Estimating Fine Root Production from Ingrowth Cores and Decomposed Roots in a Bornean Tropical Rainforest

Ayumi Katayama,Naoki Makita,Mizue Ohashi,Lip Khoon Kho,Kazuho Matsumoto,Tomonori Kume

doi:10.3390/f10010036

Abstract

Research highlights: Estimates of fine root production using ingrowth cores are strongly influenced by decomposed roots in the cores during the incubation period and should be accounted for when calculating fine root production (FRP). Background and Objectives: The ingrowth core method is often used to estimate fine root production; however, decomposed roots are often overlooked in estimates of FRP. Uncertainty remains on how long ingrowth cores should be installed and how FRP should be calculated in tropical forests. Here, we aimed to estimate FRP by taking decomposed fine roots into consideration. Specifically, we compared FRP estimates at different sampling intervals and using different calculation methods in a tropical rainforest in Borneo. Materials and Methods: Ingrowth cores were installed with root litter bags and collected after 3, 6, 12 and 24 months. FRP was estimated based on (1) the difference in biomass at different sampling times (differential method) and (2) sampled biomass at just one sampling time (simple method). Results: Using the differential method, FRP was estimated at 447.4 ± 67.4 g m−2 year−1 after 12 months, with decomposed fine roots accounting for 25% of FRP. Using the simple method, FRP was slightly higher than that in the differential method after 12 months (516.3 ± 45.0 g m−2 year−1). FRP estimates for both calculation methods using data obtained in the first half of the year were much higher than those using data after 12-months of installation, because of the rapid increase in fine root biomass and necromass after installation. Conclusions: Therefore, FRP estimates vary with the timing of sampling, calculation method and presence of decomposed roots. Overall, the ratio of net primary production (NPP) of fine roots to total NPP in this study was higher than that previously reported in the Neotropics, indicating high belowground carbon allocation in this forest.

Highlights

Tropical rainforests have high gross primary production (GPP) and huge biomass [1,2]; they play an important role on carbon cycling at a global scale
fine root production (FRP) between sampling time i and j was the fine roots being accounted for based on Osawa et al [9].−2FRPijij between sampling time i and j was the sum of differences in live fine root biomass at (∆Bij, g m−2 ), the difference in fine root necromass (∆Nij, sum−of differences in live fine root biomass at (ΔBij, g m ), the difference in fine root necromass (ΔNij, g m 2 ) and decomposed dead fine roots (d, g m−2 )
Between T3 and T4, NPPfr using the differential method was estimated at 4.25 ± 0.64 MgC ha−1 year−1 (Table 1)

Summary

Introduction

Tropical rainforests have high gross primary production (GPP) and huge biomass [1,2]; they play an important role on carbon cycling at a global scale. Higher annual temperatures in tropical area leads to higher GPP; yet, higher net primary production (NPP) is not always observed [1]. 10–60% total net primary production in tropical forests [2]. Finer et al [3] showed that the FRP in tropical forests is significantly higher than that in boreal forests. The authors found no clear relationship between FRP and mean annual temperature in forest ecosystems. FRP might not always be as high as expected in the tropics, with other factors, such as nutrient availability and forest structure impacting FRP. There might be an issue with the method used to estimate

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Conclusion