The Effect of Gamma Radiation on the Microbial Population of the Soil

Abstract

Arredondo fine sand was exposed to gamma radiation from a cobalt 60 source at doses of 1, 4, 16, 32, 64, 256, 512, 1024, and 2048 kiloroentgens (kr.). Percentage survival of fungi and bacteria decreased • wit h each increase in radiation dose to < 4% at 1024 kr. Algae were not as drastically reduced as bacteria and fungi: some survived at 2048 kr. and greatest reduction occurred above 64 kr. A few nematodes remained in the soil 2 days after irradiation with 1024 kr., but none were recoverable from doses > 256 kr. after 14 and 28 days. The effects of lower doses were not resolvable.Carbon dioxide evolution was initially reduced by ir radiation of the soil. The reduction was generally inversely related to radiation dose except for the 64kr. treatment. Later, all irradiated soils, except those which received doses > 256 kr., essentially equaled or exceeded the con trol in CO 2 production. Soils treated with 512 and 1024 kr. produced only very small amounts of CO 2 throughout the 23day period; soil receiving 256 kr. later recovered completely. The soil irradiated by 64 kr. attained the high est daily production rate. Similar relationships for CO 2 evolution occurred in an earlier study except for some shifts in time and magnitude.Nitrate production in a 14day period was progressively reduced by increasing doses of radiation. Recovery from 32 kr. or less occurred in 28 days; these soils produced at least 87% as much nitrate as the control during this period of time. Average production in 28 days at 64, 256, and 1024 kr. was 55, 7, and 3% of the control, respectively.The production of sulfate from elemental sulfur was also affected by radiation in much the same manner as nitrate production, though radiation damage at doses less than 64 kr. were not readily apparent until the third week. Two populations, one more sensitive to radiation than the other, were probably involved in this reaction.

Creation of a non-mycorrhizal control for a bioassay of AM effectiveness

“…This was the result of N flush and improved P availability. This was caused by the sterilization of a larger fraction of the soil microbiota by the higher dose, as shown by a higher share of N NH4+ in N soluble due to decreased nitrification (Popenoe and Eno 1962). Colonization rates were reduced by benomyl incorporation somewhat more than in former studies either in pots applied as a soil drench at sowing (Bailey and Safir 1978;Kough et al 1987), in the field applied as a drench of soil cores (Merryweather and Fitter 1996) or incorporated into soil (Lu and Miller 1989).…”

Effects of gamma irradiation on Holcus lanatus (Yorkshire fog grass) and associated soil microorganisms

“…Previous work on the effects of ionising radiation on soil microbial communities was mainly carried out at high doses (in the order of several kGy) designed to sterilise soil for the purpose of transportation between countries and for soil research experiments (McLaren, 1969;Johnson and Osborne, 1964). Some early studies did attempt to evaluate the effects of gamma radiation on indigenous microbial communities at doses in the range 10-400 Gy but these were mainly carried out on non-rhizosphere soil using only traditional culturing techniques (Davis et al, 1956;Stotzky and Mortensen, 1959;Popenoe and Eno, 1962;Skou, 1962). Soil microorganisms have recently been highlighted as potential reference organisms (see Pentreath and Woodhead, 2001) for consideration within frameworks for the protection of the environment from ionising radiation (Strand et al, 2001;Beresford et al, 2001).…”

Radiation Resistance of Soil Azotobacter

“…Stanovick, Giddens, and McCreery (1961) concluded that the symbiotic nitrogenfixing bacteria are more susceptible to neutrons and y rays than are other soil organisms. De-creases in bacterial and fungal populations, nitrification, and sulfate production in soils exposed to 7-radiation were observed by Popenoe and Eno (1962). Bernard and Geller (1962) reported that doses of y rays exceeding 15 kr were injurious to the soil microflora and that doses of 100 kr were lethal to Azotobacter and the nitrifying bacteria in sandy soils.…”