Water-stable aggregates and associated organic matter in forest,savanna, and cropland soils of a seasonally dry tropical region,India

The study was undertaken to quantify the distribution of soil in different size fractions of water-stable aggregates, and organic C, total N, and total P associated with these aggregates, along a gradient of forest-savanna-cropland in the Indian dry tropics. The effect of residue (wheat straw) amendment under dryland cultivation was also investigated. Proportions of macroaggregates (>0.3 mm) were highest in the forest and lowest in the cropland soil and ranged from 58–66% in forest, to 55% in savanna and 25–36% in cropland. In contrast, microaggregates (<0.3 mm) were highest in cropland (64–75%), followed by savanna (45%), and lowest in forest soil (34–42%). Organic C, total N, and total P associated with the macroaggregates ranged from 6.52–29.56, to 0.62–2.44 and 0.06–0.15 g kg^-1 soil, respectively, while the respective values in microaggregates were 4.99–22.11, 0.42–2.01, and 0.07–0.19 g kg^-1 soil. This study indicates that land-use changes (conversion of forest into savanna and cropland) reduce the organic matter input to the soil and the proportion of macroaggregates. The application of wheat straw did not significantly influence the organic C and total N levels (P>0.05) in the short term, although the proportion of macroaggregates increased, indicating an improvement in soil structure. Thus soil degradation after conversion of natural systems to cropland can be arrested up to some extent by residue input to the soil.     

蒋家沟泥石流源区土壤团聚体微结构与结构性

 云南东川蒋家沟泥石流源区的土壤是团聚体结构性很强的特殊土壤,孔隙比高,液限低,并有强烈的分散性,在环境扫描电镜下的微观结构表明:原状土壤团聚体具有3种孔隙类型,沿着孔隙溶蚀现象明显,骨架颗粒之间普遍存在架空结构,胶结物联结强度较弱。通过对土壤团聚体在原状、饱和、重塑3种状态下进行室内压缩试验,并引入综合结构势,分析土壤团聚体的结构性。结构性参数曲线在加载初期下降显著,在加载后期则变得十分平缓,表明蒋家沟泥石流源区土壤团聚体具有较强的结构性,容易发生结构失稳。因此,微观结构特性与结构性对土壤团聚体的稳定性有重要的作用。     

不同改良剂对黄绵土水稳性团聚体的改良效果及其机制

通过室内土柱培养,采用聚丙烯酰胺(Polyacrylamide,PAM)、沃特保水剂、β-环糊精、腐殖酸等4种土壤结构改良剂对黄绵土水稳性团聚体进行改良。结果表明:4种改良剂均可促进>0.25 mm水稳性团聚体的形成,在浓度0.05%～0.40%范围内,其改良效果表现为PAM>β-环糊精>沃特保水剂>腐殖酸,且黄绵土团聚体分形维数显著降低,尤以PAM改良效果最明显;在低浓度条件下,4种改良剂均可有效地降低土壤密度;土壤粒径分布表明,PAM改良黄绵土水稳性团聚体的机制是使<1 mm粒径的团聚体团聚为更大的团聚体,尤其是团聚为>5 mm的团聚体,PAM在4种改良剂中对黄绵土改良效果最好。阐明不同改良剂对黄绵土水稳性团聚体的改良效果及机制,可为合理利用改良剂改良土壤结构提供理论依据。     

Incorporation of heavy metals by the mud snail,Cipangopaludina chinensis malleata Reeve,in submerged paddy soil treated with composted sewage sludge

Summary The biomass of newborn snails was higher in paddy soil without rice plants than in the soil with rice plants. There was an inverse correlation between shell width and concentratins of Zn and Cu in snail flesh. The Zn and Cu concentrations in snail flesh were extremely high compared with those in the paddy soil surrounding the snails, possibly because snails ingest sludge, one of the main components of the composts. These results suggest that this type of snail may be used to eliminate Zn and Cu from paddy soil when composted sewage sludge has been applied.     

新疆策勒不同类型流动和半流动沙丘运移规律

通过对新疆策勒流动沙丘地、半流动沙丘地、砾质戈壁不同类型流动沙丘进行观测,研究了不同下垫面不同类型流动沙丘年运移速度、方向及其规律,为沙丘运移规律及保护绿洲生态安全提供理论依据。结果表明:沙漠—绿洲过渡带流动和半流动沙丘年平均前移距离为4.76~12.92m,半流动沙丘比流动沙丘前移速度明显减小,沙丘移动方向为东南东(99.82°—115.48°)。砾质戈壁2 m高新月形流动沙丘年移动距离为9.37 m,年移动方向为东南东(105.1°)。0.9m高盾状沙丘年运移距离19.15m,移动方向为东南东(93.77°),流动沙丘移动方向与年合成输沙势方向东南东(108°)基本一致,沙丘高度与运移速度呈二次函数反比关系。如果不采取有效的防沙措施,流动沙丘将会对策勒绿洲产生潜在的入侵威胁。     

Effects of transient anaerobic conditions in the presence of acetylene on subsequent aerobic respiration and N2O emission by soil aggregates

Our objective was to assess the effect of anaerobic conditioning in the presence of acetylene on subsequent aerobic respiration and N₂O emission at the scale of soil aggregates. Nitrous oxide production was measured in intact soil aggregates Δ (compacted aggregates without visible porosity) and Γ (aggregates with visible porosity) incubated under oxic conditions, with or without anaerobic conditioning for 6 d. N₂O emissions were much higher in aggregates that had been submitted to anaerobic conditioning than in aggregates that did not experience this conditioning, although very little NO₃⁻ remained in soil after the anaerobic period. ¹⁵N isotope tracing technique was used to check whether N₂O came from nitrification or denitrification. The results showed that denitrification was the major process responsible for N₂O emissions. The aerobic CO₂ production rate was also measured in intact soil aggregates. It was greater in aggregates submitted to anaerobic conditioning than in those that were not, suggesting that the anaerobic conditioning lead to an accumulation of small compounds including fatty acids that are readily available for microbial decomposition in aerobic conditions. This process increases the aerobic CO₂ production and favours the N₂O emissions through denitrification.     

黄河乌兰布和沙漠段沿岸不同高度典型沙丘风沙特征

为探究乌兰布和沙漠沿黄段典型沙丘的风速流场与风沙运移特征,以3座不同高度的典型沙丘为研究对象,对沙丘不同部位5个高度的风速流场、风速廓线、风速加速率及输沙量进行了测定。结果表明:(1)风速从沙丘迎风坡脚至背风坡坡脚呈现先增大后减小再增大的"S"型趋势,沙丘顶部风速最大,背风坡中部最小。(2)沙丘各部位风速的垂直变化与高度的对数值呈V=aln(z)+b线性变化规律,风速廓线斜率a由沙丘顶部向迎风坡脚与背风坡脚逐渐增大。不同高度沙丘的摩阻流速与粗糙度变化趋势不一。(3)沙丘发育尺度对沙丘迎风坡风速加速率影响明显,其沙丘发育尺度越大,对气流的反馈作用越强,迎风坡低层20cm风速加速率明显高于高层风速加速率;(4)沙丘不同部位0~100cm的输沙率随高度呈幂函数规律递减,输沙量主要集中在0~10cm内,但不均匀,大部分集中在0~4cm,且在距地高度约4~5cm处是相对输沙量不随高程变化的不变层。     

Particulate organic matter in water stable aggregates formed after the addition of C-labeled maize residues and wetting and drying cycles in vertisols

Development of soil structure and the dynamics of water stable aggregates (WSA) in many soils are known to be closely related to the cycling of soil organic matter. In some fine and medium textured soils particulate organic matter (POM) has been found to act as a nucleus for macroaggregate formation. However, this role of POM in aggregate formation has not been demonstrated in soils dominated by smectitic clay minerals. This study explored aggregation processes in a Vertisol from a semi-arid region in Northeastern Mexico in relation to the addition of ¹⁴C-labeled maize residues and application of wetting and drying cycles during 105 days of incubation. Fractionation of the WSA formed showed that labeled residues were preferentially accumulated in large macroaggregates (>2000 μm). Treatments with addition of organic residues had three to four times more intra-aggregate particulate organic matter (iPOM) in large macroaggregates than the control after 14 days of incubation. Residue-derived carbon accounted for 53% and 41% of the total carbon stored in the iPOM fraction in amended treatments with and without wetting and drying cycles, respectively. Conversely, residue-derived carbon represented <20% of the total carbon in the iPOM fraction from small macroaggregates (250-2000 μm) and microaggregates (53-250 μm). Results also showed that the amount and concentration of carbon per large macroaggregate did not differ between the large macroaggregates formed under wetting and drying and those formed in continuous moist conditions. However, due to formation of higher number of large macroaggregates per kg of soil, more carbon could be stored in amended soils under wetting and drying than in constantly wet soil: 1.4, 1.8 and 2.7 times more ¹⁴C kg⁻¹ soil after 14, 58 and 105 incubation days, respectively. The results in this study suggest that wetting and drying enhanced protection of the added maize residues inside large macroaggregates by forming more aggregates, rather than by increasing the amount of POM entrapped per aggregate. Therefore, after the addition of organic residues, this soil could accumulate more C than continuous moist soil through the influence that wetting and drying has on soil aggregation.     

Mercury Cycling in an Urbanized Watershed: The Influence of Wind Distribution and Regional Subwatershed Geometry in Central Indiana,USA

The global cycle of mercury (Hg) is reasonably well-understood, as are some of the natural and anthropogenic sources of Hg to the atmosphere. Less well understood are the regional and local characteristics of Hg deposition and subsequent watershed-scale transport, important parameters for assessing human risk to various avenues of Hg exposure. This study employed a two-part strategy for understanding coupled deposition and transport processes in central Indiana (USA), including Indianapolis, a typical large city with multiple coal-fired electric utilities and other Hg emission sources. A spatial analysis of Hg concentrations in surface soils revealed elevated Hg proximal to many of the large emission sources, with a distribution aligned along a southwest-northeast axis corresponding to the mean wind direction in this region. This soil distribution suggests some local depositional impact from local utilities, with wind modification affecting the regional pattern. Post-depositional transport of Hg was assessed using a series of streambank sampling arrays as the White River and various tributaries travelled through the urban core of Indianapolis. Streambank sediments had peak Hg concentrations in the urban core, where several local sources are present and where a number of subwatersheds join the main trunk of the White River, suggesting local emission and/or rapid Hg transport from urban subwatersheds due to their relatively high proportion of impervious surfaces. High Hg values persist in White River sediments into rural areas tens of kilometers south of Indianapolis, raising concerns for anglers collecting fish in this apparently “pristine” environment.     

Influence of cultivation on the distribution of phosphorus in three soils from NE Scotland and their aggregate size fractions

Abstract. The effect of cultivation on the P properties of whole soils and aggregate sizes separated from them was investigated for soil developed on three types of parent material. Cultivation, with associated fertilizer additions, increased both the total soil P content and extractable P of the whole soils. When the soils were separated into aggregate sizes (< 2, 2-52, 53-150 and 151 2000 μm), total soil P and resin extractable P increased with decreasing aggregate size. Water extractable inorganic P exhibited the opposite trend, while concentrations of water extractable organic P were similar from each aggregate size. Eroded aggregates can adsorb P or release P to solution, the extent of which will be dependent upon a combination of soil attributes and the prevailing solution conditions. The resulting equilibrium P concentration (EPC) of the eroded material will be markedly different from that of the whole soil. By increasing the P content, particularly of the smaller sized aggregates it is likely that the EPC of the eroded material would favour greater P desorption.     

Bifidobacteria: genetic modification and the study of their role in the colon

Bifidobacteria are among the most common bacteria in the human intestine and are thought to have a positive effect on human health. Therefore, there is an increasing interest in using these microorganisms as probiotics, either in fermented dairy products or formulated as tablets. However, convincing scientific data supporting their health claims are scarce. The study of the role of bifidobacteria in the colon is complicated by the fact that they are part of a complex ecosystem also interacting with the human host and by the fact that their in vivo study encounters many ethical constraints. Several tools have been developed at TNO with which the role of bifidobacteria can be studied. These include (i) an efficient transformation protocol for the introduction of foreign DNA into Bifidobacterium strains and (ii) in vitro models of the stomach/small intestine (TIM-1) and large intestine (TIM-2), creating an environment closely resembling that of the in vivo situation. With these tools, biomarkers from bifidobacteria quantifying their positive effect on gut health can be identified.     

The role of organic horizons and canopy to modify the chemistry of acidic deposition in some forest ecosystems

To clarify the mechanisms of pH buffering in forest ecosystems, field observations of pH and ionic concentrations in precipitation (R), throughfall (Tf), stemflow (Sf), and leachates from organ c horizons (Lo) were conducted for three years at three stands in Tomakomai (TK) and Teshio (TS) in Hokkaido, northern Japan. Weighted mean rates of H⁺ input as wet deposition at TK and TS were estimated in the range from 0.3 to 1.0 and 0.4–0.6 kmol_c ha^?1 y^?, respectively. While the net H⁺ flux was reduced significantly by the forest canopy, net fluxes of other ions by throughfall, especially for Na⁺, Cl^?, and SO₄ ^2?, were apparently greater than those by precipitation. The canopy modification of the H⁺ flux was more remarkable under deciduous stands than under coniferous stands, suggesting that the efficiency of conifers as the collectors of dry deposition is greater than that of deciduous ones. More than 50% of H⁺ flux due to throughfall was absorbed by the organic horizons and the weighted mean pH of Lo at TK and TS was in the range from 4.9 to 5.5 and 5.0–5.5, respectively. Results from field observation and field leaching experiments, showed that the major H⁺ sinks of the organic horizons are exchange reaction of Ca²⁺, Mg²⁺ and K⁺. Organic acids or organo-metallic complexes of lower pK(=5.0–5.5) played a significant role as counter anions in O horizons leachate in coniferous forests. Our results indicate the importance of biogeochemical modifications in the canopy and organic horizon in acid buffering mechanisms of forest ecosystems.     

Changes in the nitrogen localized in the lamellae systems and stroma of rice chloroplast accompanying the stages of growth

The change in the nitrogen localized in the lamellae systems and stroma region of the rice chloroplast was pursued throughout the stages of growth and, further, the relationship between the composition of the chloroplast and leaf N content was examined. A common trend accompanying the stages of growth is recognized: that in the early stages of growth the amount of nitrogen existing as a form of stroma N is larger than that of lamellae N. Thereafter, stroma N tends to decrease in relation to lamellae N and finally, lamellae N becomes a dominant nitrogenous fraction in the chloroplast. The change in the composition of the chloroplast seems to be brought about by a change in the nitrogen metabolism of the chloroplast by which the distribution of absorbed nitrogen among the nitrogenous fractions of the chloroplast differs.     

Are the links between soil aggregate size class, soil organic matter and respiration rate artefacts of the fractionation procedure?

Our aim was to see how variations in aggregate fractionation procedures influence the chemical and biological properties of different sized soil aggregates. Soil was fractionated using two different physical procedures: (1) slaking to simulate a major wetting stress in the field or (2) shaking to simulate mechanical disruption by tillage followed by wet sieving. In the slaked treatment, macro-aggregates (<250 μm dia) contained about 17% more soil organic C and had about 30% faster rates of respiration. This was in contrast to the shaken treatment where micro-aggregates (<250 μm dia) contained about 12% more soil organic C and had about 14% faster rates of respiration. The biological and chemical properties of different sized aggregates were used to describe two different models. These were the aggregate heirarchy model and one based on maximum biological activity at soil surfaces. Our results suggest that the chemical and biological properties of aggregates depend on the fractionation procedure. On this basis we suggest that the observed relationships between aggregate size and other properties, for example biological activity, must be interpreted in terms of the disruptive mechanisms used to fractionate aggregated soil. Our results suggest that the aggregate hypothesis has serious weaknesses: the aggregates measured being largely an artefact of the chosen method of separation. We therefore suggest that future work should also consider biological activities at soil pore surfaces. It is at the surface of these channels that parameters such as oxygen supply, plant roots, root exudates and fresh organic matter inputs first interact with the soil. Biological processes in this region are therefore likely to be more important than those occurring in the bulk soil.     

Thermal decomposition of specifically phosphorylated D-glucoses and their role in the control of the Maillard reaction

One of the main shortcomings of the information available on the Maillard reaction is the lack of knowledge to control the different pathways, especially when it is desired to direct the reaction away from the formation of carcinogenic and other toxic substances to more aroma and color generation. The use of specifically phosphorylated sugars may impart some elements of control over the aroma profile generated by the Maillard reaction. Thermal decomposition of 1- and 6-phosphorylated glucoses was studied in the presence and absence of ammonia and selected amino acids through pyrolysis/gas chromatography/mass spectrometry using nonpolar PLOT and medium polar DB-1 columns. The analysis of the data has indicated that glucose-1-phosphate relative to glucose undergoes more extensive phosphate-catalyzed ring opening followed by formation of sugar-derived reactive intermediates as was indicated by a 9-fold increase in the amount of trimethylpyrazine and a 5-fold increase in the amount of 2,3-dimethylpyrazine, when pyrolyzed in the presence of glycine. In addition, glucose-1-phosphate alone generated a 6-fold excess of acetol as compared to glucose. On the other hand, glucose-6-phosphate enhanced retro-aldol reactions initiated from a C-6 hydroxyl group and increased the subsequent formation of furfural and 4-cyclopentene-1,3-dione. Furthermore, it also stabilized 1- and 3-deoxyglucosone intermediates and enhanced the formation of six carbon atom-containing Maillard products derived directly from them through elimination reactions such as 1,6-dimethyl-2,4-dihydroxy-3-(2H)-furanone (acetylformoin), 2-acetylpyrrole, 5-methylfurfural, 5-hydroxymethylfurfural, and 4-hydroxy-2,5-dimethyl-3-(2H)-furanone (Furaneol), due to the enhanced leaving group ability of the phosphate moiety at the C-6 carbon. However, Maillard products generated through the nucleophilic action of the C-6 hydroxyl group such as 2-acetylfuran and 2,3-dihydro-3,5-dihydroxy-4H-pyran-4-one were retarded, due to the blocked nucleophilic atom at C-6.     

海泡石对镉污染土壤团聚体稳定性和有机碳含量的影响

通过大田试验,研究了在镉污染菜地原位钝化修复过程中海泡石对土壤团聚体组成和稳定性以及有机碳含量影响。结果表明,与对照相比,施用海泡石后整体上减少了5~8mm和0.25mm级别团聚体的数量,而2~5,1~2,0.5~1,0.25~0.5mm级别团聚体数量则不同程度增加,且随着海泡石施用量增加,其数量呈显著增加(P0.05)。在0—15cm土层中,土壤团聚体的平均质量直径(MWD)和几何平均直径(GMD)随海泡石施加浓度增加呈现先增加后降低,而在15—20cm土层中则有所降低。施用低浓度海泡石(0.5%)时,土壤有机碳(SOC)含量有所减少,最大降低了21.1%,而当海泡石添加剂量达到1%(H_1)和1.5%(H_(1.5))后,土壤有机碳含量整体上有所提高,较对照相比,最大增幅分别达到2.9%和70.3%。与对照相比,施用海泡石后增加了大团聚体中土壤有机碳的贡献率。     

Mineralisation of C and N from root, stem and leaf residues in soil and role of their biochemical quality

The influence of biochemical characteristics of 15 crop residues on C and N mineralisation in soil was investigated by following the decomposition of roots, stems and leaves of four subtropical species and one temperate species buried into the soil. The C, N and polyphenols contents were measured in different biochemical pools obtained from residues of the different organs. The mineralisation of root C was significantly lower than that of leaves and stems. Chemical analysis showed a higher polyphenol content in the leaves and a higher ligninlike content in the roots. Carbon and N mineralisation were simulated with the STICS decomposition submodel and tested against the data set. The model predicted leaf and stem C mineralisation for all five species fairly accurately, but failed to predict root C mineralisation, indirectly revealing the more complex composition of the root tissue. The results showed the interest of separately considering the different plant parts when studying plant residue decomposition and the need to develop other methods of residue quality characterisation to improve the prediction of residue decomposition.