FUNCTIONING OF THE SOIL SYSTEM - Soil Ecology - page 367

Despite the above‚ considerable differences still occur at a regional scale‚ demonstrat-
ing that other factors may also be important‚ or even predominate. Anderson and Swift
(1983) have shown that considerable overlap in leaf litter decomposition rates occurs
between temperate and tropical forests. Further‚ intra-site variation may be larger than
inter-site variation and this emphasises the importance of local edaphic and biological
factors (Figure IV.7). At this scale‚ the additional effects of clay mineralogy‚ resource
quality and invertebrate activity have also been confirmed (see‚ for example‚ Meentemeyer‚
1978; Anderson et al.‚ 1985; Darici et al.‚ 1986; Laishram and Yadava‚ 1988; Nicolai‚
1988; Seastedt et al.‚ 1988). However‚ the effects of the higher-level factors are so
powerful that they may override the effects of those‚ such as the soil fauna‚ that act
at lower levels making them difficult to detect (Andrén et al.‚ 1988‚ Persson‚ 1989).
In other situations‚ the hierarchy of factors may be less clear. In aquatic environments‚
for example‚ Irons et al.‚ (1994) found no relationship between latitude and leaf litter
decomposition. Factors specific to this environment ( i.e.‚ oxygen tension or water nutri-
ent status) may have confounded the stimulatory effect of higher temperatures on
decomposition. Similarly‚ Coleman et al. (1990) showed that reducing nematode and
micro-arthropod populations explained most of the differences in decomposition rates in
soils where climate and resource quality were expected to be the main determinants.
Interactions between levels II (soil nutrient status) and III (litter quality) of the proposed
hierarchy have been demonstrated several times. Plants growing on unproductive soils
often produce poor-quality litter with lower N and greater concentrations of secondary
compounds (polyphenols‚ terpenoids) than those growing on more fertile soils (Janzen‚
1974; Waterman‚ 1983; Baas‚ 1989). The same situation has been observed with plants
growing in atmospheres enriched in

(Coûteaux et al.‚ 1991; Woodin et al.‚ 1992;