探讨幼叶为红色的适应意义

It is well known that leaves flush red rather than green in spring and some other stages of their life span in many woody plant species. The leaf coloration involves the costs of pigment synthesis, resource loss and loss of primary production (photosynthesis), thus, it is hard to believe the redness of leaf worth nothing but a by-product of metabolism. Most previous works focused on autumn leaf color in a few species. Various hypotheses were proposed but none of them without contravention. Studies on red young leaves in spring were relatively few, despite that it is even more ubiquitous than autumn redness. In this proposal, we plan to conduct a three-year study on adaptive significance of red young leaves at a community level in different areas, including Hengduan Mountains, Shennongjia area and Wuhan. We plan to investigate leaf color of woody communities in different altitude, measuring various environmental factors that may affect leaf coloration; quantifying leaf surface reflectance spectra by a portable spectrophotometer to determine whether red color are detectable for herbivore as a visual signal; quantifying potential trade-offs between red and mechanical protection in species with obvious intraspecific variation, and the differences in photosynthetic efficiency between red and green young leaves; artificial leaf chewing and color change, combined with feeding trails to determine the effect of redness produced. The project aims to explain why red young leaves are common, the implementation of the project will provide a better understanding of the importance of leaf redness at a large scale. Our test of the anti-herbivory hypothesis will be improved by combining red color and mechanical protection, which results will provide a scientific basis for pest control as well.

很多木本植物的春季幼叶或者秋季老叶为红色，研究表明此过程植物合成了新的色素（主为花青素）。目前的研究主要针对少数物种试图解释秋叶变红色的原因，但仍存在争议；实际上红色的幼叶比秋叶更为普遍，研究却相对较少。申请者在已有研究的基础上，拟选择横断山区、神农架林区和武汉地区，在群落水平上研究红色幼叶的适应意义。计划在三个不同海拔的地区调查群落植物各时期叶色，测定各种环境因子对幼叶颜色的影响。同时定量叶表面的反射光谱，以验证红色作为啃食者警示信号的可能性。另外，选取种内叶色变异较大的物种，测定红、绿幼叶光合效率上的差异，定量红色、光合效率和机械保护之间的权衡。人工模拟啃食和叶色改变，结合饲喂实验确定红叶对植物产生的影响。该项目旨在探寻红色幼叶之所以常见的原因，项目的实施可望从大尺度上解释红叶的适应性意义；将红色和机械保护结构联系起来，更全面的认识植物对啃食者的防御适应，同时也为害虫防治提供科学依据。

很多木本植物的春季幼叶或者秋季老叶为红色，此过程主要是由于植物合成了花青素。研究发现叶片中的花青素并不是单纯的代谢副产品，而是适应环境的结果，红色幼叶可以作为一种对无脊椎啃食者的防御手段。本项目通过对中南地区位于不同海拔5个群落的调查，记录各群落中常见物种幼叶、成叶和老叶的颜色，并记录每个物种幼叶上三种主要保护组织（表皮毛、复表皮和强化角质层）的情况并分析叶色与机械保护之间的关系。发现红色幼叶广泛存在于各群落中，红色幼叶物种的保护组织的水平显著低于绿色幼叶物种，同时系统学相关分析显示叶色与机械组织在被子植物进化过程中存在相关性。这说明在亚热带地区，幼叶的红色（化学防御）和机械保护之间存在一定的互补关系，红叶是一种普遍存在的防御机制。另一方面，通过对武汉群落中常见物种的幼叶和成叶表面反射光谱分析，发现人类视觉可以区分的红叶和绿叶在亚热带主要的无脊椎啃食者（鞘翅目和鳞翅目昆虫）色觉系统中无明显差异，说明幼叶的颜色无法作为视觉信号威慑啃食者，红叶可能是通过其他方式（例如花青素的刺激性味道）来行使防御功能。这些结果不支持根据蚜虫相关研究提出的解释红色秋叶适应意义的“共进化假说”，结合目前对于叶色适应意义的其他解释，红色幼叶的功能可能是多方面的。本项目对红色幼叶的适应意义提出了新的解释，为动物-植物相互作用提供了新的视野。