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Variable internal plant nutrient content may confound plant response to environmental stress. Plant nutrient content may be controlled with relative addition rate techniques in solution culture. However, because raising large numbers of plants in flowing solution culture is difficult, we investigated the feasibility of raising plants in soil mix using relative fertilizer additions. Aspen (Populus tremuloides Michx.) clones (216, 259 and 271) planted in pots containing a peat, sand and vermiculite (2:1:1, v/v/v) soil mix were grown with exponentially increasing fertilizer concentrations and harvested periodically to assess growth. Addition rate treatments ranged from 0.01 to 0.05 day−1. The lag phase of growth, in which plants adjusted to the fertilizer regime, lasted 40 days after which plants entered the experimental period characterized by constant relative growth rates equivalent to applied fertilizer addition rates. Total plant nutrient concentration was (1) unique for each addition rate, (2) linearly related to addition rate and growth rate, and (3) tended to increase at the highest, and decrease at the lowest addition rates. Regardless, the plants appeared to have attained steady‐state conditions. Allocation of carbon to roots increased with lower addition rate treatments and was not dependent upon ontogeny. There were no treatment differences in growth response among aspen clones. Yet there were treatment differences in leaf chlorophyll and photosynthesis within the clones. For the 0.05 day−1 addition rate treatment, chlorophyll, leaf N concentration and photosynthetic rate were strongly correlated with one another, were at a maximum in recently mature leaves, and rapidly declined with leaf age. The rate of decline in these leaf characteristics was slowest in clone 271, consistent with the leaf longevity stress response reported elsewhere. Plant responses from these relative fertilizer addition trials in soil mix agree closely with those run in hydroponics, indicating that steady‐state nutrition can be achieved with a technically simple experimental assemblage. [ABSTRACT FROM AUTHOR]

The Intergovernmental Panel of Climate Change (IPCC) has concluded that the greenhouse gases carbon dioxide (CO2) and tropospheric ozone (O3) are increasing concomitantly globally. Little is known about the effect of these interacting gases on growth, survival, and productivity of forest ecosystems. In this study we assess the effects of three successive years of exposure to combinations of elevated CO2 and O3 on growth responses in afive trembling aspen (Populus tremuloides) clonal mixture in a regenerating stand. The experiment is located in Rhinelander, Wisconsin, USA (45 deg. N 89 deg. W) and employs free air carbon dioxide and ozone enrichment (FACE) technology. The aspen stand was exposed to a factorial combination of four treatments consisting of elevated CO2 (560 ppm), elevated O3 (episodic exposure-90 Mu1 1-1 hour-1), a combination of elevated CO2 and O3, and ambient control in 30 m treatment rings with three replications. Our overall results showed that our three growth parameters including height, diameter and volume were increased byelevated CO2, decreased by elevated O3, and were not significantly different from the ambient control under elevated CO2+O3. However, there were significant clonal differences in the responses; all five clones exhibited increased growth with elevated CO2, one clone showed an increase withelevated O3, and two clones showed an increase over the control with elevated CO2+O3, two clones showed a decrease, and one was not significantly different from the control.Notably, there was a significant increase in current terminal shoot dieback with elevated CO2 during the 1999/2000 dormant season. Dieback was especially prominent in two of the five clones, and was attributed to those clones growing longer into the autumnal season wh [ABSTRACT FROM AUTHOR]

Trichloroethylene (TCE) is a widespread environmental pollutant common in groundwater plumes associated with industrial manufacturing areas. We had previously isolated and characterized a natural bacterial endophyte, Enterobacter sp. strain PDN3, of poplar trees, that rapidly metabolizes TCE, releasing chloride ion. We now report findings from a successful three-year field trial of endophyte-assisted phytoremediation on the Middlefield-Ellis-Whisman Superfund Study Area TCE plume in the Silicon Valley of California. The inoculated poplar trees exhibited increased growth and reduced TCE phytotoxic effects with a 32% increase in trunk diameter compared to mock-inoculated control poplar trees. The inoculated trees excreted 50% more chloride ion into the rhizosphere, indicative of increased TCE metabolism in planta. Data from tree core analysis of the tree tissues provided further supporting evidence of the enhanced rate of degradation of the chlorinated solvents in the inoculated trees. Test well groundwater analyses demonstrated a marked decrease in concentration of TCE and its derivatives from the tree-associated groundwater plume. The concentration of TCE decreased from 300 μg/L upstream of the planted area to less than 5 μg/L downstream of the planted area. TCE derivatives were similarly removed with cis-1,2-dichloroethene decreasing from 160 μg/L to less than 5 μg/L and trans-1,2-dichloroethene decreasing from 3.1 μg/L to less than 0.5 μg/L downstream of the planted trees. 1,1-dichloroethene and vinyl chloride both decreased from 6.8 and 0.77 μg/L, respectively, to below the reporting limit of 0.5 μg/L providing strong evidence of the ability of the endophytic inoculated trees to effectively remove TCE from affected groundwater. The combination of native pollutant-degrading endophytic bacteria and fast-growing poplar tree systems offers a readily deployable, cost-effective approach for the degradation of TCE, and may help mitigate potential transfer up the food chain, volatilization to the atmosphere, as well as direct phytotoxic impacts to plants used in this type of phytoremediation. [ABSTRACT FROM AUTHOR]