The magnitude and pace of terrestrial plant extinction and macroecological change as sociated with the Triassic/Jurassic (Tr/J) mass extinction boundary have not been quantified using paleoecological data. However, tracking the diversity and ecology of primary producers provides an ideal surrogate with which to explore patterns of ecosystem stability, collapse, and recovery and to explicitly test for gradual versus catastrophic causal mechanisms of extinction. We present an analysis of the vegetation dynamics in the Jameson Land Basin, East Greenland, spanning the Tr/J extinction event, from a census collected paleoecological data set of 4303 fossil leaf specimens, in an attempt to better constrain our understanding of the causes and consequences of the fourth greatest extinction event in earth history. Our analyses reveal (1) regional turnover of ecological dominants between Triassic and Jurassic plant communities, (2) marked structural changes in the vegetation as reflected by potential loss of a mid-canopy habit, and (3) decline in generic-level richness and evenness and change in ecological composition prior to the Tr/J bound ary; all of these findings argue against a single catastrophic causal mechanism, such as a meteorite impact for Tr/J extinctions. We identify various key ecological and biological traits that increased extinction risk at the Tr/J boundary and corroborate predictions of meta-population theory or plant ecophysiological models. These include ecological rarity, complex reproductive biology, and large leaf size. Recovery in terms of generic-level richness was quite rapid following Tr/J extinctions; however, species-level turnover in earliest Jurassic plant communities remained an order of magnitude high er than observed for the Triassic. We hypothesize, on the basis of evidence for geographically ex tensive macrofossil and palynological turnover across the entire Jameson Land Basin, that the na ture and magnitude of paleoecological changes recorded in this study reflect wider vegetation change across the whole region. How exactly these changes in dominance patterns of plant primary production affected the entire ecosystem remains an important avenue of future research.

Moisture content can be a dominant factor affecting combustion especially in live fuels due to the wide range of moisture content that can be encountered with vegetation. Laboratory experiments are used to study the fire dynamics of Mediterranean Pinus halepensis needles under a range of fuel and flow conditions. A set of 80 experiments with good repeatability were conducted in the Fire Propagation Apparatus (FPA) fire calorimeter. The burning behavior is measured in terms of the evolution of the mass loss rate and the heat release rate from ignition till burn out for different forced flow velocities. Recently collected live and dead needles are compared here for the first time. Additionally, live samples aged for 15 months after collection are presented as an alternative to study changes in live needles. Two different moisture conditions are considered, fresh and oven-dry. The most flammable samples are fresh dead and 15 months aged needles, followed by oven-dry dead, and oven-dry live needles. The least flammable is fresh live needles. Overall, the results show that fire physics and chemistry vary with the fuel and flow conditions, and that moisture content is not the only difference between live and dead fuels, but that the needle bed physicochemical mechanisms matters as well. The loss of volatiles and other changes induced during oven drying is seen to lead to significant differences in the burning behavior.

Plant stomata display a wide range of short-term behavioural and long-term morphological responses to atmospheric carbon dioxide concentration ([CO(2)]). The diversity of responses suggests that plants may have different strategies for controlling gas exchange, yet it is not known whether these strategies are co-ordinated in some way. Here, we test the hypothesis that there is co-ordination of physiological (via aperture change) and morphological (via stomatal density change) control of gas exchange by plants. We examined the response of stomatal conductance (G(s)) to instantaneous changes in external [CO(2)] (C(a)) in an evolutionary cross-section of vascular plants grown in atmospheres of elevated [CO(2)] (1,500 ppm) and sub-ambient [O(2)] (13.0 %) compared to control conditions (380 ppm CO(2), 20.9 % O(2)). We found that active control of stomatal aperture to [CO(2)] above current ambient levels was not restricted to angiosperms, occurring in the gymnosperms Lepidozamia peroffskyana and Nageia nagi. The angiosperm species analysed appeared to possess a greater respiratory demand for stomatal movement than gymnosperm species displaying active stomatal control. Those species with little or no control of stomatal aperture (termed passive) to C(a) were more likely to exhibit a reduction in stomatal density than species with active stomatal control when grown in atmospheres of elevated [CO(2)]. The relationship between the degree of stomatal aperture control to C(a) above ambient and the extent of any reduction in stomatal density may suggest the co-ordination of physiological and morphological responses of stomata to [CO(2)] in the optimisation of water use efficiency. This trade-off between stomatal control strategies may have developed due to selective pressures exerted by the costs associated with passive and active stomatal control.

Heat and drought stress frequently occur together, however, their impact on plant growth and photosynthesis (P ) is unclear. The frequency, duration and severity of heat and drought stress events are predicted to increase in the future, having severe implications for agricultural productivity and food security. To assess the impact on plant gas exchange, physiology and morphology we grew drought tolerant and sensitive varieties of C3 sunflower (Helianthus annuus) and C4 maize (Zea mays) under conditions of elevated temperature for 4 weeks prior to the imposition of water deficit. The negative impact of temperature on P was most apparent in sunflower. The drought tolerant sunflower retained ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) activity under heat stress to a greater extent than its drought sensitive counterpart. Maize exhibited no varietal difference in response to increased temperature. In contrast to previous studies, where a sudden rise in temperature induced an increase in stomatal conductance (G ), we observed no change or a reduction in G with elevated temperature, which alongside lower leaf area mitigated the impact of drought at the higher temperature. The drought tolerant sunflower and maize varieties exhibited greater investment in root-systems, allowing greater uptake of the available soil water. Elevated temperatures associated with heat-waves will have profound negative impacts on crop growth in both sunflower and maize, but the deleterious effect on P was less apparent in the drought tolerant sunflower and both maize varieties. As C4 plants generally exhibit water use efficiency (WUE) and resistance to heat stress, selection on the basis of tolerance to heat and drought stress would be more beneficial to the yields of C3 crops cultivated in drought prone semi-arid regions.