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The goal of this work was to assess soil microbial respiration,determined by the assay of community-level physiological profiling in an oxygen-sensitive microplate(O2-CLPP),in response to endogenous C and several individual C substrates in the soils with different organic C contents(as a function of soil type and management practice).We also used the O2-CLPP to determine the respiratory response of these soils to endogenous C and amended C substrates with N addition.A respiratory quotient(RQ) was calculated based on the ratio of the response to endogenous soil C vs.each C-only substrate,and was related to total organic carbon(TOC).For assessing N availability for microbial activity,the effect of N supplementation on soil respiration,expressed as N_(ratio),was calculated based on the response of several substrates to N addition relative to the response without N.Soils clustered in 4 groups after a principal component analysis(PCA),based on TOC and their respiratory responses to substrates and endogenous C.These groups reflected differences among soils in their geographic origin,land use and C content.Calculated RQ values were significantly lower in natural forest soils than in managed soils for most C-only substrates.TOC was negatively correlated with RQ(r = —0.65),indicating that the soils with higher organic matter content increased respiratory efficiency.The N addition in the assay in the absence of C amendment(i.e.,only endogenous soil C present) had no effect on microbial respiration in any soil,indicating that these soils were not intrinsically N-limited,but substrate-dependent variation in N_(ratio) within soil groups was observed.
The goal of this work was to assess soil microbial respiration, determined by the assay of community-level physiological profiling in an oxygen-sensitive microplate (O2-CLPP), in response to endogenous C and several individual C substrates in the soils with different organic C contents (as a function of soil type and management practice) .We also used the O2-CLPP to determine the respiratory response of these soils to endogenous C and amended C substrates with N addition. A respiratory quotient (RQ) was calculated based on the ratio of the response to endogenous soil C vs.ach C-only substrate, and was related to total organic carbon (TOC) .For assessing N availability for microbial activity, the effect of N supplementation on soil respiration, expressed as N_ (ratio ), was calculated based on the response of several substrates to N addition relative to the response without N. Ofils clustered in 4 groups after a principal component analysis (PCA), based on TOC and their respiratory responses to substrat es and endogenous C. These groups reflected differences among soils in their geographic origin, land use and C content. Calculated RQ values were significantly lower in natural forest soils than in managed soils for most C-only substrates. TOC was negatively correlated with RQ ( r = -0.65), indicating that the soils with higher organic matter content increased respiratory efficiency. N addition in the assay in the absence of C amendment (ie, only endogenous soil C present) had no effect on microbial respiration in any soil, indicating that these soils were not intrinsically N-limited, but substrate-dependent variation in N_ (ratio) within soil groups was observed.