Root exudates from the unsuberized tips of new woody roots were collected from mature Betula alleghaniensis, Fagus grandifolia, and Acer saccharum in a northern hardwood forest. Numbers of new woody root tips were also determined for these three species. Exudates were fractioned into carbohydrates, amino acids/amides, organic acids, and 9 inorganic ions. Considerable species variation characterized the quantitative and qualitative nature of the organic fraction. Organic acids were the most abundant component. Fagus grandifolia released the largest amount of amino and organic acids per hectare, while B. alleghaniensis exuded the largest amount of carbohydrates. Sodium (possibly anomalous), K, and Ca dominated the cationic fraction, while the anionic fraction was chiefly SO4 and Cl. Betula alleghaniensis and F. grandifolia released considerably greater quantities of inorganic ions than A. saccharum, but the inorganic root exudate patterns of the three species were relatively uniform. These results indicate root exudates have some role in intrasystem nutrient cycling.
Two genotypes of kale (Brassica olerucea L). two of rape (one forage and one winter oilseed type, B riapus L) and two of swede ( B rtupus L) grown in a glasshouse were inoculated with turnip root fly (Deliafloralis Fall) eggs at 5 weeks and their roots, stems and leaves sampled after a further 8 weeks of larval feeding. Changes in total and individual glucosinolates were examined in roots, stems and leaves after attack. Damage by Dflorulis larvae to roots caused tissue weight losses in roots ranging from 26 to 48 Yo, relative to controls. The resultant plant stress also caused smaller weight losses in leaf tissue (10-27 Yo) and stems (6-20 YO). On susceptible brassica genotypes, D florulis percent pupal development and mean pupal weights were a factor of x 1.5 greater than on resistant genotypes, resulting in a difference of x 2.4 in total pupal biomass per root. There was no apparent link between D floralis susceptibility and total or individual glucosinolate content of undamaged control roots. Major differences in glucosinolate composition were found between control roots of the six brassicas. Five of the 15 compounds detected had aromatic side chains and were present in all samples. Only three of the 10 aliphatic glucosinolates were common to all six brassicas. The predominant compound in the two kale roots was prop-2-enyl glucosinolate, in the rapes 2hydroxy-but-3-enyl (forage rape cv Hobson) and 2-phenylethyl (oilseed rape cv Ariana) glucosinolates, and in the swedes 2-hydroxy-but-3-enyl glucosinolate. All brassicas showed a similar response in glucosinolate metabolism after root damage. Total glucosinolate content in roots increased due to a two to four fold increase in indole-based compounds. The largest increase for an individual compound after attack was found for I -methoxy-3-indolylmethyl glucosinolate, which increased four to 17 fold. Root damage did not significantly affect stem glucosinolate composition but in leaves caused a 1.2 fold increase in aliphatic glucosinolates with a corresponding decrease in indole-based compounds. The possible ecological and nutritional significance of glucosinolatc responses to root fly darnage is discussed.
The average annual Pb input to the northern hardwood forest at the Hubbard Brook Experimental Forest in central New Hampshire was 266 g ha−1 year−1 based on 4 years of records. Lead output via streamwater and eroded particulate matter was 5.0 and 1.1 g ha−1 year−1, respectively. Lead concentration in precipitation averaged 22 µg liter−1 and showed a significant decline over the 4 sample years (1975–1978).Lead input to the ecosystem via meteorological vectors is accumulated in the forest floor. Total current Pb content of the forest floor was 8.6 kg ha−1 and showed no significant differences along the elevation gradient of the watershed (400–800 m). Lead concentration in the forest floor was maximum on the ridge due to a minimum forest floor mass relative to the rest of the watershed. Within the forest floor, maximum Pb concentration is in the fermented (F) layer.Total Pb content of the forest biomass (stems ≥ 10 cm dbh) was 1,248 g ha−1. Lead concentration in the biota was in the following order: lichens (213 µg g−1) > mosses (190 µg g−1) > tree twigs (26 µg g−1) > roots (20 µg g−1) > bark (19 µg g−1) > leaves (7 µg g−1) = bracket fungi (7 µg g−1) > wood (0.7 µg g−1).Disturbance of the forest ecosystem through harvest cutting, other than through increased runoff, increased erosion, and transport of particulate matter, does not alter the biogeochemistry of Pb and does not result in increased mobility and export of Pb due to gross or subtle alterations of the behavior of Pb in the ecosystem.
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