Vertical distribution, nutrient concentration and seasonal changes of fine root mass in a semi-deciduous tropical dry forest and in two adjacent pastures in the Western Llanos of Venezuela

Ana Francisca González-Pedraza,Nelda Dezzeo

doi:10.17138/tgft(8)93-104

Abstract

With the objective to contribute to a better understanding of ecological consequences of deforestation on the below-ground system in the Western Llanos of Venezuela, we evaluated the vertical distribution, nutrient concentration and seasonal changes of total fine root mass (FRM) (<2 mm diameter) in a semi-deciduous tropical dry forest and in 2 adjacent pastures of Cynodon nlemfuensis: a young pasture (YP, 5 years old) and an old pasture (OP, 18 years old) in the Obispo municipality, Barinas State. This evaluation included measurements at the end of the rainy season, during the dry season and during the subsequent early rainy season in 2005/2006. Highest FRM was recorded during the dry season, which probably indicates a plant water-stress response mechanism. The highest proportion (63‒88%) of FRM was concentrated in the 10–20 cm soil layer at all studied sites, probably due to a higher nutrient and moisture content at that depth. Non-significant differences (P>0.05) were observed in the total concentrations of organic carbon, nitrogen, phosphorus, calcium and magnesium in the FRM in soils supporting forest, OP and YP at the evaluated depths. Non-significant changes in the total FRM and nutrient concentrations were observed between the sampling periods and the 3 study sites. YP soils showed a slight increase in FRM that could be associated with the root growth of secondary vegetation, which is considered a weed and is periodically removed. Our results suggest that the land use change from tropical forest to pastures has not significantly affected the mass of fine roots and their carbon and nutrient concentrations. Further studies are needed to determine if these findings apply to other ecosystems.

Highlights

Materials and MethodsFine root mass in tropical forests is the most important component of below-ground C dynamics and can contribute significantly to global net primary production (Malhi et al 2011)
With the objective to contribute to a better understanding of ecological consequences of deforestation on the below-ground system in the Western Llanos of Venezuela, we evaluated the vertical distribution, nutrient concentration and seasonal changes of total fine root mass (FRM) (
Our results suggest that the land use change from tropical forest to pastures has not significantly affected the mass of fine roots and their carbon and nutrient concentrations

Summary

Introduction

Fine root mass in tropical forests is the most important component of below-ground C dynamics and can contribute significantly to global net primary production (Malhi et al 2011). In tropical dry forests, fine root production is high, constituting an important source of carbon (C) and nutrients in the soil (Fiala et al 2017). The clearing of dry forests for the establishment of pastures can have important effects on the production and distribution of roots within the soil profile and on the contributions of C and nutrients (Jaramillo et al 2003). Studies on the replacement of tropical deciduous forests with pastures have shown important effects on C and nutrients in the soil profile (Crespo 2015), and pastures have the potential to store significant amounts of C in soils (Rodríguez et al 2013; Crespo 2015). The dense and deep root system of grasses contributes to the formation of soil aggregates and provides protection to the soil C, making it least susceptible to oxidation and eventual loss to the atmosphere (Cambardella and Elliot 1993)

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