Microbial Immobilization and Plant Uptake of Different N Forms in Three Forest Types in Shikoku District, Southern Japan

Soil microbial immobilization and plant uptake of N were evaluated for three forest types in Kochi, Shikoku district. During 196-d laboratory incubation, soil NO₃-N production in the Hinoki cypress forest was negligible for the initial 40 d and then rapidly increased, whereas NO₃-N production was rapid from the beginning in Japanese cedar and deciduous hardwood forests. Microbial immobilization of the labeled ¹⁵N decreased in the order of NH₄-N>glycine-N>NO₃-N. The ¹⁵N immobilization was higher for soil in the Hinoki cypress forest than other two soils. The delayed NO₃-N production in the Hinoki cypress forest was likely related with low availability of NH₄-N due to NH₄-N immobilization and substantial NO₃-N immobilization. In the field experiment, ¹⁵N uptake by roots decreased in the order of NH₄-N>NO₃-N>glycine-N. The absorption of the labeled ¹³C suggested direct uptake of organic N. The preference of N forms by root uptake was not different among forest types. Trees in three forest types can absorb inorganic and organic forms of N, suggesting trees absorb the N form that is the most abundant in the soil.     

Can Non-fumigant Nematicides Be an Alternative to Fumigation on Carrot Fields?

ABSTRACT

Root-knot nematodes (RKN; Meloidogyne spp.) cause enormous yield reductions in vegetable crops. While nematicides are the most effective method for controlling RKN in carrot (Dacatus carota), the efficacy of non-fumigant nematicides, compared to fumigants, is still not fully understood. The objective of this study was to evaluate the effect of 1,3-dichloropropene, a fumigant nematicide, and fluensulfone, a non-fumigant nematicide, on RKN control and yield of fresh market and processing carrot. Field experiments were conducted in a commercial farm in Lenox, GA. A randomized complete block design (r = 4) was used in a factorial arrangement of 3 nematicide treatments and 2 carrot cultivars. Nematicide treatments were the application of 1,3-dichloropropene, fluensulfone, and untreated control. Carrot cultivars were Baltimore (fresh marketing) and Belgrado (processing). In general, RKN population was low early season, averaging 0.8 RKN 100 cm^?3 of soil. RKN populations increased with crop development and there were significant differences among nematicide treatments. At harvest, RKN populations were lower for fluensulfone (1.1 RKN 100 cm^?3 of soil) and 1,3-dichloropropene (3.2 RKN 100 cm^?3 of soil) compared to Control (26.4 RKN 100 cm^?3 of soil); however, fluensulfone (91,278 kg ha^?1) had higher yield than 1,3-dichloropropene (64,154 kg ha^?1) and Control (61,908 kg ha^?1). Carrot cultivars were similar for RKN population and yield. Overall, the non-fumigant nematicide was more beneficial for carrot production than the fumigant nematicide.     

大豆叶片对多效唑的吸收、运转和分配

研究大豆叶片对~3H-MET的吸收、运转、分配规律及MET对大豆吸收~(32)P的影响表明,~3H-MET叶面施用很快被大豆吸收,施后1小时吸收量占施用量的39.17％,3小时为51.26％,6小时达61.21％,此后随着施用时间的延长。吸收能力逐渐降低,48小时达66.37％;叶片吸收的~3H-MET基本上滞留于原处理部位,占叶片吸收量的97％左右,向植株其它部位输出较少,而且主要向处理叶上部的茎和叶运转。MET叶面喷施能提高大豆植株对~(32)P的吸收和增加单株干重。     

碳酸钙与石膏对土壤磷及溶解有机碳淋溶的影响

研究碳酸钙与石膏对南澳大利亚典型土壤P和溶解有机碳淋溶的影响结果表明,碳酸钙可同时降低土壤P和溶解有机碳的淋溶,而石膏可降低土壤P淋溶和增加溶解有机碳的淋溶。     

新型有机肥的氮素在土壤中的转化及其对草莓生长和品质的影响

土壤中硝态氮和铵态氮的含量直接影响着作物的生长和品质。通过田间试验研究了不同有机肥料氮素在土壤中的转化及其对草莓生长和果实品质的影响。结果表明,施用有机肥可以提高草莓苗期土壤硝态氮的比例,硝铵比值大于尿素处理,同时有机肥处理硝铵比值从苗期至盛花期呈下降趋势,但尿素处理则表现为上升的趋势,而花序现蕾期土壤硝铵比的降低,有利于植株花蕾的形成,因此土壤硝铵比值的变化趋势一定程度上决定着草莓的产量和品质。在等量施用氮素养分的条件下,施用有机肥料均较尿素更能促进草莓生长发育和增加草莓产量。施用有机肥对草莓品质的改善作用也优于尿素,果实中糖/酸比值较无肥区提高23.7%-28.7%,较尿素区提高16.5%-21.2%。     

Effect of molecular complexity and acidity of earthworm faeces humic fractions on glutamate dehydrogenase,glutamine synthetase,and phosphoenolpyruvate carboxylase in Daucus carota α II cells

Carrot cells were grown in cultures supplemented with two hormones [2,4-dichlorophenoxyacetic acid (2,4-D) and 6-benzylaminopurine (6BAP)] and two humic fractions extracted from earthworm faeces, one with high acidity and a low apparent molecular size (<3500) and the other with low acidity and a large molecular size. 2,4-D stimulated growth through an effect on cell enlargement, while the strongly acidic humic fraction (0.2 mg l^-1) and the weakly acidic fraction (1 mg l^-1) were both less effective. With 4–16 h of pre-incubation, the highly acid humic fraction, mainly alone, induced the best increase in protein content; the effect of the weakly acid humic fraction and the hormones was generally less important. The two humic fractions also differed in their influence on glutamate dehydrogenase activity. After 2 h of pretreatment, the highly acidic fraction increased glutamate dehydrogenase activity, while the other fraction did not affect it. After 4–16 h of pre-incubation, the activity of this enzyme was still not influenced by these humic fractions. The presence of the two hormones did not interfere with the humic matter effects. Glutamine synthetase activity was not affected by a pre-incubation of up to 4 h with the two humic fractions, but it was stimulated after 8–16 h of pre-incubation. A 2,4-D+6BAP mixture stimulated glutamine synthetase activity (from +12 to +50%). Again, the presence of the hormones did not interfere with the effects induced by the humic fractions. After 16 h of pre-incubation, phosphoenolpyruvate carboxylase activity was increased by the highly acidic humic fraction (+93%) and by both humic fractions together (+34%). An explanation of the different incubation times necessary for the humic fractions to exert stimulatory effects on these enzymes is proposed here. The regulatory properties of the strongly acidic humic fraction appeared to depend on the combination of high acidity (expecially carboxylic C) with low molecular size.     

肥液浓度对单膜孔入渗NO-3-N运移特性影响的室内试验研究

该文通过室内入渗试验，研究了不同浓度的单膜孔肥液入渗NO^-₃-N的分布特性。研究表明：不同浓度的膜孔肥液入渗土壤NO^-₃-N浓度的湿润锋运移距离与土壤水分运动的湿润锋一致；肥液浓度越大，相同入渗时间的NO^-₃-N浓度锋运移距离越大，土壤剖面NO^-₃-N浓度最大值越大，相同深度处土壤NO^-₃-N浓度也越大。肥液入渗土壤NO^-₃-N浓度分布特征与湿润体深度符合分段函数模型。供水入渗过程中，NO^-₃-N浓度锋运移距离和浓度最大值均随时间的延长而增大；再分布过程中，NO^-₃-N浓度锋运移距离继续增大，而NO^-₃-N浓度最大值逐渐减小。     

实体水-虚拟水"二维三元"耦合流动理论基本框架

在变化环境下,区域水资源系统演变规律正在发生深刻变化。解决新形势下出现的水问题单单依靠传统的实体水资源规划、调度和调控手段还不够。虚拟水概念和理论的提出拓展了水文水资源的认知范畴,丰富了水问题的解决手段。然而,如何搭建虚拟水理论与传统水文水资源认知体系的统一框架,认识自然-经济-社会连续系统中水资源演化的新规律,目前学界还没有成熟统一的看法。该文首先提出了实体水-虚拟水耦合流动效应的基本理论框架,指出实体水-虚拟水耦合流动是现代环境下自然-经济-社会水资源系统呈现的新特征。其次,从文明进步和生产力发展角度,论述了人类社会水文水资源系统的演化历史,将水文水资源系统演进大体分为三个阶段:早期的实体水"一维一元"自然循环阶段,近现代的实体水"二元"水循环阶段和当前的实体水-虚拟水"二维三元"耦合流动阶段。最后,该文详细论述了实体水-虚拟水耦合流动过程的路径结构,并针对其流动过程和状态表征提出了定量表达方程,初步构建了实体水-虚拟水耦合流动基本理论框架。     

Influence of green manuring with Sesbania rostrata and Aeschynomene afraspera or urea on dynamics and uptake of nutrients by wetland rice

Nutrient concentrations in the soil and crop uptake from incorporated green manure and urea in flooded rice was studied in field experiments. Release of plant-available nitrogen (NH₄ ⁺-N) from green manure was slightly delayed compared with that from prilled urea (PU) because Sesbania rostrata L. and Aeschynomene afraspera L. released the N gradually after their decomposition, whereas N became available immediately after PU application. Exchangeable NH₄ ⁺-N concentration in soil peaked at 163 mg kg^–1 in the transplanted rice (TPR) and 198 mg kg^—1 in broadcast-seeded rice (BSR) at 0 and 1 week after PU application. Broadcast-seeded rice depleted NH₄ ⁺-N faster than did TPR because of the crop‘s vigorous growth in the former during the early stage. Soil solution NH₄ ⁺-N followed a similar trend to that of soil NH₄ ⁺-N. Incorporation of S. rostrata and A. afraspera increased the concentration of P, K⁺, Fe²⁺ and Mn²⁺ in soil solution more than did the application of PU. However, zinc concentration decreased in all treatments. Both PU and green manure increased the N status of the rice plants and enhanced the uptake of P, K, Fe, Mn and Zn by the rice crop. This suggests that application of green manures improves the uptake of these nutrients by the crop. The highest apparent N recovery was obtained with PU followed by green manure. Received: 11 November 1996     

The combined effects of enhanced UV-B radiation and selenium on growth, chlorophyll fluorescence and ultrastructure in strawberry (Fragaria × ananassa) and barley (Hordeum vulgare) treated in the field

The possible ameliorative effects of selenium (Se) addition to soil on the detrimental effects of enhanced UV-B radiation were tested on strawberry and barley during 4 months of field experiment in Kuopio, Central Finland. Control plants were exposed to ambient levels of UV radiation, using arrays of unenergized lamps. A control for UV-A radiation was also included in the experiment. Added Se, applied as H₂SeO₄, at the level of 0.1 mg kg⁻¹ soil (low dosage) and 1 mg kg⁻¹ soil (high dosage) increased Se concentrations in plants more than 10 and 100 times, respectively. After 4 months of exposure, strawberry and barley plants were harvested for biomass analysis. Chlorophyll fluorescence was measured using the Hansatech FMS2 fluorescence monitoring system. Leaf anatomy and ultrastructure were observed by light and transmission electron microscope. Several effects of UV and Se as well as their interaction were found, mostly for strawberry, but not for barley, indicating species-specific responses. Our results provided evidence that the high Se concentration in soil had no ameliorative effect but increased the sensitivity of strawberry to enhanced UV-B radiation in the field. Under ambient radiation, Se did not alter leaf growth of strawberry, whereas under UV-B radiation, the high Se addition significantly decreased leaf growth. Strawberry runner biomass was affected by the interaction of Se and UV. Under ambient radiation Se did not change dry weight of runners, but in combination with UV-A or UV-B radiation the high Se dosage decreased dry weight of runners by about 30%. Although the high Se concentration positively influenced on quantum efficiency of photosystem II (PSII) in strawberry leaves, it reduced runner biomass, leaf number and ratio of starch to chloroplast area. This suggests that the harmful effects of the high Se dosage on photosynthetic processes occurred as a result of changes in activity or/and biosynthesis of enzymes, rather than alteration of PSII. At the low concentration, Se effects were slight and variable.Although barley leaves accumulated higher Se concentrations than strawberry, there were no apparent changes in their growth, biomass or chlorophyll fluorescence due to Se effect either alone or in combination with UV-B. However, at the ultrastructural level, an enlargement in the peroxisome area was found due to combination of UV radiation with Se, suggesting the activation of antioxidative enzymes, possibly catalase. Decrease in mitochondrial density in barley cells in response to Se might be attributed to alteration of mitochondrial division. Increase in the proportion of cells with cytoplasmic lipid bodies due to combined effect of UV-B and Se indicated the alteration of lipid metabolism and the acceleration of cell senescence in barley. Main UV-B effects were found, mostly at the tissue and ultrastructural level in strawberry, but not in barley, indicating species-specific susceptibility to enhanced UV-B radiation. UV-B-treated strawberry plants developed marginally thinner leaves with reduced ratio of starch to chloroplast area in their cells, suggesting negative influence of UV-B on photosynthetic processes.