Comparing the fate of N from fertilizer treatments and root litter turnover in a Mediterranean Savanna

<p>Nutrient imbalances induced by anthropogenic N deposition may fundamentally alter plant activity and consequently, their role in biogeochemical cycling. Mechanistic understanding of N cycle processes is commonly informed by <sup>15</sup>N tracers in fertilizer applications, but over the long term most N is obtained by plants is from litter mineralization rather than ‘new’ deposition N or mineral fertilizer applications. In many ecosystems this litter pool is dominated by root remains.</p><p>Here, we will compare results between two experiments: a <sup>15</sup>N-labelled root litter experiment, and an associated conventional <sup>15</sup>N-mineral fertilizer experiment, both located in a typical, spatially heterogeneous, seasonally-arid Spanish dehesa amended with N and NP fertilizers to induce nutrient imbalances. We show that recovery of the litter tracer in soil and plants was substantially higher than the fertilizer N, especially in microsites under trees, which are rich in organic inputs. In contrast, recovery of mineral tracers was strongest in more resource-poor grassland areas.  Plant acquisition of N from the organic source was also affected by the concurrent P addition treatment while we found little evidence for a similar effect in mineral additions.</p><p>Our results imply that scaling nitrogen cycle processes informed by isotope tracers from experiments to ecosystems depends heavily on appropriateness of methodology, especially in interpreting short-term traces applied as fertilizer N.</p>

Volume measurements for quicker determination of forest litter standing crop

Litter standing crop (LSC) is the quantity of plant detritus on the floor in forested environments. Knowledge of LSC is important in understanding many ecological phenomena. These include studies of litterfall, decomposition/litter turnover rates and nutrient cycling (Anderson et al. 1983, Dent et al. 2006), general plant performance (Benítez-Malvido & Kossmann-Ferraz 1999), other ecosystem processes such as the effects of fire (Odiwe & Muoghalu 2003) and fauna (Frith & Frith 1990, Giaretta et al. 1999, Levings & Windsor 1985). The determination of accurate annual average LSC data, may require monitoring over long periods due to seasonality and sometimes sporadic nature of litterfall and decomposition rates (Clark et al. 2001). Furthermore, the effects of topography and water movement create the need for both representative site selection and sufficient spatial coverage.