Deep belowground biomass & Net Primary Productivity in a coffee - PowerPoint PPT Presentation

Deep belowground biomass & Net Primary Productivity in a coffee agroforestry system of Costa Rica Elsa Defrenet, Olivier Roupsard, Fabien Charbonnier, Alejandra Barquero, Karel van den Meersche, Diego Robelo, Christophe Jourdan

Context • Perennial plantations deal with climate changes, thus challenging sustainable plant productivity • NPP plays a key role in functioning, production and C sequestration of ecosystems • Studies on bNPP and root dynamics over long period are rather scarce • Most root studies are limited to the topsoil • Few studies on coffee NPP and none on coffee root dynamics and productivity on the whole rooting profile 2

Coffee root system 3

Objectives • Estimate the total coffee root biomass, down to the root front • Evaluate the bNPP on the whole rooting profile of coffee plantations – Root perennial structures – Fine root production • Calculate the fine root turnover rate • Characterize the effect of plant competition on these parameters due to structure of plantations: – between coffee trees: planting rows vs inter-rows – between coffee and shade trees • Characterize the effect of soil depth 4

Net Primary Productivity (NPP) NPP = G visible + D R + L + Ex + P bNPP G visible = visible growth ; ∆ R = Variation of Reserves; L = Mortality or litter production; Ex = Exportation; P = Pruning 5

Study site and plant material • Central Costa Rica (3014mm precipitations) tropical humid climate with only 3 « drier » months (Feb.-April) with less than 200mm/month • Aquiares farm (700 ha, 750-1400 m a.s.l.), 40 y old coffee plantations with native shade trees • Andisol with high allophane and OM contents, high infiltrability, high stone content • Coffea arabica L., 1.4 m x 1.1 m, 6300 plants ha -1 • Shade trees ( Erythrina sp. ) density of 7.4 trees ha -1 , 20m high, 15% canopy projection on coffee plots 6

Root biomass Voronoi polygon 1.6m² estimation method Row Compensation 12 plants ¼ of Voronoi (6 full sun – 6 shade) Voronoi polygon Stump 0-10 cm 10-30 cm Extrapolation to root Wall profile front – 4 m deep within the Wall profile inter-row within the planting row 150 cm 7

Sequential Coring sampling design 0-30 cm soil sampling  0 – 4 m (extr.) Core Diam.: 8 cm 2 studied effects: - Distance to shade tree (full sun; shade); - Sampling position (row; inter-row) 10 plants (5 full sun – 5 shade) N Decision Matrix and Max-Min calculation methods Coffee plant Eddy flux Voronoï Tower polygon Row 1 2 9 1 6 SEQUENTIAL CORING 1 2 Inter-row 1 9 Sun coffee plants 6 Shade plants 50 m 8

Total Root biomass 0 - 4 m 55% 30cm 9 9

Total Root Biomass 0 - 4 m Biomass (t ha -1 ) Plant compartment compartment Tap root 9.1 (50%) Coarse and mediuem roots 6.0 (33%) Total perennial roots 15.1 (83%) Belowground Fine roots 3.0 (17%) Total Belowground 18.1 (34%) Perennial parts (stumps only) 21.2 Pruned branches and fruits 14,4 Aboveground Total Aboveground 35,6 (66%) Total root biomass amounts 34% of total plant biomass, likely a consequence of shoot prunning every 5 years No significant differences between sun and shade coffee root biomass 10

Fine root biomass dynamics (0 – 30 cm) wet period « drier » period - ² LAI =2.2 m leaf ² m soil - ² LAI =4.4 m leaf ² m soil Fruit loading x2 Fine root biomass fluctuated seasonally 2-fold, similarly to LAI, but with a strong competition between roots and fruits 11

Fine root NPP on the topsoil (0 - 30 cm) Method FR NPP FR NPP FR NPP FR FR Global plot Row Inter-row Turnover Lifespan T ha -1 y -1 T ha -1 y -1 T ha -1 y -1 y -1 y Decision Matrix 1.64 2.14 1.14 0.72 1.39 Fairley & Alexander, 1985 Max-Min 1.38 1.93 0.96 0.85 1.18 Nadelhoffer et al, 1985 x2 FR NPP in the Row > Inter-row by 2 fold, likely a consequence of OM & nutrient concentration patches under coffee plants. No significant differences between both methods 12

bNPP - whole rooting profile (0 - 4 m) Total perennial roots: 1.3 t ha -1 y -1 37% Stumps: 1.8 t ha -1 y -1 Tap root: 0.8 t ha -1 y -1 Fine roots: 2.2 t ha -1 y -1 Medium roots: 0.3 t ha -1 y -1 63% Coarse roots: 0.2 t ha -1 y -1 Total bNPP: Total aNPP Total NPP: 17 t ha -1 y -1 3.5 t ha -1 y -1 13.5 t ha -1 y -1 13

Main conclusions • Deep root biomass and productivity frequently forgotten; first coffee root biomass estimates on whole rooting profile • 2 times more root biomass located in the row than inter-row • No significant effect of shade trees on coffee root distribution • 8% of coffee root biomass below 1.5m deep, fine roots exclusively • High value of bNPP, particularly fine roots (twice more than perennial roots) • Low value of fine root turnover rate (0.7 y -1 )  High potential for C sequestration in this agroforestry ecosystem 14

Many thanks to my colleagues … … and thank you for your kind attention 15