MECHANICAL IMPEDANCE OF ROOT-GROWTH DIRECTLY REDUCES LEAF ELONGATION RATES OF CEREALS

A dry soil is generally a hard soil. Thus, the effects of water stress and mechanical impedance on plant growth are difficult to separate. T o achieve this we have developed a growth cell that allows manipulatio n of the strength of growth media (i.e. mechanical impedance) without altering the availability of water or nutrients. We monitored leaf elo ngation rates of barley and wheat seedlings before and after the mecha nical impedance to root growth was increased. Results show that a larg e and rapid reduction (within 10 min) of leaf elongation rates occurre d after impedance to the roots was increased. The average reductions f or barley and wheat, with associated standard errors, were 22.6% (4.84 ) and 36.2% (5.48), respectively. The data are consistent with the hyp othesis that mechanical impedance of roots might have a direct negativ e effect on leaf growth even where nutrients and water are in plentifu l supply to the plant. The implications of the rate of the response ar e examined with respect to the underlying mechanisms controlling root- shoot signalling.