Alterations in the rhizosphere of conifer plantations on ferrasol within the araucaria forest domain

Abstract

The introduction of extensive tree plantations brings recognized economic benefits at the expenses of natural environments. The native Araucaria angustifolia (araucaria) and the fast-growing exotic Pinus elliottii var. elliottii (slash pine), when cultivated in monoculture, may affect differently the soil related to araucaria grown in its native environment, the Mixed Ombrophilous Forest, also called Araucaria Forest. The differences are influenced by environmental conditions, plant species and their associate microorganism, and soil mineral composition. Understanding how forest plantations affect the soil may ensure the sustainability of timber production. In order to investigate the impact of these conifers on soil geochemical and mineral evolution, especially in the rhizosphere where processes are more intense and changes occur in shorter periods of time, the present study was conducted in three instances. Chapter I: A meta-analysis of physical and chemical changes in the rhizosphere and bulk soil under woodlands, which consists of a systematic review on physical and chemical changes in rhizosphere and bulk soil promoted by conifers and broadleaved trees, established as monoculture or grown in mixed forest fragments. The soil attributes pH, phosphorus, potassium, calcium, aluminum, effective cation exchange capacity, total organic carbon and particle-size distribution were gathered from thirty-two manuscripts (170 studies from 8 countries) published in peer-reviewed journals indexed to Science Direct Core Collection from January 2000 to July 2020. The conclusion was that the influence of conifers and monocultures on soil properties is greater than broadleaved trees and establishment in mixed forests. Chapter II: Higher mineral weathering of a Ferralsol evidenced in the rhizosphere of conifer plantations grown in a subtropical climate seeks to apprise the rhizosphere effect on geochemical changes and mineralogical evolution of a deep and high weathered Ferralsol under two conifer plantations, Araucaria angustifolia and Pinus elliottii var. elliottii. It was studied the rhizosphere effect related to bulk soil, and how monoculture of the two conifers affected the soil physical, chemical and mineralogical properties. Araucaria did not affect chemical attributes, but slash pine affected total organic carbon and available phosphorus. No rhizosphere effect was observed for silt and clay content, but slash pine promoted silt decrease followed by clay increase, while in araucaria the opposite was observed. The soil did not show a broad mineral assemblage, but presented variations in the proportions of clay minerals, comprising kaolinite, illite and hydroxy-interlayered minerals (HIM), with kaolinite-enrichment in the rhizosphere and in pinus, with illite absence in slash pine soil. The proportion of crystalline iron oxides was higher in slash pine. This study evidences acceleration of soil weathering by monoculture of conifers, with higher rates in slash pine followed by araucaria, increasing the risk of soil quality loss when compared with the native Araucaria soil. Chapter III: Edaphic changes in sustainable use conifer plantations within the Mixed Ombrophylous Forest domain shows how chemical, physical and microbiological soil attributes are affected when monocultures of Araucaria angustifolia and Pinus elliottii var. elliottii are established in a high weathered Latossol within the Mixed Ombrophilous Forest ecosystem, and the importance of the sustainable managed Brazilian National Forests in protecting the natural ecosystems and hosting biodiversity. Soil was characterized in its physical (sand, silt, clay, bulk density, soil particle density and total soil porosity), chemical (pH, Al3+, H++Al3+, total organic carbon, K+, Ca2+, Mg2+, available P, total cation exchange capacity and base saturation) and microbiological (soil basal respiration, microbial biomass carbon, metabolic and microbial quotients) attributes, with slight changes in soil under the two conifers detected by univariate statistical analysis. However, multivariate analysis highlighted different impact of coniferous on soil by discriminating the clusters. The claying process promoted by slash pine suggests higher weathering rate by the activity of this conifer. This doctoral research shows that studies on the rhizosphere of trees are feasible to detect and monitor short-term impact of long-lived woody species on soil, which can be further investigated especially on the interactions between microorganisms and clay minerals.