title: Long-term effects of drought on wild and cultivated plants in the Negev desert : II. Diurnal patterns of net photosynthesis and daily carbon gain.
abstract: The seasonal change in diurnal patterns of net photosynthesis and daily carbon gain is studied in relation to the plant water status of the irrigated and non-irrigated naturally growing desert species Hammada scoparia, Zygophyllum dumosum, Artemisia herba-alba and Reaumuria negevensis. Comparison is made to cultivated Prunus armeniaca. Under non-irrigated natural conditions Hammada scoparia, a C4plant, showed one-peaked flat diurnal courses of CO2uptake which changed into a pattern of a high morning peak of CO2uptake or slightly two-speaked curves in the late dry season. In contrast, the C3species Zygophyllum dumosum, Artemisia herba-alba and Prunus armeniaca changed from one-peaked to distinct two-peaked patterns. At the end of the dry season, non-irrigated plants showed respiration only. Reaumuria negevensis had one-peaked curves with a low level of CO2uptake.There is no general relation between day-time CO2gain and pre-dawn water potential for the investigated species. In order to characterize the effect of soil drought, the CO2gain during day-time of non-irrigated plants is expressed as a percentage of the CO2gain of the irrigated counterparts. After an initial period of minimal drought effect, the relative day-time CO2gain decreases almost linearly with cumulative water stress as determined by the daily addition of pre-dawn water potentials for the non-irrigated plants since the last rainfall. The slope of decrease differs from species to species. The relation of daily CO2gain to maximal net photosynthesis is discussed. Initially, at a good plant water status, the daily CO2gain does not decrease in proportion to the maximal photosynthetic rates as a result of stomatal control at high photosynthetic activity. At increasing water stress the daily CO2gain decreases more than proportionally to the decrease of the maximal rates.
authors.affiliation: Lehrstuhl Pflanzenökologie der Universität Bayreuth, Am Birkengut, D-8580, Bayreuth, Federal Republic of Germany.
authors.forename: E -D
authors.initials: E-
authors.lastname: Schulze
authors.affiliation: Lehrstuhl für Botanik II der Universität Würzburg, Federal Republic of Germany.
authors.forename: O L
authors.initials: OL
authors.lastname: Lange
authors.affiliation: Botany Department, Hebrew University, Israel.
authors.forename: M
authors.initials: M
authors.lastname: Evenari
authors.affiliation: Lehrstuhl für Botanik II der Universität Würzburg, Federal Republic of Germany.
authors.forename: L
authors.initials: L
authors.lastname: Kappen
authors.affiliation: Lehrstuhl für Botanik II der Universität Würzburg, Federal Republic of Germany.
authors.forename: U
authors.initials: U
authors.lastname: Buschbom