Nitrogen and phosphorus regulation of soil enzyme activities in acid forest soils

Published Date

July 2016, Vol.98:171–179, doi:10.1016/j.soilbio.2016.02.017

Title 

Nitrogen and phosphorus regulation of soil enzyme activities in acid forest soils

• Author 

• Farrah R. Fatemi ^a,,
• Ivan J. Fernandez ^b
• Kevin S. Simon ^c
• David Bryan Dail ^d

• aSt. Michael's College, One Winooski Dr., Colchester, VT 05439, USA
• bSchool of Forest Resources and Climate Change Institute, University of Maine, Orono, ME, USA
• cSchool of Environment, The University of Auckland, New Zealand
• dSurface Water Quality Bureau, Santa, Fe, NM, USA

Received 31 March 2015. Revised 22 February 2016. Accepted 27 February 2016. Available online 28 April 2016.

Highlights

• •
  Chronic N enrichment typically suppressed soil hydrolytic enzyme activity.
• •
  Microbial C and P acquisition are regulated more by P than N.
• •
  Softwood soils may be more sensitive to changes in P than hardwood soils.

Abstract

The activities of soil extracellular enzymes are important in governing rates of organic matter decomposition and nutrient cycling in forest ecosystems. Measurements of soil enzyme activities can provide insights on microbial function, in terms of how much energy microbial communities are investing to acquire particular nutrients from OM substrates. In ecosystems enriched with nitrogen (N), phosphorus (P) supply may play an important role in regulating microbial activity, enzyme production, and organic matter decomposition. The response of extracellular enzyme activity to chronic N-enrichment was assessed at a long-term paired watershed N-enrichment experiment, the Bear Brook Watershed in Maine (BBWM) in hardwood and softwood forest types. Specifically, we measured the ambient (extant) activity of C hydrolyzing β-glucosidase (BG) and xylosidase (XYLO), N hydrolyzing N-acetylglucosaminidase (NAG), and P hydrolyzing acid phosphatase (AP) in the watershed subjected to chronic N-enrichment, and in the reference watershed. Secondly, in a series of soil incubations, we characterized the extent to which microbial C and P acquisition were regulated by N and P availability. In these incubations, we measured BG and AP activity response to acute (high-dose fertilizer) nutrient amendments. We hypothesized that soil enzyme activities would respond more to enhanced P availability than N, particularly in the N-enriched watershed. Our results from extant enzyme activity measurements suggest that chronic N-enrichment inhibited rather than stimulated extant soil hydrolytic enzyme activities, which could reflect suppression of microbial biomass and activity. In the acute nutrient amendment incubations, our data indicate that inorganic P was more important than N in regulating soil microbial C and P acquisition in soils from both the N-enriched and reference watersheds. Our results also indicate that the extent to which P availability regulated microbial acquisition of P in O horizon soils was greatest in softwood soils subjected to chronic N-enrichment. Findings from this study suggest that both forest type and soil inorganic P availability could be more important in influencing soil biological response to N pollution than previously recognized.

Keywords

• Microbial enzymes
• Acid phosphatase
• Phosphorus
• Nitrogen enrichment
• Paired watershed experiment

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• ∗ 
  Corresponding author.

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