Nitrogen Uptake and Accumulation in Grains of Three Winter Wheat Varieties with Altered Source--Sink Ratios

In two pot experiments, removal of the top halves of ears (halving)of three winter wheat (Triticum aestivum L.) varieties at varioustimes after anthesis increased the nitrogen content in the grainsof the lower half of the ear. The increase was greater withearly (anthesis and 5 d later) than late (15 and 25 d post-anthesis)removal in the Splendeur and Hobbit varieties, but there wereno significant differences among halving times in Maris Huntsman.Halving also increased nitrogen as a percentage of dry weightof grain. The percentage of nitrogen in the grain decreasedas the time of halving was delayed in Splendeur (expt. 1) andHobbit, but was unaffected by the time of halving in Splendeur(expt. 2) and Maris Huntsman. Nitrogen uptake of shoots afteranthesis decreased with halving. Early halving decreased nitrogenuptake to a lesser extent than did late halving in Splendeurin expt. 1 and in Hobbit, while it decreased nitrogen uptakemore than late halving in Splendeur in expt. 2 and in Mans Huntsman. Key words: Grain nitrogen, nitrogen uptake, source-sink, wheat, variety     

Senescence and net photosynthesis of the flag leaf and grain growth of wheat in response to fungicide

Green leaf area and net photosynthesis of the flag leaves of Avalon and Maris Huntsman winter wheat crops were studied in relation to grain growth following the application of the fungicide propiconazole at flag leaf emergence. Disease levels were low during grain-fill, and were not significantly affected by the fungicide. Propiconazole significantly maintained green leaf area and photosynthesis per unit area during the period of rapid flag leaf senescence, but it had no effect on stem weight, grain growth or yield.     

Dry weight accumulation and starch-synthesis enzymes in grain of cultured ears of three winter wheat varieties

Detached ears of three winter wheat ( Triticum aestivum L.) varieties were cultured in solution for 12 days with sucrose levels varying from 36.5 to 292 m M. The dry weight and starch content of grains increased asymptotically with the sucrose level in the solution. At 4 days of culture, glucose phosphate isomerase (EC 5.3.1.9) activity grain⁻¹ was lower with 36.5 m M than with higher sucrose levels in the medium; at 8 days, adenosinc diphosphoglucose pyrophosphorylase (EC 2.7.7.27) and (soluble plus bound) starch synthase (EC 2.4.1.21) activities grain⁻¹ were higher with 146 and 292 m M sucrose than with 36.5 and 73 m M sucrose. The multiple regression of starch content over these enzyme activities showed that starch synthase was relatively more important as an independent variable. The dry weight and starch content of grains were higher in the variety Maris Huntsman than in Splendeur and Hobbit. The water content of grains was lower in Splendeur than in the other two varieties. At 4 days the glucose phosphate isomerase, adenosine diphosphoglucose pyrophosphorylase and starch synthase activities grain⁻¹ were smaller in Splendeur than in Hobbit and Maris Huntsman and al 8 days they were higher in Maris Huntsman than in Hobbit and Splendeur. The varietal differences in starch content of grains were related to the activities of glucose phosphate isomerase and especially of starch synthase.     

Distribution between parts of the main shoot and the tillers of photosynthate produced before and after anthesis in the top three leaves of main shoots of Hobbit and Maris Huntsman winter wheat

The top three leaves of main shoots in crops of Hobbit and Maris Huntsman winter wheat were exposed to ¹⁴CO₂ at 22 and 16 days before and at 10 days after anthesis in 1978. The distribution of the ¹⁴C recovered in whole plants at anthesis and at maturity was measured. There was negligible loss of ¹⁴C between these two times, but some redistribution. The percentage in the tillers was negligible when the flag leaf (leaf 1) was exposed to ¹⁴CO₂, and otherwise less than 12% except for ¹⁴C absorbed by the third leaf at 16 days before anthesis, when it averaged 26% but was very variable. When ¹⁴C was supplied before anthesis, about 20% reached the grain whichever leaf had been supplied. The ear structures contained about 10% of that absorbed by the third leaf and 35% of that absorbed by the flag or second leaf. When ¹⁴C was supplied after anthesis, the amounts reaching the grain from the different leaves were: flag 82%, second 68%, third 56%. Most of the remainder was in the stem. The exposed leaf never retained more than 6%. The amount of ¹⁴C that moved from the stem to the grain between anthesis and maturity was about 50% greater in the semi-dwarf variety Hobbit than in Maris Huntsman. There was no significant varietal difference in the percentage of post-anthesis ¹⁴C reaching the grain. The ear structures of Hobbit contained about a third more ¹⁴C than those of Maris Huntsman. An additional 90 kg N ha^-1, which increased grain yield by 46%, had negligible effects on the distribution of ¹⁴C.     

Regulation of Grain Weight by Supply of Assimilates and Starch Granule Development in Three Winter Wheat Varieties

On removing the top half of the ear (halving) on several datesafter anthesis, dry weight per grain increased in three winterwheat (Triticum aestivum L.) varieties, in two pot experiments;the increase was greater with early than with late halving.The variety Splendeur had a lower dry weight and water percentagein grains than either Hobbit or Maris Huntsman. The ratio ofthe green area integrated over the post-anthesis period to thenumber of grains per ear (green area per grain) was highestin Splendeur and lowest in Hobbit in the first experiment; inthe second, Splendeur gave a lower ratio than the other twovarieties, which showed similar values. The green area per grainwas greater the earlier the ear was halved. The number of A-typestarch granules per endosperm, but not the volume per A granule(modal volume) and the modal volume of B starch granules, butnot their number, increased to a greater extent with early thanwith late halving. In Splendeur the grains had fewer A starchgranules, although these were of greater modal volume than inHobbit and Maris Huntsman and a number of B starch granulessimilar to the other two varieties, but of smaller modal volume.Maris Huntsman had more A granules than Hobbit, but with smallermodal volume. Dry weight per grain increased linearly with thenumber of A starch granules per endosperm, which in turn increasedasymptotically with green area per grain. The regressions forthe three varieties differed significantly. The influence ofthe supply of assimilates and the capacity for starch granuleformation in the regulation of grain weight is discussed. Key words: Grain weight, starch granules, assimilate supply, variety, wheat     

Effect of Nitrogen Fertilizer on Photosynthesis of Several Varieties of Winter Wheat

The rates of gross photosynthesis of the flag leaf and the nextleaf below (second leaf) in crops of winter wheat were estimatedfrom the ¹⁴C uptake of the leaves after exposure to short pulsesof ¹⁴CO₂. The photosynthetic rates of both leaves during thegrain-filling period decreased with increase in nitrogen fertilizerbecause the intensity of photosynthetically active radiationwas less at the surface of the leaves in the dense crops withadditional nitrogen. In addition, the rate of photosynthesisat saturating light intensity was slightly decreased by nitrogen.The effects of nitrogen, in decreasing the rate of photosynthesisper unit area of leaf and in increasing the leaf-area indexof the top two leaves, were such that the photosynthetic productivityper unit area of land of the flag leaf was increased by nitrogenbut the productivity of the second leaf was unaffected. Applying180 kg N ha^–1 increased the productivity of the top twoleaves by a factor of 2.3 but increased grain yield by only1.8. The photosynthetic productivity of the second leaf duringthe grain-filling period was about half that of the flag leaf. There was no difference in photosynthetic rate per unit areaof leaves of Cappelle-Desprez and Maris Huntsman which couldaccount for the larger yield of the latter cultivar. There wasa slight indication that the leaves of the semi-dwarf cultivarsMaris Fundin and Hobbit photosynthesized faster than those ofMaris Huntsman. Triticum aestivum L., winter wheat, photosynthesis, nitrogen fertilizer     

Dark Respiration of Several Varieties of Winter Wheat Given Different Amounts of Nitrogen Fertilizer

Carbon dioxide production in the dark by ears and by the restof the shoot of winter wheat grown in the field was measuredin 2 years during grain growth. The respiration rate per g d.wt of the ears was increased by nitrogen fertilizer. Ears ofthe semi-dwarf varieties Maris Fundin and Hobbit respired moreslowly than ears of Maris Huntsman and Cappelle-Desprez. Respirationrates of the rest of the shoot were unaffected by nitrogen orvariety. The amount of carbohydrate required to provide the CO₂ respiredduring the whole period of grain growth varied from 163 to 443g m^–2, or 42 to 76 per cent of the dry weight of the grain.More than half the CO₂ lost was respired by the ear. The additionof 180 kg N ha^–1, which increased grain yield by 78 percent in 1975, almost trebled the amount of CO₂ lost by the ears.The semi-dwarf varieties lost less CO₂ from ears and shootsthan did the taller ones, and had larger yields of grain. Respiration was also estimated from the difference between the¹⁴C contents of shoots sampled immediately after a 30 s exposureto ¹⁴CO₂ and at maturity. When 14C was supplied 10 days afteranthesis, the loss by maturity amounted to 16–28 per centof that initially absorbed by flag leaves and 40 per cent ofthat absorbed by the leaf below the flag leaf. Most of the lossoccurred in the first day. The loss of 14C by maturity was significantlyincreased by nitrogen fertilizer in 1975. Triticum aestivum L., wheat, respiration, nitrogen supply, fertilizer treatment     

Incidence and effects of Septoria nodorum on wheat cultivars

Wheat cultivars were grown in two field trials in which half the plots were artificially inoculated with Septoria nodorum. There were differences between cultivars in the degree of 5. nodorum infection on flag leaves and on ears. Hybrid 46, Maris Huntsman and Maris Widgeon were among those with the least infection, and Maris Ranger and Maris Templar among those with the most. Severity of infection was positively correlated with both short stature and earliness of maturity. Infection on leaves was positively correlated with infection on ears. Inoculation reduced yield by decreasing two of its components, grain number per ear and 1000-grain weight. A very early maturing cultivar, Sterling, sustained no yield loss despite severe infection; for the remaining cultivars, yield loss was positively correlated with degree of infection.     

Effects of decreasing the number of grains in ears of cvs Hobbit and Maris Huntsman winter wheat

At 6 days after anthesis, grain numbers in ears of Maris Huntsman and Hobbit winter wheat growing in the field were decreased either by removing the two lower grains in each spikelet (degraining) or by removing the top half of the ear (halving). At maturity, degraining increased the dry weight of the third grains in each spikelet of Maris Huntsman by 11% and of Hobbit by 40%, compared with third grains in intact ears. Halving increased the mean dry weight of all the grains in the lower six spikelets of the ear slightly less; it increased the number of grains in Hobbit but not in Maris Huntsman. The responses to halving in Hobbit were greater with additional nitrogen fertiliser. At 28 days after anthesis in both varieties, degraining increased grain dry weight and the amount of water, reducing sugar, amino acids and total nitrogen in third grains. Effects of halving on these properties of the two lower grains of each spikelet were much less or nil. The increases in nitrogen content of grains at 28 days and at maturity caused by degraining or halving were relatively greater than the increases in dry weight and were similar in the two varieties.     

Effects on dry weight and nitrogen content of grains of semi-dwarf and tall varieties of winter wheat caused by decreasing the number of grains per ear

The number of grains in ears of six varieties of winter wheat growing in the field was decreased by removing the top half of the ear 6 days after anthesis (halving). In the semi-dwarf varieties Hustler, Sentry and Hobbit, and in the taller varieties Armada and Flanders, the mean dry weight per grain in the lower six spikelets of halved ears was about 23% greater than the dry weight of grains in the comparable part of intact ears. In Maris Huntsman the increase in grain size amounted to only 13%. Halving increased the number of grains in the semi-dwarf varieties but not in the others. Consequently, the increases caused by halving in the total weight of grain in the lower six spikelets ranged from 41% in Hustler and Hobbit to 7% in Maris Huntsman. Halving increased the amount of nitrogen in the grain of the lower half of the ear similarly in all varieties, and relatively more than it increased dry weight. So nitrogen per cent dry weight of grain was increased, especially in Armada, Flanders and Maris Huntsman which responded least in dry weight. The uptake of nitrogen into the stem plus ear after anthesis was unaffected by halving. Most of the nitrogen that normally moved to the upper grains accumulated in the lower grains of halved ears. More nitrogen moved into the grain of intact ears of tall than of semi-dwarf varieties after anthesis, because there was greater uptake of nitrogen into the shoot from the roots.     

Effects of crop thinning and reduced grain numbers per ear on grain size in two winter wheat varieties given different amounts of nitrogen

To study the importance for final grain size in wheat (Triticum aestivum, L.) of assimilate supply and the storage capacity of the grain, two field experiments were done. In 1976 nitrogen was applied in the range from none to 180 kg ha^-1, part of the crop was thinned, and the top halves of some ears of the short variety Hobbit and of the tall variety Maris Huntsman were removed soon after anthesis. In 1977 ears of Maris Huntsman were halved 5 days after anthesis or at 30 days after anthesis when grain volume was maximum. Thinning the crop from 360 to 180 ear-bearing shoots m^-2 30 days before anthesis increased the number of grains per ear, except in the absence of nitrogen fertiliser, but did not increase grain size, grain dry weight per ear or total dry weight per culm. Removing the upper half of ears of Hobbit 5 days after anthesis increased dry weight per grain, but when this treatment was applied to Maris Huntsman either 5 days after anthesis in 1976 and 1977, or when grain volume was maximal in 1977, the grains failed to increase in dry weight. Non-grain dry weight of both varieties was increased by halving the ear. In both varieties the maximum volume of grains in halved ears was larger than in intact ears. Grain dry weight increased relatively less than volume after halving the ear of Hobbit, and the decrease in volume up to maturity was greater in halved than intact ears of both varieties. The larger grain volume in halved ears of Maris Huntsman in 1977 was associated with more endosperm cells.     

小麦开花后iPA和ABA含量的变化及与旗叶光合,根系活力和籽？…

以２个粒重不同的小麦品种为材料,研究了开花后旗叶、根系和籽粒异戊烯基腺苷（ｉＰＡ）和脱落酸（ＡＢＡ）含量的变化及其与旗叶光合速率、根系活力和籽粒样重的关系。结果表明,高粒重的鲁麦２２较低粒重的鲁麦１４,旗叶和根系ｉＰＡ含量高且速降始期推迟,ＡＢＡ含量低且速升始期推迟;与此相对应,旗叶光合速率和根系活力高且高值持续期长。鲁麦２２籽粒ｉＰＡ含量高于鲁麦１４,其ＡＢＡ含量在花后１６ｄ内高于鲁麦１４,１６     

全膜覆土下施有机肥对春小麦旗叶碳氮比、光合特性和产量的影响

于2016和2017年,以春小麦品种‘陇春27'为试验材料,在甘肃省中部半干旱雨养农业区设置定位试验,分析全膜覆土平作穴播(PMS)、全膜覆土平作穴播+有机肥(PMO)、裸地平作穴播(CK)3个处理春小麦抽穗至灌浆阶段土壤水分与群体冠层温度、净光合速率(P_n)、气孔导度(g_s)、蒸腾速率(T_r)、旗叶C/N、旗叶全氮之间的相互关系,探讨不同处理对产量及其构成要素的影响。结果表明: 施用有机肥可提高小麦生育中后期土壤含水量,PMO抽穗至灌浆阶段0～300 cm土层土壤贮水量较PMS和CK分别提高4.6%和8.5%,群体冠层温度分别降低0.1～1.3 ℃和1.4～4.9 ℃,P_n分别提高9.3%和29.7%,g_s分别提高30.9%和103.8%,T_r分别提高5.1%和55.0%,全氮含量分别提高6.6%和18.9%,C/N分别降低6.4%和22.8%。收获后,PMO较PMS和CK显著促进穗粒数和千粒重增加,籽粒产量分别提高9.1%和53.7%。抽穗至灌浆阶段旗叶P_n和g_s与C/N呈负相关性;C/N与籽粒产量呈显著负相关。因此,半干旱区全膜覆土穴播条件下施有机肥可提高春小麦抽穗至灌浆阶段土壤含水量,促进旗叶光合作用,有利于降低生理干旱胁迫强度和旗叶氮吸收同化限制,促进穗粒数和粒重增加,使产量提升。     

Powdery mildew of tobacco (Erysiphe cichoracearum DC.): Susceptibility of proximal and distal parts of leaves from different stalk positions on intact and topped field plants in relation to free amino nitrogen and carbohydrate content*

The area covered by visible mycelium of E. cichoracearum on the upper surface of leaves 4, 8, 12 and 16 of tobacco plants in field plots in Rhodesia was expressed as percentages of the proximal and distal halves at weekly intervals. Free amino nitrogen and carbohydrate in discs from proximal and distal halves of the same leaves were analysed when each leaf was expanding rapidly and was not infected, and several weeks later, when the rate of expansion had slowed down and there was slight infection. On two other occasions, similar leaf discs were inoculated with conidia, to measure the percentage germination and hyphal length from individual conidia after incubation for 2–3 days at constant temperature and humidity; duplicate discs were chemically analysed. Leaves were not susceptible until at least 6 weeks after they had emerged from the bud. Soluble carbohydrate increased and free amino nitrogen decreased during the change from resistance to susceptibility. Proximal parts of leaves were usually infected first; they initially contained less amino nitrogen and soluble carbohydrate than distal parts. All parts of the leaf seemed to be equally susceptible later, when there were no differences in their amino nitrogen or soluble carbohydrate. Upper leaves of intact plants had more natural infection than those from corresponding leaves from topped plants. More conidia germinated on discs from them and produced longer hyphae. The discs from intact plants contained less free amino nitrogen and more soluble carbohydrate than those from topped plants. The accuracy of visual assessments of susceptibility was, generally, confirmed by measurements of percentage germination and length of hyphae from individual conidia on leaf discs. Regressions of hyphal length on leaf composition showed that susceptibility was apparently related inversely to free amino nitrogen and water content and directly to insoluble carbohydrate per unit dry matter.     

施氮量和花后土壤含水量对小麦旗叶衰老及粒重的影响

在防雨池栽培条件下,研究了施氮量和花后土壤含水量对小麦旗叶衰老和粒重的影响.结果表明：各氮肥处理下,小麦旗叶SPAD值、可溶性蛋白质含量、超氧化物歧化酶（SOD）活性、过氧化氢酶（CAT）活性和光合速率（P_n）均表现为：花后土壤含水量60%～70%处理>80%～90%处理>40%～50%处理,小麦旗叶丙二醛（MDA）含量表现为：花后土壤含水量40%～50%处理>80%～90%处理>60%～70%处理,表明花后土壤含水量过高或过低均可导致小麦旗叶早衰,影响籽粒灌浆,降低粒重.在花后相同土壤含水量条件下,旗叶SPAD值、可溶性蛋白质含量、SOD活性、CAT活性和P_n均随施氮量的增加而升高,MDA含量随施氮量的增加而降低,表明增施氮肥可以延缓小麦旗叶衰老,但过量施用氮肥则不利于小麦粒重的提高,尤其是在花后土壤缺水的情况下,施用过多氮肥可导致小麦粒重下降.在小麦生产中可以将施用氮肥和控制花后土壤水分含量相结合,延缓小麦植株衰老,提高粒重.     

Wheat nitrogen metabolism during grain filling: comparative role of glumes and the flag leaf

The mobilization of nitrogen (N) compounds and the roles played by glumes and the flag leaf during grain filling were studied in bread wheat (Triticum aestivum L. cv. Florida) grown under field conditions. Glumes lost twice as much of their total N content as that lost by the flag leaf between the milk and early dough stages. In the flag leaf, glumes and grains, Glu, Asp, Ser and Ala accounted for 85% of all the reductions in the free amino acid pool. Principal component analysis of free amino acid pools separated grains from the glumes and the flag leaf, suggesting grain specific regulations in the use of free amino acids in protein synthesis. In all three organs, no decrease in Gln was detected, probably due to steady glutamine synthetase (GS; EC 6.3.1.2) activities per soluble protein in both the flag leaf and glumes. Compared with the flag leaf, glumes presented relatively smaller amounts of the chloroplast GS associated isoform. This we show is due to a lower relative number of mesophyll cells in glumes as supported by the different anatomy and the cellular pattern of the GS immunolocalization. We argue that cellular distribution plays a key role in supporting metabolism to enable the various functions undertaken by glume tissue.     

Distribution of photosynthate produced before and after anthesis in tall and semi-dwarf winter wheat, as affected by nitrogen fertiliser

In 2 years the distribution of radioactivity recovered in entire shoots of field-grown winter wheat was determined at various times after exposing the top two leaves (flag leaf or second leaf) to ¹⁴CO₂ for 30 s. In 1976 when ¹⁴C was supplied to either leaf 14 days before anthesis, 30% was in the ear at anthesis. Less than 5% was in the leaf exposed to ^I4CO₂. The remainder was equally divided between the stem above and below the flag-leaf node when the flag leaf had been exposed, and was mainly in the lower part of the stem when the second leaf had been exposed. By maturity the proportion in the stem had decreased; 20% of the total activity was in the grain and 30% was still in the ear structures. When ¹⁴C was supplied 10 days after anthesis, the proportion in the ear 24 h later ranged from 42 to 69% of that in the whole shoot when the flag leaf was exposed, and from 6 to 28% when the second leaf was exposed. At maturity these proportions increased to 92 and 85% when the ¹⁴C had been supplied to flag leaves and second leaves respectively. When ¹⁴C was supplied 25 days after anthesis to either flag leaves or second leaves, more than 90% of the activity was in the mature ears. Less than 5% of the ¹⁴C remaining at maturity from any treatment was still in the leaf exposed to ¹⁴CO₂. Between 2 and 6% of ¹⁴C supplied after anthesis was in the non-grain parts of the ear. The proportion of the ¹⁴C in the ear was greatest for the semi-dwarf varieties Maris Fundin and Hobbit, less for Maris Huntsman, and least for Cappelle-Desprez. These varietal differences were large 24 h after exposure to ¹⁴CO₂, especially in 1976. They were small and rarely significant at maturity. Nitrogen fertiliser up to 210 kg N ha^-1 had negligible effects on the distribution of ¹⁴C, although it greatly increased growth and yield, especially in 1975.     

The Influence of Leaf Removal upon the Development of the Grain of Winter Wheat

The paper describes the effects on grain development of theremoval of half the flag leaf, the entire flag leaf and allthe leaves from selected main shoots of a field crop of wheat,cultivar Maris Ranger, 7 days after anthesis. None of the treatmentsreduced grain weights in the 14 days following defoliation.Even in the next 14 days only the more severe defoliations reducedgrain weight, with the most severe treatment causing the greatestreduction. Ultimately the rate of grain growth in plants onwhich only a half of the flag leaf had been removed also fellbehind that of the controls. Final grain yields were in theorder, control plants, > plants with half the flag leaf removed,> the entire flag leaf removed, > all the leaves removed.The significance of these results in interpreting the factorslimiting grain growth in wheat is discussed.     

Response of wheat genotypes to sowing date and boron fertilization aimed at controlling sterility in a rice-wheat rotation in Nepal

Spikelet sterility in wheat (Triticum aestivum L.) is emerging as a production threat in different parts of Nepal. This study was aimed at determining the effects of sowing date and boron application in controlling spikelet sterility in four different genotypes of spring wheat in a rice-wheat system in the western hills of Nepal. Four genotypes of known different responses to boron were planted on 21 November, 6 December and 21 December, 1994 with or without boron application at 1 kg B ha-1 (i.e. 9 kg borax ha-1) on a soil that was known to be deficient in boron.The effect of sowing date was significant for the phenology, yield components, percentage sterility and grain yield. Sterility was significantly increased in the crop planted on 21 December, which had also the lowest 1000 seed weight and grain yield; there was an almost 50% grain yield reduction compared to the crop planted on 21 November. Terminal moisture stress (i.e. lack of moisture during the later part of the development) was observed in the late sown crop which also amplified the extent of sterility associated with boron deficiency. Genotypes differed in response to sowing dates and boron treatment for all of the phenological events measured, yield components, grain yield and percentage sterility. SW-41 and BL-1022 had significantly higher sterility at all sowing dates. BL-1249 showed a consistently lower% sterility over all sowing dates and boron treatments. The addition of boron significantly increased the number of grains set per spike thereby decreasing the total sterility in boron responsive genotypes SW-41 and BL-1022 while those not susceptible did not respond. The boron concentration in the flag leaf at anthesis was increased in treatments with added B in the soil but genotypes did not differ in boron concentration for any soil treatment.     

分期施氮与CO2浓度升高对小麦光合及其物质积累和产量的互作效应

采用开顶式气室和盆栽方法,以冬小麦品种‘小偃22’为材料,探讨了分期施氮与CO2浓度升高对小麦抽穗期和灌浆中期旗叶光合、地上部物质积累和产量的互作效应.结果显示:(1)不施氮条件下CO2浓度升高对小麦旗叶叶绿素含量(SPAD)和可溶性蛋白含量、光合能力、地上部花后干物质和氮素累积量、籽粒产量的影响不明显(P>0.05)或产生显著负效应;在施氮(300mg/kg土)条件下各指标均不同程度增加,且大多数达到显著水平.(2)与氮肥全部基施相比,分期施氮时CO2浓度升高使灌浆期旗叶光合能力、地上部花后干物质和氮素累积以及产量增加的幅度较大,其中以播前、返青期和孕穗期施氮比例为5∶3∶2时最明显.研究表明,适当分期施氮可能更有利于发挥CO2浓度升高对冬小麦的增产作用.