1. Functional traits distribution as causal link between environmental pressure (climate and cropping systems) and soil invertebrate abundance
Hedde M.1 ; Beaumelle L.1 ; Thénard J.1 ; Brunet N. 2; Recous S. 3
1.INRA UR251 Pessac, Versailles, France
2.INRA AgroImpact, Mons-en-Chaussée, France
3.INRA UMR FARE, Reims, France
Context
Climate change and biodiversity conservation.
Burning issues on the relationships between anthropogenic pressures and soil biodiversity.
Functional traits as explicit links between pressures and biological response (Violle et al 2007).
Hypotheses
Abundance of macro-invertebrates can be modelled by causal relationships between pressures (climate & cropping systems) and functional traits.
Path analysis can disentangle such relationships.
Experimental treatments
Cropping systems: Varying in crop rotation, mineral inputs, soil tillage and crop residues management. Modulate the quantity, the quality and the localization of trophic and non-trophic resources for soil organisms.
Climate: 5-years survey
LTER study site (ACBB site, INRA Mons, France)
Invertebrates collected by pitfall traps, in spring from 2010 to 2014 and identified as precisely as possible
Dataset: 120 observations (24 plots x 5 years).
Functional groups obtained through the BETSI database
Computation of community-weigthed mean (CWM) proportion of functional groups
‘lavaan’ library for R to compute path analysis
Initial conceptual model
Crop system
Restit (n-1)
Prof_till
Hum (n-1)
Small
zoo
Large
Sapro
Herbiv
Ab tot
Final path model
The size of the array and its darkness indicate the strength of the causal relationship.
restit(n-1): quantity of restituted residues at the end of the previous term of the rotation;
Prof_till: depth of the last tillage,
Hum(n-1): mean month humidity during the n-1 year;
Small_zoo: CWM of less-than-5-mm zoophages;
Large_zoo: CWM of more-than-5-mm zoophages;
Sapro: CWM of saprophages;
Herbiv: CWM of herbivores;
Ab_tot: total abundance of individuals
On the basis of this conceptual model
numerous path analyses using different observed variables to inform the conceptual items (climate, soil tillage & restitutions).
Functional groups based on Hedde et al (2013).
Dynamics of trophic groups distribution is mediated by agricultural practices (till deep and last year organic matter restitution) and a meteorological variable (last year mean atmospheric humidity).
Changes in total abundance can be modelled by changes in zoophages and in lower extent herbivores, but not by saprophages.
Taking into account other sites will permit to strengthen these conclusions.
Acknowledgements
Thanks to Pessac (JP Pétraud, A Trouvé, E Ollivier, N Cheviron) and AgroImpact (F Mahu, N Collanges, B Chauchard) sampling teams.
Hedde, M. et al. Biomass and Bioenergy; 55: ; 2013
Violle, C. et al. Oikos. 116: ; 2007