Maberly S C, Raven J A, Johnston A M
Department of Biological Sciences, University of Dundee, DD1 4HN, Dundee, UK.
Oecologia. 1992 Oct;91(4):481-492. doi: 10.1007/BF00650320.
The natural abundanceC/C ratios (as δC) of organic matter of marine macroalgae from Fife and Angus (East Scotland) were measured for comparison with the species' ability to use CO and HCO for photosynthesis, as deduced from previously published pH-drift measurements. There was a clear difference in δC values for species able or unable to use HCO . Six species of Chlorophyta, 12 species of Phaeophyta and 8 species of Rhodophyta that the pH-drift data suggested could use HCO had δC values in the range -8.81‰ to -22.55‰. A further 6 species of Rhodophyta which the pH-drift data suggested could only use CO had δC values in the range -29.90‰ to-34.51‰. One of these six species (Lomentaria articulata) is intertidal; the other five are subtidal and so have no access to atmospheric CO to complicate the analysis. For these species, calculations based on the measured δC of the algae, the δC of CO in seawater, and the knownC/C discrimination of CO diffusion and RUBISCO carboxylation suggest that only 15-21% of the limitation to photosynthesisin situ results from CO diffusion from the bulk medium to the plastids; the remaining 79-85% is associated with carboxylation reactions (and, via feedback effects, down-stream processes). This analysis has been extended for one of these five species,Delesseria sanguinea, by incorporating data onin situ specific growth rates, respiratory rates measured in the laboratory, and applying Fick's law of diffusion to calculate a boundary layer thickness of 17-24 μm. This value is reasonable for aDelesseria sanguinea frondin situ. For HCO -using marine macroalgae the range of δC values measured can be accommodated by a CO efflux from algal cells which range from 0.306 of the gross HCO influx forEnteromorpha intestinalis (δC=-8.81‰) in a rockpool to 0.787 forChondrus crispus (δC=-22.55‰). The relatively high computed CO efflux for those HCO -users with the more negative δC values implies a relatively high photon cost of C assimilation; the observed photon costs can be accommodated by assuming coupled, energy-independent inorganic carbon influx and efflux. The observed δC values are also interpreted in terms of water movement regimes and obtaining CO from the atmosphere. Published δC values for freshwater macrophytes were compared with the ability of the species to use CO and HCO and again there was an apparent separation in δC values for these two groups. δC values obtained for marine macroalgae for which no pH-drift data are available permit predictions, as yet untested, as to whether they use predominantly CO or HCO .
测量了来自法夫郡和安格斯郡（苏格兰东部）的海洋大型藻类有机物质的天然丰度碳/碳比（以δC表示），以便与根据先前发表的pH漂移测量结果推断出的这些物种利用CO₂和HCO₃⁻进行光合作用的能力进行比较。能够利用或不能利用HCO₃⁻的物种的δC值存在明显差异。pH漂移数据表明能够利用HCO₃⁻的6种绿藻、12种褐藻和8种红藻的δC值在-8.81‰至-22.55‰范围内。pH漂移数据表明只能利用CO₂的另外6种红藻的δC值在-29.90‰至-34.51‰范围内。这6个物种中的一个（节荚藻）是潮间带的；其他5个是潮下带的，因此无法接触大气中的CO₂而使分析复杂化。对于这些物种，根据测量的藻类δC、海水中CO₂的δC以及已知的CO₂扩散和核酮糖-1,5-二磷酸羧化酶羧化作用的碳/碳分馏进行计算表明，原位光合作用限制中只有15 - 21%是由于CO₂从大量介质扩散到质体；其余79 - 85%与羧化反应（以及通过反馈效应，下游过程）有关。对于这5个物种中的一个——血红藻，通过纳入原位比生长速率数据、实验室测量的呼吸速率，并应用菲克扩散定律计算出边界层厚度为17 - 24μm，对上述分析进行了扩展。这个值对于原位的血红藻叶片来说是合理的。对于利用HCO₃⁻的海洋大型藻类，测量到的δC值范围可以通过藻类细胞的CO₂外流来解释，其范围从岩池中肠浒苔（δC = -8.81‰）的总HCO₃⁻流入量的0.306到皱波角叉菜（δC = -22.55‰）的0.787。对于那些δC值更负的HCO₃⁻利用者，计算出的相对较高的CO₂外流意味着碳同化的光子成本相对较高；通过假设耦合的、与能量无关的无机碳流入和外流，可以解释观察到的光子成本。观察到的δC值也根据水运动模式以及从大气中获取CO₂来解释。将已发表的淡水大型植物的δC值与这些物种利用CO₂和HCO₃⁻的能力进行了比较，这两组的δC值再次出现明显分离。对于没有pH漂移数据的海洋大型藻类获得的δC值允许对它们是否主要利用CO₂或HCO₃⁻进行预测，目前尚未经过测试。
