John Pate

Bio: John Pate is an academic researcher from University of Western Australia. The author has contributed to research in topics: Xylem & Shoot. The author has an hindex of 11, co-authored 12 publications receiving 842 citations. Previous affiliations of John Pate include University of Western Ontario.

Seasonal water uptake and movement in root systems of Australian phraeatophytic plants of dimorphic root morphology: a stable isotope investigation

Abstract: A natural abundance hydrogen stable isotope technique was used to study seasonal changes in source water utilization and water movement in the xylem of dimorphic root systems and stem bases of several woody shrubs or trees in mediterranean-type ecosystems of south Western Australia. Samples collected from the native treeBanksia prionotes over 18 months indicated that shallow lateral roots and deeply penetrating tap (sinker) roots obtained water of different origins over the course of a winter-wet/summer-dry annual cycle. During the wet season lateral roots acquired water mostly by uptake of recent precipitation (rain water) contained within the upper soil layers, and tap roots derived water from the underlying water table. The shoot obtained a mixture of these two water sources. As the dry season approached dependence on recent rain water decreased while that on ground water increased. In high summer, shallow lateral roots remained well-hydrated and shoots well supplied with ground water taken up by the tap root. This enabled plants to continue transpiration and carbon assimilation and thus complete their seasonal extension growth during the long (4–6 month) dry season. Parallel studies of other native species and two plantation-grown species ofEucalyptus all demonstrated behavior similar to that ofB. prionotes. ForB. prionotes, there was a strong negative correlation between the percentage of water in the stem base of a plant which was derived from the tap root (ground water) and the amount of precipitation which fell at the site. These data suggested that during the dry season plants derive the majority of the water they use from deeper sources while in the wet season most of the water they use is derived from shallower sources supplied by lateral roots in the upper soil layers. The data collected in this study supported the notion that the dimorphic rooting habit can be advantageous for large woody species of floristically-rich, open, woodlands and heathlands where the acquisition of seasonally limited water is at a premium.

Effects of P deficiency on the uptake, flows and utilization of C, N and H2O within intact plants of Ricinus communis L.

Abstract: The influence of P deficiency on the uptake, flow and utilization of C, N and H 2 O by intact NO 3 -fed castor bean plants (Ricinus communis L.) was studied over a 9 d period in the middle of their vegetative growth. The modelling techniques incorporated data on net increments or losses of C, N and H 2 O in plant parts, photosynthetic gains in and respiratory losses of C, molar C : N ratios of solutes in phloem and xylem sap and transpirational losses of H 2 O. Plant growth was inhibited within 3 d of withholding P supply and dry matter production was less than one-third of the controls. Leaf growth was particularly depressed, while root growth was much less affected than that of the shoot. Shoot :root ratio of low-P plants was 1.5 compared with 2.6 under P supply. Over the 9 d study period total plant C and N increased by 560 and 47 mmol, respectively, in the controls, but by only 113 and 6.9 mmol in the low-P treatment. The particularly low increment of N in P-deficient plants was due principally to decreased NO 3 - uptake. Flows of C and N during the study period were markedly different between control and P-deficient plants. The partitioning profile for C in P-deficient plants showed a dramatic inhibition of net photosynthesis and attendant photoassimilate flow. Proportional downward to upward allocation of carbon increased with increase in sink size of the root relative to shoot. This was reflected in greater relative allocation of C to root dry matter and root respiration than in P-sufficient plants, and suppressed cycling of C from root to shoot via xylem. Nitrogen intake and xylem transport to the shoot of P-deficient plants were only 15% of the control and, as in the case of C, downward allocation of N predominated over upward phloem translocation. Apart from these severe changes, however, the basic patterns of N flows including xylem-to-phloem and xylem-to-xylem transfer of N were not changed, a feature highlighting the vital nature of these transfer processes even under deficiency conditions. The alterations in flows and partitioning of C, N and H 2 O in response to low-P conditions are discussed in relation to the corresponding effects of moderate salt stress in Ricinus and the conclusion is reached that changes in nutrient flows under P deficiency were more highly co-ordinated than when plants experience salt stress. Flow profiles under P deficiency which favour root growth and activity are viewed as a means for increasing the potential capability of the plant to acquire P from the nutrient medium.

Growth and Fire Response of Selected Epacridaceae of South-Western Australia

Abstract: Recruiting populations of seeder (Astroloma xerophyllum (DC.) Sond. and Leucopogon conostephioides DC.) and resprouter (Leucopogon verticillatus R.Br. and Conostephium pendulum. Benth.) epacrids were examined over an 8 year period, using time of fire, shoot morphology and root xylem ring number to age plants. The seeders commenced flowering earlier, achieved three-fold higher shoot:root ratios but accumulated much smaller root starch reserves than the resprouters. The resprouting potential of L. verticillatus was 'bud initiation-limited', since progressive shoot removal exhausted the bud-producing potential but did not fully deplete the starch reserves of the root stock. Apparent conversion efficiency of starch to new shoot biomass was 88%. The corresponding response in C. pendulum was 'energy reserve-limited', with shoot removal eliminating root starch but leaving many unexpanded buds. Dendroecological analyses of root xylem growth rings were undertaken on 15 year-old plants of C. pendulum recruiting from seed in unburnt and adjacent periodically burnt habitats. Growth ring extension of burnt plants resumed after each fire at rates faster than their unburnt counterparts, suggesting that improved access by resprouting shoots to light, water and nutrients compensated for destruction of the previous shoot system.

Heterotrophic gain of carbon from hosts by the xylem-tapping root hemiparasite Olax phyllanthi (Olacaceae).

Abstract: Heterotrophic gains of carbon from various host species by the root hemiparasitic shrub Olax phyllanthi (Labill) R.Br. were assessed using techniques based on carbon isotope discrimination (δ13C) on C3 and C4 hosts and C:N ratios of xylem sap and dry matter of host and parasite. Heterotrophic benefits (H) to Olax based on δ13C values were 30% and 19% from two nonnative C4 hosts (Portulaca oleracea and Amaranthus caudatus respectively) compared with 13% and 15% from these hosts when computed on the basis of C:N ratios of host xylem sap and C and N increments of Olax dry matter. Nitrate was the source of N available to pot cultures of the above species and estimates based on C:N ratios assumed that all N accumulated by Olax had come from nitrate absorbed by the host. Equivalent estimates of H for Olax, grown in nitrogen-free pot culture with the native N2-fixing host Acacia littorea as its sole source of N, indicated 63% and 51% dependence on host carbon when assessed in terms of xylem sap composition of host parasite respectively. Comparisons of xylem sap solutes of Olax and a range of partner hosts indicated marked selectivity in haustorial uptake and transfer of nitrate, amino compounds, organic acids and sugars. Possible implications of variations between hosts in absolute levels of C and inorganic and organic forms of N in xylem are discussed in relation to evidence of much better growth performance of Olax on Acacia littorea and other N2-fixing legumes than on non-fixers.

Stable Isotopes in Plant Ecology

Abstract: ▪ Abstract The use of stable isotope techniques in plant ecological research has grown steadily during the past two decades. This trend will continue as investigators realize that stable isotopes can serve as valuable nonradioactive tracers and nondestructive integrators of how plants today and in the past have interacted with and responded to their abiotic and biotic environments. At the center of nearly all plant ecological research which has made use of stable isotope methods are the notions of interactions and the resources that mediate or influence them. Our review, therefore, highlights recent advances in plant ecology that have embraced these notions, particularly at different spatial and temporal scales. Specifically, we review how isotope measurements associated with the critical plant resources carbon, water, and nitrogen have helped deepen our understanding of plant-resource acquisition, plant interactions with other organisms, and the role of plants in ecosystem studies. Where possible we also...

Ecology of sprouting in woody plants: the persistence niche.

Abstract: Many woody plants can resprout and many ecosystems are dominated by resprouters. They persist in situ through disturbance events such as fire, flooding or wind storms. However, the importance of 'persistence' in plant demography has been neglected in favour of 'recruitment'. Thus much research on plant regeneration, conservation and evolution has focused on the importance of safe sites, seed and seedling banks, dispersal and germination with the implied importance of de novo replacement rather than persistence. Recent research shows a growing appreciation for the role of sprouting as a form of persistence in a diversity of ecosystems and tradeoffs between the two regeneration modes.

Coevolution of roots and mycorrhizas of land plants

Abstract: Summary Here, the coevolution of mycorrhizal fungi and roots is assessed in the light of evidence now available, from palaeobotanical and morphological studies and the analysis of DNA-based phylogenies. The first bryophyte-like land plants, in the early Devonian (400 million years ago), had endophytic associations resembling vesicular‐ arbuscular mycorrhizas (VAM) even before roots evolved. Mycorrhizal evolution would have progressed from endophytic hyphae towards balanced associations where partners were interdependent due to the exchange of limiting energy and nutrient resources. Most mycorrhizas are mutualistic, but in some cases the trend for increasing plant control of fungi culminates in the exploitative mycorrhizas of achlorophyllous, mycoheterotrophic plants. Ectomycorrhizal, ericoid and orchid mycorrhizas, as well as nonmycorrhizal roots, evolved during the period of rapid angiosperm radiation in the Cretaceous. It is hypothesised that roots gradually evolved from rhizomes to provide more suitable habitats for mycorrhizal fungi and provide plants with complex branching and leaves with water and nutrients. Selection pressures have caused the morphological divergence of roots with different types of mycorrizas. Root cortex thickness and exodermis suberization are greatest in obligately mycorrhizal plants, while nonmycorrhizal plants tend to have fine roots, with more roots hairs and relatively advanced chemical defences. Major coevolutionary trends and the relative success of plants with different root types are discussed.

Dissecting the roles of osmolyte accumulation during stress

Abstract: Many plants accumulate organic osmolytes in response to the imposition of environmental stresses that cause cellular dehydration. Although an adaptive role for these compounds in mediating osmotic adjustment and protecting subcellular structure has become a central dogma in stress physiology, the evidence in favour of this hypothesis is largely correlative. Transgenic plants engineered to accumulate proline, mannitol, fructans, trehalose, glycine betaine or ononitol exhibit marginal improvements in salt and/or drought tolerance. While these studies do not dismiss causative relationships between osmolyte levels and stress tolerance, the absolute osmolyte concentrations in these plants are unlikely to mediate osmotic adjustment. Metabolic benefits of osmolyte accumulation may augment the classically accepted roles of these compounds. In re-assessing the functional significance of compatible solute accumulation, it is suggested that proline and glycine betaine synthesis may buffer cellular redox potential. Disturbances in hexose sensing in transgenic plants engineered to produce trehalose, fructans or mannitol may be an important contributory factor to the stress-tolerant phenotypes observed. Associated effects on photoassimilate allocation between root and shoot tissues may also be involved. Whether or not osmolyte transport between subcellular compartments or different organs represents a bottleneck that limits stress tolerance at the whole-plant level is presently unclear. None the less, if osmolyte metabolism impinges on hexose or redox signalling, then it may be important in long-range signal transmission throughout the plant.