Wood Volume,Foliar Chemical Composition,and Soil Nitrogen Turn Over of Metrosideros polymorpha (Myrtaceae) Stands on a Slope of Mount Haleakala,Hawaii1

An earlier study suggested that soils on the windward slope of Mount Haleakala are excessively waterlogged at low altitudes but become better drained upslope. We analyzed altitudinal changes in soil N turn over, vegetation mass, and foliar chemical composition of the dominant canopy species, Metrosideros polymorpha (Myrtaceae), on this slope. The basal areas and DBH²× height (an index for volume) of woody species ≥2 m in height increased with altitude (as opposed to a general trend elsewhere), peaked at 1800 m elev., and abruptly declined above this altitude. Foliar N and P concentrations of Metrosideros showed a similar altitudinal trend with DBH²× height values. Foliar Fe and Al concentrations steadily increased downslope, but were low again at 450 m, the lowest altitude, contrary to expectation based on waterlogging. Toxic forms of Fe and Al may retard root penetration in waterlogged soils and thus the uptake of these elements. The net N mineralization rate for topsoils incubated in situ was 78.6 μg/g/20d at 1800 m elev., while small amounts of N were immobilized at 450, 1200 and 2200 m elev. The net N mineralization rates of the topsoils, which were air-dried to their permanent wilting points and incubated at 26°C, were greater than those of the wet samples at 26°C, only for the lowest altitude. Conversely, the net N mineralization rates of the topsoils which were kept wet and incubated at the higher temperature of 26°C were greater (P < 0.1) than those of the in situ wet samples only for 1800 m elev. The rates were the same for 450 and 2200 m elev. where the soils were waterlogged and very dry, respectively; thus, N turn over was more strongly limited by moisture than by temperature in these cases. Nutrient availability improved with altitude up to 1800 m elev. in association with the moisture gradient, and appeared to be responsible for the observed pattern in vegetation mass.     

Effect of Potassium and Nitrogen Fertilizer on Switchgrass Productivity and Nutrient Removal Rates under Two Harvest Systems on a Low Potassium Soil

Biomass demand for energy will lead to utilization of marginal, low fertility soil. Application of fertilizer to such soil may increase switchgrass (Panicum virgatum L.) biomass production. In this three-way factorial field experiment, biomass yield response to potassium (K) fertilizer (0 and 68 kg?K?ha^?1) on nitrogen (N)-sufficient and N-deficient switchgrass (0 and 135 kg?N?ha^?1) was evaluated under two harvest systems. Harvest system included harvesting once per year after frost (December) and twice per year in summer (July) at boot stage and subsequent regrowth after frost. Under the one-cut system, there was no response to N or K only (13.4 Mg?ha^?1) compared to no fertilizer (12.4 Mg?ha^?1). Switchgrass receiving both N and K (14.6 Mg?ha^?1) produced 18 % greater dry matter (DM) yield compared to no fertilizer check. Under the two-cut harvest system, N only (16.0 Mg?ha^?1) or K only (14.1 Mg?ha^?1) fertilizer produced similar DM to no fertilizer (15.1 Mg?ha^?1). Switchgrass receiving both N and K in the two-cut system (19.2 Mg?ha^?1) produced the greatest (P?<?0.05) DM yield, which was 32 % greater than switchgrass receiving both N and K in the one-cut system. Nutrient removal (biomass?×?nutrient concentration) was greatest in plots receiving both N and K, and the two-cut system had greater nutrient removal than the one-cut system. Based on these results, harvesting only once during winter months reduces nutrient removal in harvested biomass and requires less inorganic fertilizer for sustained yields from year to year compared to two-cut system.     

Analysis of growth and yield of inbred and crossbred maize

In experiments with young widely spaced plants grown in sand culture, net assimilation rate (E) of two single-cross hybrids, N x S and W x M, was respectively > 20% and 13–19% greater than that of their parental inbreds, N and S, and W and M. Relative growth rate (R) of W x M exceeded that of W or M, and R of N x S exceeded that of S, but not that of N because leaf area ratio (F) of this inbred was greater than that of N x S. E of N x S was about 10% greater than that of an open-pollinated variety, OP. When the size of plants of N x S was varied by sowing seeds of different sizes, E was little affected but R increased as plant size decreased, because F increased with decrease in plant size. In a field experiment total dry weights at final harvest of N, S and OP were respectively 66, 46 and 98% of that of N x S; their respective grain weights were 47, 20 and 70% of that of N x S. N, S and OP flowered later than N x S and accumulated respectively 56, 26 and 89% as much dry matter after flowering as N x S. Grain formed 71, 65, 83 and 65% of the dry matter accumulated after flowering in N, S, N x S and OP, respectively. Up to about the time of flowering, E and R of the relatively small N and S plants were greater than those of N x S plants, but later E of N and S was smaller than that of N x S. Before flowering, when leaf area of OP was less than that of N x S, E was greater in OP than in N x S. After flowering leaf area was greater, and E smaller, in OP than in N x S.     

Nitrogen accumulation in plant tissues and roots and N mineralization under oilseeds, pulses, and spring wheat

To understand how pulse and oilseed crops might use nitrogen (N) more efficiently under varying levels of water and N availability in soil, we conducted a 2-year field study to monitor N accumulation in aboveground (AG-N) and root material at five growth stages, for canola (Brassica napus L.), mustard (Brassica juncea L.), chickpea (Cicer arietinum L.), dry pea (Pisum sativum L.) and lentil (Lens culinaris Medicum) alongside spring wheat (Triticum aestivum L.). Crops were grown in lysimeters (15 cm diameter × 100 cm deep) installed in the field in southern Saskatchewan, Canada. AG-N in all crops was greater under high-water than under low-water conditions. In oilseeds and wheat, AG-N increased until flowering then tended to level off, while in pulses it increased gradually to maturity. At maturity, dry pea and wheat had the greatest AG-N and mustard the least. Enhanced water availability increased seed N but did not affect straw N; consequently, N harvest index was greater under high-water than under low-water conditions. Root N increased until late-flowering or late-pod (dough stage in wheat) then decreased to maturity. Mustard had the lowest root N, chickpea the second lowest, and canola, wheat, dry pea, and lentil the highest. Improved water availability increased root N for oilseeds and wheat but did not affect root N in pulses. At maturity, average root N of oilseeds, pulses, and wheat was 14, 17, and 20 kg ha^-1, respectively. At the seedling stage pulse crops had about 27% of total plant N in their roots, a much greater proportion than for the non-legumes. However, by maturity all crops had about 14% of plant N in their roots. Soil NO₃-N increased gradually between seedling and maturity in non-legumes but in pulses there was a sharp spike at early flowering. Estimated apparent net N mineralized was similar for wheat and pulse crops which were greater than for canola and mustard. Soil N amounts and temporal change patterns varied substantially among crops evaluated, and these differences need to be considered in the development of diverse cropping systems where cereals, legumes, and oilseeds are included in rotation systems.     

Effects of nitrogen nutrition and root medium water potential on growth, nitrogen uptake and osmotic adjustment of rice

The effects of nitrogen (N) nutrition on growth, N uptake and leaf osmotic potential of rice plants (Oryza sativa L. ev. IR 36) during simulated water stress were determined. Twenty-one-day-old seedlings in high (28.6 × 10 ^?4M) and low (7.14 × 10 ⁴M) N levels were exposed to decreased nutrient solution water potentials by addition of polyethylene glycol 6000. The roots were separated from the solution by a semi-permeable membrane. Nutrient solution water potential was ?0.6 × 10⁵ Pa and was lowered stepwise to ?1 × 10⁵, ?2 × 10⁵, ?4 × 10⁵ and ?6 × 10⁵ Pa at 2-day intervals. Plant height, leaf area and shoot dry weight of high and low nitrogen plants were reduced by lower osmotic potentials of the root medium. Osmotic stress caused greater shoot growth reduction in high N than in low N plants. Stressed and unstressed plants in 7.14 × 10⁴M N had more root dry matter than the corresponding plants in 28.6 × 10⁴M N. Dawn leaf water potential of stressed plants was 1 × 10⁵ to 5.5 × 10⁵ Pa lower than nutrient solution water potential. Nitrogen-deficient water-stressed plants, however, maintained higher dawn leaf water potential than high nitrogen water-stressed plants. It is suggested that this was due to higher root-to-shoot ratios of N deficient plants. The osmotic potentials of leaves at full turgor for control plants were about 1.3 × 10⁵ Pa higher in 7.14 × 10^?4M than in 28.6 × 10^?4M N and osmotic adjustment of 2.6 × 10⁵ and 4.3 × 10⁵ Pa was obtained in low and high N plants, respectively. The nitrogen status of plants, therefore, affected the ability of the rice plant to adjust osmotically during water stress. Plant water stress decreased transpiration and total N content in shoots of both N treatments. Reduced shoot growth as a result of water stress caused the decrease in amount of water transpired. Transpiration and N uptake were significantly correlated. Our results show that nitrogen content is reduced in water-stressed plants by the integrated effects of plant water stress per se on accumulation of dry matter and transpiring leaf area as well as the often cited changes in soil physical properties of a drying root medium.     

Seed germination and seedling growth in the arrow bamboo <Emphasis Type="Italic">Fargesia qinlingensis</Emphasis>

Improving natural regeneration of bamboos after they die following mass flowering is critical for conservation of giant pandas. However, little is known about factors that affect seed germination and seedling growth of bamboos. We studied seed germination and seedling growth in Fargesia qinlingensis, which mass flowered in a giant panda habitat in the Qinling Mountains of China in early 2000, in laboratory and greenhouse conditions. Seed germination rate was tested under light and dark conditions 5 and 12 months after seed collection. Germination rate displayed no significant difference under light or dark conditions 5 months after seed collection, but was significantly greater in the dark than under light 12 months after seed collection, suggesting light inhibition of seed germination. A 2×2 factorial design was conducted to test the effects of nitrogen (N fertilization and non-N fertilization) and light [full sun and shade (i.e., 14% full sun)] on seedling growth and biomass allocation. N fertilization significantly increased seedling growth, resulting in greater seedling height, more branches, more leaves, greater stem biomass, and greater leaf biomass. Seedlings under 14% full sun conditions had a significantly lower percentage of biomass allocated to the stem. The root/shoot ratio was significantly greater in non-N/shade than non-N/full sun, while there was no significant difference in this ratio between N/shade and N/full sun, suggesting that nitrogen fertilization compensated for the effect of shade on biomass allocation. Our results suggest that N fertilization could be employed in restoration of F. qinlingensis stands after die-off following mass flowering.     

Aspects of nitrogen uptake and distribution in maize

The amount of nitrogen (N) taken up after treatment decreased by nearly 50% when either the top five or middle four leaf laminae of maize (Zea mays) plants were removed shortly after flowering, and by 70% when both the middle four and bottom six laminae were removed, but the amount of N moving from the remaining parts of the shoot to the grain did not change much. When all the laminae were removed little N was taken up and only 35% as much N as in untreated plants moved from the shoot to the grain. Removal of all the laminae increased the N content per cent of dry weight of both grain and shoot at final harvest, but the other treatments did not have much effect on the N concentration of any of the parts of the shoot. Plants bearing grain, whether intact or with alternate laminae removed (half-defoliated) at the time of flowering, took up N approximately in proportion to their increase in dry weight during the 4 wk after flowering. The N taken up went to the ear (husks, core and grain) and so did N from the stem and leaves. Intact and half-defoliated plants with no developing grains, because pollination had been prevented, took up no N during this period, though they accumulated about as much dry matter as did plants with grain; the N increment of the husks and core was supplied by the stem and leaves. At final harvest total and grain N content of plants per unit area of land increased by 20 and nearly 30%, respectively, with increase in population between 2·3 and 6·1 plants/m², but apparently fell slightly with further increase of population to 7·4 plants/m². Until shortly after flowering N uptake was rapid enough to maintain similar N contents per cent of dry weight of the parts of the shoot in all populations. Uptake continued at a steady rate, though a slower one than before flowering, until near the time of final harvest in the most widely spaced population. In the denser populations uptake slowed down progressively after flowering, and in the densest population it apparently ceased a few weeks before final harvest. The N concentration of the grain of maturing plants fell with increase of population, but not that of the other parts of the shoot. At final harvest N content of the grain decreased from 1·6% in the most widely spaced to 1·2% in the densest population. That of the rest of the shoot varied between 0·70 and 0·79%. Between 6 and 18 wk after sowing, N content per unit area of green parts of the leaf laminae decreased only slightly, changing from about 20 to 18 mg/dm² with 2·3 plants/m², 18 to 16 mg/dm² with 3·5 plants/m², and 16 to 13 mg/dm² in populations between 4·8-7·4 plants/m².     

Response ofBromus inermis inoculated withGlomus fasciculatum to potassium fertilization and drought stress

Summary Bromus inermis Leyss. was grown in a 2×2×2 factorial design using different levels of mycorrhizal inoculation (inoculated and noninoculated), soil water stress (Ψ₁ or −0.8 MPa) and potassium (K) fertilization (0 or 150 ppm) as factors. Soil water stress and mycorrhizal inoculation significantly reduced plant top dry weight during the 18 week study. Chlamydospore production by the mycorrhizal symbiontGlomus fasciculatum (Thaxter sensu. Gerd.) Gerd. and Trappe was significantly reduced by soil water stress of −0.8 MPa. Potassium (K) fertilization did not significantly influence plant top growth or mycorrhizal colonization. However, foliar Ca and Mg were significantly lower in plants fertilized with K. Foliar Ca and Mg concentrations of P, K, N, Mn, Zn and Cu were significantly greater in drought stressed plants whereas Ca and Mg concentrations were significantly greater in well-watered plants.     

遮阴对夏玉米干物质积累及养分吸收的影响

以振杰2号(ZJ2)、登海605(DH605)和郑单958(ZD958)为试验材料,在大田条件下设置花粒期遮阴(S₁)、穗期遮阴(S₂)、全生育期遮阴(S₃)3个遮阴处理,以自然光照条件为对照(CK),研究了遮阴对夏玉米干物质积累和氮、磷、钾吸收的影响.结果表明: 遮阴后夏玉米籽粒产量和单株干物质积累量显著降低,降低程度与遮阴时期有关,表现为S₃>S₁>S₂,其中S₁、S₂和S₃籽粒产量平均降低61.6%、25.3%和92.8%,说明花粒期遮阴较花前遮阴对夏玉米干物质积累和籽粒产量影响更大,不同品种的变化趋势相同.夏玉米植株花前养分吸收量表现为钾>氮>磷,植株吸收总量表现为氮>钾>磷.遮阴后植株氮和磷积累量显著减少,由于遮阴后干物质较对照降低程度大于对氮、磷吸收的降低程度,各处理氮、磷相对含量有所升高;遮阴后各处理植株钾吸收量较对照显著降低,但S₂处理的钾吸收降低程度大于干物质积累降低程度,钾相对含量降低,即花前遮阴对玉米钾吸收的影响大于氮和磷.     

Toxicity and repellency of some biorational insecticides toBemisia argentifolii on tomato plants

A mineral oil, an insecticidal soap, and a plant-derived surfactant were compared with a broad-spectrum pyrethroid for residual toxicity and repellency to silverleaf whitefly,Bemisia argentifolii Bellows & Perring (Homoptera: Aleyrodidae) on tomatoes (Lycopersicum esculentum Miller, cv. Lanai) under greenhouse and laboratory conditions. The materials tested were: Sunspray oil (a mineral oil), M-Pede (an insecticidal soap),Nicotiana gossei extract (a sucrose ester surfactant), Garlic Barrier (repellency only), and the pyrethroid bifenthrin (Brigade 10WP), with water as a control. For toxicity studies, whiteflies were confined on leaves which had been dipped in solutions of 0.5×, 1× and 2× field rate concentrations. Insecticide residues were compared when the leaves were wet and dry. Adult mortalities were greatest with bifenthrin and Sunspray oil, followed by M-Pede,N. gossei extract and water. Mortality from dry residue of lower rates of bifenthrin and sunspray oil was greater than mortality from wet residues, whereas M-Pede lost all activity upon drying. Dual and multiple choice tests for repellency were carried out in the greenhouse or laboratory by spraying plants or individual leaves to runoff with 1 × field concentrations. Bifenthrin and Sunspray oil repelledB. argentifolii adults for up to 7 and 5 days, respectively, followed by M-Pede and extract ofN. gossei, whereas Garlic Barrier was not significantly different from the water control in all tests. Numbers of whitefly eggs were significantly reduced on bifenthrin and Sunspray oil-treated leaves, whereas egg numbers in other treatments were not different from water. Sunspray oil as a dip proved to be at least as effective as the synthetic pyrethroid for whitefly control. A multiple-choice leaf-wheel proved to be a useful device to quickly evaluate repellent effects of several different insecticides to whitefly.     

Effect of plant population on the production and distribution of dry matter in maize

Grain and total dry weight of maize (Zea mays L.) at final harvest increased by about 50% and 30%, respectively, when the population was increased from 23000 to 48000 plants/ha, but did not increase further with population up to 74000/ha. Between 6 and 10 weeks after sowing, crop growth rate (C) increased by about 40% with increase in leaf-area index (L) from 2 to 5·5, despite a concomitant increase in moisture stress. Immediately after flowering, which occurred at 10–11 weeks, C increased up to the greatest L attained, 6·7, and would probably have reached a maximum, with L about 7, when nearly all the incident light would be intercepted by foliage. Later, the L at which C was maximal decreased, probably because the photosyhthetic efficiency of leaves decreased faster with time as L increased; 18 weeks after sowing, when L varied between 3 and 5·5, C was maximal when L was 5. The proportion of grain in the dry matter accumulated after flowering increased from 73% when population was 23000/ha to 82% when it was 60000–74000/ha. Stem weight increased until 3–4 weeks after flowering, then remained constant when population was 23000/ha, but decreased in denser populations. The fraction of the ear consisting of grain increased with population.     

The absorption of metal ions by Eichhornia crassipes

Abstract

Uptake of metals by whole Eichhornia crassipes plants and excised roots was studied using a bioassay system. Results indicate that in time-series bioassay at concentration of 10 mg L^?1 of either Zn or Cu, rapid uptake by whole plants occurred during the first 4 h, but subsequently levelled off after 48 h. A greater proportion of metals absorbed remain in the root system rather than being translocated to other parts of plant. When treated with different combinations of both Cu and Zn, some synergistic effect of metals appeared to have occurred as indicated by enhanced uptake when bioassays involved combination of metals. Absorption kinetics of monovalent K⁺ by excised Eichhornia roots after a 24-h treatment, indicated an initial linear trend over the range of 1–10 mg K L^?1, but subsequently levelled off at 15 mg K L^?1 concentration with V_max of 7.5 × 10^–6 M K g^?1 dry tissue h^?1 and K_m of 1.1 × 10^?3 M K. Potentiometric titrations revealed existence of pH-dependent charge densities on root system which have variable affinities for cations and helps explain the ability of Eichhornia roots to absorb and accumulate large amounts of metal ions especially at high pH of media.     

光温耦合的中国温带地区旱柳花期时空格局模拟

建立基于温度和光周期驱动的旱柳花期物候模型,旨在寻找影响旱柳花期时空变化的主要气象因子,揭示调控植物开花时间的生态机制,还可为改善柳絮造成的环境污染和花粉过敏等人类健康问题提供参考信息和依据。利用中国气象局农业气象观测网提供的中国温带地区1982-2011年49个站点的旱柳开花始期、盛期和末期观测资料及平行的逐日气象数据,分别对6种模型（简单积温模型、温度三基点模型、八时段温度模型、简单积温-日长模型、温度三基点-日长模型和八时段温度-日长模型）进行了参数率定和假设检验,根据外部检验结果,从中选出针对旱柳3个花期的最优物候模型,进而利用连续地理气象数据和最优物候模型重建了1982-2011年旱柳开花始期、盛期、末期和花期长度的时空变化特征。结果表明：光温耦合的物候模型对旱柳花期的模拟效果和外推效果优于仅基于温度的模型。旱柳开花始期和盛期最优模型均为八时段温度-日长模型,末期为温度三基点-日长模型,说明光周期和温度可能是影响旱柳花期开始、繁盛和结束时间的主要气象因子。同时,优选出的物候模型能够较准确地对不同年份和不同地区的旱柳花期进行模拟及预测。重建的1982-2011年旱柳平均开花始期、盛期和末期日期分别为4月24日、4月28日和5月3日,平均花期长度为9 d,始期、盛期和末期出现日期呈现出从海拔低到高、从南向北、从西向东逐渐推迟的空间格局。1982-2011年旱柳开花始期、盛期和末期在大部分地区呈提前趋势,呈显著提前趋势的面积分别占总面积的49.78%、50.01%和53.40%,花期长度变化差异不显著。     

Nitrogen fixation and growth of soybean as influenced by varying the methods of inoculation with Bradyrhizobium japonicum

The effects of inoculating soil with a water suspension of Bradyrhizobium japonicum (i) at seeding, (ii) 7, or (iii) 14 days after planting (DAP), (iv) seed slurry inoculation and (v) seed slurry supplemented with postemergence inoculation of a water suspension of Bradyrhizobium at 7 or (vi) 14 DAP, on nodulation, N₂ fixation and yield of soybean (Glycine max. [L.] Merrill) were compared in the greenhouse. The ¹⁵N isotope dilution technique was used to quantify N₂ fixed at flowering, early pod filling and physiological maturity stages (36, 52 and 70 DAP, respectively). On average, the water suspension inoculation formed the greatest number of nodules, and seed plus postemergence inoculation formed slightly more nodules than the seed-only inoculated plants (27, 19 and 12 nodules/plant respectively at physiological maturity). Seed slurry inoculation followed by postemergence inoculation at 14 DAP gave the highest nodule weight, with the plants fixing significantly more (P<0.05) N₂ (125 mg N plant⁻¹ or 56% N) than any other treatment (mean, 75 mg plant⁻¹ or 35% N). However, the higher N₂ fixation was not translated into higher N or dry matter yields. Estimates of N₂ fixed by the ostemergence Bradyrhizobium inoculations as well as plant yield were not significantly different from those of the seed slurry inoculation. Thus, delaying inoculation (e.g., by two weeks as in this study) did not reduce the symbiotic ability of soybean plants.     

Towards Miscanthus combustion quality improvement: the role of flowering and senescence

In commercially grown Miscanthus × giganteus, despite imposing a yield penalty, postwinter harvests improve quality criteria for thermal conversion and crop sustainability through remobilization of nutrients to the underground rhizome. We examined 16 Miscanthus genotypes with different flowering and senescence times for variation in N, P, K, moisture, ash, Cl and Si contents, hypothesizing that early flowering and senescence could result in improved biomass quality and/or enable an earlier harvest of biomass (in autumn at peak yield). Ideal crop characteristics at harvest are low N and P to reduce future fertilizer inputs, low K and Cl to reduce corrosion in boilers, low moisture to reduce spoilage and transportation costs, and low Si and ash to reduce slagging and consequent operational downtime. Stems and leaves were harvested during summer, autumn and then the following spring after overwinter ripening. In spring, stem contents of N were 30–60 mg kg^?1, P were 203–1132 mg kg^?1, K were 290–4098 mg kg^?1, Cl were 10–23 mg kg^?1 and moisture were 12–38%. Notably, late senescence resulted in increased N, P, K, Cl, moisture and ash contents, and should therefore be avoided for thermochemical conversion. Flowering and senescence led to overall improved combustion quality, where flowered genotypes tended towards lower P, K, Cl and moisture contents; marginally less, or similar, N, Si and ash contents; and a similar higher heating value, compared to those that had not flowered. Such genotypes could potentially be harvested in the autumn. However, one genotype that did not flower in our trial exhibited sufficiently low N and K content in autumn to meet the ENplus wood pellet standards for those traits, and some of the lowest P, moisture and ash contents in our trial, and is thus a target for future research and breeding.     

The microflora of ripening barley grain and the effects of pre harvest fungicide application

Newly-emerged ears of barley soon became colonised by micro-organisms with numbers increasing to 5·8 × 10⁵ viable propagules/g dry weight by harvest. Bacteria were numerically predominant throughout. Yeasts and yeast-like fungi were also numerous during the early stages of grain development but were exceeded by propagules of filamentous fungi during ripening, with Cladosporium spp., Alternaria alternata, Epicoccum purpurascens and Verticillium lecanii most abundant. Numbers of most micro-organisms were greatest in a wet season but Alternaria was equally abundant in hot dry weather. Application of fungicides at or after anthesis modified the grain microflora. Captafol was most effective overall in decreasing numbers of fungi. However, benomyl decreased Cladosporium inoculum more than catpafol but was ineffective against Alternaria which became more numerous on benomyl-treated grain than on untreated. Yield increases of up to 4% were obtained by late fungicide treatment, least in a hot, dry year. Germination was also increased by some treatments by up to 5%.     

Pollen movement to flowering canopies of pistillate individuals of three rain forest tree species in tropical Australia

This study measured the quantities of effective pollen vectors and their pollen loads arriving at the canopies of dioecious tropical rain forest trees in north-east Queensland. Population flowering synchrony, effective pollinator populations and pollen loads transferred between staminate and pistillate trees were compared among three insect-pollinated tree species. All three were visited by a wide range of insects, 75% of which (mostly 3–6 mm long) carried conspecific pollen. Fewer than 8% of individual insects were found to be carrying single-species pollen exclusively and none could be described as specialist pollen foragers. The introduced honeybee carried greater quantities of pollen than any native species but was not necessarily a reliable pollinator. The brief flowering periods in Neolitsea dealbata (3–4 weeks) and Litsea leefeana (4–5 weeks) populations were synchronized among individuals. Flowering in the Diospyros pentamera population extended over 15 weeks and most individuals were in flower for most of this period. Staminate trees began flowering earlier, produced more flowers and attracted relatively more insects than did pistillate trees, suggesting a density-dependent response of pollinators to flowering performance. Pollen was trapped in greater quantities on insects at staminate trees than at pistillate trees. Insect numbers increased at peak flowering periods and Diptera were the most abundant flower visitors. Anthophilous Coleoptera were more numerous at staminate than at pistillate trees in all three tree species populations. Larger quantities of pollen were mobilized during peak flowering times although the greatest quantities were transferred to pistillate canopies towards the end of the population flowering periods. Diptera carried pollen more often to pistillate N. dealbata and L. leefeana trees than did other groups whereas Coleoptera carried pollen more often to pistillate D. pentamera trees. The two contrasting flowering performances in the three tree species are discussed with reference to mechanisms that facilitate pollen transfer between staminate and pistillate trees.     

Growth and yield of six short varieties of spring wheat derived from Norin 10 and of two European varieties

Five short varieties of spring wheat derived from Norin 10: Lerma Rojo 64A (R), Penjamo 62 (P), Sonora 64 (S), Mexico 120 (M), and an unnamed selection obtained from Mexico (X), had grain yields equal to, or only slightly less than those of the taller European spring varieties Kloka (K) and Jufy I (J). Yields ranged from 500 to 580 g/m² of dry matter. The short variety NBJ115 (N) was severely infected with yellow rust and yielded only 290 g/m². Total dry weight (excluding roots) of the short varieties was less than of J and K; hence grain accounted for 49 % of the total for the short varieties and 42 % for J and K. Most of the short varieties had fewer ears than the tall ones because sowing difficulties and poor germination produced fewer plants. The relative yields of X, P, R and S seemed to be correlated with their plant and ear densities. Leaf area duration after flowering (D), based either on total green area or on green area above the flag-leaf node only, was less for the short varieties than for J and K. The apparent mean efficiency of this area in grain production (grain yield divided by D) was 50% greater for the short than for the tall varieties. The height of the short varieties ranged from 43 cm (M) to 79 cm (N). K was 92 cm and J 97 cm tall. Differences in height depended on the lengths of the top four internodes and not on number of internodes. Main shoots of all varieties produced seven or eight leaves. All varieties initiated spikelets 45–48 days after sowing. The short varieties flowered 103 days and matured 155 days after sowing; J and K flowered and matured about 1 week earlier.     

The effect of oxygen deficiency on uptake and distribution of nutrients in maize plants

Young maize (Zea mays L.) plants, 7 days after germination were exposed to nutrient solutions which were either aerated or not aerated for 14 days. Nutrients were supplied as 50% strength Hoagland’s solution or, in the case of the four ‘low nutrient’ treatments, N, P, K or Ca were supplied at the equivalent of 10% strength Hoagland’s solution. Shoot fresh weight was decreased by 25% due to lack of aeration; O₂ deficiency also impaired leaf elongation but not dry weights, suggesting that lack of O₂ in the roots impaired cell expansion in shoots more than dry weight accumulation. The distribution of N, P, K and Ca within shoots was consistent with their relative mobilities in the phloem; at least 7% of Ca in plants after 14 days of treatments was found in the oldest leaf whereas N, P and K were rapidly remobilised to younger tissues. Between 33 and 49% of the total N, P and K in the shoot was found in the 40 mm of tissue at the base of the growing leaves in plants grown for 14 days at low nutrient concentrations. Concentrations (dry weight basis) of phloem-mobile nutrients were also greatest in the growing zones of the leaves, especially in the case of N and P. Calcium, on the other hand, was found in relatively low concentrations in the youngest tissue and as with the other nutrients, concentrations declined due to low external supply, non-aeration or a combination of both. In spite of the failure of Ca to move from old to young leaves, the effect of the deficiencies of N, P and K was probably as severe as that of Ca in the youngest tissues of treated plants. Calcium uptake by the whole shoot appeared to be slightly less sensitive to O₂ deficits than that of N, P and K. This compensated for the failure of Ca to move to growing tissues during periods of low external Ca supply.     

花粒期光照对夏玉米干物质积累和养分吸收的影响

选用登海605(DH605)为试验材料,在大田条件下通过花粒期遮阴(S)和增光(L)研究不同光照对花后夏玉米产量、干物质积累和氮、磷、钾养分吸收与运转特性的影响.结果表明: 遮阴后夏玉米产量、干物质积累量及氮、磷、钾养分吸收量均显著降低;而增光有利于夏玉米干物质积累量及氮、磷、钾养分吸收量和产量的提高.2011-2013年,遮阴处理的产量较对照(自然光下)分别降低了59.4%、79.0%、60.6%;增光后产量分别增加16.3%、12.9%、6.8%.遮阴对干物质积累的影响大于其对植株氮、磷吸收量的影响,植株体内氮、磷等养分含量有所上升,而钾吸收量的下降幅度大于干物质积累,钾素相对含量降低,氮、磷、钾向籽粒的分配比例降低.增光后干物质积累和氮、磷吸收量显著上升,但对氮、磷吸收的影响更大;增光条件下,氮、磷、钾等养分向籽粒的分配比例增加.