Throughfall and canopy buffering in three sitka spruce stands in Denmark

Throughfall was studied in three even-aged sitka spruce stands in Denmark during the years 1989 to 1994. Deposition of sea salts dominated the fluxes of substances in varying degrees between years and sites. During the study period, non-marine S deposition did not change substantially. At the site most affected by animal husbandry, fluxes of NH₄ ⁺ and NO₃ ^? increased over the years. Elevated fluxes of TOC, K⁺, and PO₄ ^3? occurred in the growing season due to canopy leaching caused by attacks by the green spruce aphid. Fluxes of Cl^?, SO₄ ^2?, Na⁺, Ca²⁺, and Mg²⁺ were highest in the dormant season. Buffering of. pH was affected by the nitrogen dynamics in the canopy, and also, at least during the summer, by elevated levels of organic compounds.     

The influence of stand density and canopy position on sulfur content in needles of Norway spruce (Picea abies L. Karst.)

Analysis of total S in tree foliage has become widely accepted as a means of assessing S pollution of forests when air quality data are lacking. An investigation of total S content of mixed needle samples of different age and canopy height from two stands of young Norway spruce with different densities showed that S-content exceeded the maximum natural S-content (i.e. in the absence of SO₂-pollution) for spruce. Significantly higher average needle S contents were encountered with decreasing stand density. Changed aerodynamic roughness and physiological status of thinned trees indicated combined action of atmospheric and tree physiological variables on S deposition and uptake in forest ecosystems. A marked increase in S content from 1 yr old to older needles and from the lower to the upper canopy was observed.     

田间光照条件下应用半球图像解析玉米冠层结构参数

半球图像法是一种重要的作物冠层结构参数间接获取方法,该文针对半球图像法易受田间变化光照影响,提出一种基于多曝光图像融合映射的变化光照去除方法。首先,在田间条件下获取一组不同曝光值的冠层半球图像序列,然后通过图像亮度和曝光时间的线性方程组计算冠层的光照辐射强度图,而后采用直方图均衡化思想将不同时刻光照辐射强度图向RGB空间映射,映射后半球图像亮度均衡分布,消除光线变化对图像亮度的影响。在冠层参数解析阶段,利用Beer-Lambert定律反演玉米半球图像冠层叶面积指数(leaf area index,LAI)和平均叶倾角(mean leaf angle,MLA)的计算方法。试验结果表明,变化光照条件下半球图像冠层参数解析方法与直接测量法具有较高的相关性,LAI测量相关系数为0.970。该方法扩展了半球图像法的适用范围,为田间环境下冠层参数的自动连续监测提供了解决方案。     

基于多时相和多角度光谱信息的作物株型遥感识别初探

作物群体具有一定的冠层几何结构(株型),对于不同株型的品种,在相同的叶面积指数时冠层反射光谱往往不同,使得利用冠层反射光谱来反演叶面积指数等生物物理和生物化学参数时存在不同株型产生的误差,该文定量研究了不同叶面积指数条件下,作物株型对冠层反射光谱的影响,并提出运用波长800 nm处起身期的冠层反射光谱与该波长处拔节期和起身期冠层反射光谱的比值,可以初步实现高密度披散型品种、低密度披散型品种、高密度中间型品种、低密度中间型品种、高密度直立型品种和低密度直立型品种的遥感识别,结合一定条件下选取的15°、30°和45°观测天顶角下,与可见光和近红外波段(波长)处的二向反射冠层反射光谱数值大小进行结合,可以初步实现作物株型的遥感识别。     

基于无人机影像的冠层光谱和结构特征监测甜菜长势

甜菜是中国北方地区重要的经济作物。快速、准确、高通量的获取甜菜的地上部和块根鲜质量、块根含糖率、叶绿素含量对甜菜生产具有重要意义。该研究采用无人机搭载数码和多光谱相机,获取甜菜叶丛快速生长期、块根及糖分增长期和糖分积累期的数码影像和多光谱影像,提取了冠层的结构特征和光谱特征。选择随机森林回归（Random Forest Regression,RFR）和偏最小二乘回归（Partial Least Squares Regression,PLSR）2种建模方法基于获取的冠层特征,构建甜菜全生育期的地上部和块根鲜质量、块根含糖率和SPAD（Soil and Plant Analyzer Development）值估算模型。研究结果表明,随机森林回归模型和偏最小二乘回归模型对地上部和块根鲜质量、含糖率都做出较好的预测,R2范围分别为0.9～0.94、0.88～0.9,rRMSE范围分别为7.6%～17%、8.8%～20%。对SPAD值的预测均较弱,R2分别为0.66和0.67。为了减小输入变量集的大小以及去掉对预测不敏感的变量,该研究采用置换重要性（Permutation Importance,PIMP）来筛选冠层光谱特征和结构特征中对预测有重要影响的变量。结果表明基于筛选出的重要性特征构建的随机森林回归模型和偏最小二乘回归模型对地上部和块根鲜质量、含糖率都做出较好的预测,R2范围分别为0.89～0.94、0.74～0.91,rRMSE范围分别为7.3%～19%、7.6%～19%。对SPAD值的预测均较弱,R2分别为0.65和0.68。进一步表明随机森林回归模型在精度上略好于偏最小二乘回归模型。同时基于PIMP筛选变量的方法在保持原有精度的同时能实现降低数据收集复杂性的目的。研究结果为基于无人机遥感技术快速、准确监测甜菜长势和估测块根类作物的根部活性物质提供了参考。     

Impact of long-term N fertilization on the structural composition of spruce litter and mor humus

The aims of this study were to determine the degree of lignin degradation and to investigate changes in the chemical composition of the organic matter in the forest floor in an N fertilized Norway spruce forest soil. Needle litter and mor humus were collected from the field experiment at Skogaby in southern Sweden (56°33′N; 13°13′E). The spruce stand had been fertilized for 11 years with 100 kg N ha⁻¹ yr⁻¹ as (NH₄)₂SO₄. The degree of lignin degradation was determined with alkaline CuO oxidation followed by HPLC analysis. The chemical composition of the organic matter was characterized by CPMAS ¹³C NMR. Tannin was specifically analyzed using dipolar dephasing CPMAS ¹³C NMR and the N distribution was studied by CPMAS ¹⁵N NMR.The C-to-N ratios in the fertilized Oi and Oe layers were significantly lower than in the unfertilized layers (24 compared to 34 and 23 compared to 27, respectively). Neither the sum of the CuO oxidation products (Vanillyls+Syringyls+Cinnamyls expressed as VSC) nor the acid-to-aldehyde ratio ((Ac/Al)_V) showed any significant treatment effects. The content of aromatic C (including phenolic C) was significantly lower in the unfertilized than in the fertilized Oi layer (18 versus 21%). In the unfertilized soil, VSC was positively correlated (r=+0.63, p<0.05) with the C-to-N ratio, whereas the phenolic C content was negatively correlated (r=−0.61, p<0.05). The tannin index showed a tendency of increasing from Oi to Oe layers in both treatments. Most of the organic N was found as amide-N, whereas no heterocyclic N was detected. We have not been able to show any major C structural changes due to N fertilization. We suggest that the significantly higher content of aromatic and phenolic C in the fertilized Oi layer is due to an initial stimulation of the microbial community.     

Changes in foliar elements in red spruce seedlings after exposure to sulfuric and nitric acid mist

Red spruce (Picea rubens Sarg.) seedlings were exposed repeatedly at a field site or in a greenhouse to acidic mist containing the major sulfur and nitrogen pollutants of wet deposition in the eastern U.S.: sulfate alone, nitrate alone or with ammonium ion, and a combination of these ions. Acidities and ion concentrations ranged from below the mean to above the maximum concentration for cloudwater in the eastern U.S. Effects on elements in current-year foliage were examined after continuous or intermittent overnight exposures to mist performed over periods of 6 to 19 weeks. Principal findings from five experiments conducted over a three-year period were that acidic mist 1) increased the foliar S and/or N content when exposures were intermittent with repeated opportunities for drying of liquid on foliage; 2) decreased foliar calcium, and/or magnesium content, especially when exposures to acidic mist were continuous rather than intermittent; and 3) gave inconsistent results for foliar iron and aluminum probably because of deposition of soil particles and contamination with metals from the mist delivery system. These results indicate that long-duration exposures to cloudwater with pH below 3 may alter foliar nutrient composition and change relationships between N, S, Ca, and Mg, with potential consequences for growth and resistance to natural stress factors.     

The influence of Al on the metabolism of spruce needles

Aluminium toxicity as a consequence of increasing soil acidity is discussed as a primary factor in forest decline in middle Europe. Ecologically relevant concentrations of Al disturbed root systems of hydroponically grown spruce (Picea abies Karst.) seedlings. The needles, with a much lower Al content in comparison to the roots, were also affected by Al at these external concentrations. In this investigation needle chlorosis as the visible symptom of Al toxicity, was accompanied by decreasing pigment concentrations and photosynthetic rates as well as increasing starch levels and transpiration rates. The magnesium concentrations of roots and needles were lowered by treatment with Al. By feeding the needles directly with Mg, it was possible to differentiate between direct and indirect effects of Al on needle metabolism. Magnesium deficiency was found to drive all the experimental variables except transpiration.     

基于冠层上下部温差的冠层阻力计算

为了研究交替隔沟非充分供水下玉米冠层阻力的计算方法,于2009—2010年在中国农业科学院农田灌溉研究所作物需水量试验场进行了田间试验.根据实测资料分析了玉米气孔阻力与各环境因素的关系,基于 Jarvis (1976)多因子冠层阻力模型,引入冠层上、下部温差变量(ΔTc),提出了交替隔沟非充分供水下玉米冠层阻力的计算方法,即基于ΔTc的冠层阻力法,并分别与Jarvis(1976)、Ortega-Farias(2004)和Brisson et al(1998)法作对比研究,验证其准确性.结果表明,Javias(1976)、Ortega-Farias(2004)、基于ΔTc的冠层阻力法和Brisson (1998)的日平均冠层阻力计算结果分别为355.93、318.75、300.61和253.42 sm-1.其中,Ortega-Farias(2004)法和Javias(1976)法模拟结果分别偏高9.70%和22.50%;Brisson(1998)法模拟结果偏低12.78%;基于ΔTc的冠层阻力法计算结果比实测值偏高3.46%,二者的相关性最好,其计算结果与实测值间的平均绝对误差(MAE)、标准差(SD)和拟合度(d1)值分别为2.42、6.77和0.89,R2为0.86,计算精度优于Jarvis(1976)、Ortega-Farias (2004)和Brisson et al(1998)模型.基于冠层上、下部温差的冠层阻力计算法,考虑了作物、土壤、气候3大因素,模型的模拟范围、数据获取和精度都优于其他方法,能够较准确地表达交替隔沟非充分供水下的玉米冠层阻力.     

The effect of arsenic trioxide on the growth of white spruce seedlings

In the smelting of arsenopyrite ores during the gold extraction process, substantial amounts of As₂O₃ are released into the environment. The work described in this paper demonstrates the potential effect of this fallout on the growth of white spruce trees. Several small trees were planted in soil containing various amounts of As₂O₃ and their growth was studied over an ii mo period. Substantial retardation of the growth of the trees with As containing soil was observed.     

Forest canopy transformation of atmospheric deposition

Solute fluxes to the ground in open plots and under the forest canopy of different species were investigated in a number of long-term ecosystem studies in West Germany. From the canopy flux balance, rates of interception deposition and canopy/deposition interactions were assessed. Chemically, both open precipitation and throughfall are dilute solutions of H₂SO₄ and HNO₃ and their salts. For the sites investigated, mean pH in bulk precipitation ranged from 4.1 to 4.6, and in throughfall from 3.4 to 4.7. The increase in acidity after canopy passage at most sites indicates considerable interception deposition of strong acids to the forest stands, exceeding the rate of H+ buffering in the canopy. Evidence for buffering processes can be directly deduced from the fact that on sites with high soil alkalinity and high foliage base status, throughfall pH is usually higher than precipitation pH. Furthermore, the same idea can be concluded from changes in solution composition after canopy passage: the H⁺/SO _inf4 ^sup2? ratio is decreasing at most sites, while alkali earth cations from exchange processes occur in throughfall (Ca²⁺/SO _inf4 ^sup2? ratio increases). Solution composition and element flux data are presented for each of the sites, and the regional, orographical and site specific (species composition, ecosystem state) differentiations are discussed. A method for the assessment of total deposition and of canopy interactions such as H⁺-buffering and cation leaching is described, and results of calculations are shown. From these calculations it is concluded that forest ecosystems in Germany receive mean H⁺ loads of ca. 1 to 4 keq H⁺ · ha^?1 · a^?1 from atmospheric deposition. Acidity deposition rates seem to be related to a few key factors such as regional characteristics and ecosystem characteristics.     

Relationships between canopy transpiration, atmospheric conditions and soil water availability—Analyses of long-term sap-flow measurements in an old Norway spruce forest at the Ore Mountains/Germany

At the study site Tharandt Anchor Station in Saxony/Germany sap flow measurements are conducted in an old Norway spruce (Picea abies [L.] KARST.) stand. During the study period from 2001 to 2007 several events like thinning, long and short drought periods and a winter storm significantly affected the amount of canopy water use. We show that intra-annual variation of Ec is strongly related to VPD and PPFD. While there is a non-linear relationship between daily Ec and VPD, daily Ec is limited by daily integrated PPFD indicating stomatal control of Ec through photosynthesis. On a monthly or seasonal basis, reduction of Ec is not only related to high VPD and non-saturating PPFD, but also to higher frequencies of precipitation. In comparison to this, nearly 55% of canopy precipitation and 20% of available energy were used for transpiration during the growing season. Intensive seasonal soil water measurements at the site revealed that on average about 74% of soil water removal within the rooting zone can be related to tree water uptake. A good correlation was found between annual Ec and Ec_max, usually occurring in June or July. Further, the monthly sums of June plus July were good predictors of annual Ec. Within the study period, the extreme drought in 2003 revealed a clear threshold of soil water content by 9.5 vol% and had the most pronounced effect on annual Ec followed by a stand thinning. The winter storm “Kyrill” in January 2007 had caused loss of green needles and twigs. It is assumed that the observed reduction in Ec during spring was related to the reduced leaf biomass and potentially to root damage of bended trees. Excluding the effect of extreme drought and forest management, a mean inter-annual variation in Ec of ±15% and in Ec/VPD of ±8% remained. It is concluded that lag-effects of drought and the winter storm add lacking explanation to the inter-annual variability of canopy transpiration besides the typical variation of atmospheric conditions.     

玉米冠层内外风速变化周期特征的研究

应用Morlet连续小波变换对玉米冠层内外 4个高度风速数据的变化分析结果表明 ,1h平均风速的连续小波变换提供了不同高度风速数据所包含的多种周期分量的清晰图像 ,1d和 18d周期是 4组风速数据包含的主要周期分量。连续小波变换的平均谱显示了风速数据的时间变异性和能量在不同周期分量中的分布     

The influence of the physical attributes of a spruce shoot on momentum transfer

The drag force on fourteen three-prong spruce shoots (Picea rubens) was measured over a range of wind tunnel velocities. The boundary layer resistance to momentum transfer was found to be influenced by the shoot orientation, inclination, and flexibility. Momentum transfer was also influenced by shoot needle density; however, this influence was a function of the shoot orientation. For wind velocities below about 2.0 m s^?1, these factors did not greatly influence the momentum transfer to the shoots. For wind velocities above about 2.0 m s^?1 the momentum transfer decreased with; (1) decreasing inclination of the shoot to the airflow, (2) decreasing shoot flexibility, and (3) orientating the shoot so that the densely-needled side of the shoot faced the wind. A pair of empirical equations were derived relating momentum transfer to wind velocity.     

作物冠层微气象仪器研制与应用

研制成适用于测定作物冠层内部微气象(温度、湿度和风速)的观测仪器。应用4组温度与湿度感应器和热球式风速传感器于实验室进行标定,并在大田自然条件下进行平行对比检验。玉米观测试验结果符合小气候的基本规律,并给出更加精确和实时测量。     

The dry deposition of gaseous and participate nitrogen compounds to a spruce stand

The dry deposition of particle-bound NH₄ ⁺ and NO₃ ^– and of gaseous NH₃ and HNO₃ to a 45 year old Norway Spruce forest was determined by the inferential method. Deposition velocities were calculated from meteorological data and plant morphology by a multi-layer model which combines the transfer of the trace substances within the canopy and their absorption probabilities due to a variety of deposition mechanisms. For gaseous deposition the same mathematical concept was adopted as for particles. That means that this approach is an alternative to the common concept of resistance analogy. The mean deposition velocities found were 0.47 cm s^–1 for NH₄ ⁺ and 1.85 cm s^–1 for NO₃ ^–. While these values are in the range found in other studies, the mean deposition velocities for the gases were quite large. For NH₃ 13 cm s^–1 were found and for HNO₃ 11 cm s^–1. It is suggested that the absorption of these gases on the plant surfaces is not as effective as assumed in the model.     

冠层温度-气温差与作物水分亏缺关系的研究

试验研究了冬小麦在不同土壤水分条件下拔节～抽穗期冠层温度-气温差变化规律及其随作物生长发育期的变化状况。结果表明,作物在充分供水条件下冠层温度-气温差变化较平缓;缺水时变化较大。冠层温度-气温差随作物生长发育期的变化趋势为低水分处理高于高水分处理。冠层温度-气温差可较合理反映土壤水分变化状况和作物水分亏缺程度。     

苹果花期冠层反射光谱特征

苹果花期是果树生产与管理的关键阶段,对冠层反射光谱特征研究具有重要的理论和现实意义。该文以山东省栖霞市为研究区,通过实测的120棵苹果花期冠层反射光谱数据,在分析不同累计样本容量冠层反射光谱特征的基础上,用方差分析和相关分析的方法,系统地研究了苹果树有花与无花、不同花量、花期不同阶段、不同树龄及不同品种的冠层反射光谱特征。研究结果表明,随着累计样本容量的增加,冠层反射光谱曲线趋于稳定、平滑。有花与无花冠层光谱反射率在431～500、591～680、761～1 300 nm波段方差分析结果极显著（α=0.01）;不同花量的冠层与391～513、598～687、711～1 193 nm波段的反射率显著相关（p＜0.05）;在670 nm“红谷”附近,反射率随花量的增加而增大,在近红外761～1 300 nm波段,反射率随花量的增加而减小;不同品种之间,除嘎啦外,红富士、金帅和新红星之间不易区分。研究结果揭示了高光谱遥感在苹果花期信息获取方面的巨大潜力,为今后遥感反演模型的构建提供了依据。     

玉米叶片几何造型研究

针对虚拟作物研究中的作物个体或器官几何造型问题,用三次B样条来拟合玉米叶片的三维形态,并用虚拟模型进行玉米叶片几何特征的计算.与其它方法相比,该方法具有精度高,参数少的特点,是一种适合于玉米叶片三维造型的好方法.     

冬小麦冠层光谱红边特征分析

通过对不同N素营养水平冬小麦冠层光谱特性的田间试验研究,发现红边位移现象:在孕穗期前,红边随施N量增加向长波方向"红移";孕穗期后"红移"现象基本消失,继而发生"蓝移"。红边参数中红边斜率(dλred)与叶片N累积量(TN.D)、叶绿素含量(CHL.T)、叶绿素密度(CHL.D)的相关关系通过显著性检验,红边面积(∑dλ680~760)和叶片全N含量(N%)的相关关系通过显著性检验,红边位置(λred)、红边斜率、红边面积与叶面积指数有着密切关系,均通过极显著性检验,一些红边参数可作为小麦农学参数估测的简便方法。