Testing trait plasticity over the range of spectral composition of sunlight in forb species differing in shade tolerance

Although sunlight is essential for plant growth and development, the relative importance of each spectral region in shaping functional traits is poorly understood, particularly in dynamic light environments such as forest ecosystems.
We examined responses of 25 functional traits from groups of 11 shade-intolerant and 12 understorey shade-tolerant forb species grown outdoors under five filter treatments differing in spectral transmittance: (1) transmitting c 95% of solar radiation; (2) attenuating ultraviolet-B (UV-B); (3) attenuating all UV; (4) attenuating all UV and blue light; (5) attenuating all UV, blue, and green light.
Our results show that UV-B radiation mainly affected the biochemical traits but blue light mainly affected the physiological traits irrespective of functional strategy, whereas green light affected both sets of traits. This would suggest that differentiation among suites of functional-trait responses proceeds according to light quality. Biomass accumulation was significantly increased by UV-A radiation (contrasting treatment (2) vs (3)) among shade-intolerant but decreased by blue light among shade-tolerant species; green and red light affected whole-plant morphological development differently according to functional groups. Shade-tolerant species were more plastic than shade-intolerant species in response to each spectral region that we examined except for UV-B radiation.
Synthesis. Our results show that differences in the spectral composition of sunlight can drive functional trait expression irrespective of total irradiance received. The different responses of functional traits between functional groups imply that shade-tolerant and intolerant species have adapted to utilize spectral cues differently in their respective light environments.

尽管阳光对于植物的生长发育不可或缺，但各光谱区域在塑造植物功能性状（functional trait）中的相对重要性仍有待阐明，尤其是在森林生态系统这类动态光环境中。
我们针对11种非耐阴植物与12种林下耐阴草本植物类群的25项功能性状展开了响应分析，供试材料在室外5种不同光谱透过率的滤光处理下栽培：(1) 透过约95%的太阳辐射；(2) 滤除紫外-B（UV-B）辐射；(3) 滤除全部紫外辐射；(4) 滤除全部紫外辐射与蓝光；(5) 滤除全部紫外辐射、蓝光与绿光。
研究结果表明，无论植物的功能策略类型如何，紫外-B辐射主要影响生化性状，而蓝光主要调控生理性状，绿光则同时影响两类性状。这意味着功能性状响应组群的分化遵循光质调控规律。在非耐阴物种中，紫外-A辐射（对比处理组(2)与(3)）可显著提升生物量积累，而耐阴物种的生物量积累则因蓝光照射而降低；绿光与红光对全株形态发育的影响则因功能类群不同而存在差异。除紫外-B辐射外，耐阴物种在各检测光谱区域下的表型可塑性均高于非耐阴物种。
综合分析表明，本研究结果证实，太阳光光谱组成的差异可独立于总辐照度驱动植物功能性状的表达。不同功能类群间功能性状响应模式的差异，意味着耐阴与非耐阴物种已在各自适配的光环境中演化出差异化的光谱信号利用策略。