Light-emitting Diode Light Transmission through Leaf Tissue of Seven Different Crops
Light-emitting Diode Light Transmission through Leaf Tissue of Seven Different Crops
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发光二极管光通过七种不同作物的叶子组织的传输
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发表时间：
2015
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通讯作者：
R. Wheeler
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作者：
G. Massa;T. Graham;Timothy Haire;Cedric Flemming;Gerard Newsham;R. Wheeler
近年来，在发光二极管（LED）技术快速发展的推动下，受控环境（CE）工厂生产照明取得了重大进展。除了提高能源效率之外，led还提供了定制作物光谱的能力，这可能对种植者和研究人员都有不可估量的好处。如果照明工程师要为CE工厂生产充分优化系统，了解这些特定波段是如何被植物组织衰减的是很重要的。在本研究中，在两种不同光强（225和420 mmol·m·s）下，在CE室中种植了7种不同的温室和大田作物（萝卜、莴苣、莴苣、莴苣、莴苣、莴苣、莴苣、莴苣、莴苣、甘蓝）。完整的、完全展开的冠层上部叶片被用来测定2到3个不同植物年龄的7个不同波段（峰值为400、450、530、595、630、655和735 nm）的透光水平。植物生长的光合光子通量（PPF）环境以作物依赖的方式影响不同LED波长的光透射。在检测的时间间隔内，植物年龄对透光率没有影响。7种LED光源的特定波段透射率在不同植物类型之间也有相似的变化，蓝色和红色波长的透射率较低，绿色和琥珀色波长的透射率居中，远红色波长的透射率最高。较高的原生PPF处理比较低的原生PPF处理增加了红生菜的花青素水平。了解光传输的差异将为CE植物生长的新型节能照明架构的发展提供信息。为包括生物再生生命支持系统和垂直农业应用在内的CE植物生产提供最佳质量、数量和分布的光，可以说仍然是实现这些系统的全部经济和研究潜力的最大障碍。荧光灯、高压钠灯（HPS）和金属卤化物灯（MH）等电灯几十年来一直用于在受控环境中种植植物（Sager和McFarlane， 1997年；Wheeler， 2008年）。通常，HPS和MH灯是高功率的（例如，400到1000 W），并且作为相对的“点”光源，可能会产生光分配挑战（Cathey和Campbell， 1980）。根据灯和镇流器的类型，这些电弧放电灯可以有一个相对较短的工作寿命[例如，小于5000小时的非常高输出（VHO）荧光灯；HPS最高可达25,000小时，这意味着高运营和维护成本。此外，这些灯具有固定的光谱输出，不考虑任何随时间的退化，光谱质量在任何实际意义上都不能通过种植周期改变（Cathey和Campbell， 1980）。led目前是CE植物照明系统中最有前途的技术之一（Massa等人，2008），特别是用于空间作物生长应用（Barta等人，1992；Massa等人，2007;Mitchell, 2012； Olle和Viršile, 2013； Poulet等人，2014）。与传统的电弧放电灯相比，led具有非常长的工作寿命（例如，50,000至100,000小时）（Yeh和Chung， 2009）。此外，led在较低的温度下工作，发射相对较少的长波辐射，从工作场所安全的角度来看，本质上更安全，并且适合广泛的系统设计（Morrow, 2008； Olle和Viršile， 2013）。也许商业上最重要的是，目前最先进的红色和蓝色led的效率接近或超过40%至50%，这与10年前相比有了显着改善（Bourget, 2008； Haitz和Tsao， 2011）。由于led具有相对狭窄的光谱输出，使用不同颜色的led也提供了在整个生长周期中创建或改变光谱组合的潜力（Morrow, 2008; Yeh and Chung, 2009）。发光二极管很容易配置成不同的形状因素，例如，已用于提供冠层内照明，可以从上面和内部照射整个植物冠层（Gómez等人，2013；Lu等人，2012；Massa等人，2005；Olle和Viršile, 2013； Trouwborst等人，2010）。这种内部方法需要进一步研究，以开发适用于各种作物和生产系统的适应性概念，因此在一段时间内，顶灯系统可能仍然是CE作物生产的首选方法。植物能够吸收整个光合有效辐射（PAR）波段的光子（McCree, 1971），但长期以来人们一直认为，由于叶绿素的作用，蓝色和红色区域的吸收特别强（McCree, 1971； Rabideau等，1946）。辅助光合色素（如类胡萝卜素）能够吸收这些红蓝波段之间的波长；这些辅助色素捕获的能量可以转移到光合反应中心（索尔兹伯里和罗斯，1992）。由于其他波长不像红光和蓝光那样容易被吸收，这些波长有可能通过冠层上部叶片产生更大的通量（Kim et al., 2004; Moss and Loomis, 1952; Rabideau et al., 1946; Wang and Folta, 2013）。这些波长的较低衰减将允许穿透更深的冠层，在那里它们将通过被冠层较低的叶子吸收来促进植物的整体光合能力。光透射到冠层的程度由一系列因素决定，包括作物类型、叶龄、叶形态、冠层结构和入射光的角度（Larcher, 1975; Monteith and Unsworth, 2007）。例如，相对于叶片角度分布更亲平的物种（如胡椒），亲平草的叶片高度倾斜，允许光线直接或通过反射深入冠层（Larcher, 1975）。虽然叶片的一般几何形状（大小、形状和排列）对确定植物冠层的消光系数至关重要，但光谱质量或组成也会产生重大影响（McCree, 1971; Monteith and Unsworth, 2007; Niinemets, 2010）。在大田作物生产中，这通常不是一个问题，因为作物生长在广谱阳光下。当生产转移到由电气照明系统提供全部或部分照明的CE设施时，则接收于2014年10月20日发布。已接受于2014年11月24日发表。这项工作的支持是由佛罗里达空间资助联盟、橡树岭联合大学（ORAU）美国宇航局博士后研究奖学金计划、肯尼迪航天中心（Gioia Massa; Thomas Graham）和威斯康辛州麦迪逊轨道技术公司（ORBITEC） （LED供应商）提供的。塞德里克·弗莱明得到了NASA CIPAIR项目的支持。我们感谢Larry Koss在植物室维护和灯架组装方面的帮助。Co-first作者。应向谁提出转载请求；电子邮件gioia.massa@nasa.gov。园艺科学vol . 50(3) March 2015 501 miscellaneous
Significant advances in controlled-environment (CE) plant production lighting have been made in recent years, driven by rapid improvements in light-emitting diode (LED) technologies. Aside from energy efficiency gains, LEDs offer the ability to customize the spectrum delivered to a crop, which may have untold benefits for growers and researchers alike. Understanding how these specific wavebands are attenuated by plant tissue is important if lighting engineers are to fully optimize systems for CE plant production. In this study, seven different greenhouse and field crops (radish, Raphanus sativus ‘Cherry Bomb II’; red romaine lettuce, Lactuca sativa ‘Outredgeous’, green leaf lettuce, Lactuca sativa ‘Waldmann’s Green’; pepper, Capsicum annuum ‘Fruit Basket’; soybean, Glycine max ’Hoyt’; cucumber, Cucumis sativus ‘Spacemaster’; canola, Brassica napus ‘Westar’) were grown in CE chambers under two different light intensities (225 and 420 mmol·m·s). Intact, fully expanded upper canopy leaves were used to determine the level of light transmission, at two to three different plant ages, across seven different wavebands with peaks at 400, 450, 530, 595, 630, 655, and 735 nm. The photosynthetic photon flux (PPF) environment that plants were grown in affected light transmission across the different LED wavelengths in a crop-dependent manner. Plant age had no effect on light transmission at the time intervals examined. Specific waveband transmission from the seven LED sources varied similarly across plant types with low transmission of blue and red wavelengths, intermediate transmission of green and amber wavelengths, and the highest transmission at the far-red wavelengths. Higher native PPF increased anthocyanin levels in red romaine lettuce compared with the lower native PPF treatment. Understanding the differences in light transmission will inform the development of novel, energy-saving lighting architectures for CE plant growth. Providing the optimal quality, quantity, and distribution of light in CE plant production, including bioregenerative life support systems and vertical farming applications, arguably remains the most significant hurdle in realizing the full economic and research potential of these systems. Electric lamps such as fluorescent, high-pressure sodium (HPS), and metal halide (MH) have been used for decades to grow plants in controlled environments (Sager and McFarlane, 1997; Wheeler, 2008). Typically, HPS and MH lamps are high-powered (e.g., 400 to 1000 W) and act as relative ‘‘point’’ sources that can create light distribution challenges (Cathey and Campbell, 1980). Depending on the lamp and ballast type, these arc-discharge lamps can have a relatively short operational life [e.g., less than 5000 h for very high output (VHO) fluorescent; up to 25,000 h for HPS], which translates to high operation and maintenance costs. Furthermore, these lamps have a fixed spectral output, not accounting for any degradation over time, and the spectral quality cannot, in any practical sense, be altered through the cropping cycle (Cathey and Campbell, 1980). LEDs are currently one of the most promising technologies for CE plant lighting systems (Massa et al., 2008) and especially for space crop growth applications (Barta et al., 1992; Massa et al., 2007; Mitchell, 2012; Olle and Viršile, 2013; Poulet et al., 2014). Compared with traditional arc-discharge lamps, LEDs have exceptionally long operational life expectancies (e.g., 50,000 to 100,000 h) (Yeh and Chung, 2009). Furthermore, LEDs operate at lower temperatures, emit comparably little long wave radiation, are intrinsically safer from a workplace safety perspective, and lend themselves to a wide range of system designs (Morrow, 2008; Olle and Viršile, 2013). Perhaps most important commercially, current state-of-the-art red and blue LEDs have efficiencies that approach or exceed 40% to 50%, which is a significant improvement from where they were just 10 years ago (Bourget, 2008; Haitz and Tsao, 2011). Because LEDs have a relatively narrow spectral output, use of different colored LEDs also offers the potential for creating or changing spectral combinations throughout the growth cycle (Morrow, 2008; Yeh and Chung, 2009). Light-emitting diodes are easily configured into different form factors and, for example, have been used to provide intracanopy lighting where whole plant canopies can be irradiated from both above and from within (Gómez et al., 2013; Lu et al., 2012; Massa et al., 2005; Olle and Viršile, 2013; Trouwborst et al., 2010). Such intracanopy approaches need further research to develop adaptable concepts for a variety of crops and production systems, and hence overhead lighting systems will likely remain the preferred approach for CE crop production for some time. Plants are capable of absorbing photons throughout the photosynthetically active radiation (PAR) waveband (McCree, 1971) but it is has long been understood that as a result of chlorophyll, absorption in the blue and red regions is particularly strong (McCree, 1971; Rabideau et al., 1946). Ancillary photosynthetic pigments (e.g., carotenoids) are capable of absorbing wavelengths between these red and blue bands; the energy captured by these ancillary pigments can be transferred to the photosynthetic reaction centers (Salisbury and Ross, 1992). Because other wavelengths are not as readily absorbed as red and blue, the potential exists for greater flux of these wavelengths through the upper canopy leaves (Kim et al., 2004; Moss and Loomis, 1952; Rabideau et al., 1946; Wang and Folta, 2013). Lower attenuation of these wavelengths would allow penetration deeper into the canopy where they would contribute to the overall photosynthetic capacity of the plant through their absorption by lower canopy leaves. The degree of light transmission into the canopy is determined by a range of factors including crop type, leaf age, leaf morphology, canopy architecture, and angle of incident light (Larcher, 1975; Monteith and Unsworth, 2007). Erectophile grasses, for example, have highly inclined leaves that allow light to penetrate directly, or by reflectance, deep into the canopy relative to species with more planophile leaf angle distributions (e.g., pepper) (Larcher, 1975). Although general leaf geometry (size, shape, and arrangement) is of primary importance in determining the light extinction coefficient for a plant canopy, spectral quality or composition can also have a significant influence (McCree, 1971; Monteith and Unsworth, 2007; Niinemets, 2010). This is generally not a concern in field crop production where plants are grown under broad-spectrum sunlight. When production is moved to a CE facility where light is delivered, in whole or part, by electric lighting systems, then the Received for publication 20 Oct. 2014. Accepted for publication 24 Nov. 2014. Support for this work was provided through the Florida Space Grant Consortium, Oak Ridge Associated Universities (ORAU) NASA Post-Doctoral Research Fellowship Program, Kennedy Space Center (Gioia Massa; Thomas Graham), and Orbital Technologies Corporation (ORBITEC) Madison, WI (LED supplier). Cedric Flemming was supported through the NASA CIPAIR program. We thank Larry Koss for help with plant chamber maintenance and light stand assembly. Co-first authors. To whom reprint requests should be addressed; e-mail gioia.massa@nasa.gov. HORTSCIENCE VOL. 50(3) MARCH 2015 501 MISCELLANEOUS