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Changes in soil phosphorus and its influencing factors following afforestation in Northern China

Changes in soil carbon (C) and nitrogen (N) stocks following afforestation have been widely studied at different scales. However, soil phosphorus (P) dynamics following afforestation are poorly understood, especially at the regional scale. This paper studied the effects of prior land use (cropland, grassland, and barren land), tree species (conifer, broadleaf, shrub, and mixed), plantation age (young, middle, and old), and climate on soil total phosphorus and available phosphorus stocks change in the top 20 cm following afforestation based on a synthesis of 50 recent publications in northern China. We also considered possible confounding effects between these factors. The results showed that, overall, soil total phosphorus and available phosphorus stocks significantly decreased by 7.3% and significantly increased by 8.8%, respectively, following afforestation. Prior land use was found to be the most important driver in determining changes in soil P stocks. Compared with a significant decrease in P of afforestation of former cropland and grassland, afforestation of barren land caused no clear decrease in P. Tree species was found to have a limited effect on changes in soil P after afforestation, and broadleaf afforestation has a lower P demand than coniferous forests in the studied region. Plantation age did not affect the dynamics of P stocks. Our results showed confounding effects of precipitation, prior land use, and tree species, which impacted the estimates of the drivers of changes in P stocks. These results highlighted the importance of tree species selection and replication across sites that receive different amounts of precipitation.