Element cycling forest ecosystems

In the present chapter, I will discuss the potential of EMF to influence weathering rates of soil minerals, and review experiments where the effects of EMF on dissolution of minerals have been investigated in axenic cultures, pot cultures and field experiments. I will then discuss the influence of the nutrient status of the trees on weathering induced by EMF and, finally, to what extent this process may influence the overall cycling of elements in forest ecosystems. 

Biogeochemical cycling of elements in Forest ecosystems The plant species biomass of Boreal and Sub-Boreal Forest ecosystems accumulates a significant part of living matter of the whole planet. This value is about 700 x 10 tons of dry weight. The biomass per unit area of different Forest ecosystems varies from 100 to 300 ton/ha and even 400 ton/ha in the Eastern European Oak Forest ecosystems. The annual net primary productivity, NPP, varies from 4.5 to 9.0 ton/ha (Table 9). 

Under low-dose conditions, forest ecosystems act as sinks for atmospheric pollutants and in some instances as sources. As indicated in Chapter 7, the atmosphere, lithosphere, and oceans are involved in cycling carbon, nitrogen, oxygen, sulfur, and other elements through each subsystem with different time scales. Under low-dose conditions, forest and other biomass systems have been utilizing chemical compounds present in the atmosphere and releasing others to the atmosphere for thousands of years. Industrialization has increased the concentrations of NO2, SO2, and CO2 in the "clean background" atmosphere, and certain types of interactions with forest systems can be defined. 

In soils of non-agricultural ecosystems, above ground biomass (foliar uptake) and metal cycling is considered important (see Figure 8), due to large impact on the metal distribution in the humus layer and mineral soil profile. Especially in soils of Forest ecosystems, it may affect the accumulation in the humus layer, which is considered a very relevant compartment regarding the calculation of a critical load. In these soils, however, a steady-state element cycle is assumed, which implies that mineralization, Minj, equals litterfall, Mjf. 

BIOGEOCHEMICAL CYCLING OF ELEMENTS AND POLLUTANTS EXPOSURE IN FOREST ECOSYSTEMS... 

Table 3. Averaged fluxes of trace elements in biological cycling of Boreal and Sub-Boreal Forest ecosystems (after Dobrovolsky, 1994).

Amongst the ash elements the most abundant in biomass is calcium, which is accumulated in leaves, in trunk wood, and in twigs. Potassium is dominant in annual NPP. The masses of trace metals in biogeochemical cycling of this Oak Forest ecosystem are roughly in correspondence to their respective average values for the... 

In may be of interest to compare the fluxes of elements in biogeochemical cycles of Oak Forest ecosystem with exposure to airborne deposition input. The latter were (inkg/ha/yr)forN, 17.7 forCa, 14.7 forMg, 1.8 for K, 4.2 for Na, 1.4 forP, 1.1 for Fe, 0.07 and for Zn, 0.14. The deposition input of these elements fall into a range of 20% (calcium) to 4.5% (potassium) relative to the respective biogeochemical fluxes (see Table 9). The airborne Fe input accounts for a mere 2.5%. Simultaneously, for some heavy metals, like zinc, the deposition input is commensurate with the fluxes of biogeochemical cycle. 

In the Mixed Forest ecosystems a soil fraction less than 1 pm contains most of the elements previously confined in the forest litter and gradually involved in the biogeochemical cycle. In this fraction Cu and Mo forms account for 60-70% of the total soil content. The metals, poorly absorbable by plants, for example, Cr and V, occur in finely dispersed soil fraction in smaller amounts, about 20-30%. 

We can see that the soluble and exchange forms of these metals are present in small amounts accounting merely for a few percent of the total metal content in soil. The content of organometal species is relatively high in the upper profile rich in humic species, whereas it drops sharply in the mineral horizons. Copper is extensively involved in the biogeochemical cycle in the Forest ecosystems and this is less profound for cobalt. It is noteworthy that a large part of metals (in particular, of copper) become bound to iron hydroxides. This is typical for various trace elements, including arsenic, zinc and other elements with variable valence. 

The word Amazonia conjures up diverse images, ranging from an exotic jungle to resources for development to a vast web of ecosystems that interact with global element cycles-the focus of this book. This chapter examines the biogeochemical role of extractive reserves, a relatively new land use type within Amazonia in which nontimber forest extraction is the defining human activity. The chapter also provides examples of how participatory research with local communities can enhance the quality of the results and improve their transmission to society. 

The high rate of edaphic biological processes is the characteristic property of any tropical ecosystem. In the maximum degree this is related to the Tropical Rain Forest ecosystems. For instance, in the African Rain Forest ecosystems the soil surface receives annually from 1200 to 1500 ton/ha of various plant residues. Edaphic invertebrates and microbes transform this large mass very rapidly. A continuous forest litter is practically nonexistent in the Tropical Rain Forest ecosystems and a thin layer of dead leaves alternates with patches of bare ground. All elements that mineralized from litterfall, are taken up by the complex root system of a multi-storied forest to re-input to the biogeochemical cycling. 

If we take any part of the Alps the successive change in soil belt will be as follows the foothills lie in the zone of Broad-Leafed Forest ecosystems with Cb about 2.0 to an altitude of 600-700 m, in the south up to 800-900 m. Above them is the zone of Coniferous Forest ecosystems on mountain Podzols with moderate-to-depressed biogeochemical cycles of elements. The altitude limits are 1,400 in the north and 2,300 m in the south. Above these ecosystems is the zone of Sub-Alpine and Alpine Meadow ecosystems with depressed type of biogeochemical turnover. 

The biogeochemical cycling of elements in these ecosystems can be characterized as moderate in depressions and as semi-intensive in high mountain forest ecosystems with Cambisols the average Cb is equal to 2 and Ct is equal to 0.42. 

The southern part of the Laurentian region is covered by Podzols and Spodi-Distric Cambisols with Black Coniferous Forest ecosystems of Picea mariana, P. glauca, and Abies balsamea Larch and birch are mixed with these species. Pine Forest ecosystems of Pinus banksiana, bog mosses and lowland bogs occur in this part of the region also. The biogeochemical cycling of the elements is faster than in the northern part, but anyhow it is the depressed type of turnover (see Table 1). 

The ecosystems of Madagascar Island are represented by wet tropical forests located on the eastern slope with very acid low fertility soils and by savannas in the western slopes with Cambisols. So the biogeochemical migration of elements in western ecosystems is restricted, whereas that in the eastern tropical forest is reinforced by very intensive type of biogeochemical cycling (Cb is 0.1-0.2). 

Heinrichs H, Mayer R (1977) Distribution and cycling of major and trace elements in two Central European forest ecosystems. J Env Qual 6 402-407... 

The regulation of biogeochemical cycles by microbial populations is of most direct importance in the cycling of N, S, P, and C. Most of the ecosystem pool of these elements resides as organic forms in forest floor and mineral soil compartments. These organic complexes are subjected to microbial transformations, which regulate nitrate, sulfate and phosphate ions dynamics and availability. In turn, this influences indirectly... 

Biogeochemical cycles of individual elements, including nitrogen, have been intensively studied at the Hubbard Brook experimental Forest (HBEF) in New Hampshire, USA, since 1963, pioneering the use of the small catchment concept for understanding biogeochemical processes in the ecosystems (see Likens etal, 1977). The numerous... 

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