Effects of moisture on soil microorganisms and ... - Springer Link

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218. J. Schniirer et ai. Table. 1. Moisture content and soil water potential in the investi- gated plots. Rain plot. Irrigated plot. Date. Mois-. Mois- ture ture con- con-.
Mierob Ecol (1986) 12:217-230

MICROBIAL ECOLOGY 9 Springer-Verla$New York Inc. 1986

Effects of Moisture on Soil Microorganisms and Nematodes: A Field Experiment Johan Schnfirer,~ Marianne Clarholm, t Seen Bostr6m, 2 and Thomas Rosswall* ~Delaartmentof Microbiology,Swedish Universityof AgriculturalSciences, S-750 07 Uppsala, Sweden;and 2Departmentof Zoology,Universityof Stockholm, S-106 91 Stockholm,Sweden Abstract. The effects o f soil moisture changes on bacteria, fungi, protozoa, and nematodes and changes in oxygen consumption were studied in a field experiment. In one plot the soil was drip-irrigated daily for 10 days, while an adjacent plot experienced one rainfall and was then allowed to dry out. Oxygen consumption was the parameter measured which responded most rapidly to changes in soil moisture content. Lengths of fluorescein diaeetateactive hyphae paralleled oxygen consumption in both plots. Total hyphal length was not affected by one rainfall but increased from 700 mg -~ dry weight soil to more than 1,600 m in less than 10 days in the irrigated plot. In the rain plot, bacterial numbers doubled within 3 days and declined during the following period of drought. In the irrigated plot, numbers increased by 50% and then remained constant over the duration of the study. Only small changes in protozoan numbers were observed, with the exception of the last sampling date in the irrigated plot when large numbers of naked amoebae were recorded 2 days after a large natural rainfall. Nematode numbers, especially obligate root feeders, increased in both treatments. The increases were caused by decoiling rather than growth. The results indicate that fungal respiration was dominating, while bacteria, lacking a suitable source of energy, were less active, except for the first days.

Introduction Water availability is one of the most important parameters regulating biological activities in soil. Changes in water availability will influence soil organisms through complex interactions with nutrient conditions, soil temperature, pore size distribution, and soil atmosphere. A decrease in soil water potential can thus reduce solute diffusion and size o f waterfilled pore space but increase aeration [8]. We have reported previously that rainfall events resulted in peaks in bacterial numbers 3 days after precipitation [6], followed by increases in naked amoebae [5]. The increases were much larger in root-influenced soil.

*-"~resentaddress. Department of Water in Environmentand Society,Universityof Linkrping, S-581 83 LinkSping,Sweden.

218

J. Schniirer et ai.

1. Moisture content and soil water potential in the investigated plots Table

Rain plot Moisture conWater tent addi- g H 2 0 / tion 100 g (mm) dw

Date July 13 17 18 19

20 21 22 23 24 25 26 27 28 29

0 13 0 0 0 0 0 0 0 0 27 0 0 0

12.3 -13.3 12.3 9.4 9.4 8.4 --8.3 -22.2 ---

Irrigated plot

Water potential ( - MPa) 0.8 -0.6 0.8