Investigating the temporal impact of drainage and re-wetting on interactions between microbes, enzyme kinetics and dissolved organic compounds in peat

泥炭地生态系统拥有世界三分之一的土壤碳储量，因此是全球碳循环的重要组成部分。从历史上看，泥炭地因农业开垦而被排干，导致各种生态系统服务的退化和潜在损失，包括碳固存和通过变色(即高溶解有机碳出口)的饮用水质量。泥炭沼泽通过夹持阻挡再湿对溶解有机碳(DOC)输出的影响似乎取决于再湿后的时间长度，但其相关机制尚不清楚。对于泥炭地生态系统服务的长期管理，负责DOC输出的机制能够得到经验证明是至关重要的。最近的工作表明，泥炭地地下水位的长期恢复(4年)由于地下水位恢复后分解减少而降低了DOC浓度。然而，短期堵塞夹具会增加DOC，并在堵塞排水沟后长达一到两年的时间内变色。对短期现象的解释包括：1)排水阶段微生物产生的DOC升高的冲刷；2)排水堵塞后不再被抑制的酶的持续存在；3)土壤溶液中硫酸盐抑制减少，导致DOC释放；以及4)泥炭的疏水性，延迟重新润湿和DOC的释放1或2年。假设地下水位的长期恢复与短期地下水位升高产生了不同的生物地球化学条件，即含水饱和度与DOC浓度之间不存在直接关系。因此，假设有两种不同的机制负责短期(&lt；2年)和长期(&gt；4年)再湿事件中DOC的输出。在泥炭地，酶锁存机制(ELM)作为一种机制来解释握力阻断后DOC的短期冲洗的作用还没有得到充分的评估。在没有排水的泥炭地，酶活性受到抑制，因为顽固的酚类化合物持续存在于厌氧泥炭中，因为负责分解它们的酚氧化酶需要分子氧作为辅助因素。如果泥炭中的氧气因排水而增加，酚氧化酶的活性就会增加，从而降低酚类物质的浓度，从而增加水解酶的活性，从而促进微生物的进一步分解。然而，通过夹持阻挡恢复地下水位可能不会恢复抑制降解的酚类化合物，这意味着水解酶对泥炭结构的酶促分解可能会继续并有助于DOC冲刷。这项研究旨在研究与泥炭分解有关的关键非生物和生物参数之间的关系，泥炭长期受到不同的水文状况(即排干和夹持堵塞)，并将在实验室进行短期再湿化/干燥。拟研究的参数包括葡萄糖苷酶和酚氧化酶的详细酶动力学、微生物活性和生物量、DOC、酚类、离子和腐殖质。这将允许详细研究在不同水文条件下导致DOC释放的生物机制。其中一个重要方面是腐殖质对OM分解为DOC的影响，以及酶定位和动力学的基本方面。这项研究对于评估土地管理对固碳和水质/供应的生态系统服务的长期影响很重要。

Peatland ecosystems contain one-third of the world's soil carbon store and are therefore a significant component of the global carbon cycle. Historically, peatlands have been drained for agricultural reclamation that has led to degradation and potential loss of a variety of ecosystem services including carbon sequestration and potable water quality via discoloration (i.e. high dissolved organic carbon export). The impact of rewetting by grip-blocking on dissolved organic carbon (DOC) export in peat bogs appears dependent on the length of time following rewetting but the mechanisms responsible are poorly understood. For long-term management of ecosystem services in peatlands, it is critical that the mechanisms responsible for DOC export can be proven empirically. Recent work shows that long-term restoration of a peatland watertable (>4 years) reduces DOC concentrations due to reduced decomposition after watertable recovery. However, short-term blocking of grips increases DOC and discolouration for up to 1 or 2 years following blocking of drains. Explanations for the short-term phenomenon include 1) flushing of elevated DOC that was produced by microbes during the drainage phase; 2) the persistence of enzymes that are no longer inhibited following drain-blocking; 3) a reduction of sulphate suppression in the soil solution leading to DOC release; and 4) the hydrophobic nature of peat delaying re-wetting and the release of DOC for 1 or 2 years. It is hypothesized that the long-term recovery of the watertable creates different biogeochemical conditions than short-term watertable elevation, i.e. there is no straight forward relationship between water saturation and DOC concentrations. Thus two distinct mechanisms are hypothesized to be responsible for DOC export over short (< 2 years) and long term (> 4 years) rewetting events. The role of the enzyme-latch mechanism (ELM) as a mechanism to explain the short-term flush of DOC following grip-blocking has not been fully evaluated in peatlands. In non-drained peatlands, enzyme activities are repressed due to recalcitrant phenolic compounds that persist in the anaerobic peat because the phenol oxidase enzyme responsible for their breakdown requires molecular oxygen as a co-factor. If oxygen in the peat mass increases because of drainage, phenol oxidase activity increases, reducing the concentration of phenolics and thus increasing the hydrolase enzyme activities promoting further microbial decomposition. However, restoration of the watertable level by grip-blocking may not restore the degradation-inhibiting phenolic compounds meaning that enzymic decomposition of the peat structure by hydrolase enzymes may continue and contribute to DOC flush. This study aims to build on research examining the relationships between key abiotic and biotic parameters associated with decomposition in peat that has been subjected to different hydrological regimes over the longer term (i.e. drained vs. grip-blocked) and will be subjected to short-term re-wetting/drying in the laboratory. The parameters to be studied include detailed enzyme kinetics of glucosidase and phenol oxidase, microbial activities and biomass, DOC, phenolics, ions and humic substances. This will permit detailed examination of the biotic mechanisms responsible for DOC release under different hydrological regimes. One important aspect is the effect of humic substances on the decomposition of OM to DOC and fundamental aspects of enzyme location and kinetics. This research is important for assessing the long-term impact of land management on the ecosystem services of carbon sequestration and water quality/provision.