Dynamic responses of wheat to drought and nitrogen stresses during re-watering cycles

Temporal responses to drought and nitrogen stresses were studied on wheat (Triticum aestivum) seedlings subjected to drying and re-watering cycles. Growth traits were monitored in a soil column experiment conducted with two water and two nitrogen levels. Leaf area, dry weight, carbon and nitrogen mass, root/shoot ratio, specific leaf nitrogen, photosynthesis, transpiration, and water and nitrogen use efficiencies dynamically responded to water and nitrogen stresses as a function of the degree of specific stress over the growing period. Specific leaf nitrogen was critical for improving photosynthetic activity, and influenced water use efficiency positively but nitrogen use efficiency negatively, indicating a distinct trade-off between water and nitrogen use efficiencies. Subsequent to irrigation and the immediate alleviation of severity of water and nitrogen stresses, photosynthesis and transpiration recovered gradually over a period of 3-4 days. Extent of recovery was influenced by the degree of stress prior to re-watering and the re-watering cycles. Ignoring the dynamics of recovery from stress led to notable errors in numerical simulations of the dynamics of soil water and plant transpiration.