Effects of partial defoliation on closed canopy Eucalyptus globulus Labilladière: Growth, biomass allocation and carbohydrates

Herbivory caused by leaf-eating insects continues to be a severe risk to forest trees and forest stands. Besides quantifying the extent of defoliation, the quantification of the trees’ response to the loss of biomass is a challenge to plant ecologists and foresters alike, and an important precondition for the application of appropriate silvicultural measures. While many defoliation studies target small trees as model systems, little is known about the effect of defoliation on larger trees. In the present study, we investigated the effects of 45% removal of leaf area on growth, biomass allocation and carbohydrates of 13 m tall, four-year-old, plantation Eucalyptus globulus Labill. in southern Tasmania. Responses were measured in three crown zones (lower, middle, upper) over a period of 11 months. Height increment was unaffected by defoliation, but diameter increment was significantly reduced 155 days after treatment. Defoliation treatment had no effect on stem volume and biomass partitioning compared with the control treatment. Trees responded to defoliation by decreased branch senescence in the lower crown, greater leaf area development in the mid crown and increased specific leaf area. Defoliation reduced concentration of soluble sugars (SS) in foliage by 22% and the pools of SS in the coarse roots by 34%. Decrease in root SS was only observed in 10-15 mm diameter class and the rootball. We concluded that this four-year-old E. globulus stands with a closed canopy was able to tolerate a single, partial artificial defoliation event, which is similarly observed with younger trees.     

毛竹叶片衰老过程碳氮元素及灰分含量的季节动态

于2006年4月—2007年3月,对福建永春毛竹(Phyllostachys pubescens)成熟叶和老叶的C、N元素及灰分含量的季节动态及元素的内吸收率进行研究。结果表明:①毛竹成熟叶和老叶的C、N元素含量存在一定的季节变化,从成熟叶到老叶,C含量保持相对稳定,而N含量呈现下降趋势。②毛竹成熟叶、老叶灰分含量月变化趋势相似,毛竹成熟叶、老叶的灰分含量在秋季(10月)至翌年春季(3月)灰分含量较高,而春夏季相对较低;毛竹成熟叶的灰分含量在7.56%～15.91%之间,老叶的灰分含量在7.46%～16.67%,老叶灰分含量高于成熟叶(P=0.0199)。③毛竹叶片衰老过程N的内吸收率为36.68%。     

卧龙自然保护区油竹子（Fargesia angustissima）生理生态特征的海拔变化

全球气候变化（如温度升高）迅速而强劲地影响着高海拔地区的生态环境,致使植物生长发生变化,因此高山地区成为研究植物环境适应性及其对全球气候变化响应的理想区域。为了认清气候变化如何影响竹子的生长和生理生态特性,本文系统调查研究了卧龙自然保护区内大熊猫典型主食竹种油竹子（Fargesia angustissima（Mitford）T.P.Yi）,从其天然分布下限至上限,在卧龙自然保护区沿海拔梯度研究了分株的比叶面积（SpecificLeaf Area,SLA）、基于单位叶面积和单位叶质量的叶氮含量（Narea,Nmass）,以及组织非结构性碳水化合物（NSC）含量及其组分。研究结果表明,各调查因子对海拔的响应均是非线性的,表现为随着海拔升高,各调查值先降后升,高峰值出现在分布上限区域（1 810 m）,而最低值出现在中海拔区域（1 620 m）,反映了环境因子随海拔的非线性变化。分析认为,油竹子的生长受不同海拔环境影响较大。     

夏玉米“波式”冠层结构及对微环境和产量的影响

采用局部化控、局部去雄和局部化控+去雄方式塑造玉米波式冠层结构,并分析了该冠层结构特征及对微环境和产量的影响。结果表明:与对照比较,波式冠层玉米植株变矮,穗上部节间变长、基部节间增粗,使玉米群体形成波式冠层的同时,群体LAI增大且持续时间较长;冠层内中下部透光率增加,CO2浓度增加,相对湿度和温度降低;穗粒数和粒重显著增加,空秆率下降,在低密度条件下比对照增产207.2～682.19 kg/hm2,高密度下增产392.62～655.76 kg/hm2。     

厚朴离体叶片衰老过程的生理生化测定

随着厚朴叶片离体衰老时间的延长,蛋白质,叶绿素含量明显下降,质膜透性增加。与自由基代谢有关的超氧物歧化酶活性在叶片衰老过程中不断下降,表明自由基代谢失调引起的膜脂过氧化的加剧是厚朴叶片衰老的重要原因之一。高温加速厚朴叶片的衰老进程,而营养液则延缓了厚朴叶片的衰老。     

红麻光合特性和干物质生产的品种间差异的初步研究 Ⅱ.叶面积和比叶重

在盆栽或大田无株间相互荫蔽条件下测定30个红麻品种的单株叶面积(LA)和单株比叶重(SLW).结果表明,品种间LA差异极显著,而SLW差异不显著;不同生长季节间、苗期与生长中期之间的LA和SLW都呈显著正相关.据此,可以认为LA和SLW都是相对稳定的品种特性,可考虑用作选择较高光合能力品种(品系)的指标.此外,目前种植面积较大的品种青皮3号和722的LA均接近于所测品种的平均值,因而有可能找出LA比青皮3号和722较高的品种(品系).     

不同浓度磷酸二氢钾对紫叶矮樱叶片结构的影响

为研究外源磷酸二氢钾对紫叶矮樱叶片显微结构的影响,试验在田间条件下,3年生紫叶矮樱为试材,磷酸二氢钾浓度设置为0．1％,0．2％,0．4％,清水为对照,3次重复。试验结果表明：紫叶矮樱叶片内栅栏组织厚度与海绵组织厚度外观表现是随着浓度的增加细胞变小,细胞间隙变小,细胞排列紧密;叶片喷施磷酸二氢钾后栅栏组织和海绵组织厚度显著低于对照,细胞长度显著低于对照,叶片厚度显著低于对照;外源物质显著改变了紫叶矮樱叶片显微结构,喷施浓度越低效果越好,浓度越高改变越小。综合分析认为,较低浓度的磷酸二氢钾处理能够较好的改变紫叶矮樱的叶片显微结构。     

城市绿地园林树种叶面积指数测定方法研究——以小叶榕为例

分别采用半球面影像技术和LAI-2000冠层分析仪对华南地区最常用园林树种小叶榕(Ficus microcarpa)的叶面积指数(Leaf Area Index,LAI)进行测定、比较和分析。研究表明,2种测量仪器所测LAI值存在极显著正相关(P<0.001);用半球面影像技术测量的LAI值与冠幅、胸径和树高之间也存在极显著一元线性关系,构建回归模型分别为:LAI=0.0444Cw+1.6526,LAI=0.0088D+1.8327,LAI=0.0543H+1.6404;通过模型可估测小叶榕单株的叶面积指数,达到95%的置信区间的估测值范围。     

Nutrient composition and short-term release from <Emphasis Type="Italic">Croton macrostachyus</Emphasis> Del. and <Emphasis Type="Italic">Millettia ferruginea</Emphasis> (Hochst.) Baker leaves

A field study was conducted to investigate the nutrient content of green and abscised leaves of Croton macrostachyus Del. and Millettia ferruginea (Hochst.) Baker and their decomposition to return these nutrients to the soil in the short-term. Green and abscised leaves were collected from trees of comparable size in Wondo Genet, Ethiopia, and were incorporated into litterbags to decompose for a period of 12 weeks. Green leaves of C. macrostachyus had significantly higher nutrient concentrations than those of M. ferruginea. In both species, green leaves had significantly higher (P<0.05) C, N and P and significantly lower (P<0.05) lignin and polyphenol concentrations than abscised leaves. Fifty percent of the biomass applied was lost during the first 7 weeks in C. macrostachyus, which was about 3 times faster than that of M. ferruginea. The half-lives of N and P were 5–8 weeks and 4–6 weeks, respectively, in C. macrostachyus; the corresponding values for M. ferruginea were 6–8 and about 22 weeks, respectively. Only 15.7% and 26.8% of green and abscised leaves of C. macrostachyus, respectively, were recovered after the 12 weeks of decomposition. The corresponding values were about 3.5-fold and 2.5-fold higher for M. ferruginea. Generally, leaves with higher initial lignin, polyphenol, lignin:N and C:N ratios had lower decomposition and mineralization rates. In both species, removal of leaf biomass before abscission (e.g. by pruning) could enhance both the quantity and rate of nutrient return to the soil.     

Relationship of host recurrence in fungi to rates of tropical leaf decomposition

Here we explore the significance of fungal diversity on ecosystem processes by testing whether microfungal ‘preferences’ for (i.e., host recurrence) different tropical leaf species increases the rate of decomposition. We used pairwise combinations of γ-irradiated litter of five tree species with cultures of two dominant microfungi derived from each plant in a microcosm experiment. The experiment was designed to test whether early leaf decomposition rates differed depending on relationships between the leaf litter from which the fungi were derived (i.e., the source plant) and the leaf substrata decomposed by these fungi in microcosms. Relationships tested were phylogenetic relatedness between the source and substratum leaves, and similarity in litter quality (lignin, N and P) between the source and substratum. We found a significant interaction between microfungi and leaf species (P<0.0001), and differences among the four classes of source–substratum relationships were highly significant (P=0.0004). Combinations in which fungal source leaves were of the same species or family as the substratum, or the fungal source resembled the substratum in quality had marginally faster decomposition than when the fungal source and substratum leaves were mismatched (i.e., unrelated and of dissimilar quality). In some microcosms, a basidiomycete contaminant had a strong additive effect on decomposition of Croton poecilanthus leaves resulting in faster decomposition than with microfungi alone (P<0.0001). Comparisons among leaf–microfungal combinations were made after the effect of the basidiomycete covariate was adjusted to zero. The data on microfungi suggest differential abundance in particular hosts, which contributes to species diversity of decomposer fungi in tropical forests, affects rates of decomposition.