Báo cáo khoa học: Estimating tree canopy water use via xylem sapflow in an old Norway spruce forest and a comparison with simulation-based canopy transpiration

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Báo cáo khoa học: "Estimating tree canopy water use via xylem sapflow in an old Norway spruce forest and a comparison with simulation-based canopy transpiration" Original article Estimating tree canopy water use via xylem sapflow in an old Norway spruce forest and a comparison with simulation-based canopy transpiration estimates Barbara Köstner Eva M. Falge, Martina Alsheimer. Ralf Geyer, John D. Tenhunen Bayreuth Institute for Terrestrial Ecosystem Research (BITÖK), Department of Plant Ecology II, University of Bayreuth, 95440 Bayreuth, Germany 15 20 October 1997) (Received January 1997; acceptedAbstract - Tree xylem sapflow rates of 140-year-old Norway spruce (Picea abies) were scaledto the stand level and compared to canopy transpiration predicted by the stand gas exchangemodel STANDFLUX. Variation in sapflux densities between individual sensors was high (coef-ficient of variance 0.4) and included both variation within and between trees, but it was not dif- =ferent between two applied sapflow methodologies (radial flowmeter according to Granier, vari-able heating tissue heat balance method according to Cermák and Kucera). During the morning,a time-lag of typically 2 h elapsed between sapflow (E and predicted canopy transpiration rate ) f(E During this time total water iusehe as as high as 0.3 mm, which was l14 Lthan the estimated ess).p of wcapacity easily available water n t tree canopy (0.45 mm, on average per tree). Canopyconductance derived from stand sapflow rates (g and from STANDFLUX (g was in the same ) f ) p deficit of the airrange (g 10 mm s but a stronger decline with increasing vapor pressure ), -1 : tmax* Correspondence and reprintsAbbreviations: CBH: tree circumference at breast height; CV: coefficient of variation; DBH:tree diameter at breast height; D: vapor pressure deficit of the air; D daily maximum half-hour : maxaverage vapor pressure deficit of the air; D average vapor pressure deficit during night; dw: : darkdry weight; E forest canopy transpiration rate; E forest canopy transpiration rate derived with : c : ftime shift in xylem sapflow; E forest canopy transpiration rate predicted from STANDFLUX : p total conductance derived from shiftedModel; g canopy conductance; g xylem sapflow; g : c : f : nstotal conductance derived from non-shifted xylem sapflow; g canopy conductance predicted from : p o measurementSTANDFLUX model; g total conductance from canopy t height of D; g : t : tmaxmaximum total canopy conductance; J: sapflux density (sapflow rate per sapwood area); LAI: pro-jected canopy leaf area index; LS: total leaf surface; LW: leaf dry weight; PPFD: photosyntheticphoton flux density; SD: standard deviation; SE: standard error; SWA sapwood area at breast : bhheight; SWA sapwood area below live crown; SWV: sapwood volume. : blc(D) was observed for g as compared to g with current model parameterization. Tree water f puptake measured by xylem sapflow was higher during spring and somewhat lower during sum-mer compared with E Seasonal sums of transpiration from April to October amounted to . p108 and 103 mm seasonfor E and E respectively. Estimated tree water uptake during night -1 f , pincreased with D up to 0.5 mm per dark period (on average 16 L per tree) which was 10-140 %of total daily flux. Because this flow rate did not increase with further increases in D duringnight, it is concluded that it reflects the refilling of easily exchangeable water in the trees ratherthan a rate of night transpiration. (© Inra/Elsevier, Paris.)forest transpiration / forest conductance / night water uptake / stand gas exchange model/ Picea abiesRésumé - Estimation de la consommation en eau des arbres à partir de la mesure du fluxde sève brute dans un peuplement âgé d’épicéa, et compar ...