Different responses of two contrasting wheat genotypes to abscisic acid application

Purpose of this study was to investigate different responses of two wheat genotypes (Triticum aestivum L.) from the wet and dry climate regions to exogenous abscisic acid (ABA) application under well-watered and water-stressed conditions. Exogenous ABA was applied to the leaves by spraying and changes in dry matter accumulation and allocation, endogenous ABA content and carbon isotope ratio (δ¹³C) were monitored. The ABA application significantly decreased stem height, total biomass, total leaf area, total grain mass and leaf area/mass ratio, and significantly increased root/aboveground biomass ratio, endogenous ABA content and δ¹³C under well-watered and water-stressed conditions. Compared with the wet climate genotype, the dry climate genotype was more responsive to exogenous ABA application, resulting in lower stem height, total biomass, total leaf area, total grain mass and leaf area/mass ratio, and higher root/aboveground biomass ratio, endogenous ABA content and δ¹³C under all experimental treatments.The research was supported by the Program of “100 Distinguished Young Scientists” and “ Knowledge Innovation Engineering” of the Chinese Academy of Sciences (No. KSCX2-SW-115).     

Early growth,dry matter allocation and water use efficiency of two sympatric Populus species as affected by water stress

We exposed cuttings of two sympatric species of Sect. Tacamahaca Spach, Populus cathayana Rehder and Populus przewalskii Maximowicz, to two watering regimes in a greenhouse. In the semi-controlled environmental study, two watering treatments which were watered to 100 and 25% of field capacity were used, respectively. The effects of water deficit on early growth, biomass allocation and water use efficiency (WUE) were investigated. We found that there were significant interspecific differences in early growth, dry matter allocation and water use efficiency between two sympatric Populus species. Compared with P. cathayana, P. przewalskii showed higher shoot height, dry matter accumulation, number of leaves, total leaf area, fine root mass, fine root/total root ratio and water use efficiency under both well-watered and water-stressed treatments. On the other hand, P. przewalskii also showed higher root mass/foliage area ratio, root/shoot ratio and carbon isotope composition than P. cathayana under water-stressed treatment. The results suggested that there were different water-use strategies between two sympatric Populus species, P. przewalskii with higher drought tolerance may employ a conservative water-use strategy, whereas P. cathayana with lower drought tolerance may employ a prodigal water-use strategy. The findings confirm the existence of interspecific genetic differences in early growth, dry matter allocation and water use efficiency as affected by water stress, these variations in drought responses may be used as criteria for species selection and tree improvement.     

Sex-specific physiological and growth responses to water stress in <Emphasis Type="Italic">Hippophae rhamnoides</Emphasis> L. populations

Dioecious plant species and those occupying diverse habitats may present special analytical problems to determine effects of environmental stress. Here, sex-specific physiological and growth responses of two contrasting sea buckthorn (Hippophae rhamnoides L.) populations were recorded after exposure to different watering regimes. The populations used were from wet and dry climate regions in China, respectively. In the semi-controlled environmental study, the well-watered and water-deficiency plants which were watered to 100 % and 50 % field capacity were used, respectively. Sexual differences in height growth (HT), dry matter accumulation (DMA), root/shoot ratio (RS), specific leaf area (SLA), net photosynthesis (A), transpiration (E), instantaneous water use efficiency (WUE_i) and carbon isotope composition (δ¹³C) between the male and female individuals were detected under water-deficiency treatment in both populations tested. However, these sexual differences were not detected under well-watered treatment. On the other hand, compared with the wet climate population, the dry climate population showed lower HT, DMA, SLA, A and E, and higher RS under both watering regimes. The dry climate population also showed higher WUE_i and δ¹³C as affected by water deficit than the wet climate population. These morphological and physiological responses to drought showed that the different populations and the different sexual individuals may employ different survival strategies under environmental stress. The male individuals and the dry climate population would have a conservative water-use strategy in response to drought stress.     

Differences in some morphological, physiological, and biochemical responses to drought stress in two contrasting populations of Populus przewalskii

The cuttings of Populus przewalskii Maximowicz were exposed to three different watering regimes (100, 50, and 25% of the field capacity) in a greenhouse to characterize the morphological, physiological, and biochemical basis of drought tolerance in woody plants. Two contrasting populations of P. przewalskii were used in our study, which were from the wet and dry climate regions in western China, respectively. The results showed that there were significant differences in responses to three different watering regimes in both populations tested; drought not only significantly affected dry mass accumulation and partitioning but also significantly decreased chlorophyll pigment contents and accumulated free proline and total amino acids. On the other hand, drought also significantly increased the levels of abscisic acid, hydrogen peroxide, and superoxide radical as secondary messengers to induce the entire set of antioxidative systems including the increase of reduced ascorbic acid (ASA) content and the activities of superoxide dismutase, guaiacol peroxidase, ascorbate peroxidase, and glutathione reductase (GR). Moreover, there were different responses to drought stress between the two contrasting populations of P. przewalskii . Compared to the wet climate population, the dry climate population showed lower dry matter accumulation and partitioned more biomass to root systems, and accumulated more free proline and total amino acids for osmotic adjustment. The dry climate population also showed more efficient antioxidant systems with higher content of ASA and higher activities of ascorbate peroxidase and GR than the wet climate population.     

Differential sensitivity of canola (Brassica napus) seedlings to ultraviolet-B radiation,water stress and abscisic acid

Responses of canola (Brassica napus L.) seedlings to three ultraviolet (UV)-B levels [0 (zero), 5 (ambient) and 10 (enhanced) kJ m^?2 d^?1], two watering regimes (well-watered and water-stressed), and two abscisic acid (ABA) levels (with and without application) were investigated. Overall, enhanced UVB and water stress negatively affected plant growth and physiology, but ABA had very little effect. Enhanced UVB decreased stem height, leaf area, plant dry matter, water use efficiency and wax content, but increased concentrations of chlorophyll a, carotenoids and flavonoids, and ethylene evolution. Water stress reduced stem height and diameter, leaf area, plant dry matter, leaf weight ratio and shoot:root weight ratio under zero and ambient UVB. Water stress also reduced chlorophyll a and carotenoids in plants exposed to enhanced UVB. ABA with watering regime had significant interactive effects only on leaf dry matter and wax content. We found that enhanced UVB and water stress adversely affected B. napus seedlings. Interaction between these two factors affected plant performance. In this interaction, ABA had little significant role. Also, optimum vegetative growth and biomass were achieved under ambient UVB.     

The role of seed provenance in the early development of Arbutus unedo seedlings under contrasting watering conditions

In the last decades, several studies have reported the increase of land degradation and desertification in the Mediterranean Basin. Depending on degradation severity, ecological restoration might be needed in order to promote ecosystem recovery. The ecology of the selected species and intra specific variability should be considered in order to improve restoration options, especially facing climate change.The present study tested the hypothesis that seedlings from drier provenances would be better adapted to low water content conditions. Seeds were germinated under controlled temperature after which seedlings were grown in a phytotron under two contrasting watering regimes. Seedling performance was analysed using morphological and physiological parameters.Low water content had a clear negative effect on the seedlings’ aboveground biomass (total dry weight, root collar diameter, leaf dry weight and leaf weight ratio) and a positive effect on belowground biomass (root weight and root:shoot ratio). This response was not unequivocal, since provenances differed in morphological adaptations to low water content. Seedlings from the wettest provenance revealed a higher relative growth rate under high water content but a poor adaptation to limited water availability when compared to the other two provenances. This was observed by the absence of a significant belowground investment in this provenance. Seedlings from the wettest provenance also presented a significant reduction of total leaf area that was not observed in the other two provenances. This can however be hardly considered as a successful adaptation to cope with drought since this provenance produced less sclerophyllous leaves, less belowground biomass and also lower sapwood to leaf area ratio independently from the water content conditions. By contrast, seedlings from the dry provenance with the hottest summer had similar root collar diameter, leaf dry weight and physiological performance under both watering regimes.The observed adaptations to water regimes seem to be related with the climate of the seed source and highlighted the importance of seed provenance in ecological restoration actions using Mediterranean species. This knowledge could improve early establishment success predictions for different plant populations, allowing more reliable and cost-effective management decisions under climate change scenarios.     

Assimilation,respiration and allocation of carbon inPlantago major as affected by atmospheric CO2 levels

The response ofPlantago major ssp,pleiosperma plants, grown on nutrient solution in a climate chamber, to a doubling of the ambient atmospheric CO₂ concentration was investigated. Total dry matter production was increased by 30% after 3 weeks of exposure, due to a transient stimulation of the relative growth rate (RGR) during the first 10 days. Thereafter RGR returned to the level of control plants. Photosynthesis, expressed per unit leaf area, was stimulated during the first two weeks of the experiment, thereafter it dropped and nearly reached the level of the control plants. Root respiration was not affected by increased atmospheric CO₂ levels, whereas shoot, dark respiration was stimulated throughout the experimental period. Dry matter allocation over leaves stems and roots was not affected by the CO₂ level. SLA was reduced by 10%, which can partly be explained by an increased dry matter content of the leaves. Both in the early and later stages of the experiment, shoot respiration accounted for a larger part of the carbon budget in plants grown at elevated atmospheric CO₂. Shifts in the total carbon budget were mainly due to the effects on shoot respiration. Leaf growth accounted for nearly 50% of the C budget at all stages of the experiment and in both treatments.Abbreviations LAR leaf area ratio - LWR leaf weight ratio - RGR relative growth rate - R/S root to shoot ratio - RWR root weight ratio - SLA specific leaf area - SWR stem weight ratio     

Differences in developmental plasticity and growth rate among drought-resistant and susceptible cultivars of durum wheat (Triticum turgidum L. var. durum)

Understanding how growth and development of durum wheat cultivars respond to drought could provide a basis to develop crop improvement programmes in drought-affected tropical and subtropical countries. A greenhouse experiment was conducted to study the responses of five durum wheat cultivars to moisture stress at different developmental phases. Phenology, total dry matter (TDM), relative growth rate (RGR), leaf area ratio (LAR), net assimilation rate (NAR), leaf weight ratio (LWR), specific leaf area (SLA) and shoot:root ratio were compared. Pre-anthesis moisture stress delayed phenological development, whereas post-anthesis moisture stress accelerated it. TDM accumulation rate was different between drought-resistant and susceptible cultivars. RGR and its components changed with age and moisture availability. Drought-resistant cultivars had a high RGR in favourable periods of the growing season and a low RGR during moisture stress. In contrast, the drought-susceptible cultivar (Po) showed an opposite trend. LAR explained the differences in RGR (r=0.788) best, whereas the relationship between NAR and RGR was not significant. Even though both LWR and SLA were important factors determining the potential growth rate, LWR was of major importance to describe cultivar differences in LAR, and consequently in RGR. The drought-resistant cultivars Omrabi-5 and Boohai showed vigorous root development and/or a low shoot:root ratio. It is concluded that biomass allocation is the major factor explaining variation in RGR among the investigated durum wheat cultivars.     

Interactions between water deficit, ABA, and provenances in Picea asperata

The effects of exogenous abscisic acid (ABA) on the acclimation of Picea asperata to water deficit were investigated in two populations originating from wet and dry climate regions of China. Exogenous ABA was sprayed onto the leaves, and changes in plant growth and structure, gas exchange, water use efficiency (WUE), endogenous ABA content, and antioxidant enzyme levels were monitored. The results demonstrated that ABA application affected the two P. asperata populations in different ways during the water deficit. ABA application resulted in significantly lower CO(2) assimilation rates (A) under water deficit in plants from the wet climate population, whereas there were no significant changes in this parameter in the dry climate population. On the other hand, ABA application significantly decreased the dry shoot biomass, stomatal conductance (g(s)), transpiration rate (E), and malondialdehyde (MDA) content, and it significantly increased the leaf mass per area (LMA), root/shoot ratio (Rs), fine root/total root ratio (Ft), WUE, ABA content, and the superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT) activities under water-deficit conditions in the dry climate population, whereas ABA application did not significantly affect these parameters in the wet climate population. The results clearly demonstrated that sensitivity to an exogenous ABA application is population-dependent in P. asperata. Direct evidence is presented that variation in physiological mechanisms rather than different rates of ABA absorption explain the population differentiation in the sensitivity to exogenous ABA, and that the physiological basis for the amplified response to water deficit caused by exogenous ABA, present mainly in the dry climate population, is related to internal ABA accumulation. These results provide evidence for adaptive differentiation between populations of P. asperata, and they support the expected relationship between environmental heterogeneity and the magnitude of plastic responses in plant populations.     

狭叶红景天幼苗对水分及遮阴的生长及生理生化响应

研究植物对水分和遮阴胁迫的响应及其生理机制对制定合理的栽培管理措施十分必要。以红景天属植物为研究对象,设置土壤含水量分别为田间持水量的80%(过湿水分)、70%(正常水分)、60%(轻度干旱)、40%(中度干旱)、20%(重度干旱)5个水分梯度;设置2个遮阴处理,以全光照(遮阴率为0)为对照、黑色遮阴网遮阴(遮阴率为85%),研究狭叶红景天生长及生理生化指标的变化特征。结果表明:在不同水分处理下,与对照相比,叶绿素含量、茎干重和茎重比(SMR)显著增加(P0.05),株高、总生物量、叶面积、叶干重、叶重比(LMR)、比叶面积(SLA)、叶面积比(LAR)和叶面积根干重比(LARMR)增加,根冠比和根重比(RMR)减少;随着干旱程度加剧,丙二醛(MDA)、脯氨酸(Pro)和可溶性糖(Ss)含量增加,超氧化物歧化酶(SOD)活性总体呈先增加后减小的趋势。在遮阴处理下,株高、SMR、SLA、LAR和LARMR显著增加(P0.05),叶绿素SPAD值和叶面积增加,总生物量、根干重、根冠比和LMR显著减少(P0.05),茎干重和叶干重减少,MDA含量显著增加,Pro含量略有下降,Ss含量减少。在水分胁迫下,狭叶红景天中度干旱时通过增加酶活性抵御伤害,重度干旱超过其阈值,SOD活性下降,植物体受到伤害,Ss可能是主要的渗透调节物质。在遮阴处理下,狭叶红景天通过增加SLA避免遮阴伤害。狭叶红景天在受到环境胁迫时会通过形态改变、调节MDA含量、抗氧化酶活性和渗透调节物质来保证自身正常的生长发育。     

Effects of untreated two‐phase olive mill pomace on potted olive plantlets

Two‐phase pomace represents an important environmental problem in Mediterranean areas. With its high organic content, direct application of two‐phase pomace in the field is recommended to improve soil organic carbon levels and fertility. However, this does not consider any antagonistic effects that this application might have on root proliferation and biomass partitioning. We studied the effects of untreated two‐phase pomace on properties of growth substrate, and on shoot and root growth and biomass allocation of potted olive plantlets. A pot experiment was carried out in a greenhouse over 90 days, with five levels of two‐phase pomace and using two olive cultivars. The effects on shoot growth, leaf pigment content and maximum quantum efficiency of photosystem II (ΦPSII) were assessed each month. After 90 days, the shoot and root biomass of the olive plants was quantified, along with total organic matter, and carbon, nitrogen and polyphenol contents of the growth substrate and shoots, and the fine root nutritional status. Two‐phase pomace increased the total organic matter, total nitrogen and polyphenol contents of the growth substrate. It significantly altered biomass partitioning in the olive plantlets, with reduced shoot dry mass and leaf area, and new shoot formation. It also increased fine and total root dry mass for all two‐phase pomace levels except 40%. There were no significant differences in leaf pigment content and ΦPSII across the treatment levels. Therefore, application of untreated two‐phase pomace at more than 4% induces a severe imbalance in olive plantlet biomass partitioning, and shoot and root growth.     

Temperature Regulation of Growth and Endogenous Abscisic Acid-like Content of Tulipa gesneriana L

The ontogenetic changes of dry matter and abscisic acid (ABA)-like content in the component organs of Tulipa gesneriana L. `Paul Richter' and `Golden Melody' under two temperature storage regimes were determined. The organ dry matter and ABA showed marked differences during 13 and 5 C dry storage and during subsequent growth at 13 C. Scale dry matter of both cultivars declined sharply when grown at 13 C. The basalplate of the cultivars showed an initial gain in dry matter, but declined subsequently. The shoot of both cultivars stored at 13 C exhibited greater dry matter gain than at 5 C. In contrast, the bulblets of the cultivars at 5 C showed a much higher rate of dry matter accumulation than at 13 C.     

土壤水分对两个冬小麦品种产量和竞争能力的影响

研究了黄土塬区两个旱作冬小麦品种(长武135和平凉40,前者是后者的换代品种)在不同土壤水分条件下竞争能力和产量形成的关系。研究设2种土壤水分条件(土壤含水量为田间最大持水量的75%～80%和40%～45%),采用生态替代法设计了同一播种密度的6个播种比例组合的盆栽试验。低水分单播条件下,长武135具有较高的产量(长武135为27.59g/pot,平凉40为24.91g/pot),而混播条件下平凉40在产量和相对产量上较长武135品种具有明显的竞争优势。高水分条件下,平凉40产量随播种比例的减小下降较快(长武135产量曲线斜率35.468,平凉40为36.237)。平凉40低水分单播时花后干物质积累量较少(长武135为0.67g/pot,平凉40为0.55g/pot),而混播时较多(长武135各比例均值0.58g/pot,平凉40为0.71g/pot),导致了平凉40品种单播时产量较低和混播时产量较高。平凉40地下生物量显著大于长武135(高水分条件下,长武135为10.03g/pot、平凉40为11.51g/pot;低水分条件下二者分别为8.41g/pot和10.69g/pot),且耗水量大(高水分条件下平凉40多耗水2.72kg/pot,低水分条件下多耗0.98kg/pot),而耗水量/地下生物量的比值平凉40低于长武135,从而平凉40品种单位根量消耗的水分低于长武135。总之,在两个生长属性接近的冬小麦品种中,老品种以较大的根系生物量赢得了较高的竞争能力,消耗了较多的水分,而新品种虽然根系生物量较低,耗水量较少,但籽粒产量却较高。亦即,小麦新品种籽粒产量的提高是与根系的减少和对水资源竞争能力的下降相伴随的。     

The Distribution of Nitrate Assimilation Between Root and Shoot in Vicia faba L.

Nitrate assimilation was examined in two cultivars (Banner Winterand Herz Freya) of Vicia faba L. supplied with a range of nitrateconcentrations. The distribution between root and shoot wasassessed. The cultivars showed responses to increased applied nitrateconcentration. Total plant dry weight and carbon content remainedconstant while shoot: root dry weight ratio, total plant nitrogen,total plant leaf area and specific leaf area (SLA) all increased.The proportion of total plant nitrate and nitrate reductase(NR) activity found in the shoot of both cultivars increasedwith applied nitrate concentrations as did NO₃^–: Kjeldahl-Nratios of xylem sap. The cultivars differed in that a greaterproportion of total plant NR activity occurred in the shootof cv. Herz Freya at all applied nitrate concentrations, andits xylem sap NO₃^–: Kjeldahl-N ratio and SLA were consistentlygreater. It is concluded that the distribution of nitrate assimilationbetween root and shoot of V. faba varies both with cultivarand with external nitrate concentration. Vicia faba L., field bean, nitrate assimilation, nitrate reductase, xylem sap analysis     

不同氮浓度对兔眼蓝浆果不同品种幼苗生长和光合生理的影响

为确定兔眼蓝浆果( Vaccinium ashei Reade)不同品种苗期的适宜施氮量,以兔眼蓝浆果早熟品种‘阿拉帕哈’(‘Alapha’)、中熟品种‘园蓝’(‘Gardenblue’)和晚熟品种‘芭尔德温’(‘Baldwin’)的组培苗为实验材料,采用水培法研究了不同氮浓度(0、1、2和4 mmol·L-1)对幼苗生长、根和叶中全氮含量、叶片光合生理特性的影响。结果表明：与对照(0 mmol·L-1氮)相比,经1、2和4 mmol·L-1氮处理后3个兔眼蓝浆果品种的单株茎叶干质量显著增加,根冠比显著降低;但品种‘园蓝’的单株根干质量显著高于对照,另2个品种的单株根干质量与对照无显著差异。随着营养液中氮浓度的提高,3个兔眼蓝浆果品种根的全氮含量及品种‘阿拉帕哈’叶的全氮含量均逐渐增加,且在4 mmol·L-1氮处理下最高;品种‘园蓝’和‘芭尔德温’叶的全氮含量呈先升高后降低的趋势,且均在2 mmol·L-1氮处理下最高;各处理组根和叶的全氮含量均显著高于对照。经1、2和4 mmol·L-1氮处理后,3个兔眼蓝浆果品种叶片的叶绿素a、叶绿素b和总叶绿素含量以及PSⅡ最大光化学效率( Fv/Fm )均呈先升高后降低的趋势,且均显著高于对照。各处理组中,品种‘园蓝’叶片的净光合速率( Pn)、气孔导度( Gs)、胞间CO2浓度( Ci)和蒸腾速率( Tr)均显著高于对照;品种‘芭尔德温’叶片的Pn值在4 mmol·L-1氮处理下显著低于对照,Gs和Tr值在2 mmol·L-1氮处理下显著高于对照,Ci值与对照无显著差异;与对照相比,品种‘阿拉帕哈’叶片的Pn值在1和4 mmol·L-1氮处理下显著提高,Gs值在1 mmol·L-1氮处理下显著提高,Tr值在1和2 mmol·L-1氮处理下显著提高,而Ci值则在4 mmol·L-1氮处理下显著降低。综合分析结果显示：适度增施氮肥可提高兔眼蓝浆果不同品种幼苗的茎叶生长、改善其光合性能,但对根系生长无明显的促进作用。在营养生长期兔眼蓝浆果不同品种的需氮量存在差异,其中品种‘园蓝’更适宜高氮环境,而施用少量氮肥即可促进品种‘芭尔德温’和‘阿拉帕哈’幼苗地上部分生长。     

NaCl胁迫对杂交狗牙根品种‘苏植2号’和‘Tifgreen’生长及Na＋和K＋积累的影响

对0（对照）和20g·L-1NaCl胁迫条件下杂交狗牙根（Cynodondactylon×C.transvaalensis）品种‘苏植2号’（‘SuzhiNo.2’）和‘Tifgreen’不同部位的生长状况以及Na＋和K＋积累的差异进行了研究,并分析了2个品种间Na＋、K＋转运调控机制的差异。结果显示：在NaCl胁迫条件下,2个品种的叶片相对枯黄率、地下茎和根系的相对干质量、叶片和根系的Na＋含量和Na＋/K＋比以及钠钾选择性转运系数增加;修剪茎叶及冠层和地上部的相对干质量、植株相对总干质量以及叶片和根系的K＋含量均降低,但茎叶含水量无显著变化。NaCl胁迫条件下,不同土层中2个品种的根系相对干质量均不同程度增加,且20-40和40-60cm土层中根系干质量的增幅大于0-20cm土层;在0-20cm土层中2个品种根系的分配比例均有所降低,而在20-40和40-60cm土层中则不同程度提高。与‘Tifgreen’相比,NaCl胁迫条件下‘苏植2号’叶片相对枯黄率、Na＋含量和Na＋/K＋比更低,修剪茎叶及冠层和地上部的相对干质量、植株相对总干质量、叶片K＋含量和钠钾选择性转运系数更高;在20-40和40-60cm土层中‘苏植2号’根系相对干质量显著高于‘Tifgreen’,根系分配比例总体也高于‘Tifgreen’。综合比较结果表明：‘苏植2号’的抗盐性强于‘Tifgreen’,可能与其深层根系分配量更高和钠钾选择性转运能力较强有关。     

Physiological basis of differential response to salinity in rice cultivars

Growth analyses of rice Oryza sativa L. seedlings in salinized nutrient solution condition were conducted with 24 cultivars and lines after genetic purification. Cultivar differences in relative growth rate in salinized conditions were chiefly dependent on differences in shoot Na content. The shoot Na content was affected by Na selectivity in the root and by the leaf area ratio (LAR, leaf area per total dry weight). The contribution of LAR was equally important to that of root cultivar selectivity against Na uptake under a higher salinization condition where root selectivity against Na may be decreased due to reduced root activity. Cultivar differences in salt tolerance in highly salinized conditions were mainly attributed to differences in these two factors. A more convenient and efficient screening method for salt tolerance is proposed.     

Root growth and functioning under atmospheric CO2 enrichment

This paper examines the extent to which atmospheric CO₂ enrichment may influence growth of plant roots and function in terms of uptake of water and nutrients, and carbon allocation towards symbionts. It is concluded that changes in dry matter allocation greatly depend on the experimental conditions during the experiment, the growth phase of the plant, and its morphological characteristics. Under non-limiting conditions of water and nutrients for growth, dry matter partitioning to the root is not changed by CO₂ enrichment. The increase in root/shoot ratio, frequently observed under limiting conditions of water and/or nutrients, enables the plant to explore a greater soil volume, and hence acquire more water and nutrients. However, more data on changes in dry matter allocation within the root due to atmospheric CO₂ are needed. It is concluded that nitrogen fixation is favored by CO₂ enrichment since nodule mass is increased, concomitant with an increase in root length. The papers available so far on the influence of CO₂ enrichment on mycorrhizal functioning suggest that carbon allocation to the roots might be increased, but also here more experiments are needed.Abbreviations LAR leaf area ratio - LWR leaf weight ratio - SWR stem weight ratio - RGR relative growth rate - R/S root/shoot - RWR root weight ratio     

Carbon Economy of Carrots During Initiation of the Storage Root in Cultivars Contrasting in Shoot: Root Ratio at Maturity

Photosynthesis, respiration and growth of two cultivars of carrotwith contrasting ratios of shoot: storage root weight at maturity,were compared during initiation of the storage root at 20 °C.Partition of assimilate between shoot, roots and respirationshowed no varietal differences but distribution between storageand fibrous roots was different from the time that the storageroot could be morphologically identified. For both cultivarsover the period investigated, approximately 64% of net photosynthesiswas partitioned to the shoot with 5% lost as respiration duringthe dark and 59% used in growth. Of that exported to the rootsystem (36%), 19% (of net photosynthesis) was used in growthand 17% was lost in respiration. In the cultivar with greatershoot: storage root ratio at maturity, 4.6% was allocated tothe storage root in contrast to 7.5% in the cultivar with alesser shoot: storage ratio at maturity. It is concluded thatgreater dry matter accumulation in the storage root of the lattercultivar does not result from transient differences in respiratoryloss and is not evident in shoot to total root dry matter distributionover this period. Daucus carota L, carrot, assimilate partition, shoot, storage root, shoot: root ratio     

Some aspects of wheat cultivar response to applied phosphate

Summary Two experiments are described in which a comparison was made of differences in phosphorus contents, dry matter production and root growth between a semi-dwarf wheat (Israel M68) and a standard height cultivar (Olympic). In the first experiment, using soil as a support medium, Olympic had higher root dry weight and root to shoot ratios, but lower root and shoot phosphorus contents, than Israel M68. In the second experiment, using solution culture technique, Olympic had higher root dry weights and root to shoot ratios, but there was no cultivar difference in either root or shoot phosphorus content. This suggests an improved ability in the semi-dwarf wheat to explore the soil system. In both experiments the rate of uptake of phosphorus, when calculated per unit root fresh weight, was highest with Israel M68. Root measurements in a later experiment (Experiment 2a) indicated similar total fresh weights for both cultivars, but on a unit fresh weight basis, the semi-dwarf cultivar had a greater root number, root area and lateral root volume. Although further studies to clarify the situation are necessary, these differences may be associated with the enhanced grain yield response to superphosphate of some semi-dwarf wheats when compared to standard height cultivars. re]19751104