Influence of Salt Stress on Growth, Ion Accumulation and Seed Oil Content in Sweet Fennel

A greenhouse experiment was conducted to assess the effect of 25, 50, 75, and 100 mM NaCl on growth, ion accumulation, seed yield, and seed oil content in 67-d-old plants of Foeniculum vulgare Mill. Increasing NaCl concentration caused a significant reduction in fresh and dry masses of both shoots and roots as well as seed yield. Na⁺ and Cl^– in both shoots and roots increased, whereas K⁺ and Ca²⁺ decreased consistently with the increase in NaCl concentration. Plants maintained markedly higher Ca²⁺/Na⁺ ratios in the shoots than those in the roots, whereas that of K⁺ /Na⁺ ratios remained almost uniform in both shoots and roots. Proline content in the shoots increased markedly at the highest NaCl concentration. Oil content in the seed decreased progressively with increase in salinity.     

Counteraction of Salinity Stress on Wheat Plants by Grain Soaking in Ascorbic Acid, Thiamin or Sodium Salicylate

The interactive effects of salinity stress (40, 80, 120 and 160 mM NaCl) and ascorbic acid (0.6 mM), thiamin (0.3 mM) or sodium salicylate (0.6 mM) were studied in wheat (Triticum aestivum L.). The contents of cellulose, lignin of either shoots or roots, pectin of root and soluble sugars of shoots were lowered with the rise of NaCl concentration. On the other hand, the contents of hemicellulose and soluble sugars of roots, starch and soluble proteins of shoots, proline of either shoots or roots, and amino acids of roots were raised. Also, increasing NaCl concentration in the culture media increased Na⁺ and Ca²⁺ accumulation and gradually lowered K⁺ and Mg²⁺ concentration in different organs of wheat plant. Grain soaking in ascorbic acid, thiamin or sodium salicylate could counteract the adverse effects of NaCl salinity on the seedlings of wheat plant by suppression of salt stress induced accumulation of proline.     

Effects of NaCl and Na2SO4 on red-osier dogwood (Cornus stolonifera Michx) seedlings

Sodium chloride and sodium sulfate are commonly present in extraction tailings waters produced as a result of surface mining and affect plants on reclaimed areas. Red-osier dogwood (Cornus stolonifera Michx) seedlings were demonstrated to be relatively resistant to these high salinity oil sands tailings waters. The objectives of this study were to compare the effects of Na₂SO₄ and NaCl, on growth, tissue ion content, water relations and gas exchange in red-osier dogwood (Cornus stolonifera Michx) seedlings. In the present study, red-osier dogwood seedlings were grown in aerated half-strength modified Hoagland's mineral solution containing 0, 25, 50 or 100 mM of NaCl or Na₂SO₄. After four weeks of treatment, plant dry weights decreased and the amount of Na⁺ in plant tissues increased with increasing salt concentration. Na⁺ tissue content was higher in plants treated with NaCl than Na₂SO₄ and it was greater in roots than shoots. However, Cl^– concentration in the NaCl treated plants was higher in shoots than in roots. The decrease in stomatal conductance and photosynthetic rates observed in presence of salts is likely to contribute to the growth reduction. Our results suggest that red-osier dogwood is able to control the transport of Na⁺ from roots to shoots when external concentrations are 50 mM or less.     

干旱胁迫下胡杨实生幼苗氮素吸收分配与利用

胡杨(Populus euphratica)是塔里木河流域荒漠河岸林的建群种,水分和氮素是限制胡杨幼苗的存活及早期生长的主要因子。利用~(15)N同位素示踪技术分析水和氮素的交互作用对胡杨幼苗不同生长阶段氮素的吸收分配利用及幼苗生长的影响,进一步探究氮素对胡杨实生苗早期形态建成的作用及对干旱胁迫的缓解效应,以期提高幼苗的存活率。实验以一年生胡杨实生幼苗为研究对象,采用温室内盆栽实验,设置4个干旱处理(D_1、D_2、D_3、D_4,土壤相对含水量为:20%—25%、40%—45%、60%—65%、80%—85%)和3种氮素水平(N_0、N_1、N_2:0、3、6 g/盆)测定胡杨幼苗的生长指标和各部分的Ndff、分配率及利用率。结果表明:胡杨幼苗在土壤相对含水量60%—65%(D_3)、氮素添加量3 g/盆(N_1)时,其生长表现为最佳状态;干旱胁迫下,不同氮素添加量对胡杨幼苗各部分的Ndff值存在显著差异,N_2低于N_1;随干旱胁迫减弱(D_3、D_4),植株在生长早期(25 d)根部吸收的~(15)N优先向地上部分转运,生长后期(75 d)植株Ndff最高,其中以根系中Ndff最高;不同生长期幼苗各部分的~(15)N分配存在显著差异,根系~(15)N分配率较高,但不同氮量处理间差异不显著;随生长期的推移,植株对~(15)NH_4~(15)NO_3的利用率表现为粗根最大,各处理中D_3N_1处理均显著高于其他处理。结论:轻度干旱胁迫下添加适量的氮素能够增强植株对氮素的吸收征调能力,优化水资源获取以维持生存的重要机制。     

Effects of salinity and nitrogen on growth,ion relations and proline accumulation in Triglochin bulbosa

The effects of salinity and nitrogen on growth, ion relations and prolineaccumulation in the monocotyledonous halophyte, Triglochin bulbosa,was investigated in hydroponic culture over 5 months. The experimentaldesign was a 3 × 3 factorial with three salinity treatments (0, 150 and 300 mol m^-3 NaCl) and three levels of N (5, 10 and 20 gml^-1 N as NaNO₃). Total and root dry biomass accumulationwere significantly affected by salinity, but not by N or N × salinityinteraction. Increase in NaCl from 0 to 150 mol m^-3 had no effecton total or root dry biomass, while further increase in salinity to 300mol m^-3 significantly reduced biomass by 21% and 25%respectively. Shoot dry biomass, which was significantly affected by N andnot by salinity, increased with increase in N from 5 to 10 gml^-1. Ion concentrations in roots and shoots were significantlyaffected by salinity, but not by N or N × salinity interaction. Theconcentration of Na⁺ and Cl^- in roots and shoots increasedprogressively with an increase in salinity, while that of K⁺ decreased. Under non-saline conditions, Na⁺/K⁺ ratios were low (0.41to 0.44) and increased significantly with an increase in salinity in both rootsand shoots. Shoot sap osmotic potentials decreased progressively with anincrease in salinity. Increase in N in the hydroponic solution from 5 to20 g ml^-1 significantly increased root and shoot N by 66%and 41% respectively. Tissue concentrations of proline were significantlyaffected by salinity and substrate N but not by N × salinity interaction. Theconcentration of proline in roots and shoots increased significantly by334% and 48%, respectively, with an increase in salinity from 0 to 300mol m^-3 NaCl. Increase in substrate N from 5 to 20 g ml^-1 significantly increased proline in roots and shoots by 66% and41% respectively. The significance of substrate N on the accumulationof proline is discussed in relation to salt tolerance.     

Ionic and Osmotic Effects of Salinity on Single-Leaf Photosynthesis in Two Wheat Cultivars with Different Drought Tolerance

The effects of iso-osmotic salinity and drought stresses on leaf net photosynthetic rate (P _N) in two wheat (Triticum aestivum L.) cultivars BR 8 and Norin 61, differing in drought tolerance, were compared. In drought-sensitive Norin 61, the decline of P _N was larger than that in drought-tolerant BR 8. Under NaCl treatment, P _N decreased in two phases similarly in both cultivars. In the first phase, photosynthetic depression was gradual without any photochemical changes. In the second phase, photosynthetic depression was rapid and accompanied with a decline of the energy conversion efficiency in photosystem 2 (_PS2). Our observations suggest that the osmotic factor may induce a gradual depression of photosynthesis due to stomatal closure under both stress treatments. However, under NaCl treatment, a ionic factor (uptake and accumulation of excess Na⁺) may have direct effects on electron transport and cause more severe photosynthetic depression. The drought tolerance mechanism of BR 8 was insufficient to maintain single-leaf photosynthesis under salinity.     

Kinetin regulation of growth and secondary metabolism in waterlogging and salinity treated Vigna sinensis and Zea mays

Waterlogging mostly increased fresh weight and water content in shoots and roots of Vigna sinensis and Zea mays while salinity seemed to have a decreasing effect. There was a marked induction of proline in shoots and roots of both plants by salinity with lower values in logged plants. In addition, anthocyanin content was increased in Vigna sinensis by both treatments and in Zea mays only by salinity. Meanwhile the treatments significantly accumulated phenolic compounds in plant shoots. Also there were increased activities of phenylalanine ammonia lyase (PAL) and tyrosine ammonia lyase (TAL) in shoots and roots of both plants. Foliar application of kinetin equilibrated, if any, the effects of both treatments on contents of proline, anthocyanin and phenolic compounds as well as activities of PAL and TAL in shoots and roots of treated plants. These findings reveal that kinetin alleviates the stress symptoms and regulates the changes in phenolic metabolism of waterlogged or salinity treated Vigna sinensis and Zea mays.     

Effects of seasonal changes of soil salinity and soil nitrogen on the N-metabolism of the halophyteArthrocnemum fruticosum (L.) Moq.

Summary The N-metabolism ofArthrocnemum fruticosum (L.) Moq., growing in a saline area north-east of the Dead Sea in Jordan, was studied over its vegetative growth period from March to September 1981. Plant and soil samples were taken at monthly intervals. Water content, Na⁺, K⁺, Cl⁻, NH ₄ ⁺ , NO ₂ ⁻ and NO ₃ ⁻ concentrations were determined in the soil extracts, and the same determinations plus ash weight, soluble carbohydrates, proline, proteins andin vivo nitrate reductase in the plant roots and shoots. Soil humidity decreased and salinity increased from March to August, with re-wetting occurring in late July. K⁺ and Cl⁻ were much lower in the soils than Na⁺. Plant relative dry weight increased during summer due to the absorption of Na⁺ in addition to increased organic dry weight. The uptake of Na⁺ was not balanced by a similar uptake of Cl⁻. Ammonium and nitrate decreased in soil and plants in parallel with increasing salinity. Nitrite was only found in the roots and always in very low quantities. Proline was found only in March. The total soluble carbohydrates in the roots showed a short increase in June when the sodium in the plants also increased. It was concluded that carbohydrates may be used to balance osmotic shocks, but that another compatible compounds is necessary to maintatin long-term osmotic equilibrium. The nitrate reductase activity, measuredin vivo, and the soluble protein changed roughly in parallel with the internal nitrate from May to August, suggesting that nitrogen uptake and reduction in the plant is inhibited during summer when the soil is dry and very saline. This could be a direct effect of drought and/or salinity on the plants, or an indirect onevia an inhibition of nitrifying bacteria.     

Effect of NaCl salinity on growth,pigment and mineral element contents,and gas exchange of broad bean and pea plants

Increasing salinity of growth medium induced a reduction in growth and transpiration rate. The concentrations of chlorophylls and carotenoids were increased in most cases in broad bean leaves while in pea plants they remained more or less unchanged with the rise of salinization up to 80mM NaCl. Thereabove a significant decrease in these contents was observed. A stimulation of the net photosynthetic rate of pea was observed at the lowest levels of NaCl but at the highest levels inhibitory effect was recorded. In broad bean all salinization levels inhibited photosynthetic activity, but dark respiration of both plant species was stimulated. The content of Na⁺ in the roots and shoots of both species increased at increasing salinity. In broad bean, Ca²⁺ concentration in shoots and K⁺ and Ca²⁺ contents of roots increased at increasing salinization, while in pea plants, the content of K⁺ and Ca²⁺ was almost unaffected by salinity. Salinity induced an increase in the content of these ions in pea roots. Mg²⁺ content in shoots and roots of both broad bean and pea decreased at increasing salinity except in roots of pea, where it was generally increased.     

Silicon improves salinity tolerance in wheat plants

Durum wheat (Triticum durum cv. Gediz-75) and bread wheat (Triticum aestivum cv. Izmir-85) were grown in a complete nutrient solution in a growth room to investigate effect of silicone supplied to the nutrient solution on plants grown at salt stress. The experiment was a 2 × 2 factorial arrangement with two levels of NaCl in nutrient solution, 0 and 100 mM, and two levels of silicone (Si) in nutrient solution, 0.25 and 0.50 mM, as Na₂SiO₃. The plants grown at 100 mM NaCl produced less dry matter and chlorophyll content than those without NaCl. Supplementary Si at both 0.25 and 0.5 mM ameliorated the negative effects of salinity on plant dry matter and chlorophyll content. Membrane permeability and proline content in leaves increased with addition of 100 mM NaCl and these increases were decreased with Si treatments. Sodium (Na) concentration in plant tissues increased in both leaves and roots of plants in the high NaCl treatment and Si treatments lowered significantly the concentrations of Na in both leaves and roots. Bread wheat was more tolerant to salinity than durum wheat. The accumulation of Na in roots indicates a possible mechanism whereby bread wheat copes with salinity in the rooting medium and/or may indicate the existence of an inhibition mechanism of Na transport to leaves. Concentrations of both Ca and K were lower in the plants grown at high NaCl than in those in the control treatment and these two element concentrations were increased by Si treatments in both shoots and roots but remained lower than control values in most cases.     

盐分和干旱对沙枣幼苗生理特性的影响

以沙枣(Elaeagnus angustifolia L.)幼苗为实验材料,分别对其进行轻度干旱(土壤含水量7%—9%)、重度干旱(土壤含水量3%—5%)、100 mmol/L NaCl以及100 mmol/L NaCl处理下不同程度的盐旱共胁迫处理,处理2周后测其生理指标,包括生长指标、光合指标、渗透调节指标以及复水后生长指标,研究盐旱共胁迫对沙枣幼苗生理特性的影响。结果表明:和对照相比,轻度干旱对沙枣幼苗的生物量没有显著影响,重度干旱处理明显降低了沙枣的生物量,无论是轻度干旱还是重度干旱,都显著降低了沙枣幼苗的净光合速率、K~+含量,显著增加了Na~+含量、脯氨酸含量、可溶性糖含量、有机酸含量、总酚和类黄酮含量;和对照相比,100 mmol/L NaCl处理显著降低了沙枣幼苗的生物量、净光合速率和K~+含量,显著增加了Na~+含量、脯氨酸含量、可溶性糖含量、有机酸含量、总酚和类黄酮含量;和盐处理相比,轻度干旱和盐分共胁迫对沙枣幼苗的各项指标没有显著差异,而重度干旱和盐分共胁迫明显降低了沙枣幼苗的生物量、净光合速率;复水一周后,只有轻度干旱可以回复到对照水平。以上结果表明,盐分和干旱处理明显抑制了沙枣幼苗的生长,轻度干旱和盐分共胁迫条件下,沙枣幼苗表现出一定的交叉适应现象,而重度干旱却加重了盐害。     

Influence of Nitrogen Supply and Water Stress on Growth and Nitrogen, Phosphorus, Potassium and Calcium Contents in Pearl Millet

Influence of supra-optimal concentrations of N on growth and accumulation of N, K, P and Ca in the shoots and roots in Pennisetum glaucum (L.) R.Br. under water stress was assessed in a pot experiment under glasshouse conditions. Thirty four-day-old plants of two lines, ICMV94133 and WCA-78, were subjected to 224, 336, or 448 mg(N) kg^–1(soil) and soil moisture 100 or 30 % of field capacity for 30 d. Increasing soil N supply decreased growth of both lines under water deficit. Nitrogen content in the shoots of both lines was not affected by supra-optimal levels of N or different watering regimes, but in contrast, the root N content was increased consistently in WCA-78 with increase in soil N content. Shoot P content increased considerably in WCA-78 at the two higher N contents, but it was significantly lower at drought stress than at well-watered treatment. In contrast, shoot or root P content in ICMV94133 did not differ under both watering regimes. Potassium content in the shoots of WCA-78 was considerably increased at the two higher N contents under drought conditions. Root K content was increased in WCA-78 at the highest N content under well-watered conditions, whereas the reverse was true in ICMV94133. Calcium content in the shoots of ICMV94133 was higher under drought stress compared with that at well-watered conditions, but such pattern was not observed in WCA-78. However, root Ca content increased in both lines with increase in N supply.     

Salt-induced changes in photosynthetic activity and growth in a potential medicinal plant Bishop’s weed (Ammi majus L.)

Sixty seven-days-old plants of Ammi majus L. were subjected for 46 d to sand culture at varying concentrations of NaCl, i.e. 0 (control), 40, 80, 120, and 160 mM. Increasing salt concentrations caused a significant reduction in fresh and dry masses of both shoots and roots as well as seed yield. However, the adverse effect of salt was more pronounced on seed yield than biomass production at the vegetative stage. Calculated 50 % reduction in shoot dry mass occurred at 156 mM (ca.15.6 mS cm^–1), whereas that in seed yield was at 104 mM (ca.10.4 mS cm^–1). As in most glycophytes, Na⁺ and Cl^– in both shoots and roots increased, whereas K⁺ and Ca²⁺ decreased consistently with the successive increase in salt level of the growth medium. Plants of A. majusmaintained markedly higher K⁺/Na⁺ ratios in the shoots than those in the roots, and the ratio remained more than 1 even at the highest external salt level (160 mM). Net photosynthetic (P_N) and transpiration (E) rates remained unaffected at increasing NaCl, and thus these attributes had a negative association with salt tolerance of A. majus. Proline content in the shoots increased markedly at the higher concentrations of salt. Essential oil content in the seed decreased consistently with increase in external salt level. Overall, A. majusis a moderately salt tolerant crop whose response to salinity is associated with maintenance of high shoot K⁺/Na⁺ ratio and accumulation of proline in shoots, but P_N had a negative association with the salt tolerance of this crop.This revised version was published online in March 2005 with corrections to the page numbers.     

短期NaCl胁迫对不同小麦品种幼苗K+吸收和Na+、K+积累的影响

为研究盐胁迫下小麦幼苗生长及Na⁺、K⁺的吸收和积累规律,以中国春、洲元9369和长武134等3种耐盐性不同小麦品种为材料,采用非损伤微测技术检测盐胁迫2 d后的根系K⁺离子流变化,并对植株体内的Na⁺、K⁺含量进行测定。结果表明:短期(2d)盐胁迫对小麦生长有抑制作用,且对根系的抑制大于地上部,耐盐品种下降幅度小于盐敏感品种。盐胁迫下,小麦根际的 K⁺大量外流,盐敏感品种中国春K⁺流速显著高于耐盐品种长武134,最高可达15倍。小麦幼苗地上部分和根系均表现为Na⁺积累增加,K⁺积累减少,Na⁺/K⁺比随盐浓度增加而上升。中国春限Na⁺能力显著低于长武134,Na⁺/K⁺则显著高于长武134。综上所述,盐胁迫下造成小麦组织器官中Na⁺/K⁺比上升的主要原因是根系K⁺大量外流和Na⁺的过量积累,耐盐性不同的小麦品种间差异显著,并认为根系对K⁺的保有能力可能是作物耐盐性评价的一个重要指标。     

Effects of silicon on photosynthesis,water relations and nutrient uptake of <Emphasis Type="Italic">Phaseolus vulgaris</Emphasis> under NaCl stress

A greenhouse experiment was conducted to investigate the effects of silicon application on Phaseolus vulgaris L. under two levels of salt stress (30 and 60 mM NaCl in the irrigation water). Salinity significantly reduced growth, stomatal conductance and net photosynthetic rate, and increased Na⁺ and Cl⁻ content mainly in roots. Silicon application enhanced growth of salt stressed plants, significantly reduced Na⁺ content especially in leaves and counterbalanced the effects of NaCl on gas exchange; the effect was more evident at 30 mM NaCl. Cl⁻ content in shoots and roots was not significantly modified by silicon application; the drop in K⁺ content caused by salinity was partially counterbalanced by silicon, especially in roots.     

Alleviation of salinity stress in chickpea byRhizobium inoculation or nitrate supply

Influence of inoculation with efficient rhizobia or nitrate fertilization in alleviating salinity (NaCl, CaCl₂ and Na₂SO₄) stress was investigated in sand culture experiments. Shoot dry mass declined beyond salinity level corresponding to electrical conductivity (EC) 5.6 dS m^?1 in control or in inoculated plants and after EC 7.4 dS m^?1 in nitrate fed ones. Root growth was more sensitive and decreased at EC 3.3 dS m^?1. Nitrate reductase activity in leaves reduced at EC 3.3 dS m^?1 but in inoculated and nitrate fed plants it reduced at EC 5.6 dS m^?1. Na⁺ accumulation increased at EC 5.6 and 7.4 dS m^?1 in roots and, shoots, respectively. In inoculated and nitrate fed plants Na⁺ content in roots increased at EC 7.4 dS m^?1. Content of Ca²⁺ increased slightly only in shoots and content of K⁺ was unaffected. Besides inoculation, application of small doses of nitrogen should prove beneficial for legume cultivation in saline soils.     

不同强度盐胁迫下AM真菌对羊草生长的影响

不同浓度NaCl盐处理下,AM真菌对羊草(Leymus chinensis)的侵染能力和对植物生长的影响,从植物形态和离子含量角度探讨了AM真菌提高羊草耐盐性的作用机理。结果表明,在高盐胁迫下,AM真菌显著降低了盐胁迫效应,提高了羊草生物量,菌根效应明显。菌根化羊草的根茎比显著增加,并且N、P浓度较高,Na~+和Cl~-离子浓度较低,表明AM真菌即促进羊草对营养元素的吸收,又减少了离子毒害。菌根化羊草的Ca~(2+)和K~+离子浓度,以及P/Na~+和K~+/Na~+比高于非菌根化羊草,表明AM真菌可通过调节渗透势以避免或减缓盐胁迫造成的生理缺水。随着盐胁迫的增加,菌根化羊草对磷的依赖性逐渐转换为对钾的依赖性。研究结果有助于揭示AM真菌提高植物耐盐能力的作用机理,并对应用菌根技术修复盐化草地具有理论指导意义。     

Combination Effect of NaCl Salinity and Nitrogen Form on Mineral Composition of Sunflower Plants

The effect of two N-forms (NH₄ ⁺ and NO₃ ^–) and NaCl on pattern of accumulation of some essential inorganic nutrients was examined in sunflower (Helianthus annuus L.) cv. Hisun 33. Eight-day-old plants of were subjected for 21 d to Hoagland's nutrient solution containing 8 mM N as NH₄ ⁺ or NO₃ ^·, and salinized with and addition of NaCl to the growth medium had no significant effect on total leaf N. However, root N of NH₄-supplied plants decreased significantly with increase in NaCl concentration, whereas that of NO₃-supplied plants remained unaffected. There was no significant effect of NaCl on leaf or root P, but the NO₃-supplied plants had significa concentration of leaf P than that of NH₄-supplied plants at varying salt treatments. Salinity of the rooting med did not show any significant effect on Na⁺ concentrations of leaves or roots of plants subjected to two differen N. NH₄-treated plants generally had greater concentrations of Cl^– in leaves and roots and lower K⁺ content in leaves than NO₃-supplied plants. Ca²⁺ concentrations of leaves and roots and Mg²⁺ concentrations of leaves decreased in NH₄-supplied plants due to NaCl, but they remained unaffected in NO₃-treated plants.     

Response of barley grains to the interactive e.ect of salinity and salicylic acid

Effect of grain soaking presowing in 1 mM salicylic acid (SA) and NaCl (0, 50, 100, 150 and 200 mM) on barley (Hordeum vulgare cv Gerbel) was studied. Increasing of NaCl level reduced the germination percentage, the growth parameters (fresh and dry weight), potassium, calcium, phosphorus and insoluble sugars content in both shoots and roots of 15-day old seedlings. Leaf relative water content (RWC) and the photosynthetic pigments (Chl a, b and carotenoids) contents also decreased with increasing NaCl concentration. On the other hand, Na, soluble sugars, soluble proteins, free amino acids including proline content and lipid peroxidation level and peroxidase activity were increased in the two plant organs with increasing of NaCl level. Electrolyte leakage from plant leaves was found to increase with salinity level. SA-pretreatment increased the RWC, fresh and dry weights, water, photosynthetic pigments, insolube saccharides, phosphorus content and peroxidase activity in the stressed seedlings. On the contrary, Na⁺, soluble proteins content, lipid peroxidation level, electrolyte leakage were markedly reduced under salt stress with SA than without. Under stress conditions, SA-pretreated plants exhibited less Ca²⁺ and more accumulation of K⁺, and soluble sugars in roots at the expense of these contents in the plant shoots. Exogenous application (Grain soaking presowing) of SA appeared to induce preadaptive response to salt stress leading to promoting protective reactions to the photosynthetic pigments and maintain the membranes integrity in barley plants, which reflected in improving the plant growth.     

Carbon Balance of a Winter Wheat-Root Microbiota System Under Elevated CO2

We examined the carbon budget of young winter wheat plants and their associated microorganisms as affected by a doubling of the atmospheric CO₂ concentration (700 μmol mol^-1). Plants were grown hydroponically in pre-sterilised sand at a controlled irradiance and temperature regime. Net photosynthesis (P_N) and respiration (R_D) rates of roots and shoots were measured continuously, plant growth and carbon distribution in the plant-root medium-associated microorganism system were determined destructively in interval-based analyses. P_N in elevated CO₂ grown plants (EC) was 123% of that in the control (AC) plants when averaged over the whole life span (39-d-old plants, 34 d in EC), but the percentage varied with the developmental stage being 115, 88, and 167% in the pretillering, tillering, and posttillering phase, respectively. There was a transient depression of P_N, higher amplitude of day/night fluctuations of the chloroplast starch content, and depression of carbon content in rhizosphere of EC plants during the period of tillering. After 34 d in EC, carbon content in shoots, roots, and in rhizodepositions was enhanced by the factors 1.05, 1.28, and 1.96, respectively. Carbon partitioning between above and belowground biomass was not affected by EC, however, proportionally more C in the belowground partitioning was allocated into the root biomass. Carbon flow from roots to rhizodepositions and rhizosphere microflora was proportional to P_N; its fraction in daily assimilated carbon decreased from young (17%) to order (3-4%) plants. This revised version was published online in June 2006 with corrections to the Cover Date.