Diel versus time-integrated (daily) photosynthesis and irradiance relationships of coral reef organisms and communities
Diel versus time-integrated (daily) photosynthesis and irradiance relationships of coral reef organisms and communities
复制标题
珊瑚礁生物和群落的昼夜与时间积分（每日）光合作用和辐照度关系
作者：
Y. Sawall;E. Hochberg
热带浅水珊瑚礁最重要的能量来源是光，光的转化最终限制了珊瑚礁的生物量和生长。因此，测量底栖珊瑚礁生物和群落的生产力（初级生产力，P）对于了解珊瑚礁的功能至关重要。珊瑚礁光合作用的短期（几分钟到几小时）P测量几乎总是产生经典的双曲正切（或类似）的P-E（辐照度）关系，P迅速上升到饱和点，E增加。长期（几天到几周），自然礁群落的大规模调查通常不探索P-E关系，但少数确实显示时间积分P与高时间积分E不饱和。在本文中，我们提出了一个建模研究，以调和这一明显的矛盾。我们使用了52个已发表的短期（瞬时）P-E曲线的生物体（珊瑚，藻类）和社区（珊瑚，混合珊瑚和藻类）从不同的珊瑚礁在印度太平洋和加勒比地区，每一个加上928昼夜光变曲线，包括广泛的云覆盖的情况。昼夜光变曲线以1分钟的间隔提供瞬时E，由此我们使用不同的已发表的P-E关系计算相应的瞬时P。我们整合这两个变量来计算时间综合E和P.时间综合E变化高达18倍，由于云量和季节的变化。我们发现，尽管常规饱和的瞬时P，日尺度的P-E关系在所有情况下都接近线性，在瞬时光饱和的情况下，在白天很早就发生线性略有下降。这表明陆地生态学家提出的功能趋同假说（FCH）也适用于珊瑚礁光合作用。FCH指出，尽管短期光饱和，但植物平均吸收的光不会超过它们可以使用的光，因为资源分配是严格协调的，并且是针对最佳使用量身定制的。因此，不存在矛盾：在生长时间尺度（≥天），P应该是E的近线性函数。一个含义是，珊瑚礁P可以使用快速的光学测量，而不是传统的，费力的呼吸方法估计。未来的要求是得出光利用效率的适当值，即植物或群落将吸收的光转化为固定碳的速率。
The most important source of energy to tropical shallow water coral reefs is light, the transformation of which ultimately limits reef biomass and growth. Therefore, measurements of productivity (primary production, P) for benthic reef organisms and communities are critical to understand reef functioning. Short-term (minutes to hours) P measurements of reef photosynthesizers virtually always produce the classic hyperbolic tangent (or similar) P-E (irradiance) relationship, with P rapidly rising to a saturation point as E increases. Longer-term (days to weeks), larger-scale investigations of natural reef communities typically do not explore P-E relationships, but the few that do show no saturation of time-integrated P with high time-integrated E. In this paper we present a modeling study to reconcile this apparent contradiction. We used 52 published short-term (instantaneous) P-E curves of organisms (corals, algae) and communities (corals, mixed corals and algae) from different reefs in the Indo-Pacific and the Caribbean, each coupled with 928 diel light curves comprising a wide range of cloud cover scenarios. The diel light curves provided instantaneous E at 1-minute intervals, from which we calculated corresponding instantaneous P using the different published P-E relationships. We integrated both variables to calculate time-integrated E and P. Time-integrated E varied up to 18-fold due to changes in cloud cover and season. We found that, despite routine saturation of instantaneous P, day-scale P-E relationships were near linear in all cases, with slightly decreased linearity in cases where instantaneous light saturation occurred very early during the day. This indicates that the Functional Convergence Hypothesis (FCH) developed by terrestrial ecologists may also apply for reef photosynthesizers. The FCH states that despite short-term light saturation, plants on average do not absorb more light than they can use, since resource allocations are strictly coordinated and tailored towards an optimal use. Thus, there is no contradiction: At the growth time scale (≥ day), P should be expected to be a near linear function of E. One implication is that reef P can be estimated using rapid optical measurements, as opposed to traditional, laborious respirometry methods. The requirement going forward is to derive appropriate values for light-use efficiency, which is the rate at which the plant or community converts absorbed light into fixed carbon.