results of different plantings were combined by expressing growth as a percent deviation from the "local" source, and expressing temperature at the source as a deviation from that of the planting site. The results of the loblolly pine and Norway spruce models predicted a loss of about 5 to 10% in height growth below that expected for a genetically adapted seed source, if the average yearly temperature increases by 4 degrees C.
135 citations
TL;DR: The importance of genotypic and phenotypic variation as stress adaptations in temperate tree species among both distant and nearby sites of contrasting environmental conditions is indicated.
Abstract: Species that occupy large geographic ranges or a variety of habitats within a limited area deal with contrasting environmental conditions by genotypic and phenotypic variation. My students and I have studied these forms of ecophysiological variation in temperate tree species in eastern North America by means of a series of field and greenhouse experiments, including controlled studies with Cercis canadensis L., Fraxinus pennsylvanica Marsh., Acer rubrum L., Prunus serotina Ehrh. and Quercus rubra L., in relation to drought stress. These studies have included measurements of gas exchange, tissue water relations and leaf morphology, and have identified genotypic variation at the biome and individual community levels. Xeric genotypes generally had higher net photosynthesis and leaf conductance and lower osmotic and water potentials at incipient wilting than mesic genotypes during drought. Xeric genotypes also produced leaves with greater thickness, leaf mass per area and stomatal density and smaller area than the mesic genotypes, suggesting general coordination among leaf morphology, gas exchange and tissue water relations. Leaf phenotypic plasticity to different light environments occurred in virtually every study species, which represented a wide array of ecological tolerances. In a study of interactions of genotypes with environment, shade plants, but not sun plants, exhibited osmotic adjustment during drought and shade plants had smaller reductions in photosynthesis with decreasing leaf water potential. In that study, sun, but not shade, plants had significant genotypic differences in leaf structure, but with certain variables phenotypic variation exceeded genotype variation. Thus, genotypic variation was not expressed in all phenotypes, and phenotypes responded differentially to stress. Overall, these studies indicate the importance of genotypic and phenotypic variation as stress adaptations in temperate tree species among both distant and nearby sites of contrasting environmental conditions.
TL;DR: The effects of elevated CO(2) plus a 0, 2 or 4 degrees C climatic warming on the timing of bud burst and the subsequent risk of frost damage were assessed using a simulation model and meteorological data from three sites, Edinburgh, Braemar and Masset.
Abstract: Summary Effects of elevated COa, clone and plant nutrition on bud dormancy of Sitka spruce (Picea sitchensis (Bong.) Carr.) were examined. Sitka spruce seedlings were fumigated with ambient or elevated (ambient + 350 pmol mol-‘) concentrations of CO2 in open-top chambers for three growing seasons. In 1991 and 1992, elevated CO2 delayed bud burst in the spring and advanced bud set in the autumn. The effect of the open-top chamber on the thermal requirement for bud burst was greater than the effect of elevated CO2 (50 and 30 day degrees (Dd), respectively). In a second study, four clones of Sitka spruce taken from two provenances, at 43 and 54” N, were fumigated with ambient or elevated CO2. There was a large natural variation in the timing of bud burst and bud set among the clones. Elevated CO2 had no effect on bud dormancy of the Skidegate a clone, but it reduced the growing season of the North Bend b clone by 20 days. In a third study, Sitka spruce seedlings growing in ambient or elevated CO2, were supplied with one of three nutrient regimes, low (0.1 x potential), medium (0.5 x potential) or high (2.0 x potential), using a method and solution based on the Ingestad technique. Elevated CO2 did not affect bud dormancy in the high-nutrient treatment, but it reduced the growing season of plants in the low-nutrient treatment by 22 days. Increasing plant nutrient supply lengthened the growing season, plants flushed earlier in the spring and set bud later in the autumn. The effects of elevated CO2 plus a 0, 2 or 4 “C climatic warming on the timing of bud burst and the subsequent risk of frost damage were assessed using a simulation model and meteorological data from three sites, Edinburgh, Braemar and Masset. The model predicted that (i) doubling the CO2 concentration in the absence of climatic warming, will delay the onset of bud burst at all three sites, (ii) climatic warming in ambient CO2 will hasten bud burst and (iii) climatic warming in elevated CO2 will hasten bud burst at Edinburgh and Braemar but to a lesser extent than climatic warming alone. At Masset, a 4 “C warming was required to advance the date of bud burst of seedlings in the elevated CO2 treatment. At all three sites, elevated CO2 and climatic warming increased the mean daily temperature on the date of bud burst, thus reducing the risk of subsequent frost damage.
TL;DR: During periods of high evaporative demand, site-specific differences in the control of water loss led to more conservative water use by trees at the ridge top and, thus, to even greater drought avoidance in late summer.
Abstract: Intraspecific variations in the water relations and stomatal response of Quercus ilex L. were analyzed under field conditions by comparing trees at two locations within a Mediterranean watershed (l'Avic, Catalonia, NE Spain). Distinct environmental gradients exist between the two sites (referred to as ridge top at 975 m and valley bottom at 700 m) with greater soil depth for water storage, reduced radiation, reduced wind and higher water vapor pressure deficits at the valley bottom than at the ridge top. Osmotic adjustment and changes in tissue elasticiity did not significantly increase drought resistance in the trees studied. The leaf-to-air vapor pressure difference (Deltaw) threshold for inducing stomatal closure was higher at the ridge top (15.6 kPa MPa(-1) +/- 0.5 SE) than at the valley bottom (9.8 kPa MPa(-1) +/- 1.0 SE). However, increases in Deltaw beyond the threshold were followed by greater reductions in leaf conductance of trees at the ridge top than at the valley bottom. At both sites, maximum leaf conductance was related to predawn shoot water potential which, in turn, was related to watershed stream flow. The effects of water deficits during the dry summer of 1989 were more severe in trees at the valley bottom than at the ridge top. During periods of high evaporative demand, site-specific differences in the control of water loss led to more conservative water use by trees at the ridge top and, thus, to even greater drought avoidance (higher predawn water potentials) in late summer.
TL;DR: When the degree days before bud burst in the 1931 and 1978 Norway spruce experiments at Punkaharju were compared, it appeared that, in the older experiment, the populations had adapted to the environment at the new site as a result of selective thinning.
Abstract: To assess the long-term effects of the projected climatic change on Scots pine and Norway spruce in Finland, observations were made on the timing of bud burst in provenance experiments established in 1931-1932 and in 1978. Significant differences in the timing of bud burst were found between seed origins. The northernmost origins flushed earlier than origins from southern regions. However, no correlation was found between the effective temperature sum at which bud burst took place and the annual mean temperature sum at the original location, probably because the experiments included origins from southerly high-altitude sites. When the degree days before bud burst in the 1931 and 1978 Norway spruce experiments at Punkaharju were compared, it appeared that, in the older experiment, the populations had adapted to the environment at the new site as a result of selective thinning.
TL;DR: Giant sequoias seedlings are sensitive to atmospheric ozone until they are about 5 years old, and low conductance, high water use efficiency, and compact mesophyll all contribute to a natural ozone tolerance, or defense, or both, in foliage of older trees.
Abstract: Native stands of giant sequoia (Sequoiadendron giganteum Bucholz) are being exposed to relatively high concentrations of atmospheric ozone produced in urban and agricultural areas upwind. The expected change in environmental conditions over the next 100 years is likely to be unprecedented in the life span (about 2,500 years) of giant sequoia. We determined changes in physiological responses of three age classes of giant sequoia (current-year, 12-, and 125-year-old) to differing concentrations of ozone, and assessed age-related differences in sensitivity to pollutants by examining physiological changes (gas exchange, water use efficiency) across the life span of giant sequoia (current-year, 2-, 5-, 20-, 125-, and > 2,000-year-old trees). The CO(2) exchange rate (CER) was greater in current-year (12.1 micro mol CO(2) m(-2) s(-1)) and 2-year-old seedlings (4.8 micro mol CO(2) m(-2) s(-1)) than in all older trees (3.0 micro mol CO(2) m(-2) s(-1), averaged across the four older age classes). Dark respiration was highest for current-year seedlings (-6.5 +/- 0.7 micro mol CO(2) m(-2) s(-1)) and was increased twofold in symptomatic individuals exposed to elevated ozone concentrations. Stomatal conductance (g(s)) was greater in current-year (355 mmol H(2)O m(-2) s(-1)) and 2-year-old seedlings (200 mmol H(2)O m(-2) s(-1)) than in all older trees (50 mmol H(2)O m(-2) s(-1)), indicating that the ozone concentration in substomatal cavities is higher in young seedlings than in trees. Significant changes in water use efficiency, as indicated by C(i)/C(a), occurred in trees between ages 5 and 20 years. We conclude that giant sequoias seedlings are sensitive to atmospheric ozone until they are about 5 years old. Low conductance, high water use efficiency, and compact mesophyll all contribute to a natural ozone tolerance, or defense, or both, in foliage of older trees.
TL;DR: It was found that the aspect of exposure and branch length accounted for up to 6‰ δ 13 C difference within the foliage of individual trees of Pinus radiata D. Don, and relative branch hydraulic conductivity was much higher in short branches than in long branches.
Abstract: Although herbaceous species generally show little within plant variation in delta(13)C, trees show large spatial and temporal differences. We found that the aspect of exposure and branch length accounted for up to 6 per thousand delta(13)C difference within the foliage of individual trees of Pinus radiata D. Don. The foliage on branches 0.5 m in length was as much as 4 per thousand more depleted in (13)C than foliage on 10-m long branches, and an additional 2 per thousand more depleted on the shaded side than on the exposed side. We confirmed that on clear days, relative branch hydraulic conductivity, defined as the ratio of transpiration to the water potential gradient, was much higher in short branches than in long branches. Stomatal conductance remained high in foliage on short branches during the day, whereas it declined progressively in long-branch foliage under similar conditions. These differences were sufficient to explain the observed variation in delta(13)C in foliage on long and short branches.
TL;DR: The results indicate a role for ABA in maintaining dormancy of the terminal buds of short shoots and emphasize the relationship between tissue water status and ABA concentration.
Abstract: Annual cycles of change in bud morphology, bud burst ability, abscisic acid (ABA) concentration, and starch and water content were studied in mid-crown terminal buds of short shoots and underground basal buds of Betula pubescens Ehrh. In particular, we investigated the roles of ABA and bud water content in the regulation of bud growth. Basal buds differed morphologically from terminal buds of short shoots in that their leaf initials did not develop into embryonic foliage leaves and their total size did not increase significantly during summer. Bud burst ability, measured by forcing detached short shoots and stumps under controlled conditions, was maintained in the basal buds throughout the year, whereas the terminal buds of short shoots remained dormant until October, thereafter their bud burst ability increased gradually and reached a maximum in March-April. The ABA concentration of the basal buds was relatively constant throughout the sampling period (1-3 micro g g(DW) (-1)), whereas that of the terminal buds of short shoots, which was much higher (5-10 micro g g(DW) (-1)), showed a distinct seasonal cycle with a maximum from August to November. Bud ABA concentration decreased during the first 10 days of forcing, especially in basal buds. In both bud types, the amount of starch increased toward the autumn, declined in November, and was negligible in the terminal buds of short shoots between January and March, but in April, the amount was high again in both bud types. Water content varied characteristically in both bud types, although more distinctly in the terminal buds of short shoots, with an increase in spring before bud burst and a decrease during the summer until September. The significant morphological and physiological differences between the mid-crown terminal buds of short shoots and the underground basal buds may partly explain the characteristic growth habit of the basal buds and their development into coppice shoots after cutting the tree. The results also indicate a role for ABA in maintaining dormancy of the terminal buds of short shoots and emphasize the relationship between tissue water status and ABA concentration.
TL;DR: The study conducted in an open field to determine the optimum irradiance for establishment and growth of two oak species and two major associated woody species found that shading significantly decreased the number of leaves for all species except black cherry, but only significantly decreased leaf area in northern red oak.
Abstract: Summary The study was conducted in an open field to determine the optimum irradiance for establishment and growth of two oak species and two major associated woody species. Half-sib seedlings of black cherry (Prunus serotina Ehrh.), red maple (Acer r&rum L.), northern red oak (Quercus ruhra L.) and black oak (Q. velutina Lam.) were grown for two years under shade-cloth tents. Eight shade treatments (94,70,57, 45,37,27,20 and 8% of full sunlight) with three replications each were used. Measurements were made on seedlings harvested at the end of the first and second growing seasons. In the second year, shading significantly decreased the number of leaves for all species except black cherry, but only significantly decreased leaf area in northern red oak. Shading significantly decreased average leaf size of red maple. Average leaf size of black cherry was largest in the intermediate shade treatments and decreased significantly with increased and decreased shade. Leaf weight/leaf area (mg cm-*) increased significantly in a quadratic pattern with decreasing shade for all four species. Leaf area ratio (cm’ g-‘) decreased significantly with decreasing shade for all species except red maple in the first year and black oak in the second year. Total branch development increased significantly with decreasing shade in red maple and northern red oak, whereas indeterminate branches increased significantly with decreasing shade only in black cherry, and short branches increased significantly with decreasing shade only in red maple.
TL;DR: Drought tolerance of ponderosa pine may be improved through seed source selection and, within certain sources, family selection, andocation patterns and needle morphology appear to play a larger role than needle gas exchange patterns in determining drought tolerance in this species.
Abstract: Summary Seedlings from 27 open-pollinated families of ponderosa pine representing nine geographically diverse origins were screened for drought tolerance based on survival and growth under imposed drought Seedlings that had been preconditioned to drought survived 14 days longer than seedlings that had been well watered before being subjected to drought Seed sources varied in their ability to survive drought and this variation was accentuated by drought preconditioning Seedlings from a South Dakota source and a Nebraska source generally survived the longest under drought Seedlings from a Montana source and a New Mexico source succumbed the fastest after water was withheld Significant family within source variation in drought survival was observed for some sources In general, drought survival was poorly correlated to climate indices of the seed sources Allocation of biomass to roots, stems, and needles varied significantly among the seed sources with the most drought-sensitive sources (Montana and New Mexico) showing the most divergent allocation patterns The relation between drought survival and shoot/root ratio suggested that there is an optimum pattern of allocation for drought survival A comparison of the most and least drought-tolerant sources indicated that needle gas exchange (net photosynthesis and needle conductance to water vapor) and predawn needle water potential were similar among the sources regardless of their relative ability to survive drought Needle morphology traits often associated with variation in drought tolerance, such as stomatal density and specific leaf area, did not differ among the seed sources However, seedlings from the drought-tolerant sources had shorter needles, less surface area per needle, and fewer stomata per needle than seedlings from the drought-sensitive sources The results suggest that drought tolerance of ponderosa pine may be improved through seed source selection and, within certain sources, family selection Allocation patterns and needle morphology appear to play a larger role than needle gas exchange patterns in determining drought tolerance in this species
TL;DR: There was only a small decrease in rates of net photosynthesis from late summer through winter demonstrating that appreciable carbon gain occurs throughout the year in slash pine, and Irradiance, and to a lesser extent air temperature, were the environmental factors that exerted the most control onNet photosynthesis.
Abstract: Summary Net photosynthesis was measured under field conditions in 23-year-old slash pine ( Pinus elliottii Engelm. var. elliottii) trees to determine how it was affected by fertilization and climate. There was only a small decrease in rates of net photosynthesis from late summer through winter demonstrati ng that appreciable carbon gain occurs throughout the year in slash pine. Although fertilization s ubstantially increased leaf area and aboveground biomass, it only slightly increased the rate of net photosy nthesis. Simultaneous measurements of gas exchange in fertilized and unfertilized (control) plot s allowed the detection of a small, but statistically significant difference in average net photosynt hesis of 0.14 μmol m -2 s -1 . Irradiance, and to a lesser extent air temperature, were the environmental factors that exerted the most control on net photosynthesis. The highest rates of net photosynthesis occurred between air temperatures of 25 and 35 °C. Because air temperatures were within this range for 46% of all daylight hours during the year, air temperature was not often a significant limitation. Soil and atmo spheric water deficits had less effect on photosynthesis than irradiance or air temperature. Although the depth to the water table changed during the year from 10 to 160 cm, predawn and midday xylem pressure pote ntials only changed slightly throughout the year. Predawn values ranged from -0.63 to -0.88 MPa in the control plot and from -0.51 to -0.87 MPa in the fertilized plot and were not correlated with water table depth. There was no correlation between xylem pressure potentials and net photosynthesis, pres umably because water uptake was adequate. Although vapor pressure deficits reached 3.5 kPa during the summe r, they had little effect on net photosynthesis. Over a vapor pressure deficit range from 1.0 to 3. 0 kPa, net photosynthesis only decreased 21%. No differences in responses to these environmental fac tors could be attributed to fertilization.
TL;DR: In this paper, the morphological and physiological characteristics of shoots of large and small mature trees of two pine species with different growth patterns and tree longevities were examined, including Rocky Mountain bristlecone pine.
Abstract: Summary This study examined the morphological and physiological characteristics of shoots of large and small mature trees of two pine species with different growth patterns and tree longevities: Rocky Mountain bristlecone pine
TL;DR: In this article, the responses of growth and transpiration efficiency (W = biomass accumulation/water consumption) to ambient and elevated atmospheric CO(2) concentrations (350 and 700 micro mol mol(-1) respectively) were investigated under optimal nutrient supply in well-watered and in drought conditions in two temperate-forest tree species: Quercus petraea Liebl and Pinus pinaster Ait.
Abstract: The responses of growth and transpiration efficiency (W = biomass accumulation/water consumption) to ambient and elevated atmospheric CO(2) concentrations (350 and 700 micro mol mol(-1), respectively) were investigated under optimal nutrient supply in well-watered and in drought conditions in two temperate-forest tree species: Quercus petraea Liebl. and Pinus pinaster Ait. Under well-watered conditions, doubling the CO(2) concentration for one growing season increased biomass growth by 138% in Q. petraea and by 63% in P. pinaster. In contrast, under drought conditions, elevated CO(2) increased biomass growth by only 47% in Q. petraea and had no significant effect on biomass growth in P. pinaster. Transpiration efficiency was higher in Q. petraea than in P. pinaster in all treatments. This difference was linked (i) to lower carbon isotope discrimination (Delta), and thus lower values of the intercellular/ambient CO(2) concentration (c(i)/c(a)) ratio, in Q. petraea, (ii) to lower values of leaf mass ratio (LMR, leaf mass/whole plant mass), which we suggest was positively related to the proportion of daytime carbon fixation lost by respiration (Phi), in Q. petraea, and (iii) to slightly lower C concentrations in Q. petraea than in P. pinaster. The CO(2)-promoted increase in W was higher in Q. petraea (+80%) than in P. pinaster (+50%), and the difference was associated with a more pronounced decrease in Phi in response to elevated CO(2) in Q. petraea than in P. pinaster, which could be linked with the N dilution effect observed in Q. petraea. Because Phi also directly affects growth, the CO(2)-induced enhancement of Phi in Q. petraea is a crucial determinant of the growth stimulation observed in this species. Leaf gas exchange regulation was not the only factor involved in the responses of growth and W to elevated CO(2) and drought, other physiological processes that have crucial roles include carbon and N allocation and respiration.
TL;DR: The vulnerability of xylem to water-stress-induced embolism was remarkably similar for the two species but the leaf specific conductivity of petioles and leaf-bearing stems of the evergreen species, Ochroma, were 3.4 times higher than those of the deciduous species, Pseudobombax.
Abstract: Summary Many authors have attempted to explain the adaptive response of tropical plants to drought based on studies of water relations at the leaf level. Little attention has been given to the role of the xylem system in the control of plant water requirements. To evaluate this role, we studied the hydraulic architecture and water relations parameters of two tropical canopy trees with contrasting leaf phenologies: deciduous Pseudobombax septenatum (Jacq.) Dug and evergreen Ochromapyramidale (Cav. ex lamb) Urban, both in the family Bombacaceae. The hydraulic architecture parameters studied include hydraulic conductivity, specific conductivity, leaf specific conductivity, and Huber value. Water relations parameters include leaf water potential, stem and leaf water storage capacitance, transpiration, stomatal conductance, and vulnerability of stems to cavitation and loss of hydraulic conductivity by embolisms. Compared to temperate trees, both species showed a pattern of highly vulnerable stems (50% loss of conductivity due to embolism at water potentials less than 1 MPa) with high leaf specific conductivities. The vulnerability of xylem to water-stress-induced embolism was remarkably similar for the two species but the leaf specific conductivity of petioles and leaf-bearing stems of the evergreen species, Ochroma (e.g., 9.08 and 11.4 x 10m4 kg s-’ m-’ MPa-‘, respectively), were 3.4 and 2.3 times higher, respectively, than those of the deciduous species, Pseudobombax (e.g., 2.64 and 5.15 x 1O-4 kg s-t mm’ MPa-‘, respectively). A runaway embolism model was used to test the ability of Ochroma and Pseudobombax stems to maintain elevated transpiration rates during the higher evaporative demand of the dry season. The percent loss of leaf area predicted by the runaway embolism model for stems of Pseudobombax ranged from 5 to 30%, not enough to explain the deciduous phenology of this tree species without analysis of root resistance or leaf and petiole vulnerability to embolism.
TL;DR: The transfer matrix method of structural analysis was used to examine the hypothesis that tree stems grow to a shape that tends to equalize the average bending plus axial stresses to which they are subjected along their length, and supports the above hypothesis for the stem region above the butt swell.
Abstract: Summary The transfer matrix method of structural analysis was used to examine the hypothesis that tree stems grow to a shape that tends to equalize the average bending plus axial stresses to which they are subjected along their length. The method and computational procedures were checked by comparing computed heightdiameter profiles with those calculated using elementary stress theory for trees with simple force distributions in the crown. Measured height-diameter profiles for trees were then taken from the literature and shown to be well-fitted by profiles calculated to give uniform stress along the stems, using the most realistic average forces and force distributions within the crowns. At high wind speeds, the height-diameter profile giving uniform stress was more tapered than the profile giving uniform stress at low wind speeds. The profile giving uniform stress was similar over the normal range of average wind speeds of 2.5 to 10.0 m SC’ (at the top of the canopy). But a tree that had grown to give uniform stress along its stem in an average wind of 5 m s-’ showed markedly decreased stress with height at wind speeds of about 15 m s-t or more, and increased stress with height (to the crown base) at wind speeds of about 1.25 m SC’ or less. The fact that tree stems develop shapes in response to average conditions, but show varying stress distributions in extreme conditions, may help to explain some of the apparent evidence for non-uniform stress distribution in the literature. In general, our analysis supports the above hypothesis for the stem region above the butt swell.
TL;DR: Testing the effects of subambient, ambient and twice ambient ozone concentrations on light-saturated net photosynthesis and leaf conductance of leaves from mature trees and genetically related seedlings of northern red oak found that in seedling leaves, P(max) and g(l) were less affected by ozone exposure than in mature leaves.
Abstract: Extrapolation of the effects of ozone on seedlings to large trees and forest stands is a common objective of current assessment activities, but few studies have examined whether seedlings are useful surrogates for understanding how mature trees respond to ozone. This two-year study utilized a replicated open-top chamber facility to test the effects of subambient, ambient and twice ambient ozone concentrations on light-saturated net photosynthesis (P(max)) and leaf conductance (g(l)) of leaves from mature trees and genetically related seedlings of northern red oak (Quercus rubra L.). Gas exchange measurements were collected four times during the 1992 and 1993 growing seasons. Both P(max) and g(l) of all foliage followed normal seasonal patterns of ontogeny, but mature tree foliage had greater P(max) and g(l) than seedling foliage at physiological maturity. At the end of the growing season, P(max) and g(l) of the mature tree foliage exposed to ambient ( approximately 80-100 ppm-h) and twice ambient ( approximately 150-190 ppm-h) exposures of ozone were reduced 25 and 50%, respectively, compared with the values for foliage in the subambient ozone treatment ( approximately 35 ppm-h). In seedling leaves, P(max) and g(l) were less affected by ozone exposure than in mature leaves. Extrapolations of the results of seedling exposure studies to foliar responses of mature forests without considering differences in foliar anatomy and stomatal response between juvenile and mature foliage may introduce large errors into projections of the response of mature trees to ozone.
TL;DR: Diurnal patterns of leaf conductance, net photosynthesis and water potential of five tree species were measured at the top of the canopy in a tropical lowland rain forest in southwestern Cameroon to indicate that environmental factors may cause stomatal closure and limit photosynthesis in tropical rain forests during the midday period.
Abstract: Diurnal patterns of leaf conductance, net photosynthesis and water potential of five tree species were measured at the top of the canopy in a tropical lowland rain forest in southwestern Cameroon. Access to the 40 m canopy was by a large canopy-supported raft, the Radeau des Cimes. The measurements were made under ambient conditions, but the raft altered the local energy balance at times, resulting in elevated leaf temperatures. Leaf water potential was equal to or greater than the gravitational potential at 40 m in the early morning, falling to values as low as -3.0 MPa near midday. Net photosynthesis and conductance were typically highest during midmorning, with values of about 10-12 micro mol CO(2) m(-2) s(-1) and 0.2-0.3 mol H(2)O m(-2) s(-1), respectively. Leaf conductance and net photosynthesis commonly declined through midday with occasional recovery late in the day. Photosynthesis was negatively related to leaf temperature above midday air temperature maxima. These patterns were similar to those observed in other seasonally droughted evergreen communities, such as Mediterranean-climate shrubs, and indicate that environmental factors may cause stomatal closure and limit photosynthesis in tropical rain forests during the midday period.
TL;DR: In unfertilized plants, a downward acclimation of photosynthesis was observed early in the season (June), and was related to reductions in nitrogen and chlorophyll content and to starch accumulation, and the decrease in the slope of the A/C(i) curve suggested a decrease in Rubisco activity.
Abstract: The effects of elevated atmospheric CO(2) (700 micro mol mol(-1)) and fertilization were investigated on 2-year-old sweet chestnut (Castanea sativa Mill.) seedlings grown outdoors in pots in constantly ventilated open-sided chambers. Plants were divided into four groups: fertilized controls (+F/-CO(2)), unfertilized controls (-F/-CO(2)), fertilized + CO(2)-treated plants (+F/+CO(2)) and unfertilized + CO(2)-treated plants (-F/+CO(2)). Dry matter accumulation and allocation were measured after one growing season and CO(2) exchange of whole shoots was measured throughout the growing season. Shoot growth and total leaf area of unfertilized plants were not affected by elevated CO(2), whereas both parameters were enhanced by elevated CO(2) in fertilized plants. Elevated CO(2) increased total biomass by about 20% in both fertilized and unfertilized plants; however, biomass partitioning differed. In unfertilized plants, elevated CO(2) caused an increase in root growth, whereas in fertilized plants, it stimulated aboveground growth. At the whole-shoot and leaf levels, photosynthetic activity of both fertilized and unfertilized plants increased in response to elevated CO(2), but the seasonal pattern of this enhancement varied with nutrient treatment. In unfertilized plants, a downward acclimation of photosynthesis was observed early in the season (June), and was related to reductions in nitrogen and chlorophyll content and to starch accumulation. The decrease in the slope of the A/C(i) curve suggested a decrease in Rubisco activity. In both fertilized and unfertilized plants, shoot respiration decreased during the night in response to elevated CO(2) until mid-July. The decrease was not related to changes in sugar concentration.
TL;DR: Increased photosynthetic water use efficiency and nutrient use efficiency in response to CO(2) enrichment occurred in all three nutrient treatments and have important implications for whole-plant water and nutrient balance.
Abstract: We measured needle photosynthesis of loblolly pine seedlings grown in a factorial experiment with two CO(2) partial pressures (35 and 65 Pa) and three nutrient treatments (7 mM NH(4)NO(3) + 1 mM PO(4); 7 mM NH(4)NO(3) + 0.2 mM PO(4); 1 mM NH(4)NO(3) + 1 mM PO(4)). The data were used to parameterize a physiologically based photosynthetic model that included limitations imposed by ribulose-1,5-bisphosphate carboxylase/oxygenase activity, electron transport capacity and inorganic phosphate availability. With nonlimiting nutrients, seedlings grown at 65 Pa CO(2) had significantly higher net photosynthesis and lower stomatal conductance than seedlings grown at 35 Pa CO(2). Nutrient limitations by either N or P significantly reduced photosynthetic capacity. When either N or P was limiting, there was no effect of growth CO(2) partial pressure on photosynthesis, but stomatal conductance was significantly lower for seedlings grown at 65 Pa CO(2). Modeled biochemical parameters suggest that, in all cases, photosynthesis was co-limited by carboxylation, electron transport and phosphate regeneration. Acclimation to growth in elevated CO(2) involved a reduction in leaf N content. In the low-N and low-P treatments, modeled parameters indicated that the biochemical processes of photosynthesis were down regulated to the point that there was no effect of increasing CO(2) partial pressure. The capacity to regenerate phosphate was reduced in both low nutrient treatments, but was only reduced by elevated CO(2) when seedlings were grown under low soil P conditions. Increased photosynthetic water use efficiency and nutrient use efficiency in response to CO(2) enrichment occurred in all three nutrient treatments and have important implications for whole-plant water and nutrient balance. These data support the contention that soil nutrient status in forest ecosystems will be a critical influence on tree seedling response to increasing atmospheric CO(2) partial pressures.
TL;DR: Modifications in crown structure and allocation between open-grown and understory white pine saplings are similar to those reported for more shade-tolerant fir (Abies) and spruce (Picea) species, but the modifications were generally smaller in white pine.
Abstract: Crown architecture and growth allocation were studied in saplings of eastern white pine (Pinus strobus L.), a species classified as intermediate in shade tolerance. A comparison was made of 15 understory saplings and 15 open-grown saplings that were selected to have comparable heights (mean of 211 cm, range of 180-250 cm). Mean ages of understory and open-grown trees were 25 and 8 years, respectively. Understory trees had a lower degree of apical control, shorter crown length, and more horizontal branch angle, resulting in a broader crown shape than that of open-grown trees. Total leaf area was greater in open-grown saplings than in understory saplings, but the ratio of whole-crown silhouette (projected) leaf area to total leaf area was significantly greater in understory pine (0.154) than in open-grown pine (0.128), indicating that the crown and shoot structure of understory trees exposed a greater percentage of leaf area to direct overhead light. Current-year production of understory white pine was significantly less than that of open-grown white pine, but a higher percentage of current-year production was allocated to foliage in shoots of understory saplings. These modifications in crown structure and allocation between open-grown and understory white pine saplings are similar to those reported for more shade-tolerant fir (Abies) and spruce (Picea) species, but the modifications were generally smaller in white pine. As a result, white pine did not develop the flat-topped "umbrella" crown structure observed in understory fir and spruce, which approaches the idealized monolayer form that maximizes light interception. The overall change to a broader crown shape in understory white pine was qualitatively similar, but much more limited than the changes that occurred in fir and spruce. This may prevent white pine from persisting in understory shade as long as fir and spruce saplings.
TL;DR: Long-term water use efficiency was significantly increased by water deficit and was positively correlated with delta(13)C, and biomass per unit of water transpired, WUE was well correlated with the quotient of the daily integrals of carbon assimilation rate and stomatal conductance.
Abstract: Cuttings of three Eucalyptus globulus Labill. clones (called SM, VC, DG henceforward) were grown for 56 days in 10-I pots in a greenhouse. Every other day, eight pots of each clone were watered to field capacity (HW treatment), whereas the other eight pots of each clone received only 25% of the water needed to maintain the soil at field capacity (LW treatment). Transpirational water loss, biomass production, leaf gas exchange and water potential (at predawn and midday) were determined at different times during the experiment. Leaf tissue formed by the LW plants after the onset of the treatment was analyzed for ‘3C/12C ratio against the PeeDee Belemnite standard (S13C). The three clones differed significantly in growth capacity (SM > DG > VC) and in their response to water stress. Even though leaf water potentials were not significantly modified by withholding water, total biomass and plant leaf area were affected significantly by soil water deficits by the end of the experiment. The fastest growing clone (SM) was the most affected by water deficit. Long-term water use efficiency (i.e., biomass per unit of water transpired, WUE) was significantly increased by water deficit and was positively correlated with 6°C. Long-term WUE was well correlated with the quotient of the daily integrals of carbon assimilation rate and stomata1 conductance. The value of 6°C was negatively correlated with the variables normally positively related with growth, such as specific leaf area (SLA) and the biomass/intercepted light quotient (E), and it was positively related to the amount of carbon per unit leaf area, which is usually negatively correlated with relative growth rate.