Phytoplankton response to fluctuating light intensity and spectrum II - How fluctuations in the multiple dimensions of LIGHt shape phytoplankTON (LIGHT-ON)

波动的环境限制了人口或社区的适应能力。因此，与随机波动相比，高度可预测的波动将引发生物体和群落的不同反应。这些响应是非线性的，因此不是随时间平均的，这阻碍了基于平均环境预测未来生态系统功能。越来越多的研究证明了平均温度附近的热变率的重要性，但对温度以外的其他环境变量的研究较少。在这里，我们提出了一个基本的问题，即浮游植物生物如何应对在压力和有利条件之间经常发生的光变化，特别是如果人为强迫使这些变化超出了这些栖息地自然发生的波动水平。光波动的范围从可预测的季节和日分量到通过云层覆盖和散射在几秒钟内的随机变化，包括光的强度和光谱组成，因为吸收和散射是波长特有的。因此，光需要作为一种多维度和高度可变的资源来处理，因为变异性的时刻（振幅、频率和随机性）适用于多个波长。水生系统中高度可变的光照条件直接影响浮游植物的光合作用、呼吸作用、生长速率和生化组成。然而，大多数关于光的实证研究都将定期波动作为群落动态的驱动因素，而且大多数研究都侧重于资源的单一维度（主要是总辐照度）。本文的创新思路是研究光强与光谱的交互作用，通过不同手段调控波动的频率、幅度和随机性，了解多种波动资源对浮游植物的综合影响。我们首先分析光强度和光谱的波动如何在自然界中发生，并进行单克隆培养实验，以了解物种特异性反应。在下一步中，我们将测试种间相互作用是否会使用受控的实验室设置和多物种组合的操作来改变反应。实验将与模拟相结合，以进一步阐明潜在的机制，并预测无法通过实验充分验证的情景。最后，我们将在受控室内中生态系统和野外实验中验证我们的假设。该项目有助于了解和预测物种和群落对光强变化和光谱组成波动（如变化幅度、频率和随机性等）的响应。

A fluctuating environment constrains the ability of a population or community to adapt. Thereby highly predictable fluctuations will trigger different responses of organisms and communities than more stochastic ones. These responses are non-linear and therefore do not average across time, which hampers predicting future ecosystem functionality based on mean environments. A steadily increasing number of studies demonstrate the importance of thermal variability around the average, but less studies exist for other environmental variables besides temperature. Here, we ask the fundamental question how phytoplankton organisms cope with light variation often between stressful and advantageous conditions, especially if anthropogenic forcing shifts the variance beyond the level of fluctuations that would naturally occur in these habitats. Light fluctuations range from predictable seasonal and diurnal components to stochastic changes within seconds through cloud cover and scattering, comprising the intensity and spectral composition of light, as absorption and scattering are wavelength-specific. Thus, light needs to be addressed as a multi-dimensional and hypervariable resource, as moments of variability (amplitude, frequency and stochasticity) apply to multiple wavelengths. Highly variable light conditions in aquatic systems directly impact phytoplankton photosynthesis, respiration, growth rates, and biochemical composition. However, most of the empirical studies on light used regular fluctuations as drivers of community dynamics and the majority focused on a single dimension of the resource (mostly total irradiance). The innovative approach here is to study the interactive effect of light intensity and light spectrum, to understand the combined effects of multiple fluctuating resources on phytoplankton by manipulating the frequency, amplitude and stochasticity of fluctuations around different means. We start with analyzing how fluctuations in light intensity and spectrum occur in nature and conduct experiments with monoclonal cultures to understand species-specific responses. In the next step we test whether interspecific interactions alter the responses using controlled lab settings and manipulations for multispecies assemblages. Experiments will be associated with simulations to shed further light into underlying mechanisms and predict scenarios that cannot be sufficiently tested experimentally. Finally, we will test our hypotheses on in-situ phytoplankton communities in controlled indoor mesocosms and in field experiments. This project helps understanding and predicting species and community responses to changes in light intensity and spectral composition fluctuations (e.g. changed amplitude, frequency and stochasticity, resp.).