ABSTRACT: Photosynthesis by benthic marine macroalgae makes an important contribution to the productivity of coastal seas. Quantification of photosynthesis and productivity of macroalgal assemblages is therefore important in understanding ecosystem functioning in coastal seas and providing realistic values for coastal productivity in global models. Estimates of macroalgal productivity are often based on the photosynthetic characteristics of thallus pieces or whole thalli, and not on those of communities. Such methods may overestimate rates of productivity as they do not account for neighborhood shading effects that may reduce photosynthetic rates in macroalgal stands that typically have high densities. In order to determine whether productivity estimates based on individuals differ from those based on communities, a controlled laboratory experiment was conducted with 3 dominant sub-canopy macroalgal species (Cystophora scalaris, Xiphophora gladiata and Undaria pinnatifida) from southern New Zealand. Photosynthetic parameters (initial slope of the photosynthesis vs. irradiance [P–E] curve α, saturation irradiance Ek, maximum rate of photosynthesis Pmax and dark-respiration Rd) were obtained via P–E experiments using a custom-built respirometry chamber for a range of densities that corresponded to the minimum, average and maximum densities of these species in the field. A 5 to 7-fold decrease in Pmax was observed when the density of the algal stand was above 1 ind. m–2. Rd and α were also lower in communities than for individuals. Results illustrate that estimates based on single specimens substantially overestimate productivity and we recommend that the densities used in experiments reflect those observed in the field.
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机译：摘要：底栖海洋大型藻类进行光合作用对沿海海域的生产力做出了重要贡献。因此，定量光合作用和大型藻类组合的生产力对于理解沿海海洋中的生态系统功能以及在全球模型中为沿海生产力提供现实价值非常重要。对大型藻类生产力的估计通常基于th体或整个th体的光合特性，而不是社区的。此类方法可能会高估生产率，因为它们没有考虑到邻域阴影效应，而后者可能会降低通常具有高密度的大型藻类林分的光合速率。为了确定基于个体的生产率估算值与基于社区的生产率估算值是否存在差异，我们对3个优势亚冠层大型藻类物种（ Cysphorphora scalaris ， Xiphophora gladiata >和 Undaria pinnatifida ）。光合参数（光合作用的初始斜率与辐照度 [P–E] 曲线α，饱和辐照度 E k ，最大光合作用速率< i> P max 和暗呼吸 R d ）是通过 P–E 实验获得的使用定制的呼吸测量室，其密度范围对应于野外这些物种的最小，平均和最大密度。当藻类支架的密度高于1 ind时，观察到的 P max 降低了5到7倍。 m –2 。 R d 和α在社区中也低于个体。结果表明，基于单个样本的估计值大大高估了生产率，我们建议实验中使用的密度应反映在现场观察到的密度。
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