Walter C. Shortle

Assessment of soil calcium status in red spruce forests in the northeastern United States

Long-term changes in concentrations of available Ca in soils of redspruce forests have been documented, but remaining questions aboutthe magnitude and regional extent of these changes have precluded anassessment of the current and future status of soil Ca. To addressthis problem, soil samples were collected in 1992—93from 12 sites in New York, Vermont, New Hampshire, and Maine toprovide additional data necessary to synthesize all availableresearch results on soil Ca in red spruce forests. Sites werechosen to encompass the range of environmental conditionsexperienced by red spruce. Concentrations of exchangeableCa ranged from 2.13 to 21.6 cmolckg−1 in the Oa horizon, and from 0.11 to 0.68cmolc kg−1 in the upper 10 cm of theB horizon. These measurements expanded the range of exchangeable Ca reported in the literature for both horizons in northeastern redspruce forests. Exchangeable Ca was the largest Ca fraction in theforest floor at most sites (92% ofacid-extractableCa), but mineral Ca was the largest fraction at the three sites that also had the highest mineral-matter concentrations. Theprimary factor causing variability in Ca concentrations among siteswas the mineralogy of parent material, but exchangeable concentrationsin the B horizon of all sites were probably reduced by acidicdeposition. Because the majority of Ca in the forest floor isin a readily leachable form, and Ca inputs to the forest floor from the mineral soil and atmospheric deposition have beendecreasing in recent decades, the previously documented decreasesin Ca concentrations in the forest floor over previous decades mayextend into the future.

A Rapid and Reliable Procedure for Extraction of Cellular Polyamines and Inorganic Ions from Plant Tissues

A fast and reliable method for the extraction of cellular polyamines and major inorganic ions (Ca, Mg, Mn, K, and P) from several plant tissues is described. The method involves repeated freezing and thawing of samples instead of homogenization. The efficiency of extraction of both the polyamines and inorganic ions by these two methods was compared for 10 different tissues. In each case, the freeze-thaw procedure resulted in a precise and quantitatively equal, or greater, yield than homogenization. Freeze-thawing not only eliminates the need for various tissue homogenizers (such as polytrons, tissumizers, and mortars and pestles), but it is so simple that a large number of samples can be processed simultaneously. We routinely processed 50–80 samples for quantitation of polyamines and inorganic ions. Freeze-thawing was equally useful for the extraction of polyamines from liver, spleen, and kidney tissues of mice.

Timing, magnitude, and impact of acidic deposition on sensitive forest sites

Adverse effects of acidic deposition on forest health are most likely to occur in forests which develop a thick raw or “mor” humus layer in which the effective cation exchange capacity is highly sensitive to acid input. A study of the trend of exchangeable Ca and Mg ions in sensitive humus layers over the past six decades indicated that a downward shift in equilibrium has occurred that is consistent with theories of ion mobilization and coincident in time with increasing acidic deposition in the mid-1900s. Independent records of a base cation mobilization in wood supports the view of a change in the root zone in sensitive forest sites and in lake water chemistry. Induced nutrient deficiency in declining forest stands was indicated by a high Al∶Ca ratio in fine root tip tissue as a marker of altered uptake efficiency which leads to increased vulnerability to biotic factors and greater sensitivity to abiotic stresses. Evidence indicates that sensitive sites were damaged by acidic deposition 20 to 40 yr ago, long before the problem of “acid rain” was recognized.

Relationships among foliar chemistry, foliar polyamines, and soil chemistry in red spruce trees growing across the northeastern United States

Forest trees are constantly exposed to various types of natural and anthropogenic stressors. A major long-term goal of our research is to develop a set of early physiological and biochemical markers of stress in trees before the appearance of visual symptoms. Six red spruce (t Picea rubens Sarg.) stands from the northeastern United States were selected for collection of soil and foliage samples. All of the chosen sites had soil solution pH values below 4.0 in the Oa horizon but varied in their geochemistry. Some of these sites were apparently under some form of environmental stress as indicated by a large number of dead and dying red spruce trees. Samples of soil and needles (from apparently healthy red spruce trees) were collected from these sites four times during a two-year period. The needles were analyzed for perchloric acid-soluble polyamines and exchangeable inorganic ions. Soil and soil solution samples from the Oa and B horizons were analyzed for their exchange chemistry. The data showed a strong positive correlation between Ca and Mg concentrations in the needles and in the Oa horizon of the soil. However, needles from trees growing on relatively Ca-rich soils with a low exchangeable Al concentration and a low Al:Ca soil solution ratio had significantly lower concentrations of putrescine and spermidine than those growing on Ca-poor soils with a high exchangeable Al concentration and a high Al:Ca soil solution in the Oa horizon. The magnitude of this change was several fold higher for putrescine concentrations than for spermidine concentrations. Neither putrescine nor spermidine were correlated with soil solution Ca, Mg, and Al concentrations in the B horizon. The putrescine concentrations of the needles always correlated significantly with exchangeable Al (r2=0.73, t p≤0.05) and soil solution Al:Ca ratios (r2=0.91, t p≤0.01) of the Oa horizon. This suggests that in conjunction with soil chemistry, putrescine and/or spermidine may be used as a potential early indicator of Al stress before the appearance of visual symptoms in red spruce trees.

Dendroecological applications in air pollution and environmental chemistry: research needs

Summary During the past two decades, dendrochronology has evolved in new dimensions that have helped address both the extent and causes of impacts of regional scale environmental pollution on the productivity and function of forest ecosystems. Initial focus on the magnitude and timing of alterations of baseline growth levels of individual forest trees has now broadened to include characterization of the geographic extent of effects, their distribution among species, and their relationship to soils and biogeochemical cycles. Increasingly dendrochronology has benefitted from and contributed to improved understanding of the physiological and biogeochemical basis of air pollution effects on forest ecological processes. In addition, the need to consider levels and types of remedial action has raised concerns about the relative roles of anthropogenic and natural causative factors. The subdisciplines of dendroecology and dendrochemistry have evolved in response to those needs. Such applications have extended the field from its initial primary focus on historical growth and climatic reconstruction to an emerging role as an exploratory research tool with the potential to address basic questions about the roles of air pollution in modifying relationships between the amount, timing, distribution, and quality of tree growth and biogeochemical and atmospheric processes. In this paper we focus on two regional scale air quality issues, acidic deposition and tropospheric ozone, as stressors. We evaluate past success, current limitations, and future potential of dendrochronology as an investigative tool for both quantifying and understanding the effects of these stressors on forests. Important issues related to the use of dendrochemistry to evaluate effects of acidic deposition include the role of natural vs anthropogenic processes in cation mobilization in soils; biological and geochemical significance of increases in potentially phytotoxic metals and depletion of essential base cations in stem wood; and quantitative vs qualitative interpretation of patterns of element changes in wood related to metal mobility and species differences in accumulation. Shifts in root growth, function, and distribution and increased sensitivity of tree growth to temperature stress are important indicators that cation depletion can alter forest function and the dendroclimatic signal. Critical challenges in evaluating forest responses to ozone, include defining the relative roles of episodic and chronic exposures in seasonal and annual growth cycles, and the quantifying impacts of ozone on the water relations of trees and stands. Here high-resolution measures of diurnal growth and water use patterns have the potential to identify critical features of both pollutant exposure and plant response. These insights should enhance our analytical capabilities in examining annual-scale measures of growth and provide needed understanding of changes in relationships of growth to climate. We conclude that dendrochronology, when coupled with mechanistic understanding of underlying ecological processes influencing growth, has been, and will continue to be, a valuable monitoring and investigative tool for exploring relationships between trees and their growing environment. We expect this role to become even more important in the future as better ways are sought to evaluate and predict forest growth and function in a changing global environment.

Conservation of element concentration in xylem sap of red spruce

Abstract. We investigated the chemistry of xylem sap as a marker of red spruce metabolism and soil chemistry at three locations in northern New England. A Scholander pressure chamber was used to extract xylem sap from roots and branches cut from mature trees in early June and September. Root sap contained significantly greater concentrations of K, Ca, Mg, Mn, and Al than branch sap. Sap collected in June contained a signficantly greater concentration of Mn than sap collected in September. Sap concentration was related to forest location for N and Mn. Variations in concentrations of N and K were significantly related to the interaction of tree organ and month of collection. Variations in concentrations of P, Cu, Zn, and Fe were not attributable to tree organ, month of collection, or forest location. Patterns of element concentration in xylem sap compared to previously published data on soil solution chemistry indicated a high degree of homeostatic control of xylem sap chemistry. This control likely represents a significant allocation of resources within the tree energy budget.

Decay Column Boundary Layer Formation in Maple

The wounding of sapwood in living trees results in a cascade of processes, including the formation of wound-initiated discoloration (Shigo, 1965). In three dimensions, this discoloration appears in the form of columns parallel to the stem axis with ragged, conical ends. All published reports indicate that in living trees, decayed wood only occurs in tissue that has undergone wound-initiated discoloration. The visible degree of discoloration and other features following wounding vary from one tree species to another. The size of wounds capable of inducing the decay process range from very small branch and root stubs to the mechanical breakage of main stems of adult trees.

Tree Survival and Growth Following Ice Storm Injury

Nearly 25 million acres of forest from northwestern New York and southern Quebec to the south-central Maine coast were coated with ice from a 3-day storm in early January 1998. This storm was unusual in its size and the duration of icing. Trees throughout the region were injured as branches and stems broke and forks split under the weight of the ice. These injuries reduced the size of tree crowns and exposed wood to infection that can lead to wood decay.In addition to regional assessments, forest managers need to know how much damage to expect in the years following the storm due to loss of wood quality, loss of tree growth, or tree death. The purpose of this study was to determine tree survival, stem growth, and response to infection following injury to major hardwood tree species from the 1998 ice storm.

Regulation of DNA synthesis and cell division by polyamines in Catharanthus roseus suspension cultures.

SummaryVarious inhibitors of polyamine biosynthesis were used to study the role of polyamines in DNA synthesis and cell division in suspension cultures of Catharanthus roseus (L.) G. Don. Arginine decarboxylase (ADC; EC 4.1.1.19) was the major enzyme responsible for putrescine production. DL α-difluoromethylarginine inhibited ADC activity, cellular putrescine content, DNA synthesis, and cell division. The effect was reversible by exogenous putrescine. Ornithine decarboxylase (ODC; EC 4.1.1.17) activity was always less than 10% of the ADC activity. Addition of DL α-difluoromethylornithine had no effect on ODC activity, cellular polyamine levels, DNA synthesis, and cell division within the first 24 h but by 48 to 72 h it did inhibit these activities. Methylglyoxal bis(guanyl-hydrazone) inhibited S-adenosylmethionine decarboxylase (EC 4.1.1.50) activity without affecting DNA synthesis and cell division.

Development of wood decay in wound-initiated discolored wood of eastern red cedar.

Abstract Logs of eastern red cedar, Juniperus virginiana L., with well-developed bands of light-colored wood (“included sapwood”) within heartwood can be unsuitable for sawn wood products. This finding is in contrast to published information that the “included sapwood” is (1) a heartwood anomaly rather than sapwood and (2) its occurrence is not a reason to exclude this type of wood from commercial use. The alternative view presented here is that “included sapwood” is wound-initiated discolored wood which is the starting point for wood decay in living trees and which has adversely altered wood properties before the development of decay symptoms. Our study of the patterns of discoloration and decay, electrical resistance properties, elemental analysis, wood acidity, solubility in dilute NaOH, total phenol content, and tests of wood decay resistance indicated that the so-called included sapwood was discolored wood. This light-colored discolored wood had no greater decay resistance than sapwood, a common finding in other tree species in which “included sapwood” is found. Half the sample disks sent to our laboratory had symptomatic decay within the bands of light-colored discolored wood bounded by a phenol-enriched protective layer on the bark side and phenol-enriched heartwood on the pith side of the band. This ring-rot, even in its pre-symptomatic stage, can cause problems during processing for sawn wood products. Therefore, logs with well-developed bands of light-colored discolored wood should be considered high-risk material for some products, although they could be useful for others.