Seedling growth and survival responses to multiple soil properties in subtropical forests of south China

Soil properties and light availability have been long recognized as fundamental drivers of species distribution and are especially important during the regeneration phase. The role of nutrients such as exchangeable base cations is poorly understood, despite forests facing considerable changes in soil composition due to climatic change and atmospheric acid deposition, including in south China. With the aim of understanding the response of naturally regenerating seedling communities to a wide range of abiotic conditions, we quantified seedling growth and survival of over 2000 seedlings representing 166 morpho-species within four subtropical forests in south China, for two years. We assessed their responses to canopy openness, and a natural gradient of soil characteristics: moisture, pH, total nitrogen (N), total carbon (C), C:N ratio, available phosphorus (P), available potassium (K), calcium (Ca), iron (Fe), magnesium (Mg), manganese (Mn), and sulfur (S). We conducted our analyses at three levels: landscape (1), forest site (4), and species (7). We found statistically clear effects of several soil properties on seedling growth and survival, at all levels of analysis, while canopy openness showed a minimal negative effect on survival and none on growth. Seedling growth was positively affected by increasing soil Ca and Mn and negatively by increasing soil Mg at the landscape level (all four forest sites combined). Seedling survival responded positively to soil Fe and C:N ratio, but negatively to soil Ca, Mg, Mn, N, and S. The observed patterns were forest site- and species-specific. These results are especially relevant in a region experiencing severe changes in soil conditions as well as intense deforestation and land use change. Reforestation programs should consider the site specificity of soil properties with respect to a wide range of soil nutrients when planning restoration activities.