Why nature restoration takes time

A unique insight into the full soil community network

By Elly Morriën and the EcoFINDERS team

Soil organisms have an important role in aboveground community dynamics and ecosystem functioning. However, most studies have considered soil biota as a black box or focussed on specific groups, whereas little is known about entire soil networks. With a consortium of colleagues from Europe, in the EU-funded EcoFinders project, we show that during the course of nature restoration on abandoned arable land a compositional shift in soil biota, preceded by tightening of the belowground networks, corresponds with enhanced efficiency of carbon uptake.

We examined a chronosequence of semi-natural grasslands in The Netherlands on sandy-loam soil that were abandoned 5-10 years ago (Early), 20-28 years ago (Mid), and >30 years ago (Long-term). In mid and long-term abandoned field soil, carbon uptake by fungi increases without an increase in fungal biomass, about 10% is fungal biomass and 90% is from bacteria, or shift in bacterial to fungal ratio. In previous studies on the same chronosequence, researchers showed that fungal biomass did not increase with time since abandonment, whereas they expected fungal biomass to increase with time since abandonment. The question remained what is the functional contribution of soil fungi to soil food web development and functioning. We discovered that already at an early stage in succession half the amount of carbon that flows from plants into soil is taken up by the soil fungi. After 30 years, that share has risen to three quarters of the plant-derived carbon stored in the soil. By labelling the carbon atoms, we were able to follow the carbon flow into the soil food web. In this way, we could link the organisms to their corresponding functions in the community. This linking has never been done before at such a large scale.

These results advance our view of soil community development and consequences for ecosystem development and vegetation-soil feedbacks in terrestrial ecosystems. The implication of our findings is that during nature restoration the efficiency of nutrient cycling and carbon uptake can increase by a shift in fungal composition and fungal activity. Therefore, we propose that relationships between soil food web structure and carbon cycling in soils need to be reconsidered. Fungal/bacterial biomass ratio’s may explain part of the processes, but understanding of the whole process requires considering the activities of these organisms as well. These results may be applied in future nature restoration activities, but perhaps they can also be used in order to promote the sustainability of agricultural soils.

LINK to article: http://www.nature.com/articles/ncomms14349

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