Fine root dynamics across pantropical rainforest ecosystems.

Walter Huaraca Huasco ,Javier E Silva Espejo ,Fernando Hancco Pacha ,Terhi Riutta ,Sami W Rifai ,Forzia Ibrahim ,Luiz E O C Aragão ,Alexandra Morel ,Liliana Durand Baca ,Sheleme Demissie ,Shalom Daniel Addo-Danso ,Antonio Costa ,Kathryn J Jeffery ,Robert M Ewers ,Cécile Girardin ,Jhon Del Aguila‐Pasquel ,Alejandro Araujo Murakami ,Kennedy Owusu‐Afriyie ,Patrick Meir ,Sam Moore ,Renata Freitag ,Erick Oblitas Mendoza ,Imma Oliveras Menor ,Beisit Luz Puma Vilca ,Akwasi Duah‐Gyamfi ,Stephen Adu‐Bredu ,Beatriz Schwantes Marimon ,Filio Farfán Amézquita ,Daniel B Metcalfe ,Katharine Abernethy ,Miles R Silman ,Josué Edzang Ndong ,Lee White ,Lucy Amissah ,Noreen Majalap ,Toby R Marthews ,Christopher E Doughty ,Darcy F Galiano Cabrera ,Natacha Nssi Bengone ,Ben Hur Marimon‐Junior ,Gloria Djagbletey ,Vianet Mihindou ,Fidèle Evouna Ondo ,Carlos Alberto Quesada ,Armel Thongo M’bou ,Yadvinder Malhi

doi:10.1111/gcb.15677

Abstract

Fine roots constitute a significant component of the net primary productivity (NPP) of forest ecosystems but are much less studied than aboveground NPP. Comparisons across sites and regions are also hampered by inconsistent methodologies, especially in tropical areas. Here, we present a novel dataset of fine root biomass, productivity, residence time, and allocation in tropical old-growth rainforest sites worldwide, measured using consistent methods, and examine how these variables are related to consistently determined soil and climatic characteristics. Our pantropical dataset spans intensive monitoring plots in lowland (wet, semi-deciduous, and deciduous) and montane tropical forests in South America, Africa, and Southeast Asia (n=47). Large spatial variation in fine root dynamics was observed across montane and lowland forest types. In lowland forests, we found a strong positive linear relationship between fine root productivity and sand content, this relationship was even stronger when we considered the fractional allocation of total NPP to fine roots, demonstrating that understanding allocation adds explanatory power to understanding fine root productivity and total NPP. Fine root residence time was a function of multiple factors: soil sand content, soil pH, and maximum water deficit, with longest residence times in acidic, sandy, and water-stressed soils. In tropical montane forests, on the other hand, a different set of relationships prevailed, highlighting the very different nature of montane and lowland forest biomes. Root productivity was a strong positive linear function of mean annual temperature, root residence time was a strong positive function of soil nitrogen content in montane forests, and lastly decreasing soil P content increased allocation of productivity to fine roots. In contrast to the lowlands, environmental conditions were a better predictor for fine root productivity than for fractional allocation of total NPP to fine roots, suggesting that root productivity is a particularly strong driver of NPP allocation in tropical mountain regions.

Highlights

Fine root biomass, productivity, and residence time are key factors in shaping both ecosystem productivity and belowground carbon dynamics
Previous studies show that fine root dynamics across global forest ecosystems vary: fine root biomass and productivity are higher in tropical forests than temperate and boreal forests (Finér et al, 2011; Wang et al, 2018) and residence time increases from tropical regions towards boreal forests (Finér et al, 2011; Gill & Jackson, 2000)
We found a strong positive linear relationship between fine root productivity and soil sand content

Summary

| INTRODUCTION

Productivity, and residence time are key factors in shaping both ecosystem productivity and belowground carbon dynamics. We collected and analysed a unique dataset for fine root biomass carbon stock, productivity, residence time, and fractional allocation of total NPP to fine roots from wet, semi-deciduous, deciduous, and montane old-growth forest types that span tropical regions in South America, Africa, and Southeast Asia This global dataset is unique because (1) root dynamics data were collected to a standardized protocol across all sites; (2) soil data from all regions and sites were collected and analysed to a standardized laboratory protocol, enabling reliable cross-site comparison of the importance of soil factors; and (3) the root measurements are coupled with measurements of aboveground NPP, enabling proportional allocation to fine roots to be quantified. Are there consistent patterns in how climatic variables and physical and chemical soil properties drive fine root dynamics in tropical forests at the global scale?

| METHODOLOGY

| RESULTS

| DISCUSSION

Findings

| CONCLUSIONS