Interrelated effects of mycorrhiza and free‐living nitrogen fixers cascade up to aboveground herbivores

• Published in: Ecology and evolution Vol. 5; no. 17; pp. 3756 - 3768
• Main Authors: Khaitov, Botir, Patiño‐Ruiz, José David, Pina, Tatiana, Schausberger, Peter
• Format: Journal Article
• Language: English
• Published: England John Wiley & Sons, Inc 01.09.2015; John Wiley & Sons, Ltd
• Subjects: Aboveground–belowground interactions; Araneae; arbuscular mycorrhiza; Arbuscular mycorrhizas; Azotobacter chroococcum; Bacteria; Colonization; Fitness; Fixing; Flowers & plants; Fungi; Glomus mosseae; Herbivores; Host plants; Leaves; Microorganisms; Mites; multitrophic interactions; Natural enemies; Nitrogen; nitrogen fixation; Original Research; Phaseolus vulgaris; Plant growth; Plant tissues; Reproduction; Rhizosphere; Rhizosphere microorganisms; spider mites; Tetranychus urticae; Aboveground–belowground interactions; multitrophic interactions; spider mites; nitrogen fixation; arbuscular mycorrhiza; fitness
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.1654

Aboveground plant performance is strongly influenced by belowground microorganisms, some of which are pathogenic and have negative effects, while others, such as nitrogen‐fixing bacteria and arbuscular mycorrhizal fungi, usually have positive effects. Recent research revealed that belowground interactions between plants and functionally distinct groups of microorganisms cascade up to aboveground plant associates such as herbivores and their natural enemies. However, while functionally distinct belowground microorganisms commonly co‐occur in the rhizosphere, their combined effects, and relative contributions, respectively, on performance of aboveground plant‐associated organisms are virtually unexplored. Here, we scrutinized and disentangled the effects of free‐living nitrogen‐fixing (diazotrophic) bacteria Azotobacter chroococcum (DB) and arbuscular mycorrhizal fungi Glomus mosseae (AMF) on host plant choice and reproduction of the herbivorous two‐spotted spider mite Tetranychus urticae on common bean plants Phaseolus vulgaris. Additionally, we assessed plant growth, and AMF and DB occurrence and density as affected by each other. Both AMF alone and DB alone increased spider mite reproduction to similar levels, as compared to the control, and exerted additive effects under co‐occurrence. These effects were similarly apparent in host plant choice, that is, the mites preferred leaves from plants with both AMF and DB to plants with AMF or DB to plants grown without AMF and DB. DB, which also act as AMF helper bacteria, enhanced root colonization by AMF, whereas AMF did not affect DB abundance. AMF but not DB increased growth of reproductive plant tissue and seed production, respectively. Both AMF and DB increased the biomass of vegetative aboveground plant tissue. Our study breaks new ground in multitrophic belowground–aboveground research by providing first insights into the fitness implications of plant‐mediated interactions between interrelated belowground fungi–bacteria and aboveground herbivores. Our study provides a key example of the interrelated effects of two primarily plant‐mutualistic microorganisms, mycorrhizal fungi and free‐living nitrogen‐fixing bacteria, on herbivorous spider mites feeding on aboveground plant parts. It breaks new ground in multi‐trophic below‐aboveground research by providing first insights into the implications of plant‐mediated belowground fungi‐bacteria interactions on fitness of aboveground herbivores.