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Effects of nutrients and irradiance on PSⅡ variable fluorescence of lake phytoplankton assemblages

机译：养分和辐照度对湖泊浮游植物组合PSⅡ可变荧光的影响

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摘要

Phytoplankton from Lake Ontario and six small Canadian lakes (Dorset Lakes) were supplemented with nitrogen (N) and phosphorus (P) to determine how nutrients affect Photosystem Ⅱ (PSⅡ) variable fluorescence and photoinhibition in natural freshwater communities. Susceptibility of PSII to photoinhibition by photosynthetically active radiation (PAR) and ultraviolet radiation (UVR), as well as recovery potential, was quantified using changes in variable fluorescence and compared between N- and P-supplemented (Nu+) and non-supplemented (Nu-) Lake Ontario phytoplankton. Nu+ communities exhibited slightly higher variable fluorescence than Nu- when dark-adapted (F_v:F_m) or under constant illumination (F_q':F_m'). Rates of relative electron transport (rETR) were greater for Nu+ than Nu- phytoplankton, with higher non-photochemical quenching (NPQ) by Nu- samples. The initial slope of the rETR-irradiance curve (α) did not differ significantly between nutrient treatments, but the saturation irradiance (E_K) was significantly higher for Nu+ samples than for Nu-samples. Nutrient supplementation increased rates of PAR-and UVR-dependent damage but also recovery, so that net PSII photoinhibition was equally severe as in the absence of added N and P. Additions of N, P, and N + P did not significantly alter F_v:F_m of Dorset Lakes phytoplankton. Compared to the range of variable fluorescence observable over the diet cycle of photoinhibition and recovery in Lake Ontario, the effects of supplemental nutrients observed in this study were minor.
机译：在安大略湖和六个加拿大小型湖泊（多塞特湖）的浮游植物中补充了氮（N）和磷（P），以确定养分如何影响天然淡水群落中光系统Ⅱ（PSⅡ）的可变荧光和光抑制作用。使用可变荧光的变化来量化PSII对光合作用活性辐射（PAR）和紫外线（UVR）的光抑制的敏感性以及恢复潜力，并比较N和P补充（Nu +）和非补充（Nu -）安大略湖的浮游植物。当适应黑暗（F_v：F_m）或在恒定照明（F_q'：F_m'）时，Nu +群落显示出比Nu-略高的可变荧光。 Nu +的相对电子迁移率（rETR）大于浮游植物，Nu-样品的非光化学猝灭（NPQ）更高。在营养处理之间，rETR辐照度曲线的初始斜率（α）没有显着差异，但是Nu +样品的饱和辐照度（E_K）显着高于Nu样品。营养补充剂增加了PAR和UVR依赖性损伤的发生率，但也恢复了营养，因此净PSII光抑制作用与没有添加N和P一样严重。添加N，P和N + P不会显着改变F_v：多塞特湖浮游植物的F_m。与在安大略湖的光抑制和恢复饮食周期中观察到的可变荧光范围相比，在这项研究中观察到的补充营养的影响较小。

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