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Phosphorus
Phosphorus is another element that is used by plants both on land and in the
ocean, and so phosphorus availability in soils and in the ocean is a regulator of
biological activity. There are many
unanswered questions
relating to the phosphorus cycle. The mechanisms controlling the availability of
phosphorus in terrestrial soils and how these mechanisms respond to processes such
as acid deposition, fire, and deforestation are not well known. By these land-use
practices, we might be creating imbalances in the availability of other nutrients
that plants need. What is the flux of marine phosphorus to the oceans? How has it
changed in the past and how is it changing today? What are the consequences of these
changes? Many issues remain unanswered.
It should be apparent from these questions and from our consideration of other chemical cycles that it is not possible to consider any of these individual elements such as carbon, nitrogen, sulfur, or phosphorus alone. Plants are mainly carbon (and of course water), but they need nitrogen, sulfur, and phosphorus to flourish. So a complete understanding of the carbon cycle requires an understanding of the larger system known by the term of biogeochemical cycles. Other trace gases of lesser global importance also are lumped into this general category because they may participate in the one or more of the many pathways followed by the major chemicals in their natural cycles.