川西亚高山典型森林生态系统截留水文效应

截留是水文循环的一个重要过程,水文功能是森林生态系统功能的重要方面,林冠和枯落物截留实现对大气降水的二次分配过程.为深入认识生态系统截留的水文效应,采用野外观测和人工降雨模拟试验相结合的方法,研究了2008年和2009年5-10月贡嘎山亚高山峨眉冷杉中龄林、峨眉冷杉成熟林和针阔混交林的冠层枯落物截留能力.结果表明,峨眉冷杉中龄林2008年林冠截留率为20.9％,针阔混交林2008年和2009年林冠截留率分别为23.0％和23.6％,林冠截留率的年际间变化不大,林冠截留主要受到降雨特征影响.3种林型枯落物饱和持水能力分别为5.1、5.1和5.7 mm,显著高于林冠的饱和持水能力,但由于冠层的截留蒸发速率较高,林冠截留蒸发仍是生态系统截留蒸发的主要组成部分.     

The Effect of Leaf Litter Cover on Surface Runoff and Soil Erosion in Northern China

The role of leaf litter in hydrological processes and soil erosion of forest ecosystems is poorly understood. A field experiment was conducted under simulated rainfall in runoff plots with a slope of 10%. Two common types of litter in North China (from Quercus variabilis, representing broadleaf litter, and Pinus tabulaeformis, representing needle leaf litter), four amounts of litter, and five rainfall intensities were tested. Results revealed that the litter reduced runoff and delayed the beginning of runoff, but significantly reduced soil loss (p<0.05). Average runoff yield was 29.5% and 31.3% less than bare-soil plot, and for Q. variabilis and P. tabulaeformis, respectively, and average sediment yield was 85.1% and 79.9% lower. Rainfall intensity significantly affected runoff (R = 0.99, p<0.05), and the efficiency in runoff reduction by litter decreased considerably. Runoff yield and the runoff coefficient increased dramatically by 72.9 and 5.4 times, respectively. The period of time before runoff appeared decreased approximately 96.7% when rainfall intensity increased from 5.7 to 75.6 mm h⁻¹. Broadleaf and needle leaf litter showed similarly relevant effects on runoff and soil erosion control, since no significant differences (p≤0.05) were observed in runoff and sediment variables between two litter-covered plots. In contrast, litter mass was probably not a main factor in determining runoff and sediment because a significant correlation was found only with sediment in Q. variabilis litter plot. Finally, runoff yield was significantly correlated (p<0.05) with sediment yield. These results suggest that the protective role of leaf litter in runoff and erosion processes was crucial, and both rainfall intensity and litter characteristics had an impact on these processes.     

Application of leaf size and leafing intensity scaling across subtropical trees

Understanding the scaling between leaf size and leafing intensity (leaf number per stem size) is crucial for comprehending theories about the leaf costs and benefits in the leaf size–twig size spectrum. However, the scaling scope of leaf size versus leafing intensity changes along the twig leaf size variation in different leaf habit species remains elusive. Here, we hypothesize that the numerical value of scaling exponent for leaf mass versus leafing intensity in twig is governed by the minimum leaf mass versus maximum leaf mass (M _min versus M _max) and constrained to be ≤−1.0. We tested this hypothesis by analyzing the twigs of 123 species datasets compiled in the subtropical mountain forest. The standardized major axis regression (SMA) analyses showed the M _min scaled as the 1.19 power of M _max and the ‐α (−1.19) were not statistically different from the exponents of M _min versus leafing intensity in whole data. Across leaf habit groups, the M _max scaled negatively and isometrically with respect to leafing intensity. The pooled data''s scaling exponents ranged from −1.14 to −0.96 for M _min and M _max versus the leafing intensity based on stem volume (LIV). In the case of M _min and M _max versus the leafing intensity based on stem mass (LIM), the scaling exponents ranged from −1.24 to −1.04. Our hypothesis successfully predicts that the scaling relationship between leaf mass and leafing intensity is constrained to be ≤−1.0. More importantly, the lower limit to scaling of leaf mass and leafing intensity may be closely correlated with M _min versus M _max. Besides, constrained by the maximum leaf mass expansion, the broad scope range between leaf size and number may be insensitive to leaf habit groups in subtropical mountain forest.     

物种组成对高寒草甸植被冠层降雨截留容量的影响

高寒草甸退化减少地上生物量、叶面积指数(LAI),因而减少冠层降雨截留容量(S)。但是,未有研究评价物种组成改变对S的影响。用水浸泡法和水量平衡法研究青藏高原高寒草甸3个不同退化阶段下(未退化、轻度退化、中度退化)的S变化规律,并评价物种组成改变对S的影响。结果表明:高寒草甸退化显著减少S(P<0.05)。在未退化、轻度退化、中度退化的高寒草甸,水浸泡法测得的S分别为0.612 mm,0.289 mm 和0.217 mm;水量平衡法测得的S分别为0.979 mm,0.493 mm 和0.419 mm。物种组成改变对S的影响表现为:随着高寒草甸的3个不同退化阶段,S减少的幅度先大于后小于LAI减少的幅度。原因是:(1)在未退化的草甸,鹅绒委陵菜(Potentilla arserina)的叶面积占有显著优势,占总叶面积的31.18%;在轻度退化的草甸,禾本科植物(Graminoid)的叶面积占有显著优势,占总叶面积的44.41%,而鹅绒委陵菜是稀有种,仅占总叶面积的3.76%;在中度退化的草甸,鹅绒委陵菜的叶面积占有显著优势,占总叶面积的19.91%;(2)鹅绒委陵菜的叶单位面积吸附水量(S_L)是禾本科植物的大约2.5倍。     

Gash模型在黄土区人工刺槐林冠降雨截留研究中的应用

为了验证Gash林冠截留解析模型在黄土高原人工林中的适用性,基于2009年黄土丘陵沟壑区吕梁市王家沟小流域刺槐林样地降雨观测数据,采用Gash模型对林冠截留进行了模拟。所选刺槐林分为人工纯林,林龄约30a,阴坡,坡度24°,密度为990株/hm2,平均树高10.8 m,平均胸径12.4 cm,郁闭度0.76。根据回归方法确定了Gash模型中的主要参数,包括饱和林冠的平均蒸发速率(E珔)、林冠枝叶部分的持水能力(S)、自由穿透降雨系数(p)、树干持水能力(St)和树干茎流系数(Pt)。结果显示,2009年5月至10月人工刺槐林样地实测降雨量为366.9 mm,穿透降雨量为317.5 mm,树干茎流为10.2 mm,林冠截留量为39.2 mm。模型模拟的林冠截留量为42.4 mm,高于实测值3.2 mm,相对误差为8.2%。敏感性分析表明,S、E珔、St和pt每增加10%,林冠截留量分别增加4.7%,3.1%,1.7%和0.5%;p增加10%,林冠截留量则减少2.6%。说明树干持水能力(St)和树干茎流系数(pt)两个参数对黄土高原人工刺槐林冠截留量的预测值影响程度较小。模拟值与实测值有较好的一致性,显示Gash模型适用于黄土高原人工刺槐林冠的截留计算。     

Litterfall interception by understorey vegetation delayed litter decomposition in Cinnamomum camphora plantation forest

Aims

This study was carried out to improve our understanding of the interception effect of understorey vegetation on litter decomposition in Cinnamomum camphora plantation forest of subtropical China.

Methods

The interception simulation experiment in field was performed to determine how the litterfall interception delayed the leaf litter decomposition of C. camphora, by comparing the difference in variables among 4 litter interception locations.

Results

The results showed that total mass loss, lignin loss, cellulose loss, microbial activities (CO₂ release, fungal biomass and enzyme activities), and water content except nitrogen for litters on the crown were significantly lower than that of litters without interception. The maximum mass loss difference value among litter locations reached 35 %, indicative of obvious decomposition delay by the understorey. Litter CO₂ release, enzyme activities and water content exhibited a clear seasonal pattern, suggesting a strong relation between the degree of microbial activities and the succession of cold and warm as well as moist and dry periods. A clear nitrogen increase was observed in this experiment, indicating persistent immobilization. No clear variation pattern in nitrogen content was observed in this study, which was probably mixed by the N precipitation from acid rain.

Conclusions

The litterfall interception delayed the decomposition of leaf litter, displaying slow decomposition rate and inhibitive microbial activities by interception, which presumably resulted from low water content on the crown.     

In Situ CO2 Efflux from Leaf Litter Layer Showed Large Temporal Variation Induced by Rapid Wetting and Drying Cycle

We performed continuous and manual in situ measurements of CO₂ efflux from the leaf litter layer (R _LL) and water content of the leaf litter layer (LWC) in conjunction with measurements of soil respiration (R _S) and soil water content (SWC) in a temperate forest; our objectives were to evaluate the response of R _LL to rainfall events and to assess temporal variation in its contribution to R _S. We measured R _LL in a treatment area from which all potential sources of CO₂ except for the leaf litter layer were removed. Capacitance sensors were used to measure LWC. R _LL increased immediately after wetting of the leaf litter layer; peak R _LL values were observed during or one day after rainfall events and were up to 8.6-fold larger than R _LL prior to rainfall. R _LL declined to pre-wetting levels within 2–4 day after rainfall events and corresponded to decreasing LWC, indicating that annual R _LL is strongly influenced by precipitation. Temporal variation in the observed contribution of R _LL to R _S varied from nearly zero to 51%. Continuous in situ measurements of LWC and CO₂ efflux from leaf litter only, combined with measurements of R _S, can provide robust data to clarify the response of R _LL to rainfall events and its contribution to total R _S.     

中国主要森林生态系统水文功能的比较研究(英文)

 基于中国不同区域生态站的观测资料,着重从降雨截留（林冠截留、枯枝落叶层截持和土壤蓄水）、调节径流和蒸散等3个方面对我国主要森林生态系统的水文生态功能进行了比较研究。各生态系统林冠年截留量在134～626 mm间变动,由大到小排列为：热带山地雨林,亚热带西部山地常绿针叶林,热带半落叶季雨林,温带山地落叶与常绿针叶林,寒温带、温带山地常绿针叶林,亚热带竹林,亚热带、热带东部山地常绿针叶林,寒温带、温带山地落叶针叶林,温带、亚热带落叶阔叶林,亚热带山区常绿阔叶林,亚热带、热带西南山地常绿针叶林,南亚热带常绿阔叶林,亚热带山地常绿阔叶林。枯落物持水量可以达到自身干重的2～5倍,但也因林型而异。土壤非毛管持水量变动在36～142 mm之间,平均89 mm。常绿阔叶林的非毛管持水量通常高于100 mm,而寒温带/温带落叶阔叶林和常绿针叶林通常低于100 mm. 土壤的非毛管持水量通常占生态系统中截持水量的90%,其次是枯落物和林冠层。这说明,森林土壤在调节降雨截留中占有重要地位,其水文功能的大小取决于土壤结构和空隙度,而这些恰恰又受枯落物和森林植被特征的影响。森林皆伐后,一般地表径流会显著地增加,而适当抚育措施则对地表径流影响不大。流域径流受诸多因素的影响,包括植被、土壤、气候、地形、地貌以及人类影响导致的流域景观变化,比较研究表明森林变化对流域径流的影响尚未得到一致的规律性的结果。通过对比研究不同森林的蒸散变化,发现随降雨量的增加,森林蒸散量略有增加,而相对蒸散率却在下降,相对蒸散率在40%～90%间变动。     

东灵山林区不同森林植被水源涵养功能评价

森林植被发挥着涵养水源的作用,主要表现在以下几个方面:对降水的截留与再分配;调节河川径流,调节林内小气候,减小林内地表蒸发,改善土壤结构,减少地表侵蚀等. 通过对几种林分各层拦蓄降水和保土功能指标定性评价的基础上,用综合评定法对不同林分水源涵养和保土功能进行综合评价,选择出综合功能最好的林分,以期为北京山区的生态环境建设、植被恢复与保护提供一定的依据。在测定东灵山4种森林植被林冠层、枯枝落叶层和土壤层蓄水和土壤保持功能指标的基础上,采用综合评定法对4种森林植被水源涵养和土壤保持功能进行了评价。结果表明:各植被类型的林冠层截留各不相同,在雨季(6-9 月份) 辽东栎林的截留率最大,华北落叶松的最小;枯落物最大持水深以辽东栎林的最大,油松的最小;土壤水文特性各异,0-80 cm 土层平均容重以落叶阔叶林的最小,华北落叶松的最大;稳渗速率以落叶阔叶林的最大,油松的最小,初渗速率以辽东栎林的最大,油松的最小。不同林分水源涵养和土壤保持综合能力由大到小顺序为落叶阔叶混交林、辽东栎林、华北落叶松林、油松林。常绿阔叶灌丛水源涵养和土壤保持综合能力评价值(0.1039) 比其它植被类型少3个数量级,说明其水源涵养和土壤保持功能明显优于其它植被类型。由此可见,树种组成丰富、林下灌草盖度高、枯落物储量多的落叶阔叶混交林水源涵养和土壤保持能力最强,优于单一的阔叶林,而油松林最差。     

模拟降雨条件下玉米植株对降雨再分配过程的影响

为系统测定玉米(Zea mays)不同生长阶段的穿透雨、茎秆流和冠层截留,采用室内模拟降雨法测定了不同降雨强度、不同叶面积指数玉米冠下穿透雨和茎秆流,采用喷雾法测定了玉米不同生长阶段的冠层截留。对其进行了量化分析,并探讨了三者与玉米叶面积指数和降雨强度的关系,阐明了玉米冠下穿透雨的空间分布特征。结果表明:玉米冠下穿透雨量占冠上总降雨量比例为30.97%—94.02%,平均为63.92%;茎秆流量占降雨量比例的变化范围为5.68%—75.70%,平均为35.28%;冠层截留量在其全生育期内变化范围为0.02—0.43 mm,平均为0.16 mm,所占总降雨量比例最大仅为1%。随玉米生长,穿透雨量逐渐降低,茎秆流量和冠层截留量逐渐增加。穿透雨与茎秆流呈现此消彼长的关系,其中穿透雨率平均由93.55%降至36.23%;茎秆流率平均由5.98%增加至70.42%。降雨强度与穿透雨量和茎秆流量呈正相关关系,但是二者占总降雨量的比例与降雨强度关系不显著(P0.05)。随着玉米生长,穿透雨冠下空间分布由均匀逐渐趋向于不均匀,使降雨经过冠层后趋于向行中汇集,但在玉米生长后期,集中于行中的穿透雨量也因叶片衰败而随之降低。揭示了玉米对降雨的再分配作用特征,可为农田水分有效利用、农田生态水文过程机理和坡耕地土壤侵蚀防治提供理论依据。     

Early stage of single and mixed leaf-litter decomposition in semiarid forest pine-oak: the role of rainfall and microsite

It is well known that inherent characteristics of forest species constitute the main control of litter decomposition. In mixed forest, chemical interactions occurring through precipitation turn mechanisms of litter decomposition very uncertain and difficult to predict. Early-stage leaf litter decomposition of Quercus potosina and Pinus cembroides and their controls were examined based on Ostrofsky’s decomposition mechanisms. From June 2007 to May 2008, litterbags with pure and mixed leaf-litter of Q. potosina and P. cembroides were incubated in situ in monospecific and mixed tree stands, respectively. Sampling was carried out 3, 6, 9, and 12?months after incubation. After 12?months, two phases of decomposition of pure and mixed litter were identified; an early phase with a greater rate of mass loss of the labile litter fraction (k _L ; soluble compounds) and a later phase with a lower rate of mass loss of the recalcitrant litter fraction (k _R; lignin). The labile fraction lost was observed at three and 6?months of incubation, which coincided with the months of highest rainfall likely triggering a rapid release of soluble carbon compounds from leaf litter. Results also indicate that leaf-litter from Q. potosina had higher concentration of soluble compounds and lower lignin concentration than leaf litter from P. cembroides. Observed facilitative and inhibitory mechanisms for mass loss in Q. potosina and P. cembroides were controlled by interaction between physico-chemical litter characteristics and rainfall.     

Responses of Nitraria tangutorum to water and photosynthetic physiology in rain enrichment scenario

Under the global warming conditions, great attention has been paid to the effects of precipitation on ecophysiological characteristics in desert plants. Nitraria tangutorum is one of the dominant shrubs distributes in desert outside Minqin oasis, Gansu Province. The artificial simulated rainfall experiments were carried out in four consecutive years from 2008 to 2011, in an attempt to understand the mechanisms of the photosynthetic response in desert plant to the variation of future precipitation pattern. The water and photosynthetic physiological characteristics of leaves in N. tangutorum were examined from July 24 to 26 in 2011 under different simulated rainfall increase gradients (increased 0%, 25%, 50%, 75% and 100% of mean annual precipitation, respectively). We measured leaf traits that could reflect both leaf water status (e.g., leaf water content and leaf water potential) and photosynthetic physiology (e.g., maximum net photosynthetic rate). The results showed that leaf water content and leaf water potential of N. tangutorum increased with increasing rainfall. Leaf water content and leaf water potential of N. tangutorum in the 100% increased rainfall treatment were significantly greater by 8.51% and 12.07% than the control (0% increased rainfall treatment). But leaf dry matter content and specific leaf weight gradually decreased with increasing rainfall. Leaf dry matter content and specific leaf weight in the 100% increased rainfall treatment were significantly lower by 6.92% and 25.93% than the control. Leaf maximum net photosynthetic rate (A_max), apparent quantum yield (AQY) and light saturation point (LSP) increased with increasing rainfall, while light compensation point (LCP) gradually decreased with increasing rainfall. AQY in the 100% increased rainfall treatment was significantly greater by 70.00% than the control. However, there were no significant differences in LSP and LCP between different treatments. A_max, transpiration rate (T_r), stomatal conductance (G_s) in the 100% increased rainfall treatment were significantly greater by 81.91%, 166.07% and 110.47% than the control, respectively. On the contrary, water use efficiency (WUE) in the 100% increased rainfall treatment was significantly less 48.28% than the control. There were no significant differences in intercellular CO₂ concentration (C_i) and stomatal limitation value (L_s) between different treatments. The correlation analysis showed that there were significantly positive correlations between leaf water content, leaf water potential, T_r and G_s. However, there were significantly negative correlations between leaf dry matter content, leaf specific mass and T_r, G_s, leaf water content and leaf water potential, suggesting that leaf gas exchanges were regulated by leaf water status. Therefore, N. tangutorum could adapt to the tendency of future increasing precipitation by the coordination of water physiology and photosynthesis.     

Canopy Interception for a Tallgrass Prairie under Juniper Encroachment

Rainfall partitioning and redistribution by canopies are important ecohydrological processes underlying ecosystem dynamics. We quantified and contrasted spatial and temporal variations of rainfall redistribution for a juniper (Juniperus virginiana, redcedar) woodland and a tallgrass prairie in the south-central Great Plains, USA. Our results showed that redcedar trees had high canopy storage capacity (S) ranging from 2.14 mm for open stands to 3.44 mm for closed stands. The canopy funneling ratios (F) of redcedar trees varied substantially among stand type and tree size. The open stands and smaller trees usually had higher F values and were more efficient in partitioning rainfall into stemflow. Larger trees were more effective in partitioning rainfall into throughfall and no significant changes in the total interception ratios among canopy types and tree size were found. The S values were highly variable for tallgrass prairie, ranging from 0.27 mm at early growing season to 3.86 mm at senescence. As a result, the rainfall interception by tallgrass prairie was characterized by high temporal instability. On an annual basis, our results showed no significant difference in total rainfall loss to canopy interception between redcedar trees and tallgrass prairie. Increasing structural complexity associated with redcedar encroachment into tallgrass prairie changes the rainfall redistribution and partitioning pattern at both the temporal and spatial scales, but does not change the overall canopy interception ratios compared with unburned and ungrazed tallgrass prairie. Our findings support the idea of convergence in interception ratio for different canopy structures under the same precipitation regime. The temporal change in rainfall interception loss from redcedar encroachment is important to understand how juniper encroachment will interact with changing rainfall regime and potentially alter regional streamflow under climate change.     

六盘山华北落叶松林和红桦林枯落物持水特征及其截持降雨过程

在六盘山南坡野外调查了华北落叶松(Larix principis-rupprechtii)和红桦(Betula albo-sinensis)两个林分的枯落物数量特征,其厚度分别是3.6cm和4.0cm,储量为16.83 t/hm2和9.04 t/hm2.浸泡测定了单位重量(1.0kg/m2)枯落物的持水能力,华北落叶松林和红桦林的最大持水深分别是1.8 mm和2.7 mm.在六盘山地区自然雨强范围内(<30 mm/h),利用模拟降雨研究了枯落物的截持降雨过程,表明枯落物持水能力随雨强增大而提高;在雨强为30 mm/h时,华北落叶松林和红桦林枯落物(1.0kg/m2)的最大截持雨量为1.5mm和2.6mm,分别是浸泡测定持水能力的83.3%和96.2%,两种实验吸持水分的过程基本一致.分析表明,枯落物截持过程的吸水速率受其本身含水量大小的影响,同时构建了具有较好截持机制的枯落物截持降雨过程模型,并基于枯落物浸泡实验和模拟降雨截持实验的数据拟合了模型参数.     

荒漠草原中间锦鸡儿冠层截留特征

以荒漠草原人工中间锦鸡儿（Caragana intermedia）为研究对象,利用2016-2017年监测获取的26次降雨事件,对比分析了两组灌丛（自然组和人工组）的冠层截留特征。结果表明：（1）试验期间共观测到有效降雨33次,总降雨量为251 mm,次平均降雨量和降雨强度分别为7.6 mm和1.14 mm/h,以雨量<2 mm,雨强<1 mm/h和降雨历时2-5 h的降雨出现次数最多;（2）自然组和人工组中间锦鸡儿平均截留量分别为1.11 mm和0.72 mm,平均截留率分别为24.81%和15.95%,两组灌丛截留存在极显著差异（P < 0.01）;（3）在雨量级>15 mm时,自然组（4.57%,CV=73.38%）和人工组（5.25%,CV=51.96%）平均截留率变异性相差最大;（4）自然组和人工组截留量与降雨量,降雨历时和降雨强度之间的关系可以用幂函数描述,截留率与三者的关系均用指数函数描述较好。在降雨特征相同的情况下,灌丛形态特征是影响中间锦鸡儿冠层截留的关键因素。     

松嫩草原三种主要植物群落枯落物层生态水文功能

分析了松嫩草原主要植物群落羊草群落、虎尾草群落、碱茅群落枯落物层的蓄积量及持水能力、枯落物层对降水的截留以及枯落物层抑制土壤水分蒸发的效应.结果表明,羊草群落枯落物蓄积量最大为4.7t·hm-2,最大持水量为9.6t·hm-2,最大持水率为208.4%;虎尾草群落枯落物层蓄积量、最大持水量和最大持水率分别为3.0t·hm-2、7.4t·hm-2和262.8%;碱茅群落分别为2.6t·hm-2、5.0t·hm-2和202.2%;3种群落枯落物层对降水的截留量分别为6.57、5.79和5.26t·hm-2,随着降雨量的增加,截留量增加,截留率减小;0.5~2mm枯落物覆盖下不同含水量的土壤水分蒸发比无覆盖的土壤减少7.95%~56.79%,枯落物层减少土壤水分蒸发的效应随枯落物层厚度和土壤含水量的增大而增加.     

苏南丘陵区毛竹林冠截留降雨分布格局

降雨穿过林冠层时,由于林冠的拦截作用,改变了降雨分布格局。林冠截留是一个复杂的水文过程,受降水特征及林分特性的影响较大。本文以北亚热带苏南丘陵地区人工毛竹林(Phyllostachys edulis)为研究对象,利用2007年度各场次降雨观测数据,分析了降雨量和降雨强度与林冠截留降雨的关系,研究了林冠截留过程的特点。结果表明：（1） 研究期间共观测到102次降水事件,降水总量为1110.8mm,单次最大降雨量为110.0㎜,最小为0.55㎜,事件平均降水量为10.89mm,且绝大部分降雨为低雨强、中雨量级的降雨事件。（2） 研究期间林冠截留总量为171.72mm,占同期降雨总量的15.46%。单次林冠截留量变幅为0.21—4.55mm,截留率变幅为1.3%—100%,且随林外降雨量的递增,林冠截留率呈现递减的变化趋势,二者的关系用幂函数（I0=117.34P-0.9106）拟合效果较好。（3）在林外次降雨量小于5㎜的条件下,事件降雨量占年降雨总量的5.0%,相应的降雨事件频率为9.8%,此时林冠截留量随降雨量的增大而增加,其变幅为0.55—1.9㎜,截留量与降雨量的关系用对数函数（I=0.4931Ln(P) 0.9493）进行拟合效果较好;在单场降雨量大于5㎜时,林冠截留量随各场次降雨量的增加,其变动幅度和频率均大大增强,变化范围在0.21—4.55㎜之间,二者相关性较差。（4）降雨在7—10mm雨量级范围内时,林外降雨量和林冠截留量分别为245.14mm和47.9㎜,占其全年总量的比例均为最大,分别为22.07%和27.9%;各雨量级林冠平均截留量与平均降雨量的关系表现为对数函数关系（R2=0.7287）,而截留率与平均降雨量的关系表现为极显著的幂函数关系（R2=0.9817）,且林冠对降雨的截留作用在雨量级较小时,表现十分显著。（5）全年单场降雨强度小于0.06mm/min时,降雨事件频数为73.53%,降雨量占其总量的57.93%,林冠截留量占其总量的89.34%,降雨事件平均截留率（23.84%）远高于雨强大于0.06mm/min时的降雨事件平均截留率（3.92%）。本研究结果为长江中下游丘陵山区水土保持林和水源涵养林体系建设提供了理论依据。     

Measurement methods and variability assessment of the Norway spruce total leaf area: implications for remote sensing

Estimation of total leaf area (LA_T) is important to express biochemical properties in plant ecology and remote sensing studies. A measurement of LA_T is easy in broadleaf species, but it remains challenging in coniferous canopies. We proposed a new geometrical model to estimate Norway spruce LA_T and compared its accuracy with other five published methods. Further, we assessed variability of the total to projected leaf area conversion factor (CF) within a crown and examined its implications for remotely sensed estimates of leaf chlorophyll content (C _ab). We measured morphological and biochemical properties of three most recent needle age classes in three vertical canopy layers of a 30 and 100-year-old spruce stands. Newly introduced geometrical model and the parallelepiped model predicted spruce LA_T with an error <5 % of the average needle LA_T, whereas two models based on an elliptic approximation of a needle shape underestimated LA_T by up to 60 %. The total to projected leaf area conversion factor varied from 2.5 for shaded to 3.9 for sun exposed needles and remained invariant with needle age class and forest stand age. Erroneous estimation of an average crown CF by 0.2 introduced an error of 2–3 μg cm^?2 into the crown averaged C _ab content. In our study, this error represents 10–15 % of observed crown averaged C _ab range (33–53 μg cm^?2). Our results demonstrate the importance of accurate LA_T estimates for validation of remotely sensed estimates of C _ab content in Norway spruce canopies.     

Changes in needle nitrogen partitioning and photosynthesis during 80 years of tree ontogeny in Picea abies

Needle nitrogen partitioning and photosynthesis of Norway spruce were studied in a forest chronosequence in Järvselja Experimental Forest, Estonia. Current- and previous-year shoots were sampled from upper and lower canopy positions in four stands, ranging in age from 13 to 82 years. A/c _i curves were determined to obtain maximum carboxylation rate (V _cmax) and maximum rate of electron transport (J _max), whereas needle nitrogen partitioning into carboxylation (P _R), bioenergetics associated with electron transport (P _B) and thylakoid light harvesting components (P _L) was calculated from the values of V _cmax, J _max and leaf chlorophyll concentration. The greatest changes in studied needle characteristics took place between tree ages of 13 and 26 years, and this pattern was independent of needle age and canopy position. Needle mass per projected area (LMA) was lowest in the 13-year-old stand and mass-based nitrogen concentration (N^M) was generally highest in that stand. The values of LMA were significantly higher and those of N^M lower in the 26-year-old stand. Mass-based V _cmax and J _max were highest in the 13-year-old stand. Area-based photosynthetic capacity was independent of tree age. The proportion of photosynthetic nitrogen (P _R, P _B and P _L) was highest and that of non-photosynthetic nitrogen lowest in the 13-year-old stand. Current-year needles had lower LMA and P _L, but higher photosynthetic capacity compared to 1-year-old foliage. Needles from lower canopy positions exhibited lower LMA, area-based nitrogen concentration and photosynthetic capacity than needles from upper canopy. The period of substantial reductions in needle photosynthetic capacity and changes in nitrogen partitioning coincides with the onset of reproductive phase during tree ontogeny.     

Effect of the change of leaf angle arrangement on productivity of maize (Zea mays L.) stands

Leaf angles, frequency distribution of leaf area inclinations, leaf area index, amount of intercepted radiation, biological, vegetative and grain yields and grain yield proportion of biological yield were determined in maize stands of two population densities, 55 555 plants ha^?1 (S ₁), and 80 000 plants ha^?1 (S ₂). Also the effect of the artificial change of leaf angle upon these indices was studied. We classified normal maize stand (N) as the interstage between a planophile and a plagiophile type of canopy, that with artificially changed leaf angle (V) as an erectophile type of canopy. The relative interception of the incoming radiation in the variantsV S ₁ andV S ₂ was lower than in the variantsN S ₁ andN S ₂. The variantsV in comparison with variants N increased grain yield and biological yield.