Field measurements of dark respiration rates of roots and aerial parts in Italian ryegrass and barley.
Dark respiration rates of barley and Italian ryegrass were measured under field conditions. Root respiration rates of both species were greatest 1-2 weeks before heading. Respiration rate of tops equalled 0.06P + 0.015W for ryegrass and 0.16P + 0.0033W for barley, where P = gross photosynthetic rate and W = standing dry weight. The dark respiration rate integrated over the growing period was about half of gross photosynthesis.