The effects of elevated [CO2] and water availability on growth and physiology of peach (Prunus persica) plants

ABSTRACT

Peach (Prunus persica L.) seedlings were germinated and grown for two growing seasons either in open top chambers (OTC) with ambient (350 μmol mol^-1) or elevated (700 μmol mol^-1) [CO₂], or in an outside control plot, all located inside a glasshouse. The seedlings were grown in 10 dm³ pots and were fertilised once a week following Ingestad principles in order to supply mineral nutrients at free access rates. In the second growing season, rapid onset of water stress was imposed on rapidly growing peach seedlings by withholding water for a four-week drying cycle. In elevated [CO₂], seedlings had a total dry mass which was 33% higher than that in ambient [CO₂]. This increase was largely a consequence of increased height growth. [CO₂] and irrigation treatments had only small effects on allocation, and there was no increase in root allocation with low water availability possibly as consequence of the high-nutrient regime. Specific leaf area was significantly reduced in elevated [CO₂], and probably resulted from increases in starch concentrations. Stomatal conductance (g _s) was not affected by elevated [CO₂] both in well-watered and water-stressed seedlings. The combination of increased assimilation rate (A) and unchanged g _s led to large increases in intrinsic water use efficiency in response to elevated [CO₂]. The A/C _i curves were used to derive the parameters describing photosynthetic capacity, A_max, J_max and V_cmax . These parameters were similar among [CO₂] treatments; thus, there was no downward acclimation of photosynthesis in elevated [CO₂]. Moreover, A_max, J_max and V_cmax scaled linearly with leaf N content per unit leaf area. This indicates that the whole-plant source-sink balance of peach seedlings was not disrupted by growth in elevated [CO₂], because root volume and nutrient supply were non-restricting. These values may be used in scaling up models to improve their ability to predict the magnitude of tree responses to climate change in the Mediterranean area.     

The combined effects of elevated CO2 levels and UV-B radiation on growth characteristics ofElymus athericus (= E. pycnanathus)

Elymus athericus (Link) Kerguélen, a C₃ grass, was grown in a greenhouse experiment to determine the effect of enhanced atmospheric CO₂ and elevated UV-B radiation levels on plant growth. Plants were subjected to the following treatments; a) ambient CO₂-control UV-B, b) ambient CO₂-elevated UV-B, c) double CO₂-control UV-B, d) double CO₂-elevated UV-B. Elevated CO₂ concentrations stimulated plant growth, biomass production was 67% higher than at ambient CO₂. Elevated UV-B radiation had a negative effect on growth, biomass production was depressed by 31%. Enhanced CO₂ combined with elevated UV-B levels caused a biomass depression of 8% when compared with the control plants. UV-B induced growth depression can be modified by a growth stimulus caused by high CO₂ concentrations. Growth analysis has been performed and possible physiological mechanisms behind changing growth parameters are discussed.     

Interaction between elevated atmospheric concentration of CO2 and humidity on plant growth: comparison between cotton and radish

Cotton plants (Gossypium hirsutum L. var Deltapine 90) and radish plants (Raphanus sativus L var Round Red) were grown under full sunlight using a factorial combination of atmospheric CO₂ concentrations (350 µmol mol^-1 and 700 µmol mol^-1) and humidities (35% and 90% RH at 32 °C during the day). Cotton plants showed large responses to increased humidity and to doubled CO₂. In cotton plants, the enhanced dry matter yield due to doubled CO₂ concentration was 1.6-fold greater at low humidity than at high humidity. Apart from the direct effect of elevated CO₂ level on photosynthesis, the greater effect of doubled CO₂ concentration on dry matter yield at low humidity was probably due to: (1) increased leaf water potential caused by reduction of transpiration resulting from the negative CO₂ response of stomata to increased CO₂ concentration the consequence being greater leaf area expansion; (2) reduction of CO₂ assimilation rate at low humidity and normal CO₂ concentration as a result of humidity response of stomata causing reduction of intercellular CO₂ concentration. In contrast, apart from the very early stage of development, radish plants do not respond to increased humidity but had a relatively large response to doubled CO₂ concentration. Furthermore, due to the determinate growth pattern as well as having a prominent storage root, the extra photoassimilate derived at doubled CO₂ level is allocated to the storage root.Abbreviatios DAE day after emergence - LAD leaf areal density (leaf dry weight/leaf area) - LAR leaf area ratio (leaf area/plant dry weight) - NAR net assimilation rate - c_i internal CO₂ concentration - PPFD photosynthetic photon flux density - RGR relative growth rate - RLAGR relative leaf area growth rate - VPD vapour pressure deficit     

Comparison of effects of salt and alkali stresses on the growth and photosynthesis of wheat

The seedlings of wheat were treated by salt-stress (SS, molar ratio of NaCl: Na₂SO₄ = 1: 1) and alkali-stress (AS, molar ratio of NaHCO₃: Na₂CO₃ = 1: 1). Relative growth rate (RGR), leaf area, and water content decreased with increasing salinity, and the extents of the reduction under AS were greater than those under SS. The contents of photosynthetic pigments did not decrease under SS, but increased at low salinity. On the contrary, the contents of photosynthetic pigments decreased sharply under AS with increasing salinity. Under SS, the changes of net photosynthetic rate (P _N), stomatal conductance (g _s), and transpiration rate (E) were similar and all varied in a single-peak curve with increasing salinity, and they were lower than those of control only at salinity over 150 mM. Under AS, P _N, g _s, and E decreased sharply with rising salinity. The decrease of g _s might cause the obvious decreases of E and intercellular CO₂ concentration, and the increase of water use efficiency under both stresses. The Na⁺ content and Na⁺/K⁺ ratio in shoot increased and the K⁺ content in shoot decreased under both stresses, and the changing extents under AS were greater than those under SS. Thus SS and AS are two distinctive stresses with different characters; the destructive effects of AS on the growth and photosynthesis of wheat are more severe than those under SS. High pH is the key feature of the AS that is different from SS. The buffer capacity is essentially the measure of high pH action on plant. The deposition of mineral elements and the intracellular unbalance of Na⁺ and K⁺ caused by the high pH at AS might be the reason of the decrease of P _N and g _s and of the destruction of photosynthetic pigments.     

The influences of increased CO2 and water supply on growth,biomass allocation and water use efficiency of Sinapis alba L. grown under different wind speeds

We examined how independent and interactive effects of CO₂ concentrations, water supply and wind speed affect growth rates, biomass partitioning, water use efficiency, diffusive conductance and stomatal density of plants. To test the prediction that wind stress will be ameliorated by increased CO₂ and/or by unrestricted water supply we grew Sinapis alba L. plants in controlled chambers under combinations of two levels of CO₂ (350 ppmv, 700 ppmv), two water regimes and two wind speeds (0.3 ms^–1, 3.7 ms^–1). We harvested at ten different dates over a period of 60 days. A growth analysis was carried out to evaluate treatment effects on plant responses. Plants grown both in increased CO₂ and in low wind conditions had significantly greater stem length, leaf area and dry weights of plant parts. Water supply significantly affected stem diameter, root weight and leaf area. CO₂ enrichment significantly increased the rate of biomass accumulation and the relative ratio of biomass increase to leaf area expansion. High wind speed significantly reduced plant growth rates and the rate of leaf area expansion was reduced more than the rate of biomass accumulation. Regression analysis showed significant CO₂ effects on the proportion of leaf and stem dry weight to total dry weight. A marked plant-age effect was dependent on water supply, wind speed and CO₂ concentration. A reduced water supply significantly decreased the stomatal conductance, and water use efficiency significantly increased with a limited water supply, low wind and increased CO₂. We found significant CO₂ x wind effects for water diffusion resistance, adaxial number of stomata and water use efficiencies and significant wind x water effect for water use efficiency. In conclusion, wind stress was ameliorated by growing in unrestricted water but not by growing in increased CO₂.     

Water relations and gas exchange in olive trees under regulated deficit irrigation and partial rootzone drying

It is widely believed that partial root drying (PRD) reduces water losses by transpiration without affecting yield. However, experimental work carried out to date does not always support this hypothesis. In many cases a PRD treatment has been compared to a full irrigated treatment, so doubt remains on whether the observed benefits correspond to the switching of irrigation or just to PRD being a deficit irrigation treatment. In addition, not always a PRD treatment has been found advantageous as compared to a companion regulated deficit irrigation (RDI) treatment. In this work we have compared the response of mature ‘Manzanilla‘ olive trees to a PRD and an RDI treatment in which about 50% of the crop evapotranspiration (ET_c) was supplied daily by localised irrigation. We alternated irrigation in the PRD treatment every 2 weeks in 2003 and every 3 weeks in 2004. Measurements of stem water potential (Ψ_stem), stomatal conductance (g _s) and net CO₂ assimilation rate (A) were made in trees of both treatments, as well as in trees irrigated to 100% of ET_c (Control trees) and in Rain-fed trees. Sap flow was also measured in different conductive organs of trees under both PRD and RDI treatments, to evaluate the influence of alternating irrigation on root water uptake and tree water consumption. We found small and random differences in Ψ_stem, g _s and A, which gave no evidence of PRD causing a positive effect on the olive tree performance, as compared to RDI. Stomatal conductance decreased in PRD trees as compared to Control trees, but a similar decrease in g _s was also recorded in the RDI trees. Sap flow measurements, which reflected water use throughout the irrigation period, also showed no evidence of g _s being more reduced in PRD than in RDI trees. Daily water consumption was also similar in the trees of the deficit irrigation treatments, for most days, throughout the irrigation period. Alternating irrigation in PRD trees did not cause a change in either water taken up by main roots at each side of the trees, or in the sap flow of both trunk locations and main branches of each side. Results from this work, and from previous work conducted in this orchard, suggest that transpiration is restricted in trees under deficit irrigation, in which roots are left in drying soil when water is applied by localised irrigation, and that there is no need to alternate irrigation for achieving this effect. Section Editor: R. E. Munns     

Photosynthetic photon flux density,carbon dioxide concentration,and vapor pressure deficit effects on photosynthesis in cacao seedlings

Independent short-term effects of photosynthetic photon flux density (PPFD) of 50–400 μmol m⁻² s⁻¹, external CO₂ concentration (C _a) of 85–850 cm³ m⁻³, and vapor pressure deficit (VPD) of 0.9–2.2 kPa on net photosynthetic rate (P _N), stomatal conductance (g _s), leaf internal CO₂ concentration (C _i), and transpiration rates (E) were investigated in three cacao genotypes. In all these genotypes, increasing PPFD from 50 to 400 μmol m⁻² s⁻¹ increased P _N by about 50 %, but further increases in PPFD up to 1 500 μmol m⁻² s⁻¹ had no effect on P _N. Increasing C _a significantly increased P _N and C _i while g _s and E decreased more strongly than in most trees that have been studied. In all genotypes, increasing VPD reduced P _N, but the slight decrease in g _s and the slight increase in C _i with increasing VPD were non-significant. Increasing VPD significantly increased E and this may have caused the reduction in P _N. The unusually small response of g _s to VPD could limit the ability of cacao to grow where VPD is high. There were no significant differences in gas exchange characteristics (g _s, C _i, E) among the three cacao genotypes under any measurement conditions.     

Solar light effects on growth,net photosynthesis,and leaf morphology of in vitro kiwifruit (Actinidia deliciosa) CV hayward

Summary Proliferating axillary shoots of kiwifruit (Actinidia deliciosa A. Chev., C. F. Liang and A. R. Ferguson), var.deliciosa, cv. ‘Hayward’ were grown under solar (SL), white (WL), and blue (BL) light regimens to determine the accumulation of fresh and dry weight, proliferation rate, shoot growth (length), and the net leaf photosynthetic capacity at the CO₂ concentration ranges of 200 to 350, 400 to 600, and 1200 to 1500 ppm. An histologic study determined the effects of light source on leaf stomatal density and tissue morphology. Dry and fresh matter accumulation was greatest, but callus development most limited under the SL regimen. Shoot proliferation was highest under WL and length under BL. Net photosynthetic capacity was highest for leaves grown under SL and lowest for those under BL; the leaves exposed to the latter regimen were also thinner and exhibited a less compact arrangement of palisade cells than those under WL and SL. Leaf stomata density was highest under the BL source.     

Compensatory responses of CO2 exchange and biomass allocation and their effects on the relative growth rate of ponderosa pine in different CO2 and temperature regimes

Increases in the concentration of atmospheric carbon dioxide may have a fertilizing effect on plant growth by increasing photosynthetic rates and therefore may offset potential growth decreases caused by the stress associated with higher temperatures and lower precipitation. However, plant growth is determined both by rates of net photosynthesis and by proportional allocation of fixed carbon to autotrophic tissue and heterotrophic tissue. Although CO₂ fertilization may enhance growth by increasing leaf-level assimilation rates, reallocation of biomass from leaves to stems and roots in response to higher concentrations of CO₂ and higher temperatures may reduce whole-plant assimilation and offset photosynthetic gains. We measured growth parameters, photosynthesis, respiration, and biomass allocation of Pinus ponderosa seedlings grown for 2 months in 2×2 factorial treatments of 350 or 650 bar CO₂ and 10/25° C or 15/30° C night/day temperatures. After 1 month in treatment conditions, total seedling biomass was higher in elevated CO₂, and temperature significantly enhanced the positive CO₂ effect. However, after 2 months the effect of CO₂ on total biomass decreased and relative growth rates did not differ among CO₂ and temperature treatments over the 2-month growth period even though photosynthetic rates increased 7% in high CO₂ treatments and decreased 10% in high temperature treatments. Additionally, CO₂ enhancement decreased root respiration and high temperatures increased shoot respiration. Based on CO₂ exchange rates, CO₂ fertilization should have increased relative growth rates (RGR) and high temperatures should have decreased RGR. Higher photosynthetic rates caused by CO₂ fertilization appear to have been mitigated during the second month of exposure to treatment conditions by a 3% decrease in allocation of biomass to leaves and a 9% increase in root:shoot ratio. It was not clear why diminished photosynthetic rates and increased respiration rates at high temperatures did not result in lower RGR. Significant diametrical and potentially compensatory responses of CO₂ exchange and biomass allocation and the lack of differences in RGR of ponderosa pine after 2 months of exposure of high CO₂ indicate that the effects of CO₂ fertilization and temperature on whole-plant growth are determined by complex shifts in biomass allocation and gas exchange that may, for some species, maintain constant growth rates as climate and atmospheric CO₂ concentrations change. These complex responses must be considered together to predict plant growth reactions to global atmospheric change, and the potential of forest ecosystems to sequester larger amounts of carbon in the future.     

Regulation of mesophyll photosynthesis in intact wheat leaves by cytoplasmic phosphate concentrations

The effect of D-(+)-mannose, inorganic phosphate (Pi) and mannose-6-phosphate on net mesophyll CO₂ assimilation rate (A) and stomatal conductance (g_s) of wheat (Triticum aestivum L.) leaves was studied. The compounds were supplied through the transpiration stream of detached leaves from plants grown in sand in growth cabinets or glasshouses, with different concentrations of Pi (0.25, 1.0 and 4.0 mM) supplied during growth. In all cases, 10 mM D-(+)mannose caused 40–60% reduction of A within 30 min, though the time courses differed for flag leaves and the sixth leaf on the mainstem of glasshouse- and cabinet-grown plants. D-(+)Mannose had a similar effect on A in leaves having a fourfold range in total phosphate content. Effects of D-(+)mannose in reducing g_s were always slower than on A. When the CO₂ concentration in the leaf chamber was adjusted to maintain intercellular CO₂ concentration (C_i) constant as A declined after mannose supply, g_s still declined indicating that stomatal closure was not caused by changing C_i. Supplying mannose-6-phosphate at 10 and 1 mM and Pi at 5 and 10 mM concentrations caused rapid reductions in g_s and also direct reductions in A. The observed effects of mannose and Pi on assimilation are consistent with the proposed regulatory role of cytoplasmic Pi in determining mesophyll carbon assimilation that has been derived previously using leaf discs, protoplasts and chloroplasts.Abbreviations and symbols A net mesophyll CO₂-assimilation rate - C_a, C_i external (assimilation-chamber) and intercellular CO₂ concentration, respectively - g_s stomatal conductance - Man6P mannose-6-phosphate - Pi orthophosphate     

Cytokinin activity of disubstituted aminopurines in Amaranthus

Cytokinin (CK) receptors have different affinities for certain ligands, and consequently, studies of the plant's response to CK analogues constitute a good approach to identify active compounds that trigger specific plant responses. In this study, N⁶ and N⁶,N⁶-substituted CK analogues were synthesized and their CK-like activity was examined in the Amaranthus betacyanin and the bacterial receptor assay. The compounds showed CK-like activities that were not always associated with their binding affinity to the Arabidopsis receptors AHK3 and CRE1/AHK4. The highest level of activity in both bioassays was obtained for the N⁶-alkylaminopurines, which showed an especially high binding affinity to AHK3. In contrast to previously published data, we found remarkable activity of N⁶,N⁶-alkylbenzylaminopurines in the Amaranthus betacyanin bioassay, which was not associated with their binding affinity to the tested receptors. The N⁶,N⁶-substituted CK that showed the highest activity at the lowest concentration, N⁶,N⁶-methylbenzylaminopurine (BAP-C1), was studied to determine its effect on different leaf parameters of whole Amaranthus plants, with benzylaminopurine (BAP) used as standard compound. The interaction with ethylene was examined in plants supplied with the ethylene-synthesis inhibitor aminooxiacetic acid (AOA). After 3 d, the CKs supplied in the solution culture exerted effects on leaf dry weight and gas-exchange parameters. These effects of exogenous CKs are suggested to be ethylene-synthesis dependent.     

Effects of above- and below-ground competition from shrubs on photosynthesis, transpiration and growth in Quercus robur L. seedlings

For a tree seedling to successfully establish in dense shrubbery, it must maintain function under heterogeneous resource availability. We evaluated leaf-level acclimation in photosynthetic capacity, seedling-level transpiration, and seedling morphology and growth to gain an understanding of the effects of above- and below-ground competition on Quercus robur seedlings. Experimental seedlings were established in a typical southern Swedish shrub community where they received 1 of 4 competition levels (above-ground, below-ground, above- and below-ground, or no competition), and leaf-level responses were examined between two growth flushes. Two years after establishment, first-flush leaves from seedlings receiving above-ground competition showed a maximum rate of photosynthesis (A_max) 40% lower than those of control seedlings. With the development of a second flush above the shrub canopy, A_max of these seedlings increased to levels equivalent to those of seedlings free of light competition. Shrubby competition reduced oak seedling transpiration such that seedlings exposed to above- and below-ground competition showed rates 43% lower than seedlings that were not exposed to competition. The impaired physiological function of oak seedlings growing amid competition ultimately led to a 60-74% reduction in leaf area, 29-36% reduction in basal diameter, and a 38-78% reduction in total biomass accumulation, but root to shoot ratio was not affected. Our findings also indicate that above-ground competition reduced A_max, transpiration and biomass accumulation more so than below-ground competition. Nevertheless, oak seedlings exhibited the ability to develop subsequent growth flushes with leaves that had an A_max acclimated to utilize increased light availability. Our findings highlight the importance of flush-level acclimation under conditions of heterogeneous resource availability, and the capacity of oak seedlings to initiate a positive response to moderate competition in a shrub community.     

Carbon dioxide assimilation and growth of red spruce (Picea rubens Sarg.) seedlings in response to ozone,precipitation chemistry,and soil type

Summary The influence of ozone, mist chemistry, rain chemistry, and soil type on CO₂ assimilation and growth of red spruce (Picea rubens Sarg.) seedlings was investigated over a 4-month period under controlled laboratory and glasshouse conditions. Growth was evaluated through interval estimates of aboveground relative growth rates (RGR) and the partitioning of biomass components at harvest to root, stem, and needle fractions. Precipitation chemistry treatments and O₃ exposure dynamics were based on reported characteristics of air chemistry and/or deposition in high-elevation forests of eastern North America. The two soils were collected from Camels Hump in the Green Mountains of Vermont and Acadia National Park on the Maine coast. Soil from Acadia had higher organic content, higher levels of extractable base cations, and lower levels of extractable aluminum and heavy metals. The only treatment variables that consistently influenced the growth of P. rubens were soil type and rain chemistry. In comparison with seedlings grown in soil from Acadia National Park, those grown in Camels Hump soil had significantly less needle (27%), stem (33%), and root (26%) biomass at harvest and statistically lower aboveground RGR within 2 months after initiation of the treatments. Seedlings grown in Camels Hump soil had significantly higher levels of aluminum (6.5X), copper (1.4X), and nickel (2.7X) in new needle tissue. The only influence of precipitation chemistry on the growth of P. rubens was a pattern of greater root and shoot biomass in seedlings experiencing the more acidic rain treatments. Interactive effects among the main treatment variables (e.g., acidic mist and O₃, acidic rain and soil type) on seedling growth were not notable. Rates of CO₂ assimilation and transpiration on a per gram needle dry weight basis [mol·g^-1·s^-1] were not influenced by any of the main treatment variables or their interaction. Because neither soil type nor precipitation chemistry influenced the efficiency of CO₂ assimilation per gram dry weight of needle tissue, the physiological mechanism underlying the growth response of P. rubens is attributed to a change in either whole-plant allocation of carbon resources or a direct toxic effect in the rhizosphere on root growth.     

Characterization of photosynthesis of Populus euphratica grown in the arid region

Net photosynthetic rate (P _N), stomatal conductance (g _s), intercellular CO₂ concentration (C _i), transpiration rate (E), water use efficiency (WUE), and stomatal limitation (L_s) of Populus euphratica grown at different groundwater depths in the arid region were measured. g _s of the trees with groundwater depth at 4.74 m (D₄) and 5.82 m (D₅) were lower and a little higher than that at 3.82 m (D₃), respectively. Compared with C _i and L_s of the D₃ trees, C _i decreased and L_s increased at 4.74 m, however, Ci increased and L_s decreased at D₅. Hence photosynthetic reduction of P. euphratica was attributed to either stomatal closure or non-stomatal factors depending on the groundwater depths in the plant locations. P _N of the D₃ trees was significantly higher than those at D₄ or D₅. The trees of D₄ and D₅ did not show a significant difference in their P _N, indicating that there are mechanisms of P. euphratica tolerance to mild and moderate drought stress.     

Comparative effects of salt-stress and alkali-stress on the growth,photosynthesis, solute accumulation,and ion balance of barley plants

We compared the effects of salt-stresses (SS, 1: 1 molar ratio of NaCl to Na₂SO₄) and alkali-stresses (AS, 1: 1 molar ratio of NaHCO₃ to Na₂CO₃) on the growth, photosynthesis, solute accumulation, and ion balance of barley seedlings, to elucidate the mechanism of AS (high-pH) damage to plants and the physiological adaptive mechanism of plants to AS. The effects of SS on the water content, root system activity, membrane permeability, and the content of photosynthetic pigments were much less than those of AS. However, AS damaged root function, photosynthetic pigments, and the membrane system, led to the severe reductions in water content, root system activity, content of photosynthetic pigments, and net photosynthetic rate, and a sharp increase in electrolyte leakage rate. Moreover, with salinity higher than 60 mM, Na⁺ content increased slowly under SS and sharply under AS. This indicates that high-pH caused by AS might interfere with control of Na⁺ uptake in roots and increase intracellular Na⁺ to a toxic level, which may be the main cause of some damage emerging under higher AS. Under SS, barley accumulated organic acids, Cl⁻, SO₄ ²⁻, and NO₃ ⁻ to balance the massive influx of cations, the contribution of inorganic ions to ion balance was greater than that of organic acids. However, AS might inhibit absorptions of NO₃ ⁻ and Cl⁻, enhance organic acid synthesis, and SO₄ ²⁻ absorption to maintain intracellular ion balance and stable pH.     

Responses of photosynthesis to irradiance and temperature in soybean,Glycine max (L.) Merr

The response of photosynthesis to irradiance and temperature during growth was investigated in two soybean genotypes. Soybean is a species that can modify its structure and metabolism so as to adapt to differing light conditions; its responses to rapid changes in irradiance are characterized by their flexibility. However, the temperature during growth can change the response to irradiance: moreover, there may be a marked interaction with genotype.The response of photosynthesis to irradiance consists of changes in leaf thickness, which bring about variations in the mesophyll resistance to CO₂ transfer. The increase in net photosynthesis per unit of leaf area is due to the increase in the amount of assimilating material beneath unit of area, as corroborated by the stability of the net photosynthesis per unit volume. Moreover, the response of photosynthesis to temperature is due to the mesophyll diffusion constant which decreases with the growth temperature.     

The effect of light quality and gibberellic acid (GA3) on photosynthesis and respiration rates of pea seedlings

CO₂ exchange were measured on pea seedlings (Pisum sativum L. var. Bördi) cultivated from seeds imbibed either in water (C-plants) or in gibberellic acid (GA₃) at the concentration of 25 g/1 (GA-plants), and then grown under 17 W/m² blue light (B-plants) or 11 W/m² red light (R-plants).When measured under the same light conditions as during growth the net photosynthesis (APS) rate in B-plants was about twice higher than that in R-plants. Dark respiration (DR) rate was 70% higher in B- than in R-plants. Red light retarded the development of photosynthetic activity, but GA₃ suppressed this effect. The hormone enhanced net photosynthesis and dark respiration to the same extent.When measured under saturating white light net photosynthesis rate of C-plants was also two times higher in B-plants than in R-plants. Growth conditions had only a slight effect on the APS of GA-plants under white light. APS rates of GA-plants grown under red light were higher under white light than those of C-plants, but lower than those of plants grown under blue light.We assume that blue light induced formation of plants that were adapted to higher light intensity: red light had an opposite effect, whereas gibberellic acid induced formation of plants that were adapted to medium light intensity.     

Photoprotection, photosynthesis and growth of tropical tree seedlings under near-ambient and strongly reduced solar ultraviolet-B radiation

Seedlings of two late-successional tropical rainforest tree species, Tetragastris panamensis (Engler) O. Kuntze and Calophyllum longifolium (Willd.), were field grown for 3-4 months at an open site near Panama City (9 degrees N), Panama, under plastic films that either transmitted or excluded most solar UV-B radiation. Experiments were designed to test whether leaves developing under bright sunlight with strongly reduced UV-B are capable of acclimating to near-ambient UV-B conditions. Leaves of T. panamensis that developed under near-ambient UV-B contained higher amounts of UV-absorbing substances than leaves of seedlings grown under reduced UV-B. Photosynthetic pigment composition, content of alpha-tocopherol, CO(2) assimilation, potential photosystem II (PSII) efficiency (evaluated by F(v)/F(m) ratios) and growth of T. panamensis and C. longifolium did not differ between seedlings developed under near-ambient and reduced solar UV-B. When seedlings were transferred from the reduced UV-B treatment to the near-ambient UV-B treatment, a pronounced inhibition of photosynthetic capacity was observed initially in both species. UV-B-mediated inhibition of photosynthetic capacity nearly fully recovered within 1 week of the transfer in C. longifolium, whereas in T. panamensis an about 35% reduced capacity of CO(2) uptake was maintained. A marked increase in UV-absorbing substances was observed in foliage of transferred T. panamensis seedlings. Both species exhibited enhanced mid-day photoinhibition of PSII immediately after being transferred from the reduced UV-B to the near-ambient UV-B treatment. This effect was fully reversible within 1d in T. panamensis and within a few days in C. longifolium. The data show that leaves of these tropical tree seedlings, when developing in full-spectrum sunlight, are effectively protected against high solar UV-B radiation. In contrast, leaves developing under conditions of low UV-B lacked sufficient UV protection. They experienced a decline in photosynthetic competence when suddenly exposed to near-ambient UV-B levels, but exhibited pronounced acclimative responses.     

Gas exchange of Ginkgo biloba leaves at different CO2 concentration levels

One and a half year-old Ginkgo saplings were grown for 2 years in 7 litre pots with medium fertile soil at ambient air CO₂ concentration and at 700 μmol mol⁻¹ CO₂ in temperature and humidity-controlled cabinets standing in the field. In the middle of the 2nd season of CO₂ enrichment, CO₂ exchange and transpiration in response to CO₂ concentration was measured with a mini-cuvette system. In addition, the same measurements were conducted in the crown of one 60-year-old tree in the field. Number of leaves/tree was enhanced by elevated CO₂ and specific leaf area decreased significantly.CO₂ compensation points were reached at 75–84 μmol mol⁻¹ CO₂. Gas exchange of Ginkgo saplings reacted more intensively upon CO₂ than those of the adult Ginkgo. On an average, stomatal conductance decreased by 30% as CO₂ concentration increased from 30 to 1000 μmol mol⁻¹ CO₂. Water use efficiency of net photosynthesis was positively correlated with CO₂ concentration levels. Saturation of net photosynthesis and lowest level of stomatal conductance was reached by the leaves of Ginkgo saplings at >1000 μmol mol⁻¹ CO₂. Acclimation of leaf net CO₂ assimilation to the elevated CO₂ concentration at growth occurred after 2 years of exposure. Maximum of net CO₂ assimilation was 56% higher at ambient air CO₂ concentration than at 700 μmol mol⁻¹ CO₂.     

Combined effects of CO2 concentration and nutrient status on the biomass production and nutrient uptake of birch seedlings (Betula pendula)

Birch seedlings (Betula pendula) were grown for four months in a greenhouse at three nutrient levels (fertilization of 0, 100 and 500 kg ha^-1 monthy) and at four CO₂ concentrations (350, 700, 1050 and 1400 ppm). The effect of CO₂ concentration on the biomass production depended on the nutrient status. When mineralization of the soil material was the only source of nutrients (0 kg ha^-1), CO₂ enhancement reduced the biomass production slightly, whereas the highest production increase occurred at a fertilization of 100 kg ha^-1, being over 100% between 350 and 700 ppm CO₂. At 500 kg ha^-1 the production increase was smaller, and the production decreased beyond a CO₂ concentration of 700 ppm. The CO₂ concentration had a slight effect on the biomass distribution, the leaves accounting for the highest proportion at the lowest CO₂ concentration (350 ppm). An increase in nutrient status led to a longer growth period and increased the nutrient concentrations in the plants, but the CO₂ concentration had no effect on the growth rhythm and higher CO₂ reduced the nutrient concentrations.