Global forests cover 31% of the land area and are known as the lungs of the earth. Forests not only provide products for mankind, but also have various ecological functions such as climate regulation, natural disaster prevention, carbon fixation, oxygen release, and support for biodiversity. Nutrients are the lifeblood that restricts forest growth and development. The production and ecological functions of forests depend on the supply of nutrients. Therefore, studying the nutrient status and utilization efficiency of forests is very important for forest management. 

Researchers from the Systems Ecology Group, led by Prof. ZHANG Quanfa at Wuhan Botanical Garden, constructed an ecological parameter to measure the nutrient use efficiency of forest trees at the community level, i.e., Biomass: nitrogen (N): potassium (K): calcium (Ca): magnesium (Mg): phosphorus (P).   

Researchers find that the average Biomass: N: K: Ca: Mg: P of the global forests is about 3691: 12: 7: 13: 2: 1. This means that for every ton of forest biomass, 3.3 kg of N, 1.9 kg of P, 3.5 kg of Ca, 0.6 kg of Mg, and 0.3 kg of P are fixed. When forest products are harvest, a corresponding amount of nutrients will be taken away from the forest ecosystems. Thus, if the nutrients are not supplemented, the fertility of the forest ecosystem will become increasingly poor.   

Results reveal that tree species is an important factor affecting nutrient use efficiency. Coniferous species, such as Pinus, Spruce, and Larch, displays higher N use efficiency. The tree species of Robinia, Alnus, and Acacia, which has N-fixing nodules, shows a "luxury" utilization of N. In the soil conditions lacking in N and Ca, forest trees generally show higher use efficiency of N and Ca, respectively.    

This study can help us to understand the adaptation mechanism of forests to the environment, and also can provide certain guide for selecting tree species during afforestation.   

This research results are published in the international journal Global Ecology and Biogeography with the title "Biomass: N: K: Ca: Mg: P ratios in forest stands world-wide: Biogeographical variations and environmental controls" . Prof. ZHANG Kerong is the first author of the paper. The research was supported by the National Natural Science Foundation of China and the Chinese Academy of Sciences Youth Innovation Promotion Association.   

 Community-level nutrient use efficiency in forest stands (Image by WBG)