Characterization of an amphimull under Mediterranean evergreen oak forest (Quercus ilex): micromorphological and biodynamic descriptions

Abstract

The relationships between microorganisms and microfauna were studied in an evergreen oak ( Quercus ilex L.) forest floor located in a French Mediterranean region characterized by hot and dry summers. The soil was a brown fersialitic soil with an amphimull, i.e., a mull with a thick litter. A micromorphological study of both litter and organomineral layers was used to observe relationships between white-rot fungi and fauna, such as oribatids, millipedes, enchytraeids, and earthworms. Microbiological properties of the litter and physicochemical properties of the soil were analysed. Enchytraeids comminute the faeces of other animals, whereas earthworms form aggregates. These two opposite actions probably modify aeration and water movements in deeper layers. Brown leaves and animal faeces constitute a nutritional substrate for white-rot fungi and other animals. Inside degraded cells of rootlets and bleached leaves, fungi form calcium oxalate crystals because the absorbent complex is saturated by an excess of calcium. Enzymes such as laccases, manganese peroxidases, cellulases, or xylanases were detected in the litter at significant levels. The high activity values of phosphatases in the litter could reflect a deficiency in available phosphorus. This deficiency could partly explain a low rate of litter degradation and the presence of an OH sublayer.

The impact of parent material, climate, soil type and vegetation on Venetian forest humus forms: A direct gradient approach

“…In the absence of earthworm records we cannot go deeper in elucidating this causal relationship. The balance between unincorporated carbon and that incorporated by annelids in the mineral soil would not be entirely driven by climate, as suspected so far (Bottner et al, 1995;Graefe, 2007;Ascher et al, 2012), although other influences such as phosphorus availability have been suspected (Tagger et al, 2008), but also by the restricted soil volume available for burrowing due to the abundance of rock fragments. This 'rock fragment effect', typical of shallow calcareous soils (rzLP) on dolomite and hard limestone substrates might have important consequences on carbon sequestration (Wironen and Moore, 2006;Andreetta et al, 2011;Bonifacio et al, 2011), beside climate effects (Marland et al, 2003;Egli et al, 2010;Thornley and Cannell, 2001) and their interactions with vegetation (Paré et al, 2006;De Deyn et al, 2008;Podwojewski et al, 2011) and mineral composition (Rasmussen et al, 2006 Thum, T., Räisänen, P., Sevanto, S., Tuomi, M., Reick, C., Vesala, T., Raddatz, T., Aalto, T., Järvinen, H., Altimir, N., Pilegaard, K., Nagy, Z., Rambal, S., Liski, J.…”

Geology and climate conditions affect more humus forms than forest canopies at large scale in temperate forests

“…The particular case of amphi is worth to notice. This humus form, which has been previously confused with dysmull, hemimoder or moder (Brêthes et al, 1995), is associated with highly seasonal mullforming activity in an otherwise favourable geological context (Galvan et al, 2008;Tagger et al, 2008): the shorter the season during which invertebrate (and microbial) activity is possible, the thicker will be the organic horizon (of moder type) overlying a crumby A horizon (of mull type). This may happen both at higher elevation and in Mediterranean landscapes when the richness of the substrate (limestone, dolomitic rocks) allows the activity of subterranean animals during less favourable seasons.…”

Microbial dynamics in Mediterranean Moder humus

“…Such relations have not been, however, extensively studied (Hirobe et al 2003;Karroum et al 2005;Carletti et al 2009;Trap et al 2011). Data are especially sparse for Mediterranean forest ecosystems (Sadaka and Ponge 2003;Tagger et al 2008), where both humus (Sevink et al 1989;van Wesemael and Verstraten 1993;Vacca 2000;Peltier et al 2001;Ponge 2003;Andreetta et al 2011) and microbial communities (e.g. Monokrousos et al 2004;Goberna et al 2005;Aponte et al 2010) have been found to be valuable indicators of responses of soil to the ecological constraints represented by long and variable summer droughts.…”