Decomposers - Microbiology and Nutiient Cycling 



Soil microbiology 



Bob Benoit* 

 Walt Campbell 

 Bob Breedlove 

 Pat Flanagan 



Virginia Polytechnic Institute 

 Virginia Polytechnic Institute 

 Yale University 

 University of Alaska 



The quantity of the microbial biomass of the Barrow site is an order of magnitude less than, 

 or under some conditions may approach, the microbial biomass of wet organic soils in the lower 

 latitudes. However, the quality of the biomass and the quality of the microbial activities differ 

 as a result of the factors of low maximum temperature, freeze-thaw cycles, acid pH, and long dor- 

 mant periods when the organisms must utilize ceU reserves to survive. At the end of winter (16 

 June was the first sample date), the bulk of the soil biomass consisted of bacteria which were 

 largely gram negative short rods which were identified as members of Pseudomonas, Cytophaga, 

 Flavobacterium, and Vibrio spp. A variety of green algae, yeasts, and molds were isolated but 

 each group was present in quantities less than lOVg dry wt soils. The moss-litter layer contained 

 the greatest quantity of microorganisms and the quantity decreased with soil depth. 



The bacterial biomass reached a maximum in early July and declined in quantity in late August. 

 At peak season an average of 1.3 x 10" fungal propagules were observed on the site 2 controls. 

 E^hty-one species of micro-fungi were isolated from Barrow soils, while only 51 were recovered 

 from Prudhoe Bay soils. The extremely high concentration of yeasts in Barrow soil (1.5 x lOVg 

 soil) at peak season is one of the most unique aspects of the Barrow site. Most of microaganisms 

 studied in pure culture were capable of growth at mesophilic (20°C) and psychrophilic (0°C) temp- 

 eratures. Some thermophilic bacteria were isolated but they comprised a small part of the micro- 

 bial biomass. Table XX contains average seasonal microbial counts for site 2. 



Soil respiration was measured during July and Ai^ust as an indication of in situ microbial 

 activity. Respiration gradually decreased during this time period; this trend may be similar to the 

 burst of activity observed in spring in temperate zone soUs followed by a decline as substrate, 

 nutrients, or moisture becomes limiting. The data obtained from soil on the site 3 control plot 

 during four sample periods are shown in Table XXI. This technique was very useful in demonstra- 

 ting how perturbations often increase the rate of organic matter oxidation. This will be discussed 

 in another section of this report. A respiration rate of 10 ^tliter {fd) Oj/hr g dry soil was typical 

 in the litter layer in early July. Substrate chambers which contained a known cellulose protein- 

 soil mixture were inserted into different depths of the soil. The chambers were removed at the end 

 of the season and caloric determinations are being conducted. 



Gas exchange chambers were constructed and inserted into the soil at site 2. Time and equip- 

 ment did not permit an extensive examination of this aspect during the field season but these 

 chambers are now in place and can be used in the next field season. Preliminary evidence indi- 

 cates that the levels of carbon dioxide, oxygen and methane vary considerably in the tundra profile. 



A portable polarograph and a specially designed miniature Oj electrode were used to measure 

 in situ Oj concentration at the intensive site. The saturation of oxygen in the litter layer of the 

 drier plots (at 5 cm) varied between 30 and 60%. The concentration decreased sharply below 10 cm 

 (saturation was 10-15% at 15 cm) and it was zero below 20 cm in the soil profile. The 0^ concen- 

 tration in soil over ice wedges and in low polygon centers was frequently anaerobic at the 10-cm 

 soil depth. These data appear to correlate with plant root biomass. This electrode will be very 

 useful in future investigations where it is important to know what oxj^en is available for microbial 

 and plant processes in soil. The electrode is inexpensive; therefore, it will be possible to place 

 a number of units in soil and follow oxygen levels in soils with different moisture levels throughout 

 the season. 

 * Principal author _- 



