Fine root turnover and lifespan in the Eucalyptus grandis plantations established in Oxisol (Itatinga-SP)

Author(s)

George Rodrigues Lambais

• Document type: Doctoral Thesis
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Centro de Energia Nuclear na Agricultura (CENA/STB)
• Defense date: 2015-11-24

Examining board members

Plinio Barbosa de Camargo; Fabiano de Carvalho Balieiro; Roberto Botelho Ferraz Branco; José Leonardo de Moraes Gonçalves; Regina Celia de Matos Pires

• Advisor: Marisa de Cassia Piccolo

Abstract

Brazilian eucalyptus plantations are among the forest ecosystems in the world with the highest gross primary productivity (GPP). The total belowground carbon allocation, with mainly production and mortality of fine roots (diameter <= 2 mm), can account for 20-60% of GPP in forest ecosystems. This study aimed to evaluate the dynamic and lifespan of fine roots in E. grandis plantations (2-4 years old) established in Oxisol soils, using the non-destructive method of minirhizotrons (MR). The specific objectives of this study were divided into three chapters: i-) to evaluate the influence of soil texture (20 and 40% clay) in the dynamics of fine roots in the topsoil (0-30 cm); ii-) to study the dynamics of the fine roots in a sandy soil up to 6 m deep; iii-) to investigate the symbiotic associations of Eucalyptus fine roots (2 years old after planting) with arbuscular mycorrhizal fungi (AMF) in the upper soil layers for two contrasting soil textures, and ectomycorrhizal fungi (ECM) in deep layers of a sandy soil (4 years old after planting). Images at the interface soil-MR were taken fortnightly through a portable scanner within the MR tube over a period of two years. The WinRhizo Tron software was used to measure the length and diameter of the fine roots that appeared throughout the study period. Soil water contents were continuously monitored down to a depth of 10 m using CS615 sensors (Campbell). AMF and ECM were studied sampling soil cores. The MR technique showed that the soil texture direct influenced fine root growth in the 0-30 cm layer, with higher values in the sandy soil than in the clayey soil throughout the study period. After two years, the sandy soil reached a total cumulative length of 30 m m-2 image, which was twice as high as the clayey soil. At the same depth, fine roots had a greater colonization by AMF in the sandy soil compared to the clayey soil, with means of 38,5 and 10,5%, respectively. A weak correlation between relative extractable water and dynamics of fine roots was observed, whatever the soil texture and depth. The means of daily elongation of fine roots were 0,10 cm day-1 in the 0-2 m soil layers and 0,22 cm day-1 in the 2-6 m soil layer. The maximum daily root elongation throughout the soil profiles reached 3,5 cm day-1 at a depth of 5-6 m. A specie of ECM (Pisolithus) was identified through molecular analyzes at a depth 2-3 m. In general, the lifespan and the turnover rates of Eucalyptus fine roots were about 500 days and 0.70 yr-1, respectively, and the influences of soil texture and soil depth were not significant. The fine root longevity was significantly affected by the diameter class (< 0,3, 0,3-0,5 and 0,5-2,0 mm) and the mycorrhizal status, there was a significant difference in their longevity. The Eucalyptus trees exhibited a remarkably high capacity of soil exploration in the Oxisol studied (AU)

• FAPESP's process: 11/06412-3 - Fine root turnover in plantations in the Eucalyptus grandis in soils with different textures (Itatinga - SP)
• Grantee: George Rodrigues Lambais
• Support Opportunities: Scholarships in Brazil - Doctorate