Tradeoffs between leaf cooling and hydraulic safety in a dominant arid land riparian tree species.

Leaf carbon gain optimization in hot environments requires balancing leaf thermoregulation with avoiding excessive water loss via transpiration and hydraulic failure. The tradeoffs between leaf thermoregulation and transpirational water loss can determine the ecological consequences of heat waves that are increasing in frequency and intensity. We evaluated leaf thermoregulation strategies in warm- (>40°C maximum summer temperature) and cool-adapted (<40°C maximum summer temperature) genotypes of the foundation tree species, Populus fremontii, using a common garden near the mid-elevational point of its distribution.

Desert leaf litter decay: Coupling of microbial respiration, water-soluble fractions and photodegradation.

The mechanisms of plant litter decay in drylands are poorly understood, limiting the accuracy of nutrient-cycling models for these systems. We monitored the decay of 12 leaf litter types on the soil surface of the Sonoran Desert for 34 months and assessed what traits predicted mass loss and how exposure to different wavebands of sunlight influenced mass loss. Mass loss varied considerably among litter types, ranging from 42%-96% after 34 months in full sunlight.

Global assessment of experimental climate warming on tundra vegetation: heterogeneity over space and time.

Understanding the sensitivity of tundra vegetation to climate warming is critical to forecasting future biodiversity and vegetation feedbacks to climate. In situ warming experiments accelerate climate change on a small scale to forecast responses of local plant communities. Limitations of this approach include the apparent site-specificity of results and uncertainty about the power of short-term studies to anticipate longer term change.

The effect of urban ground cover on microclimate, growth and leaf gas exchange of oleander in Phoenix, Arizona.

We assessed how small patches of contrasting urban ground cover [mesiscape (turf), xeriscape (gravel), concrete, and asphalt] altered the microclimate and performance of adjacent oleander (Nerium oleander L.) plants in Phoenix, Arizona during fall/winter (September-February) and spring/summer (March-September). Ground-cover and oleander canopy surface temperatures, canopy air temperatures and pot soil temperatures tended to be lowest in the mesiscape and highest in the asphalt and concrete.

The influence of ultraviolet-B radiation on growth, hydroxycinnamic acids and flavonoids of Deschampsia antarctica during Springtime ozone depletion in Antarctica.

We examined the influence of solar ultraviolet-B radiation (UV-B; 280-320 nm) on the growth, biomass production and phenylpropanoid concentrations of Deschampsia antarctica during the springtime ozone depletion season at Palmer Station, along the Antarctic Peninsula. Treatments involved placing filters on frames over potted plants that reduced levels of biologically effective UV-B either by 83% (reduced UV-B) or by 12% (near-ambient UV-B) over the 63 day experiment (7 November 1998-8 January 1999) when ozone depletion averaged 17%. Plants growing under near-ambient UV-B had 41% and 40% lower relative growth rates and net assimilation rates, respectively, than those under reduced UV-B.

Photosynthetic symmetry of sun and shade leaves of different orientations.

The photosynthetic responses to light of leaves irradiated on the adaxial or abaxial surfaces, were measured for plants with contrasting leaf orientations. For vertical-leaf species of open habitats (Eryngium yuccifolium and Silphium terebinthinaceum), photosynthetic rates were identical when irradiated on either surface. However, for horizontal-leaf species of open habitats (Ambrosia trifida and Solidago canadensis), light-saturated rates of photosynthesis for adaxial irradiation were 19 to 37% higher than rates for abaxial irradiation.