Temperature sensitivity of soil enzymes along an elevation gradient in the Peruvian Andes

Andrew T Nottingham,Jeanette Whitaker,Niall P Mcnamara,Benjamin L Turner,Richard D Bardgett,Norma Salinas,Patrick Meir,Nick Ostle

doi:10.1007/s10533-015-0176-2

Abstract

Soil enzymes are catalysts of organic matter depolymerisation, which is of critical importance for ecosystem carbon (C) cycling. Better understanding of the sensitivity of enzymes to temperature will enable improved predictions of climate change impacts on soil C stocks. These impacts may be especially large in tropical montane forests, which contain large amounts of soil C. We determined the temperature sensitivity (Q10) of a range of hydrolytic and oxidative enzymes involved in organic matter cycling from soils along a 1900 m elevation gradient (a 10 °C mean annual temperature gradient) of tropical montane forest in the Peruvian Andes. We investigated whether the activity (Vmax) of selected enzymes: (i) exhibited a Q10 that varied with elevation and/or soil properties; and (ii) varied among enzymes and according to the complexity of the target substrate for C-degrading enzymes. The Q10 of Vmax for β-glucosidase and β-xylanase increased with increasing elevation and declining mean annual temperature. For all other enzymes, including cellobiohydrolase, N-acetyl β-glucosaminidase and phosphomonoesterase, the Q10 of Vmax did not vary linearly with elevation. Hydrolytic enzymes that degrade more complex C compounds had a greater Q10 of Vmax, but this pattern did not apply to oxidative enzymes because phenol oxidase had the lowest Q10 value of all enzymes studied here. Our findings suggest that regional differences in the temperature sensitivities of different enzyme classes may influence the terrestrial C cycle under future climate warming.

Highlights

Tropical forest soils contain 30 % of global soil carbon (C) (Jobbagy and Jackson 2000), a large portion of which is contained in montane forest soils due to low temperatures and slow rates of decomposition (Moser et al 2011; Zimmermann et al 2010c)
Given the lack of understanding of how climate warming will affect soil organic matter cycling in tropical montane forests, we investigated the temperature response of a range of enzymes involved in organic matter cycling (Table 1) along a tropical montane forest elevation gradient of 1900 m, where mean annual temperature (MAT) ranges from 7 °C at the highest site to 17 °C at the lowest site
The overall trend for all enzymes was a decrease in activity with elevation, which was approximately 100-fold after accounting for differences in soil C content among sites (Fig. 1; note log scale for enzyme activity)

Summary

Introduction

Tropical forest soils contain 30 % of global soil carbon (C) (Jobbagy and Jackson 2000), a large portion of which is contained in montane forest soils due to low temperatures and slow rates of decomposition (Moser et al 2011; Zimmermann et al 2010c). Microbial degradation of soil organic matter is one of the largest sources of atmospheric CO2 emissions, and is predicted to increase in the future as soil biochemical reaction rates accelerate with increasing global temperature (Davidson and Janssens 2006; Knorr et al 2005). This is of particular concern for tropical montane forests, which contain large soil C stocks and are predicted to warm considerably in the coming decades. The intrinsic temperature sensitivity of soil organic matter decomposition remains contentious, because it can be obscured by various environmental constraints (Davidson and Janssens 2006). We lack basic information on how the influence of soil

Methods

Results

Discussion

Conclusion