Slowing of nitrogen cycling and increasing nitrogen use efficiency following afforestation of semi-arid shrubland

Abstract

Nitrogen (N) and water availability are important factors affecting ecosystem productivity that can be influenced by land-use change. We hypothesized that the observed increase in carbon (C) sequestration associated with afforestation of semi-arid sparse shrubland must also be associated with an increase in N input. We tested this hypothesis by reconstructing the ecosystem N budget of two ecosystems, a semi-arid shrubland and a nearby planted pine forest, using measurements augmented with literature-based estimates. Our findings demonstrate that, contrary to our hypothesis, massive C sequestration by the pine forest could be accounted for without a change in the net N budget (i.e., neither elevated N inputs nor reduced N losses). However, in comparison to the shrubland, the forest showed an almost tripling in aboveground N use efficiency (NUE; 235 vs. 83 kg dry mass kg(-1) N) and a doubling in ecosystem level C/N ratio (16 vs. 8, for the forest and shrubland, respectively). Nitrogen cycling slowed in the forest compared to the shrubland: net N mineralization rates in soils decreased by approximately 50%, decomposition rates decreased by approximately 20%, and NO(x) loss decreased by approximately 64%. These adjustments in N cycling provide a possible basis for increased NUE and subsequent C sequestration without net change in the overall N budget, which should be addressed in future investigations.

Countervailing effects on pine and oak leaf litter decomposition in human-altered Mediterranean ecosystems

“…Nevertheless, many studies have found impacts of Mediterranean ecosystem type and land-use history on soil fertility. Soils were usually more fertile in pine forest (Fernández-Ondoño et al 2010;Gelfand et al 2011) and in oak maquis (Aranda and Oyonarte 2006;Arslan et al 2010;Aponte et al 2011) compared to the soils in Mediterranean shrublands. Differences in soil properties can further affect decomposition as the system is changing.…”

Leaf nitrogen is closely coupled to phenophases in a desert shrub ecosystem in China

“…Plant traits such as specific leaf area (SLA) and leaf nitrogen concentration (N) play a pivotal role in the light capture, CO 2 assimilation and carbon sequestration of plants (Rozendaal et al, 2006;Gelfand et al, 2012). Leaf N is strongly correlated with the rate of photosynthesis in the leaf.…”

Evidence for large carbon sink and long residence time in semiarid forests based on 15 year flux and inventory records

“…Our study was carried out in the semiarid Yatir pine forest (31°20'49"N; 35°03'07"E), for which extensive information is available from long‐term flux measurements, C and N stock inventories, and aerial photography (Bar Massada, Carmel, Tzur, Grünzweig, & Yakir, ; Gelfand, Grünzweig, & Yakir, ; Grünzweig, Gelfand, Fried, & Yakir, ; Maseyk, Grünzweig, Rotenberg, & Yakir, ; Rotenberg & Yakir, ). With 15 years of quantitative data on carbon accumulation at this site, the main objective was to test the idea that dry, semiarid forest plantations can provide a significant carbon sink as part of our efforts to slow down the increase in atmospheric CO 2 .…”