Impact of harvest residue management systems on soil structure and microbial communities under eucalyptus plantations

• Grant number: 19/11867-1
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate
• Start date: September 01, 2019
• End date: June 30, 2020
• Field of knowledge: Agronomical Sciences - Agronomy - Soil Science
• Principal Investigator: Kátia Luciene Maltoni
• Grantee: Karla Nascimento Sena
• Supervisor: Engil Isadora Pujol Pereira
• Host Institution: Faculdade de Engenharia (FEIS). Universidade Estadual Paulista (UNESP). Campus de Ilha Solteira. Ilha Solteira , SP, Brazil
• Institution abroad: University of Texas Rio Grande Valley (UTRGV), United States
• Associated to the scholarship: 17/14049-2 - Effects of eucalyptus cultivation on soil attributes and productivity on sandy soils, BP.DR

Abstract

It is known that organic matter improves soil aggregation, particularly when soils are sandy, however the stabilization of these aggregates is only possible by the connection between organic materials and mineral particles, which can be reached via root action, hyphae of fungi, or other microorganisms combinations (TISDALL; OADES, 1982). Thus, the management of sandy soils demands special attention, and even under eucalyptus cultivation, now considered a conservative land-use system, since soil tillage is reduced, has not been shown to be effective in the maintenance of organic matter in the soil, in certain situations, which demands, besides the reduction of mechanization, a better definition of the residue management from the eucalyptus harvest, which can contribute to increase the amount of soil organic matter, pH, the time of residence of this, increase the stability of the soil aggregates, the input of nutrients, activities of a diverse microbial community and other benefits (GAMA-RODRIGUES et al., 2005; BRONICK; LAL, 2005; YANG et al., 2019)The formation of aggregates, i.e., water-stable soil size classes with intrinsic varying physical and chemical characteristics (ELLIOTT, 1986), leads to the physical protection of C from mineralization by microorganisms (BALESDENT et al., 2000; SCHIMEL; SCHAEFFER, 2012). During the formation of aggregates, inter-aggregate organic matter is incorporated (SIX et al., 2004). Considering that physical access to occluded substrates is a limiting factor for organic matter breakdown in mineral soils (SCHIMEL; SCHAEFFER, 2012; TISDALL; OADES, 1982) this incorporation of organic matter into aggregates can contribute to longer term soil C sequestration (KONG et al., 2005). Soil aggregates, which are composed of primary particles and binding agents, are the basic units of soil structure (BRONICK; LAL, 2005). Soil aggregates are conventionally sub-divided into macro-aggregates (> 0.25 mm) and micro-aggregates (< 0.25 mm). Soil organic carbon (SOC) consists of various functional pools that are stabilized by soil aggregates (LUTZOW et al., 2007). Soil aggregates provide different habitats (such as aerobic and anaerobic micro-sites) that are required to support the activities of a diverse microbial community (GUPTA; GERMIDA, 2015). Soil aggregate size significantly impacts microbial communities and soil respiration. Soil total porosity and pH can regulate the distribution of soil bacteria and fungal communities within aggregates, thereby influencing soil respiration (YANG et al., 2019). However, it is unclear how it affects the microbial community composition distributed in soil aggregates, especially for fungal communities. Some studies have reported that microbial biomass and activity can be higher in macro-aggregates (> 0.25 mm) (HELGASON et al., 2010; LI et al., 2015; ZHANG et al., 2015) but also concentrated in micro-aggregates (< 0.25 mm) (JIANG et al., 2013; ZHANG et al., 2013). Most studies have used cloning and sequencing analyses to focus on the bacterial communities of aggregates (GUPTA; GERMIDA, 2015). However, macroaggregates are generally considered to be dominated by fungi (FREY, 2005), and we know very little about their fungal community dynamics. Furthermore, it is still not known how the distribution of bacteria and fungi in different aggregates regulates soil respiration at the aggregate size scale.The objectives for this proposal are to identify differences in soil respiration, organic carbon and nitrogen, among soil aggregates (large macroaggregates 4.00-2.00, macroaggregates 2.00-0.250 and microaggregates 0.250-0.00 mm); to compare the variability in bacterial and fungal communities in different-sized soil aggregates; and to identify the internal factors that influence soil aggregate respiration by analyzing the morphology, chemical properties, and microbiological communities of soil aggregates. (AU)