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马尾松Pinus massoniana广泛分布于中国南部和东南部,种植面积超过200万 hm2,具有重要的经济价值和生态功能[1]。近年来,马尾松林植物多样性较低,受病虫害严重,大面积马尾松逐渐被砍伐或被其他树种自然替代,从而转变为阔叶林以提升森林的生态效益[2]。然而,阔叶林和马尾松林的凋落物数量和质量、根系性状、土壤微生物等均存在较大差异[1, 3],影响土壤碳循环过程,造成不同林分固碳能力差异显著。土壤团聚体和土壤有机碳之间关系密切,两者相互促进。有研究表明:土壤有机碳可以作为一种胶结剂参与大团聚体的形成过程,而土壤团聚体产生的空间隔离则会对有机碳产生物理保护作用,进而提高有机碳的稳定性[4−6]。土壤有机碳和土壤团聚体与菌根真菌关系密切,而林分转变引起的重要变化之一,是与根系共生的菌根真菌类型的改变[7],但是目前关于林分转变导致的优势菌根类型变化如何影响土壤团聚体特性及稳定性的影响还不清楚。
外生菌根(ectomycorrhiza,ECM)真菌和丛枝菌根(arbuscular mycorrhiza,AM)真菌是重要的陆地植物共生真菌,能够与陆地80%以上的植物形成菌根共生体[8],它们对植物生长、植物群落和生态系统过程的影响已经被广泛研究[8−9]。菌根能够通过根外菌丝缠绕土壤颗粒从而形成团聚体,进而影响土壤结构[6, 10−13]。THORNTON等[14]研究发现:ECM真菌对土壤团聚体具有促进作用。相比于ECM,AM根外菌丝数量较少[6],因此对土壤颗粒的缠绕聚集作用可能较弱。除了菌丝的缠绕作用,菌丝代谢物是土壤团聚体的重要黏合剂。研究表明:ECM真菌菌丝分泌的疏水化合物是重要的土壤团聚体的黏合剂[14],AM真菌则通过其细胞壁组分球囊霉素相关土壤蛋白(glomalin-related soil protein,GRSP)胶结团聚土壤颗粒[15],其在土壤中能稳定存在3~12 a,对土壤团聚体具有深远影响[4, 16]。QIN等[4]研究发现:阔叶林转变为毛竹Phyllostachys pubescens林过程中,AM促进了土壤大团聚体形成。但是,目前关于不同菌根类型转变对土壤团聚体组成影响的研究还较少,不同类型菌根对土壤团聚体组成及稳定性的影响研究还不够深入。
土壤团聚体主要通过对微生物的空间隔离,从物理层面保护土壤有机碳[5]。微生物则主要通过分泌胞外水解酶获取土壤中的碳、氮、磷等养分[17]。有研究表明:水解酶活性与有机质的分解与矿化过程具有显著相关性[18]。例如,β-葡萄糖苷酶和β-纤维二糖苷酶可以将土壤有机质中的纤维素和半纤维素分解为纤维素二糖、果糖等低分子量糖[19]。因此,通过酶活性可以体现微生物对团聚体中有机碳的利用与转化过程。菌根真菌对水解酶活性的影响已被广泛报道[20],在不同养分条件下,菌根真菌可能促进或抑制微生物分泌水解酶[2, 7],但是不同类型菌根对团聚体中水解酶活性的影响还不清楚。
马尾松林是典型的ECM优势林,而阔叶林为AM优势林。本研究以中国亚热带2种典型林分马尾松林和阔叶林为对象,通过湿筛分离土壤团聚体,测定2种林分不同粒级的土壤团聚体有机碳质量分数、麦角固醇质量分数、GRSP以及土壤水解酶活性,进而探讨不同菌根类型对土壤团聚体组成和特征的影响及其可能的作用机制,为评估不同菌根类型对亚热带森林土壤碳汇的影响提供参考依据。
Impact of shifts among mycorrhizal types on soil aggregate composition and characteristics
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摘要:
目的 马尾松Pinus massoniana林向阔叶林转变驱动优势菌根类型由外生菌根(ectomycorrhiza,ECM)转向丛枝菌根(arbuscular mycorrhiza,AM)。不同类型菌根由于其菌丝生物量和分泌物的不同,对土壤团聚体的影响可能存在差异,研究优势菌根类型转变对土壤团聚体组成的影响具有重要的生态学意义。 方法 通过野外调查采样,分析了不同优势菌根类型林分土壤不同粒级团聚体的占比及碳氮质量分数、菌根真菌生物量和胞外酶活性等。 结果 与ECM占优势的马尾松林相比,AM占优势的阔叶林在土壤团聚体的组成、稳定性及碳氮质量分数上存在显著差异,大团聚体(直径d>250 μm)比例和平均质量直径显著升高(P<0.05),而粉黏粒(d<53 μm)占比显著降低(P<0.05)。此外,大团聚体碳氮比显著降低(P<0.05),所有粒级团聚体中β-葡萄糖苷酶活性与β-N-乙酰氨基葡萄糖苷酶活性均显著降低(P<0.05)。大团聚体中易提取态球囊霉素相关土壤蛋白和总球囊霉素相关土壤蛋白趋于升高,微团聚体(d为53~250 μm)和粉黏粒中易提取态球囊霉素相关土壤蛋白、总球囊霉素相关土壤蛋白和麦角固醇质量分数则显著降低(P<0.05)。随机森林结果显示:团聚体有机碳质量分数主要与易提取态球囊霉素相关土壤蛋白、总球囊霉素相关土壤蛋白、ECM生物量和酶活性的变化有关(P<0.05)。 结论 在ECM占优势的马尾松林转变为AM占优势的阔叶林的过程中,土壤团聚体的稳定性显著升高,菌根生物量是团聚体有机碳质量分数变异的重要影响因子。图5参35 -
关键词:
- 丛枝菌根 /
- 外生菌根 /
- 土壤有机碳 /
- 酶活性 /
- 球囊霉素相关土壤蛋白
Abstract:Objective It’s been observed that the transition of masson pine (Pinus massoniana) forest to broad-leaved forest generally contributes to the shift of the dominant mycorrhizal type from ectomycorrhiza (ECM) to arbuscular mycorrhiza (AM). Therefore, it’s of ecological significance to investigate the varying impact of different dominant mycorrhizal types on soil aggregate composition due to the changes in mycelial biomass and exudate, hence the current study. Method With data collected from a field experiment, analyses were conducted of soil aggregate composition as well as carbon (C) and nitrogen (N) content, mycelial biomass, and extracellular enzyme activities of three aggregate fractions. Result The conversion from masson pine forest (MF) to broad-leaved forest (BF) changed the composition and stability of soil aggregates and their carbon and nitrogen content. The proportion of macroaggregates (diameter d>250 μm) and the mean weight diameter (MWD) in BF were significantly higher than those in MF (P<0.05), while the proportion of clay (d<53 μm) and C∶N in macroaggregates showed an opposite result (P<0.05). β-glucosidase activity (BG) and β-N-acetylglucosaminidase (NAG) activity were significantly higher in the MF aggregates than in the BF aggregates (P<0.05). The content of easily extractable glomalin-related soil proteins (EE-GRSP) and total glomalin-related soil proteins (T-GRSP) in macroaggregates were higher in the BF than in the MF, while in microaggregates and clay, the EE-GRSP and T-GRSP content was significantly lower in the BF (P<0.05), compared with that in MF. Soil organic carbon in aggregates was mainly related to EE-GRSP, T-GRSP, ECM biomass, and enzyme activities. Conclusion The transition of ECM-dominated masson pine forests to AM-dominated broad-leaved forests was accompanied with a significant increase in the stability of soil aggregates, and mycorrhizal biomass was associated with the content of organic C in soil aggregates. [Ch, 5 fig. 35 ref.] -
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