The sensitivity of a large number of variable charge soils to acid rain was evaluated through examining pH-H2SO4 input curves. Two derivative parameters, the consumption of hydrogen ions by the soil and the acidtolerant limit as defined as the quantity of sulfuric acid required to bring the soil to pH 3.5 in a 0.001mol L-1 Ca(NO3)2 solution, were used. The sensitivity of variable charge soils was higher than that of constant charge soils, due to the predominance of kaolinite in clay mineralogical composition. Among these soils the sensitivity was generally of the order lateritic red soil > red soil > latosol. For a given type of soil within the same region the sensitivity was affected by parent material, due to differences in clay minerals and texture. The sensitivity of surface soil may be lower or higher than that of subsoil, depending on whether organic matter or texture plays the dominant role in determining the buffering capacity. Paddy soils consumed more acid within lower range of acid input when compared with upland soils, due to the presence of more exchangeable bases, but consumed less acid within higher acid input range, caused by the decrease in clay content. 相似文献
Sequence variation of nuclear internal transcribed spacer regions of ribosomal DNA (ITS1, 5.8S rRNA and ITS2) from Chinese
vegetable mustards (AB-genome) and its putative parents Brassica rapa (the A-genome) and Brassica nigra (the B-genome) were used to investigate the molecular phylogeny and the probable evolutional pattern of this amphidiploid
species that uniquely formed in China. Totally, 16 accessions of Chinese vegetable mustard those covering nearly all the diverse
variations were included in this study, and together with three accessions of B. rapa and one accession of B. nigra. The results disclosed two strongly supported clades, one containing four accessions of vegetable mustard which have closer
relationship with B-genome species “B.nigra” lineage and the other containing 12 accessions of B. juncea and three A-genome accessions. This classification was in disagreement with the evidence from chloroplast DNA, mitochondrial
DNA, nuclear DNA restriction fragment length polymorphism (RFLP), which suggested that B. juncea was closely related to the A-genome type. For the incongruence, we speculated that the B. juncea crops derived from Chinese have evolved through different recombined events of the diploid morphutypes and evolved unidirectional
concerted evolution. The traditional phenotypic classification of B. juncea was not wholly supported by ITS results, and hence the phylogenetic relationships among these subspecies need to be reconsidered
on molecular level. 相似文献
The bioavailability of potassium (K) depends on its speciation distribution in the soil. Different methods are commonly used to estimate K speciation including traditional single leaching (TSL) and sequential extraction process (SEP). However, K speciation is largely affected by soil pretreatment methods. The effects of both TSL and SEP soil pretreatment methods were evaluated.
Materials and methods
The TSL method classifies K speciation content based on bioavailability, while the SEP classifies the metal speciation based on the effects of environmental conditions. These two methods, together with a modified sequential single leaching (SSL) scheme, were used to evaluate five types of soil including soil without potassium fertilization, soil with long-term K fertilization, alkaline soil, red soil, and forest soil. The soil samples were gathered randomly at depths varying up to 30 cm before being dried in air at room temperature. The samples were then ground and mixed before passing through a sieve (10 mesh or 100 mesh) in order to perform K speciation analysis via the modified SSL technique, the TSL method, and the four schemes of SEP.
Results and discussion
Soil pretreatment influenced K speciation, with higher concentration in soil samples sieved through 100 mesh than through 10 mesh. In alkaline soil, potassium was observed to be associated with carbonate. For the various SEP schemes, K speciation was found to be greatest in the residual fraction, with only 3% observed in the carbonate, exchangeable, metal organic complex, or amorphous hydroxides of Fe or Mn. After following the first two steps of the SEP schemes, the available K was similar to that of the TSL method. Distribution of non-exchangeable K using the TSL method was comparable with the five combined SEP extraction steps which were all affected by environmental conditions.
Conclusions
Pretreatment affected K speciation distribution and total amount of metal in the soil. The 100 mesh sieve was more effective in estimating K soil speciation. The SEP method was acceptable for estimating K speciation, with the Krishnamurti et al. (Analyst 120:659–665, 1995) scheme as a useful appraisal of K bioavailability. Combination analyses using both TSL and SEP methods are useful techniques to enable a better understanding of K speciation transformation in soil.
以初始平均体重(2.07±0.02)g的大菱鲆(Scophthalmus maximus L.)为实验对象,进行为期70天的摄食生长实验,研究不同添加水平的发酵和未发酵豆粕对大菱鲆摄食生长的影响.用米曲霉(Aspergillusoryzae)AS 3.951对豆粕进行固态发酵.经检测.与未发酵豆粕相比较,发酵豆粕中胰蛋白酶抑制因子、植酸、大豆皂甙、水苏糖和棉籽糖的含量分别下降了46.5%、26.6%、11.7%、30.1%和19.7%.实验共制作6种等氮等能的饲料,其中以全鱼粉饲料为对照饲料;未发酵豆粕蛋白分别替代25%、40%和55%的鱼粉蛋白;发酵豆粕蛋白分别替代40%和55%的鱼粉蛋白.结果表明,饲料中添加一定量的豆粕对大菱鲆的成活率没有显著的影响(P>0.05).饲料中未发酵豆粕蛋白替代鱼粉蛋白的水平为25%时,对大菱鲆的摄食率、特定生长率、饲料效率和蛋白质效率均没有显著的影响,但替代水平为40%和55%时,以上指标显著降低(P<0.01).饲料中发酵豆粕替代水平为40%时,未降低大菱鲆的摄食率、特定生长率、饲料效率和蛋白质效率,替代水平为55%时,显著降低大菱鲆的摄食率和特定生长率(P<0.01). 相似文献