Net CO2 exchange (Rn), stomatal conductance (gj, intemal CO2 concentration (Q), and water-use efficiency (WUE) of aging leaves were measured at the beginning of the dry season in 18 species in a tropical deciduous forest in Guanacaste, Costa Rica. In selected trees, gas exchange of old leaves was also compared with that of young leaves, and stomatal responses to irradiation and dark were measured. Based on comparisons with published data, and gj declined more rapidly with leaf age in deciduous than in evergreen species. Whereas both senescence and drought were implicated as causes of these dechneš in the deciduous species, the relative importance of factors responsible for the smaller decreases in physiological activity of old leaves of the evergreen species was less obvious. In the latter trees, and WUE of aging leaves, although not always as high as in young leaves, were high enough to refiite the suggestion that old leaves are solely a liability to tropical deciduous forest trees. On the other hand, stomatal closure in the dark was incomplete, potentially allowing water loss at night and during droughts.
Four-d-old seedlings were exposed to ultraviolet-B, UV-B (20 pinol ht^), and UV-B supplemented with red, R {X 612 nin, 5 pmol nr^) or far-red, FR (X 712 nin, 4.5 pmol nr^) radiation for 30 min during the middle of tlie light phase. Three d of UV-B treatment caused reduction in shoot elongation and expansion of cotyledonaiy leaves. The reduction was largely reversed by supplementary R and FR radiations. Supplementation of FR accelerated senescence process. Similar changes were also noted in the contents of photosynthetic piginents, while the level of anthocyanin was enhanced by all treatments. Flavonoid accumulation was enhanced by UV-B, whereas R and FR radiations suppressed its synthesis to various degrees. The chlorophyll (Chl) fluorescence ratio Fy/F,„ and half-rise time of maximum fluorescence were greatly reduced by UV-B and with FR supplementation. R reversed this UV-B inhibition to a great extent. Likewise, tlie P-S dechne was higher under control and +UV-B+R than under +UV-B and +UV-B+FR treatments, At the protein level both the subunits of ribulose 1,5-bisphosphate carboxylase alone were regulated by phytochrome. All these experiments indicated a possible role of phytochrome in regulating the UV-B induced changes in plant morphology and chloroplast proteins.
A problem of measuring tilt around a single axis is discussed in detail with regard to the resultant accuracy. Ways of improving the accuracy, based on application of various mathematical equations, are proposed. Presented results of related experimental studies, performed on a tilt sensor made of a standard MEMS accelerometer, have proven that it is possible to obtain accuracy of such measurements of ca. 0.2 degrees arc. Additionally, a problem of measuring tilt of an object, which rotates within a non-vertical plane, is addressed. and Obsahuje seznam literatury