Long-term fertilization effects on active ammonia oxidizers in an acidic upland soil in China

The effects of long-term fertilization of acidic soils on ammonia-oxidizing archaea (AOA) and bacteria (AOB) communities and its ecological implications remain poorly understood. We chose an acidic upland soil site under long-term (27-year) fertilization to investigate ammonia oxidizer communities under four different regimes: mineral N fertilizer (N), mineral NPK fertilizer (NPK), organic manure (OM) and an unfertilized control (CK). Soil net nitrification rates were significantly higher in OM soils than in CK, N or NPK soils. Quantitative analysis of the distribution of amoA genes by DNA-based stable isotope probing revealed that AOA dominate in CK, N and NPK soils, while AOB dominate in OM soils. Denaturing gradient gel electrophoresis and clone library analyses of amoA genes revealed that Group 1.1a-associated AOA (also referred to as Nitrosotalea) were the most dominant active AOA population (>92%), while Nitrosospira Cluster 3 and Cluster 9 were predominant among active AOB communities. The functional diversity of active ammonia oxidizers in acidic soils is affected by long-term fertilization practices, and the responses of active ammonia oxidizers to mineral fertilizer and organic manure are clearly different. Our results provide strong evidence that AOA are more highly adapted to growth at low pH and low substrate availability than AOB, and they suggest that the niche differentiation and metabolic diversity of ammonia oxidizers in acidic soils are more complex than previously thought.     

Oxygen isotope ratios of plant available phosphate in lowland tropical forest soils

Phosphorus (P) cycles rapidly in lowland tropical forest soils, but the process have been proven difficult to quantify. Recently it was demonstrated that valuable data on soil P transformations can be derived from the natural abundance of stable oxygen isotopes in phosphate (δ¹⁸O_P). Here, we measured the δ¹⁸O_P of soils that had received long-term nutrient additions (P, nitrogen, and potassium) or litter manipulations in lowland tropical forest in Panama and performed controlled incubations of fresh soils amended with a single pulse of P. To detect whether δ¹⁸O_P values measured in the incubations apply also for soils in the field, we examined the δ¹⁸O_P values after rewetting dry soils. In the incubations, resin-P δ¹⁸O_P values converged to ∼3.5‰ above the expected isotopic equilibrium with soil water. This contrasts with extra-tropical soils in which the δ¹⁸O_P of resin-P matches the expected equilibrium with soil water. Identical above-equilibrium resin-P δ¹⁸O_P values were also found in field soils that did not receive P additions or extra litter. We suggest that the 3.5‰ above-equilibrium δ¹⁸O_P values reflect a steady state between microbial uptake of phosphate (which enriches the remaining phosphate with the heavier isotopologues) and the release of isotopically equilibrated cell internal phosphate back to the soil. We also found that soil nutrient status affected the microbial turnover rate because in soils that had received chronic P addition, the original δ¹⁸O_P signature of the fertilizer was preserved for at least eight weeks, indicating that the off-equilibrium δ¹⁸O_P values produced during microbial phosphate turnover was not imprinted in these soils. Overall, our results demonstrate that ongoing microbial turnover of phosphate mediates its biological availability in lowland tropical soils.     

Contribution of Different Organs to Grain Filling in Durum Wheat under Mediterranean Conditions I. Contribution of Post‐Anthesis Photosynthesis and Remobilization

Under Mediterranean conditions, drought affects cereals production principally through a limitation of grain filling. In this study, the respective role of post‐anthesis photosynthesis and carbon remobilization and the contribution of flag leaf, stem, chaff and awns to grain filling were evaluated under Mediterranean conditions in durum wheat (Triticum turgidum var. durum) cultivars. For the purpose, we examined the effects of shading and excision of different parts of the plant and compared carbon isotope discrimination (Δ) in dry matter of flag leaf, stem, chaff, awns and grain at maturity and in sap of stem, flag leaf, chaff and awns, this last measurement providing information on photosynthesis during a short period preceding sampling. Source–sink manipulations and isotopic imprints of different organs on final isotope composition of the grain confirmed the high contribution of both carbons assimilated by ears and remobilized from stems to grain filling, and the relatively low contribution of leaves to grain filling. Grain Δ was highly and significantly associated with grain yield across treatments, suggesting the utilization of this trait as an indicator of source–sink manipulations effects on grain yield. Chaff and awns Δ were better correlated with grain Δ than stem and leaf Δ, indicating that chaff were more involved in grain filling than other organs. Moreover, in chaff, sap Δ was highly significantly correlated with dry matter Δ. These results suggest the use of Δ for a rapid and non‐destructive estimation of the variation in the contribution of different organs to grain filling.     

土地利用变化对土壤水补给来源影响研究

为探究不同植被类型深剖面土壤水补给来源,以黄土区长武塬为研究区,采集两种土地利用方式(农地、18 a苹果园、26 a苹果园)下20 m深土壤剖面,测定土壤水及其稳定性和放射性同位素含量,基于同位素方法对不同土地利用类型下不同深度土壤水来源进行溯源分析。研究表明：(1)苹果园土壤水含量明显低于农地,说明果园耗水强度更大,对深层土壤水影响更为显著。(2)农地、18 a和26 a苹果园下降水偏移量分别为-22‰、-20‰和-6‰,说明降水补给土壤水后受到蒸发作用影响,且农地土壤水比果园受到的蒸发效应更强。(3)该区土壤水补给主要以活塞流为主;对于补给不同深度土壤的可能水源,6 m以下补给水的同位素组成(δ²H=-83.8‰,δ¹⁸O=-12.1‰)较0～6 m (δ²H=-68.8‰,δ¹⁸O=-10.1‰)更为贫化,且6 m以下补给水的氢氧稳定同位素组成与日降水量≥50 mm·d^-1的降水更相似。与农地(δ²H=-70.6‰,δ¹⁸O=-...     

稻田水体碳氮稳定同位素组成与时空变化研究

利用稳定同位素技术研究了稻田沟渠、池塘、湿地等水体的碳、氮稳定同位素组成特征与时空变化。结果表明,水中颗粒性有机物(Particulate organic matter,POM)δ13C值(稳定性碳同位素比值)在-31.5‰~-24.3‰之间变化,平均值为-27.7‰,可能主要来自于浮游植物和浮游动物的贡献。POM稳定性碳同位素比值存在明显的季节变化,呈现出春、夏季高于秋、冬季的趋势。浮游动物与POM稳定性碳同位素比值之间的时空变化存在一定的相关性,说明研究区内浮游动物对内源有机碳的利用可能主要来自POM。颗粒性有机物δ15N存在秋、冬季高于春、夏季的趋势,但空间差异不显著,其中湿地的变化幅度相对较大(3.2‰~6.3‰),δ15NPOM平均值为4.1‰,说明研究区固氮作用较小,外源物的污染程度较低。     

机器人稳态分析的一种新方法

提出一种机器人稳态分析新方法,以D-H矩阵的逆矩阵,构建由工具坐标系到机械臂关节空间坐标系之间的线性射映关系,即一种新型的雅可比矩阵,由此导出由工具坐标系到关节坐标系之间力和力矩的传递函数。和传统的稳态分析方法相比,减少矩阵叉积次数,且能得出和关节空间力和力矩关系相一致的表态式,并能用D-H矩阵验证求解的正确性。     

稳定同位素技术分析不同养殖方式下鳙饵料的贡献率

应用碳氮稳定同位素技术分析了不同养殖方式(A组:施肥;B组:施肥+1/2投饲;C组:施肥+投饲;D组:投饲)围隔中鳙(Aristichthys nobilis)肌肉碳氮稳定同位素变化情况,及其可能摄食饵料的贡献率。结果表明,A组鳙肌肉的δ13C和δ15N值分别为(–23.8±0.1)‰和(10.8±0.4)‰,显著高于B组、C组和D组的值(P0.05),后三者之间值没有显著差异。围隔中的食物源有浮游动物、颗粒有机物和饲料,它们的δ13C和δ15N值均低于消费者鳙的同位素值。3种食物在不同养殖方式下的贡献率不同,浮游动物是A组鳙的主要食物来源,平均贡献率为(65.6±3.2)%,饲料是另3个组鳙的主要食物来源,其中B组饲料的贡献率相对较大,达82.1%。说明投饲鳙后,鳙对饲料能够较好地吸收利用,但在池塘中同时培育天然饵料能有效提高饲料的贡献率,减少投饲量,降低残饵的污染。本研究旨为实践养殖中合理投饲鳙的管理技术提供理论依据。     

同位素稀释液质联用法测定鱼体中氯丙嗪的残留

建立了高效液相色谱-串联质谱(HPLC/MS/MS)分析鱼体中氯丙嗪残留的方法.样品用乙腈提取,MCX固相萃取柱净化,氨化甲醇洗脱.在正离子模式下以电喷雾串联质谱仪进行测定,采用内标法定量,氘代氯丙嗪为内标物.以欧洲鳗鲡、鳜鱼和大口黑鲈为研究对象,在1.0、5.0、25.0μg/kg添加水平下,方法平均回收率为90.1...     

Evaluation of shrimp polyculture system in Thailand based on stable carbon and nitrogen isotope ratios

ABSTRACT: To quantify the contribution by cocultured animals to waste assimilation in an intensive shrimp farm in Thailand, the food web structures of the macrobenthos in a reservoir pond, a shrimp culture pond and water treatment ponds were examined using the stable C and N isotope ratio technique. Seawater for aquaculture was drawn from a creek, and stored in a reservoir pond, used for farming the banana prawn Fenneropenaeus merguiensis in culture ponds, and then recycled through treatment ponds where the green mussel Perna viridis was cultured to remove organic wastes discharged from the farming. The clam worm Nereididae sp. and the mud creeper Cerithideopsilla cingulata in the culture pond had δ ¹³C values of −21.0‰ and −18.4‰, respectively, suggesting that shrimp feed (mean δ ¹³C = −20.7‰) was the main food source for these species. The δ ¹³C analysis also suggested that sediments (−23.7‰) in the reservoir pond and particulate organic matter (POM) (−24.0‰) and/or sediments (−25.0‰) in the treatment pond supplied carbon for most macrobenthic animals. However, green mussels in the treatment pond had a mean δ ¹³C value of −20.5‰, suggesting that shrimp feed was the main food source for this species.