Nitrogen Deposition Effects on Soil Properties, Microbial Abundance, and Litter Decomposition Across Three Shrublands Ecosystems From the Mediterranean Basin

Abstract

Atmospheric nitrogen (N) inputs in the Mediterranean Basin are projected to increase due to fossil fuel combustion, fertilizer use, and the exacerbation of agricultural production processes. Although increasing N deposition is recognized as a major threat to ecosystem functioning, little is known about how local environmental conditions modulate ecosystem function response to N addition, particularly in the context of Mediterranean-Basin ecosystems. Here, we assess how N addition affects important ecosystem properties associated with litter decomposition, soil physical-chemical properties, soil extracellular enzymatic activity and microbial abundance across three long-term N addition experimental sites in the Mediterranean Basin. Sites were located in El Regajal (Madrid, Spain), Capo Caccia (Alghero, Italy), and Arrábida (Lisbon, Portugal) and are all representative of Mediterranean shrublands. No common pattern for litter decomposition process or other studied variables emerged among the control plots of the studied sites. Nitrogen supply only affected soil pH, a major driver of decomposition, in two out of three experimental sites. Moreover, when we explored the role of N addition and soil pH in controlling litter decay, we found that the effects of these factors were site-dependent. Our results point out to local ecosystem features modulating N addition effects in controlling litter decomposition rates in Mediterranean ecosystems, suggesting that the responses of soil functioning to N deposition are site-dependent. These findings provide further knowledge to understand contrasting ecosystem responses to N additions based on a single field experiments.

Protist Diversity Responses to Experimental N Deposition in Biological Crusts of a Semiarid Mediterranean Ecosystem

“…This could be a priori a possible reason for the observed ciliate diversity reduction. However, the studied site did not show a significant pH reduction due to experimental Ndeposition, probably due to the soil type present in the area (calcareous with slightly basic pH between 7.79 and 8.01) which could have buffered the acidification (Lo Cascio et al 2021).…”

“…There have been inconsistent microbial responses to N inputs reported in other studies, producing either increased or decreased populations (Demoling et al 2008;Fierer et al 2012), suggesting that N fertilization on soil microbial diversity is likely site dependent as well (Andreetta et al 2022;Lo Cascio et al 2021). The research about microbial eukaryotic communities has shown that fungal biomass was reduced as N fertilization increased (Lan et al 2013;Lo Cascio et al 2021). However, few similar studies have been conducted to investigate the effects of N deposition in BSC on protist populations (Wang et al 2015).…”

“…The effects of N-deposition on the different components of BSC, and other soil communities, have given rise to numerous studies in these N-limited environments. This research has ranged from ecosystem properties to microbial abundance and diversity, especially in semi-arid ecosystems (Castillo-Monroy et al 2010;Lo Cascio et al 2021;Ochoa-Hueso et al 2011a, b;Wang et al 2015), in this framework of recovery from disturbances that are important for the ecosystem services provided by the BSC.…”

“…Previous works have developed long term field experiments manipulating N content to assess the effects on the diversity and composition of microbial communities in terrestrial ecosystems. These works have been focused mainly on bacterial and fungal communities (Lo Cascio et al 2021;Ochoa-Hueso et al 2011b;Wang et al 2015;Zhou et al 2017). There have been inconsistent microbial responses to N inputs reported in other studies, producing either increased or decreased populations (Demoling et al 2008;Fierer et al 2012), suggesting that N fertilization on soil microbial diversity is likely site dependent as well (Andreetta et al 2022;Lo Cascio et al 2021).…”

“…These works have been focused mainly on bacterial and fungal communities (Lo Cascio et al 2021;Ochoa-Hueso et al 2011b;Wang et al 2015;Zhou et al 2017). There have been inconsistent microbial responses to N inputs reported in other studies, producing either increased or decreased populations (Demoling et al 2008;Fierer et al 2012), suggesting that N fertilization on soil microbial diversity is likely site dependent as well (Andreetta et al 2022;Lo Cascio et al 2021). The research about microbial eukaryotic communities has shown that fungal biomass was reduced as N fertilization increased (Lan et al 2013;Lo Cascio et al 2021).…”