Abstract
AbstractMediterranean oak savannas, such as Spanish dehesas, are multiple resource‐limited ecosystems found in semiarid regions which are key contributors to interannual variability of the global carbon (C) budget. Interactions between nitrogen (N) and phosphorus (P) cycles are expected to play a major role in overall ecosystem function as anthropogenic N deposition shifts ecosystems from N to P limitation, leaving unknown how increased N availability might influence C uptake. Therefore, the fate of N additions in dehesas is important for understanding global C cycling. Using a 15N tracer experiment within fertilized (N or N + P) plots of a Holm oak dehesa, we tested the effects of ecosystem spatial heterogeneity (habitat), P addition, and time on the fate of added N. We expected that open pasture areas would retain more of the added N in biological components due to greater N limitation, that the addition of P would enhance N retention in biological components relative to N alone, and that added N would shift from being within the microbial biomass immediately after addition to being predominantly within plants at the beginning of the following growing season. We found that open pasture plots with N only had the greatest label recovery seven months after the start of the experiment, supporting the idea that open pasture was more N‐limited than under‐canopy areas. However, soil was the largest sink for added N, regardless of habitat, treatment, or time. Our results suggest that abiotic fixation of N may play an important role in modifying the effects of N deposition in dehesas.
Highlights
Atmospheric nitrogen (N) deposition causes a variety of downstream effects on ecosystems, ranging from increased productivity to groundwater contamination (LeBauer and Treseder 2008, Schlesinger 2009, Schulte-Uebbing and de Vries 2018)
N:P imbalances are largely unknown (Sardans et al 2012), especially in the context of how such imbalances might affect ecosystem N allocation. In their 2011 review, Pardo et al found that ecosystems dominated by low-biomass components are more sensitive to N deposition than ecosystems dominated by high-biomass components due to differing generation times and buffering abilities
Because previous work in Mediterranean oak savannas found up to 90% of ecosystem N was located in the top four cm of soil (Jackson et al 1988), we focused on this active section of the ecosystem as we were interested in short-term competition between plants and soil microbes, rather than long-term competition strategies that might be utilized by the slow-responding oak trees (Rivest et al 2011)
Summary
Atmospheric nitrogen (N) deposition causes a variety of downstream effects on ecosystems, ranging from increased productivity to groundwater contamination (LeBauer and Treseder 2008, Schlesinger 2009, Schulte-Uebbing and de Vries 2018). N:P imbalances are largely unknown (Sardans et al 2012), especially in the context of how such imbalances might affect ecosystem N allocation. In their 2011 review, Pardo et al found that ecosystems dominated by low-biomass components (e.g., grasslands, desserts) are more sensitive to N deposition than ecosystems dominated by high-biomass components (e.g., forests) due to differing generation times and buffering abilities. Changes in individual biomass components (Pardo et al 2011) This contrast in sensitivity makes predicting the response of mixed tree– grass ecosystems to shifts in N and P availability difficult (Sardans et al 2012). Shedding light on the linkages between C, N, and P cycles is of growing importance
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
