The effects of acid rain and ozone on biomass and leaf area parameters of shortleaf pine (Pinus echinata Mill.)

Shortleaf pine (Pinus echinata Mill.) seedlings in 24 open-top chambers were exposed to combinations of ozone (carbon-filtered (control), ambient, 1.7 x ambient, and 2.5 x ambient) and acidic precipitation (pH 5.3, 4.3 and 3.3) for 16 months (1989 harvest) or 28 months (1990 harvest). Although the effects of acid rain were generally not significant, there was a trend toward increased aboveground biomass and leaf area in seedlings subjected to the low pH treatments. Because N concentrations in the soils generally increased with decreasing pH, we concluded that the effects of acid rain on aboveground biomass and leaf area were a consequence of an increasing concentration of soil N. In the 1989 harvest, seedlings in the 2.5 x ambient ozone treatment had significantly less biomass in all aboveground plant components and significantly less total leaf area than seedlings in the 1.7 x ambient ozone treatment. In the 1990 harvest, there were no significant effects of ozone on total aboveground biomass, although there was a trend toward reduced biomass in seedlings in the 2.5 x ambient ozone treatment. Both total leaf area and leaf biomass were significantly less in seedlings exposed to 2.5 x ambient ozone for 28 months than in both control seedlings and seedlings in the 1.7 x ambient ozone treatment. The greater, but not always significant, aboveground biomass and leaf area of seedlings in the 1.7 x ambient ozone treatment compared with control seedlings may be associated with the observed increase in soil nitrate concentration as a result of increased rates of leaf senescence and litterfall.     

Anaerobic microbial degradation of selected 3,4-dihalogenated aromatic compounds

Anaerobic microbial degradation of selected 3,4-dihalogenated aromatic compounds was studied in medium inoculated with pond sediment. Sediment samples were collected from a diuron-treated pond. Diuron was dehalogenated at the para position, forming CPDMU as the sole degradation product. DCPU was similarly dehalogenated at the para position, forming MCPU as the only degradation product. Linuron degradation resulted in four products: one, CPMMU, was the result of biological dehalogenation at the para position; another, DCPMU, was the result of chemical degradation; and the other two products were unidentified. Chlorbromuron degradation formed three unidentified products. Stam, an acylanilide, was degraded, forming two products, one of which was possibly 3-chloropropioanilide. CIPC and an unidentified compound were formed from DCIP. No degradation of parent compounds or appearance of degradation products were detected in mixtures of each test compound and sterile sediment except linuron.     

Coleoptile length of barley (<Emphasis Type="Italic">Hordeum vulgare</Emphasis> L.) cultivars

Coleoptile length is related to maximum seeding depth. The coleoptile length of 44 spring barley cultivars (Hordeum vulgare L.) was determined by laying seeds on moistened filter paper and incubating at 15°C for 13 days. Significant differences in coleoptile length were noted between cultivars (P < 0.05). Most cultivars had a coleoptile length between 60 and 80 mm. Five cultivars (Buloke, Dash, Harrington, Morrell and Tallon) had a coleoptile length shorter than 60 mm. Seven cultivars (CM72, Doolup, Finniss, Fleet, Hannan, Haruna Nijo and Macumba) had a coleoptile length longer than 80 mm. No relationship was found between early growth habit or plant height and coleoptile length. The impact of different dwarfing genes on coleoptile length was discussed. Differences in coleoptile length observed should be exploited by breeders to improve the tolerance of barley to deep seeding and stubble retention. This would be a useful tool in managing climate variability and would assist barley growers to sow closer to the optimum sowing time in situations where moisture is present at depth but not on the soil surface.     

Evaluation of resistance to Dermo in eastern oyster strains tested in Chesapeake Bay

We investigated growth, Dermo disease, and survival for nine groups of oysters, Crassostrea virginica (Gmelin) cultivated in Chesapeake Bay (CB). Five regional strains (upper CB, North Carolina (NC), South Carolina (SC), Louisiana (LA) and LA triploids) and four additional hybrid strains (CB oysters mated with NC, SC, LA and Texas (TX) oysters) were held in floating rafts at three locations representative of lower CB: ‘low’ salinity (3–14 g L^?1), ‘moderate’ salinity (5–20 g L^?1) and ‘high’ salinity (14–24 g L^?1). At each site, patterns of growth and incidence of infection with Perkinsus marinus (Levine), the causative agent of Dermo disease, were similar. However, mortality trends were markedly different at each site; the CB strain being notable for accelerated mortality following infection with P. marinus. In addition, hybrids between CB and all four of the regional strains exhibited similar accelerated mortality in response to infection. Mortality was strongly correlated with infection only at the high salinity site implicating interaction of differences in both oyster strain and virulence of Dermo between moderate and high salinity areas as factors in differential mortality across sites.     

Anaerobic microbial degradation of the herbicide propanil

The fate of propanil (3,4-dichloropropionanilide) in an anaerobic soil environment was studied. Two mineral salts media, one amended with 0.05% yeast extract and 0.05% tryptone, and both with 33 μg propanil ml^?1, were inoculated with 10% (v/v) soil to establish enrichment cultures. Cultures were incubated at 30°C under an atmosphere of 95% N₂ and 5% CO₂. There was a complete loss of propanil in 15 days in soil enrichment cultures. One degradation product was detected and identified by HPLC and TLC co-chromatography as 3,4-dichloroaniline. Propanil was also degraded in a soil-free medium containing 0.05% yeast extract and 0.05% tryptone and inoculated with supernatant from a soil enrichment culture. After 100 days, propanil concentration decreased by 81%; 3,4-dichloroaniline and meta-chloroaniline were produced. No decrease in propanil concentration was detected in soil-free cultures without yeast extract and tryptone. No labeled CO₂ or volatile products were detected after 80 days in soil-free enrichment cultures containing ¹⁴C-ring-labeled propanil.     

Influence of selenium status in merino weaners on resistance to trichostrongylid infection

Weaned merino lambs, grazing pastures low in selenium, were used to investigate the effect of selenium status on immunity to trichostrongylids. Six weeks following selenium supplementation to 14 of the 27 sheep using intraruminal selenium pellets, 5000 Ostertagia circumcincta and 5000 Trichostrongylus colubriformis larvae were administered orally to all sheep. At four weeks after infection, the mean total worm burden in the selenium supplemented sheep (5537 +/- 343, n = 14) was not significantly different (P greater than 0.05) from that in the unsupplemented sheep (5614 +/- 374, n = 12) and faecal worm egg concentrations were also similar in the two treatment groups. At this time, mean red cell glutathione peroxidase activities in the supplemented and unsupplemented groups were 430 and 11 U g-1 haemoglobin, respectively, and clinical white muscle disease had been observed in the latter group. These results suggest that increasing selenium status of selenium deficient sheep by the use of intraruminal selenium supplementation, has a negligible effect on resistance to an artificial challenge infection of O circumcincta and T colubriformis.     

Evidence of lactate dehydrogenase-B allozyme effects in the teleost, Fundulus heteroclitus

The evolutionary significance of protein polymorphisms has long been debated. Exponents of the balanced theory advocate that selection operates to maintain polymorphisms, whereas the neoclassical school argues that most genetic variation is neutral. Some studies have suggested that protein polymorphisms are not neutral, but their significance has been questioned because one cannot eliminate the possibility that linked loci were responsible for the observed differences. Evidence is presented that an enzymatic phenotype can affect carbon flow through a metabolic pathway. Glucose flux differences between lactate dehydrogenase-B phenotypes of Fundulus heteroclitus were reversed by substituting the Ldh-B gene product of one homozygous genotype with that of another.     

The Use of Bioluminescence for Monitoring in planta Growth Dynamics of a Pseudomonas syringae Plant Pathogen

The use of bioluminescence was evaluated as a tool to study Pseudomonas syringae population dynamics in susceptible and resistant plant environments. Plasmid pGLITE, containing the luxCDABE genes from Photorhabdus luminescens, was introduced into Pseudomonas syringae pv. phaseolicola race 7 strain 1449B, a Gram-negative pathogen of bean (Phaseolus vulgaris). Bacteria recovered from plant tissue over a five-day period were enumerated by counting numbers of colony forming units and by measurement of bioluminescence. Direct measurement of bioluminescence from leaf disc homogenates consistently reflected bacterial growth as determined by viable counting, but also detected subtle effects of the plant resistance response on bacterial viability. This bioluminescence procedure enables real time measurement of bacterial metabolism and population dynamics in planta, obviates the need to carry out labour intensive and time consuming traditional enumeration techniques and provides a sensitive assay for studying plant effects on bacterial cells.     

Effect of external phosphorus and seed phosphorus supply on the shoot and root growth of yellow serradella,burr medic,and subterranean clover

Glasshouse studies were undertaken to compare the responses of yellow sertadella, subterranean clover, and burr medic to changes in phosphorus (P) supply. Shoot growth at 35–50 days after sowing was related to differences in their physical root characteristics and their ability to take up P under conditions of limiting and adequate P supply. Subterranean clover and burr medic were also compared in their shoot response to applied P when seed with differing concentrations of P was sown. Where P supply limited the growth of subterranean clover shoots by at least 40%, yellow sertadella produced more shoot weight, had a lower root and shoot ratio, and longer, thinner roots than both subterranean clover and burr medic. Burr medic produced less shoot weight, had a higher root and shoot ratio and shorter, thicker roots than the other two species. Yellow serradella was also able to take up more P (greater shoot P content per gram root and per meter length root) than subterranean clover, whereas burr medic had the lowest ability to take up P. When P supply was adequate for near maximum growth, yellow serradella and burr medic had similar shoot weight to subterranean clover. Yellow serradella still had the lowest root and shoot ratio, the thinnest roots and a greater shoot P content per gram and per meter roots than subterranean clover, but subterranean clover had similar or slightly longer roots. Burr medic also had the highest root and shoot ratio, but now had roots longer and as thick or thicker than subterranean clover roots. The shoot P content per gram and per meter root in burr medic relative to subterranean clover varied with experiment. Sowing seed with a higher initial concentration of P increased the curvature coefficient of the response to applied P, reduced the absolute response to applied P, and altered the comparative requirement of subterranean clover and burr medic for applied P at 90% maximum yield.     

Anaerobic microbial degradation of diuron by pond sediment

Anaerobic degradation of the herbicide diuron, 3-(3,4-dichlorophenyl-1,1)dimethylurea, was studied. Enrichment cultures were established with seven different media in the presence of diuron (40 mg/liter). Media included combinations of sediment extract, mineral salts, and various organic amendments. Cultures were inoculated with aliquots of sediment collected from a pond previously treated with diuron and were maintained under an atmosphere of 95% N₂ and 5% CO₂. All enrichment cultures completely degraded diuron in 17–25 days. In all cultures showing diuron degradation, the product identified as 3-(3-chlorophenyl)-1,1-dimethylurea appeared in approximately stoichiometric amounts. Reinjection of diuron into each culture after 26 days resulted in rapid degradation of the parent herbicide with the appearance of proportionately more 3-(3-chlorophenyl)-1,1-dimethylurea. No other product was detected after 80 days in culture and the metachloro derivative was not degraded further during this time.