Size matters: point pattern analysis biases the estimation of spatial properties of stomata distribution

© 2016 The Authors. New Phytologist © 2016 New Phytologist Trust Stomata distribution is an example of biological patterning. Formal methods used to study stomata patterning are generally based on point-pattern analysis, which assumes that stomata are points and ignores the constraints imposed by size on the placement of neighbors. The inclusion of size in the analysis requires the use of a null model based on finite-size object geometry. In this study, we compare the results obtained by analyzing samples from several species using point and disc null models. The results show that depending on the null model used, there was a 20% reduction in the number of samples classified as uniform; these results suggest that stomata patterning is not as general as currently reported. Some samples changed drastically from being classified as uniform to being classified as clustered. In samples of Arabidopsis thaliana, only the disc model identified clustering at high densities of stomata. This rei

Lignotubers in Mediterranean basin plants

Lignotubers are swollen woody structures located at the root-shoot transition zone and contain numerous dormant buds and starch reserves. This structure enables the plant to resprout prolifically after severe disturbances that remove the aboveground biomass. These are considered adaptive traits in ecosystems with highly frequent and severe disturbances—such as fire-prone ecosystems. In this paper, we aim to contribute to the knowledge of lignotubers in the Mediterranean basin and highlight the evolutionary implications. We first summarise existing knowledge on lignotuber species in the Mediterranean basin. We then provide a detailed morpho-anatomical description of early lignotubers in two common woody species (Arbutus unedo L. and Phillyrea angustifolia L.). Finally, we compare our anatomical results with those obtained in studies conducted with other lignotuberous species from different Mediterranean regions. Lignotubers were verified in 14 species in the Mediterranean basin; all being from lineages with origins dating to the Tertiary and thus pre-dating the Mediterranean climate. In A. unedo and P. angustifolia, lignotubers are macroscopically discernible in 4- and 2-year-old saplings, respectively. In these two species, the lignotubers have numerous buds protected by hypertrophied scales, and have a contorted xylem containing abundant starch. Our results challenge the traditional idea that pre-Mediterranean lineages suffered evolutionary inertia; instead, lignotuberous species may be considered examples of plants that adapted to the increased fire activity that occurred throughout the Tertiary and Quaternary. We also highlight the use of morpho-anatomical traits to unambiguously distinguish between lignotuberous and non-lignotuberous resprouting species.This work has been funded by the ‘Fondo Nacional de Desarrollo Científico’ from the Chilean government (FONDECYT 1120458), the ‘Consejo Superior de Investigaciones Científicas’ (CSIC, Spain; i-LINK + 2012 n°0556) and the TREVOL project (CGL2012-39938-C02-00) from the Spanish government. PIN is funded by ‘U-inicia 2014 Naulin PI’.Peer Reviewe

Detecting leaf pulvinar movements on NDVI time series of desert trees: a new approach for water stress detection.

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 (ΔNDVI mo-mi) and between winter and summer (ΔNDVI W-S). In this paper, we showed that the ΔNDVI mo-mi of Tamarugo stands can be detected using MODIS Terra and Aqua images, and the ΔNDVI W-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 ΔNDVI mo-mi and ΔNDVI W-S. For an 11-year time series without rainfall events, Landsat ΔNDVI W-S of Tamarugo stands showed a positive linear relationship with cumulative groundwater depletion. We conclude that both ΔNDVI mo-mi and ΔNDVI W-S have potential to detect early water stress of paraheliotropic vegetation

Pulvinar structures of Prosopis tamarugo leaves.

<p>(A) Tamarugo trees, (B) leaf angle randomly distributed during the morning when the solar radiation is low, (C) leaf angle in erectophyle position to avoid facing high solar irradiation at midday, (D) transversal section of a closed pulvinus (empty of water) during the morning, (E) transversal section of an open pulvinus (filled with water), which allows leaves to stand up and reach the erectophyle position, and (F) detail of the base of a Tamrugo pinna showing the three levels of pulvinar structures (at the base of the bipinna, of each pinna and each foliole).</p

ΔNDVI morning-midday and ΔNDVI winter-summer of the Bellavista plantation in 2007.

<p><b>Winter 2007:</b> (A) Landsat NDVI, (B) MODIS-Terra NDVI (morning), (C) MODIS-Aqua NDVI (midday), (D) ΔNDVI_mo-mi  =  B–C; <b>Summer 2006–07</b>: (E) Landsat NDVI, (F) MODIS-Terra NDVI (morning), (G) MODIS-Aqua NDVI (midday), and (H) ΔNDVI_mo-mi  =  F–G. Graphs I, J and K display the <b>ΔNDVI_W-S 2007</b>, where (I) Landsat ΔNDVI_W-S  =  A–E, (J) MODIS-Terra ΔNDVI_W-S  =  B–F, and (K) the MODIS-Terra ΔNDVI_W-S  =  C–G.</p

Time series of groundwater depth, Landsat NDVI_W, and Landsat ΔNDVI_W-S for six Tamarugo plantation stands.

<p>Blue arrows indicate precipitation events.</p

Landsat NDVI image showing the location of the Tamarugo stands (Winter 2007).

<p>Landsat NDVI image showing the location of the Tamarugo stands (Winter 2007).</p

Landsat ΔNDVI_W-S of all plantation stands in 1997, 2007, and 2011 (after a precipitation event).

<p>Landsat ΔNDVI_W-S of all plantation stands in 1997, 2007, and 2011 (after a precipitation event).</p

Time series of solar irradiation and NDVI for the B1 site (low groundwater depletion).

<p>(A) Solar irradiation, (B) MODIS 16 days composite NDVI, and (C) Landsat NDVI of the B1 site. Arrows indicate the peak of Tamarugo's vegetative period. S = summer, W = winter.</p