Technical Abstract: Up to 50% of organic C and 80% of organic N within soils can exist as amino acids, amino sugars, and carbohydrates. When not strongly bound to soil minerals or protected within stable aggregates, these compounds classes are considered relatively labile and useful indicators of soil organic matter (SOM) quality, and should be selectively decomposed during long-term soil incubations. We investigated changes in evolved CO2 profiles during thermal analysis and carbohydrate and amino compound chemistry during a year-long incubation of sandy loam grassland and woodland soils from southern Texas. Thermal analyses showed accumulations of SOM released at higher temperatures after incubation and correlations with measured increases in amino-C. Total carbohydrate-C decreased slightly faster than bulk soil C, and there were preferential losses of plant-derived carbohydrates and/or production of microbial carbohydrates during incubation, most strongly expressed in grasslands and younger woodland soils. Total N content did not change during incubation, so the reduction in extractable amino-N in older woodland soils suggested N became more chemically resistant during incubation. These data, along with previous measurements of respired CO2, indicate that changes in carbohydrate-C and amino-C did not predict mineralized CO2 yields, and that amino compounds and microbial carbohydrate-C were not selectively lost during incubation. The differing response in SOM loss (or enrichment) during incubation of the older woodland soils reveals a system with fundamentally different SOM dynamics due to woody encroachment, confirming that the "lability" or "recalcitrance" of SOM components is dependent on a number of interacting variables.