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ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Research Unit » Research » Publications at this Location » Publication #335438

Title: Root and mycorrhizal fungal foraging responses to fruit removal in apple trees

item LAVELY, EMILY - Pennsylvania State University
item ZHANG, JIANGHONG - Agricultural University Of Hebei
item ADAMS, THOMAS - Pennsylvania State University
item Bryla, David
item DEFOREST, JARED - Ohio University
item MARINI, RICHARD - Pennsylvania State University
item CRASSWELLER, ROBERT - Pennsylvania State University
item EISSENSTAT, DAVID - Pennsylvania State University

Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2018
Publication Date: 8/14/2018
Citation: Lavely, E.K., Zhang, J., Adams, T.S., Bryla, D.R., Deforest, J.L., Marini, R.P., Crassweller, R., Eissenstat, D.M. 2018. Root and mycorrhizal fungal foraging responses to fruit removal in apple trees. Plant and Soil. 146(1-2):401-416.

Interpretive Summary: Complex interactions occur among roots, mycorrhizal fungi, and other organisms in the soil, but the process is rarely studied in a holistic fashion. Both carbon (C) supply to the roots and nutrient-enriched locations in the soil can affect these interactions. In this study, we examined how shifts in C availability below ground affected root and mycorrhizal fungal proliferation in nutrient “hot spots” in the soil, as well as interactions of roots with both mycorrhizal and non-mycorrhizal fungi. We used high-density apple orchards for studying these questions, as fruit biomass is easily manipulated. Under normal production practices, upwards of 80% of the annual biomass in apple is partitioned to fruit, while only about 1% to 2% is partitioned to roots. Overall, we found that increased C availability (as result of fruit removal) caused roots to be less selective to nutrient “hot spots”. Mycorrhizal fungi were less affected by C availability, but reduced C available to roots enhanced the ability of the fungi to internally colonize the roots. In general, root proliferation was more enhanced by inorganic nutrient “hot spots”, while proliferation of the fungal hyphae was more enhanced by organic nutrient “hot spots”. Collectively, this study provides new insights into how C and nutrient availability can influence root and AMF foraging patterns.

Technical Abstract: Nutrient foraging is an energy-intensive process. Shifts in plant-available C, resulting from elevated CO2, shading or variable crop load, may affect root and mycorrhizal fungal foraging strategies and interactions with soil organisms. We manipulated root available C by removing young apple fruit and investigated the effects on root and arbuscular mycorrhizal fungal (AMF) foraging in localized nutrient-rich patches (unfertilized, inorganic N, organic N). We also examined how shifts in plant C availability affected root-fungal interactions. Root colonization by AMF and nonmycorrhizal fungi (NMF) was separated into two key processes: finding the root (external colonization) and entering the root (internal colonization). Defruiting enhanced root production three-fold across N treatments. However, in trees with fruit, about four-fold more roots proliferated selectively in the inorganic-N patch than other patches. In contrast, AMF hyphal biomass was higher in the organic-N patch and was unaffected by fruit removal. External AMF colonization was similar across treatments; however, defruiting and organic N addition reduced the probability of AMF entering roots. NMF were unaffected by defruiting or nutrient addition. Root and mycorrhizal foraging should be considered in the context of C availability. Separating external and internal colonization by AMF and NMF provides additional insight into root-microbe interactions.