Enzymic Latch Research Articles

Carbon Sequestration and the Enzymic Latch Mechanism in Red, Black and White Mangrove Soils of Florida USA.

Carbon Sequestration and the Enzymic Latch Mechanism in Red, Black and White Mangrove Soils of Florida USA.

Peatland geoengineering: an approach to strengthen enzymic latch and impede carbon emissions in post-extracted peatlands?

Peatland geoengineering: an approach to strengthen enzymic latch and impede carbon emissions in post-extracted peatlands?

The importance of moisture in regulating soil organic carbon content based on a comparison of “enzymic latch” and “iron gate” in Zoige Plateau peatland

Due to the enormous amount of carbon (C) stored in peatlands, understanding the regulator of soil organic carbon (SOC) in peatlands is critical for global C cycling. Currently, “enzymic latch” and “iron gate” are the frequently debated mechanisms that propose phenol oxidase (PHO) and Fe2+ as important regulators driving SOC cycling in peatland. Therefore, this study compared “enzymic latch” and “iron gate” in the same peatland (Zoige Plateau, the largest peatland in China) to figure out the crucial regulator of SOC content via investigating the interrelationships among soil properties, C-related enzymes, phenolics, and iron (Fe) oxides. Moreover, waterlogged and non-waterlogged soils were chosen to take samples in both dry and wet season to understand the potential role of moisture in regulating SOC content. It was found that the contents of dissolved organic C, phenolics, SOC, Fe oxides, and β-glucosidase (BG) activities in waterlogged soils were higher than those in non-waterlogged soils. Compared to the dry season, soils in the wet season had higher phenolics, SOC, and Fe oxides contents. Also, this study observed an insignificant relationship between PHO and SOC (p > 0.05) and the small amounts of Fe2+ to total Fe (<2‰) in soils. Meanwhile, the highest effect of moisture (0.89) and negligible effect of PHO (0.04) and Fe2+ (-0.08) on SOC based on pathway analysis suggested that moisture might be the crucial regulator of SOC. Furthermore, pathway analysis implied that moisture could indirectly affect SOC by adjusting BG (p < 0.05) and soluble phenolics (p < 0.05). This study provided valuable information for understanding the importance of moisture in driving C cycling and helping against soil C loss by moisture management in Zoige Plateau.

Carbon sequestration and the enzymic latch mechanism in red, black and white mangrove soils of Florida USA

Mangrove swamps are important habitat types providing vital ecological services, such as protection of coastlines from erosion and extreme weather conditions including hurricanes, recycling of nutrients and sequestration of carbon. Mangrove swamps support a wide range of biodiversity, improve water quality, provide fish for local communities. They are also used as a source of wood fuel, medication as well as for harvesting honey for the local population. Soil samples for laboratory analyses were collected from red (Rhizophora mangle), black (Avicennia germinans) and white (Laguncularia racemose) mangroves in Florida, USA to determine the biogeochemistry processes. Results of analyses indicated that the red mangrove soil is the most efficient for carbon sequestration. It had the lowest phenol oxidase activity (206.15 nmol dicq g-1 h-1), highest phenolic concentration (262.33 µg g-1) and lowest hydrolase enzyme activity (β-glucosidase) (3.04 nmol g-1 min-1) and, as a result, the highest concentration of soil organic matter (SOM) (57.9%). It is believed that the high soil water content (84.2%).) of the red mangrove, due to its proximity to the sea, is a key driver of these observations. The 'enzymic latch' mechanism appears to be prevalent in the red mangrove soil, in particular, allowing these ecosystems to be effective at carbon storage hence, could serve as an important natural tool in mitigating the effect of climate change. Preservation and conservation of mangrove swamps is vital in balancing the effect of global warming.

Carbon sequestration and the enzymic latch mechanism in red, black and white mangrove soils of Florida USA

Carbon sequestration and the enzymic latch mechanism in red, black and white mangrove soils of Florida USA

The Importance of Moisture in Regulating Soil Organic Carbon Based on a Comparison of “Enzymic Latch” and “Iron Gate” in Zoige Plateau Peatland

The Importance of Moisture in Regulating Soil Organic Carbon Based on a Comparison of “Enzymic Latch” and “Iron Gate” in Zoige Plateau Peatland

Water Table Fluctuation in Peatlands Facilitates Fungal Proliferation, Impedes Sphagnum Growth and Accelerates Decomposition

Northern peatlands are substantial carbon sinks because organic matter in peat is highly stable due to the low rate of decomposition. Waterlogged anaerobic conditions induce accumulation of Sphagnum-derived phenolic compounds that inhibit peat organic matter decomposition, a mechanism referred to as the “enzymic latch”. Recent studies have predicted that the water table in northern peatlands may become unstable. We observed that such unstable water table levels can impede the development of Sphagnum mosses. In this study, we determined the effects of low and high frequency water table fluctuation regimes on Sphagnum growth and peat organic matter decomposition, by conducting a year-long mesocosm experiment. In addition, we conducted a molecular analysis to examine changes in abundance of fungal community which may play a key role in the decomposition of organic matter in peatlands. We found that rapid water table fluctuation inhibited the growth of Sphagnum due to fungal infection but stimulated decomposition of organic matter that may dramatically destabilize peatland carbon storage. Increased pH, induced by the fluctuation, may contribute to the enhanced activity of hydrolases in peat. We demonstrated that the water table fluctuation in peatlands impeded Sphagnum growth and accelerates decomposition due to fungal proliferation. Thus, we suggested that understanding the microbial community in the northern peatlands is essential for elucidating the possible changes in carbon cycle of peatland under the changing world.

Revisiting the concept of 'enzymic latch' on carbon in peatlands.

Peatlands are long-term sinks of atmospheric carbon (C) largely due to water-saturated soil conditions, decay-resistant plant litter, and the presence of biochemical compounds such as soluble phenolics. As phenolics are known inhibitors of microbial enzymes in soils, the concept of the 'enzymic latch' on peat C was introduced, assuming that phenolics accumulate in peat water due to protection from degradation by oxidative enzymes as a result of anoxia. However, their inhibitory role in peat has not been unambiguously confirmed. We aimed to verify whether peat phenolics inhibit microbial and enzyme activities in laboratory-incubated Sphagnum litter, and bog and fen peat. Soluble humic substances were extracted from bog water as a source of natural phenolics and separated into two molecular-weight fractions. We tested the effects of (1) phenolics concentration, (2) their molecular weight and (3) anoxia on the activity of hydrolytic and oxidative enzymes, and on microbial respiration rate. The added phenolics did not suppress hydrolytic enzyme activities nor microbial respiration. Quite the contrary, phenolics addition (up to 1000mgL-1) sometimes supported enzyme and microbial activities, indicating that phenolics (or another constituent of peat humic substances) served as a source of C. The activities of hydrolytic enzymes did not vary between oxic and anoxic peat but were double in oxic than anoxic conditions in Sphagnum litter. Differences in enzymatic and microbial activities were driven by peat type with about three times greater microbial respiration rates and enzyme activities in fen peats. Our results do not support the concept of the enzymic latch, particularly its key assumption that peat phenolics inhibit hydrolytic enzymes. While the concept was established on oceanic peatlands with low phenolic concentrations, the peat microbial community in our experiments seemed acclimated to the naturally high phenolic concentrations, characteristic for other, non-oceanic northern peatlands. Thus, the enzymic latch should not be considered as a determinative mechanism preserving the global C store in peatlands.

Microbial decomposition of soil organic matter determined by edaphic characteristics of mangrove forests in East Asia

Mangrove forests cover only 0.1% of the world's continental area; however, these are a substantial carbon sink owing to the high primary production and low rate of decomposition of soil organic matter (SOM). The extremely low decomposition rate of SOM in mangrove forests is believed to be caused by low oxygen and nutrient availability as well as recalcitrant biomass from mangrove. However, only a few studies have addressed the microbial mechanism that plays a key role in the decomposition of SOM. In this study, the decomposition of SOM were determined by conducting a field survey and an lab incubation experiment using soil samples from mangrove forests in three regions; Okinawa, Shenzhen, and Hong Kong. In particular, we examined the occurrence of the enzymic latch mechanism, which involves phenolic inhibition of enzymic decomposition, in mangrove forest soils that highlights the importance of phenol oxidase as a key controlling factor. The results clearly showed that enzymic latch involved in the accumulation of SOM in the mangroves of Shenzhen and Hong Kong, whereas the accumulation of SOM in Okinawa was controlled by other mechanisms, such as the iron gate mechanism, which involves stabilization of soil carbon in iron-SOM complexes. The characteristics of mangrove forests, such as iron concentration, were shown as substantial determination factors in the dynamics of SOM. We concluded that the decomposition of SOM were strongly affected by the characteristics of mangrove forests, and the occurrence of enzymic latch in mangrove forests has a potential application in geoengineering technology to enhance the carbon sequestration capacity of mangrove forests.

Investigating whether light intensity can modify decomposition rates in peatlands through control of the ‘enzymic latch’

Root exudates released by vascular plants contain significant amounts of photosynthetically-derived low molecular weight carbon compounds and gases, such as oxygen. These compounds are reported to have a priming effect on the activity of soil microbes which, in turn, release extracellular soil enzymes. Rates of root exudation are known to correlate positively with photosynthesis rates. As such, we hypothesized that phenol oxidase activity in the rhizosphere of peatland plants could be manipulated by varying the intensity of light to which above ground biomass is exposed, in line with recent solar radiation management proposals of geoengineers. Since phenol oxidase plays a pivotal role in regulating biodegradation in peat soils, through a mechanism widely known as the ‘enzymic latch’, this approach was thought to have potential as an ecoengineering strategy designed to enhance carbon sequestration in these environments. Our experiment however, found little relationship between phenol oxidase activity and light intensity level for any of the plants analysed, although significant differences in enzyme activity were observed between plant species. It is argued therefore, that encouraging the growth of particular plant species may be more effective at enhancing carbon sequestration in peatlands than manipulating ambient light levels.

The role of molecular weight in the enzyme-inhibiting effect of phenolics: the significance in peatland carbon sequestration

Northern peatlands store 455Pg of carbon–a third of the entire global carbon store. Carbon accumulates because phenolic inhibitors slow the rate of decomposition to below that of photosynthetic production. The disproportionate importance of phenolics in peatlands is related to the unique properties of waterlogged peat soils suppressing the activity of phenol oxidase; one of the few enzymes capable of breaking these inhibitors down (a role often referred to as the “enzymic latch”). This permits accumulation of phenolic compounds that are potent inhibitors of hydrolase enzymes–major agents in the breakdown of organic matter. In our study we investigate the importance of the molecular weight of phenolics on levels of inhibition of microbial decomposition in peat. We found the higher the molecular weight, of a phenolic compound, the greater its inhibitory effect on the breakdown of organic matter.

Management strategies for medically unexplained symptoms in general practice: A qualitative study

Northern peatlands store 455 Pg of carbon–a third of the entire global carbon store. Carbon accumulates because phenolic inhibitors slow the rate of decomposition to below that of photosynthetic production. The disproportionate importance of phenolics in peatlands is related to the unique properties of waterlogged peat soils suppressing the activity of phenol oxidase; one of the few enzymes capable of breaking these inhibitors down (a role often referred to as the “enzymic latch”). This permits accumulation of phenolic compounds that are potent inhibitors of hydrolase enzymes–major agents in the breakdown of organic matter. In our study we investigate the importance of the molecular weight of phenolics on levels of inhibition of microbial decomposition in peat. We found the higher the molecular weight, of a phenolic compound, the greater its inhibitory effect on the breakdown of organic matter.

Canada: Titan International – carbon black ex-scrap tyres

Northern peatlands store 455 Pg of carbon–a third of the entire global carbon store. Carbon accumulates because phenolic inhibitors slow the rate of decomposition to below that of photosynthetic production. The disproportionate importance of phenolics in peatlands is related to the unique properties of waterlogged peat soils suppressing the activity of phenol oxidase; one of the few enzymes capable of breaking these inhibitors down (a role often referred to as the “enzymic latch”). This permits accumulation of phenolic compounds that are potent inhibitors of hydrolase enzymes–major agents in the breakdown of organic matter. In our study we investigate the importance of the molecular weight of phenolics on levels of inhibition of microbial decomposition in peat. We found the higher the molecular weight, of a phenolic compound, the greater its inhibitory effect on the breakdown of organic matter.

Is peat accumulation in mangrove swamps influenced by the “enzymic latch” mechanism?

Mangrove swamps accumulate a significant amount (45–98 %) of organic carbon in sediments; however, there is a knowledge gap in explaining the mechanism behind this. Through the analysis of substrate samples from a red mangrove (Rhizophora mangle) swamp in southwest Florida, USA, this study investigated whether the “enzymic latch”, which suppresses decomposition in northern peatlands, is prevalent in mangrove soils. Laboratory analyses were performed to investigate the four hypotheses of the “enzymic latch”. Results showed that under aerobic conditions mangroves soil samples have significantly higher phenol oxidase activity (two-fold, p < 0.05), but lower phosphatase activity (−33 %, p < 0.05), β-glucosidase activity (−14 %) and glucosaminidase activity (−11 %) compared to anaerobic conditions. Soil samples supplemented with phenol oxidase showed significantly lower phenolic concentration (−8.3 %, p < 0.01), but increased β-glucosidase (+79 %, p < 0.05), xylosidase (+99 %, p < 0.01) and glucosaminidase (+102 %, p < 0.01) activities. Supplementation of lignin-based solution significantly lowered β-glucosidase (−55 %, p < 0.001), sulphatase (−82 %, p < 0.001) and glucosaminidase (−45 %, p < 0.01) activities. Based on these findings, it is concluded that the “enzymic latch” is highly likely to play a key role in suppressing decomposition rates in red mangrove covered areas of mangrove swamps.

Peat origin and land use effects on microbial activity, respiration dynamics and exo-enzyme activities in drained peat soils in the Netherlands

This study assessed the risk of decomposition-driven soil subsidence in drained peat soils in the Netherlands, contrasting in peat origin and current land use. In a full factorial design, fen peat and bog peat were sampled from sites in use for nature conservation and for dairy farming, which contrast in history of drainage and fertilisation. In these four peat types, which frequently occur in the Netherlands, the microbial activity and respiration dynamics were studied in samples from superficial oxic peat layers by measuring Substrate Induced Respiration (SIR) and Substrate Induced Growth Response (SIGR). Total and active microbial biomass, microbial growth potential and potential exo-enzyme activities were determined in unamended samples and after nitrogen and/or glucose amendments.Remarkably, peat origin and land use did not affect basal respiration rates. In contrast, land use affected microbial biomass and potential growth rates as they were quadrupled in dairy meadows compared to nature reserves. This may be attributable to the pulses of organic and inorganic fertiliser that are being supplied in agricultural peatlands. Potential activities of oxidative exo-enzymes (phenol oxidase, POX, and phenol peroxidase, POD), in contrast, depended more on peat type, indicating a difference in peat substrate quality. Basal respiration rates and enzyme activities were not related. Phosphorus enrichment was identified as a potential driver of increased peat decomposition. The activity of the oxidative enzyme phenol oxidase and the concentration of phenolic compounds, which are considered to be the main regulators of peat decomposition according to the enzymic latch theory, were not related to respiration rates. It was concluded that decomposition theories like the enzymic latch theory (attributing a main role in the regulation of decomposition to phenolic compounds and phenol oxidase) were not supported by our research in the drained peat soils in the Netherlands.

Understanding drivers of peatland extracellular enzyme activity in the PEATcosm experiment: mixed evidence for enzymic latch hypothesis

Our objective was to assess the impacts of water table position and plant functional groups on peatland extracellular enzyme activity (EEA) framed within the context of the enzymic latch hypothesis. We utilized a full factorial experiment with 2 water table (WT) treatments (high and low) and 3 plant functional groups (PFG: Ericaceae, sedge, Ericaceae and sedge unmanipulated) in twenty-four 1 m3 intact peatland mesocosms. We measured bulk peat and porewater phase oxidative and hydrolytic enzyme activities monthly from June - October 2012. We also measured physical and porewater chemical constituents in tandem to analyze environmental influences on seasonal enzyme activities. No PFG effects on EEA with WT affecting only acid-phosphatase activity in porewater. Strong seasonal dynamics in EEAs overshadowed our manipulations. Analyses indicated phenolic concentrations were influenced by peat redox potential and negatively correlated with phenol oxidase activity as expected from enzymic latch hypothesis. However, no hydrolytic EEA was influenced by total phenolics, but driven largely by seasonal changes in soil temperature and increasing DOC concentrations in porewater. Our results suggest no support for final step in enzymic latch, in which phenolics are posited to regulate hydrolytic EEAs. Mechanisms regulating seasonal influences remain to be elucidated.

Short- and long-term effects of nutrient enrichment on microbial exoenzyme activity in mangrove peat

Mangroves receive increasing quantities of nutrients as a result of coastal development, which could lead to significant changes in carbon sequestration and soil subsidence. We hypothesised that mangrove-produced tannins induce a nitrogen (N) limitation on microbial decomposition even when plant growth is limited by phosphorus (P). As a result, increased N influx would lead to a net loss of sequestered carbon negating the ability to compensate for sea level rise in P-limited mangroves. To examine this, we quantified the short- and long-term effects of N and P enrichment on microbial biomass and decomposition-related enzyme activities in a Rhizophora mangle-dominated mangrove, which had been subjected to fertilisation treatments for a period of fifteen years. We compared microbial biomass, elemental stoichiometry and potential enzyme activity in dwarf and fringe-type R. mangle-dominated sites, where primary production is limited by P or N depending on the proximity to open water. Even in P-limited mangroves, microbial activity was N-limited as indicated by stoichiometry and an increase in enzymic activity upon N amendment. Nevertheless, microbial biomass increased upon field additions of P, indicating that the carbon supply played even a larger role. Furthermore, we found that P amendment suppressed phenol oxidase activity, while N amendment did not. The possible differential nutrient limitations of microbial decomposers versus primary producers implies that the direction of the effect of eutrophication on carbon sequestration is nutrient-specific. In addition, this study shows that phenol oxidase activities in this system decrease through P, possibly strengthening the enzymic latch effect of mangrove tannins. Furthermore, it is argued that the often used division between N-harvesting, P-harvesting, and carbon-harvesting exoenzymes needs to be reconsidered.

Short period of oxygenation releases latch on peat decomposition

Extreme summer droughts are expected to occur more often in the future in NW Europe due to climate change. These droughts might accelerate the rate of peat oxidation in drained peat areas, with impacts on soil subsidence, GHG emission and water quality. This study aimed at providing more insight in the oxidation of deep peat layers that had not previously been exposed to air, the so-called secondary decomposition.We incubated two types of peat (eutrophic and oligotrophic), sampled from permanently anoxic peat layers from nature reserves and agricultural peat meadows. Peat samples were incubated for thirteen weeks under anoxic conditions, but were exposed to air for one to eight weeks. The production of CO2 and CH4 was quantified as a proxy for decomposition; concentrations of soluble nutrients and phenolic compounds were also measured.The results showed that oxygenation led to a steep increase in the rate of decomposition, indicated by higher carbon loss rates during and after oxygenation compared to non-oxygenated samples. Carbon loss rates increased more for eutrophic peat (agricultural area: 352%, nature reserve: 182%) than for oligotrophic peat (83% and 159% respectively). Most peat samples investigated showed higher post-oxygenation CO2 and/or CH4 production compared to the anoxic pre-oxygenation period. This indicates that oxygenation stimulates decomposition, even after anoxic conditions have returned. Contrary to the enzymic latch theory, no effects of oxygenation on the concentrations of soluble or condensed phenolic compounds were detected. Soluble nutrient concentrations did not change due to oxygenation either. Noteworthy is the occurrence of pyrite mineralization and associated acidification in eutrophic peat. Thus, low summer water levels, for example due to climate change, should be avoided in order to limit exceptionally high decomposition rates and associated problems such as increasing subsidence rates, greenhouse gas emission, sulfate release and acidification.

Peatland geoengineering: an alternative approach to terrestrial carbon sequestration

Terrestrial and oceanic ecosystems contribute almost equally to the sequestration of ca 50 per cent of anthropogenic CO(2) emissions, and already play a role in minimizing our impact on Earth's climate. On land, the majority of the sequestered carbon enters soil carbon stores. Almost one-third of that soil carbon can be found in peatlands, an area covering just 2-3% of the Earth's landmass. Peatlands are thus well established as powerful agents of carbon capture and storage; the preservation of archaeological artefacts, such as ancient bog bodies, further attest to their exceptional preservative properties. Peatlands have higher carbon storage densities per unit ecosystem area than either the oceans or dry terrestrial systems. However, despite attempts over a number of years at enhancing carbon capture in the oceans or in land-based afforestation schemes, no attempt has yet been made to optimize peatland carbon storage capacity or even to harness peatlands to store externally captured carbon. Recent studies suggest that peatland carbon sequestration is due to the inhibitory effects of phenolic compounds that create an 'enzymic latch' on decomposition. Here, we propose to harness that mechanism in a series of peatland geoengineering strategies whereby molecular, biogeochemical, agronomical and afforestation approaches increase carbon capture and long-term sequestration in peat-forming terrestrial ecosystems.

Predicting the future DOC flux from upland peat catchments

This study reconstructs a long-term record of dissolved organic carbon (DOC) flux release from an upland peat catchment in Northern England in order to construct a model of future DOC flux. A structural modelling approach is used to develop models for DOC production in the acrotelm in relation to changing temperature and water table depth. DOC production in the acrotelm is coupled with a description of release of reserves of carbon from the catotelm triggered by enzymic latch mechanisms. The model needs only three parameters to be successfully matched to the data, with Nash-Sutcliffe efficiencies of over 90% against the reconstructed catchment record. Model results suggests that the half-life of the effect of drought on the catchment is 11.2 years and that the majority of DOC production comes from the acrotelm/catotelm boundary. Using the calibrated model and predictions of future rainfall and temperature, it is forecast that DOC flux from this peat-covered catchment will increase to 25 tonnes C/km 2 by 2010 at a rate of 0.48–0.88 tonnes C/km 2/year. These results imply a total DOC flux from UK rivers of 0.88–0.83 Mt C in 2002 and of the order of 1 Mt C by 2010. The implications for terrestrial carbon storage and water treatment are discussed.