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Photosynthesis, respiration and nitrogen fixation in white clover
Author(s) -
HAYSTEAD A.,
KING J.,
LAMB W. I. C.
Publication year - 1979
Publication title -
grass and forage science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.716
H-Index - 56
eISSN - 1365-2494
pISSN - 0142-5242
DOI - 10.1111/j.1365-2494.1979.tb01456.x
Subject(s) - respiration , acetylene , photosynthesis , nitrogen fixation , nitrogenase , shoot , biology , ammonia , nitrogen , botany , agronomy , zoology , horticulture , chemistry , biochemistry , organic chemistry
An apparatus in which shoot and root CO 2 exchange and acetylene reduction can be simultaneously measured in specific white cloverrhizobium associations is described. In mature stolonating clover there was a fairly constant ratio between net photosynthesis, root respiration and acetylene reduction. Of the net carbon fixed daily (12 h light of 80 W m ‐2 , 400–700 nm; day/night temperature 15°C) 12% was lost during the dark period by the shoot and 17% by the nodulated root. Changes in the rate of acetylene reduction by nodulated root systems occurred more slowly than those in rates of root respiration in response to reduced irradiance. In 21·5 h continuous darkness the rate of acetylene reduction remained constant. Responses to increased irradiance were more immediate in both root respiration and acetylene reduction. In plants maintained at 15°C in a 12‐h, 80‐W m ‐2 photoperiod there was no significant diurnal variation in acetylene reduction or root respiration. Acetylene depressed root respiration by 20%. Assuming the energy requirement of the nitrogenase system to be the same when reducing acetylene and N the depression can be used as an indication of the energy requirement of fixed N assimilation, metabolism and export in the nodulated root. Of the net carbon fixed daily 3·4% was utilized in this way in plants growing in a 12‐h photoperiod (80 W m ‐2 , 400–700 nm) at 15°C.