In contrast, chlorophyll fluorescence is a direct measure of photosynthetic activity.

相比之下，叶绿素荧光能直接地测量光合作用活动。

Although invisible to the naked eye, phytoplankton are so abundant that they are responsible for half of all the carbon absorbing photosynthetic activity on earth.

尽管我们肉眼看不见，但是浮游植物的数量太过庞大，它们承担了地球上一半的光合作用。