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  Cunninghamia lanceolata 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问题缺乏深入了解，严重制约了退化人工林改造过程中P循环的调控及人工林可持续经营措施的科学制定。本研究以杉木[Cunninghamia lanceolata，丛枝菌根(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，外生菌根(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组分转化的作用。结果表明:(1)在3种孔径的微宇宙中，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)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的微生物生物量碳(MBC)、微生物生物量氮(MBN)和微生物生物量磷(MBP)较CL也均呈增加趋势，且在MP中达到显著水平(P＜0.05)；(3)与CL相比，PM、PC和MP的酸性磷酸酶(ACP)酶活性均显著提高(P＜0.05)，β-葡萄糖苷酶(BG)酶活性和N-乙酰-葡萄糖苷酶(NAG)酶活性则只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)酶活性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)酶活性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。可见，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树种混交种植的效果最佳，土壤中的根系和菌丝通过调节微生物生物量和酶活性促进土壤中P的积累，加快P的转化。本研究为亚热带退化针叶林改造并促进土壤P高效利用的树种选择及其种植模式提供了科学依据。

Abstract:

Soil phosphorus (P) is a key nutrient limitation factor in tropical and subtropical plantation ecosystems,and the directed regulation and improvement of its availability play an important role in improving the productivity of plantations.However,the understanding of the synergistic interactions of “root-mycelium-free microorganisms” in driving soil P transformation and component redistribution within plantation ecosystems remains limited.This lack of understanding severely restricts the scientific formulation of sustainable management measures for P cycling and ecological restoration in degraded plantations.This study focused on the pure plantation (CL,control) of Cunninghamia lanceolata [Arbuscular Mycorrhiza (AM) species] and three types of artificially modified C.lanceolata plantations with broadleaf trees:Pure plantation (PM) of Mytilaria laosensis (AM species),Pure plantation (PC) of Castanopsis hystrix [Ectomycorrhiza (ECM) species],and Mixed Plantation (MP) of M.laosensis/C.hystrix.The microcosms with different aperture sizes were used to distinguish the roles of roots,mycelia,and free microorganisms in soil P transformation.The results are summarized as follows.(1) Compared with CL,PM,PC,and MP showed increased soil P fractions (HCl-P,Citrate-P,Enzyme-P,and CaCl₂-P) in the three microcosms,with significant increases observed in MP (P<0.05).(2)Microbial Biomass Carbon (MBC),Microbial Biomass Nitrogen (MBN),and Microbial Biomass Phosphorus (MBP) in PM,PC,and MP also showed an increasing trend compared with those in CL,with significant increases in MP (P<0.05).(3)Compared with CL,PM,PC,and MP presented increased Acid Phosphatase (ACP) in all the three microcosms (P<0.05),while β-D-Glucosidase (BG) and N-Acetyl-β-D-glucosidase (NAG) significantly increase in the larger and smaller aperture 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 aperture microcosms (P<0.05).There were significantly positive correlations between the activities of all types of enzymes.(4)Redundancy Analysis (RDA) showed that Soil Organic Carbon (SOC),MBP,Fine Root biomass (FR),and LAP were the primary factors driving changes in soil P fractions.The results suggest that the broadleaf transformation of pure plantation of C.lanceolata is beneficial for increasing soil P fraction accumulation and transformation,with the best results observed in mixed planting with AM and ECM tree species.Roots and mycelia in soil promote the accumulation of P in soil by regulating microbial biomass and enzyme activity,accelerating P transformation.This study provides scientific evidence for selecting P-efficient tree species and their planting configurations in the broadleaf transformation of subtropical degraded coniferous forests.