Influence of initial organic N reserves and residual leaf area on growth, N uptake, N partitioning and N storage in alfalfa (Medicago sativa) during post-cutting regrowth.
OBJECTIVE
The influence of initial residual leaf area and initial N reserves on N uptake, final N distribution, and yield in alfalfa regrowing after cutting, were studied.


METHODS
The effects of two levels of initial residual leaf area (plants cut to 15 cm, with (L+) or without (L-) their leaves) and two initial levels of N status [high N (HN) or low N (LN)] on growth, N uptake and N partitioning, allocation and storage after 29 d of post-cutting regrowth were analysed.


RESULTS
During most of the regrowth period (8-29 d after the initial harvest), HN and L+ plants had higher net N uptake rates than LN and L- plants, respectively, resulting in a greater final mineral N uptake for these treatments. However, the final partitioning of exogenous N to the regrowing shoots was the same for all treatments (67 % of total exogenous N on average). Final shoot growth, total plant N content, and N allocation to the different taproot N pools were significantly lower in plants with reduced initial leaf area and initial N reserve status.


CONCLUSIONS
Although both initial residual leaf area and initial N reserves influenced alfalfa regrowth, the residual leaf area had a greater effect on final forage production and N composition in the taproot, whereas the N uptake rate and final total N content in plant were more affected by the initial N reserve status than by the residual leaf area. Moreover, N storage as proteins (especially as vegetative storage proteins, rather than nitrate or amino acids) in the taproot allowed nitrate uptake to occur at significant rates. This suggests that protein storage is not only a means of sequestering N in a tissue for further mobilization, utilization for growth or tissue maintenance, but may also indirectly influence both N acquisition and reduction capacities.
UMR INRA/UCBN, Ecophysiologie Végétale, Agronomie & Nutritions N, C, S. Institut de Biologie Fondamentale et Appliquée, Université, 14032 Caen Cedex, France. avice@ibfa@unicaen.fr
F
F
Meuriot
J-C
JC
Avice
J-C
JC
Simon
P
P
Laine
M-L
ML
Decau
A
A
Ourry
D001692:Biological Transport / Q000187:drug effects; D018533:Biomass; D000455:Medicago sativa / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D008954:Models, Biological; D009566:Nitrates / Q000494:pharmacology; D009584:Nitrogen / Q000378:metabolism*; D018515:Plant Leaves / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D018520:Plant Shoots / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism
D009566:Nitrates; D010940:Plant Proteins; D009584:Nitrogen; C006568:ammonium nitrate