Bright Dylan I, Walsby Anthony E
1 School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK.
New Phytol. 2000 May;146(2):301-316. doi: 10.1046/j.1469-8137.2000.00640.x.
In Lake Zürich, populations of the cyanobacterium Planktothrix rubescens develop in the metalimnion during the summer and become gradually entrained in the deepening surface mixed layer during the autumn. It had previously been demonstrated that the daily integrals of photosynthetic production accounted for the growth observed in the metalimnion and greatly exceeded the smaller increase during the autumn. We have now determined the relationship between growth rate (μ) and irradiance (I) in cultures of P. rubescens strain Pla 9316 maintained at 20 °C on a 12∶12 h light∶dark cycle: the highest net growth rate averaged over the 24 h (μ ) was 0.123 d , the dark rate (μ ) was -0.020 d , the gross rate (φ = μ -μ ) was 0.144 d , the affinity coefficient (α) was 0.0273 (d μmol m s ) and the compensation point (I ) was 1.76 μmol m s . Using the corresponding coefficients calculated for the light period (μ = 0.267 d , φ = 0.287 d and α = 0.0547 (d μmol m s ) ), instantaneous growth rates could be calculated from the irradiance. Comparison with growth rates at 10 °C indicated a Q of 1.48. These coefficients were used in a modification of the Smith equation to calculate potential growth rates of Planktothrix from the irradiance and temperature at each time and depth in Lake Zürich. Data on irradiance, vertical light attenuation and temperature were used to calculate the daily integrals of biomass increase over a period of 136 d. These growth integrals gave a closer correspondence to the observed population increase than the photosynthetic integrals calculated previously from measurements made with lakewater samples dominated by Planktothrix. Photosynthetic measurements made with the Planktothrix culture indicated a maximum rate of carbon increase (0.467 d that exceeds the maximum growth rate, which suggests that other factors limit growth over long periods.
在苏黎世湖，蓝藻微红颤藻种群在夏季于温跃层中生长，并在秋季逐渐被卷入不断加深的表层混合层。此前已证明，光合生产的日积分解释了温跃层中观察到的生长情况，且大大超过了秋季较小的增长幅度。我们现已确定了在20°C、12∶12小时光暗循环条件下培养的微红颤藻菌株Pla 9316的生长速率（μ）与辐照度（I）之间的关系：24小时内的最高净生长速率（μ）平均为0.123 d⁻¹，暗呼吸速率（μ₀）为 -0.020 d⁻¹，总生长速率（φ = μ - μ₀）为0.144 d⁻¹，亲和系数（α）为0.0273（d μmol⁻¹ m² s⁻¹），补偿点（I₀）为1.76 μmol m⁻² s⁻¹。使用根据光照期计算的相应系数（μ = 0.267 d⁻¹，φ = 0.287 d⁻¹，α = 0.0547（d μmol⁻¹ m² s⁻¹）），可根据辐照度计算瞬时生长速率。与10°C时的生长速率比较表明，温度系数Q为1.48。这些系数被用于对史密斯方程进行修正，以根据苏黎世湖每个时间和深度的辐照度和温度计算微红颤藻的潜在生长速率。利用辐照度、垂直光衰减和温度数据计算了136天内生物量增加的日积分。这些生长积分与观察到的种群增长的对应程度比之前根据以微红颤藻为主的湖水样本测量计算出的光合积分更高。用微红颤藻培养物进行的光合测量表明，最大碳增加速率（0.467 d⁻¹）超过了最大生长速率，这表明其他因素在长期内限制了生长。
