Alfalfa was grown in fíeld plots at the current CO2 concentratíon (350 pmol mol"' = C350) and at 350 pmol mol"' above the current concentratíon (= c^qq). Alfalfa and weed growth, and canopy water vapor (£) and carbon dioxide exchange (f) were determined for the first year. Alfalfa yield summed for the three harvests in the first year was greater for the C700 treatment in two of the years studied, but significantly less in a third year. Weed growth was unaffected. Survival of alfalfa plants was greater at Cypo for years in which there was substantíal mortality, even when yield was not increased by the C700 treatment. In špite of a persistent reduction in leaf conductance to water vapor (gj), total canopy conductance (g^) to water vapor did not differ between CO2 treatments when averaged over years, because of compensating changes in canopy leaf area. CO2 efílux (F) at night per unit of ground area was consistently less in the cjqq treatment, even when daytime CO2 uptake was higher. Hence the periodic harvesting of alfalfa crops does not necessarily allow elevated CO2 to cause persistent growth stimulatíon nor reduced water use.
Acclimation to excess light is required for optimizing plant performance under natural environment. The present work showed that the treatment of Arabidopsis leaves with exogenous H2O2 can increase the acclimation of PSII to excess light. Treatments with H2O2 also enhanced the capacity of the mitochondrial alternative respiratory pathway and salicylic acid (SA) content. Our work also showed that the lack in alternative oxidase (AOX1a) in AtAOX1a antisense line and the SA deficiency in NahG (salicylate hydroxylase gene) transgenic mutant attenuated the H2O2-induced acclimation of PSII to excess light. It indicates that the
H2O2-induced acclimation of PSII to excess light could be mediated by the alternative respiratory pathway and SA., Q. Z. Hou, Y. P. Wang, J. Y. Liang, L. Y. Jia, H. Q. Feng, J. Wen, N. Ehmet, J. Y. Bai., and Obsahuje bibliografii