Abstract: Understanding the plant-microorganism-soil ecological stoichiometric characteristics of young Cyclobalanopsis gilva forests on site challenging for afforestation can provide a scientific basis for the optimal growth of young C. gilva forests in such conditions. We collected samples of roots, branches, leaves, as well as soils at depths of 0-10, 10-20, 20-40 and 40-60 cm from a 7-year-old C. gilva plantation established on both difficult and control sites in Tanxia forest area of Shouchang Forest Farm, Jiande City, Zhejiang Province. The ecological stoichiometric characteristics of carbon (C), nitrogen (N), and phosphorus (P) in different organs of C. gilva, soil and soil microbial biomass were compared between the difficult site and control site. The results showed that the vertical distribution patterns of soil C, N, P contents and their stoichiometric ratios on the difficult site and the control site were similar, all decreasing with the increasing soil depth. However, all those variables for different soil layers on the difficult site were lower than those on the control site, particularly the C, N, P contents in different soil layers of difficult site, as well as the C∶N and C∶P in 0-10 and 10-20 cm soil layers, showing significant reductions. Leaf C content, root and leaf N content, leaf P content, root and branch C∶P and N∶P were significantly lower on the difficult site. Conversely, root and branch P content and root C∶N were significantly higher on the difficult site. Leaf N∶P on the difficult site was 18.56, suggesting that plant growth was co-limited by both N and P, whereas it was 21.31 at the control site, indicating that plant growth was mainly limited by P. Soil microbial biomass C, N, and P on the difficult site diminished progressively with increasing soil depth, and such decrease was less pronounced compared to that on the control site across all soil depths. Soil microbial biomass C, N, and P in all layers of the difficult site was consistently lower than that on the control site. The relationships of C, N, and P contents and stoichiometric ratios among plant, microorganism, and soil components in the young C. gilva forest on the difficult site were weaker compared to those on the control site. Collectively, soil nutrient levels and microbial biomass C, N, and P on the difficult site were relatively low. Plant growth was co-limited by both N and P, and the coupling relationship among plants, microorganisms, and soil nutrients was weak. Future research could further explore the targeted nutrient management and microbial regulation measures to promote growth of C. gilva.

Key words: Cyclobalanopsis gilva, ecological stoichiometry, soil, soil microbial biomass, difficult site