根系和菌丝途径介导的杉木人工林阔叶化改造对土壤磷组分的影响

Effects of root and mycelium mediated pathways in the broadleaf transformation of Cunninghamia lanceolata plantation on soil phosphorus fractions.

关键词:  磷组分  根际  菌根真菌  微生物特征  阔叶林  杉木人工林

Key words:  Phosphorus fractions  rhizosphere  mycorrhizal fungi  microbial characteristics  broadleaf forests  fir plantations

摘要:

土壤磷（P）是热带亚热带人工林生态系统关键的养分限制因子，定向调控并提高其有效性对提升人工林生产力具有非常重要的作用。然而，目前我们对人工林生态系统中“根系-菌丝-自由微生物”的协同作用如何驱动土壤P转化及其组分再分配这一核心科学问题缺乏深入了解，严重制约该区域退化人工林改造过程中P循环的调控及可持续经营措施的科学制定。本研究以杉木（Cunninghamia lanceolata, AM树种）纯林（CL, 对照）和杉木人工林阔叶化改造后的3种人工林﹝米老排（Mytilaria laosensis, AM树种）纯林（PM）、红锥（Castanopsis hystrix, ECM树种）纯林（PC）和米老排/红锥混交林（MP）﹞作为研究对象，利用不同孔径大小（1.45 mm：允许根系、菌丝和自由微生物进入；53 μm：阻止根系但允许菌丝和自由微生物进入；1 μm：阻止根系和菌丝进入，仅允许自由微生物进入）的微宇宙区分植物根系、菌丝和土壤自由微生物对土壤P组分和转化的作用。结果表明:（1）与CL相比，PM、PC和MP的所有土壤P组分（HCl-P、Citrate-P、Enzyme-P和CaCl2-P）在3种孔径的微宇宙中均呈增加趋势，且均在MP中达到显著水平（P <0.05）；（2）PM、PC和MP在3种孔径的微宇宙中的微生物生物量碳（MBC）、氮（MBN）和磷（MBP）较CL也均呈增加趋势，且在MP中均达到显著水平（P <0.05）；（3）与CL相比，PM、PC和MP的酸性磷酸酶（ACP）在3种孔径微宇宙中均显著提高（P <0.05），β-葡萄糖苷酶（BG）和N-乙酰-葡萄糖苷酶（NAG）在大孔径和小孔径微宇宙中显著提高（P <0.05），纤维二糖水解酶（CB）在大孔径和中孔径微宇宙中显著提高（P <0.05），而亮氨酸氨基肽酶（LAP）在小孔径微宇宙中显著提高（P <0.05），且各类酶活性之间均呈显著正相关关系；（4）冗余分析（RDA）结果表明土壤有机碳（SOC），MBP、细根生物量（FR）和LAP是驱动土壤P组分变化的最主要因子。基于上述结果，我们认为对杉木人工林进行阔叶化改造有利于提高土壤P组分积累和转化，尤其以AM和ECM菌根树种混交种植的效果最佳，根系和菌丝体的加入可以通过调节微生物生物量和酶活性促进土壤P组分积累和转化，为亚热带退化针叶林改造并促进土壤P高效利用的树种及其配置模式提供科学依据。

Abstract:

Soil phosphorus (P) is a key nutrient limitation factor in tropical and subtropical artificial forest ecosystems, and the directed regulation and improvement of its effectiveness play an important role in improving the productivity of plantation forests. However, our understanding of the synergistic interactions between "roots-mycelium-free microorganisms" in driving soil P transformation and component redistribution within artificial forest ecosystems remains limited. This lack of understanding severely restricts the scientific formulation of sustainable management measures for P cycling and ecological restoration in degraded artificial forests in the region. This study focuses on pure plantation (CL, control) of C. lanceolata (AM species) and three types of artificially modified C. forests with broadleaf trees: pure plantation (PM) of M. laosensis (AM species), pure plantation (PC) of C. hystrix (ECM species), and mixed plantation (MP) of M. laosensis/C. hystrix. We use microcosms with different mesh sizes (1.45 mm: allowing roots, mycelium, and free microorganisms; 53 μm: excluding roots but allowing mycelium and free microorganisms; 1 μm: excluding roots and mycelium, allowing only free microorganisms) to distinguish the roles of plant roots, mycelium, and free microorganisms in soil P components and transformations. The results indicate: (1) Compared to CL, all soil P components (HCl-P, Citrate-P, Enzyme-P, and CaCl2-P) in PM, PC, and MP show an increasing trend in the three microcosms, with significant increases observed in MP (P < 0.05); (2) Microbial biomass carbon (MBC), nitrogen (MBN), and phosphorus (MBP) in PM, PC, and MP also show an increasing trend compared to CL, with significant increases in MP (P < 0.05); (3) Compared to CL, Acid phosphatase (ACP) in PM, PC, and MP is significantly higher in all three mesh sizes (P < 0.05), while β-D-Glucosidase (BG) and N-acetyl-β-D-glucosidase (NAG) significantly increase in the larger and smaller mesh microcosms (P < 0.05). cellobiohydrolase (CB) shows a significant increase in the larger and medium mesh microcosms (P < 0.05), while L-leucine aminopeptidase (LAP) significantly increases in the smaller mesh microcosms (P < 0.05), and there was a significant positive correlation between the activities of all types of enzymes; (4) Redundancy analysis (RDA) shows that soil organic carbon (SOC), MBP, fine root biomass (FR), and LAP are the primary factors driving changes in soil P components. Based on the above results, we believe that the broadleaf transformation of pure plantation of C. lanceolata is beneficial for increasing soil P component accumulation and transformation, with the best results observed in mixed planting of AM and ECM mycorrhizal tree species. The addition of roots and mycelium can promote soil P component accumulation and transformation by regulating microbial biomass and enzyme activity. This provides scientific evidence for selecting P-efficient tree species and their planting configurations in the broadleaf transformation of subtropical degraded coniferous forests.