Growth and Maintenance Respiration in Whole Plants, Tops, and Roots of Lolium multiflorum

Continuous measurements of CO₂-exchange were separately carried out on tops and roots of small swards of Lolium multiflorum grown in nutrient solution in growth chamber during 3–4 weeks. From these measurements, a daily carbon balance and accumulated dry matter could be established. The data were used to distinguish between two components of respiration, one proportional to growth or photosynthesis (growth respiration), the other proportional to plant dry weight (maintenance respiration). The separation of respiration in the two components was made by multiple regression analyses with daily photosynthesis or growth rate and accumulated dry matter as the independent variables. To ensure independency between the independent variables during the growth period, photosynthesis was varied by application of alternate three-day periods of high and low irradiance. From the two regression coefficients, the efficiency of converting assimilates into constructive growth (Y_G) and the maintenance coefficient (M) could be derived. Three experiments with varying length of photoperiod and dark period were carried out. The analyses were carried out for whole-plant respiration, respiration of tops and respiration of roots separately. Growth respiration for whole plants as well as for tops and for roots was lower — and hence the efficiencies higher — the longer the photoperiods were. Growth respiration and maintenance respiration were higher for roots than for tops. The high rate of root respiration may originate from release of HCO₃^? in exchange for NO₃^?. The parameters found can be utilized quantitatively in computer models of crop photosynthesis and respiration.     

Atmospheric CO2 mole fraction affects stand‐scale carbon use efficiency of sunflower by stimulating respiration in light

Plant carbon‐use‐efficiency (CUE), a key parameter in carbon cycle and plant growth models, quantifies the fraction of fixed carbon that is converted into net primary production rather than respired. CUE has not been directly measured, partly because of the difficulty of measuring respiration in light. Here, we explore if CUE is affected by atmospheric CO₂. Sunflower stands were grown at low (200 μmol mol^?1) or high CO₂ (1000 μmol mol^?1) in controlled environment mesocosms. CUE of stands was measured by dynamic stand‐scale ¹³C labelling and partitioning of photosynthesis and respiration. At the same plant age, growth at high CO₂ (compared with low CO₂) led to 91% higher rates of apparent photosynthesis, 97% higher respiration in the dark, yet 143% higher respiration in light. Thus, CUE was significantly lower at high (0.65) than at low CO₂ (0.71). Compartmental analysis of isotopic tracer kinetics demonstrated a greater commitment of carbon reserves in stand‐scale respiratory metabolism at high CO₂. Two main processes contributed to the reduction of CUE at high CO₂: a reduced inhibition of leaf respiration by light and a diminished leaf mass ratio. This work highlights the relevance of measuring respiration in light and assessment of the CUE response to environment conditions.     

The Effect of Cadmium on Net Photosynthesis, Transpiration, and Dark Respiration of Excised Silver Maple Leaves

Excised leaves of silver maple (Acer saccharinum L.) exposed to 0, 0.045, 0.090, or 0.180 mM Cd²⁴ exhibited reduced net photosynthesis and transpiration, and increased dark respiration. Rates of net photosynthesis and transpiration diminished with time and were strongly correlated with solution concentration and tissue content of Cd²⁴, Net photosynthesis and transpiration were reduced to 18 and 21%, respectively, of the untreated controls after 64 h. Dark respiration increased as much as 193% of the untreated controls but was poorly correlated with solution concentration or tissue content of Cd²⁴, Diffusive resistances of leaves to carbon dioxide and water vapor transfer increased with both increasing Cd²⁴ concentration and time. These findings are discussed in relation to stomatal function.     

The relationship between respiration and temperature in leaves of the arctic plant Saxifraga cernua

Abstract Saxifraga cernua, a perennial herb distributed throughout the arctic and subarctic regions, shows high levels of dark respiration. The amount of respiration exhibited by leaves and whole plants at any temperature is influenced by the pretreatment temperature. Plants grown at 10°C typically show higher dark respiration rates than plants grown at 20°C. The levels of alternative-pathway respiration (or cyanide-insensitive respiration) in leaves of S. cernua grown at high and low temperatures were assessed by treating leaf discs with 0.25 mol m^?3 salicylhydroxamic acid during measurements of oxygen consumption. Alternative pathway respiration accounted for up to 75% of the total respiration. Tissues from 20°C-grown plants yielded a Q₁₀ of 3.37 for normal respiration, and of 0.97 for alternative-pathway respiration. Tissues from 10°C-grown plants yielded a Q₁₀ of 2.55 for normal respiration, and of 0.79 for alternative-pathway respiration. The alternative pathway does not appear to be as temperature sensitive as the normal cytochrome pathway. A simple energy model was used to predict the temperature gain expected from these high rates of alternative-pathway respiration. The model shows that less than 0.02°C can be gained by leaves experiencing these high respiration rates.     

Atmospheric CO2 concentration does not directly affect leaf respiration in bean or poplar

It is a matter of debate if there is a direct (short‐term) effect of elevated atmospheric CO₂ concentration (C_a) on plant respiration in the dark. When C_a doubles, some authors found no (or only minor) changes in dark respiration, whereas most studies suggest a respiratory inhibition of 15–20%. The present study shows that the measurement artefacts – particularly leaks between leaf chamber gaskets and leaf surface, CO₂ memory and leakage effects of gas exchange systems as well as the water vapour (‘water dilution’) effect on DCO₂ measurement caused by transpiration – may result in larger errors than generally discussed. A gas exchange system that was used in three different ways – as a closed system in which C_a increased continuously from 200 to 4200 mmol (CO₂) mol^‐1 (air) due to respiration of the enclosed leaf; as an intermittently closed system that was repeatedly closed and opened during C_a periods of either 350 or 2000 mmol mol^‐1, and as an open system in which C_a varied between 350 and 2000 mmol mol^‐1– is described. In control experiments (with an empty leaf chamber), the respective system characteristics were evaluated carefully. When all relevant system parameters were taken into account, no effects of short‐term changes in CO₂ on dark CO₂ efflux of bean and poplar leaves were found, even when C_a increased to 4200 mmol mol^‐1. It is concluded that the leaf respiration of bean and poplar is not directly inhibited by elevated atmospheric CO₂.     

Different responses of two ecotypes of C<Subscript>3</Subscript>–C<Subscript>4</Subscript> xero-halophyte <Emphasis Type="Italic">Bassia sedoides</Emphasis> to osmotic and ionic factors of salt stress

The effects of low and moderate salinity (100 and 200 mM NaCl, respectively) and iso-osmotic stress generated by polyethylene glycol PEG (1) (–0.3 MPa) and PEG (2) (–0.6 MPa) on maximum quantum yield of photosystem II (PSII), growth, photosynthesis, transpiration, dark respiration, water use efficiency (WUE), water content, chlorophyll, proline, Na⁺ and K⁺ concentrations were investigated in shoots of two ecotypes С₃–С₄ xero-halophyte Bassia sedoides (Pall.) Aschers. Plants were grown from seeds of two Southern Urals populations (Makan and Podolsk) differing in their bioproductivity. Aboveground biomass of the Makan plants was approximately 10-fold higher than that of the Podolsk ecotype. The plants of both ecotypes were sensitive to water deficit. They showed similar decrease in biomass, water content, net photosynthesis and transpiration intensity under both low and moderate osmotic stress (PEG). However, the content of сhlorophyll and free proline in shoots of the Podolsk plants increased under moderate osmotic stress (PEG(2)). Under salinity the differences between transpiration, F_v/F_m, WUE, water content, chlorophyll and proline concentrations in shoots of two ecotypes were no found. But, the Podolsk plants showed decrease in the growth parameters (1.5-fold), increase in the dark respiration intensity (2-fold) and the Na⁺/K⁺ ratio (1.2-fold) under moderate salinity (200 mM NaCl). Thus, the reduction of bioproductivity of the Podolsk ecotype under salinity was the result of ionic rather than osmotic factor of salinity. In the Podolsk plants the additional transpiration costs and consumption of assimilates (correspondingly) increased with the toxic sodium ion accumulation under salinity. This led to decrease in the growth parameters. Thus, two B. sedoides ecotypes have different adaptive strategies of tolerance to the ionic factor of salt stress at the level of the physiological processes associated with the dark CO₂ gas exchange. Moreover, in less tolerant and productive Podolsk ecotype the increase in proline content in shoots characterized comparatively low adaptation to osmotic factor, and the increase in dark respiration and the Na⁺/K⁺ ratio pointed to relatively low resistance to ion factor of salinity as compared with the Makan ecotype.     

High relative air humidity and continuous light reduce stomata functionality by affecting the ABA regulation in rose leaves

Plants developed under high (90%) relative air humidity (RH) have previously been shown to have large, malfunctioning stomata, which results in high water loss during desiccation and reduced dark induced closure. Stomatal movement is to a large extent regulated by abscisic acid (ABA). It has therefore been proposed that low ABA levels contribute to the development of malfunctioning stomata. In this study, we investigated the regulation of ABA content in rose leaves, through hormone analysis and β‐glucosidase quantification. Compared with high RH, rose plants developed in moderate RH (60%) and 20 h photoperiod contained higher levels of ABA and β‐glucosidase activity. Also, the amount of ABA increased during darkness simultaneously as the ABA‐glucose ester (GE) levels decreased. In contrast, plants developed under high RH with 20 h photoperiod showed no increase in ABA levels during darkness, and had low β‐glucosidase activity converting ABA‐GE to ABA. Continuous lighting (24 h) resulted in low levels of β‐glucosidase activity irrespective of RH, indicating that a dark period is essential to activate β‐glucosidase. Our results provide new insight into the regulation of ABA under different humidities and photoperiods, and clearly show that β‐glucosidase is a key enzyme regulating the ABA pool in rose plants.     

The effect of lead on photosynthesis and respiration in detached leaves and in mesophyll protoplasts of Pisum sativum

Photosynthesis and transpiration rate of detached leaves of pea (Pisum sativum L. cv. Iłowiecki) exposed to solution of Pb(NO₃)₂ at 1 or 5 mmol·dm⁻³ concentrations were inhibited. The higher concentration of this toxicant decreased photosynthesis and transpiration rates 2 and 3 times respectively, and increased respiration by about 20 %, as measured after 24 hours of treatment. Similarly to Pb(NO₃)₂, glyceraldehyde solution, an inhibitor of phosphoribulokinase, at 50 mmol·dm⁻³ concentration decreased the rates of photosynthesis and transpiration during introduction into pea leaves. The rate of dark respiration, however, remained unchanged during 2 hours of experiment. The potential photochemical efficiency of PS II (Fv/Fm) and the activity of Rubisco (EC 4.1.1.39) at 5 mmol·dm⁻³ of Pb(NO₃)₂ were lowered by 10 % and 20 % respectively, after 24 hours. Neither changes in the activity of PEPC (EC 4.1.1.31) or protein and pigment contents were noted in Pb-treated leaves. The photosynthetic activity of protoplasts isolated from leaves treated for 24 or 48 hours with Pb(NO₃)₂ at 5 mmol·dm⁻³ concentration was decreased 10 % or 25 %, whereas, the rate of dark respiration was stimulated by about 40 % and 75 %, respectively. The content of abscisic acid, a hormone responsible for stomatal closure, in detached pea leaves treated for 24 h with 5 mmol·dm⁻³ of Pb(NO₃)₂ solution was increased by about 3 times; a longer (48h) treatment led to further increase (by about 7 times) in the amount of this hormone. The results of our experiments provide evidences that CO₂ fixation in detached pea leaves, at least up to 24 hours of Pb(NO₃)₂ treatment, was restricted mainly by stomatal closure.     

The effect of transpiration on thallium uptake and mobility in durum wheat and spring canola

Aims

The objective of this study was to investigate the role of transpiration on accumulation and distribution of thallium (Tl) in young durum wheat (Triticum turgidum L. var ‘Kyle’) and spring canola (Brassica napus L. cv ‘Hyola 401’) plants.

Methods

Seedlings were grown hydroponically and exposed to Tl(I) under different high relative humidity (RH) conditions which resulted in different rates of transpiration among treatments. Plants were harvested prior to exposure, after a dark period of 9 (wheat) or 10?h (canola), and after 24?h of exposure. Harvested plant material was digested and analyzed for Tl by GFAAS.

Results

Our results indicated that accumulation and distribution of Tl by plants was dependent on plant species, Tl(I) dose, duration of exposure and RH, but that the effect of RH was influenced by plant species and Tl dose. Plants exposed to Tl(I) under different RH conditions did not accumulate more Tl overall. In wheat, shoots with higher transpiration rates contained a higher Tl concentration. In canola, the rate of transpiration did not consistently affect the concentration of Tl in shoots.

Conclusions

Overall, our results suggest that accumulation and translocation of Tl by plants is influenced by environmental factors that affect transpiration, in addition to soil characteristics.     

Remarks on mixotrophic and autotrophic carbon nutrition of Vitis plantlets cultured in vitro

Two Vitis species were cultured in vitro under photoautrophic (sucrose-free culture medium) and photomixotrophic (sucrose 15 g l^-1) conditions during the period following microcutting rooting (day 34 to day 120). Several parameters were measured at the end of the culture: growth, plant dry weight, carbohydrate uptake from the medium and rates of photosynthesis and dark respiration. The two species behaved very differently. Under photoautotrophic conditions, dark respiration, net photosynthesis and daily CO₂ fixation were higher in Vitis vinifera than in Vitis rupestris. Culture under mixotrophic conditions caused increase in growth, respiration and photosynthesis in Vitis rupestris. In contrast, photosynthesis decreased in Vitis vinifera under the same conditions.     

Diagnostic parameters for selecting against novel spruce (Picea abies) decline: III. Response of photosynthesis and transpiration to O3 exposures

The dose- and time-response effects of single 4 h day-time exposures of 0.064, 0.166, 0.336, 0.452 or 0.693 μl l^?1 (ppm) O₃ followed by single 4 h night-time exposures of 0.078, 0.198, 0.378, 0.502 or 0.747 μl l^?1 O₃ on photosynthesis, transpiration and dark respiration were examined for nine Carpatho-Ukrainian (‘Rachovo’) half-sib families and for two populations. ‘Westerhof’ from the FRG and ‘Schmiedefeld’ from the GDR, of Norway spruce [Picea abies (L.) Karst.], all in their 4th growing season. Needles were scorched by 4 h exposures to 0.336 μl l^?1 O₃ and higher. The lag before photosynthesis and transpiration responded significantly to O₃ decline took from a few minutes at the highest concentration to several hours at the lower concentrations. Recovery of photosynthesis and transpiration was absent or extremely slow. Photosynthesis of the different spruce types was affected significantly differently, the most sensitive spruce having its photosynthesis suppressed 1.9 times and its transpiration 1.6 times more than the most tolerant spruce. The physiological responses of ‘Westerhof’ were less sensitive than the average ‘Rachovo’ half-sibs. Neither night transpiration nor dark respiration were affected by high doses of night O₃, preceded by day O₃ exposures. The gradients of different photosynthesis and transpiration sensitivities of the young half-sibs (and ‘Westerhof’) demonstrated a significant, positive, mutual correlation, and significant positive correlations with the gradient of novel decline symptoms of their parents growing in Danish forests. The relative photosynthesis and transpiration sensitivities may thus serve as diagnostic parameters in laboratory tests for selection against novel spruce decline.     

Diel variations in carbon isotopic composition and concentration of organic acids and their impact on plant dark respiration in different species

Leaf respiration in the dark and its C isotopic composition (δ¹³C_R) contain information about internal metabolic processes and respiratory substrates. δ¹³C_R is known to be less negative compared to potential respiratory substrates, in particular shortly after darkening during light enhanced dark respiration (LEDR). This phenomenon might be driven by respiration of accumulated ¹³C‐enriched organic acids, however, studies simultaneously measuring δ¹³C_R during LEDR and potential respiratory substrates are rare. We determined δ¹³C_R and respiration rates (R) during LEDR, as well as δ¹³C and concentrations of potential respiratory substrates using compound‐specific isotope analyses. The measurements were conducted throughout the diel cycle in several plant species under different environmental conditions. δ¹³C_R and R patterns during LEDR were strongly species‐specific and showed an initial peak, which was followed by a progressive decrease in both values. The species‐specific differences in δ¹³C_R and R during LEDR may be partially explained by the isotopic composition of organic acids (e.g., oxalate, isocitrate, quinate, shikimate, malate), which were ¹³C‐enriched compared to other respiratory substrates (e.g., sugars and amino acids). However, the diel variations in both δ¹³C and concentrations of the organic acids were generally low. Thus, additional factors such as the heterogeneous isotope distribution in organic acids and the relative contribution of the organic acids to respiration are required to explain the strong ¹³C enrichment in leaf dark‐respired CO₂.     

不同时间尺度北京蟒山油松树干液流对环境因子的响应

探究不同时间尺度蒸腾与环境因子的关系并明确其主控因子,对于理解蒸腾对环境响应规律和驱动机制具有重要的理论意义。以北京蟒山国家森林公园的油松为例,开展树干液流及气象指标、土壤温湿度等环境因子的长期定位观测,并分析不同时间尺度油松液流速率与环境因子的关系。研究结果表明,在日尺度上,土壤温度、大气相对湿度、土壤湿度与液流速率呈极显著正相关,这3个因子对液流速率变化的贡献量分别占28.3%、11.7%和10.1%;在月尺度上,土壤温度对液流速率的影响最大,贡献量占比49.7%,土壤湿度和相对湿度的贡献量分别为7.3%和6.4%;在年尺度上,相对湿度对液流速率的年际变化的贡献量高达93.3%,是关键控制因子。随着时间尺度的扩展,环境因子对油松液流速率的控制作用逐渐增强。本研究的结果可以为植物蒸腾的时间尺度转换、未来全球气候变化背景下植物蒸腾耗水特征的预测提供理论依据。     

Diagnostic parameters for selecting against novel spruce (Picea abies) decline: II. Response of photosynthesis and transpiration to acute NOx exposures

The dose- and time-response effects of sequential 3 h+3 h NO→NO₂ day time exposures [0–9 μl l^?1 (ppm) NO, 0–7.5 μl l^?1 NO₂] followed by 3 h+3 h NO→NO₂ night-time exposures (0–9.5 μl l^?1 NO, 0–9 μl l^?1 NO₂) on photosynthesis, transpiration and dark respiration were examined for nine Carpatho-Ukrainian (‘Rachovo’) half-sib families and for two populations, one from the FRG (‘Westerhof’) and one from the GDR (‘Schmiedefeld’) of Norway spruce [Picea abies (L.) Karst.], all in their 4th growing season. In a second exposure series the exposure sequence was reversed. None of the treatments induced needle scorching. The higher NO_x (NO or NO₂) concentrations reduced photosynthesis and transpiration within 1 h. The physiology of the different spruce types was affected significantly differently, the most sensitive spruce having its photosynthesis suppressed 6.6 times and its transpiration 5.5 times more than the most tolerant. ‘Westerhof’ was more sensitive to NO₂ than the average ‘Rachovo’ half-sibs. The gradients of different photosynthesis and transpiration sensitivities among the half-sibs (and ‘Westerhof’) demonstrated a significant, positive, mutual correlation, but significant negative correlations with the gradient of novel decline symptoms among their parents growing in Danish forests. The relative photosynthesis and transpiration sensitivies may thus serve as diagnostic parameters for laboratory selection of the most resistant trees to novel spruce decline. The average NO₂ flux density was three times larger than the average NO flux density. Only for NO₂ and in light was stomatal NO_x uptake larger than the total NO_x uptake. Both night transpiration and dark respiration were stimulated by high concentrations of night NO_x, preceded by day NO_x exposures.     

Influence of leaf size,orientation, and arrangement on temperature and transpiration in three high-elevation,large-leafed herbs

Summary The temperature and water relations of the largleafed, high-elevation species Frasera speciosa, Balsamorhiza sagittata, and Rumex densiflorus were evaluated in the Medicine Bow Mountains of southeast Wyoming (USA) to determine the influence of leaf size, orientation, and arrangement on transpiration. These species characteristically have low minimum stomatal resistances (<60 s m^-1) and high maximum transpiration rates (>260 mg m^-2s^-1 for F. speciosa). Field measurements of leaf and microclimatic parameters were incorporated into a computer simulation using standard energy balance equations which predicted leaf temperature (T _leaf) and transpiration for various leaf sizes. Whole-plant transpiration during a day was simulated using field measurements for plants with natural leaf sizes and compared to transpiration rates simulated for plants having identical, but hypothetically smaller (0.5 cm) leaves during a clear day and a typically cloudy day. Although clear-day transpiration for F. speciosa plants with natural size leaves was only 2.0% less per unit leaf area than that predicted for plants with much smaller leaves, daily transpiration of B. sagittata and R. densiflorus plants with natural leaf sizes was 16.1% and 21.1% less, respectively. The predicted influence of a larger leaf size on transpiration for the cloudy day was similar to clear-day results except that F. speciosa had much greater decreases in transpiration (12.7%). The different influences of leaf size on transpiration between the three species was primarily due to major differences in leaf absorptance to solar radiation, orientation, and arrangement which caused large differences in T _leaf. Also, simulated increases in leaf size above natural sizes measured in the field resulted in only small additional decreases in predicted transpiration, indicating a leaf size that was nearly optimal for reducing transpiration. These results are discussed in terms of the possible evolution of a larger leaf size in combination with specific leaf absorptances, orientations and arrangements which could act to reduce transpiration for species growing in short-season habitats where the requirement for rapid carbon fixation might necessitate low stomatal resistances.     

Growth,nodulation and nitrogen fixation in soybean as affected by air humidity and root temperature

Growth, nodulation and N₂ fixation inGlycine max L. Merr., cv. Biison as affected by the relative humidity of air (RH) during the dark period (95 or 50 – 65 %) and day/night root temperature (T_r) (28/28, 25/25, 18/18, 22/28, 22/18 °C) were studied. The growth parameters (plant fresh and dry mass, yield), nodulation (nodule number and fresh mass) and N₂ fixation abilities (total nitrogen content, nitrogenase activity) increased significantly with the increasing T_r. In addition, at the same T_r during the day all studied parameters were increased at the higher T_r during the dark period. Growth, nodulation and N₂ fixation were significantly enhanced at low RH. The findings indicate that all studied parameters could be regulated by environmental factors during the dark period.     

Mycorrhizal association between the desert truffle Terfezia boudieri and Helianthemum sessiliflorum alters plant physiology and fitness to arid conditions

The host plant Helianthemum sessiliflorum was inoculated with the mycorrhizal desert truffle Terfezia boudieri Chatin, and the subsequent effects of the ectomycorrhizal relationship on host physiology were determined. Diurnal measurements revealed that mycorrhizal (M) plants had higher rates of photosynthesis (35%), transpiration (18%), and night respiration (49%) than non-mycorrhizal (NM) plants. Consequently, M plants exhibited higher biomass accumulation, higher shoot-to-root ratios, and improved water use efficiency compared to NM plants. Total chlorophyll content was higher in M plants, and the ratio between chlorophyll a to chlorophyll b was altered in M plants. The increase in chlorophyll b content was significantly higher than the increase in chlorophyll a content (2.58- and 1.52-fold, respectively) compared to control. Calculation of the photosynthetic activation energy indicated lower energy requirements for CO₂ assimilation in M plants than in NM plants (48.62 and 61.56 kJ mol⁻¹, respectively). Continuous measurements of CO₂ exchange and transpiration in M plants versus NM plants provided a complete picture of the daily physiological differences brought on by the ectomycorrhizal relationships. The enhanced competence of M plants to withstand the harsh environmental conditions of the desert is discussed in view of the mycorrhizal-derived alterations in host physiology.     

Dark calcification and the daily rhythm of calcification in the scleractinian coral, <Emphasis Type="Italic">Galaxea fascicularis</Emphasis>

The rate of calcification in the scleractinian coral Galaxea fascicularis was followed during the daytime using ⁴⁵Ca tracer. The coral began the day with a low calcification rate, which increased over time to a maximum in the afternoon. Since the experiments were carried out under a fixed light intensity, these results suggest that an intrinsic rhythm exists in the coral such that the calcification rate is regulated during the daytime. When corals were incubated for an extended period in the dark, the calcification rate was constant for the first 4 h of incubation and then declined, until after one day of dark incubation, calcification ceased, possibly as a result of the depletion of coral energy reserves. The addition of glucose and Artemia reduced the dark calcification rate for the short duration of the experiment, indicating an expenditure of oxygen in respiration. Artificial hypoxia reduced the rate of dark calcification to about 25% compared to aerated coral samples. It is suggested that G. fascicularis obtains its oxygen needs from the surrounding seawater during the nighttime, whereas during the day time the coral exports oxygen to the seawater.     

The effect of high levels of carbon dioxide on dark respiration and growth of plants

Abstract Raising ambient levels of CO₂ during the night, between 350 and 950cm³m^?3, reduced the dark respiration rate of Medicago sativum seedlings. The percentage effect was greater for maintenance respiration than for dark respiration as a whole, and when the plants were in a low photosynthate status. Twenty-four h carbon balance studies confirmed a reduction in night time respiration and an increase of net carbon gain when night time [CO₂] was high. Growth experiments showed a small but significant increase of dry weight in Medicago sativum seedlings exposed to high [CO₂] (～ 1200 cm³m^?3) at night. This effect was greater for plants grown with Rhizobium nodules than for plants grown with nitrate in the absence of Rhizobium. A similar, but smaller and statistically non-significant effect of high night time [CO₂] on growth was found for Xanthium strumarium seedlings. The significance of these findings is discussed in relation to the rising CO₂ content of the atmosphere.     

Gibberellic acid affects growth and flowering of Philodendron‘Black Cardinal’

Changes in net photosynthetic rate (P_N), stomatal conductance (g_s), intercellular CO₂ concentrations (C_i), transpiration rate (E) and water use efficiency (WUE) were measured in Plantago major L. plants grown under sufficient soil water supply or under soil water stress conditions. The plants had high P_N in a wide range of soil water potential and temperature regimes. Soil water had little effect on P_N under ambient CO₂ concentrations, which was explained by a high carboxylation rate, but increased the dark respiration rate. Carboxylation activity at low C_i depended on RuBP regeneration, whereas at high C_i it depended on the phosphate regeneration rate. The g_s and E values were low in plants under stress as compared to the controls that resulted in an increase of WUE. The results obtained show that Plantago major plants have different ways of adaptation to soil water deficit conditions.