Long-term nitrogen addition regulates root nutrient capture and leaf nutrient resorption in Larix gmelinii in a boreal forest

Human activities accelerate global nitrogen (N) deposition, and elevated N availability may alter the stoichiometric balance of nutrients and then affect nutrient absorption by plants. The boreal forest is considered one of the world's most N-limited ecosystems, and its response to N deposition is already a hot issue. In order to explore how long-term nitrogen addition influences nutrient uptake and distribution in Larix gmelinii in a boreal forest, four N treatment levels (0, 25, 50 and 75 kg N ha(-1) yr(-1)) have been applied in a boreal forest since May 2011. Nitrogen addition significantly reduced the soil pH, significantly changed the soil N availability, increased the total N and N/P in needles and fine roots, and decreased the total P in needles and the C/N in soil. Nitrogen addition significantly reduced nitrogen resorption efficiency, and its impacts on P resorption efficiency were not significant. Nitrogen addition significantly increased the root length, surface area and diameter of 4th- and 5th-order transport fine roots. The N and N/P of needles showed seasonal variation. The needle N concentration and N/P were positively correlated with N addition, while the needle P was negatively correlated with nitrogen addition. With increase in nitrogen addition, Larix gmelinii increased its investment in its belowground parts, which may explain why Larix gmelinii tended to put more C in long-lived roots to improve its C utilization efficiency. Given the P deficiency caused by N addition, Larix gmelinii may be more likely to absorb P from the soil and adjust its C distribution to meet its P demand rather than relying on internal nutrient resorption.

Automated summary

The study found that long-term nitrogen addition had significant effects on nutrient uptake and distribution in Larix gmelinii in a boreal forest, including reducing soil pH, changing soil nitrogen availability, increasing nitrogen content in plant tissues, etc. Furthermore, nitrogen addition led to an increased investment in belowground parts and adjustment in carbon distribution to meet phosphorus demand in Larix gmelinii.