Frost-weathering on Mars: Experimental evidence for peroxide formation

Summary A laboratory study of the interaction of H₂O frost with samples of the minerals olivine (Mg,Fe)₂SiO₄ and pyroxene (Mg,Fe)SiO₃ at –11°C to –22°C revealed that an acidic oxidant was produced. Exposure of the frost-treated minerals to liquid H₂O produced a sudden drop in pH and resulted in the production of copious O_2(g) (as much as ~ 10²⁰ molecules g^–1). Exposure of frost-treated samples to 5 ml of 0.1M HCOONa solution resulted in the rapid oxidation of up to 43% of the formate to CO_2(g). These reactions were qualitatively similar to the chemical activity observed during the active cycles of the Viking lander Gas Exchange and Labeled Release Biology experiments. Attempts to identify the oxidant by chemical indicators were inconclusive, but they tentatively suggested that chemisorbed hydrogen peroxide may have formed. The formation of chemisorbed peroxide could be explained as a byproduct of the chemical reduction of the mineral. The following model was proposed. H^c was incorporated into the mineral from surface frost. This would have left behind a residual of excess OH^– _(ads) (relative to surface H⁺). Electrons were then stripped from the surface OH^– _(ads) (due to the large repulsive potential between neighboring OH^– _(ads)) and incorporated into the crystal to restore charge balance and produce a chemical reduction of the mineral. The resultant surface hydroxyl radicals could then have combined to form the more stable chemisorbed hydrogen peroxide species. While the chemisorbed peroxide should be relatively stable at low temperatures, it should tend to decay to O_(ads) + H₂O_(g) at higher temperatures with an activation energy of 34 kcal mole^–1. This is consistent with the long-term storage and sterilization behavior of the Viking soil oxidants. It is possible that as little as 0.1–1% frost-weathered material in the Martian soil could have produced the unusual chemical activity that occurred during the Viking Gas Exchange and Labeled Release experiments.This paper contains the material given in invited presentations at the COSPAR Meeting, Innsbruck, Austria, 5–7 June 1978 and at the Second Conference on Simulation of Mars Surface Properties, NASA Ames Research Center, 17–18 August 1978     

Nodulation and growth ofLablab purpureus (Dolichos lablab) in relation to rhizobium strain,liming and phosphorus

Summary Greenhouse experiments were done with two purposes: (1) to identify strains of rhizobia effective and acid-tolerant in symbiosis withLablab purpureus, and (2) to determine whether soil acidity or the symbiotic condition increased the phosphate requirement for growth.Five rhizobial strains were tested in one neutral soil, two acid soils, and the two acid soils limed to pH 6.6. In the neutral and limed soils, three of the strains were effective (CB1024, CB756, TAL169), but only two strains (CB756, TAL169) remained effective in acid soil.Strain CB756 and plus-N treatments were further compared in a factorial trial involving combinations of five levels of P with lime, no lime and CaCl₂ treatments, applied to an acid soil. Some of the treatments were also applied to plants inoculated with CB1024. Between the N-fertilized and CB756 treatments there was no clear difference in growth response to applied P, and the critical internal concentration of P for 95% of maximal growth was the same (0.22% shoot dry weight). Increasing P beyond levels needed for maximal growth increased nodulation and N concentration in plants inoculated with CB756. It lowered N concentration in N-fertilized plants. There was evidence suggesting that the P requirement of symbiotic plants increased if the soil was acid, or if CB756 were replaced by CB1024 as microsymbiont; but the critical statistical interactions were not significant.     

Effects of inorganic amendments (N,P and K) to soil on the rhizosphere microflora of antirrhinum plants infected withVerticillium dahliae Kleb

Summary A study of the inorganic amendments (N, P and K) to soil, and their effect on the rhizosphere microflora, as well as their relation to the control of wilt of antirrhinum plants caused byVerticillium dahliae Kleb. was done. Ammonium sulphate was the only chemical found to be significantly inhibitory toV. dahliae in vitro. Soil amendments (NPK) affected the rhizosphere microorganisms of the antirrhinum plants. Higher concentration of the chemicals were phytotoxic. It was further observed that ammonium sulphate, and the combined chemicals (NPK 25%) in soil delayed the senescence in healthy plants, suggests that chemical fertilisers affected the host plants directly. Addition of ammonium sulphate (0.25%), calcium nitrate (0.25%, 0.5%) combined NPK (0.25%) to soil caused considerable reduction in disease severity. It is assumed that this reduction may be caused by the (1) fungitoxic nature of the chemicali.e. ammonium sulphate, (2) antagonistic environment for the pathogen in the rhizosphere was boostedi.e. where calcium nitrate was added as soil amendments and (3) reduction in disease severity in soil-amended with combined NPK, may be due to the fact that antagonistic actinomycete population was boosted in the rhizosphere.     

Biodegradation of rice stumps by soil mycoflora

Summary Cellulose and lignin contents in left-overs of rice stump decreased due to decay caused by soil mycoflora. The loss of cellulose and lignin was considerable in presence of Curvularia and Fusarium respectively. Other tested mycoflora could also destroy cellulose and lignin to some extent. The amount of loss of cellulose and lignin increased with time of incubation of the tested mycoflora.     

Influence of a carbamate pesticide on growth,respiration (14C)-carbon metabolism and symbiosis of aRhizobium sp.

Summary Addition of aldicarb (2 methyl-2(methyl thio) propionaldehyde-0-methyl carbamoyl oxime) in the growth medium enhanced the growth ofRhizobium sp. (cowpea group) at 2 ppm level while an inhibition was observed at the normal (5 ppm) and higher (10 ppm) concentrations. Respiration of the cells was also inhibited by 5 and 10 ppm levels of the chemical eventhough a stimulation was observed at 2 ppm (lower) concentration. The insecticide, when incorporated at 5 and 10 ppm levels in the medium increased the¹⁴C-glucose incorporation and considerably altered the assimilation of the radioactive carbon in different fractions of rhizobium cells. Soil application of this insecticide (Temik 10 G) reduced the number of nodules formed and the total nitrogen content in cowpea plants inoculated with theRhizobium sp. but enhanced the dry matter production of cowpea plants.Based on the M. Sc. thesis submitted by the first author to the Tamil Nadu Agricultural University, Coimbatore-3.     

Nutrient enrichment experiments in three central Florida lakes of different trophic states

Seasonal nutrient enrichment experiments (short-term bioassays) were conducted in three Florida lakes of different trophic states to determine the effects of addition of various nutrient combinations upon chlorophyll a and phytoplankton standing crops. Nutrient enriched surface water samples with crustacean zooplankton removed were incubated in situ in clear polyethylene bags for 3 to 6 days. The 2⁵ factorial design employed two levels (ambient and enriched) of each of five nutrients [NH₄ ⁺, PO _inf4 ^sup3− , Fe⁻ -EDTA, SiO _inf3 ^sup2− and a cation (Ca²⁺ or K⁺) or trace elements]. Ammonium produced significant increases in chlorophyll a and phytoplankton standing crops in all experiments. Phosphate produced similar results in the mesotrophic lake, but the eutrophic lakes had both positive and nonsignificant responses which varied seasonally between lakes. Iron increased chlorophyll a in most experiments but affected total phytoplankton standing crop only during the summer and fall. Silicon had negative effects in some experiments. Cations and trace elements produced marked differences between lakes for chlorophyll a, but total phytoplankton standing crop showed few significant responses. Synergistic responses to two- and three-factor interactions were observed in all lakes. Differences in the responses of phytoplankton taxonomic divisions to enrichment may be responsible for much of the between lake variation in chlorophyll a and total phytoplankton volume responses. Nutrient limitations in these lakes are discussed and related to limnological factors and predictive models.     

An ecological example of the application of projection pursuit to compositional data

A modern statistical technique for the exploratory analysis of multivariate data, called projection pursuit, is described. The method consists of the extraction and display of informative one- or two-dimensional projections of the multivariate dataset. Projection pursuit has much scope for application to ecological datasets. The example in this paper concerns element concentrations in soil samples from a coastal embayment on the east coast of Australia. The application attempts to search for patterns in the soils which could be related to vegetation patterns. The compositional nature of the dataset adds a novel element to the methodology.     

The performance and distribution of species along soil salinity gradients of mangrove swamps in southeastern Nigeria

Based on periodic soil salinity measurements direct gradient analysis procedures were used to relate the performance and distribution of mangrove swamp species to salinity gradients. Variations in soil salinity were due to distance from the coast, tidal incursions and freshwater inputs. All overstorey species showed statistically significant negative correlations with salinity while most groundlayer species were positively correlated with the same factor. Based on ecological group classification, no species was found to occur on the highest values of soil salinity. There were overlapping range of occurrences and ecological optima for most species along the gradients.     

Decomposition in estuarine salt marshes: the effect of soil salinity and soil water content

The relation between decomposition rates and soil salinity and moisture conditions in tidal marshes of the Westerschelde estuary was investigated. In the first part of the study, these soil factors were experimentally manipulated in field plots which were either screened from rainwater or which received an additional weekly supply of freshwater from April to September 1989. These treatments had no clear effect on soil salinities and moisture conditions in a low marsh site. Decomposition rates of Spartina anglica leaves (kept in litterbags in the plots) also did not differ between treatments. In screened plots of a middle marsh site, decomposition rate of Elymus pycnanthus leaves decreased significantly. The effect of the experimental treatments on soil moisture content was variable, but comparatively high soil salinity values (up to 61.3) were consistently found in these plots. It is suggested that the elevated salinity levels induced the decrease in decomposition rate.In the second part of the study, cellulolytic decomposition, measured by loss of tensile strength of strips of cotton test cloth, was investigated in relation to a non-manipulated range of soil salinities (3.8–24.2), by exposing the strips in a series of tidal marshes along the salt gradient of the Westerschelde estuary. No correlation between decomposition rate and soil salinity was found. In addition, no relation was found between decomposition rate and soil water content. The results of both parts of this study lead us to the hypothesis that rate limitation of decomposition in estuarine tidal marsh soils is found at high soil salinities only.     

Classification and ecological characterization of coniferous forest phytogeocoenoses of Hokkaido,Japan

Coniferous forest phytogeocoenoses of Hokkaido Island, Japan, were studied to classify them based on vegetation characteristics, to analyse their soils, to correlate the vegetation and soil characteristics, and to provide some ecological interpretation for the phytogeocoenosis differentiation and establishment. Five forest types were distinguished based on the vegetation structure, each of which was comparable to plant association of Krajina (1960); 1. the moss type, 2. the Sasa kurilensis type, 3. the Sasa senanensis type, 4. the Carex sachalinensis type, and 5. the Dryopteris crassirhizoma type. Soil base status indicated by pH, electric conductivity, amount of calcium and magnesium, and base saturation showed a fair correlation with the forest types. The forest types were, therefore, arranged along a soil nutritional gradient. The moss type developed in the least fertile habitats whereas the Dryopteris crassirhizoma type in the most fertile habitats, and others were in between the two. It was suggested that in the island, where climate was humid with excess of soil water throughout a year, soil nutritional regime, more specifically availability of bivalent cations which tended to be removed by the excessive soil water, seemed to be a critical factor to differentiate and establish the forest types.This study was financially supported by the Science Research Grant of the (Monbusho) Japanese Goverment (Grant No. 60540422).