Phagotrophic protists are a key component of microbial communities processing leaf litter under contrasting oxic conditions
Phagotrophic protists are a key component of microbial communities processing leaf litter under contrasting oxic conditions
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DOI：
10.1111/fwb.12657
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发表时间：
2015-11
影响因子：
2.7
通讯作者：
Ute Risse‐Buhl;J. Schlief;M. Mutz
中科院分区：
文献类型：
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作者：
Ute Risse‐Buhl;J. Schlief;M. Mutz
总结的转化叶凋落物，在水生系统中的一个关键过程，是已知的减少与氧气浓度的降低，主要是由于较低的丰度和/或较不活跃的切碎大型无脊椎动物。参与凋落叶处理的水生真菌和食腐原生生物可以耐受低氧，但在这些条件下它们在凋落叶处理中的作用知之甚少。我们的目的是解开的重要性，在微生物介导的落叶处理对比好氧条件下的食原生生物。我们假设，呼吸作用，丰富的水生细菌和水生真菌的生物量，从而叶凋落物处理，增强了在存在的食腐原生生物，在常氧和低氧条件下。预计在低氧条件下比在常氧条件下更低的叶加工。在微宇宙中，氧气浓度被调节到常氧或低氧。对于总共105天，叶凋落物与三种微生物群落共培养：（i）从流叶凋落物富集的多物种细菌群落，（ii）水生真菌Heliscus lugdunensis添加到细菌群落和（iii）食源性原生生物Glaucoma laugans添加到细菌-真菌群落。氧化条件对微生物介导的叶片质量损失没有显著影响。在水生真菌的存在下，叶片质量损失更快，并通过添加噬菌体进一步加速。105天后，在细菌、细菌-真菌和细菌-真菌-吞噬原生生物群落中，叶质量分别保留约64- 79%、57-68%和55-61%的初始叶质量。在这两种好氧条件下，较低的叶片韧性表明，水生真菌有可能比单独的细菌更有效地处理叶结构成分。较低的麦角甾醇浓度和增强的叶片质量损失的组合表明，噬菌体刺激的微生物群落的叶片加工效率。在常氧条件下，叶相关的呼吸增加时，连续添加水生真菌和噬菌体的细菌群落，这与更快的叶凋落物处理在这些治疗。在低氧条件下，呼吸的所有三个微生物群落是可比的。因此，增强叶凋落物处理与水生细菌，真菌和噬菌体的处理可能是由其他代谢途径，如发酵和厌氧呼吸，或由群落组成和微生物群落的生长效率的变化。由水生细菌、真菌和食腐原生生物组成的微生物群落在一系列好氧条件下的落叶处理中起着至关重要的作用。虽然由微生物群落单独处理叶凋落物的速度比切碎无脊椎动物的存在下慢，水生细菌，真菌和食腐原生生物的相互作用可以调节叶的质量和随后的碳流动内的微生物食物网的水生生态系统。
Summary The transformation of leaf litter, a key process in aquatic systems, is known to be reduced with decreasing oxygen concentrations, mainly due to lower abundance of and/or less active shredding macroinvertebrates. Aquatic fungi and phagotrophic protists involved in leaf litter processing can tolerate low oxygen, but little is known about their role in leaf litter processing under these conditions. We aimed to unravel the importance of phagotrophic protists within microbially mediated leaf litter processing under contrasting oxic conditions. We hypothesised that respiration, abundance of aquatic bacteria and biomass of aquatic fungi, and thus leaf litter processing, are enhanced in the presence of phagotrophic protists, both under normoxic and low oxic conditions. Lower leaf processing was expected under low oxic than under normoxic conditions. In microcosms, oxygen concentration was adjusted to either normoxic or low. For a total of 105 days, leaf litter was cocultivated with three microbial communities: (i) a multispecies bacterial community enriched from stream leaf litter, (ii) the aquatic fungus Heliscus lugdunensis added to the bacterial community and (iii) the phagotrophic protist Glaucoma scintillans added to the bacteria–fungi community. Oxic condition had no significant effect on microbially mediated leaf mass loss. The leaf mass loss was faster in the presence of the aquatic fungus and further accelerated by adding the phagotrophic protist. After 105 days, leaf mass remaining approximated 64–79%, 57–68% and 55–61% of initial leaf mass in the bacteria, bacteria–fungi, and bacteria–fungi–phagotrophic protist communities, respectively. Under both oxic conditions, the lower leaf toughness indicated that the aquatic fungus had the potential to process leaf structural components more efficiently than bacteria alone. The combination of lower ergosterol concentrations and enhanced leaf mass loss indicated that phagotrophic protists stimulated the efficiency of leaf processing by the microbial community. Under normoxic conditions, leaf-associated respiration increased when successively adding an aquatic fungus and a phagotrophic protist to bacterial communities, which matches the faster leaf litter processing in these treatments. Under low oxic conditions, respiration of all three microbial communities was comparable. Thus, enhanced leaf litter processing in treatments with aquatic bacteria, fungi and phagotrophic protists was presumably caused either by other metabolic pathways such as fermentation and anaerobic respiration, or by changes in community composition and growth efficiency of the microbial community. Microbial communities composed of aquatic bacteria, fungi and phagotrophic protists play a crucial role in leaf litter processing under a range of oxic conditions. Although processing of leaf litter by microbial communities alone is slower than in the presence of shredding invertebrates, the interaction of aquatic bacteria, fungi and phagotrophic protists can modulate leaf quality and subsequently carbon flow within the microbial food webs of aquatic ecosystems.