Effects of soil freezing and drought stress on abscisic acid content of sugar maple sap and leaves

Expression profiling of ABA pathway transcripts indicates crosstalk between abiotic and biotic stress responses in Arabidopsis

Recent breakthrough on identification and characterization of PYR/PYLs as ABA receptors enables us to better understand the perception, signaling and transportation of ABA in plant. Based on publicly available microarray data, transcriptional levels of ABA signaling pathway core components were compared after stress and phytohormone treatments, including these involved in ABA metabolism, signal transduction, and catabolism. The results showed that both abiotic and biotic stress treatments increased the expression levels of ABA key metabolism and catabolism transcripts. The expression levels of PYR/PYLs were down-regulated and these of PP2Cs and ABFs were uniformly up-regulated after exogenous ABA application and under stress conditions. The results indicated that the increased ratio of PP2Cs:PYR/PYLs might be required for activation of the downstream ABA signal pathway under both abiotic and biotic stress conditions. We concluded that abiotic and biotic stress responses shared ABA signal pathway in Arabidopsis.

The extent of the North American boreal zone

The circumpolar boreal zone is one of the world’s major biogeoclimatic zones, covering much of North America and Eurasia with forests, woodlands, wetlands, and lakes. It regulates climate, acts as a reservoir for biological and genetic diversity, plays a key role in biogeochemical cycles, and provides renewable resources, habitat, and recreational opportunities. Poor agreement exists amongst scientists regarding this zone’s delimitation and the areal extent of boreal forests, even though the zone has been well-studied. This paper reviews the literature on the phytogeography of the zone and makes use of a geographic information system (GIS) and published maps to delineate a current map of the North American boreal zone and the hemiboreal subzone, which is a transitional area lying immediately to the south of the boreal zone that is usually included in the boreal zone by Europeans but excluded by North Americans. On the basis of the map described here, the boreal zone covers about 627 million ha, or 29% of the North American continent north of Mexico. If the hemiboreal subzone, at 116 million ha, is included, then 34% of the same area is covered. Forests and other wooded land (362 million ha) cover 58% of the North American boreal zone on the basis of current forest inventory data. With forests and other wooded land of the hemiboreal subzone (68 million ha) factored in, this percentage remains basically unchanged. Values reported in this paper are compared with other published statistics. Important sources of error contributing to differences in areal statistics are discussed.

Modeling coupled interactions of carbon, water, and ozone exchange between terrestrial ecosystems and the atmosphere. I: model description

A new biophysical model (FORFLUX) is presented to study the simultaneous exchange of ozone, carbon dioxide, and water vapor between terrestrial ecosystems and the atmosphere. The model mechanistically couples all major processes controlling ecosystem flows trace gases and water implementing recent concepts in plant eco-physiology, micrometeorology, and soil hydrology. FORFLUX consists of four interconnected modules-a leaf photosynthesis model, a canopy flux model, a soil heat-, water- and CO2- transport model, and a snow pack model. Photosynthesis, water-vapor flux and ozone uptake at the leaf level are computed by the LEAFC3 sub-model. The canopy module scales leaf responses to a stand level by numerical integration of the LEAFC3model over canopy leaf area index (LAI). The integration takes into account (1) radiative transfer inside the canopy, (2) variation of foliage photosynthetic capacity with canopy depth, (3) wind speed attenuation throughout the canopy, and (4) rainfall interception by foliage elements. The soil module uses principles of the diffusion theory to predict temperature and moisture dynamics within the soil column, evaporation, and CO2 efflux from soil. The effect of soil heterogeneity on field-scale fluxes is simulated employing the Bresler-Dagan stochastic concept. The accumulation and melt of snow on the ground is predicted using an explicit energy balance approach. Ozone deposition is modeled as a sum of three fluxes- ozone uptake via plant stomata, deposition to non-transpiring plant surfaces, and ozone flux into the ground. All biophysical interactions are computed hourly while model projections are made at either hourly or daily time step. FORFLUX represents a comprehensive approach to studying ozone deposition and its link to carbon and water cycles in terrestrial ecosystems.

Temperature effects on hydraulic conductance and water relations of Quercus robur L

The effects of temperature on root and shoot hydraulic conductances (g(shoot) and g(root)) were investigated for Quercus robur L. saplings. In a first experiment, conductances were measured with a High Pressure Flow Meter on excised shoots and detopped root systems. The g(root) and g(shoot) increased considerably with temperature from 0-50 degrees C. Between 15 degrees C and 35 degrees C, g(shoot) and g(root) varied with water viscosity. In a second experiment, the impact of temperature-induced changes in g(root) on sapling transpiration (E) and leaf water potential (psileaf) was assessed. Intact plants were placed in a growth cabinet with constant air and variable soil temperatures. E increased linearly with soil temperature but psileaf remained constant. As a consequence, a linear relationship was found between E and g(plant). The results illustrate the significance of g(plant) for the stomatal control of transpiration and the significance of temperature for tree water transport.