"Phytoscreening": the use of trees for discovering subsurface contamination by VOCs.

We tested the possibility of using tree cores to detect unknown subsurface contamination by chlorinated volatile organic compounds (Cl-VOCs) and petroleum hydrocarbons, a method we term "phytoscreening". The scope and limitations of the method include the following: (i) a number of widespread Cl-VOC contaminants are readily found in tree cores, although those with very high vapor pressures or low boiling points may be absent; (ii) volatile petroleum hydrocarbons were notwell-expressed in tree cores; (iii) trees should be sampled during active evapotranspiration and from directions that are well exposed to sunlight; (iv) there is not necessarily a direct correlation between concentrations measured in tree cores and those in the subsurface; (v) detection of a contaminant in a tree core indicates that the subsurface is contaminated with the pollutant; (vi) many possible causes of false negatives may be predicted and avoided. We sampled trees at 13 random locations in the Tel Aviv metropolitan area and identified Cl-VOCs in tree coresfromthree locations. Subsequently, subsurface contamination at all three sites was confirmed. Phytoscreening is a simple, fast, noninvasive, and inexpensive screening method for detecting subsurface contamination, and is particularly useful in urban settings where conventional methods are difficult and expensive to employ.

Competitive uptake of trichloroethene and 1,1,1-trichloroethane by Eucalyptus camaldulensis seedlings and wood.

The efficient use of trees for taking up volatile organic compounds (VOCs) from the subsurface for remedial and screening purposes is hampered because many poorly quantified co-occurring processes affect VOC concentrations in the tree, the most basic of which are VOC sorption and uptake by roots. Toward understanding the dominant sorption mechanisms, uptake of trichloroethene (TCE) and 1,1,1-trichloroethane (TCA) by Eucalyptus camaldulensis seedlings was studied in both single-solute and bi-solute experiments. Single-solute and bi-solute sorption experiments on wood from a mature Eucalyptus camaldulensis specimen were also carried out. Competition between TCE and TCA for sorption sites was found in both seedling uptake and wood sorption experiments, indicating that partitioning is not the sole mechanism governing compound interactions in these systems. The nonlinear single-solute sorption isotherms on wood were fit by a dual-mode model including partitioning and Langmuir terms. The dual-mode model calculated parameters were consistent with the results of the bi-solute sorption experiments. As a consequence of competitive sorption processes, uptake of individual compounds may be lower than expected when multiple VOC contaminants are present in the subsurface.

Relationship between carbohydrate concentration and root growth potential in coniferous seedlings from three climates during cold hardening and dehardening.

Greenhouse-cultured, container-grown seedlings of Aleppo pine (Pinus halepensis Mill.), radiata pine (Pinus radiata D. Don), and interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) were cold acclimated and deacclimated in growth chambers over 24 weeks. Needle and root cold hardiness and root growth potential (RGP) were measured weekly. Root, needle and stem analyses for soluble sugars and starch were performed biweekly. In all tissues, there was a close correspondence between cold hardiness and the absolute concentration of soluble sugars, as well as between the increase and decrease in concentration of soluble sugars during cold hardening and dehardening, respectively, supporting the theory that soluble sugars function as cryoprotectants in plant tissues. The magnitude of starch concentration did not parallel the magnitude of the cold hardiness attained, and changes in starch concentration were related to production and consumption factors, rather than timing of changes in cold hardiness. The rise and fall of RGP paralleled the rise and fall of total carbohydrate concentration in roots. The behavior of the three species was surprisingly similar, considering the different climates to which they are adapted.

Expression of early nodulin genes in alfalfa mycorrhizae indicates that signal transduction pathways used in forming arbuscular mycorrhizae and Rhizobium-induced nodules may be conserved.

Transcripts for two genes expressed early in alfalfa nodule development (MsENOD40 and MsENOD2) are found in mycorrhizal roots, but not in noncolonized roots or in roots infected with the fungal pathogen Rhizoctonia solani. These same two early nodulin genes are expressed in uninoculated roots upon application of the cytokinin 6-benzylaminopurine. Correlated with the expression of the two early nodulin genes, we found that mycorrhizal roots contain higher levels of trans-zeatin riboside than nonmycorrhizal roots. These data suggest that there may be conservation of signal transduction pathways between the two symbioses-nitrogen-fixing nodules and phosphate-acquiring mycorrhizae.