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How might rooted land plants have contributed to anoxic conditions in Devonian seas?

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Devonian paleogeography — Devonian Period Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the early Devonian Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.

During the Devonian Period, the colonization of landmasses by rooted plants is hypothesized to have contributed to the development of anoxic conditions in continental seas.12

The mechanism likely involved an increased influx of nutrients from the continents into marine environments. This nutrient loading could have stimulated the production of organic matter, leading to a process similar to eutrophication. As this excess organic matter decomposed, it would have consumed dissolved oxygen in the water column, potentially leading to the widespread hypoxic or anoxic conditions evidenced by the deposition of black shale during the period. These low-oxygen environments are thought to have created significant environmental stress, which may have contributed to the Devonian extinctions of various marine species.123