Macro-aggregation of soils by biological bonding and binding mechanisms and the factors affecting these: a review

Abstract

This review presents an analysis of the labile bonding (organic compounds) and binding (hyphae and roots) mechanisms involved in stabilising soil into macro-aggregates in soils (aggregates >0 · 25 mm diameter). The main emphasis is on the approaches used to study these mechanisms and the factors that affect the aggregating mechanisms at the micro-scale (<100µm) level in soils. Much of the understanding of the stabilisation of soil into macro-aggregates in field soils by labile organic C is derived primarily from the interpretations of studies where soils were incubated under artificial conditions. In addition, many recent studies have assessed the importance of labile organic C in macro-aggregation based only on whole soils analyses of hyphal length, extractable carbohydrate C, microbial biomass C, or aliphatic C. These approaches have contributed little to understanding fundamental factors that can influence the biological mechanisms of macro-aggregation under field conditions. It is proposed that greater consideration of bonding and binding aggregation mechanisms and the factors affecting the mechanisms at the micro-scale level will facilitate development of field management practices that benefit macro-aggregation. Factors influencing the location and persistence of bonding and binding mechanisms in the soil matrix are discussed.

Short-term effect of organic residue incorporation on soil aggregate stability along gradient in salinity in the lower cheliff plain (Algeria)

“…It may also be induced by the presence of labile organic compounds and the availability of high concentration of water soluble carbon considered as the main source to provide energy necessary in developing salt tolerance and stimulating microbial activity (Marschner et al, 2003). A significant correlation between microbial biomass and the mean weight diameter (r = 0.72 with MWD MB and r = 0.64 with MWD FW ) (Table 6) explained the crucial role of adding organic matter in stimulation microbial activity, particularly fungal biomass in stabilizing soil structure by increasing the cohesion through enmeshment of aggregates by filaments (Degens, 1997;Annabi et al, 2007). In our study, the increase in soil hot-water extractable polysaccharide as consequence of the organic amendment did not affect the soil structure.…”

Interactive effects of compost, plants and earthworms on the aggregations of constructed Technosols

“…Micro-aggregates (< 200 μm) are formed within macro-aggregates around POM (Oades, 1984;Six et al, 2000aSix et al, , 2000b. The decomposition of POM within macro-aggregates by microorganisms produces exopolysaccharides and other metabolites which act as persistent binding agents for the formation of micro-aggregates (as reviewed by Degens, 1997). Thus, the dynamics of soil aggregates create different ecological niches.…”

“…Because OC is considered as a major source of binding agents in aggregation (Tisdall and Oades, 1982;Degens, 1997, Cosentino et al, 2006, an increase in the proportion of organic matter when constructing new Technosols is likely to be a key factor for improving their biological functioning and accelerating their pedogenesis. It is known that adding urban organic wastes into degraded land improves their fertility (Mathan, 1994;Vetterlein and Hüttl, 1999;Pateiro-Moure et al, 2009).…”

Carbohydrates in hot water extracts of soil aggregates as influenced by long-term management

“…Some workers have observed that the hot-water-extractable carbohydrate fraction is more closely correlated with aggregation and aggregate stability than total carbohydrate or organic C content in soil (6,8,9 -12). In a review on the subject, Degens (5) found that carbohydrates extractable by hot water could be correlated with aggregation across a range of soil types.…”

“…These bonding compounds contain a combination of transient and temporary organic binding agent (4). Carbohydrates are thought to play a major role in this respect and many attempts have been made to characterize the carbohydrates involved (e.g., (1,5)). …”