肉鸭粪便排放特征的季节性变化

本研究旨在探讨肉鸭粪便的特性,并对其不同季节的污染物排放特征进行评价,为肉鸭养殖场废弃物处理和资源化利用提供依据。分4个季节进行了北京Z型肉鸭饲养试验(饲养期37 d),记录采食量、产粪量,并定期测定饲料和粪便中水分和有机质含量及总氮(TN)、P、Cu、Zn含量。结果表明:肉鸭粪便中Zn含量秋季最高, TN、P、Cu含量均为冬季最高;冬季粪便中TN含量极显著高于夏、秋两季(P0.01); P、Cu含量在冬季均极显著高于其余季节(P0.01);粪便中Cu、Zn含量均为春季最低。肉鸭粪便平均含水率为84.61%,夏季最高,春季最低;平均有机质含量为83.38%,表现为冬春秋夏。春夏秋冬四季的粪便产生量分别为338.3g?d~(-1)?只~(-1)、275.9 g?d~(-1)?只~(-1)、317.6 g?d~(-1)?只~(-1)和327.0 g?d~(-1)?只~(-1),夏季最低。TN、P、Cu、Zn的排泄系数分别为2.13 g?d~(-1)?只~(-1)、2.48g?d~(-1)?只~(-1)、2.56 mg?d~(-1)?只~(-1)、21.10 mg?d~(-1)?只~(-1);春冬两季的TN日排泄量显著高于夏秋两季; P的日排泄量表现为冬季极显著高于其余3个季节;夏季Cu的日排泄量与春季差异不显著,极显著低于秋、冬两季(P0.01)。TN在秋季排泄占比最低,春季最高;而P排泄占比为秋季最高,春季最低。肉鸭在饲养期TN、P、Cu、Zn的排泄量与对应元素的摄入量具有极显著的正相关关系(P0.01)。研究表明:季节因素能对肉鸭粪便中含水率、有机质、TN、P、Cu和Zn含量产生显著影响,同时各季节各元素的排泄量与相应元素的摄入量显著相关。     

Spatial patterns of adenylate kinase,catalase, endopeptidase and fructose-1,6-diphosphatase encoding genes allelic variation in <Emphasis Type="Italic">Aegilops tauschii</Emphasis> Coss.

Investigation of spatial patterns of adenylate kinase, catalase, endopeptidase and fructose-1,6-diphosphatase encoding genes (Ak, Cat1, Cat2, Ep, Fdp) allelic variation in Aegilops tauschii was carried out. About 300 accessions, representing all the species range were taken for the study. Cat2 and Fdp loci are completely monomorphic in ssp. strangulata and in the western part of ssp. tauschii range, as well. Both Cat2 and Fdp are highly polymorphic in the eastern part of ssp. tauschii range, with the patterns of this polymorphism being discordant in these two loci. Ak ¹⁰⁸, a rare allele with sporadical spatial occurrence, was found in ssp. tauschii only. On the contrary, Ak ⁹² is absent in ssp. tauschii: it is the most common Ak allele in ssp. strangulata in Precaspian Iran, the most moist part of the area, and is very rare in other parts of ssp. strangulata area. Ep is a highly polymorphic locus with the highest level of variation in the west of Ae. tauschii area, where this species had originated. Ep allele variation patterns are rather similar in ssp. tauschii and ssp. strangulata. The data reveal the adaptive nature of Ak, Cat2, and Fdp allele variation, while Ep polymorphism seems to be mostly neutral.     

石灰性土壤交换性钙和镁测定方法的研究

石灰性土壤交换性盐基组成的测定,通行的方法是采用70%乙醇溶液反复洗盐,再经pH 8.50.1 mol L-1氯化铵-70%乙醇(CH3CH2OH)溶液进行多次交换处理,测定交换液中的K+、Na+、Ca2+、Mg2+浓度。但此方法常常受操作步骤繁琐,以及土壤中碳酸盐的溶解量因多次浸提而增加的困扰,最终导致测定结果偏高。基于上述原因,选择不同浓度、不同pH的NH4OAc和NH4Cl 10种交换剂,对比分析10种交换剂中的碳酸盐溶解度和土壤交换性钙镁含量。结果表明,pH=8.5 1 mol L-1氯化铵-70%乙醇(CH3CH2OH)溶液较适合石灰性土壤交换性盐基的测定。此新方法是先经70%乙醇(CH3CH2OH)溶液洗盐,再用pH8.5 1 mol L-1氯化铵(NH4Cl)-70%乙醇(CH3CH2OH)溶液进行一次性交换处理,然后测定交换液的K+、Na+、Ca2+、Mg2+浓度,简化了操作程序的同时有效抑制了土壤碳酸盐的溶解,降低了测定结果的偏差。     

Dynamics of arsenic-containing compounds sorption on sediments

Background  River and lake sediments constitute complex and difficult analytical samples. On the other hand, sediments play a fundamental role in the distribution of toxic compounds in aquatic systems and in the evaluation of the current state and the course of changes taking place in the environment. Among elements present in the environment in trace concentrations, but having well-elaborated toxic properties, one of most dangerous is arsenic. The element occurs in the environment in several chemical forms, predominant are inorganic forms of As(V) and As(III), and methylated forms such as monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA). Objectives  Reported herein are experiments, which were undertaken with the aim of examining the dynamics of arsenic sorption in sediments and its dependence on speciation of the element and the pH in the environment. Simultaneously, influence of organic matter content and chemical composition of the sediments on As sorption, were investigated. Methods  Sediment samples (upper 10 cm layer) were collected from three sites located in the vicinity of Cracow:

Mineralization of nitrogen compounds in the soil under the bilberry-sphagnum birch forest (Yaroslavl Oblast)

Net mineralization of nitrogen was measured in the horizons of peaty podzolic gley soil (At1, 0–6 cm, At2, 6–10 cm, and A2, 10–20 cm) of the bilberry-sphagnum birch forest from May to the beginning of November in 2011 and 2012; it comprised 2.1 ± 0.4, 2.7 ± 0.4, 1.2 ± 0.4, and 1.9 ± 0.2, 1.9 ± 0.2, 0.8 ± 0.15 g N/m², respectively. The total of 6 ± 0.7 and 4.6 ± 0.3 g N/m² were mineralized in the soil profile in the years 2011 and 2012, respectively, with the contribution of ammonification being more than 99%. The seasonal variations in nitrogen mineralization correlated with the temperature and soil moisture content in At1 and At2 horizons. The efficiency of nitrogen mineralization in soil horizons under the birch forest was expressed by similar values, namely, 0.005 ± 0.0008, 0.0064 ± 0.0008, and 0.003 ± 0.001 mg N/g C per day, and this suggests a high efficiency of substrate utilization in the eluvial part of the soil profile. The seasonal variation of carbon dioxide production correlated with the ammonification in the At1 horizon with r = 0.85 and p = 0.03 in 2011 and 2012, and in the At2 horizon with r = 0.65 and p = 0.16 in 2012. Over the studied period, production of ammonia depended on soil moistening in the dry year of 2011 (r = 0.91; p = 0.01) and soil temperature in the wet year of 2012 (r = 0.78; p = 0.06). The productivity of the process equaled 3 ± 0.9 mg N/m², or 30 g N/ha in both years of observation.     

Effects of Green Manures and Zinc Fertilizer Sources on DTPA-Extractable Zinc in Soil and Zinc Content in Basmati Rice Plants at Different Growth Stages

Rice is very sensitive to low zinc(Zn) supply in submerged paddy soils and Zn deficiency is one of the major limiting factors in determining rice production in India. A field experiment was conducted during the summer-rainy seasons of 2009 and 2010 at the research farm of the Indian Agricultural Research Institute, New Delhi, to determine the effects of summer green manure crops and Zn fertilizers on diethylenetriaminepentaacetic acid(DTPA)-extractable(available) Zn concentration in soil and total Zn content in Basmati rice cultivar Pusa Basmati 1 at periodic intervals. Summer green manure crops included Sesbania aculeata(Dhaincha),Crotalaria juncea(Sunhemp), and Vigna unguiculata(Cowpea) and the Zn fertilizers used were ethylenediaminetetraacetic acid(EDTA)-chelated Zn, ZnSO_4·7H_2O, ZnSO_4·H_2O, ZnO, and ZnSO_4·7H_2O + ZnO. Beneficial effects of summer green manure crops and Zn fertilizers on DTPA-extractable Zn concentration in soil and total Zn content in dry matter of Basmati rice at periodic intervals were observed, with significant increases in all the determined parameters, in comparison with those in the control(no Zn application or summer fallow). The rate of increase varied among summer green manure crops and Zn fertilizers during both years. Among the summer green manures, incorporation of S. aculeata led to a significant increase in mean Zn content in Basmati rice grain and straw when compared with C. juncea, V. unguiculata, and summer fallow treatments. Among the Zn fertilizers, significant increases in Zn content in Basmati rice dry matter and DTPA-extractable Zn concentration in soil during various growth stages of the plant were recorded with EDTA-chelated Zn application, followed by the application of ZnSO_4·7H_2O, ZnSO_4·H_2O, ZnSO_4·7H_2O + ZnO, ZnO,and no Zn. The highest mean Zn content in Basmati rice grain and straw was recorded with EDTA-chelated Zn application in 2009 and 2010, respectively. The application of ZnSO_4·7H_2O was the second best treatment after EDTA-chelated Zn; however, it was statistically inferior to EDTA-chelated Zn. The lowest values were recorded with the control(no Zn application) during both years of study. The amount of Zn concentration in soil was found to be significantly positively correlated with the Zn content in Basmati rice dry matter during both years. Significantly higher levels of residual fertility in soil after the harvest of Basmati rice were observed with application of EDTA-chelated Zn and incorporation of S. aculeata when compared with those of other Zn sources and summer green manures.     

Seasonal variation in nitrogen isotopic composition of bog plant litter during 3 years of field decomposition

In this study, we describe the seasonal variation in ¹⁵N abundance in the litter of two Sphagnum species and four vascular plant species during 3 years of field decomposition in an Italian Alpine bog. Litter bags were periodically retrieved at the end of summer and winter periods, and the δ¹⁵N in residual litter was related to mass loss, litter chemistry, and climatic conditions. In Sphagnum litter, higher rates of decomposition during summer months were associated with an increase of δ¹⁵N probably due to the incorporation of microbial organic compounds rich in ¹⁵N. The litter of Eriophorum vaginatum and Carex rostrata was characterized by a decrease of δ¹⁵N, so that the final signature was significantly lower than in initial litter. On the other hand, the residual litter of Potentilla erecta and Calluna vulgaris was characterized by a final δ¹⁵N higher than in initial litter. Our data reported a seasonality of ¹⁵N abundance in the residual litter of Sphagnum species, but not in that of vascular plant species, thus highlighting the role of differences in litter chemistry.     

Diversity and function of decomposer fungi from a grassland soil

Despite the substantial interest to ecologists of the relationship between species diversity and ecosystem functioning, little is known about how the high species richness of decomposer (saprotrophic) fungi and their relative frequencies of occurrence influence the decomposition of organic matter. Three experiments were conducted to test the ability of culturable saprotrophic fungal isolates to utilise a range of artificial and more natural substrates that occur in organic matter, with the aims of (1) characterising the functional potential of ‘common’ and ‘occasional’ taxa in an upland grassland soil and (2) determining whether there was a high degree of apparent functional redundancy in these communities. ‘Function’ was defined as the ability of a fungal isolate to utilise broad categories of substrates (e.g. sugars, cellulose, lignin) that occur in organic matter and which change in proportion during decomposition. The terms ‘common/abundant/frequent’ and ‘occasional/infrequent’ usually referred here to the frequencies of occurrence of taxa estimated using Warcup soil plates. Accepting the difficulties of sampling fungi in soil, this appeared to be the most useful isolation method to produce a general picture of the microfungal community with an estimate of frequency of occurrence for every taxon obtained, and to provide cultures for use in function tests. The influence of this technique on the interpretation of the results is discussed.Forty-eight fungal isolates, obtained from an upland grassland in Roxburghshire, UK, were selected to cover the most ‘abundant’ taxa and a range of ‘occasionals’. Pure cultures of anamorphic fungi and members of the Zygomycota, Ascomycota and Basidiomycota were tested. Although there was apparently a high degree of functional redundancy (equivalence) in assemblages of culturable decomposer fungi, with ‘frequent’ and ‘infrequent’ taxa largely utilising the same substrates, the ‘infrequent’ taxa played important roles in decomposition. ‘Infrequent’ microfungi tested were potentially more active in decomposition than the ‘frequent’ taxa, i.e. several had a higher overall activity, were able to utilise a wider range of substrates and were more combative than the ‘abundant’ taxa. When ‘abundant’ and ‘occasional’ taxa from the same putative guild were inoculated together on grass litter, there was slight evidence of ‘positive’ indirect effects on decomposition and cellulose degradation. Some ‘negative’ effects on lignin degradation, probably as a result of combat, were observed.It is possible that the ‘occasional’ taxa increased the temporal resilience of the ecosystem process of decomposition, and were ‘waiting in the wings’ to replace the abundant taxa. Nevertheless, greater functional diversity could be associated with the uncultured taxa not studied here.     

三峡库区典型农业小流域次降雨产沙过程及其影响因素

为探究引起三峡库区农业小流域土壤侵蚀的主要次降雨因子,通过天然降雨观测资料,分析忠县石盘丘小流域2019年侵蚀性降雨年内分布特征和典型次降雨条件下A和B 2个集水区产沙过程的变化规律,采用相关性分析方法,揭示次降雨产沙的主要影响因素。结果表明:(1)全年119场降雨资料中,有19场为侵蚀性降雨。全年侵蚀性中雨共发生10次,是侵蚀性降雨中最常见的降雨类型。暴雨及以上降雨是造成研究区产沙量最大的降雨类型。(2)在典型中雨、大雨和暴雨产沙事件中,B集水区产沙量分别是A集水区的5.13,1.66,7.56倍。对3场典型次降雨产沙过程进行分析发现,B集水区产沙过程线随降雨历时的延长,变化程度更剧烈。(3)各PIn因子与研究区产沙量的相关性系数大小排序为PI30>PI10>PI15>PI60>PI5>PI90>PI。对各类降雨因子与研究区的产沙量进行相关性分析,系数大小排序为P>PIn>In>I>T。A、B集水区产沙量与次降雨量P和PI30均存在极显著正相关性。总之,在三峡库区开展水土保持工作时,要加强对暴雨及以上降雨造成农业小流域水土流失的监测与预警响应能力;P和PI30能较好地反映三峡库区天然次降雨对农业小流域侵蚀产沙的影响;对天然降雨条件下的次降雨侵蚀力进行估算时,可将PI30作为主要参考因子;农林水复合生态系统与结构简单的传统农耕模式相比,具有更丰富多元的层次结构,不仅能全面开发利用小流域的农业资源,更有利于保持水土,且其对降雨环境变化的适应性也更强。     

Methane emissions from different vegetation zones in a Qinghai-Tibetan Plateau wetland

We measured methane (CH₄) emissions in the Luanhaizi wetland, a typical alpine wetland on the Qinghai-Tibetan Plateau, China, during the plant growth season (early July to mid-September) in 2002. Our aim was to quantify the spatial and temporal variation of CH₄ flux and to elucidate key factors in this variation. Static chamber measurements of CH₄ flux were made in four vegetation zones along a gradient of water depth. There were three emergent-plant zones (Hippuris-dominated; Scirpus-dominated; and Carex-dominated) and one submerged-plant zone (Potamogeton-dominated). The smallest CH₄ flux (seasonal mean=33.1 mg CH₄ m⁻² d⁻¹) was observed in the Potamogeton-dominated zone, which occupied about 74% of the total area of the wetland. The greatest CH₄ flux (seasonal mean=214 mg CH₄ m⁻² d⁻¹) was observed in the Hippuris-dominated zone, in the second-deepest water area. CH₄ flux from three zones (excluding the Carex-dominated zone) showed a marked diurnal change and decreased dramatically under dark conditions. Light intensity had a major influence on the temporal variation in CH₄ flux, at least in three of the zones. Methane fluxes from all zones increased during the growing season with increasing aboveground biomass. CH₄ flux from the Scirpus-dominated zone was significantly lower than in the other emergent-plant zones despite the large biomass, because the root and rhizome intake ports for CH₄ transport in the dominant species were distributed in shallower and more oxidative soil than occupied in the other zones. Spatial and temporal variation in CH₄ flux from the alpine wetland was determined by the vegetation zone. Among the dominant species in each zone, there were variations in the density and biomass of shoots, gas-transport system, and root-rhizome architecture. The CH₄ flux from a typical alpine wetland on the Qinghai-Tibetan Plateau was as high as those of other boreal and alpine wetlands.     

中国玉米化学氮肥利用率的时空变异特征

玉米生产对我国粮食安全意义重大。化学氮肥施用是保证玉米稳产高产的一个重要条件, 但过量施用也会导致环境问题, 所以化学氮肥的施用量和利用率一直是农业科学领域关注的一个重要课题。本文通过资料搜集、数据整理和分析, 探索中国过去几十年玉米各种植区化学氮肥的当季单位面积施用量(application rate, AR)和回收利用率(recovery efficiency, RE)、农学利用率(agronomic efficiency, AE)、偏生产力(partial factor productivity, PFP)的变异特征。结果表明: 在过去的几十年内, 中国玉米生产中当季AR总体呈增长趋势, 从1970s的93.3 kg·hm^-2持续增长至21世纪初的238.2 kg·hm^-2; RE和AE都呈下降趋势, 分别从1970s的42.1%和17.0 kg·kg^-1下降至21世纪初的26.4%和9.5 kg·kg^-1; PFP在各个时期均趋于稳定, 维持在40.0 kg·kg^-1左右。在全国各玉米种植区内, 北方春播玉米区的AR各时期均较其他各区低且增速缓慢, AE和RE则偏高; 黄淮海平原春、夏播玉米区的AR增速同全国平均增速基本持平, 较全国略高, AE和RE较全国平均水平低。另外, 本研究还证实平衡施肥、使用氮高效品种以及优化农业管理等举措可成为提高我国氮肥利用率、减少资源浪费和减轻环境污染的有效途径。     

Spatio-temporal variation of anisotropy of saturated hydraulic conductivity in a tilled sandy loam soil

Knowledge on anisotropy of saturated hydraulic conductivity can improve the understanding of transport phenomena in soil. We hypothesized that saturated hydraulic conductivity (K_s) in the upper part of the root zone of an agricultural sandy loam soil was anisotropic at different soil depths and times after tillage. K_s was measured on undisturbed 100 cm³ core samples taken in the horizontal and vertical directions in up to four soil layers (Surf: surface layer (0–5 cm); Top: topsoil (10–15 cm); Trans: transition layer between topsoil and subsoil; Sub: subsoil (40–60 cm)) 1, 8 and 32 months, respectively, after mouldboard ploughing and drilling. The ratio between estimated geometric mean values for K_s in the vertical and the horizontal directions (K_ms,v/K_ms,h) was used to test the hypotheses. A total of 669 soil samples were analysed.K_ms,v/K_ms,h varied with time after tillage and between soil layers. One month after ploughing, K_ms,v/K_ms,h was <0.23 (P = 0.975) in the Trans layer with an average value of 0.084, i.e. K_ms,h was 12 times larger than K_ms,v. Anisotropy could not be documented in this layer 8 or 32 months after ploughing, i.e. K_ms,v/K_ms,h was not significantly different from 1.0. For the Surf and Top layers 32 months after ploughing, K_ms,v/K_ms,h was in the intervals 1.4–50 and 3.1–77, respectively, (P = 0.95) with average values of 8.4 and 15, respectively. Thus, K_ms,v was 8.4 respectively 15 times larger than K_ms,h in the two layers. Anisotropy was not found in these layers 1 or 8 months after tillage. Strong anisotropy was found in the Sub layer with K_ms,v/K_ms,h averaging to 14 and 32, respectively, 8 and 32 months after tillage. K_ms,v and K_ms,h generally decreased with time in the Surf, Top and Trans layers, except in the vertical direction in the Top layer between 8 and 32 months after ploughing, and in the Trans layer between 1 and 8 months after ploughing. Overall, the geometric means of K_s varied between 10^−4.0 and 10^−7.1 m s⁻¹.The results may reflect systematic effects of soil settlement and drying/wetting phenomena coupled with biological activity and the existence of stable, vertically oriented biopores in the subsoil. It appears to be necessary to consider anisotropy of K_s and its variation in the analysis and modelling of water flow and chemical transport in agricultural soils, particularly to explain heterogeneous flow phenomena at the plot and field scales.     

冰川退缩迹地植被原生演替初期关键种的碳氮磷生态化学计量特征

[目的]对贡嘎山海螺沟冰川退缩迹地植被原生演替初期关键种柳叶菜(Epilobium hirsutum)和马河山黄芪(Astragalus mahoschanicus)碳氮磷含量及生态化学计量进行研究,掌握两关键种碳氮磷及其化学计量学特征,为预测未来在全球气候变化背景下冰川退缩区域环境变化及植被演替趋势研究提供理论支持....     

外来植物紫茎泽兰入侵对菌根菌群落的影响

为了研究紫茎泽兰(Ageratina adenophora)入侵对土壤菌根真菌(mycorrhizal fungi, MF)群落的影响,采用嵌套PCR 技术分析了外来植物紫茎泽兰入侵生境内土著植物群落、土著植物与紫茎泽兰混生群落、紫茎泽兰单优群落中, 侵染紫茎泽兰及土著植物的MF 群落结构, 及紫茎泽兰与土著植物根围土壤中MF 群落结构。结果表明, 紫茎泽兰不同入侵进程MF 群落结构存在差异, 其中, 从土著植物群落的植物根内检测到内养球囊霉(Glomus intraradices)型克隆; 从土著植物与紫茎泽兰混生群落的紫茎泽兰根内也检测到内养球囊霉型克隆, 而在土著植物根内检测到1 个球囊霉属(Glomus sp 2)型克隆; 从紫茎泽兰单优群落的紫茎泽兰根内未检测到MF, 但从其根围土壤中检测到2 个球囊霉属(Glomus sp 1 和Glomus sp 2)型克隆。在土著植物与紫茎泽兰混生群落中, 从紫茎泽兰根围土壤中检测到4 个克隆型, 分别为毛舌菌阔孢(Trichoglossum hirsutum)、皂味口磨(Tricholoma saponaceum)、亚盖趋本菌(Xylobolus subpileatus)和翘鳞肉齿菌(Sarcodon imbricatus), 从土著植物根围土壤中也检测到4 个克隆型, 分别为小皮伞(Camarophyllopsis hymenocephala)、肉色香蘑(Lepista irina)、皂味口磨及亚侧耳(Panellus serotinus)型克隆; 在土著植物群落中, 从根围土壤只检测到皂味口磨型克隆。紫茎泽兰入侵改变了土著MF 群落结构, 其中在土著植物占据的土壤中以外生菌根真菌为主, 而外来植物紫茎泽兰则更多地积累了丛枝菌根真菌。文中讨论了紫茎泽兰改变入侵地土壤菌根菌群落及其可能对紫茎泽兰入侵的反馈。     

Spatial patterns of soil biological and physical properties in a ridge tilled and a ploughed Luvisol

The present study was conducted to determine the spatial heterogeneity of bulk density, soil moisture, inorganic N, microbial biomass C, and microbial biomass N in the ridge tillage system of Turiel compared to conventional mouldboard ploughing on three sampling dates in May, July, and August. The soil sampling was carried out under vegetation representing the ridge in a high spatial resolution down the soil profile. Bulk density increased with depth and ranged from 1.3 g cm⁻³ at 10 cm depth to 1.6 g cm⁻³ at 35 cm in ploughed plots and from 1.0 g m⁻³ at 5 cm to 1.4 g m⁻³ at 35 cm in the ridges. In the ploughed plots, the contents of microbial biomass C and microbial biomass N remained roughly constant at 215 and 33 μg g⁻¹ soil, respectively, throughout the experimental period. The microbial biomass C/N ratio varied in a small range around 6.4. In the ridged plots, the contents of microbial biomass C and microbial biomass N were 5% and 6% higher compared to the ploughed plots. Highest microbial biomass C contents of roughly 300 μg g⁻¹ soil were always measured in the crowns in July. The lowest contents of microbial biomass C of 85–137 μg g⁻¹ soil were measured in the furrows. The ridges showed strong spatial heterogeneity in bulk density, soil water content, inorganic nitrogen and microbial biomass.     

Nitrogen transformations in cold and frozen agricultural soils following organic amendments

Though microbial activity is known to occur in frozen soils, little is known about the fate of animal manure N applied in the fall to agricultural soils located in areas with prolonged winter periods. Our objective was to examine transformations of soil and pig slurry N at low temperatures. Loamy and clay soils were either unamended (Control), amended with ¹⁵NH₄-labeled pig slurry, or amended with the pig slurry and wheat straw. Soils were incubated at −6, −2, 2, 6, and 10 °C. The amounts of NH₄, NO₃ and microbial biomass N (MBN), and the presence of ¹⁵N in these pools were monitored. Total mineral N, NO₃ and ¹⁵NO₃ increased at temperature down to −2 °C in the loam soil and −6 °C in the clay soil, indicating that nitrification and mineralization proceeded in frozen soils. Nitrification and mineralization rates were 1.8-4.9 times higher in the clay than in the loamy soil, especially below freezing point (3.2-4.9), possibly because more unfrozen water remained in the clay than in the loamy soil. Slurry addition increased nitrification rates by 3-14 times at all temperatures, indicating that this process was N-limited even in frozen soils. Straw incorporation caused significant net N immobilization only at temperatures ≥2 °C in both soils; the rates were 1.4-3.4 higher in the loam than in the clay soil. Nevertheless, up to 30% of the applied ¹⁵N was present in MBN at all temperatures. These findings indicate that microbial N immobilization occurred in frozen soils, but was not strong enough to induce net immobilization below the freezing point, even in the presence of straw. The Q₁₀ values for estimated mineralization and nitrification rates were one to two orders-of-magnitude larger below 2 °C than above this temperature (13-208 versus 1.5-6.9, respectively), indicating that these processes are highly sensitive to a small increase in soil temperature around the freezing point of water. This study confirms that net mineralization and nitrification can occur at potentially significant rates in frozen agricultural soils, especially in the presence of organic amendments. In contrast, net N immobilization could be detected essentially above the freezing point. Our results imply that fall-applied N could be at risk of overwinter losses, particularly in fine-textured soils.     

INFLUENCE OF SALINITY AND AMMONIUM: NITRATE RATIO ON GROWTH,PHOTOSYNTHESIS, FATTY ACID AND THE ACTIVITY OF ANTIOXIDATIVE ENZYMES IN CANOLA

The effects of sodium chloride (NaCl) salinity (0 and 200 mM) and ammonium (NH₄):nitrate (NO₃) ratios (100:0, 25:75, 50:50, and 75:25) on growth, photosynthesis, fatty acids and the activity of antioxidative enzymes were investigated in canola plants. Leaf area and fresh and dry weights of leaves were significantly reduced by the salinity. The reduction in vegetative characteristics varied in both salinized and unsalinized plants according to the NH₄:NO₃ ratios so that the lowest reduction was observed with the 50:50 (NH₄:NO₃) ratio. Increased NH₄ up to 50 percent (50:50) of total N, promotes the yield at both salinized and unsalinized plants. In both salinized and unsalinized plants, the increased NH₄ and NO₃ ratio in the nutrient solution reduced the photosynthetic (Pn) rate and stomatal conductance; however, the reduction in Pn rate was severely impaired at a higher ratio of NH₄ in the nutrient solution. In both salinized and unsalinized plants, the 75:25 ratio had the lowest potassium (K) and sodium (Na) content; however, the K/Na ratio was the highest in 50:50 ratio. An increase of NH₄ in the solution led to a significant increase in NH₄ content in both salinized and unsalinized plants. Salinity increased NH₄ content so that the salinized plant had nearly twice as high NH₄ content in the leaves. The activity of nitrate reductase was increased by increasing NH₄ from 0 to 50% and then reduced at a higher ratio of NH₄ in the solution. The activities of antioxidative enzymes increased in salinized plants regardless of the NH₄:NO₃ ratios. In salinized plants, the activities of superoxide dismutase and catalase enzymes were increased by 44.4 % and 97.5%, respectively. Within salinized and unsalinized treatments, the highest activities of all antioxidant were observed in 75:25 ratio, while they remained unchanged for all NH₄:NO₃ ratios. The increased NH₄ content in the solution increased the oil content and the maximum oil content in both salinized and unsalinized plant was obtained in both 50:50 and 75:25 ratios. The percentage of oleic acid was affected by both salinity and NH₄:NO₃ ratios. The ratios of NH₄:NO₃ had no effect on the protein content; however, salinity reduced the protein content by 20%.     

Accumulation of 60Co and 134Cs in Lake Whitefish in a Canadian Shield Lake

Radionuclides were added to the anaerobic hypolimnion of a Canadian Shield lake during the summer of 1989 to simulate nuclear fuel waste leakage into the bottom waters of a lake with deep groundwater flow. Lake whitefish (Coregonus clupeaformis) were sampled in mid-October each year from 1989 to 1994, except for 1992, to determine the concentration of ⁶⁰and ¹³⁴Cs in their tissues. The radionuclides remained in the hypolimnion until lake mixing in the autumn. Subsequently, there was more loss of ⁶⁰than¹³⁴Cs from the water. After one year, 4% of the⁶⁰Co and 15% of the ¹³⁴Cs remained in the water. This decreased to about 0.4% of the ⁶⁰and 0.6% of the ¹³⁴Cs in the water after five years. Little ⁶⁰and ¹³⁴Cs were present in lake whitefish the first autumn following the radionuclide addition. In fish, the highest concentrations were recorded in October, 1990, after which concentrations gradually decreased. Cobalt-60 concentrations were lower than ¹³⁴Cs concentrations, probably because ⁶⁰has a high affinity for organic particles and was not available for uptake. The relatively high ¹³⁴Cs concentrations in fish reflects its tendency to remain in the water and its continued availability to biota. Both ⁶⁰and ¹³⁴Cs concentrations were high in the soft tissues. Co-60 was mainly distributed in the flesh, gut, gill, kidney, and liver, whereas¹³⁴Cs was mainly distributed in the flesh. The occurrence of relatively high ¹³⁴Cs concentrations in lake whitefish five years after their addition to the lake, long after ¹³⁴Cs concentrations are no longer detectable in lake water, attests to the continued persistence of this contaminant in aquatic biota.     

Above- and belowground ecosystem biomass and carbon pools in an age-sequence of temperate pine plantation forests

We assessed the successional development of above- and belowground ecosystem biomass and carbon (C) pools in an age-sequence of four White pine (Pinus strobus L.) plantation stands (2-, 15-, 30-, and 65-years-old) in Southern Ontario, Canada. Biomass and C stocks of above- and belowground live and dead tree biomass, understorey and forest ground vegetation, forest floor C (LFH-layer), and woody debris were determined from plot-level inventories and destructive tree sampling. Small root biomass (<5 mm) and mineral soil C stocks were estimated from soil cores. Aboveground tree biomass became the major ecosystem C pool with increasing age, reaching 0.5, 66, 92, and 176 t ha⁻¹ in the 2-, 15-, 30-, and 65-year-old stands, respectively. Tree root biomass increased from 0.1 to 10, 18, 38 t ha⁻¹ in the 2-, 15-, 30-, and 65-year-old stands, respectively, contributing considerably to the total ecosystem C in the three older stands. Forest floor C was 0.8, 7.5, 5.4, and 12.1 t C ha⁻¹ in the 2-, 15-, 30-, and 65-year-old stands, respectively, indicating an increase during the first two decades, but no further age-effect during the later growth phase. Mineral soil C was age-independent with 37.2, 33.9, 39.1, and 36.7 t C ha⁻¹ in the 2-, 15-, 30-, and 65-year-old stands, respectively. Aboveground ecosystem C increased with age from 3 to 40, 52, and 100 t C ha⁻¹ in the 2-, 15-, 30-, and 65-year-old stands, respectively, due to an increase in aboveground tree biomass. Belowground ecosystem C remained similiar in the early decades after establishment with 37, 39, and 39 t C ha⁻¹ in the 2-, 15-, and 30-year-old stands, but increased to 56 t C ha⁻¹ in the 65-year-old stand due to an increase in root biomass. The difference in total ecosystem C between the 2- and 65-year-old stand was 116 t C ha⁻¹. Our results highlight the importance of considering the successional development of forest ecosystem C pools, when estimating C sink potentials over their complete life cycle.     

Physical properties of tsunami-affected soils in Aceh, Indonesia: 2½ years after the tsunami

On 26 December 2004, a tsunami caused extensive loss of life, damaged property and degraded agricultural land in the province of Aceh, Indonesia. While some of the associated soil chemical changes have been documented, information on soil physical properties is sparse. The objective of this study was to quantify physical properties of some tsunami-affected upland agricultural soils in Aceh, Indonesia. Soil was sampled approximately 21/2 years after the tsunami, from the 0–0.1 m, 0.1–0.3 m and 0.3–0.5 m depths in four sites in the villages of Kling Cot Aroun in Aceh Besar sub-district, Kuta Kruen in Aceh Utara sub-district, Udjong Blang Mesjid in Bireuen sub-district and Meue in Pidie Jaya sub-district on the east coast of Aceh. These sites were located within 1 km from the sea at elevations ranging from 0 to 5 m ASL. The soils were Ultisols except for Meue, which was an Entisol. Soil properties measured were bulk density, structural stability and particle size distribution. Soil water retention, pore-size distribution and saturated hydraulic conductivity were estimated by inserting the values of bulk density, clay, sand and silt contents into pedotransfer functions from the literature. The analyses conducted during this study did not permit us to ascertain what proportion of the soil particles were of tsunami-origin. Nonetheless, deposition of finer-textured material may have occurred in two of the sites. In comparison with the greyish-white, coarse textured soil in the rest of the profile, a finer-textured yellow horizon was present in the lower slopes of the Udjong Blang Mesjid site. At Meue, clay and silt contents were higher in the surface 0.3 m than in the 0.3–0.5 m depth, although a distinct horizon was absent. Particle size distribution in all sites was dominated by the sand fraction, although clay and silt contents were relatively high (20–30 g 100 g^− 1) at Kuta Kruen. Among the sand fractions, fine sand (0.02–0.25 mm) was highest at Kling Cot Aroun, Kuta Kruen and in the “yellow horizon” at Udjong Blang Mesjid, making them more prone to hardsetting and compaction after intensive tillage. Soil compaction was present in all sites with that in the “yellow horizon” at Udjong Blang Mesjid being highest. The relatively low porosity in this layer may be beneficial, as it is likely to reduce the high rates of water drainage and nutrient leaching in this sandy soil. The more compacted soils were characterised by higher numbers of micropores (r, pore radius < 4.3 μm), lower water retention at saturation, smaller numbers of macropores (r > 14.3 μm), lower hydraulic conductivity and intensive gleying, indicating frequent waterlogging. The soils in all depths from Kling Cot Aroun and the “yellow horizon” at Udjong Blang Mesjid were very dispersive, that at Meue moderately dispersive in the 0.3–0.5 m depth but stable in the 0–0.1 m depth, and at Kuta Kruen very stable in all depths. Soil physical degradation was a feature of the soils examined, and its amelioration will be the key to improving and sustaining crop yields in these soils. Possible management interventions include organic amendments such as compost or manure, and minimum tillage options such permanent beds or zero tillage with retention of crop residues as in situ mulch together with suitable cover crops.