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  • Author or Editor: R. Paul Schreiner x
  • Journal of the American Society for Horticultural Science x
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An interplay between carbon and phosphorus is known to regulate root colonization by arbuscular mycorrhizal fungi (AMF); however, it is unclear whether plant C or plant P status plays a bigger role in controlling the abundance of arbuscules (the primary site of nutrient exchange in AMF symbiosis) in roots. In this study, ‘Pinot noir’ grapevine (Vitis vinifera) was grown in an unsterilized vineyard soil and colonized by indigenous AMF in two experiments, where photosynthetic capacity (defoliation or shading) and shoot nutrition (foliar fertilizer) were manipulated. Temporal changes in root colonization by AMF and plant growth and nutrition were determined. Foliar fertilizer application increased P and K uptake, but reduced Cu uptake in both experiments. Decreasing the photosynthetic capacity of shoots due to defoliation or shading rapidly reduced arbuscules in fine roots (within 7 to 14 days). In contrast a 3-fold increase in shoot P status from foliar fertilizer only reduced arbuscules after a more prolonged time (28 to 56 days). The combination of shading (15% of full sun) and foliar P application reduced arbuscules more than shading alone within the first month, whereas foliar P use in full sun had no influence on arbuscules within a month. Returning plants to full sun after 28 days in shade resulted in a resurgence of arbuscules in roots regardless of plant P status. Arbuscules in grapevine roots are regulated by the interaction between plant C and P status, such that high shoot P reduces arbuscule formation or maintenance more when combined with reduced plant photosynthesis. This indicates that grapevines do not reduce AMF nutrient transfer as an immediate response to elevated shoot P as long as plants are maintained in a high light environment.

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