种植模式对苜蓿固氮和固氮产物转移的影响

田间小区试验研究了不同种植模式下苜蓿的共生固氮贡献,并利用~(15)N同位素示踪技术评估了苜蓿的％Ndfa和Ndfa,以及与之混作生长的牛尾草植株中来自苜蓿固氮产物的转移量。研究表明,豆科与禾本科牧草混作对发挥草地的优势有一定影响,混作条播在干草产量、全氮产量、％Ndfa和Ndfa等方面均优于间作与混作撒播模式,且高于单作苜蓿与牛尾草的平均值。用~(15)N同位素稀释法与~(15)N天然丰度法评估苜蓿的％Ndfa与Ndfa值时,无明显差异(P<0.05),前者还能准确测出混种牛尾革植株中的固氮产物转移量,后者则大大低估,甚至不能测出固氮产物转移。     

区域土壤有机氮迁移的研究进展

农田土壤氮素迁移是影响区域环境质量的重要过程。通过综述近期在区域有机氮迁移以及稳定性同位素和模型研究方法方面的进展,指出:我国有机氮源的氮素损失在人口稠密和养殖业发达的区域已经成为非点源污染的重要来源;小流域氮素输出中可溶性有机氮是一个重要组成,其输出过程受气候以及人为引起的植被、土壤及水文过程的变化的影响;稳定性氮氧同位素可以识别水体中陆源氮污染物的分布;基于GIS的过程模型可以定量分析区域氮素迁移的数量及其环境效应。进一步提出了目前需要加强农田有机氮迁移过程及其影响机制的研究,发展基于稳定性同位素的区域氮素迁移定量方法,建立稻田生态系统和水旱轮作系统的氮素迁移定量评价模型,并归纳了减少面源污染的区域氮素迁移调控措施。     

利用核素示踪技术研究磷酸根在杭州西湖沉积物环境中的行为

运用32P同位素示踪技术,在实验室条件下研究了西湖沉积物中磷酸根的吸附和释放.结果表明:当磷酸根达最大释放量时,沉积物中的无机磷约有5%可以通过扩散等途径进入上覆水.而水层中95%的磷可以通过沉积物表面的吸附、交换等途径进入沉积物;E值测定表明:西湖沉积物含有78～184 μg/g可交换的P磷酸根的形态转化实验表明:磷酸根在15 d内大部分转化为不溶性的无机磷酸盐类,只有1.90%的标记磷以溶解态和吸附态存在.     

抗病增丝剂在蚕体内分布规律的研究

用~3H 标记抗病增丝剂,给5龄家蚕进行添食处理,以测定抗病增丝剂在家蚕体内及丝茧中的吸收和分布规律。结果表明,抗病增丝剂主要分布在绢丝腺和茧层中,而蛹体内则甚微.     

Stable isotope N and C labelling of different functional groups of earthworms and their casts: A tool for studying trophic links

Earthworms (Oligochaeta: Lumbricidae) have substantial effects on the structure and fertility of soils with consequences for the diversity of plant communities and associated ecosystem functions. However, we still lack a clear understanding of the functional role earthworms play in terrestrial ecosystems, partly because easy-to-use methods to quantify their activities are missing. In this study, we tested whether earthworms and their casts can be dual-labelled with ¹⁵N and ¹³C stable isotopes by cultivating them in soil substrate amended with ¹⁵N ammonium nitrate and ¹³C-glucose. Additionally, we also wanted to know whether (i) earthworms from different functional groups (soil-feeders vs. litter-feeders) and their casts would differ in their incorporation of stable isotopes, (ii) if enrichment levels are higher if the same amount of isotopes is applied in one dose or in staggered doses, and (iii) if isotopic enrichment in casts changes when they are stored in a conditioning cabinet or in a pot filled with soil placed in a greenhouse. Our findings show the feasibility of dual-labelling tissues and casts of both litter-feeding (Lumbricus terrestris) and soil-feeding (Aporrectodea caliginosa) earthworms using the same method. The advantage of this method is that earthworms and their casts can be labelled under realistic conditions by cultivating them for only four days in soil that received a one-time addition of commercially available stable isotopes instead of offering labelled plant material. In earthworms, the isotopic enrichment remained at a stable level for at least 21 days; labelled casts could be stored for at least 105 days without significantly decreasing their isotopic signals. This simple and efficient method opens new avenues for studying the role of these important ecosystem engineers in nutrient cycling and their functional relationships with other organisms.     

稻草和尿素配施时水稻对肥料氮和土壤氮的吸收利用

利用＾１５Ｎ同位素示踪技术,研究了稻草和尿素配施时水稻对肥料和土壤氮的吸收。结果表明,稻草单施导致土壤速效氮的生物固定,氮素供应不足是影响水稻分蘖成穗的限制因子,稻草配合尿素施用,明显改善肥料氮和土壤氮的供应,既有利于当季水稻增产,也有利于培养土壤肥力,还有利于后茬物作产量的提高 。     

Spatial heterogeneity in the relocation of added C within the structure of an upland grassland soil

A pulse of ¹³CO₂ was added to the above ground vegetation in an upland grassland to determine the effects of faunal diversity on the flux of carbon to the surface horizons of the soil. Faunal diversity was manipulated by liming and biocide treatments for three years prior to the pulse addition. The relocation of ¹³C within roots and rhizosphere soil was determined by analysis of samples of bulk soil and of specific features identified on soil thin sections on four dates after the addition of the ¹³CO₂ pulse. Analysis of bulk soils showed only a small enrichment in ¹³C and no significant effects of the treatments. Analysis by isotope ratio mass spectrometry of the products of in situ laser combustion of root material and aggregates formed from faunal excrement showed that the distribution of the newly photosynthesised ¹³C is very localised, with large spatial variability in soil and root δ¹³C at scales of less than 1 mm. δ¹³C values ranged from the natural abundance level of around −28‰ to −4.9‰ in roots and to −8.4‰ in aggregates. The small pulse and large spatial variability masked any effects of the liming and biocide treatments in these soils. However, the variability in the relocation of newly photosynthesised carbon may help to explain the large spatial variability found in bacterial numbers at the sub-mm scale within soils and emphasises the importance of the accessibility of substrates to decomposers in undisturbed structured soils.     

Variable use of plant- and soil-derived carbon by microorganisms in agricultural soils

In this study we used compound specific ¹³C and ¹⁴C isotopic signatures to determine the degree to which recent plant material and older soil organic matter (SOM) served as carbon substrates for microorganisms in soils. We determined the degree to which plant-derived carbon was used as a substrate by comparison of the ¹³C content of microbial phospholipid fatty acids (PLFA) from soils of two sites that had undergone a vegetation change from C3 to C4 plants in the past 20-30 years. The importance of much older SOM as a substrate was determined by comparison of the radiocarbon content of PLFA from soils of two sites that had different ¹⁴C concentrations of SOM.The ¹³C shift in PLFA from the two sites that had experienced different vegetation history indicated that 40-90% of the PLFA carbon had been fixed since the vegetation change took place. Thus PLFA were more enriched in ¹³C from the new C4 vegetation than it was observed for bulk SOM indicating recent plant material as preferentially used substrate for soil microorganisms. The largest ¹³C shift of PLFA was observed in the soil that had high ¹⁴C concentrations of bulk SOM. These results reinforce that organic carbon in this soil for the most part cycles rapidly. The degree to which SOM is incorporated into microbial PLFA was determined by the difference in ¹⁴C concentration of PLFA derived from two soils one with high ¹⁴C concentrations of bulk SOM and one with low. These results showed that 0-40% of SOM carbon is used as substrate for soil microorganisms. Furthermore a different substrate usage was identified for different microorganisms. Gram-negative bacteria were found to prefer recent plant material as microbial carbon source while Gram-positive bacteria use substantial amounts of SOM carbon. This was indicated by ¹³C as well as ¹⁴C signatures of their PLFA. Our results find evidence to support ‘priming’ in that PLFA indicative of Gram-negative bacteria associated with roots contain both plant- and SOM-derived C. Most interestingly, we find PLFA indicative of archeobacteria (methanothrophs) that may indicate the use of other carbon sources than plant material and SOM to a substantial amount suggesting that inert or slow carbon pools are not essential to explain carbon dynamics in soil.     

基于同位素示踪技术的糙米加湿后精米吸水率的试验研究

该研究以糙米为原料，应用同位素示踪技术研究糙米加湿调质各工艺参数对精米吸水率的影响规律。在糙米加湿调质中用氚水(H₂³O)为同位素示踪剂对所加水分标记，通过放射性测量(cpm值)确定样品吸水率；采用二次旋转正交组合试验方法设计试验，用Reda软件包处理试验数据，得出了各试验参数对精米吸水率影响关系的回归方程，分析了各试验因素对精米吸水率的影响规律，试验结论可以为掌控糙米加湿调质后精米含水率提供理论依据。     

Subsoil retention of organic and inorganic nitrogen in a Brazilian savanna Oxisol

Abstract. Nitrogen (N) loss by leaching poses great challenges for N availability to crops as well as nitrate pollution of groundwater. Few studies address this issue with respect to the role of the subsoil in the deep and highly weathered savanna soils of the tropics, which exhibit different adsorption and drainage patterns to soils in temperate environments. In an Anionic Acrustox of the Brazilian savanna, the Cerrado, dynamics and budgets of applied N were studied in organic and inorganic soil pools of two maize (Zea mays L.) – soybean (Glycine max (L.) Merr.) rotations using ¹⁵N tracing. Labelled ammonium sulphate was applied at 10 kg N ha^?1 (with 10 atom%¹⁵N excess) to both maize and soybean at the beginning of the cropping season. Amounts and isotopic composition of N were determined in above‐ground biomass, soil, adsorbed mineral N, and in soil solution at 0.15, 0.3, 0.8, 1.2 and 2 m depths using suction lysimeters throughout one cropping season. The applied ammonium was rapidly nitrified or immobilized in soil organic matter, and recovery of applied ammonium in soil 2 weeks after application was negligible. Large amounts of nitrate were adsorbed in the subsoil (150–300 kg NO₃^?‐N ha^?1 per 2 m) matching total N uptake by the crops (130–400 kg N ha^?1). Throughout one cropping season, more applied N (49–77%; determined by ¹⁵N tracers) was immobilized in soil organic matter than was present as adsorbed nitrate (2–3%). Most of the applied N (71–96% of ¹⁵N recovery) was found in the subsoil at 0.15–2 m depth. This coincided with an increase with depth of dissolved organic N as a proportion of total dissolved N (39–63%). Hydrophilic organic N was the dominant fraction of dissolved organic N and was, together with nitrate, the most important carrier for applied N. Most of this N (>80%) was leached from the topsoil (0–0.15 m) during the first 30 days after application. Subsoil N retention as both adsorbed inorganic N, and especially soil organic N, was found to be of great importance in determining N losses, soil N depletion and the potential of nitrate contamination of groundwater.