Wednesday, November 15, 2006 - 2:20 PM

Litter-Driven Changes to Biopolymer Characteristics of Particulate Soil Organic Matter Fractions along a Chronosequence of Thorn Woodland Encroachment into Grasslands.

Timothy Filley, Purdue University, 550 Stadium Drive, West Lafayette, IN 47907-2051, Thomas Boutton, Texas A&M Univ.-Dept of Rangeland Ecol., Campus Mail Stop 2126, College Station, TX 77843-2126, Julia Liao, Texas A&M Univ.-Dept.Rangeland Ecol., College Station, TX 77843-2126, and Julie Jastrow, Argonne National Laboratory, Argonne, IL 60439, United States of America.

Subtropical mesquite thorn woodlands have encroached into the grasslands of the Rio Grande Plains of Texas over the last 150 years, resulting in accrual of SOM in the upper 15 cm. We examined how changing litter chemistry impacted the chemical nature of inter and intra-aggregate soil particulate organic matter (POM) along a grassland-to-woodland chronosequence.  To accomplish this, we determined the concentration and distribution of alkaline CuO released lignin phenols and cutin and suberin-derived substituted fatty acids (SFA) of the litter input and POM from the upper 15 cm in two (14 and 80 y old) honey mesquite-dominated woody clusters and a remnant grassland.  The transition from grass to woody input was accompanied by litter with higher contents of cutin and suberin-derived SFA components and higher levels of cinammyl-containing lignin.  All POM pools responded to this change, with the largest chemical shifts for lignin occurring in free (inter-aggregate) POM and the smallest in the microaggregate-occluded (53-250 mm) POM.  Over the chronosequence, accrued lignin took on a similar chemical character and concentration, regardless of location (i.e. inter- or intra-aggregated) or size.  SFA, which increased in concentration dramatically in all fractions, showed the most dramatic increases in aggregated POM, with the effect increasing with increasing particle size.  Overall, the changes in lignin and SFA among POM in the woody clusters were consistent with a system of limited chemical and physical protection capacity responding to increased above- and belowground production of plant tissues rich in recalcitrant biopolymers (e.g. lignin and aliphatic biopolymers).