Fig. 2.

Radioisotope dilution and P exchangeability. The fraction of ³³P recovered in the soil solution in minutes after addition r(t)/R (a). Isotopically exchangeable P (E_(t)) for time spans up to 3 months was calculated as $E_{\left(t\right)}=P_{\mathrm{w}}\times \frac{R}{r_{\left(t\right)}}$, where P_w is the concentration of P in the soil solution (b). Error ranges in both plots represent one standard deviation of four values. Conceptual representation of how E_(t) is divided into time-dependent isotopically exchangeable P pools (c). Sites 1–6 have mean annual precipitations of 275, 316, 1340, 1578, 2163, and 3123 mm yr^–1, respectively