Herlory O, Richard P, Blanchard G F
1Centre de Recherche sur les Ecosystèmes Littoraux Anthropisés (CRELA), UMR 6217, Université de La Rochelle-CNRS-IFREMER, Avenue Michel Crépeau, La Rochelle, 17042 France.
2Netherlands Institute of Ecology (NIOO-KNAW), P.O. Box 140, Yerseke, 4400 AC The Netherlands.
Mar Biol. 2007;153(1):91-101. doi: 10.1007/s00227-007-0787-9. Epub 2007 Aug 25.
The light response curve methodology for microphytobenthic biofilms was studied by comparing the two most usual approaches used in pulse amplitude modulated (PAM) fluorometry. The non-sequential light curve (N-SLC) method is characterized by independent measures of the photosynthetic activity across a light gradient whereas the rapid light curve (RLC) method consists of successive measures on the same sample exposed to a stepwise increase of light intensities. Experiments were carried out on experimental microphytobenthic biofilms prepared from natural assemblages and acclimated to dark conditions. In preliminary experiments, N-SLCs were constructed from fluorescence induction curves performed at 12 different photon flux densities (PFDs). A minimum of 50 s of illumination was necessary to reach a stable light response curve; shorter illumination times resulted in underestimating the physiological parameters (α the light utilization coefficient in light-limited conditions and rETR the maximum rate of photosynthesis efficiency) of the light response curve. For the comparison between N-SLCs and RLCs, the same time of illumination (50 s) was used for each light step of RLCs so that N-SLCs differed from RLCs only by the way the amount of light was delivered, i.e., a light dose accumulation for RLC. The experimental results showed the difference between the two photobiological response curves. In the lower range of PFDs, RLCs exhibited a larger value of α; in this light-limited part of the response curve the incremental increase of PFDs limited the development of NPQ and resulted in a better optimization of electron transport rate for RLC. In the higher range of PFDs, the trend was reversed and the RLC showed a lower value of rETR than the N-SLC did; this is attributed to the light dose accumulation which likely led to a more efficient dispersion of energy, as illustrated by a higher non-photochemical quenching (NPQ). In conclusion, these results confirm that parameters derived from both methods differ in their value and do not bear the same physiological information.
通过比较脉冲幅度调制（PAM）荧光测定法中两种最常用的方法，研究了微型底栖生物膜的光响应曲线方法。非顺序光曲线（N-SLC）方法的特点是在光梯度上独立测量光合活性，而快速光曲线（RLC）方法则是对同一样品进行连续测量，样品暴露于光强逐步增加的环境中。实验是在由天然组合制备并适应黑暗条件的实验微型底栖生物膜上进行的。在初步实验中，N-SLC是根据在12种不同光子通量密度（PFD）下进行的荧光诱导曲线构建的。至少需要50秒的光照才能获得稳定的光响应曲线；光照时间较短会导致低估光响应曲线的生理参数（α，光限制条件下的光利用系数；rETR，最大光合效率）。为了比较N-SLC和RLC，RLC的每个光步骤都使用相同的光照时间（50秒），这样N-SLC与RLC的区别仅在于光的传递方式，即RLC的光剂量积累。实验结果显示了两种光生物学响应曲线之间的差异。在较低的PFD范围内，RLC的α值较大；在响应曲线的这个光限制部分，PFD的增量增加限制了非光化学猝灭（NPQ）的发展，导致RLC的电子传递速率得到更好的优化。在较高的PFD范围内，趋势相反，RLC的rETR值低于N-SLC；这归因于光剂量积累，这可能导致能量更有效地分散，如较高的非光化学猝灭（NPQ）所示。总之，这些结果证实，从两种方法得出的参数在数值上不同，并且不具有相同的生理信息。
