Effect of long-term liquid pig manure application on atrazine mineralization in a soil cultivated with maize

Soil samples were collected in plots from a field experiment in maize monoculture receiving 0, 60 and 120 m³ ha^-1 liquid pig manure (LPM) for 19 years. Soils were sampled from the 0- to 20-cm layer in August and October 1997 and in June, July and September 1998. Subsurface samples were also evaluated in September 1998. Laboratory soil radiorespirometry was used to evaluate atrazine mineralization using [U-ring-¹⁴C]-atrazine mixed with commercially available product. The effect of atrazine dose (50, 100 and 500 mg atrazine kg^-1 soil) was evaluated on soils sampled in August 1997. For the other sampling dates, the soils were spiked with 50 mg atrazine kg^-1 soil. No LPM dose effect on atrazine mineralization was obtained in the different experiments. Increasing atrazine dose to 500 mg kg^-1 decreased significantly the mineralization rate (R_i) and the maximum of atrazine mineralized (MAX), while the time needed to mineralize 50% of MAX (DT-50%) was not significantly affected. Sampling time had a significant effect on atrazine mineralization. Atrazine mineralization in the soils sampled in June 1998 showed lower R_i and MAX than in the soils sampled at the other dates. Atrazine mineralization in subsurface soils (20–60 cm) was very variable and quite high in some samples. This may be due to atrazine pre-exposure in subsoils resulting from atrazine deep movement by preferential flow.     

Identifying road mortality threat at multiple spatial scales for semi-aquatic turtles

Prioritizing sites for localized mitigation measures, and forecasting the effect of interventions on an endangered population, requires an understanding of the spatial scales at which threat processes operate. Road mortality is among the greatest threats to semi-terrestrial freshwater turtles due to the group’s life-history traits. Declining throughout much of their range, spotted (Clemmys guttata) and Blanding’s turtles (Emydoidea blandingii) are exposed to high road densities and traffic volumes in the northeastern United States. We examine the distribution of roadkill risk for spotted and Blanding’s turtles at three spatial scales. Tortuosity during upland movements was used to predict road-crossing locations at the single-movement scale. A gravity model of wetland-to-wetland interactions was then developed to identify road mortality hot spots at a broader road segment scale. Finally, road-crossing risk was assessed at the scale of focal areas that support distinct populations, using a population viability analysis to evaluate the consequences of road mortality on resident populations. The observed spatial variability of road mortality risk was high for single road crossing movements, limiting the effectiveness of static mitigation measures conducted at this scale. At the broader road segment scale, road mortality hotspots were evident. The demographic risk associated with roads varied widely among discrete populations, with probabilities of extinction over 100-year projections reaching 5.1% for spotted turtles, and 58.8% for Blanding’s turtles. We conclude that conservation interventions are most likely to be effective in mitigating the effects of road mortality when implemented at the road segment and population scales.     

Determination of the effective water conductivity of red pine sapwood

Summary The instantaneous profile method was used to establish the boundary desorption curve of the effective water conductivity function of red pine (Pinus resinosa Ait.) sapwood in the radial and tangential directions from nearly saturated to dry conditions at 18, 56 and 85 °C. The results obtained demonstrate that the effective water conductivity is a function of moisture content, temperature, and direction of flow. The effective water conductivity increases by several orders of magnitude (10⁴–10⁵) as moisture content increases from dry to nearly saturated conditions at a given temperature. The effective water conductivity also increases by a factor varying between 10 and 50 as temperature rises from 18 to 85 °C in the moisture content range considered. The variation of the moisture content–water potential relationship with temperature can explain part of the temperature effect. The effective water conductivity was generally higher in the radial direction than in the tangential direction in a ratio varying from about 1/1 to 3/1 depending on moisture content and temperature. Finally, the flux–gradient relationships obtained at given moisture contents were found to be linear, confirming the validity of using a moisture flux equation considering the water potential gradient as the driving force for the experimental conditions considered in the present work. The knowledge of the effective water conductivity function and of the moisture content–water potential relationship allows the utilization of a two-dimensional model of moisture movement in wood during drying using the gradient in water potential as the driving force for drying at temperatures up to 85 °C. Received 27 February 1998     

Genetic variation among cultivars of red clover (Trifolium pratense L.) detected by RAPD markers amplified from bulk genomic DNA

Summary The use of random amplified polymorphic DNA (RAPD) markers obtained from bulked samples was investigated for cultivar identification in red clover. Pooled samples were examined in order to minimize variation within cultivars. To determine the appropriate number of individuals to include in the bulked samples representing each cultivar, DNA samples from two, three, four, five, ten and twenty individuals were pooled. Twenty was found to be an appropriate number of red clover individuals per bulk in order to amplify only the DNA sequences shared among most individuals in each cultivar. Fourteen 10-mer primers were used to amplify genomic DNA from combined leaf samples of 15 red clover cultivars from European, Japanese and North American origins. A total of 79 amplified products, of which 55 were polymorphic, was obtained. Cultivar-specific bands were observed with 13 primers. The amplification patterns obtained from two primers could distinguish all 15 red clover cultivars. Rogers' genetic distances for all 105 pairwise comparisons were calculated to evaluate relationships among these cultivars. Cluster analysis based on these genetic distances separated these 15 cultivars into three groups, with two of the groups consisting of a single Japanese cultivar each, while the third group included cultivars from European, North American, and Japanese origins.     

A neural network experiment on the site-specific simulation of potato tuber growth in Eastern Canada

The objective of this work was to optimize a neural network (NN) for modelling potato tuber growth and its in-field variations in eastern Canada. In addition to climatic inputs, the cumulative and maximal leaf area index (LAI) were incorporated to account for in-field scale variability. Soil and genetic parameters were assumed to be integrated in LAI as suggested by earlier work. Each input and combination of inputs was evaluated from the changes they induced in MAE (mean absolute error) and RMSE (root mean square error). Results using data from several replicated on-farm experiments between 2005 and 2008 suggest that a NN model using cumulative solar radiation, cumulative rainfall and cumulative LAI can adequately model site-specific tuber growth. The MAE of the retained model was 209 kg DM ha⁻¹, which represents less than 4% of the mean final tuber yield for the 3 years of the study. Non-linear effects of explicative variables on tuber yield were attested by comparing the results of the NN simulations to those of a multiple linear regression (MLR). The failure of MLR to simulate temporal discontinuities in tuber growth supports the use of a non-linear approach such as a NN to model tuber growth.     

Integrating landscape resistance and multi-scale predictor of habitat selection for amphibian distribution modelling at large scale

Context

Species distribution modelling is a common tool in conservation biology but two main criticisms remain: (1) the use of simplistic variables that do not account for species movements and/or connectivity and (2) poor consideration of multi-scale processes driving species distributions.

Objectives

We aimed to determine if including multi-scale and fine-scale movement processes in SDM predictors would improve accuracy of SDM for low-mobility amphibian species compared with species-level analysis.

Methods

We tested and compared different SDMs for nine amphibian species with four different sets of predictors: (1) simple distance-based predictors; (2) single-scale compositional predictors; (3) multi-scale compositional predictors with a priori selection of scale based on knowledge of species mobility and scale-of-effect; and (4) multi-scale compositional predictors calculated using a friction-based functional grain to account for resource accessibility with landscape resistance to movement.

Results

Using friction-based functional grain predictors produced slight to moderate improvements of SDM performance at large scale. The multi-scale approach, with a priori scale selection, led to ambiguous results depending on the species studied, in particular for generalist species.

Conclusion

We underline the potential of using a friction-based functional grain to improve SDM predictions for species-level analysis.

     

地表状况对泥沙和化学运移影响的研究

研究土壤侵蚀过程可以为开发当代基于过程的土壤侵蚀预报模型提供理论和方法支持。位于印第安那州西拉菲特的ＵＳＤＡ -ＡＲＳ国家土壤侵蚀研究实验室 (ＮＳＥＲＬ)是全美进行土壤侵蚀过程研究和开发土壤侵蚀预报模型的中心。本报告将重点介绍ＮＳＥＲＬ关于地表状况 (也就是糙     

动物肠道的完整性及其损害

动物消化道上皮细胞易受吞食进入的有机物及有毒物质影响。消化道上皮细胞分化成很多种类 ,具有各自的功能 ,这些上皮细胞形成一层半透膜表面 ,能选择地透过液体、电解质和可溶性营养物质。并作为机体连续性物理屏障的一部分 ,可防止外来物质和有机物进入血液和其它脏器。当有机物和有毒物质损害上皮细胞时 ,机体的保护屏障就会遭到破坏。这些上皮细胞不断更新和分化以代替老化的上皮细胞 ,完成生理功能。肠道表面有一层绒毛。鸟类的绒毛存在于整个小肠和大肠 ,越往肠道后段 ,绒毛高度越低。每个绒毛的肠腔表面又排列着很多微绒毛 ,便于营养…