Natural abundance N in soil and litter across a nitrate-output gradient in New Hampshire

Stable isotopes of nitrogen are potentially a valuable tool for regional assessments of nitrogen saturation because they provide an integrated measure of the past nitrogen cycling history of a site. We measured δ¹⁵N of soil and litter, as well as net nitrification potential, at three sites across a nitrate-loss gradient in the White Mountains, New Hampshire to test the hypotheses: (1) that δ¹⁵N in soil and litter increase across a spatial gradient of nitrate loss; and (2) that δ¹⁵N in soil and litter is elevated when nitrification is elevated. δ¹⁵N was found not to vary significantly among the three sites. Patterns of leaf litter and forest floor δ¹⁵N, however, were strongly influenced by species composition in individual plots. Beech litter had significantly higher δ¹⁵N than yellow birch, sugar maple, and red maple. The conifer-dominated plots had significantly lower δ¹⁵N in both the organic soil horizons and in litter than did the hardwood-dominated plots. When we adjusted for spatial heterogeneity in mineral soil δ¹⁵N values by using an enrichment factor, δ¹⁵N_foliar − δ¹⁵N_Bs, in place of absolute soil δ¹⁵N values, a positive relationship was found with net nitrification for hardwoods. δ¹⁵N may also be a useful tool for evaluating species differences in nitrogen cycling and nitrogen uptake. The distinct pattern we observed of decreasing δ¹⁵N across the continuum from hardwood-dominated to conifer-dominated sites may suggest that local drivers (for example, nitrification rate) regulate the absolute value of foliar δ¹⁵N, while species-driven factors (e.g., timing and type of uptake) control the foliar δ¹⁵N value of one species relative to another in the same plot.     

中国木材产业资源基础及可持续性分析

论述了发展中国木材产业的战略重要性;通过分析国内木材资源与国际木材资源供给,得出了中国木材产业资源基础薄弱的结论;以实现资源基础可持续性为目的,论述了构筑中国木材产业资源基础的途径。     

庆元县锥栗特色基地建设刍议

通过对庆元县嫁接锥栗发展历史及现状分析。认为发展锥栗应开展品种选优，增加科技投入，科学规划，合理布局，科学管理，搞好示范基地建设，重视市场培育和保鲜，深加工技术的开发与研究。     

论菜竹笋丰产基地建设

论述丽水地区发展菜竹笋丰产基地的条件，菜竹笋基地标准、建设和培育的主要措施。     

广东省林业空间数据库系统的建设与应用

文章系统阐述了广东省林业空间数据库的内容及建设方案，着重分析了1：10000林业空间数据库的组成、网络结构、数据安全、数据管理、浏览等关键问题及提出解决方法，并介绍了部分应用实例。     

杉木干基萌芽能力的遗传变异

分析了两片杉木子代林伐桩和杉木无性系采穗圃萌条数量的遗传变异情况。结果表明：杉木子代林伐桩萌条数量在产地间、产地内家系间及组合间均存在极显著差异，并有中等以上遗传力；遗传变异系数在３７％～３９％之间；产地的遗传方差分量与产地内家系间的相近。伐桩萌条数量与基径粗度的关系随伐桩年龄的变化而表现不一；不同砍伐季节伐桩萌条数量也存在较大差异。杉木无性系采穗圃无性系间有效萌条数量存在极显著差异，无性系的萌芽能力有较高的重复力。     

青檀耐荫性的初步研究

在连续３年测定比较几个不同树种的生理特性和树冠结构的基础上，本文对青檀的耐荫性进行了初步分析，结果表明，青檀的耐荫性随年龄的增大而降低，１２年生以前，青檀是耐荫的；１３至２５年生之间，青檀是喜光树种；２６年生以后青檀则逐渐变为阳性树种。比较的结果还表明，青檀的耐荫性较马尾松强，较杉木弱，从总体看属中偏阳树种。     

田间和盆栽核桃与柿子苗木光合特性的初步研究

研究了核桃(Juglans regia L.)、柿子(Diospyros kaki L.f.)两种苗木在田间和盆栽栽培条件下的光合特性。通过室内人工控制光强和CO2浓度,测得盆栽的核桃、柿子的光补偿点分别是62 μmol CO2/m2·s、40μmol CO2/ m2·s;饱和点分别是1 582 μmol CO2/m2·s、1 064 μmol CO2/m2·s;CO2补偿点分别是135 ml/L、230 ml/L。6月的晴天,核桃、柿子盆栽栽培中的净光和速率日变化呈"双峰"型;田问栽培中仅出现1次高峰。两种栽培均出现"午休"现象。     

浅谈无标底招投标

无标底招标投标制度是国际通用的、比较成熟的、科学合理的工程承包交易方式,是1项公认的国际惯例。     

桩基钻孔偏位处治方法简介——介绍一种钻孔入岩倾斜偏位的处理方法

采用冲击钻进行桩基础钻孔施工,经常会出现入岩倾斜偏位的现象,如果处理不当,就会造成 废桩。这里介绍一种简单而有效的处治方法——用混凝土封底法,针对这种现象进行处理。