Patterns of nitrogen and phosphorus pools in terrestrial ecosystems in China

<p>Recent increases in atmospheric carbon dioxide (CO₂) and temperature relieve the limitation of these two on terrestrial ecosystem productivity, while nutrient availability constrains the increasing plant photosynthesis more intensively. Nitrogen (N) and phosphorus (P) are critical for plant physiological activities and consequently regulates ecosystem productivity. Here, for the first time, we mapped N and P densities of leaves, woody stems, roots, litter and soil in forest, shrubland and grassland ecosystems across China, based on an intensive investigation in 4175 sites, covering species composition, biomass, and nutrient concentrations of different tissues of living plants, litter and soil. Forest, shrubland and grassland ecosystems in China stored 7665.62 × 10⁶ Mg N, with 7434.53 × 10⁶ Mg (96.99%) fixed in soil (to a depth of one metre), and 32.39 × 10⁶ Mg (0.42%), 59.57 × 10⁶ Mg (0.78%), 124.21 × 10⁶ Mg (1.62%) and 14.92 × 10⁶ Mg (0.19%) in leaves, stems, roots and litter, respectively. The forest, shrubland and grassland ecosystems in China stored 3852.66 × 10⁶ Mg P, with 3821.64 × 10⁶ Mg (99.19%) fixed in soil (to a depth of one metre), and 3.36 × 10⁶ Mg (0.09%), 14.06 × 10⁶ Mg (0.36%), 11.47 × 10⁶ Mg (0.30%) and 2.14 × 10⁶ Mg (0.06%) in leaves, stems, roots and litter, respectively. Our estimation showed that N pools were low in northern China except Changbai Mountains, Mount Tianshan and Mount Alta, while relatively higher values existed in eastern Qinghai-Tibetan Plateau and Yunnan. Southern China held quite small P pools, which may limit some plant-related process. P densities in plant organs were higher in the North and East China, while soil P density was higher in the South and West China. These patterns of N and P densities could potentially improve existing earth system models and large-scale researches on ecosystem nutrients.</p>