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United States Department of Agriculture

Agricultural Research Service

Research Project: SOIL MANAGEMENT FOR ENHANCED AGRICULTURAL PRODUCTIVITY AND SUSTAINABLE BIOFUEL FEEDSTOCK PRODUCTION Title: Degree of woody encroachment into grasslands controls soil carbohydrate and amino compound changes during long-term laboratory incubation

Authors
item Creamer, Courtney -
item Filley, Timothy -
item Olk, Daniel
item Plant, Alaine -
item Peltre, Clement -
item Top, Sara -
item Boutton, Thomas -

Submitted to: Organic Geochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 7, 2012
Publication Date: August 14, 2012
Citation: Creamer, C.A., Filley, T.R., Olk, D.C., Plant, A., Peltre, C., Top, S.M., Boutton, T.W. 2012. Degree of woody encroachment into grasslands controls soil carbohydrate and amino compound changes during long-term laboratory incubation. Organic Geochemistry. 52:23-31. Available: http://www.sciencedirect.com/science/article/pii/S0146638012001714.

Interpretive Summary: Storage of carbon in soil benefits the soil and atmosphere in many ways, including improved soil fertility. Carbon accumulates in soil under woody shrubs that are gradually moving into grasslands worldwide, but the reasons for this accumulation are unknown, which complicates its management. To better understand the carbon accumulation, the types of carbon found in woody shrub soils and grassland soils in southern Texas were studied before and after a one-year incubation. We found that the carbon types did not entirely explain the amount of carbon lost from the soil during the incubation through microbial decomposition. Contributions of carbon types to this loss differed between the woody shrub soils and the grassland soils. Our findings indicate that carbon accumulation in soil is affected by several factors, which can vary in importance depending on the soil and vegetation. This knowledge will benefit managers of grassland soils and researchers who seek to understand the factors of soil carbon accumulation.

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.

Last Modified: 10/24/2014
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