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1999 (1)
1996 (1)
1Author    Domingo Morales3, Juliane Peters3, M. Soledad, Jim Énez3, Michael Tauszb, Astrid Wonischb, Dieter GrillbRequires cookie*
 Title    Gas Exchange of Irrigated and Non-Irrigated Pinus canariensis Seedlings Growing Outdoors in La Laguna, Canary Islands, Spain  
 Abstract    Chlorophyll fluorescence, gas exchange, water potential and relative water content were measured in the needles of five year old seedlings of Pinus canariensis in order to know their response to mild water stress. Two trial plots of ten plants per plot, of similar age and characteristics were irrigated daily until the experiment was undertaken, then one of the plots was left without watering while the other one was irrigated as before. After a week of treatment, the water potential at midday did not change in any of the irrigated or non-irrigated plants maintaining around -0 .4 MPa, and the relative water content changed from 93% in irrigated to 84% in non-irrigated seedlings. The stomatal conductance decreased 60% in non irrigated plants and as a result C 0 2 assimilation decreased by 50% and transpiration was reduced at a higher proportion (70%), indicating a good control against water loss, before any change in water status in the needles could be observed suggesting an isohydric water economy in this plant. 
  Reference    Z. Naturforsch. 54c, 693—6 (1999); received December 14 1998/March 21 1999 
  Published    1999 
  Keywords    Pinus canariensis, Mild Water Stress, Gas Exchange, Water Potential, Chlorophyll Fluorescence, Seedlings 
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 TEI-XML for    default:Reihe_C/54/ZNC-1999-54c-0693.pdf 
 Identifier    ZNC-1999-54c-0693 
 Volume    54 
2Author    Aloysius Wild, Peter Sabel, Lucia Wild-Peters, Ursula SchmiedenRequires cookie*
 Title    Photosynthesis and Transpiration in Damaged and Undamaged Spruce Trees  
 Abstract    The investigations presented here focus on the C 0 2/H 20 gas exchange in damaged and undamaged spruce trees while using open-air measurements as well as measurements under defined conditions in the laboratory. The studies were performed at two different sites in the Hunsrück and the Westerwald mountains. In the laboratory the C 0 2/H 20 gas exchange was measured on detached branches under controlled conditions in the course of two years. C 0 2 saturation curves were also generated. In addition C 0 2 compensation points were deter­ mined employing a closed system. In the natural habitat diurnal course measurements of photosynthesis and transpiration as well as light-saturation curves for photosynthesis were performed. In parallel with the photosynthesis and transpiration measurements, measure­ ments of the water potential were taken at both locations. The photosynthetic capacity and transpiration rate show a typical annual course with pro­ nounced maxima in spring and late summer and minima in summer and winter. The needles of the damaged trees exhibit higher transpiration rates and a distinct reduction in photosyn­ thesis than the needles of the undamaged trees during two seasons. The diurnal course mea­ surements of net photosynthesis and transpiration show a maximum in photosynthesis and transpiration in the afternoon in May and September, but a characteristic midday depression in July. Photosynthesis was markedly lower and transpiration higher in the needles of the damaged trees. The damaged trees show a lower increase in the light and C 0 2 saturation curves and higher C 0 2 compensation points as compared to the undamaged trees. The water potential reaches much lower values during the course of the day in needles of the dam­ aged trees. The reduction of the photosynthetic rate on one hand and the increase in transpiration on the other hand result in an extrem e lowering of the water use efficiency in photosynthesis. The damage to the thylakoid membranes and to the guard cells obviously results in a pro­ found disturbance of the physiological hom eostasis o f the needles and could thus lead to premature needle loss. 
  Reference    Z. Naturforsch. 51c, 200 (1996); received Decem ber 27 1995/January 29 1996 D edicated to 
  Published    1996 
  Keywords    birthday C 0 2/H 20 Gas Exchange C 0 2 Compensation Point, Photosynthesis, Picea abies, Transpiration, Water Potential, Forest D isease 
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 TEI-XML for    default:Reihe_C/51/ZNC-1996-51c-0200.pdf 
 Identifier    ZNC-1996-51c-0200 
 Volume    51