Mineral changes in the rhizospheres of conifer plantations for a weathered subtropical soil

Authors: HUMMES, ANA PAULA - Orise Fellow; INDA, ALBERTO - University Of Rio Grande Do Sul; Olk, Daniel - Dan; BORTOLUZZI, EDSON - University Of Rio Grande Do Sul

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2024
Publication Date: 4/26/2024
Citation: Hummes, A.P., Inda, A.V., Olk, D.C., Bortoluzzi, E.C. 2024. Mineral changes in the rhizospheres of conifer plantations for a weathered subtropical soil. Soil Science Society of America Journal. https://doi.org/10.1002/saj2.20682.
DOI: https://doi.org/10.1002/saj2.20682

Interpretive Summary: Growing plants can change the properties of their underlying soils, sometimes for the worse. We compared the effects of an imported American pine tree that was grown for wood production on Brazilian soils compared to a local Brazilian tree either grown also for wood production or found in its natural woodland. Our results showed that the local Brazilian tree when grown for wood production better restored soil properties toward their natural state under the natural woodland, while the imported pine tree caused greater changes in soil properties, including faster degradation. These results suggest that imported species might have greater potential to alter local soil conditions than do local species. They illustrate one potential concern when importing foreign species. These results are of interest to managers of tree farms and to soil scientists.

Technical Abstract: The rhizosphere is more susceptible to biochemical and physicochemical responses to external inputs than is the surrounding bulk soil, and by extents and speeds that depend on several factors. The purpose of this study is to examine the physical, chemical and mineralogical aspects of the rhizosphere and bulk soil, in two conifer monocultures grown on a highly weathered subtropical soil in Brazil. The rhizosphere effects of the native araucaria (Araucaria angustifolia) and the exotic slash pine (Pinus elliottii) in long-term monocultures were investigated, while araucaria trees in a natural section of the forest served as the control. The rhizosphere chemical attributes were similar in araucaria and slash pine plantations, but total organic matter and available phosphorus levels were lower in slash pine than in the control. No differences were detected in silt and clay contents between rhizosphere and bulk soil for all sites. However, slash pine promoted silt decrease and clay increase in the rhizosphere compared to the control. Silt content in the araucaria monoculture was the same as in the control, while clay content was lower. The clay mineral assemblage comprised kaolinite, illite and hydroxy-interlayered minerals, with kaolinite enrichment in the rhizospheres of araucaria and in pine soil, illite depletion in slash pine soil and in araucaria rhizosphere, high crystalline iron oxide in slash pine soil, and differences in the relative proportions of mineral composition among sites. This study demonstrated an acceleration of soil weathering by conifer monocultures, with araucaria monoculture tending to restore soil properties toward the native forest, while slash pine tending to cause more negative impacts to soil.