Nitrogen reserve status affects the dynamics of nitrogen remobilization and mineral nitrogen uptake during recovery of contrasting cultivars of Lolium perenne from defoliation

Abstract

Nitrogen (N) allocated to leaf growth in forage grasses and legumes following severe defoliation is predominately mobilized from the remaining root and leaf sheath tissues, since both N uptake from the soil and N # fixation are severely down-regulated for several days. The hypothesis that a low N reserve status at the time of defoliation limits N remobilization and leaf regrowth was tested with contrasting cultivars of Lolium perenne (cvs Aberelan and Cariad) in flowing solution culture. Plants were grown under ' high ' or ' low ' (uptake of N decreased by 50 %) regimes of N supply for 10 d before a single severe defoliation. Labelling with "&N was used to assess the importance of N reserves, including putative vegetative storage proteins, relative to N translocated from concurrent uptake, as a source of leaf N during regrowth. Leaf regrowth, N uptake and N mobilization were all affected by previous N supply. Low plant N status at the time of defoliation increased regrowth dry weight of ' Aberelan ' by 10 % and translocation of N absorbed from the medium by 23 %, while mobilization of N reserves was decreased by 56 %. On the contrary, regrowth dry weight of ' Cariad ' was decreased by 23 %, and translocation of N absorbed by 21 % in low plant N status, compared with high plant N status. Concentrations of soluble protein in roots and remaining leaf sheaths decreased after defoliation in plants only under optimal N supply. Analysis of soluble proteins in sheath material by SDS-PAGE suggested that three polypeptides (55, 36.6 and 24 kDa) might function as vegetative storage proteins, although they were of low abundance in plants, subjected to monthly harvests, grown in controlled conditions and in the field. The apparent antagonism between uptake of NH % + or NO $ − by roots and mobilization of N reserves is discussed together with evidence for functional vegetative storage proteins in L. perenne.

Dynamic niche sharing in dry acidic grasslands -a 15N-labeling experiment

“…Our observation indicated seasonal and successional dynamics in N-form utilization of plant species especially with varying site-specific conditions, such as mineral soil-N concentration or plant interaction (density) which occur during succession (see also Louahlia et al 1999;McKane et al 2002;Jumpponen et al 2002;Kahmen et al 2006). The observation of C. canescens and R. acetosella across three successional stages showed that both species used the same N-sources, but in different amounts.…”

Exogenous proline and proline-enriched Lolium perenne leaf extract protects against phytotoxic effects of nickel and salinity in Pisum sativum by altering polyamine metabolism in leaves

“…Like in various other naturally prolineaccumulating plants (Suresh et al, 2008), LP leaves also contain high concentrations of proline (Kemble and MacPherson, 1954). Beside this, LP leaf extract contains significant amounts of various inorganic nutrients and organic compounds like nitrogen, phosphorus, calcium, potassium, magnesium, fiber, carbohydrates, and proteins (Louahlia et al, 1999;Harrington et al, 2006). However, utilization of this natural proline source in mitigating salinity-and/or nickel-induced deleterious effects cannot be found in the literature.…”

Regrowth dynamics of Calamagrostis epigejos after defoliation as affected by nitrogen availability

“…It has been well established that plant nutrient status at the time of defoliation is an important determinant of subsequent regrowth (Ourry et al 1989, Thornton and Millard 1996, Volenec et al 1996, Louahlia et al 1999.…”

“…Higher contents of nitrates, free amino acids and soluble proteins were frequently observed in plants grown under high N availability (Morvan-Bertrand et al 1999a, Louahlia et al 1999, Gloser 2002. Although the high content of soluble nitrogen compounds is not necessarily connected with rapid plant regeneration, the magnitude and dynamics of mobilization of nitrogen reserves after defoliation usually depends on the plant N status at the time of defoliation (Ourry et al 1989, Louahlia et al 1999. Dependence of defoliated plants on nitrogen and carbon reserves also varies throughout regrowth (De Visser et al 1997, Morvan-Bertrand et al 1999a.…”

“…The most important organs for storage of reserves in grasses are frequently stubble and root, where considerable mobilization of both carbon and nitrogen during plant regrowth has been observed (Ourry et al 1988, Louahlia et al 1999, Morvan-Bertrand et al 1999b). On the other hand, little is known about the role of rhizomes of rhizomatous grasses in plant regeneration after defoliation.…”