Quantitative estimates of uptake and internal cycling of 14N-labeled fertilizer in mature walnut trees

Abstract

Uptake and internal cycling of nitrogen (N) in mature walnut trees was studied over a period of 6 years using (15)N-depleted fertilizer and full-canopied walnut (Juglans regia L. cv Hartley) trees. The magnitude of internal N cycling, i.e., the availability of N for new growth from internal N pools, was quantified using both the percent annual depletion (PAD) and the N balance budget approaches. There was good agreement between the two measures, and about 60% of annual N demand was derived from N redistribution from internal pools. The remaining 40% of annual tree N demand was met by an influx of N from the soil/fertilizer pool. Trees were excavated, processed and analyzed after 6 years to determine total tree N content and labeled N recovery. Trees recovered 29.4% of the labeled N applied and, based on previous evidence, we assumed that tree accumulation of labeled N occurred entirely in the first year. Labeled N in the fruits and leaves harvested in the first year represented 26% of the total labeled N accumulated, and the remaining 74% of the labeled N accumulated that year was stored and used to support development of annual organs in subsequent years. In the first year, the early maturing catkins did not accumulate labeled N, indicating their exclusive reliance on internal N. Using the atom% (14)N excess values of catkins and an exponential decline equation to determine turnover rate, the Mean Residence Time (MRT) of storage N in the tree was estimated to be 2.0 years. The size of the cycling pool of storage N in the tree was estimated to be about 50% of the total N content of perennial tree parts. Our data support the hypotheses that: (1) in any given year, mature walnut trees store the majority of soil and fertilizer N absorbed and within 2 years following uptake the N is remobilized and used for new growth, and (2) about half of the total N content of the perennial parts of mature walnut trees is present as nonstructural N and is available for recycling.

Coupling Sap Flow Velocity and Amino Acid Concentrations as an Alternative Method to 15N Labeling for Quantifying Nitrogen Remobilization by Walnut Trees

“…When shoot growth was completed, N remobilization had provided around 54% of total N to new shoots. This result is consistent with the values of 60% estimated for larger walnut trees grown in the orchard by Weinbaum and Van Kessel (1998), although higher values of 75% have also been reported for field-growing walnut trees by Deng et al (1989). Similar percentages of N derived from remobilization for new growth were found in young pear (Pyrus communis) trees (Taglivani et al, 1997), in kiwifruit (Actinidia deliciosa) in orchard conditions (Ledgard and Smith, 1992), and in B. pendula, 40% (Millard et al, 1998).…”

“…A second hypothesis is that the amino acids were specific to N remobilization, but that remobilization of N taken up in 1999 (hence labeled N) and in 1998 (hence unlabeled N) occurred concurrently. The latter hypothesis is supported by the fact that Weinbaum and Van Kessel (1998) demonstrated that N assimilated in a given year can be remobilized 2 years later in walnut. In this case, changes in APE during the 80 d after bud burst could be attributable to changes in the relative importance of remobilization from labeled N taken up in 1999 and unlabeled N taken up in 1998.…”

“…It should be noted that we estimated the importance of remobilization of N stored during the previous year only. However, our trees already had reserve organs (tap root and trunk mainly) in early 1999, and N stored during a given year can be used 2 years after, as observed in walnut (Weinbaum and Van Kessel, 1998). Thus, the percentage of total N derived from remobilization for new shoot growth in walnut was probably higher than 54%.…”

Nitrogen in Citrus: Signal, Nutrient, and Use Efficiency

“…More recently, Boaretto et al ( 2010 ) estimated the NUpE averaged in 36% and 52% for orange and lemon trees (3 years old), respectively, both grafted on Swingle citrumelo. Similar values ranging between 25% and 80% were obtained not lately in mature trees grown in the fi eld (Dasberg et al 1984 ; Feigenbaum et al 1987 ;Weinbaum and Van Kessel 1998 ) and citrus rootstock seedlings (Lea-Cox and Syvertsen 1996 ) . The young nonbearing citrus plant, conversely, exhibited lower values of FUE by <5% (Weinert et al 2002 ) and <6% (Menino et al 2007 ) in the fi rst year after transplantation, while Lea-Cox et al ( 2001 ) reported FNR values ranging from 14.9% to 39.3% in bearing Redblush grapefruit, 4 years old.…”

Partitioning of remobilised N in young beech (Fagus sylvatica L.) is not affected by elevated [CO2]

“…roots and stem) served as N stores for spring growth in deciduous trees, e.g. Betula pendula [10], Juglans regia [19] or Prunus persica [14]. Marmann et al [8] showed that in Fraxinus excelsior N was mainly stored in the roots, whereas our data indicate that in beech N stocks in coarse roots and stem contributed about the same portion to new shoot growth.…”