Zhang, Qian, Boutton, Thomas W., Hsiao, Che-Jen, Mushinski, Ryan , Wang, Liming, Bol, Roland and Klumpp, Erwin (2023) Soil colloidal particles in a subtropical savanna : biogeochemical significance and influence of anthropogenic disturbances. Geoderma, 430 . 116282. doi:10.1016/j.geoderma.2022.116282 ISSN 0016-7061.

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Abstract

Soil colloids (diameter < 1000 nm) are comprised mainly of clay minerals and organic matter, and play major roles in determining ion exchange capacity and in regulating key biogeochemical processes. Consequently, it is important to understand how soil colloids and their functions are influenced by land cover and anthropogenic disturbances. In grasslands, savannas, and other dryland ecosystems across the globe, woody plants are encroaching due to livestock grazing, fire suppression, elevated CO2 concentrations, and climate change. These major land cover changes could influence soil colloidal properties, with implications for soil C, N, and P cycles. We assessed how woody encroachment, livestock grazing, and fire interact to influence soil colloidal properties in a juniper-oak savanna. Surface soils (0–10 cm) from the southern Great Plains (Texas, USA) were collected from long-term treatments differing in grazing intensity (none, moderate, and heavy) and fire history. Within each treatment, soil samples were taken under grass, juniper, and oak canopies. Water dispersible soil colloids (WDC, d < 500 nm) were isolated and analyzed by asymmetric flow field-flow fractionation and their P species by liquid-state 31P-nuclear magnetic resonance spectroscopy (31P NMR). Soil beneath oak and juniper canopies had smaller WDC and elevated colloidal organic carbon (OC) and P concentrations, especially in nanocolloid (<30 nm) and fine colloid (30–160 nm) size fractions. Woody encroachment enriched Ca, Fe, Al, Si and Mg in WDC in the ungrazed control, but not in any of the other grazed or burned areas. Colloidal soil P mainly occurred as orthophosphate and orthophosphate diesters, and was present as OC-Ca-P complexes in fine and medium colloid fractions (30–500 nm), while P in the nanocolloid fraction (<30 nm) was in direct association with Ca. Moderate grazing did not affect the retention of colloidal P, while heavy grazing potentially increased the loss risk of colloidal P. Fire accelerated soil P loss from colloid fractions only in woody areas. Our findings highlight that woody encroachment strengthens the retention of OC and P by soil colloids, consequently increasing overall C and P pools in savanna soils.

Item Type:	Journal Article
Subjects:	S Agriculture > S Agriculture (General)
Divisions:	Faculty of Science, Engineering and Medicine > Science > Life Sciences (2010- )
Library of Congress Subject Headings (LCSH):	Soil colloids , Soil absorption and adsorption, Soil management -- Southern States, Soil science
Journal or Publication Title:	Geoderma
Publisher:	Elsevier
ISSN:	0016-7061
Official Date:	February 2023
Dates:	Date Event February 2023 Published 30 November 2022 Available 18 November 2022 Accepted
Volume:	430
Article Number:	116282
DOI:	10.1016/j.geoderma.2022.116282
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Open Access (Creative Commons)
Date of first compliant deposit:	1 February 2023
Date of first compliant Open Access:	1 February 2023
RIOXX Funder/Project Grant:	Project/Grant ID RIOXX Funder Name Funder ID 201608420100 China Scholarship Council http://dx.doi.org/10.13039/501100004543 1003961 (Hatch Project) National Institute of Food and Agriculture http://dx.doi.org/10.13039/100005825 UNSPECIFIED Texas A and M University-Kingsville http://dx.doi.org/10.13039/100010859

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