Climate, soil nutrients, and stand characteristics jointly determine large-scale patterns of biomass growth rates and allocation in Pinus massoniana plantations

Stand biomass growth rate and allocation are essential for understanding carbon sequestration rates and carbon cycling in forest ecosystems. However, large-scale patterns of biomass growth rates (BGR) and biomass allocation in mono-species plantations and their responses to stand characteristics (e.g., stand density and stand age) and environmental factors (e.g., climate and soil nutrients) remain unclear. Based on biomass data obtained from published studies and our field survey, the growth rates of shoot, root, and whole-tree biomass and the root - shoot ratio (FR/S) of Pinus massoniana across its distribution range in China were analyzed. Our results showed that BGR decreased with longitude and latitude, while FR/S increased with longitude but decreased with latitude and altitude. Stand density, the mean annual temperature (MAT), and the soil carbon to phosphorus (C/P) ratio positively related to BGR and explained 54.0 ∼ 62.8%, 12.5 ∼ 21.7%, and 13.3 ∼ 21.3% of the variation in BGR, respectively. FR/S was negatively related to stand density and the soil carbon to nitrogen (C/N) ratio but positively related to mean annual precipitation (MAP). Stand density made a greater contribution (63.0%) to the variation in FR/S than MAP (19.2%) and soil C/N (12.4%). These results suggest that stand density had the strongest effect on biomass growth rates and belowground/aboveground biomass allocation of P. massoniana plantations in this subtropical region, but the effects of climatic factors and soil nutrients were also important. Our findings will aid plantation management, including measures that could be taken to achieve a carbon balance under future global change, as well as enhance the carbon sink capacity of forests.