The accumulation of microbial residues and plant lignin phenols are more influenced by fertilization in young than mature subtropical forests

Abstract

Soil microbial residues and plant-derived compounds are important components of the stable carbon (C) pool in forest soil. It is not well understood how microbial residues and plant lignin phenols respond to nutrient inputs in subtropical forests of different ages, especially in mature forest stands. Here, a 5-year nitrogen (N) and phosphorus (P) fertilization (addition) management experiment was conducted in two stages of subtropical forests (<40- and > 80-year). We found that the concentrations of amino sugars (i.e., microbial residues) and plant lignin phenols and their contributions to soil organic carbon (SOC) were significantly higher in the > 80-year forests than in the < 40-year forests. In the < 40-year forests, N addition increased amino sugars and lignin phenols and their contributions to SOC, whereas P addition decreased muramic acid (bacterial-derived) and its contribution to SOC. In the > 80-year forests, however, N and P addition had no significant effect on amino sugars and lignin phenols and their contributions to SOC. Overall, soil total amino sugars and lignin phenols could be directly and indirectly affected by forest age and N addition, and could be only indirectly impacted by P addition. Our results suggest that microbial residues and plant lignin phenols are sensitive to the nutrient additions in the young forests, which have a greater potential for the soil stable C sequestration in comparison with the mature forests.