ALGAE AS COMPETITORS FOR GLUCOSE WITH HETEROTROPHIC BACTERIA 1
ALGAE AS COMPETITORS FOR GLUCOSE WITH HETEROTROPHIC BACTERIA 1
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藻类与异养细菌作为葡萄糖的竞争者 1
作者：
N. Kamjunke;B. Köhler;N. Wannicke;J. Tittel
溶解有机碳(DOC)是水环境中有机碳的主体。混合营养藻类利用DOC的重要性尚不清楚，因为异养细菌被认为是更有效的利用者。根据机制竞争理论，我们验证了藻类在光照下将DOC浓度降低到比黑暗中更低的水平，从而导致异养菌竞争排斥的假说。我们研究了(A)作为模型底物的两种藻类和混合细菌种群对葡萄糖的吸收动力学，(B)藻类和细菌在恒化器中对葡萄糖的竞争，(C)恒化器中不连续的葡萄糖供应的影响，以及(D)在藻类和细菌的培养中所获得的最低葡萄糖浓度。细菌比藻类表现出更高的比葡萄糖摄取率。在恒化器中，藻类在黑暗中灭绝，在光线下共存，在那里它们将细菌密度降低到较低水平。与连续添加底物相比，不连续的葡萄糖供应促进了藻类生长。一些藻类在黑暗中消耗葡萄糖的浓度低于在光照下的浓度，并且显示出低于或等于细菌的残余葡萄糖浓度。残留浓度与异速生长性状(细胞体积)和光合势(Chl含量)无关。总体而言，这一假设不被支持，对DOC的竞争机制明显不同于对颗粒猎物的竞争机制。然而，由于一些藻类的残余葡萄糖浓度低于或等于细菌，藻类对DOC的暗吸收在许多水域的深层可能是重要的。
Dissolved organic carbon (DOC) constitutes the bulk of organic carbon in aquatic environments. The importance of DOC utilization by mixotrophic algae is unclear since heterotrophic bacteria are regarded as more efficient users. We tested the hypothesis that algae decrease the DOC concentration in the light to lower levels than in darkness resulting in competitive exclusion of heterotrophic bacteria according to the mechanistic competition theory. We investigated (a) the uptake kinetics of glucose as a model substrate by two cultured algae and mixed bacteria populations, (b) the competition for glucose between algae and bacteria in chemostats, (c) the effect of discontinuous glucose supply in chemostats, and (d) the minimum glucose concentrations achieved in cultures of algae and bacteria. Bacteria showed higher specific‐glucose‐uptake rates than algae. In chemostats, algae became extinct in the dark and coexisted in the light where they decreased bacteria to lower densities. Discontinuous glucose supply promoted the algae compared to continuous substrate addition. Several algae consumed glucose to lower concentrations in the dark than in the light and showed lower or equal residual glucose concentrations than bacteria. Residual concentrations were not related to allometric traits (cell volume) and photosynthetic potential (chl content). Overall, the hypothesis was not supported, and mechanisms of competition for DOC obviously differed from those for particulate prey. However, since some algae showed lower or equal residual glucose concentrations than bacteria, algal dark uptake of DOC may be important in deep layers of many waters.