Unexpected phenology and lifespan of shallow and deep fine roots of walnut trees grown in a silvoarable Mediterranean agroforestry system
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Background and Aims
Fine roots play a major role in the global carbon cycle through respiration, exudation and decomposition processes, but their dynamics are poorly understood. Current estimates of root dynamics have principally been observed in shallow soil horizons (<1 m), and mainly in forest systems. We studied walnut (Juglans regia × nigra L.) fine root dynamics in an agroforestry system in a Mediterranean climate, with a focus on deep soils (down to 5 m), and root dynamics throughout the year.
Sixteen minirhizotron tubes were installed in a soil pit, at depths of 0.0–0.7, 1.0–1.7, 2.5–3.2 and 4.0–4.7 m and at two distances from the nearest trees (2 and 5 m). Fine root (diameter ≤ 2 mm) dynamics were recorded across three diameter classes every 3 weeks for 1 year to determine their phenology and turnover in relation to soil depth, root diameter and distance from the tree row.
Deep (>2.5 m) root growth occurred at two distinct periods, at bud break in spring and throughout the winter i.e., after leaf fall. In contrast, shallow roots grew mainly during the spring-summer period. Maximum root elongation rates ranged from 1 to 2 cm day−1 depending on soil depth. Most root mortality occurred in upper soil layers whereas only 10 % of fine roots below 4 m died over the study period. Fine root lifespan was longer in thicker and in deeper roots with the lifespan of the thinnest roots (0.0–0.5 mm) increasing from 129 days in the topsoil to 190 at depths > 2.5 m.
The unexpected growth of very deep fine roots during the winter months, which is unusual for a deciduous tree species, suggests that deep and shallow roots share different physiological strategies and that current estimates based on the shortest root growth periods (i.e., during spring and summer) may be underestimating root production. Although high fine root turnover rates might partially result from the minirhizotron approach used, our results help gain insight into some of the factors driving soil organic carbon content.
KeywordsAlley cropping Juglans Deep root growth Root elongation rate Root mortality Root turnover
This study was financed by the French ANR funded project ECOSFIX (Ecosystem Services of Roots - Hydraulic Redistribution, Carbon Sequestration and Soil Fixation, ANR-2010-STRA-003-01), by the ADEME funded project AGRIPSOL (Agroforestry for soil protection) and by la Fondation de France. We thank the farmers Mr. Henri and Alain Breton, for their authorization to open the deep pit. We are very grateful to our INRA colleagues Jean-François Bourdoncle, Lydie Dufour, Alain Sellier and Didier Arnal for their help with field and laboratory work and logistics. The Restinclières farm is the property of the Conseil Départemental de l’Hérault, which provides financial support to INRA since 1995 for the monitoring of agroforestry systems, and their support is warmly appreciated.
- Andrianarisoa KS, Dufour L, Bienaime S, Zeller B, Dupraz C (2015) The introduction of hybrid walnut trees (Juglans nigra x regia cv. NG23) into cropland reduces soil mineral N content in autumn in southern France. Agrofor Syst, in pressGoogle Scholar
- Balandier P, Dupraz C (1999) Growth of widely spaced trees. A case study from young agroforestry plantations in France. Agrofor Syst 99:151–167Google Scholar
- Brunner I, Bakker MR, Björk RG, Hirano Y, Lukac M, Aranda X, Børja I, Eldhuset TD, Helmisaari HS, Jourdan C, Konôpka B, López BC, Pérez CM, Persson H, Ostonen I (2013) Fine-root turnover rates of European forests revisited: an analysis of data from sequential coring and ingrowth cores. Plant Soil 362:357–372CrossRefGoogle Scholar
- Chantereau J, Goislot K, Albaric L, Thellier T, Fabre D (2012) Synchronism between adventitious root and leaf development in hydroponic sorghum. J SAT Agric Res 10:1–5Google Scholar
- Chaudhry AK, Khan GS, Siddiqui MT, Akhtar M, Aslam Z (2003) Effect of arable crops on the growth of poplar (Populus deltoides) tree in agroforestry system. Pak J Agric Sci 40:82–85Google Scholar
- Clough Y, Barkmann J, Juhrbandt J, Kessler M, Wanger TC, Anshary A, Buchori D, Cicuzza D, Darras K, Putra DD, Erasmi S, Pitopang R, Schmidt C, Schulze CH, Seidel D, Steffan-Dewenter I, Stenchly K, Vidal S, Weist M, Wielgoss AC, Tscharntke T (2011) Combining high biodiversity with high yields in tropical agroforests. PNAS 108:8311–8316CrossRefPubMedPubMedCentralGoogle Scholar
- Cox DR (1972) Regression models and life-tables. J Roy Stat Soc B 34:187–220Google Scholar
- Crawley MJ (2012) The R Book, Second Edition. 27. Survival analysis. Wiley, 1218 p.Google Scholar
- Dupraz C, Fournier C, Balvay Y, Dauzat M, Pesteur S, Simorte V (1999) Influence de quatre années de culture intercalaire de blé et de colza sur la croissance de noyers hybrides en agroforesterie. Bois et Fôrets des Agriculteurs Actes du colloque de Clermont-Ferrand 20:95–114Google Scholar
- Dupraz C, Liagre F (2008) Agroforesterie, des arbres et des cultures. Editions France-Agricole, Paris, p 413Google Scholar
- Gavaland A, Burnel L (2005) Croissance et biomasse aérienne de noyers noirs. Chambres d’agriculture 945:20–21Google Scholar
- Graefe S, Hertel D, Leuschner C (2008) Estimating fine root turnover in tropical forests along an elevational transect using minirhizotrons. Biotropica 40(536):542Google Scholar
- IUSS Working Group WRB (2007) World Reference Base for Soil Resources 2006, first update 2007. World Soil Resources Reports No. 103. FAO, RomeGoogle Scholar
- Joslin JD, Henderson GS (1987) Organic matter and nutrients associated with fine root turnover in a white oak stand. For Sci 33:330–346Google Scholar
- Khan GS, Chaudhry AK (2007) Effect of spacing and plant density on the growth of poplar (Populus deltoides) trees under agro-forestry system. Pak J Agric Sci 44:321–327Google Scholar
- Leshem B (1965) The annual activity of intermediary roots of the aleppo pine. For Sci 11:291–298Google Scholar
- R Development Core Team (2013) R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, AustriaGoogle Scholar
- Therneau T (2014) A package for survival analysis in S. R package version 2.37-7Google Scholar
- Torquebiau EF (2000) A renewed perspective on agroforestry concepts and classification. Comptes rendus de l’Académie des sciences. Série III. Sci de la vie 323:1009–1017Google Scholar
- Waisel T, Eshel A, Beeckman T, Kafkafi U (2002) Plant roots: the hidden half, 3rd edn. Marcel Dekker, Inc., NewYorkGoogle Scholar
- Young A (1997) Agroforestry for Soil Management. Wallingford UK p. 320Google Scholar