Thursday, 13 July 2006

Time-Scales and Ecological Significance of Pedogenic Processes.

Victor O. Targulian, Institute of Geography, RAS, Staromonetniy lane, 29, Moscow, 119017, Russia and Pavel V. Krasilnikov, Institute of Biology KarRC RAS, Pushkinskaya st., 11, Petrozavodsk, 185610, Russia.

The Soil System (SS) is perceived as the open multiphase system functioning and self-organizing within the belowground tier of the land biosphere. The SS functioning starts immediately at 0-time, when the “flux-factors” (climate and biota) meet with the “site-factors” (parent material and relief). From this “moment” the innumerable multiphase reactions are initiated between the SS and the environment (external functioning) and among internal atmo-hydro-bio- and litho-components of the SS (internal functioning). Many of the SS functioning reactions have a cyclic mode; however, these cycles are neither completely closed, nor completely reversible. Therefore these cycles produce a set of residual products of functioning: gaseous, liquid and solid. Gas and liquid products are renewed rapidly and cannot be retained within the SS. Only the stable solid phase products of the SS functioning can be retained and accumulated in situ within the system. The working hypothesis is that pedogenesis sensu stricto comprises formation, selection, accumulation and differentiation of the residual solid phase products of functioning within the SS. It is perceived that the pedogenesis is the synergetic process of SS self-organization tending to reach steady state, i.e. attractor of the system. From this point of view the SS functioning is the infinite phenomenon, if not interrupted by denudation or burial, but the pedogenesis, by contrast, is the finite self-terminating process during the SS existence. The pedogenesis is usually subdivided into a set of specific pedogenic processes (SPP), which could be assessed by their finity-infinity, reversibility-irreversibility and their characteristic times. Such SPP, as weathering of primary silicates, formation of stable phyllosilicates, total leaching of substances from soil, translocations of clays, and Si, Al, Fe oxides within the solum are usually finite and irreversible processes. Other SPP, as organic matter transformation, red-ox metabolism of iron, salts and carbonates migrations, structuring, bioturbation are dynamically equilibrated with the environment and reversible during pedogenesis. The whole set of SPP was assessed in terms of their individual characteristic times (ICT) and grouped into three clusters: fast SPP with ICT of n x 101-2 years, medium-rate SPP with ICT of n x 103 years and slow SPP with ICT of n x 104 -6 years. The real pedogenesis includes ñomplex and manifold interactions of SPP with various rates and ICT; these interactions form the direct linkages and feedbacks between faster and slower processes throughout the whole soil formation. Basing on these conclusions we perceive the WRB diagnostic horizons and properties as a partial attractors of soil self-organization and subdivide them into three groups according to their characteristic times: horizons and properties with short, medium and long ICT. To assess the ecological significance of different SPP, hence, of different diagnostic horizons and properties we divide the whole set of the WRB horizons and properties (39 ones) into two groups: “good attractors” and “bad attractors”. “Good attractors” are those states of the SS (horizons and properties), upon reaching which it becomes more favorable for biota than in its previous states in terms of biological productivity and/or biodiversity. They include 12 out of 39 diagnostic horizons (about 31 %): mollic, chernic, umbric, melanic, fulvic horizons of humus accumulation, andic, cambic, nitic, argic, vitric horizons and fluvic material of mineral matter transformation, migration and addition. They are mainly shaped by biotic-ruled fluxes and cycles, which are comparable to or exceed the effect of abiotic ones, or by ecologically favorable changes in soil mineral matter. In this case, biota transforms and improves the belowground habitat rather than adapts to it. “Bad attractors” are those states of the soil system, upon reaching which it becomes less favorable for biota than in its previous states. They include 27 out of 38 horizons and properties (about 71%) produced mainly by weathering, leaching and translocation processes. These attractors are shaped by the mutual action of biotic and abiotic fluxes and cycles with the predominance of abiotic ones. In this case, biota adapts to the belowground environment rather than transforms it. These conclusions compel us to assess the different results of the pedogenesis in more realistic way: dividing its real favorable and adverse results and avoiding the widespread biospheric euphoria.

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