The advent of flowering plants on land has been suggested previously as a potential trigger for Cretaceous innovations in the marine realm by providing a greater energetic base for marine ecosystems through a more nutrient-rich terrestrial runoff. The scope of the angiosperm radiation certainly was unprecedented—flowering plants came to represent the large majority of species in all terrestrial floras in a geologically short span of time—and angiosperms possess much higher photosynthetic and hydraulic capacities than all other plants. Angiosperm evolution could have affected both the organic and inorganic content of terrestrial runoff, but the magnitude of these changes is in question. Angiosperms are more productive than other plants, suggesting an increase in organic matter runoff, but that quantity is small in comparison to native marine photosynthesis even in the modern angiosperm-dominated world. Changing the inorganic nutrient content of terrestrial runoff requires changing weathering rates, but angiosperms and earlier appearing vascular plants appear to be little different in this respect. Thus, the potential for angiosperms to have strongly influenced marine evolution may have been small. The greatest opportunity for angiosperms to have changed weathering rates may come from their impact on terrestrial climate. Their greatly elevated transpiration capacities feed rainfall and this enhancement of the hydrological cycle means that angiosperms may have increased weathering rates in aggregate even if they have little effect individually. The timing of the angiosperm radiation is both crucial and problematic, since their rise to ecological dominance is thought to lag significantly behind their increase in species diversity, thereby diminishing the correspondence with events in the marine realm.
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Vol. 15 • No. 2