Controlling growth and chemical composition of saplings by iteratively matching nutrient supply to demand: a bootstrap fertilization technique.

We developed a fertilization technique that results in the control, and maintenance at defined rates and levels, of growth and tissue composition of plants of different sizes and developmental stages growing at exponential and nonexponential rates in solid media under naturally fluctuating light and temperature regimes. Clonal cottonwood (Populus deltoides Bartr.) saplings were grown in sand. Low concentrations of nutrient solution were added daily at different constant exponentially increasing rates for 20-30 days to produce plants with different growth rates and tissue nutrient composition. Matching nutrient supply to measured growth demand by bootstrapping, where bootstrapping is the use of an iterative equation that calculates demand from either actual or desired growth rates, maintained these differences for 20-40 days. Nutrient additions controlled growth of saplings with growth rates between 2.0 and 4.0% day(-1), heights between 13.9 and 37.5 cm, dry weights between 0.70 and 3.90 g, leaf nitrogen contents between 1.2 and 3.9%, and leaf carbon/nitrogen ratios between 42.1 and 12.5. The technique was reproducible in a greenhouse without temperature, humidity, or light control, and is easily modified to suit different plant species, plants of various sizes, and various growing conditions.

Clonal variation of Populus tremuloides responses to diurnal drought stress.

We have developed an automated microprocessor controlled system for subjecting hydroponically grown plants to drought. Pumps and valves were used to move nutrient solutions into and out of a system of culture vessels in a growth chamber to provide periods of drought. Drought conditions were obtained by exposing the roots of hydroponically grown clones of aspen, Populus tremuloides Michx., to air in culture vessels temporarily emptied of nutrient medium. Over a 3-week period, the daily duration of drought was increased from 0 to 6 h. During this period, the plants became increasingly tolerant to drought, as shown by a decreasing propensity to wilt. All three clones sustained diurnal drought periods of 6 h for up to 5 weeks without detectable deterioration of health. Typical drought stress symptoms were observed including inhibition of growth, increased tissue amino acid content, and decreased water, solute, and turgor potentials in young leaves. In all clones, control plants had leaf water potentials between -1.0 and -1.6 MPa, whereas leaf water potentials of drought-treated plants were significantly lower, ranging from -1.7 to -3.0 MPa. Only one of the clones showed a significant decrease in leaf solute potential in response to drought. The decrease in leaf solute potential paralleled the decrease in water potential resulting in no significant difference in turgor potential. The other two clones had nonsignificant decreases to more negative leaf solute potentials under drought conditions resulting in significantly lowered turgor potentials. Leaf water potentials, solute potentials, and turgor potentials of the drought-treated plants returned to control values within two hours after rewatering. The growth inhibitions observed could not have been the consequence of loss of turgor. These results demonstrate genetic differences among aspen clones in water relations responses to drought.

Response of tree seedlings to aluminum.

This review focuses on the mechanisms underlying aluminum (Al) toxicity in trees. The major topics discussed include the uptake and localization of Al, effects of Al on growth and composition, factors determining the response to Al, proposed mechanisms of Al resistance, and the occurrence of Al phytotoxicity under field conditions.

Sensitivity of red oak (Quercus rubra L.) and American beech (Fagus grandifolia Ehrh.) seedlings to sodium salts in solution culture.

Sodium salt sensitivity of red oak (Quercus rubra L.) and American beech (Fagus grandifolia Ehrh.) was evaluated in solution culture. Both species showed symptoms of salt injury when grown in the presence of less than 10 mM Na. In red oak, leaf symptoms first appeared at a sodium concentration of 6.0 mM and leaf weight was significantly reduced at 7.5 mM Na. Leaf, stem and root dry weights of American beech were significantly reduced in the presence of 4.0 mM sodium. In both species, browning of leaf margins and necrosis were evident in the Na-treated plants. The observed symptoms were associated with high concentrations of sodium in the tissues. Neither species appears to have control over sodium uptake and translocation.

Effects of aluminum on growth, development, and nutrient composition of honeylocust (Gleditsia triacanthos L.) seedlings.

Hydroponic experiments were conducted to determine the effects of aluminum (Al) on root development, shoot morphology and the nutrient composition of honeylocust seedlings (Gleditsia triacanthos L.). Seedlings were grown at pH 4 in a nutrient solution containing 0, 50, 150, 600 or 1500 microM Al. Within seven days, there were significant differences in root growth and root nutrient composition between control seedlings and seedlings grown in the presence of 150 or 600 microM Al. By day 14, significant reductions in leaf production and plant height were observed in seedlings treated with 1500 microM Al. At the lowest Al concentration, 50 microM, leaf size and expansion rates were significantly lower than in the controls. By the third week of the experiment, Ca and Mg concentrations in young leaves of the Al-treated seedlings were significantly lower than in leaves of control plants. Analysis of old leaf tissue, however, revealed no consistent pattern of nutrient concentration with Al treatment.

Ribulose-1,5-bisphosphate carboxylase activity of Populus tremuloides Michx. bark tissues.

Ribulose-1,5-bisphosphate (RubP) carboxylase was isolated from bark tissue of Populus tremuloides Michx. by a one-step Sephadex G l00-120 column chromatography procedure. The peak fraction had specific activity of 1.3 micromol CO(2) mg(-1) chlorophyll min(-1). The bark RubP carboxylase activity was comparable to that of leaf tissues. Thus, young corticular tissues are photosynthetically competent and contain sufficient RubP carboxylase to account for the reported rates of photosynthesis.

System development for linked-fermentation production of solvents from algal biomass.

Five species of the genus Dunaliella (D. tertiolecta, D. primolecta, D. parva, D. bardawil, and D. salina) were examined for glycerol accumulation, growth rate, cell density, and protein and chlorophyll content. The suitability of each algal species for use as a fermentation substrate was judged according to glycerol accumulation and quantities of neutral solvents produced after sequential bacterial fermentations. When grown in 2 M NaCl, with 24 mM NaHCO(3) or 3% CO(2) at 28 degrees C and with 10,000 to 15,000 lx of incident light on two sides of a glass aquarium, four of the five species tested produced ca. 10 to 20 mg of glycerol per liter of culture. Clostridium pasteurianum was found to convert an algal biomass mixture supplemented with 4% glycerol to ca. 16 g of mixed solvents (n-butanol, 1,3-propanediol, and ethanol) per liter. Acetone was not detected. Additionally, it has been demonstrated that Dunaliella concentrates of up to 300-fold can be directly fermented to an identical pattern of mixed solvents. Overall solvent yields were reduced by >50% when fermentations were performed in the presence of 2% NaCl. These results are discussed in terms of practical application in tropical coastal zones.

Photosynthesis and Respiration of Developing Populus tremuloides Internodes.

The photosynthetic and respiratory performance of developing internodes of Populus tremuloides was evaluated by infrared gas analysis. Anatomical and morphological transitions were related to metabolic activity. Photosynthetic rates ranged from 6.0 to 10.0 milligrams CO(2) per decimeter squared per hour in the youngest internodes to 2.5 to 3.8 milligrams CO(2) per decimeter squared per hour in internodes with fully developed bark tissues. Respiration exceeded the rate of photosynthesis on the average by a factor of two. Stem photosynthesis increased with temperature up to 40 degrees C and declined steeply between 40 and 50 degrees C. Stem respiration increased nearly linearly to temperatures as high as 50 degrees C.

Chloroplast glutathione reductase.

Glutathione reductase (EC 1.6.4.2) activity is present in spinach (Spinacia oleracea L.) chloroplasts. The pH dependence and substrate concentration for half-maximal rate are reported and a possible role in chloroplasts is proposed.

Diurnal and Seasonal Patterns of Photosynthesis and Respiration by Stems of Populus tremuloides Michx.

The photosynthetic and respiratory rates of 5- to 7-year-old aspen stems (Populus tremuloides Michx.) were monitored in the field for 1 year to determine the seasonal patterns. The stem was not capable of net photosynthesis, but the respiratory CO(2) loss from the stem was reduced by 0 to 100% depending on the time of year and the level of illumination as a result of bark photosynthesis. The monthly dark respiratory rate ranged from 0.24 mg CO(2)/dm(2). hr in January to a maximum 7.4 mg CO(2)/dm(2). hr in June. Individual measurements ranged from 0.02 mg CO(2)/dm(2). hr in February to 12.3 mg CO(2)/dm(2). hr in June. Gross photosynthesis followed a pattern similar to the dark respiratory rate. The mean monthly rate was highest in June (1.65 mg CO(2)/dm(2). hr) and lowest in December (0.02 mg CO(2)/dm(2). hr). Individual measurements ranged from 0.0 mg CO(2)/dm(2). hr in winter to 5.5 mg CO(2)/dm(2). hr in July.Winter studies showed that stem respiration continued down to -11 C, the coldest temperature during this study. Upon warning to -3 C, the dark respiratory rate showed a sudden sharp increase (7- to 12-fold) which required many hours to return to normal levels. No measurable photosynthesis occurred below -3 C. Between -3 and 0 C, the maximal photosynthetic rate was reduced to less than 50% of the respiratory rate, but increased to 89% between 5 to 10 C.On a yearly basis, bark photosynthesis in P. tremuloides reduced the stem respiratory CO(2) loss by 28.7% on a daytime basis and an estimated 16 to 18% on a 24-hour basis.