Modeling the variability in annual carbon fluxes related to biological soil crusts in a Mediterranean shrubland

Biogeosciences Discussions 01/2009; DOI: 10.5194/bgd-6-7295-2009
Source: OAI

ABSTRACT Biological soil crusts (BSC) constitute a spatially prominent part of the photosynthesizing vegetation in many dryland ecosystems. This study assesses the annual net carbon deposition related to BSC growth in a Mediterranean shrubland for the years 2001–2003 using a model developed to account for the nature of hydration in the poikilohydric life trait of the BSC. Data for BSC-related net CO2 fluxes were obtained from in-situ measurements at the International Long-term Ecological Research site Sayeret Shaked (ILTER-SSK) in the northern Negev Desert, Israel. The BSC was smooth to rugose, up to 15 mm thick and consisted mainly of mosses, cyanobacteria and cyano-lichens. In order to obtain annual estimates, BSC-related CO2 fluxes were correlated with climate records provided by the meteorological station of the Terrestrial Ecosystem Monitoring Site network (TEMS) adjacent to SSK. The annual carbon deposition related to BSC growth was assessed from (1) an overall mean of net CO2 flux multiplied with annual activity periods of BSC based on precipitation records, and (2) from a simple precipitation-driven activity model (PdAM). This model combines an algorithm, previously developed to model gas exchange processes in vascular plants, with an empirical module that switches the algorithm on as soon as water is available to maintain activity of poikilohydric BSC. Based on a constant BSC area index of 0.6 m2 m−2 at ILTER-SSK, the final model suggests a large inter-annual variability in BSC-related net carbon deposition ranging from 7 to 51 kg ha−1 yr−1.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Dryland ecosystems account for ~27% of global soil organic carbon (C) reserves, yet it is largely unknown how climate change will impact C cycling and storage in these areas. In drylands, soil C concentrates at the surface, making it particularly sensitive to the activity of organisms inhabiting the soil uppermost levels, such as communities dominated by lichens, mosses, bacteria and fungi (biocrusts). We conducted a full factorial warming and rainfall exclusion experiment at two semiarid sites in Spain to show how an average increase of air temperature of 2-3°C promoted a drastic reduction in biocrust cover (~ 44% in four years). Warming significantly increased soil CO2 efflux, and reduced soil net CO2 uptake, in biocrust-dominated microsites. Losses of biocrust cover with warming through time were paralleled by increases in recalcitrant C sources, such as aromatic compounds, and in the abundance of fungi relative to bacteria. The dramatic reduction in biocrust cover with warming will lessen the capacity of drylands to sequester atmospheric CO2 . This decrease may act synergistically with other warming-induced effects, such as the increase in soil CO2 efflux and the changes in microbial communities, to alter C cycling in drylands, and to reduce soil C stocks in the mid to long term. This article is protected by copyright. All rights reserved.
    Global Change Biology 07/2013; · 8.22 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Poikilohydric desiccation tolerance enables lichens and bryophytes to survive long periods of water limitation and to recover quickly by rehydration. The evolutionary success of this strategy is reflected by the fact that cryptogams inhabit almost all terrestrial habitats from the tropics to cold and hot deserts. As ecosystem components, lichens and bryophytes may considerably impact the surrounding environment through frequent desiccation–rewetting cycles. What are the differences in mechanism and functioning to successfully compete with vascular plants in many micro-sites and habitats? This chapter reviews key issues of cryptogamic desiccation tolerance with particular emphasis on the following aspects: (1) Comparison of mechanisms and processes of water exchange. (2) Function and impacts of micro-scale fluxes to illustrate the effects of desiccation–rewetting cycles on the environment. (3) Global patterns of lichens and bryophytes as an indication for their ecological relevance.
    Plant Desiccation Tolerance, Ecological Studies Vol. 215 12/2010: pages 65-87; Springer Berlin Heidelberg.

Full-text (4 Sources)

Available from
May 31, 2014