共查询到20条相似文献,搜索用时 718 毫秒
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<正>1选择适宜的物候期秋季树木大量落叶至土壤封冻是最适宜的栽植时间,即10月~12月份,并且在此时期内越早越好。秋季当树苗大量落叶后,苗木地上部水分蒸腾量减少,根系处在缓慢生长阶段,此时栽植,根系还有一个小的生长高峰,伤根极易愈合,并能生长出部分新根,春天发芽时较之春季栽植的苗木就少去了一个根系愈合的过程,生理活动的顺序是根系早,地上部晚,先由根供应水和养分,再生根发芽,养分供应早,生长早,成活率高,长势旺,而春季栽植的苗木是先发芽,再由根系供应养分,一旦根系愈合较晚,就有可能造成树体养分消耗殆尽,容易出现回芽现象,影响成活率,生长势也较差。 相似文献
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初雪 《绿色中国(A版)》2008,(24)
1乔桢推开门,一阵小北风先他一步吹进教室,有个女生忍不住咳嗽起来,最初轻咳,然后听起来就有些撕心裂肺。她坐在靠暖气的地方,身体裹得像一只小棕熊。乔桢站在讲台上,开始点名,喊到江恩美时,她举起手,没有抬头,整个人恹恹地缩在外套里,精神不振,这该死的感冒啊。乔桢首先记住了她,他每讲几句话,她就在下面咳,伴奏一样。后来,大家觉得实在有趣,就开始笑。乔桢的第一堂课,就这样匆匆结束了。她最后一个走出教室, 相似文献
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相传,在很久很久以前,一只美丽的凤凰从南方飞来,发现了一片绿洲:贺兰山雄距西北,重峦叠嶂,势若奔马;黄河襟带东南,不舍昼夜,款款北流;山河之间,稻针织绿,麦浪翻金,渠网平畴,水映晴光;满眼望去,是一片绵绵芊芊的鲜嫩绿色。于是,美丽的凤凰留下了,留在这风光秀美的塞上江南,变成 相似文献
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毛叶山桐子(Var vestita Diels),属大风子科,山桐子属,是山桐子(Idesia polycarpa Maxim.)的变种.落叶乔木,高8~15 m,树皮光滑,灰白色,皮孔大而明显.叶卵形至卵状心形,厚纸质,长8~16 cm,宽6~14 cm,先端锐尖至短渐尖,基部心形或近心形.叶缘有疏锯齿,表面光滑有光泽,背面密生灰色短柔毛,基部掌状5~7出脉,叶柄红色,长6~15 cm,圆柱形,幼具短柔毛,顶端有两个较大腺体.圆锥花序长15~30 cm,下垂,花黄绿色,芳香.浆果球形,红色、直径6~8mm,有多数种子,种子卵形,褐色,长1mm,径0.3 mm.花期5~6月,果熟期9~11月. 相似文献
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油松-沙棘混交模式对生境和油松生长的影响 总被引:5,自引:0,他引:5
在陕北黄土丘陵沟壑区,以油松纯林为对照,对油松与沙棘行状混交、行状混交沙棘平茬、带状混交、宽行混交和宽行混交沙棘平茬林地的沙棘郁闭度、高度、光照强度、土壤水分、土壤密度、土壤空隙度、土壤养分及油松的存活率、高度、地径、顶梢年生长量等进行13年的监测研究.结果表明:行状混交与宽行混交的沙棘郁闭度、高度均高于行状混交沙棘平茬、宽行混交沙棘平茬和带状混交;林地的光照强度为油松纯林的较高,带状混交、宽行混交沙棘平茬、行状混交沙棘平茬的居中,宽行混交和行状混交的较低;土壤储水量在11年后表现为行状混交与宽行混交的较高,行状混交沙棘平茬、带状混交与宽行混交沙棘平茬的居中,油松纯林的较低;土壤密度、土壤空隙度、土壤养分表现为沙棘郁闭度、高度越高,土壤密度越低,土壤空隙度、土壤养分越高.与油松纯林相比,行状混交和宽行混交油松的高度和地径在6年以后明显较低,存活率在7年以后显著降低;行状混交沙棘平茬、宽行混交沙棘平茬与带状混交的油松高度在7年以后较高,行状混交沙棘平茬与宽行混交沙棘平茬的油松高度在10年以后高于带状混交的油松;行状混交沙棘平茬、宽行混交沙棘平茬与带状混交的油松地径在9年以后大于油松纯林的油松地径;行状混交沙棘平茬、宽行混交沙棘平茬和带状混交的油松顶梢年生长量在6年以后较大,行状混交和宽行混交的较小.油松与沙棘混交,行状混交沙棘平茬、宽行混交沙棘平茬和带状混交促进了油松的生长,行状混交和宽行混交降低了油松的存活率,抑制了油松的生长. 相似文献
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He Qingtang Song Conghe College of Forest Resources Environment Beijing
Forestry UniversityBeijing l P.R. China 《中国林学(英文版)》1994,(2)
EffectsofForestontheBudgetsofWater,EnergyandGasesintheEnvironmentHeQingtang,SongCongheCollegeofForestResourcesandEnvironment,... 相似文献
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Effect of hill fire on upland soil in Hong Kong 总被引:7,自引:0,他引:7
The present study compares the soil chemical properties of a new burnt site and an old burnt site, which had experienced three and one fire(s) respectively since 1988. The new burnt site is presently reduced to grassland and the old burnt site to mixed grassland/scrubland. Repeated fires raised soil pH by 0.27–0.33 units, exchangeable H and K by over 100%, but reduced total exchangeable acidity by 85%, organic matter by 86%, total Kjeldahl nitrogen by 75%, NH4 by 44%, NO3 by 42%, total phosphorus by 66%, exchangeable Na by 42%, Ca by 83%, Mg by 41%, Mn by 14%, Fe by 12% and Zn by 4% of the new burnt site against the old burnt site. Fire similarly reduced the effective cation exchange capacity (ECEC) and the base saturation by 85% and 90%, respectively. The occurrence of successive fires is therefore hazardous to the environment and in the absence of fire for 6 years the old burnt site has accumulated sufficient organic matter and nitrogen needed for the invasion of the more nutrient-demanding tree species. The selection of tree species and site preparation pertaining to enhancement planting of the fire-disturbed slopes to accelerate forest development are discussed. 相似文献
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在棚舍笼养环境下,使用0.05%棉酚饵剂和0.2%莪术醇饵剂对小白鼠的抗生育效果进行了对比试验研究。结果表明:交配前喂饲0.05%棉酚饵剂和0.2%莪术醇饵剂,与对照组相比较,怀胎下降率、平均胎仔下降率分别为20.0%、9.1%和60.0%、37.5%;交配后喂饲0.05%棉酚饵剂和0.2%莪术醇饵剂,与对照组相比较,怀胎下降率、平均胎仔下降率分别为25.0%、28.1%和33.3%、9.1%;两种抗生育剂对小白鼠均有显著的抗生育作用,但以0.2%莪术醇在交配前喂饲效果最佳;两种抗生育剂对小白鼠无毒性反应。 相似文献
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甲醛胁迫对3种室内观赏植物的生理生化影响 总被引:1,自引:0,他引:1
采用盆栽试验研究了甲醛胁迫后黄常山、短梗大参和袖珍椰子3种室内观赏植物叶片的生理生化指标变化,结果表明:甲醛胁迫后3种植物的生理生化指标与对照相比均有不同程度的变化。当甲醛浓度达到最高值288mg/m3时,与对照相比,黄常山叶片质膜相对透性升高64%,MDA含量升高178%,叶绿素含量降低51%,SOD与POD活性分别降低26%和55%;短梗大参叶片质膜相对透性升高10%,MDA含量升高19%,叶绿素含量降低43%,SOD与POD活性分别降低24%和25%;袖珍椰子叶片质膜相对透性升高9%,MDA含量降低24%,叶绿素含量降低30%,SOD与POD活性分别增加41%和36%。以生理生化指标的变化为基础,采用隶属函数法对3种植物的甲醛抗性进行综合评判,其抗性由强至弱为:袖珍椰子>短梗大参>黄常山。 相似文献
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[目的]为了明确舞毒蛾幼虫对Mn^2+和Co^2+胁迫的响应机制。[方法]采用0.40 mmol·g^-1 Mn^2+和0.83 mmol·g^-1 Co^2+的两种混合饲料分别喂食舞毒蛾4龄幼虫,测定了Mn^2+和Co^2+(LC30)对舞毒蛾4龄幼虫体质量、营养取食情况、营养成分含量及总抗氧化力。[结果]与对照组相比较,其取食量、虫粪量、体质量增长量均显著降低;Mn^2+处理组可溶性蛋白含量降低33.76%,碳水化合物含量降低57.56%,海藻糖含量降低64.05%,脂质含量降低27.77%;处理组可溶性蛋白含量降低47.46%,碳水化合物含量降低59.45%,海藻糖含量降低59.16%,脂质含量降低33.71%;Mn^2+处理组总抗氧化力增加28.25%,处理组总抗氧化力增加82.54%.表明Mn^2+和Co^2+对舞毒蛾幼虫取食量、虫粪量、体质量增长量、可溶性蛋白含量、碳水化合物含量、海藻糖含量、脂质含量均有显著的抑制作用,对其总抗氧化力有显著的促进作用。[结论]舞毒蛾幼虫是主要通过提高自身抗氧化力来应对重金属的胁迫,从而提高自身对重金属的抗性。 相似文献
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本文采用卫星遥感影像与实地调查、查阅林地管理档案信息相结合的方法对西双版纳傣族自治州2017年林地变更情况进行了调查,同时将结果与2016年林地变更调查结果比对,并分析了林地资源现状、森林覆盖率变化情况、林地动态变化和原因。结果表明,西双版纳州2017年林地面积总量净增227.58hm^2,同比增加0.02%,其中,有林地(乔木林)面积减少2072.29hm^2,疏林地面积净增145.23hm^2,灌木林地面积净增1112.25hm^2,未成林地面积减少1131.69hm^2,苗圃地面积净增3.66hm^2、无立木林地面积净增3154.78hm^2、宜林地面积减少1006.35hm^2,林业辅助生产用地面积净增21.99hm^2。 相似文献
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A shortleaf pine (Pinus echinata Mill.) ripping study was established by the Missouri Department of Conservation in March 1988 at the Logan Creek Conservation
Area, USA. The objective of the study was to evaluate the effects of ripping on soil chemical and physical properties, on
free-to-grow status, and on survival and growth of planted shortleaf pine seedlings. After 16 years, ripping increased exchangeable
calcium; however, it had no long-term effects on soil particle size, organic carbon, pH, exchangeable potassium and exchangeable
magnesium. Ripping increased the percentage of free-to-grow saplings by 3.8% after two growing seasons. Ripping improved survival
by 4% during the 1st three growing seasons and by 7.1% at age 16. After two growing seasons, ripping improved crown spread
by 13.6%, height by 14.2%, diameter by 14%, and volume by 41.2%. At age 16, ripping no longer had an effect on shortleaf pine
height and had reduced diameter by 5.3% and volume by 11.0%. Our results suggest that ripping 1) had no effect on long-term
physical properties or chemical properties of the soil, 2) had no effect on the number of free-to-grow seedlings, and 3) produced
short-term benefits on survival and growth of planted shortleaf pine. 相似文献