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.     

Light absorption by phytoplankton and chromophoric dissolved organic matter in the drainage basin and estuary of the Neuse River, North Carolina (U.S.A.)

1. We examined the absorption of solar radiation by phytoplankton and chromophoric dissolved organic matter (CDOM) taking into account riparian shading in the rivers, reservoirs, swamps of the Neuse River Estuary and its drainage basin. 2. In the streams, CDOM typically absorbed 55 and 64% of photons in the spectral range of 400–700 nm (photosynthetically active radiation, PAR) and 500–600 nm, respectively. The large proportion of photons absorbed by CDOM indicates high potential for abiotic photochemial reactions in the 500–600 nm region. 3. Despite the high concentration of nutrients, phytoplankton contributed little (2%) to the total absorption of PAR in the streams. Small (<30 m wide) streams typically received only 7% of incident PAR that impinged onto the more exposed reservoirs and estuary. Riparian shading and the low contribution of phytoplankton to the total absorption resulted in conditions where phytoplankton absorbed nearly two orders of magnitude less PAR in the streams than in the estuary and reservoirs. 4. The results indicated that riparian shading and non‐algal absorbing components can significantly restrict phytoplankton production in nutrient‐rich streams with a high concentration of CDOM flowing throughout forested catchments.     

我国陆地生态系统的植物太阳能利用率

本文计算分析了我国陆生植物在各种情况下的净初级生产力及其太阳能利用率。 计算表明,每年进入我国960万平方公里国土上的太阳总辐射Q和光合有效辐射PAR分别为13×10~(18)千卡和6.4×10~(18)千卡,其所含能量约合标准煤20,000亿吨和10,000亿吨。在充分利用我国光、温、水气候资源,而其他条件都处于最适状况时每年净初级气候潜力Y_(ptw)的全国总量为250亿吨(植物质干重,下同)。由植被产量的实际资料与气候因子的经验关系估算的自然植被产量Y_n的全国总量为每年70亿吨。 就全国加权平均单产而言,净初级光能潜力Y_p=87吨/公顷·年;净初级光温潜力Y_(pt)=50吨/公顷·年;净初级气候潜力Y_(ptw)=30吨/公顷·年;自然植被生产力Y_(?)=8吨/公顷·年;现阶段主要农作物的净初级实际生产力Y_α=8.7吨/公顷·年。各省区情况见表1。 太阳能利用率:就全国加权平均而言,如果把总辐射Q计为100％,则光合有效辐射PAR约占49％;具有最佳叶冠层的高产植物在生长盛期对Q的利用率上限为7％;相应于Y_p、Y_(pt),Y_(ptw)和Y_n的太阳能利用率R_p、R_(pt)、R_(ptw)和R_n分别为2.5％,1.4％、0.82％和0.22％,我国当前主要农作物的净初级产量对我国农田上Q的利用率R_α为0.28％。各省区情况见表2。     

Cooling streams with riparian trees: Thermal regime depends on total solar radiation penetrating the canopy

Riparian planting is often recommended for stream restoration, notably to mitigate solar heating of stream waters. However, plant leaves shade photosynthetically active radiation (PAR, 400–700 nm) more efficiently than the near-infrared (NIR, 700–3000 nm) wavelengths that comprise about half of incident solar radiation and so contribute equally to water heating. Total solar radiation (NIR + PAR) exposure at the reach scale is needed to avoid bias when predicting the thermal response of streams. In this article, we alert stream ecologists and riparian restorers to the water heating contribution of NIR and provide a means to account for both NIR and PAR in total solar radiation penetrating riparian canopies. We used spectral pyranometers to simultaneously measure total solar radiation and its NIR component under different tree canopies over a wide range of shade conditions as indexed by PAR exposure. Measurements were made during full overcast (diffuse lighting) conditions so as to ‘sample’ transmission of radiation through the complete canopy. The NIR proportion of sub-canopy solar radiation increased steadily with increasing shade and was appreciably greater under willow than pine canopies, while NZ native broadleaf rainforest had intermediate (rather variable) NIR content. Our trend lines for different tree canopies permit total sub-canopy solar radiation to be estimated from PAR exposure for unbiased modelling of stream thermal regimes.     

水稻冠层光截获、光能利用与产量的关系

以两优培九和武香粳14号水稻品种为材料,在不同栽插密度和施氮水平下进行2年田间试验,研究水稻冠层光合有效辐射(PAR)截获率、光能利用率与水稻产量的关系.结果表明:分蘖期至成熟期,各处理水稻冠层平均PAR反射率为3.45％,其中,分蘖期至抽穗期的冠层反射PAR占冠层总PAR损失的10.90％,显著小于抽穗期至成熟期的22.06％.分蘖期至成熟期的冠层PAR转化率随栽插密度的增加而减少,随施氮量的增加而增大;分蘖期至抽穗期的冠层PAR转化率高于抽穗期至成熟期.在分蘖期至成熟期,冠层PAR利用率随栽插密度和施氮量的增加而增大,各处理中两优培九的平均PAR利用率(1.83 g· MJ-1)显著高于武香粳14(1.42 g·MJ-1);武香粳14因生育期较长,分蘖期至成熟期的入射PAR及中、高栽插密度处理的PAR截获量均高于两优培九.水稻不同生长阶段冠层PAR截获率和利用率与产量呈显著正相关,PAR转化率与产量也呈正相关,但相关性不显著.因此,在保持较高PAR截获率的基础上提高冠层PAR转化率,进而提高冠层PAR利用率,有利于水稻高产.     

Model simulations of spatial distributions and daily totals of photosynthesis in Eucalyptus grandis canopies

Summary A simulation model for radiation absorption and photosynthesis was used to test the hypothesis that observed nonuniform distributions of nitrogen concentrations in young Eucalyptus grandis trees result in greater amounts of daily assimilation than in hypothetical trees with uniform N distributions. Simulations were performed for trees aged 6, 9, 12 and 16 months which had been grown in plantations under a factorial combination of two levels of fertilization and irrigation. Observed leaf N distribution patterns yielded daily assimilation rates which were only marginally greater (<5%) than for hypothetical trees with uniform distributions. Patterns of assimilation distribution in individual tree crowns closely resembled those for absorbed radiation, rather than for N. These conclusions were unaffected by three choices of alternative leaf area density distributions. The simulation model was also used to calculate hourly and daily rates of canopy assimilation to investigate the relative importance of radiation absorption and total canopy nitrogen on assimilation. Simulated hourly rates of carbon assimilation were often lightsaturated, whereas daily carbon gain was directly proportional to radiation absorbed by the tree crown and to total mass of N in the leaves. Leaf nitrogen concentrations determined photosynthetic capacity, whereas total leaf area determined the amount of radiation absorbed and thus the degree to which capacity was realized. Observed total leaf area and total crown N were closely correlated. The model predicted that nitrogen use efficiences (NUE, mol CO₂ mol^–1 N) were 60% higher for unfertilized than for fertilized trees at low levels of absorbed photosynthetically active radiation (PAR). Nitrogen use efficiency was dependent on fertilizer treatment and on the amount of absorbed PAR; NUE declined with increasing absorbed PAR, but decreased more rapidly for unfertilized than for fertilized trees. Annual primary productivity was linearly related to both radiation absorbed and to mass of N in the canopy.     

Row orientation effect on UV-B,UV-A and PAR solar irradiation components in vineyards at Tuscany,Italy

Besides playing an essential role in plant photosynthesis, solar radiation is also involved in many other important biological processes. In particular, it has been demonstrated that ultraviolet (UV) solar radiation plays a relevant role in grapevines (Vitis vinifera) in the production of certain important chemical compounds directly responsible for yield and wine quality. Moreover, the exposure to UV-B radiation (280–320 nm) can affect plant–disease interaction by influencing the behaviour of both pathogen and host. The main objective of this research was to characterise the solar radiative regime of a vineyard, in terms of photosynthetically active radiation (PAR) and UV components. In this analysis, solar spectral UV irradiance components, broadband UV (280–400 nm), spectral UV-B and UV-A (320–400 nm), the biological effective UVBE, as well as the PAR (400–700 nm) component, were all considered. The diurnal patterns of these quantities and the UV-B/PAR and UV-B/UV-A ratios were analysed to investigate the effect of row orientation of the vineyard in combination with solar azimuth and elevation angles. The distribution of PAR and UV irradiance at various heights of the vertical sides of the rows was also studied. The results showed that the highest portion of plants received higher levels of daily radiation, especially the UV-B component. Row orientation of the vines had a pronounced effect on the global PAR received by the two sides of the rows and, to a lesser extent, UV-A and UV-B. When only the diffused component was considered, this geometrical effect was greatly attenuated. UV-B/PAR and UV-A/PAR ratios were also affected, with potential consequences on physiological processes. Because of the high diffusive capacity of the UV-B radiation, the UV-B/PAR ratio was significantly lower on the plant portions exposed to full sunlight than on those in the shade.     

Importance of the green color,absorption gradient,and spectral absorption of chloroplasts for the radiative energy balance of leaves

Terrestrial green plants absorb photosynthetically active radiation (PAR; 400–700 nm) but do not absorb photons evenly across the PAR waveband. The spectral absorbance of photosystems and chloroplasts is lowest for green light, which occurs within the highest irradiance waveband of direct solar radiation. We demonstrate a close relationship between this phenomenon and the safe and efficient utilization of direct solar radiation in simple biophysiological models. The effects of spectral absorptance on the photon and irradiance absorption processes are evaluated using the spectra of direct and diffuse solar radiation. The radiation absorption of a leaf arises as a consequence of the absorption of chloroplasts. The photon absorption of chloroplasts is strongly dependent on the distribution of pigment concentrations and their absorbance spectra. While chloroplast movements in response to light are important mechanisms controlling PAR absorption, they are not effective for green light because chloroplasts have the lowest spectral absorptance in the waveband. With the development of palisade tissue, the incident photons per total palisade cell surface area and the absorbed photons per chloroplast decrease. The spectral absorbance of carotenoids is effective in eliminating shortwave PAR (<520 nm), which contains much of the surplus energy that is not used for photosynthesis and is dissipated as heat. The PAR absorptance of a whole leaf shows no substantial difference based on the spectra of direct or diffuse solar radiation. However, most of the near infrared radiation is unabsorbed and heat stress is greatly reduced. The incident solar radiation is too strong to be utilized for photosynthesis under the current CO₂ concentration in the terrestrial environment. Therefore, the photon absorption of a whole leaf is efficiently regulated by photosynthetic pigments with low spectral absorptance in the highest irradiance waveband and through a combination of pigment density distribution and leaf anatomical structures.     

Using a Simple Apparatus to Measure Direct and Diffuse Photosynthetically Active Radiation at Remote Locations

Plant canopy interception of photosynthetically active radiation (PAR) drives carbon dioxide (CO₂), water and energy cycling in the soil-plant-atmosphere system. Quantifying intercepted PAR requires accurate measurements of total incident PAR above canopies and direct beam and diffuse PAR components. While some regional data sets include these data, e.g. from Atmospheric Radiation Measurement (ARM) Program sites, they are not often applicable to local research sites because of the variable nature (spatial and temporal) of environmental variables that influence incoming PAR. Currently available instrumentation that measures diffuse and direct beam radiation separately can be cost prohibitive and require frequent adjustments. Alternatively, generalized empirical relationships that relate atmospheric variables and radiation components can be used but require assumptions that increase the potential for error. Our goal here was to construct and test a cheaper, highly portable instrument alternative that could be used at remote field sites to measure total, diffuse and direct beam PAR for extended time periods without supervision. The apparatus tested here uses a fabricated, solar powered rotating shadowband and other commercially available parts to collect continuous hourly PAR data. Measurements of total incident PAR had nearly a one-to-one relationship with total incident radiation measurements taken at the same research site by an unobstructed point quantum sensor. Additionally, measurements of diffuse PAR compared favorably with modeled estimates from previously published data, but displayed significant differences that were attributed to the important influence of rapidly changing local environmental conditions. The cost of the system is about 50% less than comparable commercially available systems that require periodic, but not continual adjustments. Overall, the data produced using this apparatus indicates that this instrumentation has the potential to support ecological research via a relatively inexpensive method to collect continuous measurements of total, direct beam and diffuse PAR in remote locations.     

Modification of leaf cytology and anatomy in Brassica napus grown under above ambient levels of supplemental UV-B radiation.

Plants exposed to natural solar radiation usually show acclimation responses on a daily and seasonal basis. Many of these responses are complex and modified by interactions with acclimation responses to other climatic factors. While changes in photosynthetically active radiation (PAR, 400-700 nm) are the driving force for many acclimation responses in plants, radiation outside the PAR range is also important. Recently, interest has increased in the potential role of UV-A (320-400 nm) and UV-B (280-320 nm) components of sunlight in plant developmental, physiological and daily acclimation processes. In order to explore the role of UV-B further, Brassica napus L. cv Paroll plants were grown to maturity under 13 kJ d(-1) of biologically effective ultraviolet-B radiation (UV-B(BE), 280-320 nm) plus 800 micromol photons m(-2) s(-1) photosynthetically active radiation (PAR, 400-700 nm) or PAR alone. Leaf anatomy and palisade cell structure were quantified using stereological techniques. The leaves of plants grown under UV-B radiation exhibited an increase in overall leaf width, although no change in leaf anatomy was discerned. Palisade cells in UV-B exposed leaves showed a significant decrease in chloroplast, mitochondrial, starch, and microbody volume density (Vv), while the vacuolar Vv increased compared to cells exposed to PAR only. In UV-B exposed leaves, there was an increase in the appressed and non-appressed thylakoid surface area density (Sv) within the chloroplasts. Since the relative proportion of appressed to non-appressed thylakoid surface area did not change, both thylakoid systems changed in concert with each other. Thylakoid stacks were broader and shorter in leaves subjected to UV-B. In general these responses were similar to those which occurred in plants moved from a high to low PAR environment and similar to mature plants exposed to 13 kJ d(-1) UV-B(BE) for only a short period of time. Although UV absorbing pigments increased by 21% in UV-B exposed leaves, there was no significant difference in chlorophyll a,b or carotenoid content compared to plants exposed to only PAR.     

水稻冠层光截获、光能利用与产量的关系

以两优培九和武香粳14号水稻品种为材料,在不同栽插密度和施氮水平下进行2年田间试验,研究水稻冠层光合有效辐射(PAR)截获率、光能利用率与水稻产量的关系.结果表明： 分蘖期至成熟期,各处理水稻冠层平均PAR反射率为3.45%,其中,分蘖期至抽穗期的冠层反射PAR占冠层总PAR损失的10.90%,显著小于抽穗期至成熟期的22.06%.分蘖期至成熟期的冠层PAR转化率随栽插密度的增加而减少,随施氮量的增加而增大;分蘖期至抽穗期的冠层PAR转化率高于抽穗期至成熟期.在分蘖期至成熟期,冠层PAR利用率随栽插密度和施氮量的增加而增大,各处理中两优培九的平均PAR利用率(1.83 g·MJ^-1)显著高于武香粳14(1.42 g·MJ^-1);武香粳14因生育期较长,分蘖期至成熟期的入射PAR及中、高栽插密度处理的PAR截获量均高于两优培九.水稻不同生长阶段冠层PAR截获率和利用率与产量呈显著正相关,PAR转化率与产量也呈正相关,但相关性不显著.因此,在保持较高PAR截获率的基础上提高冠层PAR转化率,进而提高冠层PAR利用率,有利于水稻高产.     

Application of underwater light measurements in nutrient and production studies in shallow rivers

Due to fluctuations in water turbidity, river depth and total reflection from one river section to another, plant production is poorly correlated to solar radiation incident on the water surface. A relationship was observed between daily relative photosynthesis and photosynthetically available radiation (PAR) at the plant depth for Cladophora, with a correlation coefficient (r) of 0·73. Therefore, the effect of low light levels can be compensated for when evaluating nutrient-growth relationships for Cladophora in the field.     

Modelling environmental limits to light use efficiency for a canopy of two broad-leaved tree species with contrasting leaf habit

We used outputs from a model of canopy carbon uptake [Dungan et al. (2004) Functional Ecology 18: 34–42] and measurements of irradiance (PAR, 400–700 nm) intercepted by the canopy to investigate the effect of daily changes in environmental conditions on daily light use efficiency, ε, for a canopy comprising two broadleaved New Zealand tree species with contrasting leaf habit. Irradiance absorbed by the canopy was 93% of the incident irradiance, and seasonal changes in the proportion of this absorbed by leaves of each species was estimated with a detailed model of leaf area phenology. Over the year, ε for semi-deciduous wineberry (Aristotelia serrata) was 0.43 g C MJ-1 PAR, with maximum and minimum values of 0.80 g C MJ-1 PAR and 0.07 g C MJ-1 PAR in summer and winter respectively. In contrast annual ε was 0.60 g C MJ-1 PAR for winter deciduous fuchsia, with a maximum value of 0.92 g C MJ-1 PAR in spring. The most important environmental regulator of ε for both species was τ, atmospheric transmissivity. Maximum values for ε were estimated on days when τ ≈0.2, on cloudy days in mid-summer. Limits to photosynthesis from restricted root-zone water availability were also important, showing that drought limitations can restrict ε even at a field site with annual rainfall of 4800 mm. Environmental limits to photosynthesis and ε have been investigated for only a few canopy tree species. Uncertainty in models of the national carbon budget required for reporting purposes would be reduced by considering the environmental regulation of ε for a wider range of tree species.     

Using the expolinear growth equation for modelling crop growth in year-round cut chrysanthemum

The aim of this study was to predict crop growth of year-round cut chrysanthemum (Chrysanthemum morifolium Ramat.) based on an empirical model of potential crop growth rate as a function of daily incident photosynthetically active radiation (PAR, MJ m-2 d-1), using generalized estimated parameters of the expolinear growth equation. For development of the model, chrysanthemum crops were grown in four experiments at different plant densities (32, 48, 64 and 80 plants m-2), during different seasons (planting in January, May-June and September) and under different light regimes [natural light, shading to 66 and 43 % of natural light, and supplementary assimilation light (ASS, 40-48 micro mol m-2 s-1)]. The expolinear growth equation as a function of time (EXPOT) or as a function of incident PAR integral (EXPOPAR) effectively described periodically measured total dry mass of shoot (R2 > 0.98). However, growth parameter estimates for the fitted EXPOPAR were more suitable as they were not correlated to each other. Coefficients of EXPOPAR characterized the relative growth rate per incident PAR integral [rm,i (MJ m-2)-1] and light use efficiency (LUE, g MJ-1) at closed canopy. In all four experiments, no interaction effects between treatments on crop growth parameters were found. rm,i and LUE were not different between ASS and natural light treatments, but were increased significantly when light levels were reduced by shading in the summer experiments. There was no consistent effect of plant density on growth parameters. rm,i and LUE showed hyperbolic relationships to average daily incident PAR averaged over 10-d periods after planting (rm,i) or before final harvest (LUE). Based on those relationships, maximum relative growth rate (rm, g g-1 d-1) and maximum crop growth rate (cm, g m-2 d-1) were described successfully by rectangular hyperbolic relationships to daily incident PAR. In model validation, total dry mass of shoot (Wshoot, g m-2) simulated over time was in good agreement with measured ones in three independent experiments, using daily incident PAR and leaf area index as inputs. Based on these results, it is concluded that the expolinear growth equation is a useful tool for quantifying cut chrysanthemum growth parameters and comparing growth parameter values between different treatments, especially when light is the growth-limiting factor. Under controlled environmental conditions the regression model worked satisfactorily, hence the model may be applied as a simple tool for understanding crop growth behaviour under seasonal variation in daily light integral, and for planning cropping systems of year-round cut chrysanthemum. However, further research on leaf area development in cut chrysanthemum is required to advance chrysanthemum crop growth prediction.     

阳光紫外辐射对室内水培发状念珠藻生理特性的影响

发状念珠藻（Nostoc flagelliforme Bornet & Flahault）是一种重要的陆生经济蓝藻,室内培育出的原植体如何适应阳光辐射的问题尚需探讨。为此,作者将室内水培发菜置于阳光下培养,测定了其生长、有效光化学效率（F/Fm&#900;）和色素的变化。结果表明,较高的可见光（PAR,395－700 nm）和紫外辐射（UVR,280－395 nm）均导致水培发菜的F/Fm&#900;下降。第1天中午,PAR和UVR分别使F/Fm&#900;下降了54％和13％;傍晚,F/Fm&#900;有部分恢复。UVR对发菜适应阳光2d后的生长无负面作用。发菜在适应全阳光辐射期间,紫外吸收物质（Scytonemin和Mycosporine-like amino acids）含量不断增加,9d后,分别增加了124倍和9倍。这些紫外吸收物质的增加对发菜细胞降低光抑制,适应阳光辐射,起到了重要作用。本研究的结果可为水培发菜室外培养方法的建立提供一定的理论依据。     

Effects of solar radiation on bacterial and fungal density on aquatic plant detritus

1. The effects of solar radiation on bacterial and fungal growth on aquatic macrophyte detritus were studied in a microcosm experiment. Senescent leaves of Phragmites australis were incubated for 63 days in shallow water in the shade under photosynthetically active radiation (PAR) together with ultraviolet radiation, or under filters removing either ultraviolet B (UVB) or both UVB and ultraviolet A (UVA). 2. Bacterial abundance and bacterial ³H-leucine incorporation in the water were measured, together with α- and β-D-glucosidase activity. In addition, bacterial abundance and fungal biomass associated with the litter were measured. 3. The results indicate that both PAR and UVA affect the micro-organisms involved in the decomposition of leaf litter. The α/β-D-glucosidase activity ratio was less than one in irradiated and more than one in shaded microcosms, suggesting a change in the substrate dissolved organic matter composition towards more β- than α-glycosidic linkages as a result of solar radiation. 4. Microcosms receiving UVB displayed a significantly higher β-D-glucosidase activity than shaded microcosms, and those exposed to PAR or PAR + UVA, demonstrating the potential importance of UVB radiation. 5. The free-living bacteria tended to be dominated by filamentous forms in microcosms subject to solar radiation, especially PAR, and attached microbial communities showed a greater tendency to be dominated by bacteria in irradiated microcosms than in shaded microcosms.     

Exposure of eggs to solar UV‐B leads to reduced hatching rates in two sparid fishes,red sea bream Pagrus major and black sea bream Acanthopagrus schlegeli

Hatching success was examined under exposure to solar ultraviolet radiation (UVR) using filters to give three different light conditions [C1: UV‐B, UV‐A and photosynthetically active radiation (PAR), C2: UV‐A and PAR, C3: PAR] in red Pagrus major and black Acanthopagrus schlegeli sea bream. Hatching rate of both species was reduced by an exposure over a 2 day period to UVR and was not significantly different between two species under the three light conditions.     

不同株行距配置对夏大豆群体结构及光截获的影响

以田间试验(2006—2007年)为基础,分析了地上部干物质、叶面积指数(LAI)、光合有效辐射(PAR)、光能利用率和植株形态指标变化特征,夏大豆‘鲁豆4号’(Glycine maxcv.Ludou 4)在同一密度(3.09×105株/hm2)下设5种株行距配置方式,即行距×株距分别为18 cm×18 cm(A)、27 cm×12 cm(B)、36 cm×9 cm(C)、45 cm×7.2 cm(D)、54 cm×6 cm(E)。结果表明,大豆在生育期间干物质变化因株行距不同而产生差异,2006和2007生长季的各处理干物质分别在播种后第70天和90天达到最高,播种后第80天和100天时,A处理比E处理分别高21.6%和34.0%;不同层次干物质积累重心随行距加大有上移趋势。各处理LAI随行距扩大、株距减少有下降趋势,其中,A和B处理LAI表现较稳定,LAI相对较高且时间较长。光能利用率随行距加大有降低趋势,A和B处理显著高于E处理(P0.05)。夏大豆在不同株行距配置下,株粒数、百粒重与产量相关系数分别为0.941*和0.926*(2006年),0.995*和0.892*(2007年),随行距变小PAR透射率降低、截获率和光能利用率上升而产量增加,A和B处理产量显著高于E处理(P0.05)。说明夏大豆在雨养农业条件下,植株相对均匀分布可改善群体结构和增强光截获,进而提高群体光能利用率和产量。     

Lipid composition of the red alga Tichocarpus crinitus exposed to different levels of photon irradiance

We examined variations in the lipid composition of the marine red alga Tichocarpus crinitus exposed to different levels of photon irradiance: 70-80% and 8-10% of the incident photosynthetically active radiation (PAR). The content of storage and structural lipids was significantly affected by the light intensity. Exposure of T. crinitus to low light conditions induced an increase in the abundance of structural components of the cell membranes, especially sulfoquinovosyldiacylglycerol, phosphatidylglycerol (PG) and phosphatidylcholine, while growth of algae at high light intensity resulted in a 1.5-folder increase in the level of storage lipids, i.e. triacylglycerols. There were no significant differences in the fatty acid composition of the total lipid pool in algae grown under different light conditions. However, the content of the most unsaturated acid, 20:5n-3, was slightly higher in T. crinitus under 8-10% PAR compared to those at 70-80% PAR. Each lipid class was found to have a characteristic fatty acid composition. The relative proportions of fatty acids esterifying monogalactosyldiacylglycerol (MGDG) and PG were significantly affected by irradiance conditions. Exposure of algae to low light resulted in increase in the content of 20:5n-3 in MGDG and in decrease in the level of this acid in PG. The concentration of trans-16:1 acid in PG increased in algae grown under high light intensity. Light conditions influenced on total lipid content, which made up 4.2+/-0.5 and 3.4+/-0.3 mg g-1 fresh weight in algae exposed to 8-10% PAR and 70-80% PAR, respectively. We suggest that variations in the lipid composition of T. crinitus exposed to different levels of light intensity may be a response of alga to light conditions and it can be considered as one of the mechanisms of adaptation of T. crinitus to varying incident light intensity.