Earthworms change the distribution and availability of phosphorous in organic substrates

Abstract

In laboratory controlled soil microcosms, the distribution and availability of phosphorous (P) were determined in the surface-casts and the burrows-linings of the anecic earthworm L. terrestris and were compared with non-ingested soil. To simulate more realistic earthworm community conditions, a combination of L. terrestris plus the endogeic A. caliginosa was tested. For a 2-month period, the earthworms were given two organic food substrates: rye-grass littered onto the soil surface and sewage sludge mixed with soil. The following treatments were designed: (i) soil alone (S), (ii) soil and sewage sludge (SS), soil and rye-grass litter (SL), and (iv) soil, litter and sludge (SSL). Analyses were performed for P contents (total, available and organic), organic matter content (organic carbon, C org and total nitrogen, N tot ) and the two acid and alkaline phosphatase activities (AcPA and AkPA). Earthworms enhanced AcPA and were also responsible for additional AkPA in soil. The two AcPA and AkPA increased not only in surface-casts but also in burrows-linings that paralleled with the decrease of organic P in SL and SSL treatments. The stimulation of AcPA began quickly and declined rapidly in casts (from 19 to 8 mmol phenol g K1 dry wt h K1 , respectively at week 2 and 8 in the SL treatment) but it was initiated later and maintained at a high level for longer in burrows (more than 10 mmol phenol g K1 dry wt h K1 at week 8 in the SL treatment). Significant positive correlations were found between the AkPA activities and N tot contents (rZ0.95, pZ0.001) and to a lesser extend with C org contents (rZ0.76, pZ0.05) in casts from the SL treatment, while AcPA significantly correlated with N tot (rZ0.91, pZ0.004) but not with C org (rZ0.72, pZ0.06). P availability was always highest in casts. However, the available P contents decreased sharply over time in casts and were still low in burrow-linings, suggesting that a large part of inorganic P produced was rapidly immobilized for the microbial growth. Total P content was unchanged except in the SL treatment in which it increased in casts and burrows (ca. 725 mg g K1 , at week 4). Organic P was first the highest in casts and then decreased over time (from 168 at week 1 to 140 mg g K1 at week 8 in the SL treatment). This study illustrates that earthworms facilitate P transfer downward increasing a P patchy distribution in the soil, and significantly change the biogeochemical status of P (availability, organic phosphorous pool, AcPA activities) in certain hot spots such as casts and burrow-linings.

Role of Earthworm in Improving Soil Structure and Functioning

“…Microbial activity is increased in the presence of earthworms, leading to nitrogen-mineralization and immobilization through direct or indirect benefits by earthworms 44 . Earthworms were also reported to increase the availability of phosphorus by facilitating changes in the biogeochemical status of P in burrow-linings 45 . In a pot experiment with earthworms, higher levels of plant available P resulted in increased plant growth from 15.7 to 16.8 g dry biomass per pot 46 .…”

Threshold behaviour in hydrological systems as (human) geo-ecosystems: manifestations, controls, implications

“…3) (Zachmann et al, 1987;Kladivko et al, 1991;Roth et al, 1991;Flury, 1996;Mohanty et al, 1998;Stamm et al, 1998;Stamm et al, 2002). Earthworms are as classical ecosystem engineers of special interest in this context because they build long-lasting soil structures that exert a significant influence on water flows (Edwards et al, 1990b(Edwards et al, , 1992Smettem, 1992;Shipitalo and Butt, 1999) and solute transport (Edwards et al, 1993;Zehe and Flühler, 2001a, b;Domínguez et al, 2004;Alekseeva et al, 2006;Le Bayon and Binet, 2006) but also on organic matter dynamics, pedogenetic processes and plant growth (Lavelle et al, , 2004Hedde et al, 2005;Milcu, 2005;Milcu et al, 2006). However, whether or not connected structures are activated during a given rainfall event depends on the interplay of initial soil moisture and rainfall forcing.…”

Role of Soil Macrofauna in Phosphorus Cycling

“…The higher levels of water-soluble inorganic P (C P ) in the termite nests presented in Table 8.1 may also result from the transformation of organic P through enzymatic activity in the fresh biostructures, as observed for earthworm casts (Sharpley and Syers 1976;Le Bayon and Binet 2006). Comparisons of phosphatase activities between termite nests and adjacent soils have already been made for several termite species (López-Hernández et al 1989b;Roose-Amsaleg et al 2005).…”

“…The x-and y-axes are represented in log-log scales. Modified from Chapuis-Lardy et al (2009) studies reported increased enzymatic activity in earthworm casts and the stimulation of microbial activity (Sharpley and Syers 1976;James 1991;López-Hernández et al 1993;Chapuis and Brossard 1995;Brossard et al 1996;Le Bayon and Binet 2006). However, Zhang et al (2000) observed an increase of inorganic P in soils in the presence of earthworms, despite a decrease of acid and alkaline phosphatase activities in earthworm casts, suggesting that P-containing organic matter is digested in the gut rather than in the casts.…”