Root biomass, turnover and net primary productivity of a coffee agroforestry system in Costa Rica: effects of soil depth, shade trees, distance to row and coffee age.

Elsa Defrenet (1) , Olivier Roupsard (1) , Karel van den Meersche (1) , Fabien Charbonnier (1) , Junior Pastor Pérez-Molina (2) , Emmanuelle Khac (1) , Ivan Prieto (3) , Alexia Stokes (4) , Catherine Roumet (3) , Bruno Rapidel (5, 6) , Elias de Melo Virginio Filho (2) , Victor J Vargas (2) , Diego Robelo (3, 7) , Alejandra Barquero (8) , Christophe Jourdan (1)

1 UMR Eco&Sols - Ecologie fonctionnelle et biogéochimie des sols et des agro-écosystèmes
2 CATIE - Centro Agronomico Tropical de Investigacion y Ensenanza
3 CEFE - Centre d’Ecologie Fonctionnelle et Evolutive
4 UMR AMAP - Botanique et Modélisation de l'Architecture des Plantes et des Végétations
5 UMR SYSTEM - Fonctionnement et conduite des systèmes de culture tropicaux et méditerranéens
6 Cirad - Centre de Coopération Internationale en Recherche Agronomique pour le Développement
7 UM - Université de Montpellier
8 Cafetalera Aquiares

In Costa Rica, coffee (Coffea arabica) plants are often grown in agroforests. However, it is not known if shade-inducing trees reduce coffee plant biomass through root competition, and hence alter overall net primary productivity (NPP). We estimated biomass and NPP at the stand level, taking into account deep roots and the position of plants with regard to trees. Stem growth and root biomass, turnover and decomposition were measured in mixed coffee/tree (Erythrina poeppigiana) plantations. Growth ring width and number at the stem base were estimated along with stem basal area on a range of plant sizes. Root biomass and fine root density were measured in trenches to a depth of 4 m. To take into account the below-ground heterogeneity of the agroforestry system, fine root turnover was measured by sequential soil coring (to a depth of 30 cm) over 1 year and at different locations (in full sun or under trees and in rows/inter-rows). Allometric relationships were used to calculate NPP of perennial components, which was then scaled up to the stand level. Annual ring width at the stem base increased up to 2·5 mm yr(-1) with plant age (over a 44-year period). Nearly all (92 %) coffee root biomass was located in the top 1·5 m, and only 8 % from 1·5 m to a depth of 4 m. Perennial woody root biomass was 16 t ha(-1) and NPP of perennial roots was 1·3 t ha(-1) yr(-1) Fine root biomass (0-30 cm) was two-fold higher in the row compared with between rows. Fine root biomass was 2·29 t ha(-1) (12 % of total root biomass) and NPP of fine roots was 2·96 t ha(-1) yr(-1) (69 % of total root NPP). Fine root turnover was 1·3 yr(-1) and lifespan was 0·8 years. Conclusions Coffee root systems comprised 49 % of the total plant biomass; such a high ratio is possibly a consequence of shoot pruning. There was no significant effect of trees on coffee fine root biomass, suggesting that coffee root systems are very competitive in the topsoil.

Mots clés: Allometry; agroforestry; fine root decomposition; growth rings; sequential coring; tree rings

Mots clés: allométrie; npp; racine fine; agroforesterie; coffea arabica; erythrina poeppigiana; cerne

Domaines: Sciences du Vivant [q-bio]

Elsa Defrenet, Olivier Roupsard, Karel van den Meersche, Fabien Charbonnier, Junior Pastor Pérez-Molina, et al.. Root biomass, turnover and net primary productivity of a coffee agroforestry system in Costa Rica: effects of soil depth, shade trees, distance to row and coffee age.. Annals of Botany, 2016, 118 (4), pp.833-851. ⟨10.1093/aob/mcw153⟩. ⟨hal-01606585⟩