Constant and diurnally-varying temperature regimes lead to different temperature sensitivities of soil organic carbon decomposition

In a 122-day incubation experiment with two soil types under four temperature treatments, we examined whether the temperature sensitivity of soil organic carbon (SOC) decomposition differed between constant and diurnally-varying soil temperature regimes. We calculated the Q₁₀ values after accounting for changes in substrate availability and quality among treatments over time. The Q₁₀ values under constant temperature regime were consistently and significantly higher than those under diurnally-varying temperature regime, particularly in the later stages of decomposition (by up to 30%). This result indicated that different temperature regime was one of the important factors causing the current controversy about the temperature sensitivity of SOC decomposition in published reports.     

Dynamics of extracellular DNA decomposition and bacterial community composition in soil

Microbial necromass is an important source of stabilized organic matter in soil, yet the decomposition dynamics of necromass constituents have not been adequately characterized. This includes DNA, a nutrient-rich molecule that when released into the environment as extracellular DNA (eDNA) can be readily used by soil microorganisms. However, the ecological relevance of eDNA as a nutrient source for soil microorganisms is relatively unknown. To address these deficits, we performed a laboratory experiment wherein soils were amended with ¹³C-labeled eDNA and clay minerals known to interact with DNA (kaolinite and montmorillonite). The amount of eDNA-carbon remaining in the soil declined exponentially over time. Kaolinite amendment decreased eDNA decomposition rates and, after 30 days, retained a higher fraction of eDNA-carbon (∼70% remaining) than control or montmorillonite soils (∼40% remaining), indicating that clay mineral sorption can stabilize eDNA-derived carbon in soil. Sequencing of bacterial 16S rRNA genes showed that during the incubation the relative abundance of the added eDNA's sequence decreased by 98%, 92% and 99% in the control, montmorillonite, and kaolinite amended soils respectively. These results suggest that the fraction of eDNA-carbon that remained in the soil was incorporated into microbial biomass, firmly bound to soil constituents, or fragmented and no longer amenable to sequencing. In addition, the eDNA amendment affected the composition of the bacterial community. Specifically, the relative abundance of select phyla (Planctomycetes and TM7) and genera (e.g., Arthrobacter and Nocardioides) were elevated in soils that received eDNA, suggesting these groups may be particularly effective at degrading eDNA and using it for growth. Taken together, these results indicate that while eDNA is consumed by bacteria in soil, a fraction of eDNA material is resistant to decomposition, particularly when stabilized by soil minerals, suggesting a substantial amount of recalcitrant eDNA could accumulate over time.     

Environmental stress response limits microbial necromass contributions to soil organic carbon

The majority of dead organic material enters the soil carbon pool following initial incorporation into microbial biomass. The decomposition of microbial necromass carbon (C) is, therefore, an important process governing the balance between terrestrial and atmospheric C pools. We tested how abiotic stress (drought), biotic interactions (invertebrate grazing) and physical disturbance influence the biochemistry (C:N ratio and calcium oxalate production) of living fungal cells, and the subsequent stabilization of fungal-derived C after senescence. We traced the fate of ¹³C-labeled necromass from ‘stressed’ and ‘unstressed’ fungi into living soil microbes, dissolved organic carbon (DOC), total soil carbon and respired CO₂. All stressors stimulated the production of calcium oxalate crystals and enhanced the C:N ratios of living fungal mycelia, leading to the formation of ‘recalcitrant’ necromass. Although we were unable to detect consistent effects of stress on the mineralization rates of fungal necromass, a greater proportion of the non-stressed (labile) fungal necromass C was stabilised in soil. Our finding is consistent with the emerging understanding that recalcitrant material is entirely decomposed within soil, but incorporated less efficiently into living microbial biomass and, ultimately, into stable SOC.     

基于分解机制的多目标蝙蝠算法

在分析蝙蝠算法性能基础上,将蝙蝠算法融入分解机制,提出了一种基于分解机制的多目标蝙蝠算法。为了进一步提高算法的多样性,将差分进化策略引入算法中。对14个具有复杂Pareto前沿的多目标优化问题(LZ-09系列和ZDT系列)测试不同邻域规模对算法性能的影响,结果表明新算法的邻域规模为20时性能最优;将其与MOEA/D-DE和NSGA-II算法进行对比分析,结果显示该算法的分布性、收敛性和多样性均优于另外两种算法。为了验证其求解含有约束问题的性能,将其应用于滑动轴承多目标优化设计问题中,获得的Pareto前沿分布均匀,表明算法具有工程实用性,是求解复杂高维多目标问题的有效方法。     

多环芳烃微生物降解的研究进展

多环芳烃(PAHs)是一类普遍存在于环境中的难降解的有机污染物。对多环芳烃的来源、分布、危害、处理方法等进行了综述,并对该领域的研究方向进行了展望。     

哀牢山木果石栎林凋落物矿质元素含量的研究

研究表明：木果石栎林凋落物年产量每公顷5．5－7．1吨。凋落物中落叶占80％。每公顷凋落叶中含氮91．5kg，磷3．7kg，钙101kg，铝5．7kg，钾42．1kg，钠0．3kg，镁10．7kg，锰5．6kg和铁1．9kg。每年4．6月为凋落物降落的高峰期。凋落物消失参数是基于测定凋落物的现存量与年凋落物量之间的比率，其系数范围为0．73-0．94。分解率的测定是采用该群落中七种优势树种的叶子）木果石栎、景东石栎、腾冲栲、长尾青冈、滇木荷、大花八角、米饭树和箭竹）为材料，在塑料网袋中进行，结果不同种间分解率有差异，其年分解率为68％－96％。分解率与采集地无关。各种植物凋落物中灰分元素含量有较大差异。     

高效降解纤维素菌株的选育

[目的]筛选纤维素酶活性高且酶活稳定的纤维素降解菌。[方法]以木霉为出发菌株,用紫外线对其进行诱变处理,通过平板初筛和摇瓶复筛筛选出纤维素酶活力高且酶活稳定的优良突变株,然后分别以滤纸、甘蔗渣、麦秆和稻壳为目标降解物对优良突变株进行底物降解试验。[结果]经紫外线诱变、初筛、复筛,共选育出3株纤维素酶活力高且酶活稳定的优良突变株N1、N2、N3,其中N3的产酶活力最高（348 U/ml）,为出发菌株的2.13倍;N3对各种底物的降解效果均优于出发菌株,分别以滤纸、甘蔗渣、麦秆和稻壳为唯一碳源时,其失重率分别为48.68%、41.28%、26.53%和23.47%。[结论]该研究选育出了高效降解纤维素的菌株N3。     

玉米生长对石灰性土壤无机碳与有机碳释放的根际效应

利用IsoSource模型三源区分玉米根际土壤CO2释放来源(根源呼吸、土壤无机碳与有机碳释放),研究玉米根际效应对石灰性土壤无机碳与有机碳释放的影响.在玉米拔节期(24～53 d)、抽穗期(54～66 d)和灌浆期(67～99 d)末分别破坏性取样,测定根系、土壤有机碳和无机碳的13C含量等指标;自拔节期开始至生育期...     

The fate of condensed tannins during litter consumption by soil animals

Condensed tannins (CT) can strongly affect litter decomposition, but their fate during the decomposition process, in particular as influenced by detritivore consumption, is not well understood. We tested the hypothesis that litter CT are reduced by the gut passage of two functionally distinct detritivores of Mediterranean forests, the millipede Glomeris marginata, and the land snail Pomatias elegans, as a fixed proportion of initial litter CT, but more so in Pomatias since snails are known to have a more efficient enzymatic capacity. Contrary to our hypothesis, both detritivore species reduced litter CT to near zero in their faecal pellets irrespective of the wide range in initial leaf litter CT concentrations of 9-188 mg g⁻¹ d m among three Mediterranean tree species (Pistacia terebinthus, Quercus ilex, Alnus glutinosa) and different decomposition stages of their litter. The almost complete disappearance of CT even from some litter types highly concentrated in CT, due to either degradation by gut microorganism or complexation of CT into insoluble high molecular weight structures, suggests a high “de-tanning” efficiency across functionally distinct detritivore species. The transformation of CT-rich litter into virtually CT-free faecal pellets by detritivores might be highly relevant for the subsequent decomposition process in ecosystems with a high macrofauna abundance and CT-rich plant species such as Mediterranean forests.     

Does adding microbial mechanisms of decomposition improve soil organic matter models? A comparison of four models using data from a pulsed rewetting experiment

Contemporary soil organic matter (SOM) models have been successful at simulating decomposition across a range of spatial and temporal scales using first-order kinetics to represent the decomposition process; however, recent work suggests the simplicity of the first-order representation of decomposition is not adequate to capture the microbially-driven dynamics of SOM decomposition over short timescales. For example, the response of soils to drying-rewetting events may best be explained by microbial and/or exoenzyme controls on decomposition. To test if adding these microbial mechanisms improves the ability of SOM models to simulate the response of soils to short-term environmental changes, we developed four different SOM decomposition models with varying mechanistic complexity and compared their ability to simulate soil respiration from a pulsed drying-rewetting laboratory-based experiment. Specifically, we tested the ability of the models to capture the timing and magnitude of soil CO₂ efflux in response to rewetting or constant moisture conditions. The results of the comparison suggest that the inclusion of exoenzyme and microbial controls on decomposition can improve the ability to simulate pulsed rewetting dynamics; however, less mechanistic first-order models prevail under steady-state moisture conditions. These modeling results may have implications for understanding the long-term response of soil carbon stocks in response to local and regional climate change.