PARTITIONING OF BIOMASS IN WATER-STRESSED AND NITROGEN-STRESSED COTTON DURING PRE-BLOOM

The partitioning of biomass between aboveground parts and roots, and b etween vegetative and reproductive plant parts plays a major role in d etermining the ability of cotton (Gossypium hirsutum L.) to produce a crop in a given environment. We evaluated the single and combined effe cts of water and N supply on the partitioning of biomass in cotton pla nts exposed to two N supply levels, 0 and 12 mM of N, and two water re gimes, well irrigated and water-stressed at an early reproductive stag e. The N treatments began when the third true leaf was visible, while water deficit treatments were imposed over the N treatments when the p lants were transferred into controlled-environment chambers at a leaf area near 0.05 m(2). Both water deficits and N deficits inhibited tota l biomass accumulation and its partitioning in cotton. Water deficit a lone and N deficit alone inhibited the growth of leaves, petioles, and branches, but did not inhibit growth of the stem and enhanced the acc umulation of biomass in squares. When water deficit was superimposed o n N deficit, leaf growth was inhibited, although to a lesser extent th an when it was the sole stress factor, and the accumulation of biomass in squares was also inhibited, Yet, the dry weight of squares in plan ts exposed to water and N deficits was greater than that of non-stress ed plants. Water and N deficits, either alone or in combination, did n ot inhibit the growth of the tap root. Growth of lateral roots was not inhibited either by water deficit alone or in combination with N defi cit, but was enhanced when plants were exposed to N deficit alone. Exp osure to water deficit alone or in combination with N deficit decrease d the shoot:root ratio through the inhibition of shoot growth. Exposur e to N deficit alone decreased the shoot:root ratio through the combin ation of shoot growth inhibition and root growth enhancement.