Physiological and growth responses of Triodia under induced drought conditions ex situ and the role of functional traits

Background/Question/Methods

Triodia is an abundant genus of hummock grasslands which dominate most of arid and central Australia. Within this genus exists two distinct morphological classes which separate along water gradients at both regional and local scales. The genus spans a range of micro- and macro-climatic regimes, however little is known about the physiological and functional traits that underpin the distribution of the species and morpho-classes across landscapes, substrates and gradients in water availability. A glasshouse experiment was conducted to measure the performance of seven Triodia species under drought conditions to ascertain whether differences in physiology and growth rate exist between species and the two morpho-classes. From these results we aimed to identify several functional attributes of Triodia that are advantageous under drought conditions to allow for the prediction of species and morpho-class suitability to areas of differing water availability.

Results/Conclusions

Leaf anatomical analysis reaffirms the distinction of two separate morpho-class within the genus. Anatomical analysis also suggests that an increased mesophyll resistance as seen in one morpho-class may result in differences in water efficiency and conductance between the two classes of Triodia. Ex situ, the two morpho-classes demonstrated differences in growth rate in both above and below ground biomass allocation. Consistent with current literature, preliminary results see a slower growth rate as exhibited by one morpho-class appearing to be a more advantageous trait under drought conditions when compared to its the fast growing counterpart. At the initial stages of drought, it appears that the effects of growth rate on drought tolerance were masked by several counteracting xeromorphic traits belonging to fast-growing morpho-class such as the internalisation of stomata via leaf rolling and the production of resin. As drought intensified, the advantage of a slower growth rate on water conservation became apparent with the slow-growing species out-performing the fast growing species in above ground living plant biomass. This research addresses the effects of plant form on plant function, simultaneously providing insight into the underlying functional traits constraining Triodia species distributions. This work points to the need for simultaneous measures of anatomical, physiological and ecological variables to disentangle the complex nature of trait – environment relationships in this important genus.