Bacterial traits, organism mass, and numerical abundance in the detrital soil food web of Dutch agricultural grasslands

Abstract

This paper compares responses to environmental stress of the ecophysiological traits of organisms in the detrital soil food webs of grasslands in the Netherlands, using the relationship between average body mass M and numerical abundance N. The microbial biomass and biodiversity of belowground fauna were measured in 110 grasslands on sand, 85 of them farmed under organic, conventional and intensive management. Bacterial cell volume and abundance and electrophoretic DNA bands as well as bacterial activity in the form of either metabolic quotient (qCO 2 ) or microbial quotient (C mic / C org ) predicted the response of microorganisms to stress. For soil fauna, the logarithm of body mass log(M ) was approximately linearly related to the logarithm of numerical abundance log(N ) with slope near )1, and the regression slope and the proportion of predatory species were lower in intensive agroecosystems (more reduced substrates with higher energy content). Linear regression of log(N ) on log(M ) had slope not far from )3/4. The approach to monitoring data illustrated in this paper could be useful in assessing land-use quality.

Can Transgenic Maize Affect Soil Microbial Communities?

“…Bacteria are abundant and very diverse [29][30][31][32][33] and can respond rapidly to environmental perturbations [32][33][34][35][36], for instance during competition for nutrients required for bacterial growth and activity [34][35][36]. All the results in these studies showed an evident response of bacteria in bulk soil to the addition of transgenic plant residues.…”

Scaling and power-laws in ecological systems

“…the 'thinning law') and the same is observed in the analysis of size-structured food webs (Cohen et al, 2003;Mulder et al, 2005). Although this might seem mostly a philosophical problem it has important implications when working with scaling relationships, for causality specifies the way error propagates in deriving scaling relationships from known ones (Taper and Marquet, 1996).…”

“…Although this relationship seems to be stronger in mammals than in other taxa, such as birds (Bini et al, 2001;Dobson et al, 2003), and might be affected by the scale of analysis, level of data aggregation, type of environment, latitude, taxa, trophic position, census area and method of statistical analysis (see reviews in Cotgrave, 1993;Cyr, 2000;Gaston and Blackburn, 2000;Silva et al, 2001), recent analysis of this relationship underscores the empirical generality of the -3/4 scaling exponent as well as its strong theoretical support (Li, 2002;Belgrano et al, 2002. Furthermore, as shown by Marquet et al (1990), this relationship holds in local communities when a wide spectrum of taxonomic groups are included (see also Cyr et al, 1997;Schmid et al, 2000;Cohen et al, 2003;Mulder et al, 2005; but see Dugan et al, 1995;Navarrete and Menge, 1997), although the exponent is closer to -1 (which is expected when analyzing species in more than one trophic level, see discussion below) and is maintained in the face of perturbations affecting changes in the abundance and identity of species (Fig.·1, see also de Boer and Prins, 2002;Cohen et al, 2003). The existence of temporal invariance in this relationship further testifies to its importance in understanding ecological dynamics (Marquet, 2000).…”

Biotechnology, environmental forcing, and unintended trophic cascades

“…Micro-arthropods are usually 1-5 orders of magnitude A combination of single traits (adult body sizes, feeding-strategies) within different clades contributes to the entire decomposition process. Like other ecosystem services, the nutrient cycling process is not affected by single trophic levels larger than their faunal prey, while grazing nematodes are 5-10 orders of magnitude larger than their microbial prey, in terms of average mass of bacterial cells (Mulder et al 2005b). These distinctly separate pathways imply that micro-arthropods like the Scutacaridae (top species) feed on varying compartments at lower trophic levels (intermediate species) at different points in time, linking belowground compartments into a larger soil and litter food web.…”

“…In contrast to soil organisms, detritus is organic but dead and difficult to be defined as entity (Mulder et al 2005b;Dunne 2006). Besides phytophagous arthropods, which are per se expected to become affected by the cry gene if they have the appropriate receptors, empirical evidence for belowground effects at other trophic levels is controversial.…”