Key Laboratory of Aquatic Botany and Watershed Ecology, Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan, 43007, China.
Key Laboratory of Aquatic Botany and Watershed Ecology, Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan, 43007, China.
J Environ Manage. 2022 Jan 1;301:113940. doi: 10.1016/j.jenvman.2021.113940. Epub 2021 Oct 14.
Forest conversion can drastically impact carbon (C) and nutrient processes and microbial stoichiometry, which will modify soil organic C (SOC) stock. However, SOC stock dynamics and its underlying mechanisms induced by long-term forest conversion remain unclear. Three well-protected plantations converted from natural forests for 36 years were compared, i.e., Cryptomeria fortunei (CF), Metasequoia glyptostroboides (MG) and Cunninghamia lanceolata (CL), with a natural forest (NF) as a control. SOC stock size and stability across three soil depths (0-10, 10-30 and 30-60 cm) were examined with aggregate-based method. Forest floors and fine roots were treated as C and nutrient inputs while soil respiration (Rs) was treated as C output. Soil microbial biomass C, nitrogen and phosphorus were measured to calculate microbial stoichiometry, as well as microenvironment and soil physicochemical properties. The relationships between SOC stock (size and stability) and these factors were explored using structural equation model. The results showed that microbial stoichiometry had strong or strict homeostasis at each soil depth. At 0-10 cm soil deep, SOC stock size varied with tree species (following the rank of CL > NF ≈ CF > MG) but its stability increased in all forest conversion types, regulated by forest floor quantity and quality associated with Rs; at 10-30 cm soil deep, the SOC stock sizes decreased in CF and MG, but SOC stock stability increased in MG, jointly driven by fine root quality and microenvironment; at 30-60 cm soil deep, SOC stock size decreased but its stability increased in MG, whereas both its size and stability had few changes in CF or CL, modified by soil physicochemical property associated with microbial stoichiometry and Rs. Overall, the effects of microbial stoichiometry and microenvironment on SOC stock were not pronounced. Thus, SOC stock size changed with soil depth and tree species but its stability tended to be steady at all depths varying with tree species. These results suggest that SOC stock size and stability are mainly determined by self-regulation process of forest ecosystems over more than three-decade after forest conversion, which will help us more accurately assess C sequestration strategies regarding long-term forest conversion.
森林转换会极大地影响碳（C）和养分过程以及微生物化学计量，从而改变土壤有机碳（SOC）储量。然而，长期森林转换引起的 SOC 储量动态及其潜在机制仍不清楚。本研究比较了 36 年生由天然林转换而来的 3 种人工林（柳杉、水杉和杉木）和 1 片天然林（NF），采用基于团聚体的方法研究了 3 个土壤深度（0-10、10-30 和 30-60 cm）的 SOC 储量大小和稳定性。将凋落物和细根视为 C 和养分输入，而土壤呼吸（Rs）视为 C 输出。测定土壤微生物生物量 C、N 和 P，以计算微生物化学计量，并研究微环境和土壤理化性质。采用结构方程模型探讨了 SOC 储量（大小和稳定性）与这些因子之间的关系。结果表明，在每个土壤深度，微生物化学计量均具有较强或严格的内稳态。在 0-10 cm 土壤深处，SOC 储量大小随树种而变化（遵循杉木＞天然林≈柳杉＞水杉的顺序），但在所有森林转换类型中，SOC 储量稳定性均增加，这由与 Rs 相关的凋落物数量和质量调控；在 10-30 cm 土壤深处，柳杉和水杉的 SOC 储量大小降低，而水杉的 SOC 储量稳定性增加，这与细根质量和微环境共同驱动有关；在 30-60 cm 土壤深处，水杉的 SOC 储量大小降低而稳定性增加，而柳杉或杉木的 SOC 储量大小和稳定性变化不大，这由与微生物化学计量和 Rs 相关的土壤理化性质所调控。总体而言，微生物化学计量和微环境对 SOC 储量的影响不显著。因此，SOC 储量大小随土壤深度和树种而变化，但在所有深度随树种变化，其稳定性趋于稳定。这些结果表明，SOC 储量大小和稳定性主要由森林转换后 30 多年来森林生态系统的自我调节过程决定，这将有助于我们更准确地评估长期森林转换的碳固存策略。
