Fig. 8

The response of SPPs to biochar application, n means the number of observations: a estimated meta-averages without correction for publication bias; b estimated meta-averages corrected for publication bias (PET & PEESE model). An effect is significant (P < 0.05) if its 95% confidence interval (CI) does not include 1. The biochar treatment is considered to have no effect when the \(lnRR=1\), a positive effect when \(lnRR>1\), and a negative effect when \(lnRR <1\). Confidence intervals are not symmetrical around the effect sizes because they were back-transformed from the log response ratio