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1.
Aldini G Piccoli A Beretta G Morazzoni P Riva A Marinello C Maffei Facino R 《Fitoterapia》2006,77(2):121-128
The antioxidant profile of extracts from solid olive residue (SOR) of c.v. Coratina, a cultivar widely diffused in the south of Italy, using both cell-free and cell-based experimental models, was investigated. A total hydroalcoholic extract (polyphenols content 19.7%) and a purified extract (Oleaselecttrade mark) (polyphenols content 35.1%) were tested for their ability to quench the stable free radical DPPH, the peroxyl radicals (ORAC assay), by monitoring the loss in fluorescence of R-phycoerythrin induced by the peroxyl radical generator AAPH and their ability to inhibit the cumene hydroperoxide-induced lysis of rat red blood cells (RBC). The total hydroalcoholic extract showed IC(50) 26.96+/-1.53 microg/ml in the DPPH assay, that 10 microg/ml were equivalent to 2.11+/-0.12 microg/ml Trolox (ORAC assay) and IC(50) 1.7+/-0.20 microg/ml in the RBC hemolysis. The Oleaselect extract was 4 to 5 folds more active than the hydroalcoholic extract in all the experimental models, with IC(50) values of 7.36+/-0.38 microg/ml in the DPPH test and of 0.38+/-0.03 microg/ml in RBC; the antioxidant activity in the ORAC assay was slightly greater than that of Trolox (10 microg/ml equivalent to 11.45+/-0.40 microg/ml). The scavenging effect of the extract in the ORAC assay was compared to that of verbascoside (the main polyphenol component) and of caffeic acid (the basic constituent of verbascoside): the results indicate that caffeic acid (10 microg/ml equivalent to 35.70+/-2.95 microg/ml Trolox) is more potent than verbascoside (10 microg/ml equivalent to 15.42+/-1.21 microg/ml Trolox) in entrapping peroxyl radicals. Finally the antioxidant activity of the Oleaselect extract was confirmed in human umbilical endothelial cells (EC) exposed to the site-specific peroxyl radical inducer AAPH, where a massive lipid peroxidation process (marker the fluorescence probe BODIPY) takes place, paralleled by a marked loss of cell viability (calcein assay). The purified extract (1-20 microg/ml) pre-incubated with EC for 1 h dose-dependently inhibited both the lipid-peroxidation damage and cell death. Taking into account the total polyphenol content, these results clearly indicate a greater antioxidant activity for the purified extract, due to a cooperative antioxidant interaction among its polyphenol constituents. 相似文献
2.
Root morphology, biomass, and (14)C distribution were studied in two 2-year-old Populus trichocarpa x P. deltoides hybrids, which originated from hardwood cuttings, to determine the pattern of root distribution in a plantation and to refine methods for root recovery. The trees were labeled with (14)CO(2) and harvested after a 72-hour chase period. Roots attached to each labeled tree were analyzed for morphological traits at the time of harvest. Detached roots from within a 1-m(3) volume of soil surrounding each tree were separated from the soil and sorted on the basis of rooting depth and root diameter. Lateral roots > 2 mm in diameter had a largely horizontal orientation at their point of origin from the cutting and extended horizontally up to 4 m from the cutting. This resulted in considerable overlap of root systems in the plantation. Results from (14)C labeling indicated that 24 +/- 4% (+/- SD) of the carbon exported from branches-labeled within two weeks after branch budset-was translocated to the root system. Dilution of the root (14)C label indicated that from 0 (> 5 mm diameter roots) to 75% (< 2 mm diameter roots) of the roots recovered from within the 1-m(3) volume of soil surrounding a harvested tree originated from other trees. Total root biomass was 6 +/- 1 Mg ha(-1) for both hybrids. Sixty percent of the root biomass was recovered directly from excavation, 16% from coarse-sieving excavated soil, and 24% from re-sorting sieved soil. The study indicated that root growth of hybrid poplars may be rapid and extensive and that detailed sorting of soil subsamples substantially improves the recovery of fine roots < 2 mm in diameter. 相似文献
3.
Whitehead D Walcroft AS Scott NA Townsend JA Trotter CM Rogers GN 《Tree physiology》2004,24(7):795-804
Responses of photosynthesis to carbon dioxide (CO2) partial pressure and irradiance were measured on leaves of 39-year-old trees of manuka (Leptospermum scoparium J. R. Forst. & G. Forst.) and kanuka (Kunzea ericoides var. ericoides (A. Rich.) J. Thompson) at a field site, and on leaves of young trees grown at three nitrogen supply rates in a nursery, to determine values for parameters in a model to estimate annual net carbon uptake. These secondary successional species belong to the same family and commonly co-occur. Mean (+/- standard error) values of the maximum rate of carboxylation (hemi-surface area basis) (Vcmax) and the maximum rate of electron transport (Jmax) at the field site were 47.3 +/- 1.9 micromol m(-2) s(-1) and 94.2 +/- 3.7 micromol m(-2) s(-1), respectively, with no significant differences between species. Both Vcmax and Jmax were positively related to leaf nitrogen concentration on a unit leaf area basis, and the slopes of these relationships did not differ significantly between species or between the trees in the field and young trees grown in the nursery. Mean values of Jmax/Vcmax measured at 20 degrees C were significantly lower (P < 0.01) for trees in the field (2.00 +/- 0.05) than for young trees in the nursery with similar leaf nitrogen concentrations (2.32 +/- 0.08). Stomatal conductance decreased sharply with increasing air saturation deficit, but the sensitivity of the response did not differ between species. These data were used to derive parameters for a coupled photosynthesis-stomatal conductance model to scale estimates of photosynthesis from leaves to the canopy, incorporating leaf respiration at night, site energy and water balances, to estimate net canopy carbon uptake. Over the course of a year, 76% of incident irradiance (400-700 nm) was absorbed by the canopy, annual net photosynthesis per unit ground area was 164.5 mol m(-2) (equivalent to 1.97 kg C m(-2)) and respiration loss from leaves at night was 37.5 mol m(-2) (equivalent to 0.45 kg m(-2)), or 23% of net carbon uptake. When modeled annual net carbon uptake for the trees was combined with annual respiration from the soil surface, estimated net primary productivity for the ecosystem (0.30 kg C m(-2)) was reasonably close to the annual estimate obtained from independent mensurational and biomass measurements made at the site (0.22 +/- 0.03 kg C m(-2)). The mean annual value for light-use efficiency calculated from the ratio of net carbon uptake (net photosynthesis minus respiration of leaves at night) and absorbed irradiance was 13.0 mmol C mol(-1) (equivalent to 0.72 kg C GJ(-1)). This is low compared with values reported for other temperate forests, but is consistent with limitations to photosynthesis in the canopy attributable mainly to low nitrogen availability and associated low leaf area index. 相似文献
4.
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. 相似文献
5.
Effects of photosynthetic photon flux density (PPFD) on leaf gas exchange of lychee (Litchi chinensis Sonn.) were studied in field-grown "Kwai May Pink" and "Salathiel" orchard trees and young potted "Kwai May Pink" plants during summer in subtropical Queensland (27 degrees S). Variations in PPFD were achieved by shading the trees or plants 1 h before measurement at 0800 h. In a second experiment, potted seedlings of "Kwai May Pink" were grown in a heated greenhouse in 20% of full sun (equivalent to maximum noon PPFD of 200 micromol m(-2)xs(-1)) and their growth over three flush cycles was compared with seedlings grown in full sun (1080 micromol m(-2)xs(-1)). Young potted plants of "Kwai May Pink" were also grown outdoors in artificial shade that provided 20, 40, 70 or 100% of full sun (equivalent to maximum PPFDs of 500, 900, 1400 and 2000 micromol m(-2)xs(-1)) and measured for shoot extension and leaf area development over one flush cycle. Net CO2 assimilation increased asymptotically in response to increasing PPFD in both orchard trees and young potted plants. Maximum rates of CO2 assimilation (11.9 +/- 0.5 versus 6.3 +/- 0.2 micromol CO2 m(-2) s(-1)), dark respiration (1.7 +/- 0.3 versus 0.6 +/- 0.2 micromol CO2 m(-2) s(-1)), quantum yield (0.042 +/- 0.005 versus 0.027 +/- 0.003 mol CO2 mol(-1)) and light saturation point (1155 versus 959 micromol m(-2) s(-1)) were higher in orchard trees than in young potted plants. In potted seedlings grown in a heated greenhouse, shoots and leaves exposed to full sun expanded in a sigmoidal pattern to 69 +/- 12 mm and 497 +/- 105 cm(2) for each flush, compared with 27 +/- 7 mm and 189 +/- 88 cm(2) in shaded seedlings. Shaded seedlings were smaller and had higher shoot:root ratios (3.7 versus 3.1) than seedlings grown in full sun. In the potted plants grown outdoors in 20, 40, 70 or 100% of full sun, final leaf area per shoot was 44 +/- 1, 143 +/- 3, 251 +/- 7 and 362 +/- 8 cm(2), respectively. Shoots were also shorter in plants grown in shade than in plants grown in full sun (66 +/- 5 mm versus 101 +/- 2 mm). Photosynthesis in individual leaves of lychee appeared to be saturated at about half full sun, whereas maximum leaf expansion occurred at higher PPFDs. We conclude that lychee plants can persist as seedlings on the forest floor, but require high PPFDs for optimum growth. 相似文献
6.
Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) branch segments were used to test the hypothesis that compression wood reduces xylem transport efficiency. Whole 3-year-old segments were first measured for specific conductivity (k(s), m(2) s(-1) MPa(-1)), then split lengthwise into upper and lower halves, the latter containing all or most of the compression wood in the segment. Halves were then remeasured for k(s) using a new technique that prevents leakage of permeating fluid during measurements. Lower branch halves had significantly lower k(s) than upper halves (6.4 +/- 0.3 versus 9.3 +/- 0.3 m(2) s(-1) MPa(-1) x 10(-4), respectively; n = 36), and despite their larger size, significantly lower hydraulic conductivity (k(h), m(4) s(-1) MPa(-1)) than upper halves. Lower branch halves had higher specific gravity (0.51 +/- 0.01 versus 0.45 +/- 0.01; n = 36), lower water content (123 +/- 2% versus 155 +/- 3%; n = 36), and larger proportions of volume occupied by both cell wall and air than upper halves. Lower halves had more tracheids per annual ring than upper halves (73 +/- 3 versus 63 +/- 2 per radial transect, respectively; n = 36), but tracheids were shorter and had narrower lumens than those of upper branch halves. Differences in hydraulic properties between upper and lower halves suggest that compression wood does reduce xylem transport efficiency. In contrast, the amount of compression wood in each sample did not explain any variation in whole unsplit sample hydraulic properties. 相似文献
7.
Carswell FE Meir P Wandelli EV Bonates LC Kruijt B Barbosa EM Nobre AD Grace J Jarvis PG 《Tree physiology》2000,20(3):179-186
The vertical profile in leaf photosynthetic capacity was investigated in a terra firme rain forest in central Amazonia. Measurements of photosynthesis were made on leaves at five levels in the canopy, and a model was fitted to describe photosynthetic capacity for each level. In addition, vertical profiles of photosynthetic photon flux density, leaf nitrogen concentration and specific leaf area were measured. The derived parameters for maximum rate of electron transport (J(max)) and maximum rate of carboxylation by Rubisco (V(cmax)) increased significantly with canopy height (P < 0.05). The highest J(max) for a single canopy level was measured at the penultimate canopy level (20 m) and was 103.9 &mgr;mol m(-2) s(-1) +/- 24.2 (SE). The highest V(cmax) per canopy height was recorded at the top canopy level (24 m) and was 42.8 +/- 5.9 &mgr;mol m(-2) s(-1). Values of J(max) and V(cmax) at ground level were 35.8 +/- 3.3 and 20.5 +/- 1.3 &mgr;mol m(-2) s(-1), espectively. The increase in photosynthetic capacity with increasing canopy height was strongly correlated with leaf nitrogen concentration when examined on a leaf area basis, but was only weakly correlated on a mass basis. The correlation on an area basis can be largely explained by the concomitant decrease in specific leaf area with increasing height. Apparent daytime leaf respiration, on an area basis, also increased significantly with canopy height (P < 0.05). We conclude that canopy photosynthetic capacity can be represented as an average vertical profile, perturbations of which may be explained by variations in the environmental variables driving photosynthesis. 相似文献
8.
Roots of hardwoods have been shown to be more vulnerable to xylem cavitation than stems. This study examined whether this pattern is also observed in a conifer species. Vulnerability to cavitation was determined from the pressure required to inject air into the vascular system of hydrated roots and stems, and reduce hydraulic conductance of the xylem. According to the air-seeding hypothesis for the cavitation mechanism, these air pressures predict the negative xylem pressure causing cavitation in dehydrating stems. This was evaluated for stems of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and white fir (Abies concolor (Gord. & Glend.) Lindl.). The air-injection method was applied to roots and stems of different sizes and positions in Douglas-fir trees. Roots, especially smaller roots with a xylem diameter < 5 mm, were more vulnerable to cavitation than stems. Mean cavitation pressure for smaller roots was -2.09 +/- 0.42 versus -3.80 +/- 0.19 MPa for larger roots (> 8 mm diameter). Within the shoot system, smaller stems (< 5 mm diameter) were most vulnerable to cavitation, having a mean cavitation pressure of -4.23 +/- 0.565 versus -5.27 +/- 0.513 MPa for large stems (> 8 mm diameter). There was no correlation between tracheid diameter and mean cavitation pressure within root or stem systems, despite larger tracheid diameters in roots (23.3 +/- 3.9 micro m) than in stems (9.2 +/- 1.6 micro m). Smaller safety margins from cavitation in roots may be beneficial in limiting water use during mild drought, and in protecting the stem from low xylem pressures during extreme drought. 相似文献
9.
We tested the hypothesis that transfer conductance (gi) of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings is reduced by water stress. Seedlings were irrigated with a solution of 25% polyethylene glycol so as to impose water stress rapidly, thereby limiting acclimatory responses. Transfer conductance was measured pre-treatment and post-treatment by two methods. Water stress reduced net photosynthesis by 20-50%. The initial slope of the rate of photosynthesis (A) over the intercellular carbon dioxide (CO2) concentration (Ci) response was reduced by water stress, indicating that reduced photosynthesis was not wholly accounted for by reduced stomatal conductance. The carbon isotope and chlorophyll fluorescence methods both indicated that water stress decreased gi. From isotopic measurements with 1% O2, gi was 0.076 +/- 0.009 (mean +/- SE) mol m(-2) s(-1) in well-watered seedlings and 0.044 +/- 0.004 mol m(-2) s(-1) in water-stressed seedlings. Fluorescence estimates of gi were 0.08 +/- 0.01 mol m(-2) s(-1) in well-watered seedlings and 0.044 +/- 0.004 mol m(-2) s(-1) in water-stressed seedlings. The drought-induced reduction in gi was responsible for the reduction in slope of the A/Ci response, and thus there was no difference in the slope of the A over the chloroplastic CO2 concentration (Cc) response between treatments and no indication of impaired mesophyll metabolism. These data illustrate that impairments of mesophyll metabolism can be revealed only from analysis of the A/Cc response. 相似文献
10.
Biophysical constraints on leaf expansion in a tall conifer 总被引：3，自引：0，他引：3
The physiological mechanisms responsible for reduced extension growth as trees increase in height remain elusive. We evaluated biophysical constraints on leaf expansion in old-growth Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees. Needle elongation rates, plastic and elastic extensibility, bulk leaf water (Psi(L)) and osmotic (Psi(pi)) potential, bulk tissue yield threshold and final needle length were characterized along a height gradient in crowns of > 50-m-tall trees during the period between bud break and full expansion (May to June). Although needle length decreased with increasing height, there was no height-related trend in leaf plastic extensibility, which was highest immediately after bud break (2.9%) and declined rapidly to a stable minimum value (0.3%) over a 3-week period during which leaf expansion was completed. There was a significant positive linear relationship between needle elongation rates and plastic extensibility. Yield thresholds were consistently lower at the upper and middle crown sampling heights. The mean yield threshold across all sampling heights was 0.12 +/- 0.03 MPa on June 8, rising to 0.34 +/- 0.03 MPa on June 15 and 0.45 +/- 0.05 MPa on June 24. Bulk leaf Psi(pi) decreased linearly with increasing height at a rate of 0.004 MPa m(-1) during the period of most rapid needle elongation, but the vertical osmotic gradient was not sufficient to fully compensate for the 0.015 MPa m(-1) vertical gradient in Psi(L), implying that bulk leaf turgor declined at a rate of about 0.011 MPa m(-1) increase in height. Although height-dependent reductions in turgor appeared to constrain leaf expansion, it is possible that the impact of reduced turgor was mitigated by delayed phenological development with increasing height, which resulted in an increase with height in the temperature during leaf expansion. 相似文献
11.
We determined fine root biomass and production of 15-, 35- and 100-year-old Scots pine (Pinus sylvestris L.) stands during three growing seasons. Fine roots were sampled by the soil core method. Mean (+/- SE) annual fine root biomass of Scots pine in the 15-, 35- and 100-year-old stands was 220 +/- 25, 357 +/- 21 and 259 +/- 26 g m(-2), respectively. Fine root biomass of the understory vegetation was 159 +/- 54 g m(-2), 244 +/- 30 and 408 +/- 81 g m(-2), and fine root necromass was 500 +/- 112, 1,047 +/- 452 and 1,895 +/- 607 g m(-2) in the sapling, pole stage and mature stands, respectively. Both understory and Scots pine fine root production increased with stand age. Mean annual Scots pine fine root production was 165 +/- 131, 775 +/- 339 and 860 +/- 348 g m(-2) year(-1) in the sapling, pole stage and mature stand, respectively. The respective mean annual production of all fine roots (Scots pine and understory) was 181 +/- 129, 1,039 +/- 497 and 1,360 +/- 869 g m(-2) year(-1). The Scots pine and understory fine root biomass, necromass and production varied in relation to stand age, although the variation was not statistically significant. 相似文献
12.
Fast-growing tree clones selected for biomass plantations are highly productive and therefore likely to use more water than the agricultural crops they replace. We report field measurements of transpiration through the summer of 1994 from two poplar clones, Beaupré (Populus trichocarpa Torr. & A. Gray x P. deltoides Bartr. ex Marsh.) and Dorschkamp (P. deltoides x P. nigra L.), grown as unirrigated short-rotation coppice in southern England. Stand transpiration was quantified by scaling up from sap flow measurements made with the heat balance method in a sample of stems. Leaf conductances, leaf area development, meteorological variables and soil water deficit were also measured to investigate the response of the trees to the environment. High rates of transpiration were found for Beaupré. In June, when soil water was plentiful, the mean (+/- SD) transpiration rate over an 18-day period was 5.0 +/- 1.8 mm day(-1), reaching a maximum of 7.9 mm day(-1). Transpiration rates from Dorschkamp were lower, as a result of its lower leaf area index. High total leaf conductances were measured for both Beaupré (0.34 +/- 0.17 mol m(-2) s(-1)) and Dorschkamp (0.39 +/- 0.16 mol m(-2) s(-1)). Leaf conductance declined slightly with increasing atmospheric vapor pressure deficit in both clones, but only in Beaupré did leaf conductance decrease as soil water deficit increased. 相似文献
13.
We used a novel digital autoradiographic technique that enabled, for the first time, simultaneous visualization and quantification of spatial and temporal changes in carbon allocation patterns in ectomycorrhizal mycelia. Mycorrhizal plants of Pinus sylvestris L. were grown in microcosms containing non-sterile peat. The time course and spatial distribution of carbon allocation by P. sylvestris to mycelia of its mycorrhizal partners, Paxillus involutus (Batsch) Fr. and Suillus bovinus (L.): Kuntze, were quantified following 14C pulse labeling of the plants. Litter patches were used to investigate the effects of nutrient resource quality on carbon allocation. The wood-decomposer fungus Phanerochaete velutina (D.C.: Pers.) Parmasto was introduced to evaluate competitive and territorial interactions between its mycelial cords and the mycelial system of S. bovinus. Growth of ectomycorrhizal mycelium was stimulated in the litter patches. Nearly 60% of the C transferred from host plant to external mycorrhizal mycelium (> 2 mm from root surfaces) was allocated to mycelium in the patches, which comprised only 12% of the soil area available for mycelial colonization. Mycelia in the litter patch most recently colonized by mycorrhizal mycelium received the largest investment of carbon, amounting to 27 to 50% of the total 14C in external mycorrhizal mycelium. The amount of C transfer to external mycelium of S. bovinus following pulse labeling was reduced from a maximum of 167 nmol in systems with no saprotroph to a maximum of 61 nmol in systems interacting with P. velutina. The 14C content of S. bovinus mycelium reached a maximum 24-36 h after labeling in control microcosms, but allocation did not reach a peak until 56 h after labeling, when S. bovinus interacted with mycelium of P. velutina. The mycelium of S. bovinus contained 9% of the total 14C in the plants (including mycorrhizae) at the end of the experiment, but this was reduced to 4% in the presence of P. velutina. The results demonstrate the dynamic manner in which mycorrhizal mycelia deploy C when foraging for nutrients. The inhibitory effect of the wood-decomposer fungus P. velutina on C allocation to external mycorrhizal mycelium has important implications for nutrient cycling in forest ecosystems. 相似文献
14.
Wood density influences both the physiological function and economic value of tree stems. We examined the relationship between phosphorus (P) supply and stem wood density of Eucalyptus grandis Hill ex Maiden seedlings grown with varying soil P additions and determined how changes in wood anatomy and biomass partitioning affect the relationship. Plant height, stem diameter and total biomass increased by 400-500% with increasing P supply. Stem wood density decreased sharply from 520 to 380 kg m(-3) as P supply increased to 70 mg P kg(soil) (-1). Further increases in P supply to 1000 mg P kg(soil) (-1) had no effect on wood density. The increase in wood density at low soil P supply arose principally from enhanced secondary wall thickening of stem fiber cells. Cell wall thickness increased from 3.6 to 4.5 microm as soil P supply decreased. Because fiber cell diameter was independent of soil P (12 microm +/- 0.3), the proportion of the stem occupied by cell wall material increased as P supply declined. The enhanced secondary wall thickening of stem fiber cells at low P supply was not associated with changes in whole-plant biomass partitioning. Instead, low P supply appeared to alter biomass partitioning within the stem in favor of secondary wall thickening. Thus, increased wood density in E. grandis seedlings grown at low P soil supply was associated with inhibited stem cambial activity, resulting in an increased proportion of photoassimilates available for secondary wall thickening of fiber cells. 相似文献
15.
Root and hypocotyl elongation, water status and solute accumulation were studied in osmotically stressed seedlings of the tropical tree, Colophospermum mopane (Kirk ex Benth.) Kirk ex J. Léonard, which grows in hot arid areas of southern and central Africa. Seeds were imbibed for 24 h and then subjected to a polyethylene-glycol-generated osmotic stress of -0.03 (control), -0.2, -0.8, -1.6 or -2.0 MPa for 60 h. Seedlings subjected to moderate water stress (-0.2 MPa) had higher root growth rates (2.41 +/- 0.24 mm h(-1)), greater final root lengths (111 +/- 3.8 mm) and longer cells immediately behind the root elongation zone than control seedlings (1.70 +/- 0.15 mm h(-1) and 93 +/- 3.9 mm, respectively). Root lengths of seedlings in the -0.8 and -1.6 MPa treatments were similar to those of control seedlings, whereas the -2.0 MPa seedlings had significantly shorter roots. Both root and hypocotyl tissues exhibited considerable osmotic adjustment to the external water potential treatments. Seedlings in the -0.03, -0.2, and -0.8 MPa treatments had similar cell turgor pressures (0.69 +/- 0.10, 0.68 +/- 0.07 and 0.57 +/- 0.04 MPa, respectively), whereas the -2.0 MPa treatment lowered cell turgor pressure to 0.17 +/- 0.04 MPa. Root vacuolar osmotic pressures were generally similar to sap osmotic pressures, indicating that the increased root elongation observed in moderately water-stressed seedlings was not caused by increased turgor pressure difference. Neutral-fraction solute concentrations, including the osmoticum pinitol, increased approximately two-fold in root sap in response to a low external water potential. In hypocotyl sap of seedlings in the -2.0 MPa treatment, pinitol more than doubled, sucrose increased from about 2 to 75 mol m(-3) but glucose and fructose remained unchanged and, as a result, total sugars increased only slightly. The benefits of rapid early root elongation and osmoticum accumulation under conditions of water stress are discussed in relation to seedling establishment. 相似文献
16.
We tested the hypothesis that, in tropical pioneer tree species, vertical leaf angle contributes to high carbon gain because it minimizes damage caused by high irradiances. Diurnal changes in leaf gas exchange and chlorophyll fluorescence were measured in east-facing (EL), west-facing (WL) leaves, and in leaves artificially held horizontal (HL) in the uppermost canopy of Macaranga conifera (Zoll.) Muell. Arg. Maximum values of net photosynthetic rate (P(n)) for EL and HL reached 12 &mgr;mol m(-2) s(-1), whereas maximum P(n) for WL was only 6 &mgr;mol m(-2) s(-1). Midday depressions of P(n) and stomatal conductance occurred at high photosynthetic photon flux densities (PPFD), especially for HL. Photosystem II quantum yield (DeltaF/F(m)') of HL for a given PPFD at the leaf surface was lower in the afternoon than in the morning. Values of DeltaF/F(m)' for HL measured at dusk were lower than those measured just before dawn, suggesting that HL suffered from high light and heat load. Variations in the morphology and physiology of the canopy leaves were associated with different light environments, and there was circumstantial evidence of a transitional point at a PPFD of about 20-30% of full sunlight. Maximum P(n) and nitrogen (N) content were higher in upper canopy leaves than in lower canopy leaves, and the differences were mainly associated with differences in lamina thickness. We conclude that the vertical leaf angle and thick lamina of the top canopy leaves contributed to enhance total carbon gain of the whole plant. 相似文献
17.
Ten-year-old 'Tai So' lychee (Litchi chinensis Sonn.) trees growing on a sandy loam soil in subtropical South Africa (latitude 25 degrees S) were watered weekly (well-watered treatment) or droughted from late July until January (drought treatment). After 16 weeks, at which time the trees obtained most of their water from below 150 cm, average soil water content at 0 to 150 cm depth was 14.5 +/- 0.1% in the well-watered treatment and reached a minimum of 7.6% in the drought treatment. At Week 7, minimum leaf water potential (Psi(L)) in the morning and early afternoon declined to -2.6 and -2.8 MPa, respectively, in droughted trees compared with -1.5 and -2.2 MPa, respectively, in well-watered trees. From Week 9, stomatal conductance and net CO(2) assimilation rate ranged from 70 to 300 mmol m(-2) s(-1) and 3 to 13 micro mol CO(2) m(-2) s(-1), respectively, in well-watered trees. The corresponding values for droughted trees were 50 to 180 mmol m(-2) s(-1) and 2 to 6 micro mol CO(2) m(-2) s(-1). Five weeks after rewatering the droughted trees, gas exchange had not recovered to the rate in well-watered trees, although tree water status recovered within a week of rewatering. In the well-watered trees, water use (E(t)) was 26 +/- 1 mm week(-1) with evaporation (E(p)) of 20 to 70 mm week(-1) indicating a crop factor (k(c) = E(t)/E(p)) of 0.4 to 1.2. Before anthesis, tree water status did not affect extension growth of floral panicles or leafy shoots. In contrast, no vegetative shoots were initiated after fruit set in the droughted trees when Psi(L) in the morning declined to -2.5 MPa. Water deficits reduced initial fruit set by 30% and final fruit set by 70% as a result of fruit splitting (41.2 +/- 4.0% versus 10.0 +/- 1.3%). Water deficits did not alter the sigmoidal pattern of fruit growth, but reduced yield from 51.4 +/- 5.5 kg tree(-1) in well-watered trees to 7.4 +/- 3.3 kg tree(-1) in droughted trees. 相似文献
18.
Specific leaf area (SLA) and leaf area index (LAI) were estimated using site-specific allometric equations for a boreal black spruce (Picea mariana (Mill.) BSP) fire chronosequence in northern Manitoba, Canada. Stands ranged from 3 to 131 years in age and had soils that were categorized as well or poorly drained. The goals of the study were to: (i) measure SLA for the dominant tree and understory species of boreal black spruce-dominated stands, and examine the effect of various biophysical conditions on SLA; and (ii) examine leaf area dynamics of both understory and overstory for well- and poorly drained stands in the chronosequence. Overall, average SLA values for black spruce (n = 215), jack pine (Pinus banksiana Lamb., n = 72) and trembling aspen (Populus tremuloides Michx., n = 27) were 5.82 +/- 1.91, 5.76 +/- 1.91 and 17.42 +/- 2.21 m2 x kg-1, respectively. Foliage age, stand age, vertical position in the canopy and soil drainage had significant effects on SLA. Black spruce dominated overstory LAI in the older stands. Well-drained stands had significantly higher overstory LAI (P < 0.001), but lower understory LAI (P = 0.022), than poorly drained stands. Overstory LAI was negligible in the recent (3-12 years old) burn sites and highest in the 70-year-old burn site (6.8 and 3.0 in the well- and poorly drained stands, respectively), declining significantly (by 30-50%) from this peak in the oldest stands. Understory leaf area represented a significant portion (> 40%) of total leaf area in all stands except the oldest. 相似文献
19.
Root respiration uses a significant proportion of photosynthetically fixed carbon (C) and is a globally important source of C liberated from soils. Mangroves, which are an important and productive forest resource in many tropical and subtropical countries, sustain a high ratio of root to shoot biomass which may indicate that root respiration is a particularly important component in mangrove forest carbon budgets. Mangroves are often exposed to nutrient pollution from coastal waters. Here we assessed the magnitude of fine root respiration in mangrove forests in Belize and investigated how root respiration is influenced by nutrient additions. Respiration rates of excised fine roots of the mangrove, Rhizophora mangle L., were low (4.01 +/- 0.16 nmol CO(2) g(-1) s(-1)) compared to those measured in temperate tree species at similar temperatures. In an experiment where trees where fertilized with nitrogen (N) or phosphorus (P) in low productivity dwarf forests (1-2 m height) and more productive, taller (4- 7 m height) seaward fringing forests, respiration of fine roots did not vary consistently with fertilization treatments or with forest stature. Fine roots of taller fringe trees had higher concentrations of both N and P compared to dwarf trees. Fertilization with P enhanced fine root P concentrations in both dwarf and fringe trees, but reduced root N concentrations compared to controls. Fertilization with N had no effect on root N or P concentrations. Unlike photosynthetic C gain and growth, which is strongly limited by P availability in dwarf forests at this site, fine root respiration (expressed on a mass basis) was variable, but showed no significant enhancements with nutrient additions. Variation in fine root production and standing biomass are, therefore, likely to be more important factors determining C efflux from mangrove sediments than variations in fine root respiration per unit mass. 相似文献
20.
We evaluated the response of Japanese larch (Larix kaempferi Sieb. & Zucc.) to elevated atmospheric CO(2) concentration ([CO(2)]) (689 +/- 75 ppm in 2002 and 697 +/- 90 ppm in 2003) over 2 years in a field experiment with open-top chambers. Root activity was assessed as nitrogen, phosphorus and potassium uptake rates estimated from successive measurements of absorbed amounts. Dry matter production of whole plants was unaffected by elevated [CO(2)] in the first year of treatment, but increased significantly in response to elevated [CO(2)] in the second year. In contrast, elevated [CO(2)] increased the root to shoot ratio and fine root dry mass in the first year, but not in the second year. Elevated [CO(2)] had no effect on tissue N, P and K concentrations. Uptake rates of N, P and K correlated with whole-plant relative growth rates, but were unaffected by growth [CO(2)], as was ectomycorrhizal colonization, a factor assumed to be important for nutrient uptake in trees. We conclude that improved growth of Larix kaempferi in response to elevated [CO(2)] is accompanied by increased root biomass, but not by increased root activity. 相似文献