Responses of the Components of Northern Hardwood Soil Respiration to Experimental Warming and Moisture Additions.

As climate warms, the availability of soil moisture may play a critical role in determining the responses of the autotrophic and heterotrophic components of soil respiration.  The objective of this study was to assess changes in soil respiration in response to experimental soil warming and determine how this response was altered by the interacting effects of moisture availability.  We experimentally altered the soil environment of a sugar maple-dominated northern hardwood forest, using three replications of four treatments: control, soil warming (+ 4^oC), water addition (ambient + 30%) and warming plus water addition, using 10 by 10 m experimental plots.  Warming was initiated in later summer 2010.  Measurements from 2009 and 2010 indicate that no pre-treatment differences existed among the groups of plots designated to receive each experimental treatment.  After treatments were initiated, soil respiration was 66% greater for the warming and warming plus water treatments, and unchanged for the water only treatment.  These data are for a time period during when ambient soil moisture was plentiful, and thus the lack of effects for moisture addition is not surprising.  As additional data from warmer, drier part of the 2011 growing season becomes available, we anticipate significant interactive effects of the soil moisture manipulation.  We also are quantifying root biomass and respiration rates, microbial biomass, respiration and community composition, and soil enzyme activity and carbon content.  During the initial warming in 2010, root respiration increased with warming and especially with warming and water addition, thus its response did not mirror that for soil respiration.  As detailed data on responses for all of these factors becomes available, we will use this knowledge to improve our understanding of how the components of soil respiration respond to the interactive effects of temperature and moisture and the implications of these responses for long-term ecosystem carbon balance.