不同林龄马尾松生长及生物量分配研究

对渝东重庆石柱林场不同林龄(8a、20 a、30 a)马尾松生长及生物量分配状况研究,结果表明:①马尾松的胸径和树高在幼龄林(8a)和中龄林(20a)生长速度最快,材积量则在成熟期(30a)达到最大.②马尾松各器官生物量和总量随着林龄的增加而增加,树干的生物量增长速度最快,在成熟期最高,达到72.68％.③各林龄马尾松林内,各层次生物量的高低排序都为乔木层、枯落物层、草本层、灌木层;乔木层生物量和林地地上总生物量均随着林龄的增加而增加,并占有绝对的优势;灌木层、草本层和枯落物层占地上部分总生物量比重则逐渐降低.④马尾松林的地上部分各林层的净生产力在中龄林的高低排序都为乔木层、枯落物层、草本层、灌木层,幼龄林和成熟林则表现为乔木层、草本层、枯落物层、灌木层;乔木层生产力在地上总生产力中占绝对比重.     

陇东黄土高原沟壑区刺槐和油松人工林的生物量和碳密度及其分配规律

【目的】基于陇东黄土高原沟壑区刺槐人工林和油松人工林样地调查数据,分析其生物量、碳含量、碳密度及其分配规律,为该地区人工林碳效益估算提供基础数据。【方法】以陇东黄土高原沟壑区12年生刺槐人工林和12年生油松人工林为研究对象,采用样地调查与生物量实测的方法,研究刺槐人工林和油松人工林乔木不同器官、灌草层和枯落物层生物量,以及刺槐人工林和油松人工林乔木层、灌草层、枯落物层和土壤层碳储量及其分配特征。【结果】刺槐人工林乔木层平均碳含量(468.44 g·kg －1)低于油松人工林乔木层平均碳含量(512.77 g· kg －1);刺槐林乔木各器官碳含量为458.00～496.96 g·kg －1,不同器官碳含量表现为干＞枝＞叶＞根＞皮,油松人工林乔木各器官碳含量为503.83～536.27 g·kg －1,不同器官碳含量依表现干＞叶＞枝＞皮＞根;刺槐林草本层、灌木层及枯落物层平均碳含量分别为390.52,398.72和402.82 g·kg －1,油松林草本层、灌木层及枯落物层平均碳含量分别为413.17,436.85和414.03 g·kg －1;随着土壤深度增加,刺槐林和油松林土壤碳含量依次降低,0～10 cm土层土壤含量显著高于10～20,20～30和30～50 cm土层;刺槐林0～50 cm 土层土壤平均碳含量(4.96 g·kg －1)高于油松林(4.45 g·kg －1);刺槐林植被层生物量为54.80 t·hm －2,乔木层、草本层和灌木层分别占95.88%,2.65%和1.46%;油松林植被层生物量为24.37 t·hm －2,乔木层、草本层和灌木层分别占93.43%,5.17%和1.40%;刺槐林枯落物层生物量和碳密度分别为1.36和0.55 t·hm －2,分别是植被层的2.48%和2.12%,油松林枯落物层生物量和碳密度分别为0.92和0.39 t·hm －2,分别是植被层的3.78%和3.09%;刺槐林和油松林土壤层碳密度分别为31.15和24.35 t·hm －2,0～10 cm土壤层碳密度较高,分别占0～50 cm土层土壤碳密度的40.19%和38.73%;刺槐林植被层生物量(54.80 t·hm －2)高于油松林植被层生物量(24.37 t·hm －2);刺槐林和油松林生态系统总碳密度分别为57.60和37.38 t·hm －2,且均表现为土壤层＞植被层＞枯落物层。【结论】刺槐林和油松林植被层生物量表现为乔木层＞草本层＞灌木层,乔木层生物量均以树干占比最大,分别为40.02%和37.29%;2种人工林生态系统碳密度主要分布在土壤和植被中,且刺槐人工林生态系统具有较高的固碳能力。     

海南沿海木麻黄人工林林下植被生物量

采用样地调查法,对海南沿海木麻黄人工林林下植被进行调查、并测定其生物量。结果表明:木麻黄人工林林下灌木层地上部分生物量大于地下部分生物量,草本层地下部分生物量大于地上部分生物量;灌木层各器官的生物量分配规律为干(3.41 t·hm-2)根(3.19 t·hm-2)叶(2.10 t·hm-2)枝(1.41 t·hm-2),干和根的生物量比例较大;灌木层、草本层生物量与总生物量均呈正相关关系,灌木层生物量与草本层生物量则呈负相关关系,说明灌木层与草本层存在竞争。     

甘肃黄土丘陵区侧柏人工幼林的碳密度及分配特征

【目的】以甘肃黄土丘陵区宁县人工林地为研究区,探讨侧柏人工林碳密度及其分配特征,为黄土丘陵区人工林生态效益评估提供理论依据。【方法】以不同林龄侧柏人工林(7,10,12和14年生)为研究对象,每个林龄分别设置3块样地,分乔木层、灌木层、草本层和枯落物层进行调查取样,然后在每块样地采集0～100 cm土层的土样,用元素分析仪 LiquiTOCⅡ测定植物和土壤碳含量,研究甘肃黄土丘陵区侧柏人工幼林的碳含量、碳密度及其分配特征。【结果】侧柏不同器官碳含量为447.51～513.93 g·kg －1,表现为果实＞树叶＞树干＞粗枝＞细枝＞细根＞根桩＞树皮＞粗根＞大根＞中根＞小根;灌木层和草本层均以根的碳含量最低,枯落物层未分解层碳含量高于半分解层,且各组分碳含量差异显著;土壤层(0～100 cm )碳含量为23.31～96.08 g·kg －1,且随林龄增加而增大,随土壤深度增加而下降;侧柏人工林生态系统中,乔木层碳密度占植被层碳密度比例最大,高于灌木层、草本层和枯落物层;0～100 cm土层土壤碳密度占整个生态系统碳密度比例最大,且随着林龄增加而增大,且差异显著;7,10,12和14年生侧柏人工幼林生态系统碳密度分别为37.56,44.67,50.87和56.34 t·hm －2,乔木层、林下植被层、枯落物层和土壤层的碳密度均随林龄增加而增大。【结论】黄土丘陵区7,10,12和14年生侧柏人工幼林的乔木层不同器官碳含量差异显著(P＜0.05),相同器官碳含量差异不显著(P＞0.05);侧柏人工林生态系统碳库表现为土壤层＞乔木层＞草本层＞枯落物层＞灌木层;侧柏人工林各层的碳密度都随林龄增加而增大;乔木层、灌木层、草本层和枯落物层碳密度分配比例随林龄增加而增大,而土壤层碳密度比例随林龄增加而减少。     

不同林龄尾巨桉林地土壤有机碳储量变化差异

为桉树人工林的土壤质量评价提供科学依据,研究了不同林龄(1a、2a、3a、5a、7a)尾巨桉林地0~60cm土壤和枯落物的碳含量及碳储量,测算了不同林龄桉树林地叶面积指数,乔木层、灌木层、草本层和枯落物层生物量。结果表明：土壤有机碳含量随土层深度增加而呈降低趋势,不同林龄0~20 cm土层有机碳含量差异显著,不同林龄相同土层之间土壤有机碳储量差异不显著;枯落物碳储量差异显著,大小顺序为：5 a (4.83 t·hm-2)>7 a (3.89 t·hm-2)>3 a (2.66 t·hm-2)>2 a (2.43 t·hm-2)>1 a (1.56 t·hm-2);0~60 cm土层土壤碳储量与叶面积指数呈负相关关系,与林龄、乔木层生物量、灌木层生物量、草本层生物量、枯落物层生物量之间呈正相关性,但相关性都不显著。     

辽东山区长白落叶松天然更新调查

调查辽东山区长白落叶松人工林的长白落叶松天然更新数量、幼苗的存活和生长状况以及其幼树出现的生境.结果表明:在结实的长白落叶松人工林内均有1年生落叶松幼苗,其数量与人工林种子库落叶松种子数量有关,其存活和生长(高生长和叶片数量)状况明显受林分开阔度、地面植被盖度和枯落物的影响.1年生长白落叶松幼苗在林内生长缓慢,一般高生长不超过6 cm,地径生长不超过0.1 cm,叶片数量不超过25针.长白落叶松天然更新幼苗4月末开始出现,6月份幼苗数量最多,9月份林内大部分幼苗死亡.这表明长白落叶松幼苗在林下不能正常存活和生长,而影响其存活和生长的主要因素是光照、草本灌木和地面枯落物.另外,长白落叶松林下很难见到幼树,只有在有种源、光照充足、草本灌木和枯落物少,以及土壤较湿润的生境中能见到其幼树.     

六盘山华北落叶松人工纯林枯落物储量的空间变异分析

在六盘山南侧设置2个20 m×20 m的华北落叶松人工林样地,研究枯落物储量的空间分布.结果表明:枯落物储量空间差异明显,2个样地的枯落物储量平均值为1.80和1.68 kg·m-2,最大值为2.96和2.71 kg·m-2,最小值为0.35和0.34 kg·m-2,最大和最小值的比值变化在8～9之间;在不考虑测点空间位置及取样间距的情况下,2个样地枯落物储量的变异系数为0.41和0.56;枯落物储量的空间分布受空间结构性和随机性的多种因素影响,其中林地微地形能解释枯落物储量空间变异的56%,局部洼地利于更多枯落物堆积;2个样地枯落物储量的空间分布函数曲线的理论模型均符合球状模型,且空间自相关程度较呔;当以95%的置信区间准确估计华北落叶松林样地的枯落物储量时,最小取样数量为9个1 m×1 m的样方.     

塔里木河下游荒漠植被地上生物量空间分布与地下水埋深关系

【目的】研究荒漠植被地上生物量随距河道距离的空间分布特征,并结合地下水埋深数据分析地上生物量与地下水埋深之间的关系,以期为干旱荒漠区生态环境恢复和重建提供理论依据。【方法】以塔里木河下游英苏断面荒漠河岸林植被为对象,于2014年9月下旬在英苏断面布设垂直河道、100 m×100 m的标准地20块,形成长2 000 m的连续样带,记录标准地内乔木、灌木的物种数、总个体数及冠幅、株高、胸径等形态因子,根据胡杨生物量模型和获取的灌木标准枝鲜质量,分别计算胡杨和灌木的地上生物量;将标准地进一步分割为4块50 m×50 m的样地,在每个样地对角线两侧随机布设6~8个1 m×1 m的样方,记录草本种类、个体总数等因子,并将样方内草本齐地面刈割,获取地上生物量数据。结合样带植被群落地上生物量数据和地下水埋深数据,拟合二者之间的方程,并进行显著性检验。【结果】塔里木河下游荒漠植被地上生物量与距河道垂直距离和地下水埋深均显著负相关(P0.05),总地上生物量、乔木层和灌木层地上生物量均随距河距离增大而减少,草本地上生物量则呈"先小幅度增加后持续减少"的单峰型变化趋势;样带内乔灌草总地上生物量主要分布在地下水埋深4 m(距河0~300 m)范围内,地上生物量可达855.06 g·m-2;当地下水埋深在4~5.5 m(距河道300~1 000 m)时,地上生物量为321.08 g·m-2,减少62.45%;当地下水持续降到5.5 m(距河道1 000~2 000 m)时,地上生物量只有110.19 g·m-2,比河道附近减少了87.11%。【结论】塔里木河下游荒漠植被群落组成和地上生物量随距河道距离和地下水埋深变化呈现显著的空间异质性,表明地下水埋深是影响荒漠植被群落组成和地上生物量的一个重要因子,同时也反映出河道作为荒漠河岸林的主要水源控制荒漠植被的空间分布和结构,体现出极端干旱区生态系统空间分布和结构特征的特殊控制机制。     

长江上游绵阳官司河流域低山丘陵区不同植被类型生物多样性分析

本文用多样性指数（Shannon—Wiener指数、Simpson指数）、均度指数（Pielou指数）、丰富度指数（Margalef指数、Menhinick指数）对绵阳官司河流域5种不同的人工林进行生物多样性分析,结果表明：经过植被恢复,各林分类型生物多样性都有所提高,同时水土保持效益也明显提高,土壤侵蚀量减少了42％;在5种植被类型中,乔木层中以针阔混交林的生物多样性最高,灌木层以松柏混交林和麻栎林的生物多样性最高,草本层以松柏混交林的生物多样性最高;5种植被类型中,灌木层地上部分生物量以针阔混交林最大为1849．37kg·hm^-2,马尾松纯林最小为747．37kg·hm^-2,其大小顺序为：针阔混交林〉柏木纯林〉栎类林〉松柏混交林〉马尾松纯林;草本层植物地上部分部总生物量大小顺序为：松柏混交林〉柏木纯林〉栎类林〉针阔混交林〉马尾松纯林。     

气候和枯落物质量对印度东部亚热带森林凋落叶分解和营养回归的影响(英文)

为了评价印度东部曼尼普尔亚热带橡树混交林中的土壤养分收支平衡情况,研究了全年不同月份的3个主要树种,枹栎(Quercus serrata)、木荷(Schima wallichi)和滇石栎(Lithocarpus dealbata)的枯落物分解和营养回归情况。印度东部橡树林是生产柞蚕丝的重要经济树种。林下2-7月月枯落物为25.6 g·m-2(7月)和198.0 g·m-2(2月),年枯落物为1093 8g·m-2。在初始月(11月3),滇石栎森林壤土的氮和碳浓度最高,其次是在枹栎林。最低的是木荷林。但就木质素和纤维素含而言,木荷林中的最高,其次是袍栎林和滇石栎林。滇石栎林(k=0.54)具有较高的枯落物分解率,这与月初枯落物中含有较高的氮和碳浓度以及低含量的纤维素相符合。然而,在木荷森林中枯落物分解率低,是与月初时森林土中具有低浓度氮和碳及高浓度木质素和纤维素相符合。在不同月份,剩余的生物量与木质素、碳、碳氮比和纤维素含量呈正相关,但与氮含量呈负相关。由于环境条件的影响,在寒冷和冬季枯落物分解率最低,而在雨季枯落物分解率最高。图3表5参52。     

Seasonal variations in species diversity, dry matter and net primary productivity of herb layer of Quercus leucotrichophora-Pinus roxburghii mixed forest in Kumaun Himalaya, India

Plant biomass, species diversity and net primary productivity are presented for herb layer of banj oak (Quercus leucotrichophora A. Camus)-chir pine (Pinus roxburghii Sarg.) mixed forest in Kumaun, central Himalaya, India. The species diversity declined from a maximum (3.56) in September to a minimum (2.11) in December. The monthly live shoots biomass exhibited a single peak growth pattern with highest live shoot biomass of 185 g·m-2 in August. The seasonal pattern showed that the maximum above-ground production (131 g·m-2) occurred during the rainy season and the minimum (1 g·m-2) during winter season. The below-ground production was maximum during winter season (84 g·m-2) and minimum during summer season (34 g·m-2). The annual net shoot production was 171 g·m-2 and total below-ground production was 165 g·m-2. Of the total input 61% was channeled to above-ground parts and 39% to below-ground parts. Transfer of live shoots to dead shoots compartments and that of dead shoots to litter compartments was 61% and 66%, respectively. The total dry matter disappearance was 61% of the total input within annual cycle. The herb layer showed a net accumulation of organic matter, indicating the seral nature of the community.     

半红树植物杨叶肖槿幼苗耐盐性研究

温室内对半红树植物杨叶肖槿幼苗进行7个盐度(5、8、11、14、17、20、23 g·kg-1)的胁迫处理,并对各处理下杨叶肖槿的生长量、生物量、生理指标和光合速率进行测定,结合生理指标进行适应度分析.结果表明:杨叶肖槿的苗高、地径、叶片数、根、茎、叶干质量及总生物量随着盐度的上升均呈下降趋势,在盐度为5、8 g·kg...     

桂西南岩溶区不同恢复模式群落生物量及林下植物多样性

[目的]研究桂西南岩溶区不同恢复模式群落的生物量及其林下植物多样性的特点,为该区域的生物多样性保护、生态功能恢复效果评价积累基础数据。[方法]以桂西南岩溶区4种不同恢复模式为研究对象,采用样方法对林下植物多样性进行研究;采用收获法研究灌木层与草本层的地上、地下生物量及凋落物层现存量;采用异速生长模型来估算乔木层的地上生物量,并参考IPCC根茎比来量化乔木的地下生物量。[结果]表明:共调查记录林下植物85种,隶属于46科,81属,其中,灌木植物25科,46属,50种;草本植物21科,35属,35种;不同恢复模式群落生物量的变化趋势为自然恢复林(166.66 t·hm-2)任豆林(48.61 t·hm-2)吊丝竹林(36.54 t·hm-2)灌草坡(0.96 t·hm-2)。[结论]不同恢复模式灌木层物种丰富度差异不显著,最高的为灌草坡(16种),其次为任豆林(15种),最低为自然恢复林(12种);草本层物种丰富度最高的为任豆林(12种),其次为灌草坡(10种),最低为自然恢复林(4种)。自然恢复林乔木不同组分生物量与任豆林、吊丝竹林之间差异显著(P0.05);灌草坡的灌木、草本地上生物量与吊丝竹林、任豆林、自然恢复林之间差异显著(P0.05)。吊丝竹林、任豆林的灌草生物量表现为草本层灌木层,而灌草坡与自然恢复林的灌草生物量则表现为灌木层草本层。     

Estimation of shrub biomass by airborne LiDAR data in small forest stands

The presence of shrub vegetation is very significant in Mediterranean ecosystems. However, the difficulty involved in shrub management and the lack of information about behavior of this vegetation means that these areas are often left out of spatial planning projects. Airborne LiDAR (Light Detection And Ranging) has been used successfully in forestry to estimate dendrometric and dasometric variables that allow to characterize forest structure. In contrast, little research has focused on shrub vegetation. The objective of this study was to estimate dry biomass of shrub vegetation in 83 stands of radius 0.5 m using variables derived from LiDAR data. Dominant species was Quercus coccifera, one of the most characteristic species of the Mediterranean forests. Density of LiDAR data in the analyzed stands varied from 2 points/m² to 16 points/m², being the average 8 points/m² and the standard deviation 4.5 points/m². Under these conditions, predictions of biomass were performed calculating the mean height, the maximum height and the percentile values 80th, 90th, and 95th derived from LiDAR in concentric areas whose radius varied from 0.50 m to 3.5 m from the center of the stand. The maximum R² and the minimum RMSE for dry biomass estimations were obtained when the percentile 95th of LiDAR data was calculated in an area of radius 1.5 m, being 0.48 and 1.45 kg, respectively. For this radius, it was found that for the stands (n = 39) where the DTM is calculated with high accuracy (RMSE lower than 0.20 m) and with a high density of LiDAR data (more than 8 points/m²) the R² value was 0.73. These results show the possibility of estimating shrub biomass in small areas when the density of LiDAR data is high and errors associated to the DTM are low. These results would allow us to improve the knowledge about shrub behavior avoiding the cost of field measurements and clear cutting actions.     

六盘山主要植被类型的生物量及其分配

2009年,在宁夏六盘山南部林区香水河小流域,调查研究了主要森林类型的生物量及其层次和器官分配。结果表明:不同森林的活体植被总生物量(t·hm^-2)差别较大,依次为华山松(102.70)>桦木林(84.42)>山杨林(79.97)>华北落叶松人工林(58.37)>疏林(44.91),按各类森林面积加权平均为78.37,远高于灌丛(20.77)、草地(1.07)和草甸(2.29)。各类森林的枯落物现存量(t·hm^-2)为:华北落叶松人工林(18.21)>华山松林(11.99)>桦木林(10.90)>山杨林(7.67)>疏林(7.06),也都远高于灌木林(3.13)、草甸(0.82)和草地(0.49)。森林生物量集中在乔木层(占91.04%),灌木层仅占8.09%,草本层更低至0.87%。森林生物量的器官分配比例:乔木层为树干(54.06%)>枝(21.04%)>根(16.92%)>皮(5.34%)>叶(2.65%);灌木层为枝干(62.68%)>根(30.55%)>叶(6.77%);草本层为地上茎叶(58.82%)>根(41.18%)。乔木层地上与地下生物量比值的平均值为4.49,几种阔叶林都在4.0左右,但华北落叶松林为6.41,华山松林为5.80,都远大于灌木林的2.82、草地的1.89及草甸的1.20。不同林分的生物量均随林龄和林冠郁闭度的增大而几乎线性增加,并随林分密度的增加而增大,但在密度超过900株·hm^-2后生物量增速减缓并渐趋其最大值。     

利用深黄被孢霉发酵生产油脂的初步研究

为提高微生物油脂产量,以产油微生物深黄被孢霉为试验菌株,采用单因素试验设计,通过摇瓶培养,研究了产脂培养基中碳源、氮源种类及其浓度、接种量、初始pH值、无机盐离子对菌体生长和油脂积累的影响,确定了深黄被孢霉摇瓶发酵产油脂的优化培养条件为:葡萄糖100 g.L-1,酵母粉3.0 g.L-1,接种量为20%,pH值为5.0~6.0,硫酸镁(MgSO4.7H2O)0.5 g.L-1,磷酸二氢钾(KH2PO4)2.0 g.L-1。在优化培养条件下菌体生物量为20.62 g.L-1,油脂含量为43.02%,油脂产量为8.87 g.L-1。     

Seasonal and spatial variation of nitrogen dynamics in the litter and surface soil layers on a tropical dry evergreen forest slope

Seasonal and spatial variability of litterfall and NO₃⁻ and NH₄⁺ leaching from the litter layer and 5-cm soil depth were investigated along a slope in a tropical dry evergreen forest in northeastern Thailand. Using ion exchange resin and buried bag methods, the vertical flux and transformation of inorganic nitrogen (N) were observed during four periods (dry, early wet, middle wet, and late wet seasons) at 15 subplots in a 180-m × 40-m rectangular plot on the slope. Annual N input via litterfall and inorganic N leached from the litter layer and from 5-cm depth soil were 12.5, 6.9, and 3.7 g N m⁻² year⁻¹, respectively, whereas net mineralization and the inorganic N pool in 0–5-cm soil were 7.1 g N m⁻² year⁻¹ and 1.4 g N m⁻², respectively. During the early wet season (90 days), we observed 82% and 74% of annual NO₃⁻ leaching from the litter layer and 5-cm soil depth, respectively. Higher N input via leaf litterfall in the dry season and via precipitation in the early wet season may have led to higher NO₃⁻ leaching rate from litter and surface soil layers during the early wet season. Large spatial variability in both NO₃⁻ vertical flux and litterfall was also observed within stands. Small-scale spatial patterns of total N input via litterfall were significantly correlated with NO₃⁻ leaching rate from the surface soil layer. In tropical dry evergreen forests, litterfall variability may be crucial to the remarkable seasonal changes and spatial variation in annual NO₃⁻ vertical flux in surface soil layers.     

西藏南伊沟林芝云杉林生物量与生产力研究

采用样地调查及标准样木收获法,研究西藏米林南伊沟成熟林芝云杉(Picea likiangensis var.linzhiensis林乔木层、灌木层、草本层、死亡木、凋落物层的生物量与生产力及其分配规律.结果表明:林芝云杉林生态系统总的生物量为367.49 t·hm-2,其中乔木层生物量最高276.64 t·hm-2,占总生物量的75.28％,其次是凋落层的生物量40.65 t·hm-2,占总生物量的11.06％.在乔木层中,干材生物量201.23 t·hm-2 (69.32％),皮25.53 t·hm-2(8.79％),枝17.80 t·hm-2(6.13％),叶3.33 t·hm-2(1.15％),根42.87 t·hm-2(14.61％).随着树木的生长,干材生物量所占比例增大,而枝、叶的比例则减小.林芝云杉林生态系统生产力为10.65 t·hm-2·a-1,其中乔木层最高5.00 t·hm-2·a-1,占总生产力的46.94％,其次为凋落层3.40 t·hm-2·a-1,占总生产力31.94％.在乔木层中仍以树干生产力最大2.58 t·hm-2 ·a-1,依次为枝(0.89 t·hm-2·a-1)、叶(0.67t·hm-2·a-1)、根(0.54t·hm-2·a-1)、皮(0.33 t·hm-2 ·a-1).     

Water harvesting in a ‘runoff-catchment’ agroforestry system in the dry lands of Ethiopia

A major production constraint in arid and semiarid areas of Ethiopia is a lack of water for crop growth. Run off water can be harvested by channeling it into micro- catchments (MC) where it slowly infiltrates into the soil. The increased moisture provides more plant growth in these dry lands. An experiment using MC was conducted in eastern Ethiopia to study the growth of four multipurpose tree species intercropped with grass. Trees and grass were grown in 25 m² and 100 m² MC. Plant height, root collar diameter, and mortality rate of trees were determined 12 months after planting. Dry matter yield of grasses and trees were measured and nutrient analysis of plant tissues was determined. In a separate experiment the biomass of trees was determined after 2.5 years of continuous growth without grass competition. Soil moisture, organic matter, texture and bulk density of the soils were also determined. Mean tree height was 10% greater in the 100 m² than in the 25 m² MC. Root collar diameter and survival rate showed similar increase with 13% and 7.8% respectively. Acacia saligna and Leucaena leucocephala showed better growth in both plot sizes than the indigenous Acacia seyal and Acacia tortilis. The dry matter yield of grass (Panicum maximum) was over 12 tons/ha and 8 tons/ha in the 100 m2 and 25 m2 plots respectively. Soil moisture content was greater in MC than in control plots with no water harvesting structures with 31% and 24% during the wet and dry seasons respectively. The use of water harvesting can improve fodder production and carrying capacity of the dry lands of Ethiopia.     

Effect of planting density on plant growth and camptothecin content of Camptotheca acuminata seedlings

C. acuminata seedlings cultivated in greenhouse were transplanted into the fields with 5 designed planting densities (11, 16, 25, 44 and 100 plants·m⁻²) in May of 2004 and were harvested in the middle of September of 2004. The seedling growth indexes including plant height and crown width, biomass allocation, camptothecin (CPT) content and CPT yield of different organs (young leaf, old leaf, stem, and root) were studied. For the 5 selected planting densities, the plant biomass, height, crown width, and total leaf area ofC. acuminata seedlings all showed highest values at the planting density of 25 plants·m⁻². CPT content in young leaves was higher than that in other organs of seedlings and presented an obvious change with the variation of planting densities and with the highest value at density of 100 plants·m⁻², while for other organs no significant variation in CPT content was found with change of planting density. The accumulation of CPT was enhanced significantly at the planting density of 25 plants·m⁻². It is concluded that for the purpose to get raw materials with more CPT fromC. acuminata, the optimal planting density ofC. acuminata seedlings should be designed as 25 plants·m⁻². Foundation item: This paper was supported by the National Natural Science Foundation of China (No. 3970086) and Heilongjiang Province Foundation for Distinguished Youth Scholars (JC-02-11) Biography: Wei Huan-yong (1978-), male, Graduate in College of Life Sciences, Northeast Forestry University, Harbin 150040, P. R. China. Responsible editor: Zhu Hong