Papers by Ignatious Matimati
Plant Ecology, 2013
With a high percentage of endemics along the west coast of South Africa, especially in the family... more With a high percentage of endemics along the west coast of South Africa, especially in the family Aizoaceae, the region is considered one of the earth's biodiversity hot spots. It has been suggested that the diversity and radiation of the Aizoaceae are coincident with low but predictable rainfall and lack of competition between species. In this study we examine the relationship between water source and the efficiency of PSII photochemistry for representative Aizoaceae and non-Aizoaceae. We do this to determine the extent to which the different genera are adapted to the frequent, low volume, precipitation characteristic of the region and to ascertain the extent to which there is competition for water. Our water isotope results show that the Aizoaceae use shallow surface water while the non-Aizoaceae use a deeper water source. We are however not able to show the extent to which the Aizoaceae utilize fog or dew. Our chlorophyll fluorescence results show that there are no differences in efficiency of PSII photochemistry between the species in the wet season. The decline from wet to dry season for the Aizoaceae is, however, more dramatic than that of the non-Aizoaceae reflecting the differences in rooting depth between the different families. These results suggest that, during the dry season, there is no competition for resources between families but there is competition between species. We conclude that the adaptation to using shallow water, coupled with susceptibility to drought of adult short lived Aizoaceae may be a, mechanism for the diversification of this family.
Ecohydrology, 2012
Dwarf succulents persist in the arid Succulent Karoo despite the low-water storage capacities of ... more Dwarf succulents persist in the arid Succulent Karoo despite the low-water storage capacities of their contracted leaves and stems that are inadequate for enduring severe and prolonged drought. We examined the contribution of non-rainfall moisture (fog, dew, water vapour) to the water budgets and relative abundance of two endemic dwarf succulents Agyroderma pearsonii and Cephalophyllum spissum. Non-rainfall moisture was measured with automated lysimeters containing bare quartz-gravel soils and introduced A. pearsonii and C. spissum individuals at hourly intervals spanning an 8-month wet winter to dry summer period. Total non-rainfall atmospheric moisture intercepted by the bare quartz-gravel substrate of 137Á6 mm, of which water vapour adsorption contributed 56Á2 mm, fog 78Á2 mm and dew 3Á4 mm, was virtually equivalent to the rainfall amount of 142Á7 mm. Agyroderma pearsonii intercepted 228Á4 mm of non-rainfall moisture of which water vapour adsorption contributed 117Á1 mm, fog 104Á4 mm and dew 6Á9 mm. This was nearly three times the non-rainfall amount of 88Á7 mm y À1 intercepted by C. spissum, of which water vapour contributed 44Á3 mm, fog 41Á3 mm and dew 3Á1 mm. The greater quantity of non-rainfall moisture intercepted by A. pearsonii corresponded with its threefold greater leaf abundance and twofold greater canopy cover than that of C. spissum. We conclude that non-rainfall moisture, especially the absorption of atmospheric water vapour by soils and its uptake by the extensive network of superficial roots of dwarf quartz-field succulents are vital in sustaining their growth and survival and in determining their distributions and relative abundance.
Agricultural and Forest Meteorology, 2012
Stem diameter variations relative to atmospheric vapour pressure deficits and the corresponding d... more Stem diameter variations relative to atmospheric vapour pressure deficits and the corresponding differences in pre-dawn and late dusk foliar organic acids were measured in 4 evergreen and 2 partly drought deciduous succulent shrubs. These methods were compared at two arid South African sites in distinguishing CAM and C 3 photosynthetic modes. Changes in stem diameter were continuously recorded at 2 h intervals using linear variable differential transducers, known as stem diameter variation sensors. Annual data collected over varying climatic conditions revealed that rapid changes in the stem diameter in response to vapour pressure deficit concurred with typical foliar acid trends expected for CAM and C 3 photosynthetic modes. Nocturnal foliar acidification, which typifies the CAM mode, was predominant in evergreen shrubs Cephalophyllum framesii, Ruschia bolusiae, Ruschia stricta and Zygophyllum cordifolium whilst C 3 mode was prevalent in drought deciduous Lycium cinereum and Tripteris sinuata. Diurnal trends in foliar acidification concurred with the predicted patterns in stem diameter variations for CAM and C 3 modes, thus confirming the potential application of stem diameter sensors in distinguishing CAM and C 3 modes in arid environments. Daily amplitudes in stem diameter were significantly reduced by nocturnal fog and dew precipitation in a C 3-CAM shrub. This supports earlier studies that the CAM mode in facultative and CAM-cycling plants does not only conserve water, but may also aid in water absorption. Stem microvariation changes revealed CAM-C 3 variations that were concealed when measuring CAM activity from total foliar acids. This technique may be very important considering that even the dependable carbon isotope technique underestimates the number of CAM-equipped plants in natural systems.
Journal of Experimental Botany, 2013
Transpiration may enhance mass-flow of nutrients to roots, especially in low-nutrient soils or wh... more Transpiration may enhance mass-flow of nutrients to roots, especially in low-nutrient soils or where the root system is not extensively developed. Previous work suggested that nitrogen (N) may regulate mass-flow of nutrients. Experiments were conducted to determine whether N regulates water fluxes, and whether this regulation has a functional role in controlling the mass-flow of nutrients to roots. Phaseolus vulgaris were grown in troughs designed to create an N availability gradient by restricting roots from intercepting a slow-release N source, which was placed at one of six distances behind a 25 μm mesh from which nutrients could move by diffusion or mass-flow (termed 'massflow' treatment). Control plants had the N source supplied directly to their root zone so that N was available through interception, mass-flow, and diffusion (termed 'interception' treatment). 'Mass-flow' plants closest to the N source exhibited 2.9-fold higher transpiration (E), 2.6-fold higher stomatal conductance (g s), 1.2-fold higher intercellular [CO 2 ] (C i), and 3.4-fold lower water use efficiency than 'interception' plants, despite comparable values of photosynthetic rate (A). E, g s , and C i first increased and then decreased with increasing distance from the N source to values even lower than those of 'interception' plants. 'Mass-flow' plants accumulated phosphorus and potassium, and had maximum concentrations at 10 mm from the N source. Overall, N availability regulated transpiration-driven mass-flow of nutrients from substrate zones that were inaccessible to roots. Thus when water is available, mass-flow may partially substitute for root density in providing access to nutrients without incurring the costs of root extension, although the efficacy of mass-flow also depends on soil nutrient retention and hydraulic properties.
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Papers by Ignatious Matimati