Mojica Kristina D A, Behrenfeld Michael J, Clay Megan, Brussaard Corina P D
Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR, United States.
Department of Marine Microbiology and Biogeochemistry, Royal Netherlands Institute for Sea Research, Den Burg, Netherlands.
Front Microbiol. 2021 Aug 24;12:706137. doi: 10.3389/fmicb.2021.706137. eCollection 2021.
For nearly a century, phytoplankton spring blooms have largely been explained in the context of abiotic factors regulating cellular division rates (e.g., mixed-layer light levels). However, the accumulation of new phytoplankton biomass represents a mismatch between phytoplankton division and mortality rates. The balance between division and loss, therefore, has important implications for marine food webs and biogeochemical cycles. A large fraction of phytoplankton mortality is due to the combination of microzooplankton grazing and viral lysis, however, broad scale simultaneous measurements of these mortality processes are scarce. We applied the modified dilution assay along a West-to-East diagonal transect in the North Atlantic during spring. Our results demonstrate positive accumulation rates with losses dominated by microzooplankton grazing. Considering the dynamic light environment phytoplankton experience in the mixed surface layer, particularly in the spring, we tested the potential for incubation light conditions to affect observed rates. Incubations acted as short-term 'light' perturbations experiments, in which deeply mixed communities are exposed to elevated light levels. These "light perturbations" increased phytoplankton division rates and resulted in proportional changes in phytoplankton biomass while having no significant effect on mortality rates. These results provide experimental evidence for the Disturbance-Recovery Hypothesis, supporting the tenet that biomass accumulation rates co-vary with the specific rate of change in division.
近一个世纪以来，浮游植物春季水华现象主要是在非生物因素调节细胞分裂速率（如混合层光照水平）的背景下得到解释。然而，新的浮游植物生物量的积累意味着浮游植物的分裂与死亡率之间存在不匹配。因此，分裂与损失之间的平衡对海洋食物网和生物地球化学循环具有重要意义。浮游植物死亡的很大一部分原因是微型浮游动物的捕食和病毒裂解的共同作用，然而，对这些死亡过程进行大规模同步测量的情况却很少见。我们在春季沿北大西洋从西到东的对角线断面应用了改良的稀释试验。我们的结果表明存在正积累率，损失主要由微型浮游动物的捕食造成。考虑到浮游植物在混合表层尤其是春季所经历的动态光照环境，我们测试了培养光照条件影响观测速率的可能性。培养过程相当于短期的“光照”扰动实验，即深层混合群落暴露于升高的光照水平下。这些“光照扰动”提高了浮游植物的分裂速率，并导致浮游植物生物量成比例变化，而对死亡率没有显著影响。这些结果为干扰 - 恢复假说提供了实验证据，支持了生物量积累率与分裂的特定变化率共同变化这一原则。
