Fig. 2: Changes in soil P density and stock from the 1980s to the 2020s based on resampling observations.

a Frequency distributions of the soil P density during the two sampling periods. The soil P density is fitted with a ln-normal distribution and the horizontal axis is displayed on a ln scale. The frequencies of samples are shown as bars, with the curves for the probability density functions shown as orange (1980s) and blue (2020s) lines. b Relationships between soil P density in the 1980s and the 2020s. The soil P density is fitted with a in-normal distribution. The dashed line indicates the ordinary least-squares fit of the linear equation for soil P density between the two sampling periods. The shading accompanying the dashed fitted line represents the 95% confidence interval. c Changes in the soil P density during the two sampling periods. The temporal changes of the soil P density were examined with linear mixed-effects models in which the fixed effect was the sampling period and the random effect was the sampling plot. Asterisks indicate that the null hypothesis could be rejected at a significance level of **0.01 and ***0.001. The standard errors are indicated in part c. The error bars represent 95% confidence intervals. d Changes in the soil P stock derived from the large-scale resampling investigations. The change in soil P stock was calculated based on the P density and the proportion of each soil type in a given ecosystem.