Carbon-Degrading Enzyme Activities Stimulated by Increased Nutrient Availability in Arctic Tundra Soils

Abstract

Climate-induced warming of the Arctic tundra is expected to increase nutrient availability to soil microbes, which in turn may accelerate soil organic matter (SOM) decomposition. We increased nutrient availability via fertilization to investigate the microbial response via soil enzyme activities. Specifically, we measured potential activities of seven enzymes at four temperatures in three soil profiles (organic, organic/mineral interface, and mineral) from untreated native soils and from soils which had been fertilized with nitrogen (N) and phosphorus (P) since 1989 (23 years) and 2006 (six years). Fertilized plots within the 1989 site received annual additions of 10 g N⋅m-2⋅year-1 and 5 g P⋅m-2⋅year-1. Within the 2006 site, two fertilizer regimes were established – one in which plots received 5 g N⋅m-2⋅year-1 and 2.5 g P⋅m-2⋅year-1 and one in which plots received 10 g N⋅m-2⋅year-1 and 5 g P⋅m-2⋅year-1. The fertilization treatments increased activities of enzymes hydrolyzing carbon (C)-rich compounds but decreased phosphatase activities, especially in the organic soils. Activities of two enzymes that degrade N-rich compounds were not affected by the fertilization treatments. The fertilization treatments increased ratios of enzyme activities degrading C-rich compounds to those for N-rich compounds or phosphate, which could lead to changes in SOM chemistry over the long term and to losses of soil C. Accelerated SOM decomposition caused by increased nutrient availability could significantly offset predicted increased C fixation via stimulated net primary productivity in Arctic tundra ecosystems.

Neutral effect of nitrogen addition and negative effect of phosphorus addition on topsoil extracellular enzymatic activities in an alpine grassland ecosystem

“…This result did not support the resource allocation theory Keeler et al, 2008), which predicted that N addition would increase the activities of C-and P-cycling enzymes, but suppress the activity of N-cycling enzymes. The lack of a N addition effect on soil enzymes in this study was unexpected, given that the amount of N we added was at the high end of N-addition experiments and that a positive effect of N addition on C-and P-acquiring enzymes has often been observed in other ecosystems (e.g., Koyama et al, 2013;Saiya-Cork et al, 2002;Wang et al, 2008). However, Bell et al (2010) also found that soil enzyme activity was unresponsive to N addition across all seasons in a temperate old field.…”

“…Increased nutrient availability often has multiple effects on aboveground organisms, including biodiversity loss (Hooper et al, 2012) and their associated ecosystem functioning and services (Isbell et al, 2013;Smith et al, 1999). Meanwhile, nutrient availability can be amplified by climate warming by enhancing microbial decomposition of soil organic matter (Bardgett et al, 2008) which, in turn, stimulates plant growth and mediates ecosystem carbon storage (Koyama et al, 2013;Mack et al, 2004;Waldrop et al, 2004). However, the responses of belowground microorganisms to nutrient addition remains poorly understood (Leff et al, 2015).…”

Decoupled above‐ and belowground responses to multi‐decadal nitrogen and phosphorus amendments in two tundra ecosystems

“…), including these same soils with NP addition in an earlier study (Koyama et al. ). In fact, this P‐acquisition response to P amendments is more common than C‐ or N‐acquisition responses in the literature (reviewed in Burns et al.…”

“…, Koyama et al. ), and to a limited extent, above‐ and belowground combined (Chapin et al. , Gough et al.…”

Imbalanced nutrient recycling in a warmer ocean driven by differential response of extracellular enzymatic activities

“…However, these values of sensitivity to temperature correspond to the cold‐adapted communities and enzymes of Arctic seawater, and they are expected to be higher than those of temperate waters since cold‐adapted enzymes tend to be more responsive to increasing temperature than warm‐adapted enzymes (German, Marcelo, Stone, & Allison, ). Additional information about the sensitivity to temperature of βG activity is available from studies of terrestrial systems ( E a ranging 0.27–0.72 eV, (Trasar‐Cepeda, Gil‐Sotres, & Leirós, ; Wallenstein, Mcmahon, & Schimel, ; German et al., ; Stone et al., ; Steinweg, Jagadanna, Frerichs, & Mayes, ; Koyama, Wallenstein, Simpson, & Moore, ; Bárta, Šlajsová, Tahovská, Picek, & Šantrůčková, )) while much fewer data are available for LAP ( E a ranging −0.33 to 0.62 eV, (Wallenstein et al., ; Koyama et al., ; Bárta et al., )) or AP ( E a ranging 0.39–0.48 eV, (Bárta et al., )). Maybe the striking lack of data for marine systems arises from the general consideration of the temperature as a sparse driver of the extracellular enzyme activity when characterizing the carbon and nutrient cycling in the marine environments (Arnosti et al., ) while being considered as fundamental driver in terrestrial systems.…”