Abstract
Nitrogen (N) deposition is a key driver of global change with significant effects on carbon (C) cycling, species fitness, and diversity; however, its effects on Mediterranean ecosystems are unclear. Here, we simulated N deposition in an N-fertilization experiment with 15N-labeled fertilizer in a montane evergreen Mediterranean holm oak forest, in central Catalonia, to quantify short-term impacts on leaf, leaf litter elemental composition, and resorption efficiency in three dominant species (Quercus ilex, Phillyrea latifolia, and Arbutus unedo). We found that even under drought conditions, 15N isotope analysis of leaf and leaf litter showed a rapid uptake of the added N, suggesting an N deficient ecosystem. Species responses to N fertilization varied, where A. unedo was unaffected and the responses in P. latifolia and Q. ilex were similar, albeit with contrasting magnitude. P. latifolia benefited the most from N fertilization under drought conditions of the experimental year. These differences in species response could indicate impacts on species fitness, competition, and abundance under increased N loads in Mediterranean forest ecosystems. Further research is needed to disentangle interactions between long-term N deposition and the drought predicted under future climate scenarios in Mediterranean ecosystems.
Highlights
Accepted: 7 May 2021Nitrogen (N), which is an essential element for plant nutrition, is involved in complex cycling in terrestrial ecosystems that involves biotic and abiotic processes, such asN2 -fixation, mineralization, nitrification, ammonification, and denitrification [1,2,3]
There were between-year differences in C:P ratios in P. latifolia, where there were increases of 4.83 ± 3.36% and 3.05 ± 0.86% in untreated control and fertilized plots, respectively (difference between treatments: p < 0.05; ±standard error (SE) showed; Figure 2a, Table S1), and ratios of N:P differed for A. unedo, where there were 1.64 ± 1.65% decreases and 1.12 ± 1.38% increases in the untreated and treated plots from 2014 to
The overall macro-elements reduction and micro-elements variation in control plots between 2014 and 2015, as seen in Figure 7, are inherent effects of the exceptional drought in 2015. These year to year effects of drought are consistent with the drought experiments carried out in the same studied Mediterranean forest, where reduction of foliar N [50,51], P [52,53,54], and micro nutrients variation [55,56] were described to be associated to the drought treatment
Summary
Accepted: 7 May 2021Nitrogen (N), which is an essential element for plant nutrition, is involved in complex cycling in terrestrial ecosystems that involves biotic and abiotic processes, such asN2 -fixation, mineralization, nitrification, ammonification, and denitrification [1,2,3]. Nitrogen (N), which is an essential element for plant nutrition, is involved in complex cycling in terrestrial ecosystems that involves biotic and abiotic processes, such as. Anthropogenic activities since the industrial and agricultural revolutions, those associated with fossil fuel combustion, cultivation of N2 -fixing crops, and production of N fertilizer using the Haber-Bosch process, increasingly influence the global N-cycle as they are often key sources of N in terrestrial ecosystems, driving fluxes of similar magnitudes to natural fluxes [4,5,6]. N addition to ecosystems alters the first N cycle, increasing N mineralization, nitrification, and nitrate leaching rates, and thereafter other ecosystem variables such as P-cycle [5], and is associated with a long-term plant community diversity decrease [10].
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