施肥对热带雨林下种植砂仁土壤氮矿化和硝化作用的影响

采用封顶埋管法(Close-TopIncubation)研究了施肥后西双版纳热带雨林下种植砂仁土壤的氮素净氨化、净硝化和净矿化速率。结果表明,种植砂仁的热带雨林土壤有机氮的净氨化、硝化和矿化速率明显受外来无机氮的影响,施入铵态氮肥后,土壤中的氨化速率明显提高(P<0.01),由对照土壤的-0.66(mg·kg-1·30d-1)增加至施肥处理土壤的1.65(mg·kg-1·30d-1),但硝化速率和矿化速率却显著降低(P<0.01),分别由对照土壤的6.79(mg·kg-1·30d-1)和6.13(mg·kg-1·30d-1)减少至施肥处理土壤的2.60(mg·kg-1·30d-1)和4.25(mg·kg-1·30d-1),导致了土壤中NH4+-N的积累。     

Epidemiology of beet necrotic yellow vein virus in sugar beet at different initial inoculum levels in the presence or absence of irrigation

A field experiment was set up in 1988 to study the development of rhizomania disease of sugar beet at different inoculum levels of beet necrotic yellow vein virus (BNYVV) in soil. Five, tenfold different, inoculum levels were created by addition of the approximate amounts of 0, 0.5, 5, 50 and 500 kg infested soil per ha (the latter corresponding to 0.01% v/v calculated to the tillage layer). A drip irrigation treatment was applied to study the influence of soil moisture on disease. Susceptible sugar beet, cv. Regina, was grown for three consecutive years.In the first year, root symptoms were not observed, but BNYVV-infected plants were detected by ELISA in low numbers at all inoculum levels at harvest. After late drilling in 1989, high numbers of infected plants, up to 90–100% in plots with the highest inoculum level, were detected already in June. Root symptoms were also observed from June onwards. In both these years disease incidence increased in time and was significantly influenced by the initial inoculum level. In the third year, the whole field was heavily diseased, and only for the non-irrigated plots incidence differed for different initial inoculum levels. The expression of symptoms by BNYVV-infected plants was influenced by initial inoculum level, thus by the amount and timing of primary infection.Root weight at harvest was not affected, but sugar content decreased with increasing inoculum level already in 1988, leading to a reduction in sugar yield of 10% at the highest inoculum level. In 1989, both root weight and sugar content decreased progressively with increasing inoculum level, resulting in sugar yield reductions of 11–66% (down to approximately 3000 kg ha^–1) for low to high inoculum levels compared to the control. As the control plots became contaminated, all yields were low in 1990, still showing a decrease with increasing inoculum level in the non-irrigated plots, but an overall mean sugar yield of 3323 kg ha^–1 for the irrigated ones.Sodium and -amino nitrogen content of the root, additional quality parameters determining extractability of sucrose, showed an increase and decrease, respectively, with increasing initial inoculum level already in the first year. The relative differences in contents compared to those from the control were largest for Na content. A significant negative correlation was found between Na (mmol kg^–1 root) and sugar content (% of fresh weight); linear for 1988, exponential for 1989 and 1990.In spring 1989, the infestation of individual plots was assessed using a quantitative bioassay estimating most probable numbers (MPNs) of infective units of BNYVV per 100 g dry soil. The relationship between the MPns determined and root weight, sugar content and sugar yield at harvest could be described by Gompertz curves. The increase in disease incidence with increasing MPN in 1989 was adequately fitted with a logistic equation.     

生物固氮细菌的应用

分类论述了生物固氮细菌在农业作物上、生态环境的保护上、动物消化道的固氮作用,同时分析和评价了生物固氮的研究和应用前景。     

昭通植烟土壤的有机质与氮含量

在昭通市8个产烟县(区)采集605个植烟耕层土壤进行分析。结果表明,昭通植烟土壤有机质和全氮含量中偏高,平均含量分别为2.63%和0.13%,处于中上以上水平含量的土壤样本分别占76.19%和67.6%。速效氮含量平均107.28 mg/kg,处于中上以上水平含量的土壤样本占95.37%。各产烟县(区)植烟土壤有机质和全氮含量地域分布差异较大,其中镇雄县和威信县较高,巧家县和永善县较低。全市植烟土壤有机质和氮素含量从地理分布上表现出由南向北递增、自东向西递减的趋势。     

Comparison of uptake of different N forms by soil microorganisms and two wet-grassland plants: A pot study

Two common plant species of temperate wet grasslands, Carex acuta and Glyceria maxima, were tested for their preferences in the uptake of different nitrogen (N) sources (amino acid, ammonium, nitrate) and their ability to compete for these sources with soil microorganisms. The experiment was a one-day incubation study with plants growing in soil obtained from the field, which was supplied with a solution containing the three N sources, one at a time labeled with ¹⁵N. The bulk of the N demand of both species was covered by nitrate-N, which was the dominant N form in the soil at the time of the experiment. Ammonium-N was taken up less strongly, and organic N formed only a negligible part of their nutrition. The assimilated inorganic N was preferentially transported to apical meristem of the youngest leaf, while organic N remained mostly in the roots. The fast-growing Glyceria took up more N and was a better competitor vis-à-vis soil microbes for rarer N forms than Carex. However, both plants were poor competitors for N vis-à-vis soil microbes, irrespective of the N form. Microbes took up nitrate ca. five times faster and organic N more than a hundred times faster than plants. Correspondingly, the calculated turnover time of microbial N was 17 days, compared to 40 days for N in plant roots. A significant amount of added ¹⁵N was found at non-exchangeable sites in the soil, which points to the importance of microbial N transformation and abiotic N fixation for N retention in soil. In summary, the preferential assimilation of inorganic N by the wetland plants studied here and their poor ability to compete for N with soil microbes over the short term agree with the results of studies carried out with other species from temperate grasslands.     

Effects of Supplementing a Basal Diet of Chloris gayana Hay with One of Three Protein-rich Legume Hays of Cassia rotundifolia,Lablab purpureus and Macroptilium atropurpureum Forage on Some Nutritional Parameters in Goats

Growth and digestibility experiments were conducted on growing East African type goats offered Chloris gayana hay supplemented with one of three high-protein (119–128 g CP/kg DM) legume hays, Cassia rotundifolia (cassia), Lablab purpureus (lablab) or Macroptilium atropurpureum (siratro), and crushed maize to investigate the feed intake, digestibility, growth and urinary excretion of purine derivatives. Goats in the supplemented groups had higher total dry matter and nitrogen intakes and higher N retention and body mass gains than unsupplemented counterparts. The digestibility of dry matter, organic matter and neutral detergent fibre were increased by protein supplementation. Animals on supplemented diets had higher fractional outflow rates of particulate matter from the rumen. The production of protein by ruminal microbes and the efficiency of microbial N production were increased by supplementation. It was concluded that a mixture of low-quality grass hay (61.9 CP/kg DM) and either cassia, lablab or siratro hay, and maize grain can provide a productive balanced diet for growing goats.     

猪源唾液乳杆菌对生长猪氮表观消化率及血清指标的影响

本研究旨在探讨猪源唾液乳杆菌对生长猪氮表观消化率和血清指标的影响。选用平均体重为(35.22±0.86)kg长×大二元杂交猪81头,随机分成3组,每组3个重复,每个重复9头。对照组饲喂基础日粮,试验组分别在基础日粮中添加0.20%、0.40%猪源唾液乳杆菌冻干制剂,试验期为30 d。结果表明:添加0.20%、0.40%的猪源唾液乳杆菌冻干制剂可显著提高生长猪氮表观消化率(P<0.05);与对照组相比,2个试验组猪血清白球比显著降低(P<0.05),尿素氮、乳酸脱氢酶、肌酸激酶含量分别比对照组降低了14.77%和13.42%(P<0.05)、16.92%和20.0%(P<0.05)、28.96%和23.00%(P<0.01),但2个试验组间差异不显著(P>0.05)。结果提示,日粮中添加猪源唾液乳杆菌能够提高生长猪氮表观消化率,改善血清指标,减少应激,且以添加剂量为0.20%时效果最好。     

不同放牧制度对荒漠草原表层土壤氮素空间异质性的影响

以荒漠草原不同放牧制度下表层土壤氮素含量为研究对象,采用GS+软件和地统计学分析方法对其空间异质性分布进行了研究.结果显示,划区轮牧区表层士壤碱解氮含量显著低于对照区和自由放牧区,土壤全氮含量没有发生显著性变化.样点间土壤氮素含量差异表明,表层土壤氮素含量存在空间异质性.划区轮牧使得土壤碱解氮含量和土壤全氮含量空间分布受随机因素影响大,自由放牧使土壤全氮含量空间分布受随机因素影响大,围封状态的对照区土壤碱解氮含量和土壤全氮含量空间分布几乎不受随机因素影响.划区轮牧能够减小土壤氮素空间分布的异质性,自由放牧导致表层土壤碱解氮含量空间差异较大.在划区轮牧区,土壤碱解氮含量和土壤全氮含量空间分布都比较均匀,呈片状分布,自由轮牧区土壤碱解氮整体呈破碎斑块分布.     

Regulation of urease production in soil by microbial assimilation of nitrogen

Summary Studies of the effects of different forms of N on urease production in soils amended with organic C showed that although microbial activity, as measured by CO₂ production, was stimulated by the addition of NH₄ ⁺ or NO₃ ^- to C-amended soils (200 mol glucose-C g^–1 soil), urease production was repressed by these forms of N. The addition of L-methionine sulfoximine, an inhibitor of inorganic N assimilation by microorganisms, relieved the NH₄ ⁺ and NO₃ ^- repression of urease production in C-amended soil. The addition of sodium chlorate, an inhibitor of NO₃ ^- reduction to NH₄ ⁺ by microorganisms, relieved the NO₃ ^- repression of urease production, but did not eliminate the repression associated with NH₄ ⁺. These observations indicate that microbial production of urease in C-amended soils is not directly repressed by NH₄ ⁺ or NO₃ ^-, but by products formed by microbial assimilation of these forms of N. This conclusion is supported by our finding that the biologically active L-isomers of alanine, arginine, asparagine, aspartate, and glutamine, repressed urease production in C-amended soil, whereas the D-isomers of these amino acids had little or no influence on urease production. This work suggests that urease synthesis by soil microorganisms is controlled by the global N regulon.