Influence of Soil Drought on Plant Growth, Assimilation and Dissimilation of CO2 and Accumulation of Photosynthates in Field Bean (Vicia faba L. minor) During Pod Formation and Rapid Pod Growth

Field bean planes cultivar Nadwiślański were submitted to soil drought (30 % of field soil water capacity) for 5 days at the stage of pod formation (A) and of rapid pod growth (B) and then exposed for 20 minutes to ¹⁴CO₂. Radioactivity of leaves, stems, roots, and pods or pod shells and seeds was measured 1, 5, 24 and 48 hours after exposition.
In both stages soil drought reduced by about five times total CO₂ assimilation, mainly owing to lower activity of the photosynthetic apparatus and also, though less so, to reduced leaf growth. Photosynthetic activity referred to the dry weight of the leaves dropped to 22-35% of controls. Accumulation of photosynthetates in generative organs was much less depressed than ¹⁴CO₂ assimilation. 48 hours after exposition to ¹⁴CO₂ of drought treated plants, the contents of ¹⁴C of pods in phase A, and seeds in phase B, amounted to respectively 24% and 36% of assimilated ¹⁴C and equalled 91.5% and 74% of the corresponding values for controls.
The progressive decline of radioactivity in leaves and stems after ¹⁴CO₂ exposition was distinctly correlated to the rise of radioactivity of generative organs both in soil drought treated plants and in controls. Slightly lower values of correlation coefficients in drought treated plants may indicate impairment under drought conditions of synchronization in processes of unloading and accumulation of assimilates.
In plants drought treated in phase A the ability to dissimilate ¹⁴C was reduced to about 59% of that in controls, but when drought was applied in phase B, dissimilation rate was about three times as high.     

Effect of Low Soil Temperature on Weight Increase, Gas Exchange and Distribution of 14C-Assimilates in Seedlings of a Maize Hybrid

Seedlings of a maize hybrid sensitive to chilling initially grew in the growth chamber of the phytotron at 20/ 17°C (day/night) and after the formation of the fourth leaf, the soil temperature was lowered to 5°C. Under such growth conditions the dynamics of dry weight change, gas exchange and the distribution of ¹⁴C-assimilates in seedlings were examined. The low soil temperature inhibited daily growth of dry weight of whole seedlings more than their photosynthesis. Simultaneously, it was also responsible for a greater increase in dissimilative losses.
During 37 hours (day-night-day), following exposure to ¹⁴CO₂, dissimilation in seedlings in cool soil (5°C) and in non-chilling conditions amounted to 35.1 % and 23.4 % of assimilated ¹⁴C (AC), respectively. At lower soil temperature relatively high dissimilative losses were observed on the first day after exposure (23.5 %), lower at night (9.9 %) and the lowest on the following day - merely 1.7 % AC. Higher losses of ¹⁴C under chilling conditions occurring on the first day were a result of limited photosynthetic refixation of ¹⁴CO₂ At night, however, they were associated with a prolonged period of intensive translocation of assimilates to the stem. It was assumed that an excessive accumulation of assimilates in leaf blades might be an additional factor responsible for increased dissimilative losses at low temperature during the first twenty-four hours. In the third period of measurements, as a result of a limited transport of ¹⁴C, dissimilative losses were lower than in previous ones and were not dependent upon soil temperature.     

Plant Growth Regulators Influence 14CO2 Assimilation and Translocation of Assimilates in Indian Mustard

Effect of plant growth regulators Naphthalene acetic acid (NAA), Gibberellic acid (GA₃) and Kinetin on ¹⁴CO₂ assimilation, partitioning of ¹⁴C into major biochemical fractions and translocation of assimilates was studied in different parts of Indian Mustard ( Brassica juncea ) at late ripening stage. Leaves, stem and pod walls are photosynthetically active and are important sources for seed filling. NAA and kinetin increased the ¹⁴CO₂ assimilation rate in all the three photosynthetically active parts. All the three growth regulators increased the export of ¹⁴assimilates out of source organs and increased the movement of assimilates into the reproductive parts (pods). The increased movement of photoassimilates into the developing pods may be due to the stimulation of sink activity by the growth regulators which resulted in the higher demand for photoassimilates. It was suggested that growth regulators may increase yield by altering distribution of assimilates in the mustard plants.     

Effect of High Temperature Stress on 14CO2 Assimilation and Partitioning in Indian Mustard

Effect of heat stress on ¹⁴CO₂ assimilation and translocation by different parts was investigated in Indian mustard ( Brassica juncea (L.) Czern.]. Heat stress reduced ¹⁴CO₂ assimilation by leaves, stem and pods. Export of radioactive carbon from upper and lower leaves, upper and lower stem and stem of terminal raceme was inhibited in response to heat stress. Import of ¹⁴C-photosynthates into pods was also inhibited by heat stress indicating reduction in sink strength of the developing pods.     

Untersuchungen zur Assimilatverteilung in Ackerbohnen (Vicia faba L.) während der Blühphase

Investigations about the distribution of assimilates during flowering in broad beans ( Vicia faba L.)
The distribution of assimilates during flowering was studied on single plants exposed to ¹⁴CO₂ in the field. The plants were harvested 1, 3, 15 days after exposition and at ripening. Results:
1. At the begin of flowering the nodes with flowers assimilated much ¹⁴C with a tendency of higher contents in the more above situated nodes. The concentration of ¹⁴C was similar in blades, stalks and flowers.
2. The assimilates incorporated after 24 hours were only to a small amount translocated afterwards. Only 3 % went to the apical region. An intensive restorement out of the blades took place at the time of ripening.
3. In the midst of flowering the concentration of ¹⁴C was lower in the nodes with open flowers than in those with shut or with pods. At that time pods are already strong sinks that withdraw assimilates from blades and stalks.
4. At the time when large and small pods are growing on the lower and middle nodes, the nodes in the apical region will be deprived of assimilates (effects of dominance).
5. Roots and nodules had low but stable contents and concentrations of ¹⁴C during flowering. These descended distinctly at ripening.     

High Temperature Influence 14CO2 Assimilation and Allocation of 14C into Different Biochemical Fractions in the Leaves of Indian Mustard

Influence of high temperature stress on photosynthesis and allocation of carbon into different biochemical fractions in mature leaves of Indian mustard [ Brassica juncea (L) Czern] was investigated. Heat stress reduced ¹⁴CO₂ fixation and inhibited the translocation of carbon from the leaves. Allocation of ¹⁴C into starch and residue fractions was significantly lower in heat stressed plant leaves. Starch content was significantly reduced in heat stressed plants.     

Pflanzenwachstum durch CO2/HCO3-Eintrag über die Wurzel

Plant Growth after Application of CO₂/HCO₃ to the Roots
After applying H¹⁴CO₃ to the root system of summer wheat in hermetically sealed pots, absorption and incorporation of HCO₃ in the sugar-, starch-, and fibre-fraction (approximately 50 % of the absorped ¹⁴C) could be shown. This fraction reached 0.44–1.21 % of total C-assimilation of the shoot during growing stage F9/F10 on the Feeke-scala. 1/3 of the HCO₃-fraction resting in the soil was bound organically indicating that microorganisms may be able to utilize exogenous anorganic CO₂/HCO₃ for their photosynthesis.     

Genotypische Unterschiede in der Translokation von zwischengelagertem 14C aus dem Halm in die Körner bei Sommerweizen (Triticum aestivum L.)

Genotypic differences in the translocation of temporarily stored ¹⁴C from the stem to the grains in spring wheat (Triticum aestivum L.)
In three field experiments with two spring wheat genotypes (Kolibri and breeding line 93117 ), changes in the total nonstructural carbohydrates (TNC) of the stem were observed after anthesis. Maximum values were measured in the third or fourth week following anthesis when stems contained 300 to 400 mg TNC. Thereafter TNC content declined up to maturity.
Flag leaves of individual shoots or all plants in micro-plots were labelled with ¹⁴C 5 days prior to anthesis, at anthesis or 5 days after anthesis to observe long term movements of assimilates during grain filling. After a chase period of two to three days, 60 to 80 % of total ¹⁴C recovered in the shoot was in the stem. From total ^l4C recovered two to three days after labelling, Kolibri had translocated 12.5 to 27.0 % into the grains by maturity whereas this portion was significantly higher for the breeding line 93117 (22.5 to 43.9 %). It was concluded that genotypes differ in the translocation of soluble carbohydrates from the stem to the grains. These differences were not related to parameters describing the 'source-sink' relationship, such as leaf area, grain number or grain size. However, the lower translocation rates of Kolibri coincided with a lower TNC concentration in the stem dry matter. This was due to a higher stem weight at anthesis, a longer period of stem elongation and a higher incorporation of assimilates into structural carbohydrates in non elongating stem parts after anthesis. It was therefore suggested that the accumulation of TNC in the stem and the remobilisation of these reserves for grain filling are determined partly by factors related to the carbohydrate metabolism in the stem.     

14CO2 Assimilation and Translocation of 14C-Photosynthates by Different Parts of Indian Mustard (Brassica juncea L.)

The role of leaves, stem and reproductive parts in ¹⁴CO₂ fixation and subsequent photosynthate translocation was studied in Indian mustard ( Brassica juncea L.) at three growth stages. The data indicated that leaves, stem and pods are important sources of photosynthates for seed filling. At bud emergence stage leaves are the principle site of ¹⁴CO₂, fixation. The contribution of leaves declines at subsequent stages, where as the contribution of pod walls increased from bud emergence stage to ripening stage. The contribution of the stem remains more or less constant at all three growth stages studied. Although stem can fix ¹⁴CO², at bud emergence and flowering stages it imported ¹⁴C-photosynthates from leaves. However, stem exported photosynthates during subsequent growth stages.     

Translocation of 14C-sucrose within the Ear in Durum and Aestivum Wheat Varieties

Excised ears of Triticum durum (HD 4502 and B 449) and T. aestivum (Kalyansona and Kundan) varieties were cultured in ¹⁴C-sucrose, and the uptake and distribution of ¹⁴C within the ear was examined. Species-level differences in the distribution of ¹⁴C to spikelets at basal, middle and apical positions in the wheat ear (vertical distribution) were observed. T. aestivum var. Kalyansona and Kundan showed no limitation in vertical translocation of ¹⁴C-sucrose, whereas in T. durum there was a decrease in the distribution of ¹⁴C to apical spikelets. Within a spikelet, the distribution of ¹⁴C-sucrose to distal grains was significantly less than that to proximal grains in all the genotypes.     

14C-labelled Assimilate Distribution in Flowering Maize Plants

Maize ( Zea mays L.) plants were grown in the field and labelled with ¹⁴CO₂ at four leaf positions from silking up to maturity. The ear leaf was the most important source of labelled photosynthates to the ear, followed by the first leaf blade above and below the ear. The movement of labelled assimilates from the second leaf blade below the ear was predominantly downwards. The ear became an important sink soon after silking and continued in importance till harvest.
Initially assimilates were partitioned within the ear as husk < cob < grains but at harvest as grains < cob < husk. There was considerable remobilization of assimilates from the husk and stem. Removal of leaves drastically altered the pattern of distribution of labelled photosynthates and the direction of movement was determined by the position of the source leaf blade and the defoliation treatment. Darkening the leaf blades did not much alter the translocation of the labelled photosynthate and increased slightly its proportion to the grains. The removal of the ear severely altered the pattern of distribution of ¹⁴C, which was mostly deposited in the stem.     

The Translocation of 14C-Sucrose and 14C-Benzyl Adenine in Winter Wheat (Tritkum aestivum L.) in the Period of Kernel Formation

The transport and distribution of ^14C-sucrose and ^14C-BA were studied in internode segments with ear of two winter wheat cultivars with a different mass of kernels in the period of kernel formation. While ^MC-sucrose was transported and accumulated intensively in the developing ear, ^14C-BA was transported much less and only a small part of it was found in the ear. With the ear development the accumulation of both ¹⁴C-sucrose and ¹⁴C-BA in the ear increased but the ¹⁴C-BA distribution pattern (ratio of the internode/kernel and the rest of the ear) did not change significantly. In the period of one to two weeks after anthesis the accumulation of ¹⁴C-sucrose and ¹⁴C-BA was higher in the kernels of the Slavia cv., i.e. in the cultivar with a higher mass of kernels.     

Conversion of SO2−4-S and Changes in Glucosinolate Content in Leaves of Rape Seedlings Transplanted

The conversion of SO^2-₄ -S and changes in content of S in various constituents in leaves of rape seedlings transplanted were investigated by using (NH₄)₂³⁵SO₄ as a tracer to exploit formation and accumulation of glucosinolates in oilseed rape. Seedlings grown under sandy culture absorbed ³⁵SO^2-₄ which was added to the cultural solution and incorporated into amino acids, glucosinolates and proteins rapidly. Distribution of extractable ³⁵S with 70 % methanol in glucosinolates in leaves declined with time from labelling, while those in amino acids rised correspondingly. Per cents of ³⁵S incorporated into bound form in total ³⁵S increased linearly and those of ³⁵S into glucosinolates and amino acids decreased with time within five days from labelling. After that the relative amounts of ^3SS in three constituents was basically constant. Content on dry weight basis of labelled glucosinolates and amino acids expressed as μmol S/g.d.w. increased linearly with time from labelling with absorption of ³⁵SO^2-₄from soil by the seedlings under soil culture. Compared with seedlings grown under sandy culture, more ³⁵S was incorporated into glucosinolates in leaves of seedlings grown under soil culture.     

Changes in Content of Glucosinolates and its Accumulation in Siliquae and Seeds of Oilrape (Brassica napus L.)

Rape plants were labelled by applying (NH⁴)₂³⁵SO₄ to soil. Changes in content of ³⁵S in various constituents in pods and grains were determined during siliquae development to exploit formation and accumulation of glucosinolates in oilseed rape. Content of ³⁵S in glucosinolates expressed as μmol S/g.d.w. and its relative amounts in extractable forms in young siliquae were in constant level within one week after flowering, but either absolute content or relative content of ³⁵S in glucosinolates increased largely by two weeks after flowering, thereafter the distribution of extractable ³⁵S in glucosinolates of siliquae and grains increased linearly as proceeding of its development, ³⁵S in extracts of grains almost was in form of glucosinolates after 8 weeks from flowering. Amounts of both ³⁵S in glucosinolates and dry matter per pod increased linearly with time after flowering. According to the changes of amounts of ³⁵S in other constituents per pod, it could be supposed that glucosinolates accumulated in seeds might be transported from other organs together with nutrients.     

Carbon and Nitrogen Transport during Grain Filling in Rice Under High-temperature Conditions

Rice ( Oryza sativa cv. Koshihikari) seedlings were grown in a sandy dune soil in pots with a basal dressing of N (0.5 g N), P and K. Two N treatments were applied, a +N treatment in which a top dressing of ¹⁵N-labeled 0.5 g N was supplied on July 20 and a −N treatment in which no additional fertilizer was supplied. During the grain-filling stage from August 6 to 13, plants were subjected to one of three temperature treatments; controlled low temperature, LT (day/night 28/23 °C), controlled high temperature, HT (35/30 °C) and uncontrolled glasshouse temperature, UT (day/night averages, 38/26 °C). All plants were then exposed to ¹³CO₂ for 1 h on August 11 in a growth chamber at 25 °C. On August 13, all plants were harvested and the ¹³C and ¹⁵N abundances and starch and sugar concentrations in the ears, shoots and roots were determined. The ¹³C content of the ear was lower in UT than in LT irrespective of the +N or −N treatment. The translocation of ¹⁵N to the ears was also slightly depressed in UT compared with LT. Under high-temperature conditions (HT and UT), the starch content per plant was reduced for −N, but for +N, it was not significantly different among the temperature treatments. A high accumulation of sucrose was observed in all plant parts under UT conditions. It is suggested that extreme high day temperatures during the grain-filling period may reduce starch synthesis in the grains and, especially so under N-deficient conditions. High temperatures also induce an accumulation of sucrose and a decrease in carbon and nitrogen transport from the shoots to the ears via the phloem.     

Effect of Soil Moisture and Potassium Fertilizer on Shoot Water Potential, Photosynthesis and Partitioning of Carbon in Mungbean and Cowpea

The effect of different rates of potassium (K⁺) on shoot water potential, photosynthesis and carbon movement (using ¹⁴C) at the V3/4 growth stages was studied in mungbean ( Vigna radiata L. Wilczek), a drought-susceptible legume, and cowpea ( Vigna unguiculata L. Walp), a drought-tolerant legume, grown under low- and high-irrigation regimes under controlled conditions. Soil moisture and K⁺ affected all measured parameters in the two species. The rate of photosynthesis was higher at reduced water stress when K⁺ was applied. The impact was greater in cowpea, which had an inherently high rate of carbon assimilation. Mungbean and to a lesser extent cowpea allocated greater quantities of carbon to roots under dry conditions, especially with added K⁺. The distribution of ¹⁴C into other plant parts was also increased at higher rates of K⁺ application under both soil moisture regimes. Thus, application of K⁺ seems to have a beneficial effect in overcoming soil moisture stress and increasing physiological parameters and carbon partitioning in these two important tropical food legumes.     

Nitrogen Fixation by Hybrids of White Clover (Trifolium repens L.) and Trifolium nigrescens

Development of hybrids between white clover ( Trifolium repens L.) and Trifolium nigrescens provides a novel route for genetically improving the reproductive capacity of white clover, provided the hybrids are agronomically viable, particularly with respect to N₂ fixation. A comparative study of growth and rates of N₂ fixation over 21 days was conducted with the parental species, F ₁ hybrids and backcross hybrids, in flowing solution culture, without a supply of mineral N to the plants. T. nigrescens was unable to fix N₂ in association with the strains of Rhizobium leguminosarum biovar. trifolii selected for inoculation. Rates of N₂ fixation per plant increased in the order T. nigrescens < F ₁ hybrid < T. repens < backcross 1. Specific rates of N₂ fixation (days 0–21) increased in the order T. nigrescens < F ₁ hybrid < backcross 1 <  T. repens . Dry matter production and nodule biomass per plant increased at a higher rate in backcross 1 hybrids than in T. repens. The results suggest that the potential for N₂ fixation by backcross 1 hybrids is at least as great as that by T. repens .     

Stoffbildung, CO2-Gaswechsel, Kohlenhydrat- und Stickstoffgehalt von Winterweizen bei erhöhter CO2-Konzentration und Trocken-streß

Dry Matter Production, CO₂ Exchange, Carbohydrate and Nitrogen Content of Winter Wheat at Elevated CO₂ Concentration and Drought Stress
Methods of mathematical modelling and simulation are being used to an increasing degree in estimating the effects of rising atmospheric CO₂ concentration and changing climatic conditions on agricultural ecosystems. In this context, detailed knowledge is required about the possible effects on crop growth and physiological processes. To this aim, the influence of an elevated CO₂ concentration and of drought stress on dry matter production, CO₂ exchange, and on carbohydrate and nitrogen content was studied in two winter wheat varieties from shooting to milk ripeness. Elevated CO₂ concentration leads to a compensation of drought stress and at optimal water supply to an increase of vegetative dry matter and of yield to the fourfold value. This effects were caused by enhanced growth of secondary tillers which were reduced in plants cultivated at atmospheric CO₂ concentration. Analogous effects in the development of ear organs were influenced additionally by competitive interactions between the developing organs. The content and the mass of ethanol soluble carbohydrates in leaves and stems were increased after the CO₂ treatment and exhausted more completely during the grain filling period after drought stress. Plants cultivated from shooting to milk ripeness at elevated CO₂ concentration showed a reduced response of net photosynthesis rate to increasing CO₂ concentration by comparison with untreated plants. The rate of dark respiration was increased in this plants.     

种植密度对不同株型玉米冠层光能截获和产量的影响

为了明确密植栽培中不同株型玉米的冠层光能截获、物质生产与产量的关系,以不同株型玉米陕单609 (紧凑型)、秦龙14 (中间型)和陕单8806 (平展型)为试验材料,设置4个种植密度(4.5×104、6.0×104、7.5×104和9.0×104株hm–2),于2016—2017年开展大田试验,研究密度对形态特性、冠层光分布、灌浆参数以及干物质积累等的影响。结果表明,陕单609、秦龙14和陕单8806两年平均产量依次为12,176、9624和8533 kg hm–2,分别在9.0×104、7.5×104和6.0×104株hm–2达到高产,产量较低密度分别提高了26.9%、20.4%和19.7%;随着种植密度的增加,叶面积降低,LAI和叶向值增加,在高密度下陕单609中间层由于较大的叶片和叶向值能截获更多的光能,秦龙14次之;灌浆速率达到最大时的天数(Dmax)、粒重(Wmax)、籽粒最大灌浆速率(Gmax)、平均灌浆速率(Gave)、籽粒活跃灌浆期(P)均随密度的增加而降低,高密度下陕单609的Dmax分别较秦龙14和陕单8806早1.4 d和3.0 d, Wmax和P分别高于秦龙14 (0.3g和3.3 d)和陕单8806 (1.1 g和5.4 d);吐丝后干物质积累量、干物质转运量及其对籽粒的贡献率随密度的增加呈先升高后降低的趋势。在高密度下,陕单609花后干物质积累量、花后干物质转运量和干物质转移对籽粒的贡献高于秦龙14 (5.1%、36.0%、33.5%)和陕单8806 (26.6%、46.7%、59.1%)。穗位层光能截获与产量(r=0.631)显著正相关(P0.05),与花后干物质积累量(r=0.661)和平均灌浆速率(r=0.859)极显著相关(P0.01)。可见,与秦龙14和陕单8806相比,紧凑型品种陕单609密植下调控穗上部叶片直立,改善冠层中下部光分布,维持较高的光合绿叶面积,延缓冠层叶片衰老,增加花后营养器官光合产物的积累以及籽粒灌浆速率,实现了增产。     

Allometric Relationships of Growth Components in Maize (Zen mays L.) Cultivars

Allometric relationship (W₁=αW₂^β, where α and β are the parameters) was fitted among growth components in two maize cultivars viz., Decani hybrid and Deccan 101 in order to obtain estimates of other components of the plant system which are time consuming measurements. The results of the agronomic field trial conducted at the University of Agricultural Sciences, Bangalore were used. This model's predictability was compared with linear regression model. In both the cultivars, allometric model using leaf area (LA - W₂.) and leaf dry matter (LDM - W₂) simulated total dry matter production (DMP - W₂) by 79 to 98 % of actual values. Further allometric model fitted well to predict stem dry matter by 91 to 93 % using LDM and LA 89 to 92 % using LDW. Whereas linear regression model estimated total DMP by 95 to 96 % using cob dry matter. In case of LDM - LA association, linear regression model was found to be the best than other model. The leaf area decreased after silking in both the cultivars and the ratio of growth rates of DMP – LA ( β ₂) was negative. Between cultivars, cv. Deccan 101 had higher R² values in most of the relationships than cv. Deccan hybrid indicating the varietal difference.