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Báo cáo lâm nghiệp: "The effect of nitrogen content on the of Scots pine needles and shoots photosynthesis"

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Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài: The effect of nitrogen content on the of Scots pine needles and shoots photosynthesis...

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Nội dung Text: Báo cáo lâm nghiệp: "The effect of nitrogen content on the of Scots pine needles and shoots photosynthesis"

The effect of nitrogen content on the photosynthesis of Scots pine needles and shoots H. Smolander 1 P. Oker-Blom 2 The Finnish Forest Research Institute, Suonenjoki Research Station, SF-77600 Suonenjoki, and 2 University of Helsinki, Department of Silviculture, Unioninkatu 40 B, SF-00170 Helsinki, Finland Introduction Materials and Methods One yr old experimental shoots were collected A close dependency between photosyn- from 5 young Scots pine (Pinus sylvestris L.) thetic capacity and nitrogen content of stands in Suonenjoki (62°39’ N, 27°05’ E) be- leaves has been shown (e.g., DeJong, tween 5 and 30 June 1988. The sites of the 1982). For coniferous trees, however, a stands varied from poor sandy soil with Callu- na vulgaris vegetation to a fertile site with large variation in the relationship has been grass-herb vegetation. A randomly selected found. It has been proposed that the rea- shoot from the uppermost whorl of each tree son for this could be that the nitrogen was used in measurements of photosynthesis. content, by affecting needle growth, Morphological characteristics and silhouette to total needle area ratios were measured for a changes the pattern of mutual shading shoot from the uppermost whorl and for 1 st within a shoot, which is the basic element order and 2nd order shoots just below. The used in studying photosynthesis of conif- photosynthetic capacity of 10 shoots (2 erous trees (Linder and Rook, 1984). The trees/stand) and silhouette to total needle area aim of this study was to analyze separate- ratio of 93 shoots (3 trees/stand) were mea- sured. ly the effect of nitrogen content on the The photosynthesis of excised shoots was photosynthetic capacity of individual measured in a diffuse radiation field using an needles and on within-shoot shading. open flow IRGA-system. In order to eliminate Needle photosynthesis was approximated the effect of within-shoot shading, about two- thirds of the needles on a shoot were removed by measuring the photosynthesis of the night before the day of measurement. The ’thinned’ shoots in a diffuse radiation field. air temperature was 20°C, external C0 2 Within-shoot shading was quantified in concentration was 340 ppm and vapor pressure terms of the mean silhouette area to total deficit 5-10 mbar in the chamber. The horizon- tal photon irradiance (measured by LI-190SR) needle area ratio of a shoot, which deter- was increased in an integrating sphere from 0 mines the relative interception rate per to 1 000, in 7 or 8 steps and a stea- 1 S 2 M - UMOI unit of needle area on the shoot (Oker- dy state photosynthetic rate was obtained at Blom and Smolander, 1988). each irradiance level. A non-rectangular hyper-
bola was fitted to the measured photosynthetic rates using the method of least squares and the value at 2000 pmol was used as an 1 s 2 m- ’ estimate of the photosynthetic capacity. The silhouette area of each shoot was mea- sured photographically at 6 different inclinations of the shoot axis to the plane of projection. The effect of asymmetry of the shoot was eliminated by rotating the shoot 4 times in increments of 60° for each inclination angle. The mean sil- houette area with respect to a spherical shoot orientation was calculated as a weighted aver- age of the 24 silhouette areas measured. The mean silhouette to total needle area ratio (STAR) was then obtained by dividing mean sil- houette area by the total needle area of a shoot, which was approximated as x times the project- ed needle area (measured by a LiCOR leaf area meter) Oker-Blom and Smolander, 1988). Finally, needles were dried for 48 h at 80°C and their nitrogen content determined by the Central Laboratory of the Finnish Forest Research Institute using a LECO CHN-600 analyzer. Results and Discussion Despite the large variation in site fertility, the range of nitrogen concentration varied only from 0.49 to 1.5% of dry weight of needles. The low values of nitrogen content are due to the fact that measure- ments were made during the growing phase of new shoots. The photosynthetic radiation responses of the shoots measured in a diffuse radia- tion field were similar to those measured for single leaves (Fig. 1The nitrogen content had ;a clear effect on the photo- synthetic capacity of needles (Fig. 2). However, because of the narrow range of nitrogen content, the regression was not as close as is generally obtained for broadleaved trees. In this material, the nitrogen conl:ent explained 62% of the
In conclusion, nitrogen content can variation in photosynthetic capacity, whe- increase shoot photosynthesis in 2 ways: reas coefficients of determination >90% by increasing photosynthetic capacity of are typical for broadleaved trees. needles and by increasing light intercep- The STAR-values of shoot were posi- tion efficiency per unit area of needle sur- tively correlated to nitrogen contents (Fig. face on the shoot. 3), contrary to what we had expected. Apparently, some changes in shoot struc- ture eliminated the expected increase in References mutual shading caused by enhanced needle growth. The STAR-value of a shoot DeJong T.M. (1982) Leaf nitrogen content and is most sensitive to the needle density on C0 assimilation capacity in peach. J. Am. 2 the shoot axis and the angle between Hortic. Sci. 107, 955-959 needle and shoot axis, while needle Linder S. & Rook D.A. (1984) Effects of mineral nutrition on carbon dioxide exchange and parti- length, for example, has a much smaller tioning of carbon in trees. In: Nutrition of Plan- effect. In our material, the needle density tation Forests. (Bowen G.D. & Nambiar E.K.S., decreased with increasing nitrogen con- eds.), Academic Press, London, pp. 211-236 tent (Fig. 4) and the needle angle increa- Oker-Blom P. & Smolander H. (1988) The ratio sed with increasing nitrogen content (Fig. of shoot silhouette area to total needle area in Scots pine. For. Sci. 34, 894-906 5).

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