We investigated the water use of Caatinga vegetation, the largest seasonally dry forest in South America. We identified and analysed the environmental phenological drivers in woody species and their relationship with transpiration. To monitor the phenological evolution, we used remote sensing indices at different spatial and temporal scales: normalized difference vegetation index (NDVI), soil adjusted vegetation index (SAVI), and green chromatic coordinate (GCC). To represent the phenology, we used the GCC extracted from in-situ automated digital camera images; indices calculated based on sensors included NDVI, SAVI and GCC from Sentinel-2A and B satellites images, and NDVI products MYD13Q1 and MOD13Q1 from a moderate-resolution imaging spectroradiometer (MODIS). Environmental drivers included continuously monitored rainfall, air temperature, soil moisture, net radiation, and vapour pressure deficit. To monitor soil water status and vegetation water use, we installed soil moisture sensors along three soil profiles and sap flow sensors for five plant species. Our study demonstrated that the near-surface GCC data played an important role in permitting individual monitoring of species, whereas the species’ sap flow data correlated better with NDVI, SAVI, and GCC than with species’ near-surface GCC. The wood density appeared to affect the transpiration cessation times in the dry season, given that species with the lowest wood density reach negligible values of transpiration earlier in the season than those with high woody density. Our results show that soil water availability was the main limiting factor for transpiration during more than 80% of the year, and that both the phenological response and water use are directly related to water availability when relative saturation of the soil profile fell below 0.25.
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The present paper aims to confirm the nature of secretory structures found on the petiole and leaf margins of Sapium biglandulosum Müell. Arg. The anatomy, ontogenesis and histochemistry were studied by light microscopy, whereas mono-and disaccharides in the exudates were detected by high performance liquid chromatography. The exudate from the petiole had a total sugar concentration of 32.5% (w/v), of which 38.1% was fructose, 43.7% glucose and 18.2% sucrose. The petiolar gland started its development from a group of meristematic cells that underwent asynchronous divisions. At the end of the ontogenesis, a well structured vascularised gland made up of a palisade secretory epidermis, secretory parenchyma and a secretory pore was observed. Leaf-margin glands showed a similar anatomy. Histochemical tests revealed the presence of proteins, pectins, carbohydrates, tannins and anthocyanins. On the basis of our results, there is compelling evidence that the studied glands are in fact extrafloral nectaries.
Little attention has been paid to species of Chamaecrista sect. Apoucouita (Leguminosae-Caesalpinioideae), especially regarding anatomical studies. When only vegetative material is available, the identifi cation of such species may be diffi cult. Additionally, vegetative material of some species of C. sect. Apoucouita may be even harder to identify because they can resemble species of Inga Mill. (Leguminosae-Mimosoideae). Th e present study focused on recognizing morphoanatomical characters of leaves that are taxonomically useful for the species of C. sect. Apoucouita by employing standard anatomical techniques. Th e arrangement of the vascular system in the petiole/rachis, dorsiventral mesophyll, mucilage idioblasts in the epidermis of leafl ets and hypostomatic leaves were some of the characters shared by all species studied. Length of the petiole, position and type of extrafl oral nectaries, leafl et venation, presence and type of papillae on the epidermis of the leafl et blades and sclereids in the mesophyll were some of the characters useful in the distinction of taxa. Th e vascular arrangement of the petiole/rachis is a promising character in the distinction of species of C. sect. Apoucouita and Inga. Based on morphoanatomical data, the taxonomic revision of some species and varieties ascribed to C. sect. Apoucouita is suggested.
Nectaries are specialized structures that secrete nectar. Several species of Chamaecrista possess nectaries on the petiole, which have been shown to vary widely in morphology and the chemical nature of their secretion. However, a comprehensive investigation of the nectaries of the clade formed by sect. Chamaecrista, Caliciopsis and Xerocalyx has yet to be performed. Our study aimed to confi rm whether or not the leaf glands of species of this clade are in fact nectaries, determine the chemical nature of their secretion and expand the morphoanatomical database on leaf nectaries in Chamaecrista with the intention of contributing to the taxonomy and phylogeny of the genus. Samples from herbarium and fi eld-collected material were subjected to standard methods for light and scanning electron microscopy. Four diff erent forms of nectaries were observed: urceolate, patelliform, verruciform and cupuliform. Th e nectaries were found to comprise a single-layered epidermis, nectary parenchyma, subnectary parenchyma and vascularization. Polysaccharides, lipids, phenolic compounds and proteins were detected in secretions. Although anatomical similarities were observed among the studied species, their morphology diff ered. Moreover, the glands are indeed nectaries and are similar to those observed in other species of the genus Chamaecrista. Th ese data hold potential taxonomic usefulness for the studied sections.
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