Measurements of net radiation absorbed by isolated acid lime trees (Citrus latifolia Tanaka)

摘要

By using net radiometers mounted on a circular frame rotating around the canopy, measurements of total all-wave radiation absorbed by two 'Tahiti' acid lime trees were carried out in an orchard in Piracicaba, Sao Paulo State, Brazil. The rotating system around the canopy of a tree was formerly idealized and used in New Zealand, allowing integration of all-wave radiation and photosynthetically active radiation absorbed. In an experiment in December 1997, a first device using six net radiometers mounted on a light frame was used. A bigger device, more like the one used in New Zealand, in terms of the number of radiometers and the frame, with a different torque system, was used in another tree on some days from July to September 2000. The performance of both devices is discussed, including the possible error sources when using the first model (1997) and the problems of torque transmission on the second. Despite the lack of a test to check the performance of the device and the problems presented in theyear 2000, the results confirm the possibility of providing reliable measurements of the net radiation absorbed by isolated trees. Relations of the net radiation per unit area of projected canopy on the ground were determined with integrated values overdifferent time scales (from 15 min to 24 h). Unique relations between net radiation and incoming solar radiation were obtained for both trees over several time scales. These relations are applicable only to high leaf density conditions and canopy geometry similar to the used in this study.