玉米/蒜苗套作系统中土壤微生物和土壤酶状况分析

对玉米蒜苗套作根区进行隔膜、隔网和无隔处理以及各自单作处理,通过处理间的相互比较,分析影响套作产量的主要土壤因素。结果表明:套作蒜苗土壤微生物上升其主要原因是根系间的非接触物质交换;套作玉米除此外,地上部环境的改变也使根部土壤微生物数量上升。根系间的非接触效应还使蒜苗、玉米土壤过氧化氢酶、蔗糖酶活性提高,而环境因素的改变也使玉米过氧化氢酶,蒜苗脲酶活性提高。相关性分析表明:微生物对蒜苗根际土壤酶活性的影响大于对玉米土壤酶的影响。     

Organochlorine and Metal Accumulation in Fish (Phoxinus phoxinus) Along a North-South Transect in the Alps

Southern populations of the European minnow fromremote oligotrophic mountain lakes along an Alpinenorth-south transect accumulated more p,p DDE andPCBs than northern populations. As these semi-volatileorganochlorines predominantly evaporate in warmcountries, higher rates of condensation (deposition)are assumed to occur in the southern slopes of theAlps. The higher accumulation of lead and cadmium insouthern population is rather attributed to geogenicand specific environmental impacts than to atmosphericdeposition. Increasing liver ratios of [glutathionedisulfide]/[glutathione], a potential indicator foroxidative stress, from north to south reflect thegenerally higher toxic load at remote sites at thesouthern edge of the Alps. However, histopathologicalchanges in the liver did not correlate withaccumulated toxicants indicating that deposition doesnot lead to severe lesions but induces specificmechanisms for detoxification.     

新型有机肥的氮素在土壤中的转化及其对草莓生长和品质的影响

土壤中硝态氮和铵态氮的含量直接影响着作物的生长和品质。通过田间试验研究了不同有机肥料氮素在土壤中的转化及其对草莓生长和果实品质的影响。结果表明,施用有机肥可以提高草莓苗期土壤硝态氮的比例,硝铵比值大于尿素处理,同时有机肥处理硝铵比值从苗期至盛花期呈下降趋势,但尿素处理则表现为上升的趋势,而花序现蕾期土壤硝铵比的降低,有利于植株花蕾的形成,因此土壤硝铵比值的变化趋势一定程度上决定着草莓的产量和品质。在等量施用氮素养分的条件下,施用有机肥料均较尿素更能促进草莓生长发育和增加草莓产量。施用有机肥对草莓品质的改善作用也优于尿素,果实中糖/酸比值较无肥区提高23.7%-28.7%,较尿素区提高16.5%-21.2%。     

Radiocesium transfer from Andosols to brown rice in the northern and northwest areas of Tochigi Prefecture,in the first 3 years following the 2011 Fukushima Daiichi nuclear power plant accident

ABSTRACT

Following the Fukushima Daiichi Nuclear Power Plant accident of 2011, the potential for radiocesium transfer from contaminated soils, such as Andosols, to agricultural crops became a significant concern. Andosols account for up to 70％ of paddy soils in the northern and northwest areas of Tochigi Prefecture, where the radiocesium concentration is 1000 Bq kg^?1 or greater in the soil of some fields. The present study was carried out in order to determine the phytoavailability of radiocesium in Andosols by comparing it with that of gray lowland soils in the first 3 years following the accident. The transfer factor (TF) tended to be higher in Andosols than in gray lowland soils, leading to higher radiocesium concentrations in brown rice grown in Andosols. The exchangeable potassium (Ex-K₂O) in Andosols was highly and negatively correlated with TF, followed by clay. The Ex-K₂O value was positively correlated with the clay/total carbon (T-C) value, suggesting that a high T–C ratio could weaken K₂O adsorption on clay mineral sites; hence, the low clay/T-C values can partially explain the relatively large TF values of Andosols. Samples with Ex-K₂O contents less than 200 mg kg^?1 and with low clay/T-C values showed striking decreases in TF values from 2011 to 2012. However, the decrease from 2012 to 2013 was quite small; radiocesium in these samples was potentially available for rice uptake for a long time, likely due to the reversible adsorption and fixation characteristics of allophane. Most gray lowland soil samples showed very low TF values over the 3 years of the study, except for those with TF values greater than 0.1 due to low Ex-K₂O and clay contents; the geometric mean (GM) value of TF was below 0.01 in 2012. The extraction of exchangeable radiocesium (Ex-Cs) with a 1 mol L^?1 ammonium acetate solution may not be an appropriate method for explaining the variability in radiocesium TF in Andosols. This is because the Ex-Cs value was significantly correlated with Ex-K₂O in Andosols, but not in gray lowland soils, indicating that Ex-K₂O explained this variability in relation to Ex-Cs.     

A new yam bean (Pachyrhizus spp.) interspecific hybrid

The yam bean (Pachyrhizus spp.) is a legume tuber / root crop locally grown in Central America, South America and Asia. The tuber is usually consumed raw for its refreshing taste and high moisture content. A recently found P. tuberosus type from a small ecogeographic region in the tropical lowlands of Peru has a high tuber dry matter content and this so-called Chuin-Type is consumed like manioc. This study was conducted to determine the possibility to use the Chuin-Type as a source to incorporate high dry matter into the remaining yam bean gene pool. Three P. tuberosus (Chuin) accessions were crossed with 15 P. ahipa accessions from the Andean highlands resulting in six successful interspecific hybridisations. Successful crosses were confirmed by morphological and agronomical traits as well as multivariate statistics. All hybrid plants were fertile and vigorous. Owing to the fertility and vigour of interspecific hybrids it is assumed that a hybrid between P. tuberosus and P. ahipa might already evolved in the area of origin and that interspecific hybridisation is appropriate to improve the tuber dry matter content in the yam bean which might give the crop new forms of food and processing use.     

Effect of molecular complexity and acidity of earthworm faeces humic fractions on glutamate dehydrogenase,glutamine synthetase,and phosphoenolpyruvate carboxylase in Daucus carota α II cells

Carrot cells were grown in cultures supplemented with two hormones [2,4-dichlorophenoxyacetic acid (2,4-D) and 6-benzylaminopurine (6BAP)] and two humic fractions extracted from earthworm faeces, one with high acidity and a low apparent molecular size (<3500) and the other with low acidity and a large molecular size. 2,4-D stimulated growth through an effect on cell enlargement, while the strongly acidic humic fraction (0.2 mg l^-1) and the weakly acidic fraction (1 mg l^-1) were both less effective. With 4–16 h of pre-incubation, the highly acid humic fraction, mainly alone, induced the best increase in protein content; the effect of the weakly acid humic fraction and the hormones was generally less important. The two humic fractions also differed in their influence on glutamate dehydrogenase activity. After 2 h of pretreatment, the highly acidic fraction increased glutamate dehydrogenase activity, while the other fraction did not affect it. After 4–16 h of pre-incubation, the activity of this enzyme was still not influenced by these humic fractions. The presence of the two hormones did not interfere with the humic matter effects. Glutamine synthetase activity was not affected by a pre-incubation of up to 4 h with the two humic fractions, but it was stimulated after 8–16 h of pre-incubation. A 2,4-D+6BAP mixture stimulated glutamine synthetase activity (from +12 to +50%). Again, the presence of the hormones did not interfere with the effects induced by the humic fractions. After 16 h of pre-incubation, phosphoenolpyruvate carboxylase activity was increased by the highly acidic humic fraction (+93%) and by both humic fractions together (+34%). An explanation of the different incubation times necessary for the humic fractions to exert stimulatory effects on these enzymes is proposed here. The regulatory properties of the strongly acidic humic fraction appeared to depend on the combination of high acidity (expecially carboxylic C) with low molecular size.     

A GC/MS method for the assessment of N and C incorporation into soil amino acid enantiomers

Identifying the transformation process of amino acid enantiomers was essential to probe into the fate, turnover and aging of soil nitrogen due to their important roles in the biogeochemical cycling. If this can be achieved by differentiating between the newly biosynthesized and the inherent compounds in soil, then the isotope tracer method can be considered most valid. We thereby developed a gas chromatography/mass spectrometry (GC/MS) method to trace the ¹⁵N or ¹³C isotope incorporation into soil amino acid enantiomers after being incubated with ¹⁵NH₄⁺ or U-¹³C-glucose substrates. The most significant fragments (F) as well as the related minor ions were monitored by the full scan mode and the isotope enrichment in amino acids was estimated by calculating the atom percentage excess (APE). ¹⁵NH₄⁺ incorporation was evaluated according to the relative abundance increase of m/z F+1 to F for neutral and acidic amino acids and F+2 to F (mass 439) for lysine. The assessment of ¹³C enrichment in soil amino acids was more complicated than that of ¹⁵N due to multi-carbon atoms in amino acid molecules. The abundance ratio increment of m/z F+n to F (n is the original skeleton carbon number in each fragment) indicated the direct conversion from the added glucose to amino acids, but the total isotope incorporation from the added ¹³C can only be calculated according to all target isotope fragments, i.e. the abundance ratio increment summation from m/z (Fa+1) through m/z (Fa+T) represented the total incorporation of the added ¹³C (Fa is the fragment containing all original skeleton carbons and T is the carbon number in the amino acid molecule). This method has a great advantage especially for the evaluation of high-abundance isotope enrichment in organic compounds compared with GC/C/IRMS. And in principle, this technique is also valid for amino acids besides enantiomers if stereoisomers are not concerned. Our assessment approach could shine a light on investigating the biochemical mechanism of microbial transformation of N and C in soils of terrestrial ecosystem.     

缓/控释氮素肥料玉米苗期养分释放特点

采用盆栽试验．模拟田间生态环境．研究施用不同种缓／控释氮素肥料玉米苗期土壤尿素态氮、硝态氮、铵态氮和速效态氮含量，分析比较其在玉米苗期氮素养分释放特点。研究表明，在玉米苗期，施用醋酸酯淀粉包膜脲酶抑制剂nBPT涂层尿素肥料。土壤中尿素态氮和铵态氮的积累量最多．分别为21．72mg／kg和48．31mg／kg；醋酸酯淀粉包膜尿素肥料，硝态氮和速效氮含量最多．分别为102．90mg／kg和135．25mg／kg；丙烯酸树脂包膜脲酶抑制剂nBPT涂层尿素肥料，尿素自膜内迁移到土壤中的量较少，硝态氮和速效态氮含量最少。分别为53．74mg／kg和93．70mg／kg。包膜与脲酶抑制剂nBPT相结合的缓／控释肥料，对减少土壤石硝态氮的生成效果最为明显．明显优于其他缓／控释肥料．丙烯酸树脂包膜nBPT涂层尿素肥料控释效果最好。     

田林老山中山杉木人工林生产力及营养元素循环的研究

广西田林县老山林场中山区气候冷凉潮湿,土壤肥力较高,能满足杉木速生要求。17年生杉木人工林乔木层的生物量达138.46t/ha,平均净生产量为8.15t/ha·a,与杉木中心产区相当。乔木层对N,P,K,Ca,Mg5种营养元素的吸收量为224.04kg/ha·a,其中42.3％存留在林木层,42.5％通过凋落物,15.2％通过降雨淋洗归还土壤。通过凋落物归还是N,P,Ca,Mg归还的主要途径,K的归还主要通过降雨淋洗;K,Ca,Mg的循环系数较大,分别达到0.58,0.68和0.60;N,P相对较小,分别为0.48和0.33。林木正处于生长旺盛阶段,杉木对5种营养元素的吸收量、存留量和归还量以及循环系数都有较高水平,生物量积累也较大。     

Organic C and N stabilization in a forest soil: Evidence from sequential density fractionation

In mineral soil, organic matter (OM) accumulates mainly on and around surfaces of silt- and clay-size particles. When fractionated according to particle density, C and N concentration (per g fraction) and C/N of these soil organo-mineral particles decrease with increasing particle density across soils of widely divergent texture, mineralogy, location, and management. The variation in particle density is explained potentially by two factors: (1) a decrease in the mass ratio of organic to mineral phase of these particles, and (2) variations in density of the mineral phase. The first explanation implies that the thickness of the organic accumulations decreases with increasing particle density. The decrease in C/N can be explained at least partially by especially stable sorption of nitrogenous N-containing compounds (amine, amide, and pyrrole) directly to mineral surfaces, a phenomenon well documented both empirically and theoretically. These peptidic compounds, along with ligand-exchanged carboxylic compounds, could then form a stable inner organic layer onto which other organics could sorb more readily than onto the unconditioned mineral surfaces (“onion” layering model).To explore mechanisms underlying this trend in C concentration and C/N with particle density, we sequentially density fractionated an Oregon andic soil at 1.65, 1.85, 2.00, 2.28, and 2.55 g cm⁻³ and analyzed the six fractions for measures of organic matter and mineral phase properties.All measures of OM composition showed either: (1) a monotonic change with density, or (2) a monotonic change across the lightest fractions, then little change over the heaviest fractions. Total C, N, and lignin phenol concentration all decreased monotonically with increasing density, and ¹⁴C mean residence time (MRT) increased with particle density from ca. 150 years to >980 years in the four organo-mineral fractions. In contrast, C/N, ¹³C and ¹⁵N concentration all showed the second pattern. All these data are consistent with a general pattern of an increase in extent of microbial processing with increasing organo-mineral particle density, and also with an “onion” layering model.X-ray diffraction before and after separation of magnetic materials showed that the sequential density fractionation (SDF) isolated pools of differing mineralogy, with layer-silicate clays dominating in two of the intermediate fractions and primary minerals in the heaviest two fractions. There was no indication that these differences in mineralogy controlled the differences in density of the organo-mineral particles in this soil. Thus, our data are consistent with the hypothesis that variation in particle density reflects variation in thickness of the organic accumulations and with an “onion” layering model for organic matter accumulation on mineral surfaces. However, the mineralogy differences among fractions made it difficult to test either the layer-thickness or “onion” layering models with this soil. Although SDF isolated pools of distinct mineralogy and organic-matter composition, more work will be needed to understand mechanisms relating the two factors.