Transpiration of containerized Picea abies seedlings grown with different irrigation regimes

Abstract

Norway spruce seedlings were grown in 50 ml pots, and irrigated when 30, 50, 70 and 90% of the liquid held at container capacity was left in the substrate. The total volume of nutrient solution added was smallest in the irrigation regime with the most frequent irrigation, and increased with decreased irrigation frequency. This was an effect of increased leaching with decreased irrigation frequency. Within each irrigation regime, the transpiration rate of the highest transpiring seedling was three times that of the lowest transpiring one. The transpiration rate was linearly related to shoot volume, independent of irrigation regime for approximately 50 days. Thereafter, the relationship became curvilinear and more affected by irrigation regime. The deviation from linearity was ascribed to an increased stomatal resistance when the growth substrate became drier. Towards the end of the experiment, the seedlings subjected to the most frequent irrigation transpired on a per seedling basis approximately four times more than seedlings subjected to the least frequent irrigation. Even on a shoot volume (or shoot dry weight) basis the transpiration was 2.5 times higher for seedlings with the most frequent irrigation compared to the ones in the least frequent irrigation. In conclusion, frequent irrigation with small volumes could be a way to reduce the risk for individual seedlings to experience the extreme conditions of drought and drowning, which could be one way to grow more uniform seedlings. Besides, the reduced drainage should reduce the pollution hazards, and more nursery resources could be converted to nursery products.

Key words:

• climate chamber
• peat
• perlite
• phase distribution
• shoot volume