Earthworm-Mycorrhiza Interactions Can Affect the Diversity, Structure and Functioning of Establishing Model Grassland Communities

Abstract

Both earthworms and arbuscular mycorrhizal fungi (AMF) are important ecosystem engineers co-occurring in temperate grasslands. However, their combined impacts during grassland establishment are poorly understood and have never been studied. We used large mesocosms to study the effects of different functional groups of earthworms (i.e., vertically burrowing anecics vs. horizontally burrowing endogeics) and a mix of four AMF taxa on the establishment, diversity and productivity of plant communities after a simulated seed rain of 18 grassland species comprising grasses, non-leguminous forbs and legumes. Moreover, effects of earthworms and/or AMF on water infiltration and leaching of ammonium, nitrate and phosphate were determined after a simulated extreme rainfall event (40 l m−2). AMF colonisation of all three plant functional groups was altered by earthworms. Seedling emergence and diversity was reduced by anecic earthworms, however only when AMF were present. Plant density was decreased in AMF-free mesocosms when both anecic and endogeic earthworms were active; with AMF also anecics reduced plant density. Plant shoot and root biomass was only affected by earthworms in AMF-free mesocosms: shoot biomass increased due to the activity of either anecics or endogeics; root biomass increased only when anecics were active. Water infiltration increased when earthworms were present in the mesocosms but remained unaffected by AMF. Ammonium leaching was increased only when anecics or a mixed earthworm community was active but was unaffected by AMF; nitrate and phosphate leaching was neither affected by earthworms nor AMF. Ammonium leaching decreased with increasing plant density, nitrate leaching decreased with increasing plant diversity and density. In order to understand the underlying processes of these interactions further investigations possibly under field conditions using more diverse belowground communities are required. Nevertheless, this study demonstrates that belowground-aboveground linkages involving earthworms and AMF are important mediators of the diversity, structure and functioning of plant communities.

Anecic earthworms (Lumbricus terrestris) alleviate negative effects of extreme rainfall events on soil and plants in field mesocosms

“…It should be noted, however, that water infiltration is highly heterogeneous in space (Hassler et al 2014), and that the experiment was performed in intact soil, rather than in a homogenised substrate. Water infiltration may indeed be unpredictable even under highly controlled conditions: for instance, in a greenhouse experiment that simulated a heavy rainfall event similar to ours (40 mm), anecic earthworms increased water infiltration (Zaller et al 2011), but the effect was not repeatable in a subsequent experiment with similar methodology (Zaller et al 2014).…”

“…In particular, earthworms may have improved the availability of N to plants (van Groenigen et al 2014), for instance by incorporating the surface-applied manure into the rhizosphere and releasing N through mucus and casts, stimulating microbial activity and turnover (Postma-Blaauw et al 2006). It is possible that earthworm-enhanced N availability to plants more than compensated for any leaching induced by intense rainfall; but L. terrestris usually increases N losses through leaching (Domínguez et al 2004;Costello and Lamberti 2008;Zaller et al 2011). To ensure that the plants would not be N-limited during the experiment, we had fertilized all the mesocosms with manure more than 1 month before seeding.…”

Herbivory of an invasive slug is affected by earthworms and the composition of plant communities

“…The loss of plant species diversity in grasslands has been shown to affect abundance, biomass and activity of earthworms [18-21]. On the other hand, effects of earthworms have been shown to benefit certain plant functional groups more than others [22-25] affecting plant community structure and diversity [26]. The role of earthworms has been most often studied on a single plant species, while only few have investigated effects on plant communities [27-31].…”

Independent role of belowground organisms and plant cultivar diversity in legume-grass communities

“…This indicates that AMF promoted the growth of the mycotrophic plants (van der Heijden et al, 2003), since Haynes (1980) suggested that T. pratense may be more mycotrophic than L. perenne. In previous studies AMF were found to have positive effects on T. pratense aboveground biomass (Eisenhauer et al, 2009;Zaller et al, 2011b;Sabais et al, 2012). However, studies reported inconsistent results for L. perenne.…”