ISSN:
1573-5036
Keywords:
ammonium uptake
;
HATS
;
LATS
;
N remobilization
;
nitrate uptake
Source:
Springer Online Journal Archives 1860-2000
Topics:
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Notes:
Abstract Several studies have previously shown that shoot removal of forage species, either by cutting or herbivore grazing, results in a large decline in N uptake (60%) and/or N2 fixation (80%). The source of N used for initial shoot growth following defoliation relies mainly on mobilisation of N reserves from tissues remaining after defoliation. To date, most studies investigating N-mobilisation have been conducted, with isolated plants grown in controlled conditions. The objectives of this study were for Lolium perenne L., grown in a dense canopy in field conditions, to determine: 1) the contribution of N-mobilisation, NH4 + uptake and NO3 - uptake to growing shoots after defoliation, and 2) the contribution of the high (HATS) and low (LATS) affinity transport systems to the total plant uptake of NH4 + and NO3 -. During the first seven days following defoliation, decreases in biomass and N-content of roots (34% and 47%, respectively) and to a lesser extent stubble (18% and 43%, respectively) were observed, concomitant with mobilisation of N to shoots. The proportion and origin of N used by shoots (derived from reserves or uptake) was similar to data reported for isolated plants. Both HATS and LATS contributed to the total root uptake of NH4 + and NO3 -. The Vmax of both the NH4 + and NO3 - HATS increased as a function of time after defoliation, and both HATS systems were saturated by substrate concentrations in the soil at all times. The capacity of the LATS was reduced as soil NO3 - and NH4 + concentrations decreased following defoliation. Data from 15N uptake by field-grown plants, and uptake rates of NH4 + and NO3 - estimated by excised root bioassays, were significantly correlated, though uptake was over-estimated by the later method. The results are discussed in terms of putative mechanisms for regulating N uptake following severe defoliation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1004728327955
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