Spatial dependence and the relationship of soil organic carbon and soil moisture in the Luquillo Experimental Forest,Puerto Rico

We used geo-spatial statistical techniques to examine the spatial variation and relationship of soil organic carbon (SOC) and soil moisture (SM) in the Luquillo Experimental Forest (LEF), Puerto Rico, in order to test the hypothesis that mountainous terrain introduces spatial autocorrelation and crosscorrelation in ecosystem and soil properties. Soil samples (n = 100) were collected from the LEF in the summer of 1998 and analyzed for SOC, SM, and bulk density (BD). A global positioning system was used to georeference the location of each sampling site. At each site, elevation, slope and aspect were recorded. We calculated the isotropic and anisotropic semivariograms of soil and topographic properties, as well as the cross-variograms between SOC and SM, and between SOC and elevation. Then we used four models (random, linear, spherical and wave/hole) to test the semi-variances of SOC, SM, BD, elevation, slope and aspect for spatial dependence. Our results indicate that all the studied properties except slope angle exhibit spatial dependence within the scale of sampling (200 – 1000 m sampling interval). The spatially structured variance (the variance due to the location of sampling sites) accounted for a large proportion of the sample variance for elevation (99%), BD (90%), SOC (68%), aspect (56%) and SM (44%). The ranges of spatial dependence (the distances within which parameters are spatially dependent) for aspect, SOC, elevation, SM, and BD were 9810 m, 3070 m, 1120 m, 930 m and 430 m, respectively. Cross correlograms indicate that SOC varies closely with elevation and SM depending on the distances between samples. The correlation can shift from positive to negative as the separation distance increases. Larger ranges of spatial dependence of SOC, aspect and elevation indicate that the distribution of SOC in the LEF is determined by a combination of biotic (e.g., litterfall) and abiotic factors (e.g., microclimate and topographic features) related to elevation and aspect. This demonstrates the importance of both elevation and topographic gradients in controlling climate, vegetation distribution and soil properties as well as the associated biogeochemical processes in the LEF.This revised version was published online in May 2005 with corrections to the Cover Date.     

刺梨及其近缘种PCR实验体系的建立与优化

以刺梨及其近缘种月季为试材,进行了RAPD-PCR实验参数的确立和优化试验。结果表明,刺梨及月季25μL反应体系的最优组成为2.5μL10×反应缓冲液,2mmol/LMg2+,0.2mmol/LdNTP,1.6mg/L模板DNA,0.4μmol/L随机引物和1.2UTaqDNA多聚酶。经PCR扩增验证,此反应体系亦适宜于刺梨的部分近缘种,可有效用于RAPD分析;通过将退火温度提高至50℃或采用“Touchdown”扩增程序,并在50μL反应体系中适当增加特异引物对浓度(1.0μmol/L),模板DNA(4.0mg/L)和TaqDNA多聚酶(3.0U/管)的使用量,建立起适合于刺梨特异DNA片段检测及回收的特异PCR扩增实验体系,为刺梨的分子克隆奠定了技术基础。     

试验统计方法课程教学改革探索与实践

介绍了试验统计方法课程的基本理论体系和教学目标,指出了试验统计方法课程教学中存在的主要问题,并提出了课程教学改革理念及思路,以为试验统计方法课程教学改革提供参考。     

现代机械制造工艺与精密加工技术探析

社会主义市场经济逐年发展，各行各业都在不断成长，机械制造工业也有了较大的发展，现代机械制造工艺的运用渐渐成熟。但是我国的机械制造基础比较薄弱，现代机械制造工艺与精密加工技术都需要深层的研究和实践。文章阐述了现代机械制造工艺和精密加工技术的基本情况，并分析了它们的特点，希望能够以此对现代机械制造工艺与精密加工技术有个明晰的介绍。     

Genome-edited crops: how to move them from laboratory to market

Recent breakthroughs in CRISPR technology allow specific genome manipulation of almost all crops and have initiated a revolution in precision crop breeding. Rationally-based regulation and widespread public acceptance are needed to propel genome-edited crops from laboratory to market and to translate this innovative technology into agricultural productivity.     

自动施肥系统开发与性能测试

目的 开发一种适应于以固态水溶肥为原料的自动施肥系统,测试分析自动施肥系统性能。方法 主控机采用ARM9电路控制模块可实现对轮灌编组、预搅拌时长、施肥开始与结束时间、施肥持续时长、施肥量等参数的设置;选择以蠕动泵为注肥装置,通过变频器控制注肥泵电机功率的方式控制注肥速率,控制施肥量。对装置核心部件搅拌器额定功率、计量方式、溶肥搅拌参数、排肥速度及固液相比例等主要参数等进行设计与测试。结果 电感脉冲计量方式标准误差最大值1.26%,误差小、性价比好,确定其为本装置采用的计量方式;搅拌器以1.5 Kw额定功率、38 r/min转速搅拌、肥液浓度在1.1~1.3 g/mL、预搅拌时间30 min时,罐内各液位输出肥液浓度值差异不显著(P< 0.05),达到对肥料浓度均匀性的设计要求。结论 将施肥开始前的预搅拌时间设为30 min、搅拌转速设为38 r/min、肥液浓度不高于1.3 g/mL,输出肥液浓度有较好的均匀性,实现精准施肥。     

农业技术经济学实验教学探索

研究了开展农业技术经济学实验教学的必要性,根据课程内容,确定了动态经济效果评价等实验项目,选择Excel、SPSS、Eviews、LINDO、DEAP软件作为实验教学软件,并分析了实验实施的各个环节。     

一类二维加权积分数值求积方法及其误差分析

针对一类二维加权积分的数值计算方法及误差分析进行研究,参照一维广义高斯积分数值求积方法提出一种具有较高代数精度的计算方法并对其误差做分析,同时给出几个简明的结果。这些结果可用到诸如小波分解,图像处理与多分辨数字信号处理等领域。