Soil respiration variations respond to microclimate variations in biofuel crop ecosystems
Global warming, not only the increase of average temperature but also the increasing frequency and severity of extreme events, has been widely discussed in the past decades. It may change the metabolism of natural and agricultural ecosystems. However, how the climate variation affects biofuel crop ecosystems is still barely known. Biofuels, assumed to neutralize carbon emissions in fossil fuel combustion, have long been debated because that the production of bioenergy may release a huge quantity of carbon dioxide especially during the processes of land use conversion from reserved or agricultural lands to biofuel farms. Soil respiration (Rs), as the major carbon emission parts in agricultural ecosystem, plays an important role on carbon budget. How it responds to climate variation underneath different biofuel crop types and land use histories may affect the amount of carbon emission when there is a dramatic increasing conversion to biofuel productions from reserved or other agricultural land uses.
To answer this question, we conducted research in Kellogg Biological Station, MI. Two types of land use histories (brome grass under Conservation Reserve Program (CRP) and corn-soybean rotation farms (AGR)) were converted to three no-tillage crops (corn (C), switchgrass (Sw) and local prairie matrix (Pr)), respectively, in addition to a non-disturbed CRP reference site in 2010. Rs, with microclimate variables (i.e., soil temperature (Ts) and soil moisture (VWC)) were monitored biweekly during growing season from the second year after land use conversion. We estimated seasonal patterns of soil respiration, soil temperature and soil moisture by the application of trigonometric mathematics and searching for parameter values based on Maximum Likelihood Estimates. Based on MLE results, we obtained residuals of Rs and Ts. By doing this, we are able to analyze whether soil respirations of certain biocrops are sensitive to soil temperature deviations.
We discovered that, among the seven plots, only Rs from corn production with CRP history was sensitive to soil temperature and soil water content deviations. In this case, soil respiration decreases then predicted when the deviations of soil water content decreases and the deviations of soil temperature increases. Other sites does not find visual relationship in other sites. Our results implied that soil respiration is more sensitive to soil water content in annual crop (corn) farms with high soil carbon and nitrogen contents (CRP history) than those in other lands. Soil respiration in perennial cellulosic crop farms is more stable than that in corn farms.