1. !!!!1UMR!iEES)Paris,!Montpellier,!France;!2IWMI,!Vien<ane,!Laos;!3Faculty!of!Agriculture,!KKU,!Khon!Kaen,!Thailand;!4UMR!iEES)Paris,!IRD,!Vien<ane,!Laos;!!5DALaM,!Vien<ane,!Laos!
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EMPIRICAL EVIDENCE OF THE CONTRIBUTION OF FINE DEEP ROOTS TO
TERRESTRIAL CARBON STOCKS
Jean-Luc Maeght1, Corentin Clement2, Santimaitree Gonkhamdee3, Chanthanousone Thammahacksa4, Oloth
Sentaheuanghoung5, Christian Hartmann4, Alain Pierret4,*
CONTACT
Alain Pierret - alain.pierret@ird.fr
IRD - Institute of Ecology and Environmental Sciences –
Paris
c/o National Agriculture and Forestry Research Institute (NAFRI)
P.O. Box 4199 Ban Nongviengkham, Vientiane, Lao P.D.R.
Introduction
Managing plant root carbon stocks, particularly at depth, could be an effective and readily available means to mitigate climate change. Yet, existing data,
particularly in SE Asia, remain highly uncertain and highlight the need for improved field investigations (Fig. 1)1
• Estimates of soil organic carbon (SOC) are currently based on a sampling depth of 0.3 m2
• Soils are much and deeper than 1 m and biological activity extends several metres into the soil and bedrock3,4
• Fine-root production represents about a quarter of terrestrial net primary production globally5
• Root-derived carbon is more easily retained in soil than carbon inputs from litterfall6,7.
References
1Yuen, J.Q., et al. (2013). For. Ecol. Manage., 310, 915–926.
2Aalde H et al. (2006) IPCC Guidelines for National Greenhouse Gas Inventories, vol 4. IGES,
Kanagawa
3Richter DD, Markewitz D (1995) Bioscience 45:600–609.
4Maeght J-L, Rewald B, Pierret A (2013) Front Plant Sci. doi: 10.3389/fpls.2013.00299.
5McCormack ML, et al. (2015) New Phytol 1469- 8137.doi:10.1111/nph.13363.
6Rasse D.P., Rumpel C., Dignac M.F. (2005). Plant and Soil 269: 341-356.
7Schmidt MWI, et al. (2011). Nature 478: 49-56.
8Böhm W (1979) Methods of studying root systems. Springer-Verlag 188 pp.
9Pierret A, et al. (2013) Plant Soil. doi: 10.1007/s11104-013-1795-9
10Kraenzela M et al. (2003) Forest Ecology Management 173, 213-225
11Petsri S et al. (2007) Environment and Natural Resources J. No. 5. 10 p.
12Cheng C et al. (2007) J Environ Sci (China) 19:348–52.
Methodology
We collected and measured fine roots (< 2 mm) from in teak (Tectona grandis L.) and rubber
tree (Hevea brasiliensis Müll. Arg) plantations at locations across SE Asia, - Luang Prabang,
Laos; Buriram and Songkla, Thailand; Medan, Indonesia - at soil depths of 3 to 20 m, using
the coring method8 (Fig. 2).
We used IJ_Rhizo9 to estimated root lengths and diameters. Specific root length (SRL), i.e.
the length of root per unit dry root biomass was used to estimate the root dry biomass (RDB)
distribution along soil profiles following the equation:
RDB[z] = RLD[z] x [Z]/SRL
where RDB[z] (in Mg/ha) is root dry biomass in a soil depth layer of thickness [Z] (m), RLD[z]
is root length density (m/m3) in this soil layer and SRL is specific root length (m/g).
Results
• Evidence gained in Southeast Asia shows that species such as teak tree and rubber tree grow substantial
amounts of fine roots at considerable soil depths (Fig. 3), irrespective of climate and soil type.
• For teak trees aged 15 years, fine roots up to 12 m accounted for 12 Mg C ha-1, i.e. one order of magnitude more
than some published reports10 or 30% of the aboveground carbon content found in teak tree plantations of similar
age11.
• For rubber trees aged 20 years, fine roots up to nearly 20 m accounted for 6 to 8 Mg C ha-1 which is nearly half
the value reported for roots of all sizes, in rubber tree plantations at Hainan Island, China12.
Conclusions
• Fine root biomass is likely to be one of the main components of the terrestrial carbon budget.
• Deep rooting is a trait shared by many woody and non-woody plant species.
• We therefore advocate in favour of more comprehensive and precise measurements of fine and deep roots.
• Increased knowledge about the deep rooting traits of variety of plants
and crops will have direct and tangible influence on how we manage
natural and cultivated ecosystems, in particular with regards to climate
change mitigation
• Government and development agencies should get involved in
developing a better root carbon database jointly with researchers to
assess total eco-system carbon stocks prior to implementing any land
use or development project.
Figure 1. Below-ground carbon biomass for 11 land-covers in SE Asia: Thick lines
correspond to adjusted ranges of values after the removal of outlying values. Ranges
corresponding to teak and rubber tree plantations are indicated in red. Note that the
ranges reported here include all root types, not only fine roots as in Figure 3
(adapted from Yuen et al., 20131).
Figure 3. Examples of deep rooting profiles of rubber trees
in Southern Thailand and teak trees in Laos. Fine root
biomass below 1 m is about three-fold that above 1 m.
Roots may still be present below the sampled depths.
Cumulative fine root (Mg C / ha)
Soildepth(m)
121086420
2 4 6 8 10 12 14
Cumulative fine root (Mg C / ha)
0 2.5 5 10
Soildepth(m)
151050
Figure 2. Collecting undisturbed soil cores for fine
root biomass quantification at a depth of about 3 m
in a rubber tree plantation in Songkla province,
southern Thailand (photo J.-L. Maeght, IRD). Rubber trees
Teak trees