Ecophysiological Key Processes in Agricultural and Forest Ecosystems
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Elemental cycling in ecosystems depends on the structure of the biocoenoses and the ecophysiological key processes regulating the input, allocation and mineralization of compounds, elements and energy (Stocker et al. 1999). The four key processes driving elemental and energy fluxes in the vegetation are: (1) the reduction of atmospheric CO2 during photosynthesis which provides the energy for growth and maintenance of plant, animal and microbial communities, (2) allocation of assimilates to plant organs and to the environment via exudates, leachates and litter and (3) requirements for maintenance, growth and storage. These three processes are regulated by endogenous and exogenous factors and adjust to environmental conditions to stabilize the vegetative and generative development of the biocoenoses. Plant exudates and residues are deposited onto the soil and: (4) decomposition then completes the element cycling. Decomposition provides energy and nutrients to the heterotrophic macro- and microbiota and, in addition, ensures the nutrient availability of auto- and heterotrophic organisms. The mineralization liberates CO2 from soil derived from microbial and faunal activity. In addition, respiration of belowground components of plants considerably contributes to the in situ soil respiratory activity in ecosystems.
The ecophysiology of the vegetation and soil microbiota is largely controlled by external factors like microclimate and the composition of organic matter, such as the lignin/N ratio (Richards 1987). However, the biotic response to external factors suggests that adjustment and interactions of plants and soil microbiota can reduce the role of external constraints. For instance, the strategy of the microbial consortium may promote the decomposition rate rather than temperature when passing thresholds (Schulze 2000).
Anthropogenic ecosystem activities and related moderate and strong human impact with respect to, for instance, N input is particularly considerable as it modifies both primary production and decomposition processes and also the interactions between ecosystem components. Therefore, this Chapter addresses the adjustment of key processes during C assimilation, partitioning and decomposition in agricultural (arable land, grassland) and forest ecosystems in the Bornhöved Lake District.
KeywordsMicrobial Biomass Beech Forest Soil Respiration Rate Light Compensation Point Corylus Avellana
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