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Contribution of Current Photosynthates to Root Respiration of Non‐Nodulated Medicago sativa : Effects of Light and Nitrogen Supply
Author(s) -
Lötscher M.,
Gayler S.
Publication year - 2005
Publication title -
plant biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.871
H-Index - 87
eISSN - 1438-8677
pISSN - 1435-8603
DOI - 10.1055/s-2005-872881
Subject(s) - respiration , biology , photoperiodism , medicago sativa , sowing , botany , shoot , agronomy , zoology , horticulture
The effects of light (PFD) and nitrogen (N) supply on root respiration of new C (currently assimilated carbon, R new ) and old C ( R old ) were analysed in non‐nodulated Medicago sativa . Plants were pre‐treated with high/low PFD and high/low N supply with a regular 16/8 h light/dark cycle. Five to eight weeks after planting current photosynthates were labelled with 13 C and their contribution to root respiration was continuously measured during a 24 h day/night cycle. PFD conditions during labelling were either those of the pre‐treatments (control, 25 or 6 mol m ‐2 d ‐1 ) or, for high PFD plants, 6 mol m ‐2 d ‐1 by shortening the photoperiod or reducing irradiance. The fraction of new C in the respiratory CO 2 increased during the light period, but remained constant in the dark period. In control plants, R new contributed 40 % to the daily root respiration in high PFD/high N conditions. Continuously low PFD increased (50 %) and low N decreased (26 %) the contribution of R new . Exposing plants from high PFD pre‐treatments to a short photoperiod or to low PFD stimulated R old , indicating mobilisation of reserve C. This stimulation was more pronounced in plants with high N supply than in those with low N supply. Comparison with other legumes suggested that R new in root respiration was mainly defined by the ratio between the assimilatory capacity of the shoots and the maintenance costs of roots with a short‐term capacity of buffering respiratory demand by mobilisation of reserves in situations of fluctuating PFD.