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Biotic interactions in the rhizosphere as structuring forces for plant communities

Final Activity Report Summary - BIORHIZ (Biotic interactions in the rhizosphere as structuring forces for plant communities)

BIORHIZ was a European Union funded research and training network aiming at training researchers in the early stages of their career in the field of multitrophic interactions. This is a rapidly growing area of major importance, pivotal for unravelling the consequences of human induced global changes on the composition and functioning of ecosystems, on which human societies depend for a sustainable future. The crucial question for BIORHIZ was how interactions between soil organisms and plant roots might influence the performance of plants, their interactions with aboveground associated enemies and symbionts, and the soil system processes. A wide diversity of organisms is involved in these interactions, including decomposers, enemies and mutualists. BIORHIZ partners elucidated mechanisms of interactions in the root zone of plants, i.e. the ‘rhizosphere’, modifying plant growth and vegetation structure. BIORHIZ results enhanced our understanding of the functioning of natural and semi-natural ecosystems under change.

Dramatic declines in diversity and abundance of species associated with farmland in Europe were previously reported and the sustainability of current intensive farming practices was contested. Nevertheless, the role of ecological relationships in the soil and their consequences for the structure and functioning of aboveground communities had received relatively little attention. Recent studies suggested that these interactions, which were usually ‘out of sight out of mind’, were pivotal for understanding changes in the aboveground, more visible biodiversity.

The hotspot for ecological interactions in the soil is the rhizosphere, where plants manipulate microbial communities to improve nutrient availability, combat their soil-borne enemies and associate with symbiotic mutualists. These belowground interactions are indirectly affecting, as well as affected by, aboveground interactions. Therefore, understanding the relationships between biodiversity and ecosystem functioning in terrestrial ecosystems required the coupling of belowground and aboveground biodiversity since both systems depended on each other.

The project outcomes, which were described in detail in BIORHIZ homepage (http://www.zi.ku.dk/biorhiz/) were the following:

1. plant nitrogen uptake and growth depended on the genetic background of crop and plant species. For optimising crop nutrient acquisition, feedbacks on the quality and quantity of fertilizers on crop breed, crop species and crop developmental stage ought to be considered.
2. breeding of crop plants towards cultivars able to interact with rhizosphere symbionts and other soil food web components, rather than just towards maximum performance at high mineral nutrient concentrations, was necessary.
3. root infecting and free living soil organisms complemented each other in fostering plant nutrition and plant growth, thus calling for the development of management systems sustaining the full diversity of rhizosphere symbionts and preventing losing positive synergistic interactions from nutrient uptake.
4. products to foster the functioning of specific soil food web components, e.g. via mycorrhizal inocula, had to be developed in order to increase plant nutrient mobilisation and plant defence against belowground and aboveground natural enemies. This was expected to allow for reduced fertiliser use, because of increased intrinsic nutrient mobilisation and plant uptake, reduced leaching losses and enhanced sustainable crop protection.
5. the composition of the belowground and aboveground food web modulated plant pest infestation, thus enabling the development of crop-specific management systems and the application of complementary organisms to cancel out negative individual effects, reducing chemical pest control.