Foliar Aluminum Research Articles

Controls on foliar aluminium accumulation among populations of the tropical shrub Melastoma malabathricum L. (Melastomataceae).

Aluminium (Al) accumulation is a common trait expressed in at least 60 plant families and particularly prevalent in tropical woody plants. However, the functional significance and genetic or physiological controls on Al accumulation are currently unknown. We tested the hypothesis that differential expression of Al accumulation among wild populations of the Al-accumulating tropical shrub Melastoma malabathricum L. is associated with habitat-related variation in total and exchangeable soil Al concentrations. Mature leaves and seeds were sampled from 20 populations of M. malabathricum growing in six habitats across Peninsular Malaysia, and soil was collected from each site. The seeds were grown in hydroponic solutions comprising 50% Hoagland's solution amended with Al in the form of 1.0 mM AlCl3 to test the hypothesis that differential expression of foliar Al accumulation is an inherited trait. Foliar Al concentrations varied significantly among populations, but were not consistently different among plants growing in different habitats and showed no relationship to total or exchangeable Al concentrations in soils collected at the 20 sites. Mean foliar Al concentration in wild plants was positively correlated with foliar calcium (Ca) concentrations, and with total soil nitrogen (N), Ca and magnesium (Mg) concentrations, across the 20 populations, and Al addition increased foliar concentrations of phosphorus, Ca, Mg and potassium in seedlings. The differential expression of Al accumulation in M. malabathricum populations is uncoupled to local variation in soil Al concentrations, but may be sensitive to local soil-related variation in the availability of other macro-nutrients, in particular N, Ca and Mg. Further research on the factors controlling Al uptake should focus on the plasticity of this trait within populations of Al accumulators and interactions with micro-habitat variation in the availability of the macronutrient cations.

Evidence of foliar aluminium accumulation in local, regional and global datasets of wild plants

• High foliar concentrations of aluminium (Al) have been reported in numerous plant species, but progress on the understanding of the functional significance of this trait is constrained by the absence of a quantitative analysis of its distribution among plant lineages and across biomes. • We constructed a global dataset of foliar Al and nutrient concentrations for 1044 plant species from literature sources and new data collections in Brunei Darussalam. • Our results provide statistical support for the existence of Al accumulators and non-Al accumulators in global, regional and local floras based on foliar Al concentrations. A value of 1 mg Al g(-1) leaf dry mass is a suitable threshold to distinguish between these two groups in a sample of species that lacks any geographical reference. However, a higher threshold foliar Al concentration is required to distinguish between Al accumulators in tropical (2.3-3.9 mg Al g(-1) leaf dry mass) than in temperate (1.1 mg Al g(-1) leaf dry mass) floras. There was a phylogenetic signal in the foliar concentrations of Al, but phylogeny did not explain the difference in the mean foliar Al concentration between tropical and temperate floras in a phylogenetically controlled analysis. • Phylogeny and soil chemistry are potential factors driving Al accumulation in certain groups of plants.

Effects of Fertilizer and Low Rates of Imidacloprid on Adelges tsugae (Hemiptera: Adelgidae)

Healthy hemlock trees, Tsuga canadensis (L.) Carrière, and hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), populations should favor retention and population growth of adelgid predators such as Laricobius nigrinus Fender (Coleoptera: Derodontidae) and Sasajiscymnus tsugae (Sasaji & McClure) (Coleoptera: Coccinellidae). Eastern hemlock trees between 15 and 38 cm diameter at breast height (dbh) were treated with 0, 10, or 25% of 1.5 g imidacloprid (Merit 75 WP) per 2.5 cm dbh and were either fertilized or not, in a 3 by 2 factorial design. After 2 yr, imidacloprid reduced the numbers of ovisacs and eggs found on trees in a dosage-dependent manner, while enhancing tree growth parameters such as new shoots or needles and the length of new shoots. Fertilized trees had greater adelgid fecundity, which was positively correlated with total foliar N in both winter generations. In February 2009 (27 mo after imidacloprid treatment), higher imidacloprid dosages to unfertilized trees resulted in reduced adelgid fecundity. Concentrations of N, P, and K were higher in the foliage of trees treated with insecticide, whereas foliar aluminum concentrations were consistently lower in trees with higher insecticide dosages. Trees treated with low rates of imidacloprid were healthier than untreated trees, but only trees treated with the 0.1 x dosage had sufficient adelgids to possibly sustain predators over extended periods.

Forest Vegetation Monitoring and Foliar Chemistry of Red Spruce and Red Maple at Acadia National Park in Maine

The USDA Forest Service Forest Health Monitoring (FHM) program indicators, including forest mensuration, crown condition classification, and damage and mortality indicators were used in the Cadillac Brook and Hadlock Brook watershed forests at Acadia National Park (ANP) along coastal Maine. Cadillac Brook watershed burned in a wildfire in 1947. Hadlock Brook watershed, undisturbed for several centuries, serves as the reference site. These two small watersheds have been gauged and monitored at ANP since 1998 as part of the Park Research and Intensive Monitoring of Ecosystems Network (PRIMENet). Forest vegetation at Hadlock Brook was dominated by late successional species such as Acer saccharum, Fagus grandifolia, Betula alleghaniensis, Acer rubrum and Picea rubens. Forest vegetation at Cadillac Brook, on the other hand, was younger and more diverse and included those species found in Hadlock as well as early successional species such as Betula papyrifera and Populus grandidentata. Differences in forest species composition and stand structure were attributed to the severe wildfire that affected the Cadillac Brook watershed. Overall, the forests at these ANP watersheds were healthy with a low percentage (</=22%) of trees showing symptoms of damage.Foliar nitrogen (N) concentrations were higher in A. rubrum and P. rubens trees growing in Hadlock Brook watershed, but differences were significant only for P. rubens. Foliar aluminum (Al) concentrations were also higher in both species growing in Hadlock Brook watershed but differences were significant only for A. rubrum. Foliar calcium (Ca) and manganese (Mn) concentrations, on the other hand, were significantly lower in Hadlock Brook watershed for both species. Foliar potassium (K) was significantly higher for P. rubens growing in Hadlock Brook. No differences in foliar concentrations of magnesium (Mg), phosphorus (P), boron (B), copper (Cu) and lead (Pb) were found between watersheds. The higher foliar N concentrations as well as higher foliar concentrations of Ca and Al might indicate early stages of N saturation and acidification in Hadlock Brook watershed as also suggested by Hadlock Brook stream N flux data in published PRIMENet studies at ANP.

Determination of Aluminum, Calcium, and Magnesium in Fraser Fir (Abies fraseri) Foliage from Five Native Sites by Atomic Absorption Spectrometry: The Effect of Elevation upon Nutritional Status

The Fraser fir (Abies fraseri) is a conifer native to high elevation sites in the southern Appalachians that has recently suffered severe mortality because of an exotic insect, the balsam woolly adelgid (BWA). The companion tree of the Fraser fir, the red spruce (Piceae rubens) has suffered relatively mild decline induced by acidic deposition, due to reduction of extractable calcium and magnesium levels in the soil, while causing an increase in extractable aluminum. We hypothesized that acidic deposition may be involved, along with the BWA, in inducing Fraser fir decline. Our hypothesis was tested by collecting Fraser fir foliage and soil from five sites on Clingman's Dome, NC/TN, Roan Mountain, NC/TN, and Mount Rogers, VA, and determining foliar and extractable soil aluminum, calcium, and magnesium. Foliar aluminum was done by graphite furnace atomic absorption (GFAAS) with continuum source background correction, while all other analyses were done by flame AAS. The analysis of composite samples was shown to provide improved precision by a factor of 2–4 for elemental analysis of a class of conifers compared to averaging individual analyses. Although aluminum levels were larger and calcium/aluminum ratios were smaller at the high elevation sites at two mountains, calcium levels were statistically the same at the high and low elevation sites. Consequently, it is difficult to definitively conclude that acidic deposition has contributed to Fraser fir decline.

Increased dark respiration and calcium deficiency of red spruce in relation to acidic deposition at high-elevation southern Appalachian Mountain sites

Rates of net photosynthesis and dark respiration of red spruce (Picearubens Sarg.) foliage were examined in relationship to soil and foliar nutrient status at three elevations across each of three mountains in the southern Appalachians. These studies tested our previously stated hypothesis that increased dark respiration and reduced growth were associated with natural or induced nutrient deficiency at higher elevation sites. A consistent and highly significant reduction in the ratio of net photosynthesis to dark respiration was found at the highest sites on each mountain compared with lower sites, as had been previously reported for the initial two test sites. This response was produced by significant increases in dark respiration that were associated with low foliar calcium levels and high foliar aluminum levels found at the higher elevation sites in this region. Net photosynthesis was generally comparable between sites. A consistently inverse relationship between dark respiration and foliar calcium was found across highest and lowest elevation sites, while the midelevation sites, where calcium:aluminum ratios were highest, showed less evidence of respiratory response to calcium. Calcium in shoots was significantly reduced in association with increasing levels of soil aluminum in the rooting zone across all sites. Collectively, these studies suggest that reduced calcium supply, occurring in association with competitive inhibition of calcium uptake by high concentrations of aluminum found in soil, may have reduced the availability of carbon for red spruce growth at higher elevation sites. Inferential evidence examined, including atmospheric deposition levels, soil solution chemistry, and historical tree-ring chemistry, suggests that acidic deposition would have been a contributing factor in inducing or amplifying calcium deficiency.

Seasonal patterns of photosynthesis and respiration of red spruce saplings from two elevations in declining southern Appalachian stands

Exploratory studies were initiated at two high-elevation red spruce (Picearubens Sarg.) stands in the Great Smoky Mountains of western North Carolina to document the magnitude and physiological basis of differences in tree growth at the two sites. Increment core data indicate that conditions have become relatively less favorable for mature trees at the upper site during the past 20 years and that annual height growth of sapling trees has been 40% less at that site compared with a similar site at an elevation 215 m lower. Seasonal measurements of net photosynthesis and dark respiration rates of saplings indicated that differences in sapling growth rates at the upper site were associated with increases in dark respiration and less favorable net photosynthesis:dark respiration ratios. Basal diameter increment was most closely associated with differences in current net photosynthesis rates among trees at the upper site, whereas height and diameter growth of the upper canopy related most closely to the net photosynthesis rate among lower-elevation trees. Reduced foliar calcium and magnesium, reduced foliar chlorophyll, increased foliar aluminum, and low ratios of calcium:aluminum were found at the upper site. Tissue and soil aluminum levels that are in the range of those associated with aluminum toxicity to red spruce provide a preliminary indication that current high atmospheric inputs of the strong anions SO4 and NO3 to acidic soils may be adversely affecting growth and physiology of trees at the high-elevation site.