NITROGEN AVAILABILITY AND FRUITING INFLUENCE NITROGEN CYCLING IN STRAWBERRY

As the primary nutrient applied to and used by strawberry, N allocatio n and cycling within the plant may play an important role in determini ng plant vigor and productivity. Our objectives were to determine 1) h ow N availability and fruit production affect N and fertilizer N (FN) partitioning among and within the vegetative tissues of 'Tribute' stra wberry (Fragaria x ananassa Duch.) and 2) if the root N pool is tempor ary storage N. Plants were fed N-15-depleted NH4NO3 (0.001 atom percen t N-15) for the initial 8 weeks, then were grown for 12 weeks with or without NH4NO3 with a natural N-15 abundance (0.366 atom percent N-15) , and were maintained vegetative or allowed to fruit. The vegetative t issues were sampled at 6 and 12 weeks. Neither N availability or fruit ing 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 r oots were higher with continuous N than with no N. Nitrogen availabili ty was the dominant treatment effect on all plants at 12 weeks; contin uous 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 inhib ited root growth and N accumulation at 6 weeks but had little effect a t 12 weeks. The roots were a strong dry matter and N sink from 6 to 12 weeks. The FN pools, from the N-15-depleted FN supplied during the in itial 8 weeks, exhibited changes similar to those of total N in plants not receiving N, in contrast to plants receiving continuous N where t otal leaflet and petiole N content increased while FN content declined . Total FN per plant declined nearly 26% over 12 weeks; the decline wa s greater in plants receiving N continuously than in those not receivi ng N, but the magnitude of the decline was not affected by fruiting. I ncreasing atom percent N-15 values, primarily in plants receiving cont inuous N after the initial 8 weeks of receiving N-15-depleted FN, indi cated that N cycling occurred through all tissues and N pools, proport ionally 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 a vailable for re-allocation to other tissues, although N cycling throug h it was evident. Rather, leaflet N was primarily remobilized to other tissues.