Variation in biomass allocation and root functional parameters in response to fire history in Brazilian savannas

Soizig Le Stradic,Giselda Durigan,Catherine Roumet,Leonardo Cancian,Alessandra Fidelis

doi:10.1111/1365-2745.13786

Abstract

Abstract Fire is a fundamental ecological factor in savannas because it affects vegetation dynamics and ecosystem functioning. However, the effects of fire on below‐ground compartments, including biomass and root traits, and their regeneration remain poorly understood. In this study, we assess the variation of above‐ and below‐ground plant components along fire‐history gradients in Brazilian open savannas and investigate whether changes in vegetation and soil properties are associated with the responses of below‐ground biomass and root traits. The study was conducted in eight sampling areas of open savanna (campo sujo, i.e. vegetation having low woody cover) within the Cerrado (Brazilian savannas), located along a gradient of time since the last fire (1–34 years); the number of fires that occurred within the past 34 years (0–9 fires) varied by sampling area. In each sampling area, we measured above‐ and below‐ground biomass, root depth distribution, root functional parameters and nutrient levels in the upper soil layers (0–10 cm). Rapid recovery of above‐ground live biomass after a fire was primarily due to resprouting of graminoids. This recovery was associated with an increase in absorptive root biomass in the upper soil layer in the most recently burnt sites, whereas root biomass was unaffected in deeper layers. Root parameters remained constant regardless of fire history but responded to variations in vegetation structure and soil properties. Specific root length (SRL) decreased with K, Mg2+, Al3+, N and C and increased with P concentration. In contrast, root tissue density (RTD) and absorptive root proportion were negatively correlated with soil P. RTD was strongly associated with the above‐ground biomass of graminoids. Soil texture impacted the root system: the proportion of absorptive roots increased with fine sand content in the soil, inversely to transport root biomass. The relationship between fire and soil properties was insignificant. Synthesis. In savannas, fire stimulates absorptive root biomass in response to the higher demand for below‐ground resources. This response is correlated with shoot regrowth after a fire. Variations in morphological root parameters are not directly associated with fire history; instead, they reflect differences in soil chemistry, especially soil P and graminoid biomass changes.

Highlights

In many regions, fire is a significant determinant of plant community structure and ecosystem functioning, affecting nutrient cycling, carbon storage, and plant regeneration (Higgins et al., 2007; McLauchlan et al, 2020; Pellegrini, Hobbie, et al, 2020)
Whereas our current understanding of biomass allocation and root traits in savannas has primarily focused on tree species and coarse roots (Tomlinson et al, 2012; Wigley et al, 2019; Zhou et al, 2020), information about the response of fine root traits in plant communities dominated by grasses, such as open savannas, is lacking
We investigated whether root biomass and fine root traits associated with resource acquisition and conservation vary along a fire regime gradient

Summary

Introduction

Fire is a significant determinant of plant community structure and ecosystem functioning, affecting nutrient cycling, carbon storage, and plant regeneration (Higgins et al., 2007; McLauchlan et al, 2020; Pellegrini, Hobbie, et al, 2020). Fire regimes are modified in response to significant changes in land use and climate (Rogers et al, 2020) Open ecosystems, such as savannas, are shaped by recurrent surface fires (every 3–5 years in the Cerrado in Brazil, Miranda et al, 2009; Rissi et al, 2017). Whereas our current understanding of biomass allocation and root traits in savannas has primarily focused on tree species and coarse roots (Tomlinson et al, 2012; Wigley et al, 2019; Zhou et al, 2020), information about the response of fine root traits in plant communities dominated by grasses, such as open savannas (but see Oliveras et al, 2013; Simpson et al, 2021), is lacking. We investigated whether root biomass and fine root traits associated with resource acquisition and conservation vary along a fire regime gradient

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Results

Conclusion