A growth model of a single sugi (Cryptomeria japonica) tree based on the dry matter budget of its aboveground parts

Growth of a single sugi (Cryptomeria japonica (L.f.) D. Don.) tree was analyzed on the basis of a dry matter budget. The aboveground net production rate and death rate were defined as the anabolic rate and catabolic rate, respectively. Growth rate of aboveground tree weight, v(w) (kg(dw) year(-1)), was defined as follows: v(w) = v(p) - v(d) (1) where v(p) (kg(dw) year(-1)) is the aboveground net production rate and v(d) (kg(dw) year(-1)) is the aboveground death rate. The value of v(d) is obtained by measuring the monthly clippings of new dead leaves and branches attached to a sample tree. The value of v(w) was calculated as the annual difference in the estimated aboveground tree weight, w(T) (kg(dw)). Finally, the value of v(p) was estimated as the sum of the values of v(d) and v(w). The following allometric relationships were found between v(p) and w(T) and between v(d) and w(T): v(p) = aw(T) (alpha), v(d) = bw(T) (beta) (2). Combining Equations 1 and 2 gives a growth equation, Bertalanffy's equation, of the sample tree. dw(T)/dt = v(w) = aw(T) (alpha) - bw(T) (beta) (3). Because the growth curve of w(T) was derived from Equation 3, the analysis of the growth of w(T) is based on direct measurement of the dry matter budget.     

An analysis of light effects on foliar morphology,physiology, and light interception in temperate deciduous woody species of contrasting shade tolerance

Maximum Rubisco activities (V(cmax)), rates of photosynthetic electron transport (J(max)), and leaf nitrogen and chlorophyll concentrations were studied along a light gradient in the canopies of four temperate deciduous species differing in shade tolerance according to the ranking: Populus tremula L. < Fraxinus excelsior L. < Tilia cordata Mill. = Corylus avellana L. Long-term light environment at the canopy sampling locations was characterized by the fractional penetration of irradiance in the photosynthetically active spectral region (I(sum)). We used a process-based model to distinguish among photosynthesis limitations resulting from variability in fractional nitrogen investments in Rubisco (P(R)), bioenergetics (P(B), N in rate-limiting proteins of photosynthetic electron transport) and light harvesting machinery (P(L), N in chlorophyll and thylakoid chlorophyll-protein complexes). On an area basis, V(cmax) and J(max) (V(a) (cmax) and J(a) (max)) increased with increasing growth irradiance in all species, and the span of variation within species ranged from two (T. cordata) to ten times (C. avellana). Examination of mass-based V(cmax) and J(max) (V(m) (cmax) and J(m) (max)) demonstrated that the positive relationships between area-based quantities and relative irradiance mostly resulted from the scaling of leaf dry mass per area (M(A)) with irradiance. Although V(m) (cmax) and J(m) (max) were positively related to growth irradiance in C. avellana, and J(m) (max) was positively related to irradiance in P. tremula, the variation range was only a factor of two. Moreover, V(m) (cmax) and J(m) (max) were negatively correlated with relative irradiance in T. cordata. Rubisco activity in crude leaf extracts generally paralleled the gas-exchange data, but it was independent of light in T. cordata, suggesting that declining V(m) (cmax) with increasing relative irradiance was related to increasing diffusive resistances from the intercellular air spaces to the sites of carboxylation in this species. Because irradiance had little effect on foliar nitrogen concentration, the relationships of P(B) and P(R) with irradiance were similar to those of V(m) (cmax) and J(m) (max). Shade-intolerant species tended to have greater P(B) and P(R) and also larger V(a) (cmax) and J(a) (max) than more shade-tolerant species. However, for the whole material, P(B) and P(R) varied only about 50%, whereas V(a) (cmax) and J(a) (max) varied more than 15-fold, further emphasizing the importance of leaf anatomical plasticity in determining photosynthetic acclimation to high irradiance. Leaf chlorophyll concentrations and fractional nitrogen investments in light harvesting increased hyperbolically with decreasing irradiance to improve quantum use efficiency for incident irradiance. The effect of irradiance on P(L) was of the same order as its effect in the opposite direction on M(A), leading to either a constant model estimate of leaf absorptance with I(sum) or a slightly positive correlation. We conclude that leaf morphological plasticity is a more relevant determinant of foliage adaptation to high irradiance than foliage biochemical properties, whereas biochemical adaptation to low irradiance is of the same magnitude as the anatomical adjustments. Although shade-tolerant species did not have greater chlorophyll concentrations and P(L) than shade-intolerant species, they possessed lower M(A), and could maintain a more extensive foliar display for light capture with constant biomass investment in leaves.     

Metabolism of deuterium- and tritium-labeled gibberellins in cambial region tissues of Eucalyptus globulus stems

Deuterium- and tritium-labeled gibberellins (GAs) were applied to stems of 3-year-old Eucalyptus globulus Labill. saplings and 9-month-old potted seedlings. Cambial region tissues surrounding the application point were collected 6, 24 or 48 h later. Twenty-four hours after application of 5 &mgr;g of [(2)H(2)]GA(20), 7% of the cambial region GA(20) pool, 7% of the GA(1) pool and 58% of the GA(29) pool were labeled with deuterium based on selected ion monitoring of purified extracts subjected to gas chromatography-mass spectrometry. The relatively low percent dilution of endogenous GAs by [(2)H(2)]GAs suggests that the exogenous application of [(2)H(2)]GA(20) did not result in substrate overloading, indicating that these conversions probably occur naturally within cambial region tissues. Extracts from similar cambial region tissues fed tritium-labeled GAs were sequentially fractionated by SiO(2) partition chromatography, C(18) reversed phase HPLC and N(CH(3))(2) HPLC. The radioactivity profiles indicated metabolism of GA(20) to GA(1) and GA(29), GA(1) conversion to GA(8), GA(4) to GA(34) and GA(9) to GA(51). Gibberellins GA(34), GA(51) and GA(29) are C-2beta-hydroxylated catabolites of low biological activity, whereas GA(1) and GA(4) are probably effectors of growth in the Eucalyptus stem and shoot. Evidence for C-13 hydroxylation of GA(4) to GA(1), GA(9) to GA(4) or GA(9) to GA(20) in the stem was inconclusive. Thus, although GA(4) and GA(9) are native to cambial region tissues, GA(1) is probably not produced from them in significant quantities. We conclude that the early C-13-hydroxylation pathway; i.e., conversion of GA(19) to GA(20) to GA(1), is the major pathway of GA(1) biosynthesis.     

Partititioning concurrent influences of nitrogen and phosphorus supply on photosynthetic model parameters of Pinus radiata

Responses of photosynthesis (A) to intercellular CO(2) concentration (C(i)) were measured in a fast- and a slow-growing clone of Pinus radiata D. Don cultivated in a greenhouse with a factorial combination of nitrogen and phosphorus supply. Stomatal limitations scaled with nitrogen and phosphorus supply as a fixed proportion of the light-saturated photosynthetic rate (18.5%) independent of clone. Photosynthetic rates at ambient CO(2) concentration were mainly in the V(cmax)-limited portion of the CO(2) response curve at low-nitrogen supply and at the transition between V(cmax) and J(max) at high-nitrogen supply. Nutrient limitations to photosynthesis were partitioned based on the ratio of foliage nitrogen to phosphorus expressed on a leaf area basis (N(a)/P(a)), by minimizing the mean square error of segmented linear models relating photosynthetic parameters (V(cmax), J(max), T(p)) to foliar nitrogen and phosphorus concentrations. A value of N(a)/P(a) equal to 23 (mole basis) was identified as the threshold separating nitrogen (N(a)/P(a) < or = 23) from phosphorus (N(a)/P(a) > 23) limitations independent of clones. On an area basis, there were significant positive linear relationships between the parameters, V(cmax), J(max), T(p) and N(a) and P(a), but only the relationships between T(p) and N(a) and P(a) differed significantly between clones. These findings suggest that, in genotypes with contrasting growth, the responses of V(cmax) and J(max) to nutrient limitation are equivalent. The relationships between the parameters V(cmax), J(max), T(p) and foliage nutrient concentration on a mass basis were unaffected by clone, because the slow-growing clone had a significantly greater leaf area to mass ratio than the fast-growing clone. These results may be useful in discriminating nitrogen-limited photosynthesis from phosphorus-limited photosynthesis.     

Responses of foliar gas exchange to long-term elevated CO(2) concentrations in mature loblolly pine trees

Branches of field-grown mature loblolly pine (Pinus taeda L.) trees were exposed for 2 years (1992 and 1993) to ambient or elevated CO(2) concentrations (ambient + 165 micro mol mol(-1) or ambient + 330 micro mol mol(-1) CO(2)). Exposure to elevated CO(2) concentrations enhanced rates of net photosynthesis (P(n)) by 53-111% compared to P(n) of foliage exposed to ambient CO(2). At the same CO(2) measurement concentration, the ratio of intercellular to atmospheric CO(2) concentration (C(i)/C(a)) and stomatal conductance to water vapor did not differ among foliage grown in an ambient or enriched CO(2) concentration. Analysis of the relationship between P(n) and C(i) indicated no significant change in carboxylation efficiency of ribulose-1,5-bisphosphate carboxylase/oxygenase during growth in elevated CO(2) concentrations. Based on estimates derived from P(n)/C(i) curves, there were no apparent treatment differences in dark respiration, CO(2) compensation point or P(n) at the mean C(i). In 1992, foliage in the three CO(2) treatments yielded similar estimates of CO(2)-saturated P(n) (P(max)), whereas in 1993, estimates of P(max) were higher for branches grown in elevated CO(2) than in ambient CO(2). We conclude that field-grown loblolly pine trees do not exhibit downward acclimation of leaf-level photosynthesis in their long-term response to elevated CO(2) concentrations.     

Effects of nitrogen source and defoliation on growth and biological dinitrogen fixation of Gliricidia sepium seedlings

Effects of four N sources and two defoliation treatments on growth and nitrogenase activity of Gliricidia sepium (Jacq.) Walp seedlings were studied in a greenhouse. All nutrients were supplied in irrigation water to the sterile growing medium. The N sources were: (1) 100 mg l(-1) of N supplied as NO(3) (-) (high-NO(3) (-)), (2) 50 mg l(-1) of N supplied as NO(3) (-) and inoculation with Rhizobium spp. medium-NO(3) (-)), (3)100 mg l(-1) of N supplied as NH(4)NO(3), and (4) inoculation with Rhizobium spp without mineral N (N(2)). At 35 weeks after sowing, mean total biomass was 130.5, 50.5, 22.9 and 17.4 g seedling(-1) in the NH(4)NO(3), N(2), medium-NO(3) (-) and high-NO(3) (-) treatments, respectively. The root/shoot ratio was high in all of the N treatments (1.73-2.77) because the seedlings had big taproots. The medium-NO(3) (-) treatment completely inhibited nodulation, whereas seedlings in the N(2) treatment were profusely nodulated. At 32 weeks after sowing, groups of seedlings in the N(2) and high-NO(3) (-) treatments were subjected to 50 or 100% defoliation. Closed-chamber acetylene reduction assays of intact root systems were conducted to compare nitrogenase activity at 7, 14 and 28 days after defoliation (DAD). At 7 and 14 DAD, nitrogenase activity of completely and partially defoliated seedlings was about 10 and 60%, respectively, of that of undefoliated controls. At 28 DAD, nitrogenase activity of completely defoliated seedlings was twice the predefoliation value, whereas nitrogenase activity of partially defoliated seedlings was only 87% of the predefoliation value. Recovery of nitrogenase activity was strongly correlated with foliage regrowth in the completely defoliated seedlings, but not in the partially defoliated seedlings. Abundant belowground C and N reserves in the large taproot probably contributed to the rapid recovery from defoliation. Accumulation of belowground biomass may also improve defoliation tolerance of mature trees.     

Growth and nutrition of Betula pendula at different relative supply rates of zinc

Small birch plants (Betula pendula Roth) were cultivated in a hydroponic spray solution where the relative growth rate (R(G); day(-1)) was controlled by the relative supply rate of zinc (R(Zn); day(-1)). After an adjustment phase to steady-state growth, R(G) equaled R(Zn). The R(Zn) treatments were 0.05, 0.125 and 0.20 day(-1) with free access to all other nutrients. In an additional treatment, there was free access to all nutrients, including zinc (FA treatment). The pH of the nutrient solution was approximately 4.5 and conductivity was 100 &mgr;S cm(-1). The duration of each treatment depended on R(Zn) and ranged from 4 (FA treatment) to 10 weeks (at R(Zn) = 0.05 day(-1)). The plants showed persistent and typical zinc-deficiency symptoms at steady-state growth when R(G) was 0.05 and 0.125 day(-1), whereas there were few symptoms when R(G) was 0.2 day(-1). The Zn concentration of the plants ranged from 8 (at R(Zn) = 0.05 day(-1)) to 21 &mgr;g g(DM) (-1) (DM = dry mass) (at R(Zn) = 0.2 day(-1)) and was approximately 42 &mgr;g g(DM) (-1) in the FA treatment. Uptake rates of Zn, calculated per root growth rate (&mgr;mol g(DM, root) (-1)), were about 2.8 times higher at R(Zn) = 0.20 day(-1) than at R(Zn)= 0.05 day(-1). The root and stem biomass fractions were approximately constant at all supply rates of Zn, whereas the leaf biomass fraction tended to increase with increasing supply rate of Zn. Net assimilation rate was constant from FA to an R(Zn) of 0.125 day(-1) but decreased by a factor of about 2 at R(Zn) = 0.05 day(-1). Leaf area ratio and specific leaf area were smaller at low supply rates of zinc than at high supply rates.     

Analysis of the relationships among O(3) uptake, conductance, and photosynthesis in needles of Pinus ponderosa

We studied the effects of O(3) uptake on conductance (g(wv)) and photosynthesis (A) in needles of ponderosa pine (Pinus ponderosa Laws.) seedlings exposed for 70 days to one of three O(3) regimes-Low-O(3) (0.1 micro mol mol(-1) daily peak), High-O(3) (0.2 micro mol mol(-1) daily peak), and Low/High-O(3) (alternating 2 days Low-O(3) and 2 days High-O(3)). Seedlings exposed to charcoal-filtered air served as controls. Total O(3) exposures, expressed as ppm-h (the sum of the average hourly concentration in ppm ( micro mol mol(-1)) over the exposure period), were 77, 135, 105 and 4 for the Low-O(3), High-O(3), Low/High-O(3) and control treatments, respectively. Conductance (g(wv)) declined to about 60% of the value in control seedlings by Day 6 in seedlings in the High-O(3) treatment and by Day 37 in seedlings in the Low/High-O(3) treatment, but g(wv) did not decline at all in seedlings in the Low-O(3) treatment. At the end of the 70-day experiment, cumulative O(3) uptake, calculated from measured g(wv) values and assuming an internal O(3) concentration of zero, was 12.2, 13.5, and 14.7 mmol m(-2) for seedlings in the Low-O(3), Low/High-O(3), and High-O(3) treatments, respectively; however, O(3) uptake was reduced by 0, 24, and 36%, respectively, from that expected if there had been no decline in g(wv). With increasing total O(3) exposure, A declined, but the reduction was not strictly cumulative, i.e., A measured on Days 49 and 70 was similar for a given treatment even though both total O(3) exposure and uptake had increased. At the end of the experiment, A at near saturating CO(2) (1000 micro mol mol(-1)) and saturating photosynthetic photon flux density was reduced by about 25, 40 and 50% in seedlings in the Low-O(3), Low/High-O(3) and High-O(3) treatments, respectively, compared to the control seedlings. The ratio of internal to external CO(2) concentrations, an indicator of relative change in stomatal limitation of A, did not change over time and did not differ among treatments, suggesting that A and g(wv) decreased in parallel. After 40-60 days without O(3), A of seedlings in all O(3) treatments was not significantly different. Our data indicate that O(3)-induced stomatal closure was a result of reduced A and that decreased g(wv) reduced O(3) uptake to a rate that needles of ponderosa pine could tolerate without exhibiting further reductions in gas exchange capacity.     

Analyses of delta(13)C and delta(18)O in tree rings of Callitris columellaris provide evidence of a change in stomatal control of photosynthesis in response to regional changes in climate

We examined relationships between stable isotopes of carbon (delta(13)C) and oxygen (delta(18)O) in tree rings of Callitris columellaris F. Muell in the semi-arid Pilbara region of north-western Australia. To test the hypothesis that stomatal control of photosynthesis decreases during drier periods, we developed delta(13)C and delta(18)O chronologies spanning 1919-1999, and used a permutation regression approach to relate a 21-year running correlation between delta(13)C and delta(18)O to rainfall and temperature at Marble Bar and our study site. The relationship between delta(13)C and delta(18)O switched from being always negative before 1955 to being consistently positive after 1976, suggesting an increase in stomatal control of photosynthesis in recent decades. Changes in the delta(13)C-delta(18)O relationship reflected changes in rainfall, which has increased in the region by 30% since 1976. The correlation between delta(13)C and delta(18)O was positively related to the 21-year running mean of normalized rainfall anomalies at both the study site (P = 0.045, Adj. r(2) = 0.47) and Marble Bar (P = 0.046, Adj. r(2) = 0.48). In addition, the delta(13)C-delta(18)O correlation was negatively related (P = 0.047, Adj. r(2) = 0.61) to temperatures at Marble Bar. Our interpretation of the role of changes in climate affecting the relationship between tree-ring delta(13)C and delta(18)O is supported by evidence from the isotope composition of foliage samples: foliar delta(13)C and delta(18)O were negatively correlated with log stomatal conductance (delta(13)C, r = -0.41; delta(18)O, r = -0.42), whereas the correlation between foliar delta(13)C and delta(18)O was positive (r = 0.63, P = 0.027) after the summer wet period. Our data indicate that stomatal control of photosynthesis in Callitris adjusts to region-wide changes in climate and that, in a warmer and drier world, trees might adapt by increasing non-stomatal control of photosynthesis.     

Scaling foliar respiration to the stand level throughout the growing season in a Quercus rubra forest

Stand-level, canopy foliar carbon loss (R(can)) was modeled for a virtual Quercus rubra L. monoculture at two sites differing in soil water availability in a northeastern deciduous forest (USA) throughout the 2003 growing season. Previously reported foliar respiratory temperature responses of Q. rubra were used to parameterize a full distributed physiology model that estimates R(can) by integrating the effects of season, site and canopy position, and represents the best estimation of R(can). Model sensitivity to five simplified parameterization scenarios was tested, and a reasonable procedure of simplification was established. Neglecting effects of season, site or canopy position on respiration causes considerable relative error in R(can) estimation. By contrast, assuming a constant E(0) (a temperature response variable of the respiration model), or a constant night temperature (mean nighttime temperature) caused only a small relative error (< 10%) compared with the full model. From June 8 to October 28, 2003, modeled R(can) of the virtual Q. rubra monoculture was, on average, 45.3 mmol CO(2) m(-2) night(-1) on a ground-area basis (or 334 mmol CO(2) kg(-1) night(-1) on a biomass basis) and 101 mmol CO(2) m(-2) night(-1) (or 361 mmol CO(2) kg(-1) night(-1)) at the drier site and the more mesic site, respectively. To model R(can) of Q. rubra (or other Quercus species with similar respiratory properties), variations in the base respiration rate across season, site and canopy position need to be fully accounted for, but E(0) may be assumed constant. Modeling R(can) at the mean nighttime temperature would not strongly affect estimated canopy carbon loss.     

Hydraulic resistance in Acer saccharum shoots and its influence on leaf water potential and transpiration

A new method is presented for measuring whole-shoot hydraulic conductance, K(T) (kg s(-1) MPa(-1)). The method was also used to determine other conductance values in maple (Acer saccharum Marsh.) stem segments of differing diameter including: K(h) (absolute conductance or conductance per unit pressure gradient, kg s(-1) m MPa(-1)), K(s) (specific conductance or K(h) per unit wood area, kg s(-1) m(-1) MPa(-1)), and LSC (leaf specific conductance or K(h) per unit leaf area, kg s(-1) m(-1) MPa(-1)). A regression of K(T) versus stem basal diameter, D (m), gave K(T) = 5.998 x 10(-2) D(1.402) (R(2) = 0.986 for D from 0.001 to 0.1 m) and a regression for leaf area, A(L) (m(2)), gave A(L) = 4.667 x 10(3) D(2.007) (R(2) = 0.981 for D from 0.001 to 0.3 m). More than 50% of the resistance to water flow in large shoots (0.1 m in diameter and 8 to 10 m long) was contained in branches less than 0.012 m in diameter, i.e., in the distal 1.5 m of branches. We used the regressions to predict the steady state difference in pressure potential, P, between the base of a shoot of diameter D and the average pressure potential at the apices of the shoot; the relation is given by P = 7.781 x 10(4) E D(0.605), where E is the average evaporative flux density (kg s(-1) m(-2)) in the leaves attached to the shoot. After comparing the predictions of this equation to field observations of E and leaf water potential and stomatal conductance, we concluded that the hydraulic conductance of large maple shoots is sufficiently low to prevent maximum stomatal conductance in maple leaves.     

Physiological and morphological responses of olive plants to ozone exposure during a growing season

We studied physiological (gas exchange and stomatal aperture) and morphological (individual leaf area and stomatal density) responses in leaves of five-year-old olive plants (Olea europaea L. cvs. Frantoio and Moraiolo) exposed to filtered air containing < 3 ppb O(3) or 100 ppb O(3) for 5 h day(-1) for 120 days in fumigation chambers. After 100 days of treatment, leaf drop and development of necrotic spots were observed in O(3)-fumigated plants of Moraiolo but not of Frantoio. Significant reductions in photosynthetic activity (57%) and stomatal conductance (69%) were detected in O(3)-fumigated plants of Frantoio compared with control plants. In O(3)-fumigated plants of Moraiolo, the decrease in photosynthetic activity (17%) was not statistically significant, but a significant reduction in stomatal conductance (40%) was observed. In both cultivars, leaves that developed after exposure to O(3) showed decreased stomatal aperture (63.6 and 54.8% with respect to the Frantoio and Moraiolo controls, respectively) and one-sided leaf area, and increased stomatal density compared with control leaves. Actual transpiring stomatal surface decreased substantially in both Frantoio (59.8%) and Moraiolo (56.3%) in response to O(3) treatment. Relative transpiring stomatal surface (RTSS) in Frantoio decreased from 0.54 (control) to 0.27% (O(3) treated) of total leaf surface. The corresponding values for Moraiolo were 0.79 and 0.42%. However, because the RTSS of Moraiolo leaves in the O(3) treatment was 0.42 versus 0.27% in Frantoio, the potential uptake of O(3) was higher for Moraiolo plants than for Frantoio plants. The large O(3)-induced reduction in transpiring stomatal surface in both cultivars could have significant effects on olive productivity in the Mediterranean area, where high O(3) concentrations persist for long periods during the year.     

Carbon dioxide exchange of developing avocado (Persea americana Mill.) fruit

Net efflux of CO(2) from attached avocado (Persea americana Mill.) fruit was measured periodically from three weeks after anthesis to fruit maturity. Net CO(2) exchange was determined in daylight (light respiration, R(l)) at a photosynthetic photon flux (PPF) greater than 600 micromol m(-1) s(-1), and in the dark (dark respiration, R(d)). Dark respiration and R(l) were highest during the early cell division stage of fruit growth (about 25 and 22 nmol CO(2) g(dw) (-1) s(-1), respectively) and decreased gradually until fruit maturity to about 1 and 0.5 nmol CO(2) nmol CO(2) g(dw) (-1) s(-1), respectively. Fruit photosynthesis, calculated from the difference between R(d) and R(l), ranged from 0.5 to 3.1 nmol CO(2) g(dw) (-1) s(-1). Net rate of CO(2) assimilation on a fruit dry weight basis was highest during the early stages of fruit growth and reached the lowest rate at fruit maturity. Net rate of CO(2) assimilation of fruit exposed to light was 0.4 to 2.5% of that for fully expanded leaves. Although the relative amount of carbon assimilated by the fruit was small compared with the total amount of carbon assimilated by the leaves, the data indicate that avocado fruit contribute to their own carbon requirement by means of CO(2) assimilated in the light.     

Fluxes of Ca(2+), K(+) and Cl(-) across the surfaces of detached needles from Sitka spruce trees: pathways and compartmentation

Uptake and efflux of (36)Cl(-), (45)Ca(2+) and (42)K(+) were measured in water-infiltrated detached needles from Sitka spruce (Picea sitchensis (Bong.) Carr.) trees incubated in 1 mol m(-3) KCl or CaCl(2) or 2 mol m(-3) NaCl solutions or in artificial rain water containing mmol m(-3) amounts of these ions. Surface efflux was measured separately from leakage from the cut ends of the needles. Needles loaded with (36)Cl(-) and killed in liquid N(2) before elution displayed a rapid and extensive loss of radioisotope, indicating that mesophyll cell membranes were the limiting factor for (36)Cl(-) exchange. Data for live needles revealed a novel phase of (36)Cl(-) efflux, with an exchange halftime of about 20 min, which was faster than that for either the vacuole or the cytoplasm, but much slower than that for the free space. The novel phase was interpreted as representing diffusion of Cl(-) through the predominantly negatively charged cuticle. Killing needles loaded with (45)Ca(2+) or (42)K(+) also increased efflux relative to that from live needles, but only to a limited degree, indicating that the main factor limiting cation efflux was the cuticle. During the first hours of (45)Ca(2+) uptake, the isotherms displayed a shoulder, indicating that there was a significant Donnan free space phase in the cuticle for Ca(2+). A shoulder was absent from (42)K(+) uptake isotherms because of the preferential adsorption of divalent cations on the exchange sites.     

Nocturnal stomatal conductance effects on the delta(18)O signatures of foliage gas exchange observed in two forest ecosystems

We report field observations of oxygen isotope ((18)O) discrimination during nocturnal foliage respiration ((18)Delta(R)) in branch chambers in two forest ecosystems: a Sitka spruce (Picea sitchensis (Bong.) Carr.) plantation in Scotland; and a beech (Fagus sylvatica L.) forest in Germany. We used observations and modeling to examine the impact of nocturnal stomatal conductance on the (18)O/(16)O (delta(18)O) signatures of foliage gas exchange at night. We found that nocturnal stomatal conductance can influence the delta(18)O signature by affecting: (1) the bidirectional diffusion of CO(2) into and out of the leaf (with isotopic equilibration); and (2) the (18)O enrichment of the foliage water with which the CO(2) equilibrates. Both effects were manifest in high apparent (18)Delta(R) values and enriched delta(18)O signatures of foliage water at night. The effects were more pronounced for Sitka spruce because of its higher nocturnal stomatal conductance and higher specific leaf water content compared to beech. We found that taking the effects of nocturnal stomatal conductance into account may change the sign of the delta(18)O signature of nocturnal foliage respiration, generally thought to decrease the delta(18)O of atmospheric CO(2). We conclude that nocturnal stomatal exchange can have a profound effect on isotopic exchange depending on species and environmental conditions. These effects can be important when using delta(18)O signatures of canopy CO(2) to distinguish foliage and soil respiration, and when modeling the delta(18)O signature of CO(2) exchanged between ecosystems and the atmosphere.     

杉木双系种子园无性系开花习性与异交率及其间的关系研究

基于对杉木双系种子园中成对无性系开花习性的多年观察及多年对杉木双系种子园的同工酶实验,运用EM算法估计各无性系的异交率大小,并使用DPS统计软件,详实地研究了异交率与开花习性诸多因素间的关系,其结果为:Y=0.877 7+0.104 4X1-0.615 8X2+0.354 4X3-0.061 8X4。上式中:X1为异系雄球花量,X3为异系开花同步性指数,它们对异交率的影响有正效应;而X2为系内开花同步性指数,X4为X3/X2之比,它们对异交率的影响有负效应。影响力的大小次序为:X2>X4>X3>X1。根据异交率与开花习性的关系研究,可以发现:今后新建杉木双系种子园时,挑选系内开花同步性小,而系间开花同步性大的双亲材料时,其后代异交率较高。     

Photosynthetic responses to needle water potentials in Scots pine after a four-year exposure to elevated CO(2) and temperature

Effects of needle water potential (Psi(l)) on gas exchange of Scots pine (Pinus sylvestris L.) grown for 4 years in open-top chambers with elevated temperature (ET), elevated CO(2) (EC) or a combination of elevated temperature and CO(2) (EC + ET) were examined at a high photon flux density (PPFD), saturated leaf to air water vapor pressure deficit (VPD) and optimal temperature (T). We used the Farquhar model of photosynthesis to estimate the separate effects of Psi(l) and the treatments on maximum carboxylation efficiency (V(c,max)), ribulose-1,5-bisphosphate regeneration capacity (J), rate of respiration in the light (R(d)), intercellular partial pressure of CO(2) (C(i)) and stomatal conductance (G(s)). Depression of CO(2) assimilation rate at low Psi(l) was the result of both stomatal and non-stomatal limitations on photosynthetic processes; however, stomatal limitations dominated during short-term water stress (Psi(l) < -1.2 MPa), whereas non-stomatal limitations dominated during severe water stress. Among the nonstomatal components, the decrease in J contributed more to the decline in photosynthesis than the decrease in V(c,max). Long-term elevation of CO(2) and temperature led to differences in the maximum values of the parameters, the threshold values of Psi(l) and the sensitivity of the parameters to decreasing Psi(l). The CO(2) treatment decreased the maximum values of V(c,max), J and R(d) but significantly increased the sensitivity of V(c,max), J and R(d) to decreasing Psi(l) (P < 0.05). The effects of the ET and EC + ET treatments on V(c,max), J and R(d) were opposite to the effects of the EC treatment on these parameters. The values of G(s), which were measured simultaneously with maximum net rate of assimilation (A(max)), declined in a curvilinear fashion as Psi(l) decreased. Both the EC + ET and ET treatments significantly decreased the sensitivity of G(s) to decreasing Psi(l). We conclude that, in the future, acclimation to increased atmospheric CO(2) and temperature could increase the tolerance of Scots pine to water stress.     

Organic and inorganic sulfur transport in the xylem sap and the sulfur budget of Picea abies trees

Temporal changes in inorganic and organic sulfur compounds (sulfate, glutathione, cysteine, methionine) were analyzed in xylem sap of 40-year-old Norway spruce (Picea abies (L.) Karst.) trees growing on acidic soils at a healthy and a declining stand in the Fichtelgebirge (North Bavaria, Germany). Studies were carried out (1) to quantify glutathione (GSH) transport in the xylem of spruce, (2) to study the significance of reduced sulfur versus sulfate (SO(4) (2-)) transport in the xylem, and (3) to compare total sulfur (S) transport in the xylem with the amount of foliar uptake of SO(2) in an air-polluted environment. Glutathione was the main reduced S compound in the xylem ranging in concentration from 0.5 to 5 &mgr;mol l(-1). Concentrations of inorganic SO(4) (2-) in the xylem sap were up to 50 times higher than those of GSH ranging from 60 to 230 &mgr;mol l(-1). During the growing season, concentrations of all S compounds in the xylem were highest in May (up to 246 &mgr;mol l(-1)) and decreased during summer and fall (up to 21 &mgr;mol l(-1)). On average, SO(4) (2-) concentrations in xylem sap were 30% higher at the declining site compared with the healthy site. Diurnal changes in organic S compounds were significant for GSH and cysteine with high concentrations during the night and low concentrations during the day. Diurnal changes in inorganic concentrations were not significant. Xylem sap concentrations of SO(4) (2-) and cysteine were twice as high and GSH concentrations were tenfold higher in surface roots than in branches. At both sites, transport of organic S was low (up to 3% of total S) compared to transport of SO(4) (2-). Annual transport of total S in the xylem (SO(4) (2-) was the main component) ranged from 60 to 197 mmol tree(-1) year(-1) at the healthy site and from 123 to 239 mmol tree(-1) year(-1) at the declining site. Although gaseous uptake of SO(2) was estimated to be similar at both sites (38 mmol tree(-1) year(-1); Horn et al. 1989), the ratio between annual gaseous uptake of SO(2) and transport of S in the xylem was 1:4 and 1:5 at the healthy and declining sites, respectively.     

Water use by whitebark pine and subalpine fir: potential consequences of fire exclusion in the northern Rocky Mountains

In subalpine forests of the northern Rocky Mountains, fire exclusion has contributed to large-scale shifts from early-successional whitebark pine (Pinus albicaulis Engelm.) to late-successional subalpine fir (Abies lasiocarpa (Hook.) Nutt.), a species assumed to be more shade tolerant than whitebark pine and with leaf to sapwood area ratios (A(L):A(S)) over twice as high. Potential consequences of high A(L):A(S) for subalpine fir include reduced light availability and, if hydraulic sufficiency is maintained, increased whole-tree water use. We measured instantaneous gas exchange, carbon isotope ratios and sap flow of whitebark pine and subalpine fir trees of different sizes in the Sapphire Mountains of western Montana to determine: (1) whether species-specific differences in gas exchange are related to their assumed relative shade tolerance and (2) how differences in A(L):A(S) affect leaf- and whole-tree water use. Whitebark pine exhibited higher photosynthetic rates (A = 10.9 micromol x m(-2) x s(-1) +/- 1.1 SE), transpiration rates (E = 3.8 mmol x m(-2) x s(-1) +/- 0.7 SE), stomatal conductance (g(s) = 166.4 mmol x m(-2) x s(-1) +/- 5.3 SE) and carbon isotope ratios (delta13C = -25.5 per thousand +/- 0.2 SE) than subalpine fir (A = 5.7 micromol x m(-2) x s(-1) +/- 0.9 SE; E = 1.4 mmol x m(-2) x s(-1) +/- 0.3 SE; g(s) = 63.4 mmol x m(-2) x s(-1) +/- 1.2 SE, delta13C = -26.2 per thousand +/- 0.2 SE; P < 0.01 in all cases). Because subalpine fir had lower leaf-area-based sap flow than whitebark pine (QL = 0.33 kgx m(-2) x day(-1) +/- 0.03 SE and 0.76 kg x m(-2) x day(-1) +/- 0.06 SE, respectively; P < 0.001), the higher A(L):A(S) in subalpine fir did not result in direct proportional increases in whole-tree water use, although large subalpine firs used more water than large whitebark pines. The linear relationships between tree size and daily water use (r2 = 0.94 and 0.97 for whitebark pine and subalpine fir, respectively) developed at the Sapphire Mountains site were applied to trees of known size classes measured in 12 natural subalpine stands in the Bob Marshall Wilderness Complex (western Montana) ranging from 67 to 458 years old. Results indicated that the potential for subalpine forests to lose water by transpiration increases as succession proceeds and subalpine fir recruits into whitebark pine stands.