Abstract
Peatland ecosystems contain one-third of the world’s soil carbon store and many have been exposed to drought leading to a loss of carbon. Understanding biogeochemical mechanisms affecting decomposition in peatlands is essential for improving resilience of ecosystem function to predicted climate change. We investigated biogeochemical changes along a chronosequence of hydrological restoration (dry eroded gully, drain-blocked <2 years, drain blocked <7 years and wet pristine site), and examined whether hydrological legacy alters the response of β-glucosidase kinetics (i.e. type of inhibition) to short-term drying and waterlogging. In the dry eroded gully at depth, low phenolic concentrations were associated with enhanced β-glucosidase enzyme activities (Vmax) but short-term drying and waterlogging caused a significant increase of dissolved organic carbon (DOC) and phenolics associated with increases in Vmax (enzyme production) and Km (indicative of competitive inhibition). Inhibition within the drain blocked and pristine sites at depth exhibited non-competitive inhibition (decreased Vmax), whilst uncompetitive inhibition (decreased Vmax and Km) occurred in surface peat explained by variation in humic substances and phenolics. These results suggest that loss of carbon by short-term drought or rewetting may occur from sites with a legacy of drought due to the release of non-inhibitory phenolics that permits enhanced enzyme activity.
Highlights
Peatland ecosystems contain one-third of the world’s soil carbon store and are a significant component of the global carbon cycle[1]
Baseline gravimetric water content was significantly lower in eroded gully (EG) compared to Ditch-blocked
Surface soil organic matter (SOM) content was significantly lower in EG (P < 0.005) and drain blocked
Summary
Peatland ecosystems contain one-third of the world’s soil carbon store and are a significant component of the global carbon cycle[1]. Decomposition of OM and ultimate CO2 release depend on the combined response of extracellular and intracellular (microbial), enzymatically mediated reactions[14] Extracellular enzymes such as β-glucosidase catalyze the initial enzymatic hydrolysis of a variety of complex polysaccharides in peat to simple monomers (i.e. glucose) that can be transported actively www.nature.com/scientificreports/. Freeman et al and Fenner & Freeman describe in detail the enzyme latch mechanism responsible for decomposition of peat, in which oxygen (O2) constraints on the enzyme phenol oxidase prevent the decomposition of peatland carbon due to phenolic compounds inhibiting hydrolase enzymes[17, 18] This enzymic latch sits within a regulatory pathway of process-specific limitations, which are sequentially removed as drought proceeds, constituting a biogeochemical cascade with potent positive feedbacks to carbon loss[18]. Change in Vmax and Km may reflect shifts in the microbial community structure[36, 37] such as the bacterial-to-fungal ratio that may alter carbon allocation to the extracellular enzyme pool affecting the kinetic characteristics such as more rapid conformational changes[14]
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