Nitrogen availability and fruiting influence nitrogen cycling in strawberry

As the primary nutrient applied to and used by strawberry, N allocation and cycling within the plant may play an important role in determining plant vigor and productivity. Our objectives were to determine 1) how N availability and fruit production affect N and fertilizer N (FN) partitioning among and within the vegetative tissues of 'Tribute' strawberry (Fragaria x ananassa Duch.) and 2) if the root N pool is temporary storage N. Plants were fed ¹⁵N-depleted NH₄NO₃ (0.001 atom percent ¹⁵N) for the initial 8 weeks, then were grown for 12 weeks with or without NH₄NO₃ with a natural ¹⁵N abundance (0.366 atom percent ¹⁵N), and were maintained vegetative or allowed to fruit. The vegetative tissues were sampled at 6 and 12 weeks. Neither N availability or fruiting had consistent effects on dry mass (DM) across all tissues at 6 or 12 weeks. At 6 weeks, the total N content of all tissues except the roots were higher with continuous N than with no N. Nitrogen availability was the dominant treatment effect on all plants at 12 weeks; continuous N increased leaflet, petiole, and total vegetative DM and total n of all tissues. Insoluble reduced N (IRN) was the major N pool within all tissues at 6 and 12 weeks regardless of treatment. Fruiting inhibited root growth and N accumulation at 6 weeks but had little effect at 12 weeks. The roots were a strong dry matter and N sink from 6 to 12 weeks. The FN pools, from the ¹⁵N-depleted FN supplied during the initial 8 weeks, exhibited changes similar to those of total N in plants not receiving N, in contrast to plants receiving continuous N where total leaflet and petiole N content increased while FN content declined. Total FN per plant declined nearly 26% over 12 weeks; the decline was greater in plants receiving N continuously than in those not receiving N, but the magnitude of the decline was not affected by fruiting. Increasing atom percent ¹⁵N values, primarily in plants receiving continuous N after the initial 8 weeks of receiving ¹⁵N-depleted FN, indicated that N cycling occurred through all tissues and N pools, proportionally more in the soluble reduced N pool but quantitatively more in the IRN pool. The root N pool was not a 'temporary' N storage site available for re-allocation to other tissues, although N cycling through it was evident. Rather, leaflet N was primarily remobilized to other tissues.