Multi-wavelength Chl a fluorometers are increasingly applied to assess phytoplankton photosynthetic capacity and composition, but their usefulness is limited by uncertainties in fluorescence excitation spectra (FES). We investigated this issue using the Phyto-PAM fluorometer to evaluate the effects of innate and irradiance-dependent variations in background (F) and variable (F_v) FES on analysis of three pigment groups (cyanobacteria, chlorophytes and chromophytes). The effects on group-specific estimates of minimum fluorescence (F₀), a proxy for biomass, and F_v/F_m, the quantum yield of photochemistry, presented some challenges to the interpretation of group-specific results. F₀ estimates usually had a 5–15% margin of error, even when measuring highly uneven mixtures, and applying imperfectly matched calibration FES or stressing samples with photosynthetically active and ultraviolet radiation; errors in F_v/F_m were commonly < 15%. Despite such relatively good accuracy, estimates for F₀ and, especially, F_v/F_m are unreliable for groups at low relative abundance, and results can sometimes be reported for groups not actually present. We report margins of error for different levels of relative abundance to inform interpretation of measurements from natural communities and show that F and F_v spectra for some taxa can differ in ways that produce severe errors in F₀ and F_v/F_m estimates if used uncritically.

多波长叶绿素一荧光计被越来越多地应用于评估浮游植物光合能力和组合物，但是它们的用途是通过在荧光激发光谱（FES）的不确定性的限制。我们使用植物性PAM荧光评估先天免疫和辐射上的变化的背景（的影响研究过此问题˚F）和可变（˚F _v）FES三个色素团（蓝藻，绿藻和chromophytes）的分析。对组特异性估计的最小荧光（F ₀），生物量的代用品和F _v / F _m的影响，光化学的量子产率，对解释特定于组的结果提出了一些挑战。即使在测量高度不均匀的混合物，并应用不完全匹配的校准FES或用光合作用和紫外线照射样品时，F ₀估计值通常具有5-15％的误差范围；F _v / F _m的误差通常<15％。尽管精度相对较高，但仍可估算F ₀，尤其是F _v / F _m相对丰度低的组不可靠，有时可以报告不存在的组的结果。我们报告了不同相对丰度水平的误差幅度，以解释自然群落的测量结果，并表明，某些分类群的F和F _v谱可能会以严重差异产生F ₀和F _v / F _m估计值（如果使用）的方式不同不加批判地