Abstract
Four experiments on the simulation of a persistent drought period were carried out with cloned Picea abies (L.) Karst. trees: two in the field under varying weather conditions and two in a climate chamber under variously manipulated humidity conditions. Patterns of diurnal dynamics in gas exchange rates and water potential were monitored and analyzed. The first phase of the drought was characterized by relatively high daily maxima for photosynthesis and transpiration. With decreasing humidity during the day, the values dropped steeply, and the declines were larger and occurred earlier on each passing day of the drought period. When soil water potential was lower than -2000 hPa, maximum stomatal aperture was greatly reduced despite a humid atmosphere. Under these conditions, rates of photosynthesis and transpiration decreased less steeply from the daily maxima and differences between maxima and minima were small. In the field, the daily sums of transpiration and photosynthesis were more dependent on atmospheric conditions than on soil water potential. In the growth chamber experiments, the daily sums of transpiration and photosynthesis decreased continuously as the soil dried, at first steeply until a soil water potential of -2000 hPa was reached, then slowly. Predawn water potential values fluctuated under field conditions, but tended to decrease with time, whereas needle osmotic potential increased slightly. Because relative humidities did not reach 100% in the growth chamber, predawn water potentials of plants in the growth chamber were never higher than -1.0 MPa although the soil was saturated. In the experiment with a high average air humidity during the daily stress period, relatively high predawn water potentials were maintained until lower soil water potentials of -8000 hPa were reached. Results were used to assess the importance of evaporative demand versus soil drying on stomatal responses within the context of current concepts of plant water relations. The observed trends in diurnal dynamics can be explained solely by the interdependency of leaf conductance and water potential. Stomata react directly to the ratio of water supply to demand. The central role of peristomatal transpiration in this system is emphasized.
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Claims 12
Claim · model-written summary
Early in drought, daily maximum photosynthesis and transpiration were relatively high.
- Taxon
- Picea abies
Picea abiest0 - Outcome
- photosynthesis and transpiratione0
- Direction
- relatively highe0
- Qualifier
- first phase of the droughte0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The first phase of the drought was characterized by relatively high daily maxima for photosynthesis and transpiration.”
t0“Picea abies”
Claim · model-written summary
As humidity fell during the day, gas exchange dropped more steeply and earlier on successive drought days.
- Taxon
- Picea abiesPicea abiest0
- Outcome
- gas exchange ratese1
- Direction
- droppede0
- Qualifier
- larger and occurred earlier on each passing daye0
- Setting
- decreasing humidity during the daye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“With decreasing humidity during the day, the values dropped steeply, and the declines were larger and occurred earlier on each passing day of the drought period.”
e1“Patterns of diurnal dynamics in gas exchange rates and water potential”
t0“Picea abies”
Claim · model-written summary
Maximum stomatal aperture was greatly reduced below a soil water potential of -2000 hPa, despite humid air.
- Taxon
- Picea abiesPicea abiest0
- Outcome
- maximum stomatal aperturee0
- Direction
- greatly reducede0
- Qualifier
- despite a humid atmospheree0
- Setting
- soil water potential was lower than -2000 hPae0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“When soil water potential was lower than -2000 hPa, maximum stomatal aperture was greatly reduced despite a humid atmosphere.”
t0“Picea abies”
Claim · model-written summary
At low soil water potential, photosynthesis and transpiration declined less steeply from daily maxima, with small max-min differences.
- Taxon
- Picea abiesPicea abiest0
- Outcome
- rates of photosynthesis and transpiratione0
- Direction
- decreased less steeplye0
- Qualifier
- differences between maxima and minima were smalle0
- Setting
- soil water potential was lower than -2000 hPae1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Under these conditions, rates of photosynthesis and transpiration decreased less steeply from the daily maxima and differences between maxima and minima were small.”
e1“When soil water potential was lower than -2000 hPa”
t0“Picea abies”
Claim · model-written summary
In the field, daily transpiration and photosynthesis sums depended more on atmospheric conditions than soil water potential.
- Taxon
- Picea abiesPicea abiest0
- Outcome
- daily sums of transpiration and photosynthesise0
- Qualifier
- more dependent on atmospheric conditionse0
- Comparator
- soil water potentiale0
- Setting
- fielde0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In the field, the daily sums of transpiration and photosynthesis were more dependent on atmospheric conditions than on soil water potential.”
t0“Picea abies”
Claim · model-written summary
In growth chambers, daily transpiration and photosynthesis sums fell continuously as soil dried, steeply to -2000 hPa and then slowly.
- Taxon
- Picea abiesPicea abiest0
- Outcome
- daily sums of transpiration and photosynthesise0
- Direction
- decreased continuouslye0
- Qualifier
- at first steeply until a soil water potential of -2000 hPa was reached, then slowlye0
- Setting
- growth chamber experimentse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In the growth chamber experiments, the daily sums of transpiration and photosynthesis decreased continuously as the soil dried, at first steeply until a soil water potential of -2000 hPa was reached, then slowly.”
t0“Picea abies”
Claim · model-written summary
Predawn water potential fluctuated in the field but tended to fall over time.
- Taxon
- Picea abiesPicea abiest0
- Outcome
- Predawn water potential valuese0
- Direction
- decreasee0
- Setting
- field conditionse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Predawn water potential values fluctuated under field conditions, but tended to decrease with time”
t0“Picea abies”
Claim · model-written summary
Needle osmotic potential increased slightly over time in the field.
- Taxon
- Picea abiesPicea abiest0
- Organ / stage
- needlee0
- Outcome
- needle osmotic potentiale0
- Direction
- increased slightlye0
- Setting
- field conditionse1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“whereas needle osmotic potential increased slightly.”
e1“Predawn water potential values fluctuated under field conditions”
t0“Picea abies”
Claim · model-written summary
Growth chamber predawn water potential never exceeded -1.0 MPa despite saturated soil.
- Taxon
- Picea abiesPicea abiest0
- Outcome
- predawn water potentialse0
- Direction
- never higher thane0
- Value
- -1.0 MPae0
- Qualifier
- although the soil was saturatede0
- Setting
- growth chambere0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“predawn water potentials of plants in the growth chamber were never higher than -1.0 MPa although the soil was saturated.”
t0“Picea abies”
Claim · model-written summary
With high average humidity, relatively high predawn water potential persisted until soil water potential reached -8000 hPa.
- Taxon
- Picea abiesPicea abiest0
- Outcome
- predawn water potentialse0
- Direction
- relatively highe0
- Qualifier
- until lower soil water potentials of -8000 hPa were reachede0
- Setting
- high average air humidity during the daily stress periode0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In the experiment with a high average air humidity during the daily stress period, relatively high predawn water potentials were maintained until lower soil water potentials of -8000 hPa were reached.”
t0“Picea abies”
Claim · model-written summary
The authors explain diurnal trends by interdependence of leaf conductance and water potential.
- Taxon
- Picea abiesPicea abiest0
- Outcome
- observed trends in diurnal dynamicse0
- Qualifier
- interdependency of leaf conductance and water potentiale0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The observed trends in diurnal dynamics can be explained solely by the interdependency of leaf conductance and water potential.”
t0“Picea abies”
Claim · model-written summary
The authors state that stomata respond directly to the ratio of water supply to demand.
- Taxon
- Picea abiesPicea abiest0
- Outcome
- Stomata reacte0
- Qualifier
- ratio of water supply to demande0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Stomata react directly to the ratio of water supply to demand.”
t0“Picea abies”