美国黑核桃实生苗生态生理过程对环境因素响应的数值模拟(Ⅲ):植株冠层光合作用数理模型

以1-2年生北加州黑核桃为试材,建立了具有较高分辨能力的植株群体结构、光分布模型和冠层光合作用模型．将植株冠层按叶面积指数划分为若干层次。上下层之间水平面上太阳辐照度按Monsi＆Saeki所提出的指数递减规律分布．冠层内太阳散射光的消光系数由冠层结构决定,而直射光的消光系数则决定于冠层结构与太阳在天空的位置．在同一层次。将叶片的叶倾角划分为6个等级。将叶片的水平位置划分为8个方位．设同一层次中水平面上的太阳辐照度相同。某一方位角和叶倾角的叶面的直接辐射由太阳视运动方程决定．以此为基础,分别计算“光斑区”和“遮荫区”内叶片的光合速率,并通过数值积分计算整个冠层的光合速率及光合日总量．用田间实测资料验证了冠层内太阳辐射分布模型和冠层光合作用模型．敏感性试验分析表明。模型对环境因子和生物学因素有良好的响应．     

生态学报第25卷总目录

第1期江苏典型淤长岸段潮滩盐生植被及其土壤肥力特征………………………………………………………………沈永明,曾华,王辉,等(1)玉米冠层内太阳直接辐射三维空间分布的模拟………………………………………………………………………王锡平,郭焱,李保国,等(7)四川大头茶在不同群     

水稻冠层光合有效辐射的时空分布特征

以2个不同株型水稻品种为材料,设置高、中、低3个施氮水平,利用SunScan冠层分析仪于灌浆期系统测定了不同施氮水平下不同株型水稻品种植株形态和冠层内光合有效辐射(PAR)的时空分布状况.结果表明:施氮量对水稻株高、穗弯曲度和茎叶夹角有明显影响;群体叶面积的垂直分布呈中部上部下部的分布特征,最大分层叶面积指数(LAI)出现在0.60相对高度处.冠层内平均PAR透光率从顶部向下递减,且在冠层上中部递减迅速,下部递减缓慢;平均PAR透光率随施氮量的增加而递减;平均PAR透光率日变化表现为早晚较低,中午较高;平均PAR透光率随向下累积LAI的增加呈指数递减,群体消光系数K的日变化表现为早晚较高,中午较低,灌浆期的K值介于0.35～0.50.水稻冠层内PAR的三维空间分布表现为冠层上中部水平面上PAR透光率高,光斑面积大;下部水平面上PAR透光率低,光斑少;同一冠层高度水平面上的PAR光强呈不均匀分布.株型紧凑的水稻品种,冠层透光率高,透光率日变化大,群体消光系数小.     

人工同龄纯林冠层辐射场模拟模型I.理论计算

充分考虑坡地人工林冠层结构特征和叶面积空间分布的异质性,分别相邻树冠遮荫和目的树冠遮荫对树冠内辐射场的影响,建立的人工林冠层辐射场模型,可模拟树冠内任意点,在一年内任一时刻内的辐射及其直接和散射分量,以及以1h为步长的日总辐射等,为人工林可持续经营和冠层光合生产力模拟奠定基础。     

人工同龄纯林冠层辐射场模拟模型Ⅰ理论计算

充分考虑坡地人工林冠层结构特征和叶面积空间分布的异质性,分别相邻树冠遮荫和目的树冠遮荫对树冠内辐射场的影响,建立的人工林冠层辐射场模型,可模拟树冠内任意点,在一年内任一时刻的辐射及其直接和散射分量,以及以1h为步长的日总辐射等,为人工林可持续经营和冠层光合生产力模拟奠定基础。     

森林冠层辐射的数值模拟

一、引言太阳辐射是树木和各种作物生长过程中所需能量的直接或间接源泉。一定强度的太阳辐射达到林冠层表面时,由于叶、枝等器官的吸收、反射和透射作用,使得冠层内的辐射分布有其独具的特征。本文综合考虑天空散射和叶片的内部散射作用,从辐射通量的角度在计算机上模拟了各向同性叶角分布的冠层中辐射通量的分布特征,讨论了单叶反射系数和透射系     

河套地区小麦/玉米套作群体光能瞬时传输的数学模拟

作物间套作群体冠层中叶片水平向和垂向分布的不均匀性给其光能截获的连续测定带来了很大困难.为了量化小麦/玉米套作群体不同生长阶段的光能吸收,本文建立了模拟该套作群体光合有效辐射(PAR)瞬时传输的几何模型,并用大田实测值对模型进行验证.结果表明:几何模型可有效地模拟小麦/玉米套作群体冠层底部的PAR强度.小麦/玉米6∶2套作(I62)群体模型估算结果与实测值的线性回归方程的决定系数为0.947,小麦/玉米12∶4套作(I124)群体模拟结果与实测值的线性回归方程的决定系数为0.950.2012和2013年I62套作群体截获的PAR分别为1061.4和924.3 MJ·m-2,在所有处理中最高.2012年I62和I124套作群体相对于单作的PAR截获比率分别为1.29和1.19,2013年I62和I124套作群体相对于单作的PAR截获比率分别为1.21和1.16.     

双季稻光合生产模型的建立与应用

综合已有作物模型(包括冠层结构、冠层光分布和冠层光合作用与干物质生产模型)的优点,构建了双季稻光合生产模型.利用独立的田间试验资料,对冠层内的光分布和干物质积累量进行了初步检验;利用模型定量分析了直接辐射在上挺下挺、上挺下披和上披下披3种典型株型水稻冠层内水平面上和叶面上的分布、冠层日光合量及其随叶面积指数的变化特征.结果表明: 模拟值与观测值之间具有较好的一致性,预测双季稻冠层内光分布的根均方差、相对根均方差和相关系数分别为12.01 J·m^-2·s^-1、8.2%和0.9929;预测双季稻干物质积累量的根均方差、相对根均方差和相关系数分别为0.83 t·hm^-2、14.6%和0.9772,表明模型预测性较好;上挺下披株型水稻的冠层日光合量最高,取决于较大的叶面受光量、叶片光合效能和叶面积指数.     

不同品种水稻群体冠层光谱特征比较研究

应用分光光谱辐射仪对不同株型水稻品种的冠层光谱辐射能进行观测和计算,比较分析了不同冠层群体光谱分布特征的差异性。结果表明,不同株型水稻品种群体冠层内太阳光谱辐射反率α,透射率β和吸收率τ及消光系数K存在明显差异,尤其以蓝光辐射（400－510nm)差异最为显著。在水稻生长后期,这些差异表现更为突出。     

水稻群体冠层光分布及光合作用模型

作物冠层光分布及光合作用模型,是作物栽培学、作物育种学研究的共同基础,对优化设计和评价作物株型、模拟作物生长发育与对环境变化的响应研究都有十分重要的价值.本文根据水稻群体冠层结构的特点,在虚拟切层法的基础上,建立了水稻群体冠层光分布及光合速率模型,模型包括冠层形态子模型、冠层光分布子模型和冠层光合速率子模型等.利用本模型,对设定的15625种水稻株型的光合速率进行了模拟计算,获得水稻最佳株型模型.结果表明,水稻群体光合速率与叶片数、叶含氮量、叶长、叶宽和叶倾角等5因素密切相关;最佳株型的上述5因素在冠层上部取值大,向下逐渐变小.     

Evaluating a three dimensional model of diffuse photosynthetically active radiation in maize canopies

Diffuse photosynthetically active radiation (DPAR) is important during overcast days and for plant parts shaded from the direct beam radiation. Simulation of DPAR interception by individual plant parts of a canopy, separately from direct beam photosynthetically active radiation (PAR), may give important insights into plant ecology. This paper presents a model to simulate the interception of DPAR in plant canopies. A sub-model of a virtual maize canopy was reconstructed. Plant surfaces were represented as small triangular facets positioned according to three-dimensionally (3D) digitized data collected in the field. Then a second sub-model to simulate the 3D DPAR distribution in the canopy was developed by dividing the sky hemisphere into a grid of fine cells that allowed for the anisotropic distribution of DPAR over the sky hemisphere. This model, DSHP (Dividing Sky Hemisphere with Projecting), simulates which DSH (Divided Sky Hemisphere) cells are directly visible from a facet in the virtual canopy, i.e. not obscured by other facets. The DPAR reaching the center of a facet was calculated by summing the amounts of DPAR present in every DSH cell. The distribution of DPAR in a canopy was obtained from the calculated DPARs intercepted by all facets in the canopy. This DSHP model was validated against DPAR measurements made in an actual maize (Zea mays L.) canopy over selected days during the early filling stage. The simulated and measured DPAR at different canopy depths showed a good agreement with a R ² equaling 0.78 (n=120).     

Daylight spectra (400–740 nm) beneath sunny,blue skies in Tasmania,and the effect of a forest canopy

Abstract The photosynthetically active radiation (PAR) incident on a horizontal surface at an open mountain site is positively correlated with solar altitude for sunny, blue sky conditions. The proportion of red light in PAR decreases with increasing solar altitude, while that of blue increases. These results are consistent with the wavelength dependency of Rayleigh and Mie scattering. The ratio of near infrared radiation to PAR decreases with increasing solar altitude towards solar noon and with decreasing solar altitude towards sunset. Thus surface reflection seems to be an important part of the light climate. The relative transmission of daylight through a forest canopy to a horizontal surface is not correlated with solar altitude for sunny, blue sky conditions at a mountain site. The amount of diffuse daylight is negatively correlated with per cent canopy interception, and the amount of direct sunlight is negatively correlated with per cent solar track interception. Daylength is negatively correlated with both canopy and solar track interceptions. The proportion of red light in PAR increases with increasing solar altitude, while that of blue decreases. These results are opposite those for the open site and are due to the spatial patterns of canopy obstruction of the sky vault, and of the spectral quality of daylight across the sky. The ratio of near infrared radiation to PAR in shadelight increases with increasing canopy interception due to the selective scattering properties of the canopy. The ratio for shadelight is positively correlated with the ratio for sunflecks.     

Spectral composition of photosynthetically active radiation penetrating into a Norway spruce canopy: the opposite dynamics of the blue/red spectral ratio during clear and overcast days

The spectral composition of photosynthetically active radiation (PAR) during clear and overcast days was studied above the canopy (U) and at two layers of a dense Norway spruce stand [Picea abies (L.) Karst.] characterized with an average LAI = 7.3 ± 0.8 (middle layer: M) and 12.3 ± 0.7 (lower layer: L). Whereas the spectral composition of PAR incoming on the canopy surface during cloudy days (characterized by diffuse index DI > 0.7) was almost independent of the solar elevation angle, the proportion of the blue-green spectral region of PAR was significantly reduced at low elevation angles during days with prevailing direct radiation (DI < 0.3). The PAR spectrum at both M and L levels was only slightly enriched in the green spectral region (more pronounced for DI < 0.3). The penetration of diffuse radiation into the canopy resulted in a slight (approx. 5%) reduction of the blue region proportion that remained stable during the day. On the contrary, under clear sky conditions the penetration of blue and red radiation was dependent on the solar elevation in an opposite manner in comparison with the spectral composition of PAR incident on canopy, giving almost twofold proportion of the blue part of the spectrum at a low elevation angle at M layer. We suggest that the blue enhancement of the spectrum within the Norway spruce canopy during clear days is due to a specific spatial arrangement of the assimilatory apparatus of a coniferous stand. Further, the possible consequences of the observed dynamics of the PAR spectrum inside the canopy during clear days on the efficiency of PAR absorption of the needles located within the canopy are discussed.     

海岸带复合梨园的光能分布与利用规律

采用方格法和分层法相结合的技术对江苏省如东县棉花原种场林网保护区内13年生梨园的树冠结构特征和光能分布与利用规律进行了系统研究。结果表明:梨树叶幕光能分布状况直接受叶面积系数、树冠结构、太阳位置及光强的影响。各层叶幕中的光合有效辐射(PAR)分布随自然光照条件的变化而改变,其日平均透光率大小和PAR日变化范围均从叶幕外围向内膛随累积叶面积系数(LAI)的增加而减弱;不同生长时期及不同天气变化下树冠光能分布存在明显的差异性;树冠结构与累积LAI对PAR的分布及利用率具有决定性的影响。在生产实践中,通过密度调控、整形修剪等农业技术措施,维持成年梨园盛果期高效光合生产的叶幕厚度在2.5m以上,有效LAI为4左右,是增强梨树光合生产能力、提高产量和品质的有效措施。     

Effects of kaolin application on light absorption and distribution, radiation use efficiency and photosynthesis of almond and walnut canopies

BACKGROUND AND AIMS: Kaolin applied as a suspension to plant canopies forms a film on leaves that increases reflection and reduces absorption of light. Photosynthesis of individual leaves is decreased while the photosynthesis of the whole canopy remains unaffected or even increases. This may result from a better distribution of light within the canopy following kaolin application, but this explanation has not been tested. The objective of this work was to study the effects of kaolin application on light distribution and absorption within tree canopies and, ultimately, on canopy photosynthesis and radiation use efficiency. METHODS: Photosynthetically active radiation (PAR) incident on individual leaves within the canopy of almond (Prunus dulcis) and walnut (Juglans regia) trees was measured before and after kaolin application in order to study PAR distribution within the canopy. The PAR incident on, and reflected and transmitted by, the canopy was measured on the same day for kaolin-sprayed and control trees in order to calculate canopy PAR absorption. These data were then used to model canopy photosynthesis and radiation use efficiency by a simple method proposed in previous work, based on the photosynthetic response to incident PAR of a top-canopy leaf. KEY RESULTS: Kaolin increased incident PAR on surfaces of inner-canopy leaves, although there was an estimated 20 % loss in PAR reaching the photosynthetic apparatus, due to increased reflection. Assuming a 20 % loss of PAR, modelled photosynthesis and photosynthetic radiation use efficiency (PRUE) of kaolin-coated leaves decreased by only 6.3 %. This was due to (1) more beneficial PAR distribution within the kaolin-sprayed canopy, and (2) with decreasing PAR, leaf photosynthesis decreases less than proportionally, due to the curvature of the photosynthesis response-curve to PAR. The relatively small loss in canopy PRUE (per unit of incident PAR), coupled with the increased incident PAR on the leaf surface on inner-canopy leaves, resulted in an estimated increase in modelled photosynthesis of the canopy (+9 % in both walnut and almond). The small loss in PRUE (per unit of incident PAR) resulted in an increase in radiation use efficiency per unit of absorbed PAR, which more than compensated for the minor (7 %) reduction in canopy PAR absorption. CONCLUSIONS: The results explain the apparently contradictory findings in the literature of positive or no effects of kaolin applications on canopy photosynthesis and yield, despite the decrease in photosynthesis by individual leaves when measured at the same PAR.     

Solar radiation transmission in and around canopy gaps in an uneven-aged <Emphasis Type="Italic">Nothofagus betuloides</Emphasis> forest

The transmission of direct, diffuse and global solar radiation in and around canopy gaps occurring in an uneven-aged, evergreen Nothofagus betuloides forest during the growing season (October 2006–March 2007) was estimated by means of hemispherical photographs. The transmission of solar radiation into the forest was affected not only by a high level of horizontal and vertical heterogeneity of the forest canopy, but also by low angles of the sun’s path. The below-canopy direct solar radiation appeared to be variable in space and time. On average, the highest amount of transmitted direct solar radiation was estimated below the undisturbed canopy at the southeast of the gap centre. The transmitted diffuse and global solar radiation above the forest floor exhibited lower variability and, on average, both were higher at the centre of the canopy gaps. Canopy structure and stand parameters were also measured to explain the variation in the below-canopy solar radiation in the forest. The model that best fit the transmitted below-canopy direct solar radiation was a growth model, using plant area index with an ellipsoidal angle distribution as the independent variable (R ² = 0.263). Both diffuse and global solar radiation were very sensitive to canopy openness, and for both cases a quadratic model provided the best fit for these data (R ² = 0.963 and 0.833, respectively). As much as 75% and 73% of the variation in the diffuse and global solar radiation, respectively, were explained by a combination of stand parameters, namely basal area, crown projection, crown volume, stem volume, and average equivalent crown radius.     

A simple method to estimate photosynthetic radiation use efficiency of canopies

BACKGROUND AND AIMS: Photosynthetic radiation use efficiency (PhRUE) over the course of a day has been shown to be constant for leaves throughout a general canopy where nitrogen content (and thus photosynthetic properties) of leaves is distributed in relation to the light gradient. It has been suggested that this daily PhRUE can be calculated simply from the photosynthetic properties of a leaf at the top of the canopy and from the PAR incident on the canopy, which can be obtained from weather-station data. The objective of this study was to investigate whether this simple method allows estimation of PhRUE of different crops and with different daily incident PAR, and also during the growing season. METHODS: The PhRUE calculated with this simple method was compared with that calculated with a more detailed model, for different days in May, June and July in California, on almond (Prunus dulcis) and walnut (Juglans regia) trees. Daily net photosynthesis of 50 individual leaves was calculated as the daylight integral of the instantaneous photosynthesis. The latter was estimated for each leaf from its photosynthetic response to PAR and from the PAR incident on the leaf during the day. KEY RESULTS: Daily photosynthesis of individual leaves of both species was linearly related to the daily PAR incident on the leaves (which implies constant PhRUE throughout the canopy), but the slope (i.e. the PhRUE) differed between the species, over the growing season due to changes in photosynthetic properties of the leaves, and with differences in daily incident PAR. When PhRUE was estimated from the photosynthetic light response curve of a leaf at the top of the canopy and from the incident radiation above the canopy, obtained from weather-station data, the values were within 5 % of those calculated with the more detailed model, except in five out of 34 cases. CONCLUSIONS: The simple method of estimating PhRUE is valuable as it simplifies calculation of canopy photosynthesis to a multiplication between the PAR intercepted by the canopy, which can be obtained with remote sensing, and the PhRUE calculated from incident PAR, obtained from standard weather-station data, and from the photosynthetic properties of leaves at the top of the canopy. The latter properties are the sole crop parameters needed. While being simple, this method describes the differences in PhRUE related to crop, season, nutrient status and daily incident PAR.     

Low clouds and cloud immersion enhance photosynthesis in understory species of a southern Appalachian spruce-fir forest (USA)

High-altitude forests of the southern Appalachian Mountains (USA) are frequently immersed in clouds, as are many mountain forests. They may be particularly sensitive to predicted increases in cloud base altitude with global warming. However, few studies have addressed the impacts of immersion on incident sunlight and photosynthesis. Understory sunlight (photosynthetically active radiation, PAR) was measured during clear, low cloud, and cloud-immersed conditions at Mount Mitchell and Roan Mountain, NC (USA) along with accompanying photosynthesis in four representative understory species. Understory PAR was substantially less variable on immersed vs. clear days. Photosynthesis became light-saturated between ～100 and 400 μmol · m(-2) · s(-1) PAR for all species measured, corresponding closely to the sunlight environment measured during immersion. Estimated daily carbon gain was 26% greater on clear days at a more open canopy site but was 22% greater on immersed/cloudy days at a more closed canopy site. F(v)/F(m) (maximum photosystem II efficiency) in Abies fraseri seedlings exposed to 2.5 min full sunlight was significantly reduced (10%), indicating potential reductions in photosynthesis on clear days. In addition, photosynthesis in microsites with canopy cover was nearly 3-fold greater under immersed (2.6 mmol · m(-2) · h(-1)) vs. clear conditions (0.9 mmol · m(-2) · h(-1)). Thus, cloud immersion provided more constant PAR regimes that enhanced photosynthesis, especially in shaded microsites. Future studies are needed to predict the survival of these refugial forests under potential changes in cloud regimes.     

Modulation of the bacterial response to spectral solar radiation by algae and limiting nutrients

SUMMARY 1. The response of bacterial production (measured as [³H]TdR incorporation rate) to spectral solar radiation was quantified experimentally in an oligotrophic high-mountain lake over 2 years. Bacterial responses were consistent: ultraviolet-B (UVB) was harmful, whereas ultraviolet-A (UVA) + photosynthetically active radiation (PAR) and PAR enhanced bacterial activity. Full sunlight exerted a net stimulatory effect on bacterial activity in mid-summer but a net inhibitory effect towards the end of the ice-free period.
2. Experiments were undertaken to examine whether the bacterial response pattern depended on the presence of algae and/or was modulated by the availability of a limiting inorganic nutrient (phosphorus, P). In the absence of algae, [³H]TdR incorporation rates were significantly lower than when algae were present under all light treatments, and the consistent bacterial response was lost. This suggests that the bacterial response to spectral solar radiation depends on fresh-C released from algae, which determines the net stimulatory outcome of damage and repair in mid-summer.
3. In the absence of algae, UVB radiation inhibited bacteria when they were strongly P-deficient (mean values of N : P ratio: 46.1), whereas it exerted no direct effect on bacterial activity when they were not P-limited.
4. P-enrichment of lake water markedly altered the response of bacteria to spectral solar radiation at the end of ice-free period, when bacteria were strongly P-deficient. Phosphorus enrichment suppressed the inhibitory effect of full sunlight that was observed in October, both in whole lake water (i.e. including algae) and in the absence of algae. This indicates that the bacterial P-deficiency, measured as the cellular N : P ratio, was partly responsible for the net inhibitory effect of full sunlight, implying a high bacterial vulnerability to UVB.