Deep belowground biomass & Net Primary Productivity in a coffee agroforestry system of Costa Rica

Deep belowground biomass & Net Primary Productivity in a coffee agroforestry system of Costa Rica

Elsa Defrenet, Olivier Roupsard, Fabien Charbonnier, Alejandra

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

• 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

Objectives

NPP

=

G

+

D

R

+

L

+

Ex

+

P

G_visible = visible growth; ∆R = Variation of Reserves; L = Mortality or litter production; Ex = Exportation; P = Pruning

Net Primary Productivity (NPP)

bNPP

• 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

Study site and plant material

7 Voronoi polygon Stump 150 cm 0-10 cm 10-30 cm Wall profile within the planting row Wall profile within the inter-row ¼ of Voronoi Voronoi polygon Row Compensation 12 plants

(6 full sun – 6 shade)

Extrapolation to root front – 4 m deep

Root biomass

estimation method

8

Sequential Coring sampling design

2 studied effects:

- Distance to shade tree (full sun; shade); - Sampling position (row; inter-row)

10 plants (5 full sun – 5 shade)

Decision Matrix and Max-Min calculation methods N

Voronoï polygon Row Inter-row Coffee plant SEQUENTIAL CORING Sun coffee plants Shade plants Eddy flux Tower 50 m 1 2 9 1 6 1 2 9 1 6

0-30 cm soil sampling  0 – 4 m (extr.) Core Diam.: 8 cm

Total Root biomass 0 - 4 m

9 9

55% 30cm

Plant compartment compartment Biomass (t ha-1₎

Belowground

Tap root 9.1 (50%)

Coarse and mediuem roots 6.0 (33%) Total perennial roots 15.1 (83%) Fine roots 3.0 (17%)

Total Belowground 18.1 (34%)

Aboveground

Perennial parts (stumps only) 21.2 Pruned branches and fruits 14,4

Total Aboveground 35,6 (66%)

Total Root Biomass 0 - 4 m

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

11

Fine root biomass dynamics (0 – 30 cm)

wet period

« drier » period

LAI =4.4 m_leaf² m_soil-_{² LAI =2.2 m}

leaf² msoil-²

x2

Fine root biomass fluctuated seasonally 2-fold, similarly to LAI, but with a strong competition between roots and fruits

Method FR NPP Global plot T ha-1 _y-1 FR NPP Row T ha-1 _y-1 FR NPP Inter-row T ha-1 _y-1 FR Turnover y-1 FR Lifespan y Decision Matrix

Fairley & Alexander, 1985 1.64 2.14 1.14 0.72 1.39 Max-Min

Nadelhoffer et al, 1985 1.38 1.93 0.96 0.85 1.18

Fine root NPP on the topsoil (0 - 30 cm)

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

x2

13 Tap root: 0.8 t ha-1_y-1 Stumps: 1.8 t ha-1_y-1 Coarse roots: 0.2 t ha-1_y-1 Medium roots: 0.3 t ha-1_y-1

Total bNPP:

3.5 t ha

_y

bNPP - whole rooting profile (0 - 4 m)

Fine roots: 2.2 t ha-1_y-1

63%

Total perennial roots:

1.3 t ha-1_y-1

37%

Total aNPP

• 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

15 … and thank you for your kind attention