Biogeochemical Hotspots in Forested Landscapes: The Role of Vernal Pools in Denitrification and Organic Matter Processing
- 759 Downloads
Quantifying spatial and temporal heterogeneity in ecosystem processes presents a challenge for conserving ecosystem function across landscapes. In particular, many ecosystems contain small features that play larger roles in ecosystem processes than their size would indicate; thus, they may represent “hotspots” of activity relative to their surroundings. Biogeochemical hotspots are characterized as small features within a landscape that show comparatively high chemical reaction rates. In northeastern forests in North America, vernal pools are abundant, small features that typically fill in spring with snow melt and precipitation and dry by the end of summer. Ephemeral flooding alters soil moisture and the depth of the soil’s oxic/anoxic boundary, which may affect biogeochemical processes. We studied the effects of vernal pools on leaf-litter decomposition rates, soil enzyme activity, and denitrification in vernal pools to assess whether they function as biogeochemical hotspots. Our results indicate that seasonal inundation enhanced leaf-litter decomposition, denitrification, and enzyme activity in vernal pools relative to adjacent forest sites. Leaves in seasonally flooded areas decomposed faster than leaves in terra firme forest sites. Flooding also influenced the C, N, and P stoichiometry of decomposing leaf litter and explained the variance in microbial extracellular enzyme activity for phosphatase, β-d-glucosidase, and β-N-acetylglucosaminidase. Additionally, denitrification rates were enhanced by seasonal flooding across all of the study pools. Collectively, these data suggest that vernal pool ecosystems may function as hotspots of leaf-litter decomposition and denitrification and play a significant role in decomposition and nutrient dynamics relative to their size.
Keywordsephemeral wetland biogeochemical hotspot leaf-litter decomposition denitrification soil enzymes
We would like to thank Dennis Anderson for help in the lab and Randi Jackson for help in the field. This work was funded by Maine’s Sustainability Solutions Initiative (National Science Foundation Award Number: 0904155). We would also like to thank the subject editor and the anonymous reviewers who provided comments that enhanced the quality of this manuscript.
- APHA. 1998. Standard methods for the examination of water and waste water. Association APH editor. Washington, DC: American Water Works Association and Water Environment Federation. p 1268.Google Scholar
- Bell CW, Fricks BE, Rocca JD, Steinweg JM, McMahon SK, Wallenstein MD. 2013. High-throughput fluorometric measurement of potential soil extracellular enzyme activities. J Vis Exp. http://www.jove.com/video/50961/high-throughput-fluorometric-measurement-potential-soil-extracellular.
- Brady NC, Weil RR. 2007. The nature and properties of soils. Lebanon: Prentice Hall.Google Scholar
- Calhoun A, deMaynadier PG. 2008. Science and conservation of vernal pools in northeastern North America. Boca Raton: CRC Press.Google Scholar
- Chrost RJ, Ed. 1991. Microbial enzymes in aquatic environments. New York: Springer.Google Scholar
- Cisneros-Dozal LM, Trumbore SE, Hanson PJ. 2007. Effect of moisture on leaf litter decomposition and its contribution to soil respiration in a temperate forest. J Geophys Res Biogeosci 112:10.Google Scholar
- Fernandez IJ. 2008. Carbon and nutrients in Maine forest soils. Station MAaFE editor. Technical Bulletin. Orono: Maine Agricultural and Forest Experiment Station.Google Scholar
- Groffman P, Holland EA, Myrold DD, Robertson GP, Zou X. 1999. Denitrification. In: Robertson GP, Coleman DC, Bledsoe CS, Sollins P, Eds. Standard soil methods for long-term ecological research. Oxford: Oxford University Press. Google Scholar
- Hunter ML Jr. 1991. Coping with ignorance: the coarse-filter strategy for maintaining biodiversity. Washington, DC): Island Press. pp 266–81.Google Scholar
- Langhans SD, Tiegs SD, Uehlinger U, Tockner K. 2006. Environmental heterogeneity controls organic-matter dynamics in river-floodplain ecosystems. Pol J Ecol 54:675–80.Google Scholar
- Lovett GM, Jones C, Turner MG, Weathers KC, Eds. 2005. Ecosystem function in heterogenous landscapes. New York: Springer.Google Scholar
- Mulholland PJ, Hall RO, Sobota DJ, Dodds WK, Findlay SEG, Grimm NB, Hamilton SK, McDowell WH, O’Brien JM, Tank JL, Ashkenas LR, Cooper LW, Dahm CN, Gregory SV, Johnson SL, Meyer JL, Peterson BJ, Poole GC, Valett HM, Webster JR, Arango CP, Beaulieu JJ, Bernot MJ, Burgin AJ, Crenshaw CL, Helton AM, Johnson LT, Niederlehner BR, Potter JD, Sheibley RW, Thomas SM. 2009. Nitrate removal in stream ecosystems measured by N-15 addition experiments: denitrification. Limnol Oceanogr 54:666–80.CrossRefGoogle Scholar
- Palmer MA, Febria CM. 2012. The heartbeat of ecosystems. Sci China C 336:1393–4.Google Scholar