Hydrogen (H 2 ) is a by-product of the symbiotic nitrogen fixation (N 2 fixation) between legumes and root-nodule bacteria (rhizobia). Some rhizobial strains have an uptake hydrogenase enzyme (commonly referred to as Hup + ) that recycles H 2 within the nodules. Other rhizobia, described as Hup − , do not have the enzyme and the H 2 produced diffuses from the nodules into the soil where it is consumed by microorganisms. The effect of this phenomenon on the soil biota and on the soil itself, and consequent stimulation of plant growth, has been demonstrated previously. Soybeans [Glycine max (L.) Merr.] cv. Leichhardt, inoculated with either a Hup + strain (CB1809) or one of two Hup − strains (USDA442 or USDA16) of Bradyrhizobium japonicum and uninoculated soybeans, plus a non-legume control [capsicum (Capsicum annuum L.)] were grown in the field at Ayr, North Queensland, Australia. The objectives were to examine (1) relationships between N 2 fixation and H 2 emission, and (2) the influence H 2 -induced changes in soil might have during the legume phase and/or on the performance of a following crop. Strains CB1809 and USDA442 were highly effective in N 2 fixation ("good" fixers); USDA16 was partly effective ("poor" fixer). The soil had a large but nonuniformly distributed naturalised population of B. japonicum and most uninoculated control plants formed nodules that fixed some N 2 . These naturalised strains were classified as "poor fixers" of N 2 and were Hup + . H 2 emissions from nodules were assessed for all treatments when the soybean crop was 62 days old. Other parameters of symbiotic N 2 fixation and plant productivity were measured when the crop was 62 and 96 days old and at crop maturity. Immediately after final harvest, the land was sown to a crop of maize (Zea mays L.) in order to determine the consequences of H 2 emission from the soybean crop on maize growth. It was estimated that soybeans inoculated with USDA442, the highly effective Hupstrain of B. japonicum, fixed 117 kg shoot N/ha (or about 195 kg total N/ha if the fixed N associated with roots and nodules was taken into account), and contributed about 215,000 l H 2 gas per hectare to the ecosystem over the life of the crop. The volume of H 2 evolved from soybeans nodulated by the Hup + strain CB1809 was only 6% of that emitted by the USDA442 treatment, but there was no indication that soybean inoculated with USDA442 benefited from the additional H 2 input. The shoot biomass, grain yield, and amounts of N fixed (105 kg shoot N/ha, Plant Soil (175 kg total N/ha) by the CB1809 treatment were little less than for USDA442 plants. Three days after the soybean crop was harvested, the plots were oversown with maize along the same row lines in which the soybeans had grown. This procedure exposed the maize roots to whatever influence soybean H 2 emission might have had on the soil and/or the soil microflora immediately surrounding soybean nodules. The evidence for a positive effect of soybean H 2 emission on maize production was equivocal. While the consiste...

A total of 134 species of Coleoptera (100 of staphylinids, 13 of hydrophilids and 21 of histerids) was extracted from pads of cattle dung placed in four contrasting habitats in both Hluhluwe Game Reserve, Natal, South Africa, and the surrounding pastoral regions. Pads were exposed to colonists for 24 h on eight occasions over one year. Forty-six species and species complexes were captured in numbers sufficient to permit analysis of their distribution patterns. Of 27 species significantly influenced by vegetation type, 22 were more abundant in unshaded situations and five more abundant in situations shaded by high profile vegetation. The total numbers of individual predatory staphylinids were evenly distributed between vegetation types, but members of coprophagous staphylinid and other predatory taxa were more numerous in unshaded situations. Of 13 species significantly influenced by soil type, six were more abundant on clay and seven more abundant on deep sand. The total numbers of individual coprophagous oxyteline staphylinids were greater on clay than on sand, but the members of predatory taxa, including staphylinids, were evenly distributed across soil types. Of 14 species showing significant seasonal changes in abundance, 13 were more abundant in hot wet months and one in cool dry months. The total numbers of hydrophilid individuals were greater in the cool dry season, but the other taxa were active predominantly in the rainy season. Most species were present in similar numbers in both the game reserve and pastoral regions. Enclosure of dung pads within wiremesh cones to exclude large dung-burying beetles resulted in reduced colonization by most beetle species regardless of their size.

No abstract

No abstract