Colonization of a Deglaciated Moraine: Contrasting Patterns of Carbon Uptake and Release from C3 and CAM Plants

Abstract

IntroductionCurrent glacier retreat makes vast mountain ranges available for vegetation establishment and growth. As a result, carbon (C) is accumulated in the soil, in a negative feedback to climate change. Little is known about the effective C budget of these new ecosystems and how the presence of different vegetation communities influences CO2 fluxes.MethodsOn the Matsch glacier forefield (Alps, Italy) we measured over two growing seasons the Net Ecosystem Exchange (NEE) of a typical grassland, dominated by the C3 Festuca halleri All., and a community dominated by the CAM rosettes Sempervivum montanum L. Using transparent and opaque chambers, with air temperature as the driver, we partitioned NEE to calculate Ecosystem Respiration (Reco) and Gross Ecosystem Exchange (GEE). In addition, soil and vegetation samples were collected from the same sites to estimate the Net Ecosystem Carbon Balance (NECB).ResultsThe two communities showed contrasting GEE but similar Reco patterns, and as a result they were significantly different in NEE during the period measured. The grassland acted as a C sink, with a total cumulated value of -46.4±35.5 g C m-2 NEE, while the plots dominated by the CAM rosettes acted as a source, with 31.9±22.4 g C m-2. In spite of the different NEE, soil analysis did not reveal significant differences in carbon accumulation of the two plant communities (1770±130 for F. halleri and 2080±230 g C m-2 for S. montanum), suggesting that processes often neglected, like lateral flows and winter respiration, can have a similar relevance as NEE in the determination of the Net Ecosystem Carbon Balance.

Evidence for a non-linear carbon accumulation pattern along an Alpine glacier retreat chronosequence in Northern Italy

“…precipitation increased up to 800–1,000 mm (Penna et al, 2014). Further details about geomorphology and glacial cover are reported in Habler, Thöni & Grasemann (2009), Knoll & Kerschner (2009) and Varolo et al (2016).…”

“…The gas exchange measurements were done with the use of an automated closed transparent chamber (LI 8100-104C) attached to the analyzer LI 8100 (Li-Cor Biosciences, Lincoln, NE, USA). The measurements (see Varolo et al, 2016; Galvagno et al, 2017; Pavelka et al, 2018; Zhao et al, 2018 for comparison and evaluation of the technique) were conducted on 15 numbered iron collars, 20 cm diameter, divided into groups of five plots (C1; …C5) in each of the three transects. To understand the response of the selected small ecosystem to solar radiation, Nylon filters having the same dimension of the collar were inserted in increasing number inside the chamber, in order to progressively intercept the solar radiation.…”

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“…Mean annual air temperature and precipitation (the mean values from the long-term observation , recorded at the closest weather station (Hydrographic Office of the Autonomous Province of Bozen-Bolzano) were 6.6 °C, and 550 mm at 1570 m a.s.l, where at 2000 m a.s.l precipitation increased up to 800-1000 mm (Penna et al, 2014). Further details about geomorphology and glacial cover are reported in Habler et al (2009), Knoll et al (2009) and Varolo et al (2016). After a preliminary botanical survey, used to define the main plant species and communities present on the area, we used photographs taken on the collars to define the plant composition inside each collar.…”

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“…Mean annual air temperature and precipitation (the mean values from the long-term observation , recorded at the closest weather station (Hydrographic Office of the Autonomous Province of Bozen-Bolzano) were 6.6 °C, and 550 mm at 1570 m a.s.l, where at 2000 m a.s.l precipitation increased up to 800-1000 mm (Penna et al, 2014). Further details about geomorphology and glacial cover are reported in Habler et al (2009), Knoll et al (2009) and Varolo et al (2016.…”

“…The gas exchange measurements were done with the use of an automated closed transparent chamber (LI 8100-104C) attached to the analyzer LI 8100 (Li-Cor Biosciences, Lincoln, Nebraska, USA. The measurements (see Varolo et al, 2016;Galvagno et al, 2017;Pavelka et al, 2018;Zhao et al, 2018 for comparison and evaluation of the technique) were conducted on 15 numbered iron collars, 20 cm diameter, divided into groups of five plots (C1; …C5) in each of the three transects.…”