Table 1.

Dry matter, nodule number, and nodule individual weight of +CO₂ and –CO₂ alfalfa plants

Parameter	Treatments
	Saranac		Insaranac
	+CO2	–CO2	+CO2	–CO2
Shoot dry matter (mg plant−1)	373±160	143*±84	243±40	253±43
Root dry matter (mg plant−1)	153±56	61*±20	109±29	114±6
Nodule dry matter (mg plant−1)	24.3±9.8	12.1±7.9	3.7±1.7	4.6±2.3
Total dry matter (mg plant−1)	550±220	216*±114	355 ±70	370 ±48
Nodule number	24±19	40±11	38±15	56±40
Nodule individual dry weight (mg nodule−1)	1.60±1.06	0.31±0.22	0.11±0.07	0.12±0.12

Plants were grown for 3 weeks with different levels of CO₂ concentration in the root/nodule compartment. ‘Insaranac’ forms fix^–-nodules. Nitrogen nutrition of ‘Saranac’ depended on nitrogen fixation while ‘Insaranac’ plants received 2.5 mg N d⁻¹ as KNO₃. Data are means of four replicates ±sd. An asterisk indicates a statistically significant difference from the +CO₂ treatment of ‘Saranac’ or ‘Insaranac’ (t test, P ≤0.05).