Year-end Sale % OFF 
Abstract
Heliotropic leaf movement or leaf ‘solar tracking’ occurs for a wide variety of plants, including many desert species and some crops. This has an important effect on the canopy spectral reflectance as measured from satellites. For this reason, monitoring systems based on spectral vegetation indices, such as the normalized difference vegetation index (NDVI), should account for heliotropic movements when evaluating the health condition of such species. In the hyper-arid Atacama Desert, Northern Chile, we studied seasonal and diurnal variations of MODIS and Landsat NDVI time series of plantation stands of the endemic species Prosopis tamarugo Phil., subject to different levels of groundwater depletion. As solar irradiation increased during the day and also during the summer, the paraheliotropic leaves of Tamarugo moved to an erectophile position (parallel to the sun rays) making the NDVI signal to drop. This way, Tamarugo stands with no water stress showed a positive NDVI difference between morning and midday (ΔNDVImo-mi) and between winter and summer (ΔNDVIW-S). In this paper, we showed that the ΔNDVImo-mi of Tamarugo stands can be detected using MODIS Terra and Aqua images, and the ΔNDVIW-S using Landsat or MODIS Terra images. Because pulvinar movement is triggered by changes in cell turgor, the effects of water stress caused by groundwater depletion can be assessed and monitored using ΔNDVImo-mi and ΔNDVIW-S. For an 11-year time series without rainfall events, Landsat ΔNDVIW-S of Tamarugo stands showed a positive linear relationship with cumulative groundwater depletion. We conclude that both ΔNDVImo-mi and ΔNDVIW-S have potential to detect early water stress of paraheliotropic vegetation.
Highlights
Heliotropism or ‘solar tracking’ is the ability of many desert plant species and crops to move leaves and flowers as a response to changes in the position of the sun throughout the day [1]
Partial foliage loss during the period MaySeptember and the peak of the vegetative period occurring around October seemed to have only a marginal effect on the normalized difference vegetation index (NDVI) time series, noticeable as a small drop followed by a peak around
The seasonal variation is the main feature of the annual NDVI signal, and the DNDVIW-S may be used to detect the leaf pulvinar movement occurring in the Tamarugo canopy under natural conditions
Summary
Heliotropism or ‘solar tracking’ is the ability of many desert plant species and crops to move leaves and flowers as a response to changes in the position of the sun throughout the day [1]. Diurnal leaf movements of Tamarugo plants (Prosopis tamarugo Phil.) were first described by Chavez et al [9] under laboratory conditions, and later by Chavez et al [8] for adult trees in the field. These diurnal leaf movements corresponded to paraheliotropic movements since the leaves moved to an erectophyle leaf distribution (facing away from the sun) around midday when solar irradiation was maximum. The paper of Chavez et al [8] showed that leaf pulvinar movements caused diurnal changes of Tamarugo’s canopy spectral reflectance and NDVI signal, which was negatively correlated to diurnal solar irradiation values
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
