Soil respiration characteristics of tropical soils from agricultural and forestry land-uses at Wondo Genet (Ethiopia) in response to C, N and P amendments

In most parts of tropical Africa, conversion of forests into agricultural lands is often accompanied by drastic changes in soil properties. However, little study has been done to examine changes in biological properties of soils from different land-uses in response to addition of C and nutrients. We conducted this study with the aim of investigating nutrient limitations for microbial activity in soils from agricultural (farm) and forest land-uses at Wondo Genet (Ethiopia) after amendment with C and limiting nutrients. We measured CO₂ respiration rates from the soils incubated in the laboratory before and after addition of glucose-C together with N and/or P in excess and/or limiting amounts. Based on the respiration kinetics, we determined the basal respiration (BR), substrate-induced respiration (SIR), specific-microbial growth rate (μ), respiration maxima (R_max), % of glucose-C respired, and microbially available N and P in the soils. We found that N was more limiting than P for the micro-biota in the soils considered, suggesting the presence of ample amounts of indigenous P that could be extracted by the micro-biota, if provided with C. Addition of P resulted in a respiration pattern with two peaks, presumably reflecting different N pools being available over time. The SIR, Respiration maxima, μ and microbially available P were higher in soils from the farm, while %C respired was higher in the forest, suggesting increased C costs for micro-biota to be able to utilize nutrients that are strongly bound to organic-matter or clay minerals. Depending on land-use, about 49-69% of added glucose-C was respired during two and a half weeks time, but differences between N or P additions were not significant. The correlation between soil physical and chemical properties and respiration parameters, however, depended on whether N or P was limiting. We concluded that examining the soil respiration kinetics could provide vital information on nutritional status of micro-organisms under different land-uses and on potential availability of nutrients to plants.     

河溪近自然治理的基本模式与应用界限

河溪系统是流域管理中最基本和最重要的单元。在分析传统河溪治理的基础上,简要地介绍了河溪近自然治理的概念、发展和特征,提出了河溪近自然治理的原则,并对河溪近自然治理的基本模式进行了探讨。     

Tillage effect on nutrient stratification in narrow- and wide-row cropping systems

Recent research has indicated that conservation systems with narrow-rows have potential for higher crop productivity on southeastern USA Coastal Plains Soil. The objective of this study was to determine how surface tillage and subsoiling affect nutrient distribution in the soil profile in narrow- and wide-row systems. A secondary objective was to determine the effect of row position on soil pH and nutrient concentrations in the wide-row system. Soil samples were collected in 1996 from plots that had been growing soybean (Glycine max (L.) Merr.) double cropped with wheat (Tritiucum aestivum L.) for 3 years and then again in 1999 after 3 years of continuous corn (Zea mays L.). Narrow-row spacing was 19 cm for soybean and 38 cm for corn. Wide-row spacing was 76 cm for both soybean and corn. Wheat was grown in 19 cm wide-rows. Soil samples were randomly collected from throughout the plots in the narrow-row culture. In the wide-row culture, separate samples were collected from the row and from between rows. Treatments were surface tillage (disc tillage (DT) and no surface tillage (NT)), with different frequencies of subsoiling. The soil type was Goldsboro loamy sand (fine-loamy, siliceous, thermic, Aquic Kandiudult). Soil samples from four depths (the surface 5 cm of the A horizon, the remainder of the A horizon, the E horizon, and the top 7.5 cm of the B horizon) were analyzed for pH, P, K, Ca, and Mg. Nutrient concentrations and pH differed little between row spacings at any depth after either 3 or 6 years. Differences due to subsoiling appeared mainly due to nutrient removal as the treatments with more intense subsoiling had higher yield and lower concentrations of nutrients (except K). Concentrations of P, Mg, and Ca at the soil surface tended to be higher in NT than in DT, especially in the mid-rows of the 76 cm wide-row systems. The data suggest only small differences in soil nutrient stratification can be expected as growers adopt narrow-row crop production systems with intensive subsoiling.     

Nematode migration and nutrient diffusion between vetch and barley material in soil

This paper deals with migration of nematodes along nutrient gradients in soil. Portions of barley straw and green vetch leaves were mixed with soil and buried at 6, 12, 18, and 50 mm distance from each other in soil. During the following 12 weeks respiration activity, microbial (SIR) biomass, nitrogen limitation of respiration activity in soil slurries all indicated that nitrogen was transferred in the soil from the nutrient rich vetch to the nutrient poor barley at least during the first 3 weeks of the experiment. Twelve out of 39 taxonomic groups of nematodes showed different growth in the two plant material-soil mixtures. Only one of these taxonomic groups (long rhabditid larvae) suggested that migration could have contributed to population development; for three other groups (short rhabditid larvae, Aphelenchoides, and Bursilla) nutrient transport through the soil was the likely mechanism for a distance-dependant population development. We suggest that for most microbivorous nematodes, except larvae of fast growing bacterivores, migration over distances exceeding one centimetre does not contribute markedly to population development even when cues such as nutrient gradients to stimulate the activity exist.     

Extrinsic and intrinsic controls on the distribution of the critically endangered cress, Ischnocarpus exilis (Brassicaceae)

Ischnocarpus exilis, a critically endangered cress, persists in one small population in a 1m² section of a limestone tower in the South Island, New Zealand. The importance of intrinsic (seed production, dispersal ability and habitat specificity) and extrinsic factors (weed competition) acting to restrict the distribution of this threatened species were investigated with a field experiment, demographic monitoring and soil seed bank analysis. I. exilis is not confined to its present site because of high habitat specificity, but rather is limited by low seed production and limited dispersal as well as by competition with invasive weeds. Conservation management of this critically endangered species should focus on controlling weeds and on establishing new populations in suitable weed-free habitat.     

Avian population and community processes in forest ecosystems: Long-term research in the Hubbard Brook Experimental Forest

Long-term studies in relatively undisturbed forest ecosystems, such as occur in many of the USFS’ Experimental Forests, provide valuable insight into bird population and community processes, information pertinent to forest management and bird conservation. Major findings from 40 years of research in the Hubbard Brook Experimental Forest in north-central New Hampshire reviewed here show that the distributions and abundances of bird species are dynamic, even within well-developed and mature forests, and that species respond differently to habitat (vegetation) structure, food availability, and other features of the forest environment. At the local scale, bird population demography is most affected by factors that influence fecundity and recruitment, mainly food availability, weather, nest predators, and density dependent processes. Fecundity is strongly correlated with subsequent recruitment and is critical for maintaining breeding population size. Events in the non-breeding season, however, also influence the abundance and demography of breeding populations, indicating the need to assess factors operating throughout the species’ annual cycle. At the landscape scale, populations in temperate forests are spatially structured by each species’ response to habitat and environmental patterns, but also by social interactions such as competition and conspecific attraction. Settlement patterns and ultimately reproductive performance depend on habitat quality, based on vegetation structure, food availability and nest predator effects that vary across the landscape. Results from these long-term studies centered at Hubbard Brook provide a mechanistic understanding of avian population dynamics and community responses. The results provide a framework for predicting how future changes in habitat quality, climate, and other environmental threats may influence bird populations and communities in north-temperate forests.     

作物QTL定位的应用及限制性因素

综述了作物数量性状位点(QTL)定位的主要应用及限制性因素,并提出了相应的改进措施。     

乳牛骨软症的调查研究

本文对哈尔滨奶牛场发生的以异嗜、跛行等为特征的乳牛疾病进行了调查研究,分析研究了日粮成分,临床表现,血清钙、无机磷、镁和羟脯氨酸的含量及变化,以及尾椎密度的测定值。结果表明,日粮中钙过多,磷、镁供给不足,钙、磷比例过大是致病的主要原因。并分析研究了乳牛血液生化指标的变化和尾椎骨密度的测定法对诊断和监测骨软症和钙、磷、镁代谢动态的意义。     

钼,镁合施对平菇1012生态效应的研究

平菇子实体内钼,镁富集量,平菇产量,营养成分均与钼、镁添加剂施用浓度相关。钼浓度为484.05mg/kg,镁浓度为1016.92mg/kg时,平菇子实体内钼富集量极大值达13.76mg/kg。钼浓度高于538.35mg/kg,镁浓度高于662.48mg/kg时,镁富集量与钼、镁浓度呈正相关。钼浓度为489.14mg/kg,平菇产量高达158.44g/瓶;钼浓度为538.92mg/kg时,蛋白质含量最大达31.3％。在钼、镁的某些浓度范围内,平菇体内钼、镁富集存在拮抗作用。钼浓度为538.35mg/kg时,镁富集量极小值为0.217％;镁浓度为1087.61mg/kg时,产量最小值为155.01g/瓶;镁浓度为690.52mg/kg时,蛋白质含量最小值为31.20％。当镁浓度高于1087.61mg/kg时,平菇产量与平菇体内镁富集量呈正相关;镁浓度高于690.52mg/kg时,平菇体内蛋白质含量与镁富集量呈正相关。