fdalmeidavalente@gmail.com; marllon.castro22007@gmail.com; lucascarvalhogomes15@hotmail.com; julio_n2003@yahoo.com.br; ivosilva@ufv.br; teo@ufv.br
*Correspondence:
Fernanda Valente,fdalmeidavalente@gmail.com
Department of Soil, Universidade Federal de Viçosa, Viçosa MG 36570-900, Brasil.
Abstract
Planting trees is one of the most effective activities in recovering soil organic carbon (SOC) stocks of degraded areas, but we still lack information on how different tree species can influence soil respiration, one of the main sources of dioxide carbon (CO2) to the atmosphere. This study aimed to explore the influence of different forest species on the autotrophic and heterotrophic components of the total soil respiration in a bauxite mining area under reclamation. We analysed the soil CO2efflux under five treatments: i) monoculture of clonal Eucalyptus; ii) monoculture of Anadenanthera peregrina (L.); iii) a mixed plantation of 16 native forest species (Nat); iv) a mined area without vegetation cover; and v) a natural forest cover. This design allowed exploring the soil CO2 dynamics in a gradient of recovery, from a degraded area to natural vegetation. Additionally, we measured soil temperature, moisture and soil characteristics. Soil CO2 efflux increased with increasing forest species cover in the rainy months. There was no significant change in CO2 efflux among the tree species. Heterotrophic soil respiration contributed to 64% of total soil CO2 efflux and was associated with litter decomposition. Amongst the abiotic variables, increases in soil moisture had the most influence on CO2 efflux. Therefore, these results help to understand the factors that underpin the loss of SOC and can orient management practices to improve soil organic matter and restore soil quality in degraded areas.
Keywords: Land reclamation; bauxite, CO2 flux, soil organic matter, Atlantic rainforest
Introduction
Soil respiration is one of the main sources of terrestrial dioxide carbon (CO2), which increase in the atmosphere has been associated with global warming (Köchy et al ., 2015; Shrestha & Lal, 2006). Soil is the largest C reservoir in terrestrial ecosystems, containing about twice as much C as the atmosphere (Kuzyakov & Cheng, 2001) and three times as much as the vegetation (Granier et al ., 2000). Soil respiration is a combination of root respiration, root associated microbes and mycorrhizal association (autotrophic respiration) and the respiration of microorganisms during the decomposition process of both soil organic matter and litter (heterotrophic respiration) (Fontaine et al. , 2003; Hansonet al ., 2000; Millard et al ., 2010; Bujalský et al. , 2014). However, the magnitude of the temporal variations and the biotic and abiotic factors that influence the efflux of CO2 from the Reclamaid Mine Degraded Land (RMDL) in process of recovery are still not well understood. Understanding the factors that underline soil CO2 flux can orient management practices to improve soil organic matter (SOM) and restore soil quality in degraded areas. Mining activities promote drastic changes in the landscape, where the total removal of vegetation cover and topsoil results in intense soil disturbances, which can lead to a decrease of SOM due to the increase in CO2 efflux (Lorenz & Lal, 2007; Shrestha & Lal, 2006). The recovery process for these soils aims to restore the organic matter content with the restitution of vegetation cover that can provide carbon assimilation through photosynthesis (Shrestha & Lal, 2006). The carbon stored in the shoots and roots is important in reactivating nutrient cycling, increasing soil carbon stocks.
Soil CO2 efflux is a sensitive indicator of soil metabolic activity and an important tool to investigate the SOM dynamics (Kuzyakov & Cheng, 2001; Haney et al. 2008). Increase SOM and nutrient cycling are major objectives to recovery soil in degraded areas and the analysis of soil CO2 efflux can give important insights about the rehabilitation process (Subke & Bahm, 2010). The rates of soil CO2 efflux in mining areas under recovery are associated with the soil organic carbon contents, nutrient availability and environmental variables (Ahirwal et al., 2017, Ahirwal & Maite, 2018). Mukhopadhyay &Maite (2014) compared a mined area in recovery with grassland and natural forest and found that the highest values of soil CO2 in the grassland were associated with the higher levels of organic matter, microbiological activity and root biomass. Temperature is an important driver of soil CO2efflux, and Bujalský et al. (2014) found that soil respiration was associated with temperature and higher contents of organic carbon and root biomass comparing recovered mined area and natural regeneration. Although few studies report the influence of tree species on soil respiration (Yohannes et al., 2010), there is a lack of studies that explore the influence of tree species on the components of soil respiration in mined areas under reclamation.
The study of CO2 efflux under field conditions can generate important information about changes in land use and management, however, there is a large gap in such studies for forest ecosystems in tropical regions (Wei et al. , 2010), especially in mining areas in the process of recovery. The main hypothesis of this study was that soil respiration in recovering mined areas is not influenced by the composition and density of the tree species used, but they present a strong relation with soil moisture and temperature. Therefore, this study aimed to determine (i) the CO2 efflux during the dry and rainy months in an area of bauxite mining revegetated with different forest species, (ii) the contribution of heterotrophic and autotrophic respiration to total soil respiration, and (iii) the influence of biotic and abiotic variables on soil CO2efflux.
Material and Methods
Study area and experimental design
The study was carried on a bauxite mined area at 780 m altitude in São Sebastião da Vargem Alegre (21°1’58” S and 42°35’8” W), Minas Gerais state, Brazil. The climate predominant is Cwa (Köppen), with hot and rainy summers and a well-defined dry season. The annual precipitation is 1,287 mm and temperature average of 20.3ºC (INMET, 2016). The domain soils are Oxisols, which is depth weathered and present low nutrients availability (Santos et al., 2013; Soil Survey Staff, 2014). Before started the mining, the soil surface layer (0.00-0.20 m) was removed and stored next to the area for one year. During the topographic reconfiguration of the mined area, the soil stored was used to cover the areas followed by a decompaction process using a subsoiler at a depth of 0.60 m.
The experiment was installed in March 2011 using a randomized block design with split plots and three replicates. The plots (40 × 18 m) comprised the following forest cover:Anadenanthera peregrina (L.) Speg (Ap); clonal Eucalyptus(a hybrid from a cross between Eucalyptus urophylla andEucalyptus grandis - clone AEC144®) (Euc) and a mixed plantation (Nat) consisting of 16 native forest species from the region. In addition, we installed plots in a native forest at the second stage of regeneration (Woodland) and in an post-mined area kept without vegetation (Ncov).
Table 1 – Trees species and phenological groups of the mixed plantation treatment.