ARTICLE IN PRESS Pedobiologia 50 (2006) 207—215 www.elsevier.de/pedobi Growth rates of Aporrectodea caliginosa (Oligochaetae: Lumbricidae) as influenced by soil temperature and moisture in disturbed and undisturbed soil columns Nikita S. Eriksen-Hamel, Joann K. Whalenà Department of Natural Resource Sciences, Macdonald Campus, McGill University, 21,111 Lakeshore Road, Ste-Anne-de-Bellevue, Quebec, H9X 3V9, Canada Received 8 May 2005; accepted 26 October 2005 KEYWORDS Summary Earthworms; Earthworm growth is affected by fluctuations in soil temperature and moisture and Aporrectodea hence, may be used as an indicator of earthworm activity under field conditions. caliginosa; There is no standard methodology for measuring earthworm growth and results Instantaneous obtained in the laboratory with a variety of food sources, soil quantities and growth rate; container shapes cannot easily be compared or used to estimate earthworm growth Temperature; in the field. The objective of this experiment was to determine growth rates of the Moisture; endogeic earthworm Aporrectodea caliginosa (Savigny) over a range of temperatures Container shape (5–20 1C) and soil water potentials (À5toÀ54 kPa) in disturbed and undisturbed soil columns in the laboratory. We used PVC cores (6 cm diameter, 15 cm height) containing undisturbed and disturbed soil, and 1 l cylindrical pots (11 cm diameter, 14 cm height) with disturbed soil. All containers contained about 500 g of moist soil. The growth rates of juvenile A. caliginosa were determined after 14–28 days. The instantaneous growth rate (IGR) was affected significantly by soil moisture, temperature, and the temperature  moisture interaction, ranging from À0.092 to 0.037 dÀ1. Optimum growth conditions for A. caliginosa were at 20 1C and À5kPa water potential, and they lost weight when the soil water potential was À54 kPa for all temperatures and also when the temperature was 5 1C for all water potentials. Growth rates were significantly greater in pots than in cores, but the growth rates of earthworms in cores with undisturbed or disturbed soil did not differ significantly. The feeding and burrowing habits of earthworms should be considered when ÃCorresponding author. Tel.: +1 514 398 7943; fax: +1 514 398 7990. E-mail address: [email protected] (J.K. Whalen). 0031-4056/$ - see front matter & 2005 Elsevier GmbH. All rights reserved. doi:10.1016/j.pedobi.2005.10.008 ARTICLE IN PRESS 208 N.S. Eriksen-Hamel, J.K. Whalen choosing the container for growth experiments in order to improve our ability to extrapolate earthworm growth rates from the laboratory to the field. & 2005 Elsevier GmbH. All rights reserved. Introduction of soil in containers with volumes ranging from 0.12 to 2.2 l (Butt et al., 1994; Whalen and Parmelee, Earthworms are known to accelerate nutrient 1999; Baker and Whitby, 2003). In these studies, mineralization and improve soil fertility in tempe- loose soil was packed or placed into the container rate agroecosystems (Lee, 1985; Edwards and before earthworms were added. Bohlen, 1996). The contribution of various earth- We hypothesize that earthworm growth rates will worm species to nutrient mineralization is affected differ when earthworms are grown in disturbed soil by their feeding habits and life-history strategies, than in undisturbed soil. An undisturbed soil core because individuals from different ecological obtained from the field will likely contain some groups are active in different parts of the burrows and macropores that facilitate earthworm soil profile when environmental conditions are movement and reduce their energy expenditure in favourable (Bouche´, 1977; Brown et al., 2004). moving through soil, thereby increasing growth Furthermore, earthworm-mediated nutrient miner- rates. Containers may constrain earthworm move- alization may be related to their activity and ment, reducing the energy used to burrow and growth (Marinissen and de Ruiter, 1993). Earthworm increasing the energy allocated for growth. Whalen growth rates are very responsive to fluctuations in and Parmelee (1999) reported that growth rates of soil temperature and moisture, and may be used to Aporrectodea tuberculata (Eisen) were similar in estimate activity and dynamics of earthworm 0.12 l laboratory pots and 7.9 l field cores, but populations (Buckerfield et al., 1997). In temperate juvenile Lumbricus terrestris L. had slower growth agricultural soils, earthworm growth is fastest at rates in field cores than in laboratory cultures. The soil temperatures from 15–20 1C when the soil amount of soil and shape of the culture vessel used moisture is close to field capacity (Daniel in laboratory studies should provide growth data et al., 1996; Holmstrup, 2001; Wever et al., 2001; that is representative of earthworm activity under Baker and Whitby, 2003). However, soil tempera- field conditions. tures range from about 0–25 1C and there may be The objectives of our experiment were: (1) to periodic flooding and drought during the crop determine how growth rates of Aporrectodea growing season. Researchers wishing to estimate caliginosa were influenced by soil temperature nutrient mineralization from earthworms require and moisture; and (2) to determine whether detailed information on how earthworm growth earthworm growth rates were influenced by soil rates fluctuate with changing soil temperature and disturbance and culture vessel shape. moisture conditions. There is no standard methodology for measuring earthworm growth rates. A review of the literature reveals that growth rates for the major lumbricid Materials and methods earthworm species have been determined using a variety of food sources, amounts of soil and Collection of earthworms and soils containers (Butt, 1997; Fayolle et al., 1997; Whalen and Parmelee, 1999; Booth et al., 2000). When Juvenile individuals of A. caliginosa were col- provided with abundant organic matter with a high lected by hand sorting in September 2003 from N content, earthworms grow faster than when they fields under alfalfa (Medicago sativa L.) and receive a restricted amount of food or one with a soybean (Glycine max (L.) Merrill) production at low N content (Bostro¨m and Lofs-Holmin, 1986; the Macdonald Campus Farm of McGill University, Bostro¨m 1988; Daniel, 1991). Many earthworms Ste-Anne-de-Bellevue, Que´., Canada. Earthworms grow faster when they consume finely ground than were reared for about 6 weeks at room tempera- coarsely ground organic substrates (Bostro¨m and ture (20 1C) in soil from the field site, moistened to Lofs-Holmin, 1986; Lowe and Butt, 2003). Little is near field capacity. Newly emerged earthworms known of the relationships between the amounts of (o0.25 g) and pre-clitellite earthworms (40.70 g) soil or the shape of the culture vessel may have on were excluded from the analysis as their earthworm growth rates. Growth rates have been growth rates may not be truly representative of measured commonly in the laboratory in 40–2000 g juvenile earthworms. Yet, fewer than 20% of the ARTICLE IN PRESS Earthworm growth rates in soil columns 209 earthworms in this study were excluded from the 24 h. The next day the earthworms were washed, analysis due to being smaller or larger than the gently blotted dry with paper towels and weighed desired size range (0.25–0.70 g). (gut-free fresh weight). One earthworm was added The soil was a sandy-loam mixed, frigid Typic to each pot, which was then sprayed with approxi- Endoquent of the Chicot series taken from a field mately 3 ml water to remoisten the earthworm and under soybean production. It had a pH (H2O) of 6.3, soil surface. Pots were placed into controlled a C content of 30.2 g C kgÀ1, and contained climate incubators at four temperatures in dark- 580 g kgÀ1 sand, 300 g kgÀ1 silt and 120 g kgÀ1 clay. ness for the duration of the experiment. Soils were air-dried to about 10% gravimetric Earthworms were reared in pots for 8 weeks and moisture content (À200 kPa matric potential) be- were removed every 13–15 days for weight mea- fore use. The earthworm food was composted surements. At each weighing, earthworms were cattle manure containing about 383 g C kgÀ1 and washed, placed on a moistened paper to void their 19.9 g N kgÀ1 (Carlo Erba Flash NC Soils Analyzer, guts for 24 h, weighed (gut-free fresh weight) and Milan, Italy). then returned to the same pot for 13–15 days. Washing and keeping the earthworms on a mois- tened paper for 24 h insures that the earthworms Calculation of soil moisture content from different soil moisture treatments have equal hydration status when weighed. Before returning Four soil gravimetric moisture contents (15%, earthworms to the pots, about 1 g (dry matter 20%, 25%, and 30%) were used to test earthworm basis) of manure was added to the soil surface, pots growth in response to moisture conditions. Since were weighed and tap water was added to replace matric potential is a more meaningful way to moisture lost through evaporation. When dead express biological water availability, we converted earthworms were found, they were removed and the gravimetric moisture content to matric poten- a replacement earthworm of similar weight and age tial using the Rosetta software program (Schaap, class was added to the pot. The growth rates for 2000). A SSCBD (texture and bulk density) pedo- replacement earthworms were considered to be transfer function was used to predict the para- missing values in the statistical analysis. meters necessary for calculating matric potential using the van Genuchten function for water retention (van Genuchten, 1980; Schaap et al., Core experiment 1998). The calculated matric potentials (7stan- dard deviation, S.D.) were À5(71), À11 (72), The experiment was designed as a completely À23 (74), À54 (714) kPa, corresponding to 30%, randomised factorial design with three tempera- 25%, 20%, and 15% gravimetric moisture content, tures (10, 15 and 20 1C), three soil water potentials respectively.