Factors influencing decline in soil pH in Hawaiian Eucalyptus and Albizia plantations

Soil pH declined from 5.9 to 5.0 in 8 years beneath plantations of Eucalyptus saligna (Sm.) in Hawaii. In stands of Albizia falcataria, (L.) Fosberg, the soil pH change was more dramatic, declining from 5.9 to 4.6. We measured several components of soil acidity beneath four mixtures of the two tree species to gain insight on the processes responsible for the decline in soil pH. These components were studied using an empirical method of comparing acid quantity, degree of neutralization (depletion of base cations), and acid strength. The decline in soil pH differed between species as a result of differences in the degree of neutralization of the soil exchange complex; the larger decrease in soil pH under Albizia was produced by greater acidification of the exchange complex. Empirical titration curves suggested that differences in acid strength moderated the divergence in soil pH beneath the species. Had the acids accumulating in the soil under Albizia been as strong as those in the Eucalyptus soil, the difference in soil pH would have been greater. Though the two species had contrasting effects on soil pH, the differences in degree of neutralization, responsible for the pH decline, were small compared with differences in the amount of cations stored in tree biomass. Continued supply of nutrient cations (from weathering or fertilization) will ultimately control both the extent of soil pH decline and the level of productivity sustained by the forest.     

Effects of 'Agri-SC' soil conditioner on soil structure and erodibility: some further observations

Abstract. In field and laboratory experiments the conditioner‘Agri-SC’has shown improvements in the structure of loamy sand soils in east Shropshire, UK. It resulted in statistically significant decreases in soil bulk density values and increases in soil porosity and aggregate stability. Further experiments are in progress on both loamy sand and silt loam soils.     

拖拉机集材对迹地土壤条件及苗木生长影响的研究(Ⅱ)——拖拉机对集材道苗木生长影响的灰色动态分析

履带式拖拉机和轮式拖拉机由于其走行机构的不同,其集材道土壤压实也存在差异,特别衡量土壤压实的两个重要指标——土壤硬度和孔隙度——两种机型不一致。通过对调查测定数据进行计算处理以及用灰色系统理论进行动态分析,结果表明:与轮式拖拉机相比,履带式拖拉机对苗木生长是有利的。     

三峡水库重庆库区移土培肥的效益分析——以云阳县为例

应用前后对比分析法,对三峡水库重庆库区云阳县移土培肥一期与二期工程进行效益分析;得出移土培肥工程将给三峡库区带来巨大的生态效益、经济效益和社会效益的结论;说明该工程不仅能带动库区经济发展,并对其社会及生态环境产生深远影响。     

Preparation of algal-oligosaccharide mixtures by bacterial agarases and their antioxidative properties

ABSTRACT:   Algal-oligosaccharide-lysates (AOL), derived from six agars and four algal polysaccharide extracts (APE), were treated with 100–500 activity units (AU) of MA103-agarases or MAEF108-agarases, and their antioxidative properties evaluated. Soluble total polyphenols (TP) were between 462.2 ± 1.6 gallic acid equivalents (GAE, µg/mL) and 70.6 ± 17.4 GAE. The DPPH radical scavenging capacity of all AOL went from 68.3 ± 0.7% to 0.5 ± 0.1%. The ferrous ion chelating capacity of all AOL went from 93.1 ± 0.2% to 21.7 ± 0.9%. Evaluation of the H₂O₂ scavenging capacity of all AOL was between 35.9 ± 5.4% and 0.1 ± 0.2%. The reducing power of all AOL went from 51.3 ± 2.6 to 3.2 ± 6.8 expressed as µg/mL ascorbic acid. In DPPH radical scavenging capacity, ferrous ion chelating capacity and reducing power etc., the AOL derived from the APE of Porphyra dentate (digested by 500 AU of MAEF108-agarases) were highest, in all test sets. However, the AOL derived from the APE of Monostroma nitidum (digested by 500 AU of MAEF108-agarases) had the highest H₂O₂ scavenging capacity in all test sets. The order of antioxidative activity performance of all AOL treated in this experiment, by these four antioxidative methods, is as follows: ferrous ion chelating capacity > DPPH radical scavenging capacity > H₂O₂ scavenging capacity > reducing power; this may be related to their polyphenols, small molecular weight polysaccharides or simple sugar constituents. In this study, it is demonstrated that various agarases derived from algal oligosaccharide mixtures possess good potential for use as a health food, due to their antioxidative capacity.     

不同DEM分辨率下的坡面土壤侵蚀模型的坡长因子提取对比研究

采用基于GIS的非累计流量的坡长直接提取算法(NCSL)和空间分析提取法(SAC)对陕北省安塞县10个样区的坡长进行提取,并计算相应的坡长因子。对不同DEM分辨率下的坡长提取结果对比,结果表明:NCSL对坡长的提取精度明显好于SAC的提取结果,其中DEM在5、10 m分辨率下的提取精度最好,且二者计算的坡长因子值差异不大,因此,可采用10 m分辨率NCSL方法提取坡长。     

高校食品物性学课程教学实践的思考

食品物性学是一门重理论基础,实践性强,涉及面广的课程。该文介绍了我国食品物性学课程教学和研究现状,并提出了提升食品特性学课程的教学质量措施。主要包括:借举国内外教学成果、与多学科相融合、加强实践教学等。     

Fungal abundance and distribution as influenced by clearing and land use in a vertic soil of Argentina

The influence of native vegetation clearing and different further soil managements on fungal propagule population diversity was studied in the present work. In each of the 3 years (1998, 1999, and 2000), soil samples were collected at the depth of 0–7.5 cm from sites under native vegetation (V0); naturalized prairie, cleared in 1982 (P16); conventional tillage, cleared in 1972 (T26); and direct drilling, cleared in 1958 (D40). Fungal population size and relative abundance of fungal genera were studied by plate counts and further identification of isolates on potato dextrose agar. The undisturbed site and the other sites with increasing time elapsed since native vegetation clearing and different management history showed a distinctive distribution of fungal genera. There were significant differences (p<0.05) among the sites in the abundance of fungal genera analyzed in all the 3 years. Principal component analysis based on relative fungal genus abundance differentiated the sites with 75% variance explained by the first and second components. Diversity and abundance of isolated fungal genera were increased as density of Penicillium spp. decreased, suggesting a competitive effect of this fungal genus. The largest diversity was found in the site under no-till management. The different distribution and relative abundance of the fungal genera studied seemed to be influenced strongly by the management and the presence of surface residue in the no-tilled site.