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Abstract

We explore the question of how long elements cycle in terrestrial ecosystems and show that to address this question, a broader conceptual framework is needed that specifies ages and transit times. We calculated age and transit time distributions of five elements in a forest and two grassland ecosystems. Moreover, we assessed how ages and transit times of elements change in various scenarios. Mean age and mean transit time of all elements were smaller in the two grassland ecosystems than in the forest ecosystem due to the smaller element stocks in the grasslands in relation to the inputs. Phosphorus (P) had the largest mean transit time and mean age of all elements in the forest ecosystem (450 and 469 years) as well as in the high elevation grassland (82 and 80 years). Mean ages and mean transit times changed linearly with the stock in one pool. Changes in the internal cycling of elements in the ecosystem that did not imply the introduction of another pool had no effect on age and transit time. However, the introduction of a stable P pool in the mineral soil led to a divergence of mean transit time and mean age of P. Taken together, based on the probabilistic approach proposed here, we were able to precisely calculate not only the mean times elements need to transit different ecosystems and the ages they reach while cycling the ecosystems, but also the probability distribution of ages and transit times.