Nitrogen enrichment lowers Betula pendula green and yellow leaf stoichiometry irrespective of effects of elevated carbon dioxide.

Elevated carbon dioxide (C

Comparison of palaeobotanical observations with experimental data on the leaf anatomy of durmast oak [Quercus petraea (Fagaceae)] in response to environmental change

To test whether stomatal density measurements on oak leaf remains are reliable tools for assessing palaeoatmospheric carbon dioxide concentration [CO2], under changing Late Miocene palaeoenvironmental conditions, young seedings of oak (Quercus petraea, Liebl.) were grown at elevated vs. ambient atmospheric [CO2] and at high humidity combined with an increased air temperature. The leaf anatomy of the young oaks was compared with that of fossil leaves of the same species. In the experiments, stomatal density and stomatal index were significantly decreased at elevated [CO2] in comparison to ambient [CO2]. Elevated [CO2] induced leaf cell expansion and reduced the intercellular air space by 35%. Leaf cell size or length were also stimulated at high air humidity and temperature. Regardless of a temperate or subtropical palaeoclimate, leaf cell size in fossil oak was not enhanced, since neither epidermal cell density nor length of the stomatal apparatus changed. The absence of these effects may be attributed to the phenological response of trees to climatic changes that balanced temporal changes in environmental variables to maintain leaf growth under optimal and stable conditions. Quercus petraea, which evolved under recurring depletions in the palaeoatmospheric [CO2], may possess sufficient phenotypic plasticity to alter stomatal frequency in hypostomatous leaves allowing high maximum stomatal conductance and high assimilation rates during these phases of low [CO2]. (C) 1998 Annals of Botany Company

Vegetation history across the Permian-Triassic boundary in Pakistan (Amb section, Salt Range)

Hypotheses about the Permian–Triassic floral turnover range from a catastrophic extinction of terrestrial plant communities to a gradual change in floral composition punctuated by intervals indicating dramatic changes in the plant communities. The shallow marine Permian–Triassic succession in the Amb Valley, Salt Range, Pakistan, yields palynological suites together with well-preserved cuticle fragments in a stratigraphically well-constrained succession across the Permian–Triassic boundary. Palynology and cuticle analysis indicate a mixed Glossopteris–Dicroidium flora in the Late Permian. For the first time Dicroidium cuticles are documented from age-constrained Upper Permian deposits on the Indian subcontinent. Close to the Permian–Triassic boundary, several sporomorph taxa disappear. However, more than half of these taxa reappear in the overlying Smithian to Spathian succession. The major floral change occurs towards the Dienerian. From the Permian–Triassic boundary up to the middle Dienerian a gradual increase of lycopod spore abundance and a decrease in pteridosperms and conifers are evident. Synchronously, the generic richness of sporomorphs decreases. The middle Dienerian assemblages resemble the previously described spore spikes observed at the end-Permian (Norway) and in the middle Smithian (Pakistan) and might reflect a similar ecological crisis