DISPOSITION OF NITROGEN AND SOLUBLE SUGARS IN MANITOU SPRING WHEAT AS INFLUENCED BY N FERTILIZER, TEMPERATURE AND DURATION AND STAGE OF MOISTURE STRESS

Manitou spring wheat (Triticum aestivum L.) was grown at combinations of three different day/night temperatures (27/12 °C, 22/12 °C and 17/12 °C), three levels of fertilizer N (58, 116 and 174 kg N/ha), and three moisture stresses (nominally −0.03, −1.5 and −4.0 MPa) applied for four durations (viz., no stress throughout, stress from (i) four-tiller (Tg), (ii) boot (Bt), or (iii) flowering (Fl) stages to harvest (Hvst)). Plant and soil samples were analyzed at eight growth stages. Plants grown at 22/12 °C or 17/12 °C and given 116 or 174 kg N/ha lost some N between heading and flowering. Plant N content (dry weight × % N) was depressed by moisture stress in proportion to the duration of the stress even though N concentration was increased. Plant N content was not greatly affected by temperature due to the compensating effects of temperature on dry matter and N concentration. N content of heads was depressed most by moisture stress applied from the Bt stage. Between Fl and Hvst the roots, leaves and stems lost an average 27, 39 and 63% of their N content, respectively. Stems could have contributed a maximum of about 30%, roots 14%, leaves 10% and chaff 7% of the grain N content at Hvst; thus, almost 40% of the grain’s N was taken up during grain filling. An average 75% of the aboveground plant N was located in the grain. At 27/12 °C nonstructural carbohydrate (NSC) concentration in stems reached a maximum at Fl compared to dough stage at 22/12 °C, but it decreased rapidly thereafter. In contrast to N concentration, NSC concentration in stems was lowest at 27/12 °C; also, moisture stress from Bt or Tg stages decreased NSC concentration. Like N content, NSC content was reduced in proportion to the duration of moisture stress. High temperature, N fertilizer, and moisture stress from Tg or Bt stages (conditions favoring high grain protein) increased the proportion of the vegetative organs’ weight loss, between Fl and Hvst, that was N-linked. The amount of NSC-associated dry matter lost from stems during grain filling was generally greater for late or low moisture stressed plants, for plants grown under cooler conditions, and for plants grown at higher N rates (conditions favoring greater grain yields). Of the moisture treatments, stress applied from Fl increased NSC-associated dry matter lost from stems the most, probably suggesting that assimilate translocation was used by the plant to compensate for reduced flag-leaf-produced photosynthate. Respiration losses associated with NSC translocation from stems to heads was greater at 22/12° than at 17/12 °C; there was little NSC translocation apparent at T27/12 °C.Key words: Plant nitrogen, soluble sugars, nitrogen effect, temperature effect, moisture stress effect, spring wheat (Triticum aestivum L.)