Nitrogen (N) deposition induced by human activities can heavily afect the biogeochemical cycles of forest ecosystems. In this respect, long-term fertilization experiments are important tools to explore the responses of forests to altered N availability. In this vision, in two beech (Fagus sylvatica L.) forests of LTER and ICP-Forests Networks, we have simulated increased N deposition using a mineral fertilizer. The two experimental sites are located in Italy, Collelongo (Abruzzo) and Cansiglio (Veneto). In both forests, in suficiently structural homogeneous areas, nine to twelve 30 × 30 m plots were established and randomly assigned to treatments increasing the natural N deposition by 0 kg N ha-1 (control), 30 kg N ha-1 and 60 kg N ha-1. The fertilizer was distributed to the soil at the beginning, in the middle and at the end of the 2015 and 2016 growing seasons. For only the Cansiglio site, a fourth treatment was tested, distributing the lower dose (30 kg N ha-1) above the canopy. Leaves were sampled at the end of the 2016 growing season. A vertical light gradient along the canopy was identified in both forests and the efects of N fertilization on leaf C to N ratio (C:N), C and N isotope compositions (? 13C, ?15N) and structural and biochemical traits (LMA, pigments) were examined. Significant relationships were found between ?13C, LMA and N content per unit of leaf area in both sites, with higher values in Collelongo for both N and ?13C. A progressive 15N-enrichment was observed at all the light exposition levels with the increasing of fertilizer dose. In the Collelongo site, the highest N dose enhanced the N content per unit of leaf dry mass and decreased the C:N in the shade canopy leaves compared to control. Conversely, in the Cansiglio site the sun canopy leaves of fertilized plots showed a higher N content per unit area and a 13C-enrichment compared to control. Moreover, the fertilization above the canopy induced an increase of the C:N ratio. The correlations of these results with biochemical and structural data and possible morpho-physiological implications are under analysis. In conclusion, our study highlights a gradient of leaf physiological traits along the vertical canopy profile in response to diferent N supplies, depending on the site characteristics, fertilizer dose and distribution approach, causing a change in the N allocation strategy within the canopy and afecting important leaf ecophysiological traits at the forest ecosystem level.
Responses of beech forests to N fertilization: C to N ratio, C and N isotope composition, structural and biochemical traits along the canopy vertical profile
Andrea Scartazza;Daniela Di Baccio;Bruno De Cinti;Mario Cammarano;Ettore D'Andrea;Francesco Mazzenga;Pierluigi Bombi;Flavia Sicuriello;
2017
Abstract
Nitrogen (N) deposition induced by human activities can heavily afect the biogeochemical cycles of forest ecosystems. In this respect, long-term fertilization experiments are important tools to explore the responses of forests to altered N availability. In this vision, in two beech (Fagus sylvatica L.) forests of LTER and ICP-Forests Networks, we have simulated increased N deposition using a mineral fertilizer. The two experimental sites are located in Italy, Collelongo (Abruzzo) and Cansiglio (Veneto). In both forests, in suficiently structural homogeneous areas, nine to twelve 30 × 30 m plots were established and randomly assigned to treatments increasing the natural N deposition by 0 kg N ha-1 (control), 30 kg N ha-1 and 60 kg N ha-1. The fertilizer was distributed to the soil at the beginning, in the middle and at the end of the 2015 and 2016 growing seasons. For only the Cansiglio site, a fourth treatment was tested, distributing the lower dose (30 kg N ha-1) above the canopy. Leaves were sampled at the end of the 2016 growing season. A vertical light gradient along the canopy was identified in both forests and the efects of N fertilization on leaf C to N ratio (C:N), C and N isotope compositions (? 13C, ?15N) and structural and biochemical traits (LMA, pigments) were examined. Significant relationships were found between ?13C, LMA and N content per unit of leaf area in both sites, with higher values in Collelongo for both N and ?13C. A progressive 15N-enrichment was observed at all the light exposition levels with the increasing of fertilizer dose. In the Collelongo site, the highest N dose enhanced the N content per unit of leaf dry mass and decreased the C:N in the shade canopy leaves compared to control. Conversely, in the Cansiglio site the sun canopy leaves of fertilized plots showed a higher N content per unit area and a 13C-enrichment compared to control. Moreover, the fertilization above the canopy induced an increase of the C:N ratio. The correlations of these results with biochemical and structural data and possible morpho-physiological implications are under analysis. In conclusion, our study highlights a gradient of leaf physiological traits along the vertical canopy profile in response to diferent N supplies, depending on the site characteristics, fertilizer dose and distribution approach, causing a change in the N allocation strategy within the canopy and afecting important leaf ecophysiological traits at the forest ecosystem level.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
