Small swards of mycorrhizal and non-mycorrhizal subterranean clover plants were grown in an artificial rooting medium in pots so as to form a closed canopy, by which time plants were about 5 weeks old and had 30 % infection in mycorrhizal roots. Specific rates of dark respiration of mycorrhizal and uninfected populations of plants were compared in an incubation chamber after exposure of the sward to standard light flux density and temperature on a 12 h day/12 h night cycle. Growth efficiencies were measured by exposing a sward to variable light flux density at constant temperature and monitoring the CO2-exchange rate.
The dark respiration rate of whole plants decreased during darkness from an initial value measured immediately after the start of incubation to one about 20% lower after 12 h. Rates for excised roots decreased to about 35% of the initial value. When compared on the same basis the specific rate of dark respiration of mycorrhizal plants did not differ from that of uninfected plants. Likewise, mycorrhizal plants and uninfected plants displayed the same growth efficiency, for both used about 30 % of the net CO2 gain during the light period for purposes of biosynthesis. This parameter was not affected by phosphate nutrition. Mycorrhizal and uninfected plants responded to change in light flux density in a similar manner.
It is concluded that when CO2 fluxes are measured on a whole-plant basis over a 24 h period, mycorrhizal and uninfected plants of subterranean clover grown as swards, have essentially similar carbon economies.