Seasonal Time Course Research Articles

An analysis of needle yellowing in healthy and chlorotic Norway spruce(Picea abies) in a forest decline area of the Fichtelgebirge(N.E. Bavaria)

In a forest decline area (Fichtelgebirge, N.E. Bavaria, FRG), annual time courses of chloroplast pigments in both healthy and chlorotic Norway spruce were studied. The seasonal time courses of green and apparently healthy trees did not generally differ from those reported in the literature for spruce trees of other regions. Chlorophyll content increased from May to October, remained relatively constant or declined slightly during the fall and early winter, and finally decreased markedly from March to early May when pigment is at its minimum before bud break. The annual maximal chlorophyll content increased with needle age from the current year's needles to 4-yearold needles. While carotene content reached its highest concentration in August, the xanthophylls did not peak until February or March. Pigment dynamics of chlorotic trees with lower concentrations, corresponded to those of undamaged trees. Chlorophyll deficits resulted from less pigment formation as well as pigment loss during the growing period. Even when the content of total chlorophyll was low, the ratio of chlorophyll a/chlorophyll b remained almost unchanged. In conjunction with the chlorophyll reductions, a decrease in the chlorophyll/carotenoid ratio and an increase in the xanthophyll/carotene ratio occurred. The periods of needle-chlorophyll reduction did not correlate with those periods of highest concentrations of atmospheric sulphur dioxide, the main air pollutant at the stand. However, chlorophyll formation ceased in the older needle age classes of chlorotic trees when the new flush was sprouting, indicating that nutritional deficiencies affect needle yellowing more than possible direct needle damage by air pollutants.

Photoperiodicity and circannual levels of LH, FSH, and testosterone in normal and castrated male, white-tailed deer.

To establish the relation between photoperiodicity and the levels of LH, FSH, and testosterone (T) in plasma, three intact and three castrated adult male white-tailed deer were sampled once a month for 2-3 years. The rang of average LH levels in controls varied between 0.8 and 2.0 ng/mL; the levels in castrates were considerably higher, 3.4 to 8.9 ng/mL. Average levels of FSH varied in controls between 25 and 112 ng/mL and in castrates between 141 and 240 ng/mL. A significant correlation between the seasonal time course of LH and FSH was found in castrated, but not in intact bucks. In castrates both gonadotropins exhibit two major elevations coinciding with spring and fall equinoxes in March and September. The seasonal time course of FSH in castrates correlates highly with seasonal levels of FSH in controls. However, the time course of the LH curve in controls is substantially different from the curve in castrates, presumably owing to feedback mechanisms. A possible role of testicular estradiol in this feedback is discussed. In controls, peak T levels are reached in December, i.e., 3 months after maximum levels of FSH and 5 months after peak levels of LH were detected. It appears that male deer undergo two periods of reproductive stimulation (one in the spring, the other in the fall). However, the organism responds with the full range of gonadal and behavioral mechanisms leading to the initiation of the rut only during the fall.

Leaf Area Index Estimates for Wheat from LANDSAT and Their Implications for Evapotranspiration and Crop Modeling1

AbstractGround measurements of leaf area index (LAI) are tedious and costly. If they could be estimated spectrally from earth observation satellite data, evapotranspiration and photosynthesis models that use LAI as inputs could be implemented for large areas. Thus, we related LAI measurements of winter wheat (Triticum aestivum, L.) made in Kansas during the 1974–1975 and 1975–1976 growing seasons to three spectral vegetation indexes in the literature: transformed vegetation index (TVI), green vegetation index (GVI), and perpendicular vegetation index (PVI). The three vegetation indexes were each significantly linearly correlated (r = 0.70** to 0.95**) with measured LAI from the time LA1 was ≃ 0.3 until plant senescence, and their seasonal time courses were similar to those of directly measured LAI. Thus the indexes capture information on crop development and growing conditions manifested by LAI. We conclude that LAI can be calibrated in terms of the vegetation indexes to provide crop model inputs for as many fields as are of interest, or can serve as an independent check on model calculations when not used as a direct input to physical and physiological process models affected by the amount of vegetation present.