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In northern forests, large amounts of missing N that dominate N balances at scales ranging from small watersheds to large regional drainage basins may be related to N-gas production by soil microbes. We measured denitrification rates in forest soils in northeastern North America along a N deposition gradient to determine whether N-gas fluxes were a significant fate for atmospheric N inputs and whether denitrification rates were correlated with N availability, soil O2 status, or forest type. We quantified N2 and N2O fluxes in the laboratory with an intact-core method and monitored soil O2, temperature and moisture in three forests differing in natural and anthropogenic N enrichment: Turkey Lakes Watershed, Ontario; Hubbard Brook Experimental Forest, New Hampshire; and Bear Brook Watershed, Maine (fertilized and reference plots in hardwood and softwood stands). Total N-gas flux estimates ranged from <1 in fertilized hardwood uplands at Bear Brook to >100 kg N ha(-1) year(-1) in hardwood wetlands at Turkey Lakes. N-gas flux increased systematically with natural N enrichment from soils with high nitrification rates (Bear Brook < Hubbard Brook < Turkey Lakes) but did not increase in the site where N fertilizer has been added since 1989 (Bear Brook). Our results show that denitrification is an important and underestimated term (1-24% of atmospheric N inputs) in N budgets of upland forests in northeastern North America, but it does not appear to be an important sink for elevated anthropogenic atmospheric N deposition in this region.

The subclinical and clinical Plasmodium elongatum and Plasmodium relictum infections of captive-reared African black-footed penguins (Spheniscus demersus) were evaluated in nine adult and 29 juvenile penguins in the Baltimore Zoo (Maryland, USA) during summer 1988 and winter 1989. Two diagnostic methods were used: Giemsa-stained thin blood films, and subinoculation of penguin blood into 1-day-old Peking ducklings. Chloroquine and primaquine treatment was applied to all parasitemic juvenile penguins. Twenty-nine parasite-free, juvenile penguins were monitored for parasitemia by Giemsa-stained thin blood films every two weeks for 26 weeks of their first outdoor exposure. Eighteen of 29 penguins experienced naturally acquired malaria; 14 were infected with P. elongatum, three with P. relictum, and one bird had a mixed P. relictum and P. elongatum infection. Eleven of 18 juveniles became parasitemic again after chloroquine and primaquine treatments. Based on Giemsa-stained thin blood smears and subinoculation of penguin blood into 1-day-old ducklings, performed in a mosquito-free environment in winter, nine adult penguins had no evidence of Plasmodium spp. infection. After dexmethasone-induced immunosuppression, four of six of these nonparasitemic adult penguins were found to be infected with P. relictum by the blood inoculation method.

Twenty-nine juvenile, captive-reared African black-footed penguins (Spheniscus demersus) were hematologically monitored every 2 wk over the period of 24 wk during their first outdoor exposure. Blood samples taken from the penguins were screened for 12 blood evaluation parameters. Parasitemic penguins were medically treated. Eighteen birds (62.1%) experienced naturally acquired malaria and 11 birds (37.9%) remained nonparasitemic. A total of 32 avian malaria episodes were noted; 25 (78.1%) were identified as Plasmodium elongatum, 5 (15.6%) as Plasmodium relictum, and 2 (6.3%) as Plasmodium spp. One P. elongatum (3.4%) and 3 P. relictum (10.3%) infections were fatal. All deaths occurred during the first episode of parasitemia. Gross lesions of the birds that died included hepatomegaly and splenomegaly. Interstitial pneumonia with schizonts was observed on histological examinations. The range, mean, and SD of 12 hematological parameters were determined for nonparasitemic and parasitemic penguins. Differences between these groups in total white blood cell (WBC) counts and relative lymphocytosis (LYMPHS) were not significant. The combined classes of total WBC counts (> 20.0 x 10(3)/microliters) and LYMPHS (> 60.0%) are not indicative of avian malaria infection in African penguins. No correlations were found between changes in the values of blood parameters with season or age of penguins. Treatment of parasitemic birds significantly reduced expected mortality from 50.0% to 13.8%.

Sorghum bicolor genotypes, near isogenic with different alleles at the third maturity locus, were compared for development, for responsiveness to GA(3) and a GA synthesis inhibitor, and occurrence and concentrations of endogenous GAs, IAA, and ABA. At 14 days the genotype 58M (ma(3) (R)ma(3) (R)) exhibited 2.5-fold greater culm height, 1.75-fold greater total height, and 1.38-fold greater dry weight than 90M (ma(3)ma(3)) or 100M (Ma(3)Ma(3)). All three genotypes exhibited similar shoot elongation in response to GA(3), and 58M showed GA(3)-mediated hastening of floral initiation when harvested at day 18 or 21. Both 90M and 100M had exhibited hastening of floral initiation by GA(3) previously, at later application dates. Tetcyclacis reduced height, promoted tillering, and delayed flowering of 58M resulting in plants which were near phenocopies of 90M and 100M. Based on bioassay activity, HPLC retention times, cochromatography with (2)H(2)-labeled standards on capillary column GC and matching mass spectrometer fragmentation patterns (ions [m/z] and relative abundances), GA(1), GA(19), GA(20), GA(53), and GA(3) were identified in extracts of all three genotypes. In addition, based on published Kovats retention index values and correspondence in ion masses and relative abundances, GA(44) and GA(17) were detected. Quantitation was based on recovery of coinjected, (2)H(2)-labeled standards. In 14 day-old-plants, total GA-like bioactivity and GA(1) concentrations (nanograms GA/gram dry weight) were two- to six-fold higher in 58M than 90M and 100M in leaf blades, apex samples, and whole plants while concentrations in culms were similar. Similar trends occurred if data were expressed on a per plant basis. GA(1) concentrations for whole plants were about two-fold higher in 58M than 90M and 100M from day 7 to day 14. Concentrations of ABA and IAA did not vary between the genotypes. The results indicate the mutant allele ma(3) (R) causes a two- to six-fold increase in GA(1) concentrations, does not result in a GA-receptor or transduction mutation and is associated with phenotypic characteristics that can be enhanced by GA(3) and reduced by GA synthesis inhibitor. These observations support the hypothesis that the allele ma(3) (R) causes an overproduction of GAs which results in altered leaf morphology, reduced tillering, earlier flowering, and other phenotypic differences between 58M and 90M or 100M.

Four gibberellins, GA(53), GA(19), GA(20), and GA(1), were detected by bioassay, chromatography in two HPLC systems, and combined gas chromatography-mass spectroscopy-selected ion monitoring (GC-MS-SIM) in etiolated soybean (Glycine max [L.] Merr.) hypocotyls. GC-MS-SIM employed [(2)H(2)]-labeled standards for each endogenous gibberellin detected, and quantities estimated from bioassays and GC-MS-SIM were similar. This result plus the tentative detection of GA(44) and GA(8) (standards not available) indicates that the early-C-13-hydroxylation pathway for gibberellin biosynthesis predominates in soybean hypocotyls. Other gibberellins were not detected. Growth rates decreased after transfer to low water potential (psi(w)) vermiculite and were completely arrested 24 hours after transfer. The GA(1) content in the elongating region of hypocotyls had declined to 38% of the 0 time value at 24 hours after transfer to low psi(w) vermiculite, a level which was only 13% of the GA(1) content in control seedlings at the same time (24 hours posttransfer). Rewatering seedlings following 24 hours growth in low psi(w) vermiculite resulted in a complete recovery in elongation rate, an increase in GA(1) (20% at 2 hours, two-fold at 8 hours, eightfold at 24 hours), and a decrease in ABA levels (tenfold at 2 hours). Treatment of well-watered seedlings with the GA-synthesis inhibitor tetcyclacis (TCY) resulted in lowered GA(1) levels and increased ABA levels. When seedlings grown 24 hours in low psi(w) vermiculite were rewatered with TCY, recovery of the elongation rate was delayed and reduced, and the decline in ABA levels was slowed. Addition of GA(3) restored the elongation rate inhibited by TCY. Seedlings were growth responsive to exogenous GA(3), and this GA(3)-promoted growth was inhibited by exogenous ABA. The data are consistent with the hypothesis that changes in GA(1) and ABA levels play a role in adjusting hypocotyl elongation rates. However, the changes observed are not of sufficient magnitude nor do they occur rapidly enough to suggest they are the primary regulators of elongation rate responses to rapidly changing plant water status.