Effects of rhizobium, arbuscular mycorrhizal fungi and anion content of simulated rain on subterranean clover.

An experiment was conducted to determine the extent to which rhizobia, mycorrhizal fungi, and anions in simulated rain affect plant growth response to acid deposition. Germinating subterranean clover seeds were planted in steam-pasteurized soil in pots and inoculated with Rhizobium leguminosarum, Glomus intraradices, Glomus etunicatum, R. leguminosarum + G. intraradices, R. leguminosarum + G. etunicatum, or no microbial symbionts. Beginning 3 weeks later, plants and the soil surface were exposed to simulated rain in a greenhouse on 3 days week(-1) for 12 weeks. Rain solutions were deionized water amended with background ions only (pH 5.0) or also adjusted to pH 3.0 with HNO3 only, H2SO4 only, or a 50/50 mixture of the two acids. Glomus intraradices colonized plant roots poorly, and G. intraradices-inoculated plants responded like nonmycorrhizal plants to rhizobia and rain treatments. Variation in plant biomass attributable to different rain formulations was strongest for G. etunicatum-inoculated plants, and the effect of rain formulation differed with respect to nodulation by rhizobia. The smallest plants at the end of the experiment were noninoculated plants exposed to rains (0.38 g mean dry weight total for 3 plants pot(-1)). Among nonnodulated plants infected by G. etunicatum, those exposed to HNO3 rain were largest, followed by plants exposed to HNO3 + H2SO4, pH 5.0, and H2SO4 rain, in that order. Among plants inoculated with both R. leguminosarum + G. etunicatum, however, the greatest biomass occurred with pH 5.0 rains, resulting in the largest plants in the study (1.00 g/3 plants). Treatment-related variation among root and shoot biomass data reflected those for whole-plant biomass. Based on quantification of biomass and N concentrations in shoot and root tissues, total N content of plants inoculated with G. etunicatum alone and exposed to the HNO3 + H2SO4 rains was approximately the same as plants inoculated with R. leguminosarum + G. entunicatum and exposed to pH 5 rains. Thus, the acid-mixture rains and rhizobia under no acid deposition provided approximately equal amounts of N in biomass. The significant interactions among rain formulation and the symbiotic status of the plants suggest that conclusions concerning the impact of acid deposition on plants in the environment cannot be considered reliable because most experiments on which such assessments are based have not tested confounding influences of microorganisms and precipitation characteristics.

Accumulation of starch in roots and foliage of loblolly pine (Pinus taeda L.): effects of season, site and fertilization.

Accurate predictions of stand response to nitrogen fertilization require a better understanding of the plant processes associated with stand nutrition. This study examined the relationship between stand nutrition and starch accumulation in roots and foliage of loblolly pine (Pinus taeda L.). A field study was located on the lower Coastal Plain of North Carolina on four sites of differing soil types. Stands of 8-year-old trees were fertilized with nitrogen (225 kg ha(-1)) or nitrogen plus phosphorus (225 kg N ha(-1) + 75 kg P ha(-1)) in 1981. Roots and foliage were collected from five trees per plot at six sampling dates from July 1983 through January 1985 and analyzed for starch. Starch concentrations showed seasonal fluctuations, with levels generally highest in early spring prior to budbreak. Root starch concentrations were lowest in autumn, whereas foliar concentrations were lowest in winter.

Temperature-dependent anomalies in the growth of microorganims.

Davey, C. B. (North Carolina State University, Raleigh), Raymond J. Miller, and Larry A. Nelson. Temperature-dependent anomalies in the growth of microorganisms. J. Bacteriol. 91:1827-1830. 1966.-Water in the liquid phase (0 to 100 C) has been shown, by others, to undergo subtle changes in its physical structure at approximately 15, 30, 45, and 60 C. It has been suggested that these temperature-dependent anomalies in the structure of water may have biological implications. After incubation in a polythermostat, direct cell counts were made to determine temperature-growth interactions for the four bacteria which were used to cover the temperature range from 5 to 70 C: Pseudomonas fragi, 5 to 25 C; Streptococcus faecalis, 20 to 40 C; Bacillus coagulans, 35 to 55 C; and B. stearothermophilus 1518 smooth, 50 to 70 C. In all cases, growth was suppressed at the predicted temperatures, suggesting a strong interaction between the structure of water and biological activity.