Plants influence future nature restoration via soil life

Vegetation on a former cornfield.

Former cornfield in Assel (gemeente Apeldoorn).

Attempts to convert former agricultural land into species-rich grassland or heath do not always succeed – which is a pity, because in the Netherlands these semi-natural ecosystems are degrading fast. So, how important is soil life for this ecosystem restoration? The results of research done by Paul Kardol of NIOO-KNAW for his PhD are helping to answer this critical question.

Paul Kardol has demonstrated that the soil life of former arable fields can accelerate or retard ecosystem restoration. In “new nature”, growth-retarding and disease-inducing soil organisms accelerate the change in vegetation. Yet on older “ex-fields”, favourable soil organisms seem to be maintaining the restored ecosystem. Some of these helpful soil organisms are already present in the field, albeit in low numbers. Others come in from the surroundings and colonise the new nature area slowly, multiplying if they find the soil conditions and plants favourable. Via the composition of the soil life, the plants determine the further development of the soil life and thus the future plant growth.
Kardol, a biologist, investigated the relationship between soil life and vegetation in a series of plots in the south of the Veluwe region which had been taken out of agriculture at various times from the recent past to 35 years ago. He recorded the plant species present and raised them in a greenhouse, in soil from the former fields. Arable weeds – which dominate the plant community after land has been taken out of production – had their growth retarded by the soil life, whereas the species from the older ecosystem restoration areas had their growth accelerated. In this way, plant growth developed rapidly from the first pioneers to a rich group of successors. The ecological legacy in the soil is clearly influential.
Kardol then conducted greenhouse experiments. In soil from a recently abandoned arable field he planted six of the commonest pioneer weed species: shepherd’s purse, Canadian fleabane, field pansy, and the grasses marsh foxtail, loose silky-bent and annual meadow-grass. Next, he replanted these six weeds in the soil they had come from and found that each species grew worst in its own soil. The grasses grew less well in soil from the other grasses, but the herbaceous species had less influence on each other. Kardol filtered the bacteria and fungi from the soil and added them to sterile soil. He was able to demonstrate that these microscopic soil organisms probably account for the plants’ reactions to the different soils. It is these microorganisms that form the legacy of the first plants.
To be able to apply these findings in practice we need to understand how you can deploy soil life on a large scale to assist ecosystem restoration. Kardol explains: “Just adding beasties to the soil doesn’t work. They get eaten up or elbowed out by other soil life, or don’t have enough to eat. Solving this is the next big challenge. But the principle does work.”