DROUGHT EFFECTS ON GROWTH AND CARBON PARTITIONING IN A TALL FESCUE SWARD GROWN AT DIFFERENT RATES OF NITROGEN FERTILIZATION

摘要

The effects of drought on plant water and nitrogen status, shoot growth and carbon partitioning between root and shoot, were studied during two summer regrowth cycles of a tall fescue sward grown at different rates of application of nitrogen fertilizer. Nitrogen fertilizer was the main factor influencing the relative partitioning of the newly assimilated C-14. Drought did not prevent the expression of the effect of nitrogen fertilization on carbon partitioning. The highest carbon partitioning coefficients to roots (15-30 per cent) were measured in swards having the lowest nitrogen status. With the high nitrogen fertilization rate, water shortage increased the carbon partitioning to roots from 6 to 13 per cent (means for both regrowths, before rewatering). This increase mainly occurred in the surface horizon of soil (0-20 cm). However, an estimate in absolute terms showed that root growth was not increased by drought. Water shortage impaired the sward nitrogen status. It is therefore proposed that at least part of the change in the carbon allocation pattern induced by drought was mediated via an effect on nitrogen nutrition. The importance of the drought-induced modification of carbon partitioning is discussed.