concept

Limiting nutrient

The element scarcest relative to what organisms need, and therefore the one that sets how much an ecosystem can produce, no matter how abundant everything else is. This is Liebig's law of the minimum: growth follows the shortest supply, not the total. On short timescales nitrogen is usually the proximate limiter; across millennia phosphorus is the ultimate one, because a nitrogen shortfall always opens a niche for nitrogen-fixing organisms to fill while a phosphorus shortfall has no equivalent escape — no organism can draw phosphorus from the air.