T338 Rock Transforming to Soil—The Weathering Engine Intersects with the Carbon Cycle

Wednesday, 25 October 2017
1:30 PM - 5:30 PM
Skagit 3

EFFECTS OF ROOT AND RHIZOSPHERE PROCESSES ON DEEP SOILS AND BEDROCK

Paper number: T338-6
Program: Technical Sessions
Time: 2:45 PM – 3:00 PM

Authors

Abstract

The A-horizon of soil is continually subjected to rhizospheric processes of growing roots. As roots senesce the root and its rhizosphere are mixed back into the bulk soil through bioturbation and decomposition processes. Below the zone of bioturbation there are fewer roots; however when these deep roots senesce and decay the physical and biogeochemical changes induced by root processes remain, marking the passage of the root through the deep soil. Rhizospheric zones below bioturbated soil persist as regions of higher carbon content, secondary mineral formation, and weathered primary minerals.

SOM accumulation and stabilization over time is an important process as soils are a large carbon reservoir. The association of SOM with poorly crystalline or short-range-ordered secondary minerals is important for carbon stabilization. Fate of root exudates in deep soil and processes controlling the extent and spatial association of exudates with mineral phases are as yet undefined. We employ a variety of scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) techniques to image rhizosphere and associated carbon-mineral interactions. Sub-micron exploration of field relations provides valuable information on SOM-mineral interactions.

Soils of the Santa Cruz marine terrace chronosequence are used to illustrate changes in deep rhizosphere (> 1m) through time. Cracks and soil ped faces are often covered by a network of roots embedded in organic deposits (biofilm). In these soils microscopy reveals secondary clay minerals associated with and perhaps forming in organic-rich biofilms that occur along rooting zones (rhizosphere). We hypothesize that the synthesis of secondary clays in the rhizosphere is a mode of C incorporation in secondary minerals.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-299098

© Copyright 2017 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.