Browsing by Author "Moore, Timothy E"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Open Access
    Investigating the functional and adaptive significance of leaf size and shape variation in Jamesbrittenia (Scrophulariaceae (s.s). tribe Manulae) : an experimental and comparative approach
    (2007) Moore, Timothy E; Verboom, George Anthony; Cramer, Michael D
    The adaptive significance of variety in leaf forms remains a mystery for many plant groups. This study aimed, using a combined experimental and comparative approach, to investigate the functional significance of leaf size and shape variation, as well as the patterns of leaf form variation in the genus Jamesbrittenia within the context of phylogenetic history. Leaf sizes 63-measured Jamesbrittenia varied between 0.006cm² (in J. microphylla) and 6.52cm² (in J. megaphylla). Correlations between leaf form and the environment suggest leaf size and shape are primarily adapted to water availability, with only leaf dimension being significantly associated with temperature, while, soil fertility shows no relationship with leaf size. Life history is important, however, as broader leaved annuals and species with shorter-lived leaves are associated with more arid habitats. Results of the experimental trials suggest that the primary function leaf size and shape reduction is to reduce water loss, and not to increase heat shedding. While larger leaves transpire more on a leaf-by-leaf basis, transpiration may be higher in broader leaved species at the whole-plant due to higher total plant transpiration. Thus, it is suggested a reduction in leaf size and dimension in Jamesbrittenia is an adaptation to more arid environments. Alternatively, a change in life history may enable a plant to escape harsh periods and capitalise on favourable times. A small- to intermediate-leaved, perennial ancestor is inferred for Jamesbrittenia, which was associated with arid regions in either the summer or winter rainfall regions of southern Africa. Shifts to an annual life history in Jamesbrittenia are associated with a shift to drier habitats, particularly in the arid winter rainfall region of South Africa.
  • Thumbnail Image
    Item
    Open Access
    The role of water and nutrient availability in determining above and below ground allocations in a C4 grass Stipagrotis ciliata desf. de Winter
    (2007) Moore, Timothy E; Carrick, Peter J; February, Edmund C
    In order to understand the impacts climate change will have on plants it is important to understand the role of functional diversity in determining plant success across a range of environments. Two populations of Stipagrostis ciliata were compared at two sites - drier coastal and wetter inland - that varied in their water and nutrient availability. Analysis indicates an inverse relationship between rainfall and N availability, with the drier coastal site having significantly lower soil and plant δ¹⁵N (Zadi= -1.964, p<0.05). Plant percent N decreased by 63% between the coastal and inland site. Mean root: shoot ratios also differed significantly between sites (Zadi= -1.964, p<0.05). Although total rooting depth did not appear to differ between sites, in total more root material was found per plant at the inland site, with 40% of all root material occurring directly below the plant. At the coastal site, a greater proportion of root material was allocated laterally in the upper 10cm of soil. As expected, water use efficiency, based on δ¹³C, was higher at the drier coastal site. It is proposed that plants will alter above and below- ground allocation depending on the nature of the limiting resource. In dry environments, more root material in upper soil layers, and a faster growth rate associated with higher shoot allocation, may enhance water uptake. Where nutrients are limiting, increased root biomass might increase nutrient, especially N interception. Competition may also be higher at low nutrient sites.