Previous research has demonstrated positive effects of biodiversity on ecosystem productivity. We propose these effects strengthen through time because of a positive feedback of productivity on soil fertility, including levels of soil calcium and cation exchange capacity. Plant productivity could add organic matter to the soil, improving nutrient supply and therefore leading to further gains in productivity. We use data on soil chemical compositional changes across 23 years in a biodiversity experiment.
The experiment was conducted at the Cedar Creek Ecosystem Science Reserve in a grassland ecosystem in Minnesota, USA. The experiment, Biodiversity II (e120), manipulates plant biodiversity with levels of 1, 2, 4, 8, and 16 plant species. Soil cores were taken at 0-20 cm deep and measured for % soil organic matter (OM), soil % carbon (C) and % Nitrogen (N), soil pH, ammonium acetate (pH 7) extractable Ca, Mg, K, Na, Al, and cation exchange capacity (CEC).
Results/Conclusions
Greater plant biodiversity was associated with higher levels of soil nutrients. Regressions showed a saturating dependence of soil CEC, Ca, Mg, K, soil pH, % soil N, % soil C and % soil organic matter on plant diversity (All p<0.001, K: F=106.6, R2=0.41; CEC: F=38.4, R2=0.20; Ca: F=37.1, R2=0.196; pH: F=19.9, R2=0.12; Mg: F=19.6, R2=0.11; %C: F=17.5, R2=0.098; %N: F=16.5, R2=0.098).
The rate of change in productivity was positively correlated with the rate of change of soil CEC (R2=0.12, F=20.1, p<0.001). We additionally tested for the dependence of productivity on the log of the number of species, soil CEC, and % soil N. The regression had an R2 of 0.63 with significant effects for all three variables (logNumSp: F=75.76, p<0.001; CEC: F=19.7, p<0.001; %N: F=5.09, p=0.025). Different species were responsible for the accumulation of different nutrients. These results present a new avenue of research to disentangle the interrelated effects of biodiversity on productivity and of biodiversity on the accumulation of base cations (Ca, Mg, K).