Báo cáo lâm nghiệp: A comparison of the photosynthetic radiation response of Scots pine shoots in direct and diffuse radiation

Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài: A comparison of the photosynthetic radiation response of Scots pine shoots in direct and diffuse radiation...
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Báo cáo lâm nghiệp: " A comparison of the photosynthetic radiation response of Scots pine shoots in direct and diffuse radiation"A comparison of the photosynthetic radiation response ofScots pine shoots in direct and diffuse radiation T. Lahti 3P. Oker-Blom 1 H. Smolander 2! University of Helsinki, Department of Silviculture, Unioninkatu 40 B, 00170 Helsinki,2 Finnish Forest Research Institute, Suonenjoki Research Station, SF-77600 Suonenjoki, and3 University of Helsinki, Botanical Museum, Unioninkatu 44, SF-00 170 Helsinki, FinlandIntroduction Materials and Methods The material consisted of 9, 1 yr old shoots col-The directional distribution of radiation lected from a young Scots pine stand. The netincident on a coniferous shoot has been rate of photosynthesis of the excised shootsshown to have a large effect on the rate of was measured in a direct and a diffuse (spheri-shoot photosynthesis (e.g., Zelawski et cal) radiation field, using an open flow IRGA-al., 1973). In a multidirectional radiation system (URAS 3G). The temperature in the assimilation chamber was 20°C, ambient C0 2field, the irradiance on the needle surface concentration was 340 ppm and the air waterarea of a shoot becomes more evenly dis- vapor pressure deficit was 9 ± 1 mbar.tributed than in the case of a highly The distribution of radiation within each shootdirectional field, and the rate of photosyn- simulated using a Monte Carlo method (cf. wasthesis per unit of intercepted radiation Smolander et al., 1987) and using a model de-should logically be higher (cf. Oker-Blom, scribing shoot geometry based on certain mor-1985). The aim of this study was to com- phological characteristics of the shoot (cf. Oker-Blom et al., 1983). Using the simulatedpare the rates of photosynthesis of Scots distributions and assuming the photosyntheticpine (Pinus sylvestris L.) shoots in diffuse light curve for the photosynthetic unit to be aand direct radiation and to test a shoot Blackman type curve (c£ Oker-Blom, 1985),photosynthesis model based on the hypo- shoot photosynthesis was calculated as the integrated response of the photosynthetic units.thesis that shoot photosynthesis can be Parameters of the Blackman curve were esti-expressed as the integrated response of mated iteratively using the method of leastthe photosynthetic units of the shoot which squares to give the best fit between measuredare assumed to have an invariant photo- and calculated photosynthesis for the shoot insynthetic light-response curve. direct radiation.* Present address: University of Georgia. School of Forest Resources, Athens, GA 30602, U.S.A. .eorqia ores,t esources. In simulating the irradiance distributions, 2 length of the photon pathway within the needledifferent approaches were used. In the 1st before reaching the point under consideration.case, the photosynthetic units of the shoot wererepresented by needle surface area elements,i.e., the distribution of irradiance on the needlesurface area was simulated. In the 2nd case,the photosynthetic units were represented by Resultspoints within the needles and the irradiance (thephoton field strength) at these points wassimulated. The first approach is consistent with Measured rates of photosynthesis of athe assumption that the photosynthetic units are shoot subjected to direct and diffuse radia-evenly distributed on the needle surface andthat needles are optically black, i.e., there is no tion, respectively are shown in Fig. 1. a needle. In thetransmission of radiation within When the radiation is expressed in terms2nd approach, the photosynthetic units are of the (simulated) mean irradiance on theassumed to be uniformly distributed within the needle surface area (Fig. 1 B), the rate ofneedle and the transmission of radiation wasassumed to be an exponential function of the photosynthesis represents the photosyn-thetic response per unit of intercepted representative value which corresponds to transmission of 5% per mm of pathradiation and the difference between the a length within the needle (cf. Gates et ...