THE RELATIONSHIP BETWEEN CROWN SIZE AND RING WIDTH IN PINUS-SYLVESTRIS L STEMS - DEPENDENCE ON INDOLE-3-ACETIC-ACID, CARBOHYDRATES AND NITROGEN IN THE CAMBIAL REGION

Indole-3-acetic acid (IAA), carbohydrates, total nitrogen and amino ac ids in the cambial region and bark were measured at the top (10-year-o ld internode) and bottom (1.3 m) of the main stem of 50-year-old Pinus sylvestris L. trees, having different rates and longitudinal gradient s of annual ring width formation. The trees were sampled during the mo st active period of wood production (June 23, July 15) and at the end of this period (August 23). Trees with a small crown and relatively sl ow growth rate (S-trees) were compared with trees in the same stand th at had a large crown and fast growth rate (F-trees) as a result of thi nning and fertilization. The effect of bottom pruning fast-growing tre es (pruned F-trees) was also investigated. The F-trees had greater woo d production than the S-trees at both the stem top and bottom. The dif ference was larger at the stem bottom, thus the relative decrease in r ing width down the stem was steeper in the S-trees. The amount of sucr ose and IAA per cm2 in cambial region tissues was higher in F-trees th an in S-trees. However, the differences in annual ring width between t reatments and within trees were not reflected in the concentrations (e xpressed per gram fresh weight) of these substances, measured either i n differentiating xylem, the cambium plus phloem, or in the cambial re gion as a whole. The concentrations of total nitrogen and amino acids were slightly higher in the F-trees than in the S-trees. Pruning the F -trees reduced wood production, particularly at the stem bottom, inhib ited the springtime increase in starch, and decreased the amounts of s ucrose and IAA per cm2 in the cambial region. However, it was evident that the concentrations of sucrose, IAA, amino acid and nitrogen in th e cambial region were not related to ring width. During June and July, the concentrations of these substances were generally higher at the s tem bottom in the pruned F-trees than in the F-trees. The results prov ide evidence that it is the activity of the cambium rather than the av ailability of carbohydrates that determines the allocation of wood pro duction along the tree stem. The results also indicate that tracheid p roduction is not directly related to the IAA concentration in the camb ial region.