Excess Supply of Nutrients, Fungal Community, and Plant Litter Decomposition: A Case Study of Avian-Derived Excreta Deposition in Conifer Plantations

1.1 Excess supply of nutrients and terrestrial ecosystems Human activities have greatly accelerated emissions of both carbon dioxide and biologically reactive nutrients such as nitrogen (N) to the atmosphere (Canfield et al., 2010), which cause environmental changes affecting ecosystem processes and biodiversity in forests. Excess supply of N of anthropogenic origin to forest soils, such as combustion of fossil fuels, production of N fertilizers, and cultivation of N-fixing legumes, is an example of such environmental changes often leading to a decrease of the rate of carbon dioxide evolution and decomposition (Fog, 1988; Berg and Matzner, 1997) and a concomitant increase in the amount of soil carbon stock (deVries et al., 2006; Zak et al., 2008). These changes are primarily attributable to the reduced activity of fungal ligninolytic enzymes that play crucial roles in the turnover of soil organic carbon and are known to be sensitive to N deposition (Sinsabaugh, 2010). However, such changes in the enzymatic activity are not consistently associated with changes in the abundance and diversity of fungi that are responsible for the activity (Waldrop and Zak, 2006; Blackwood et al., 2007; Hassett et al., 2009). This discrepancy merits further studies to examine the response of ecological and functional properties of fungal communities to excess supply of N and its consequences on the dynamics of carbon and N in forest soils. The transfer of nutrients by waterbirds from aquatic to terrestrial ecosystems provides similar situations to the anthropogenic supply of nutrients because birds feed on fish in the aquatic zone and deposit their waste rich in nutrients to the terrestrial parts of their habitats. Such allochthonous input of N and other nutrients to terrestrial ecosystems can lead locally to substantial enrichment of soils and plants and alter food webs, nutrient cycling, and