Abstract
Abstract. Accurately quantifying soil base cation pool sizes is essential to interpreting the sustainability of forest harvests from element mass-balance studies. The soil-exchangeable pool is classically viewed as the bank of “available” base cations in the soil, withdrawn upon by plant uptake and leaching and refilled by litter decomposition, atmospheric deposition and mineral weathering. The operational definition of this soil bank as the exchangeable (salt-extractable) pools ignores the potential role of “other” soil nutrient pools, including microbial biomass, clay interlayer absorbed elements, and calcium oxalate. These pools can be large relative to “exchangeable” pools. Thus neglecting these other pools in studies examining the sustainability of biomass extractions, or need for nutrient return, limits our ability to gauge the threat or risk of unsustainable biomass removals. We examine a set of chemical extraction data from a mature Norway spruce forest in central Sweden and compare this dataset to ecosystem flux data gathered from the site in previous research. The 0.2 M HCl extraction released large pools of Ca, K, Mg, and Na, considerably larger than the exchangeable pools. Where net losses of base cations are predicted from biomass harvest, exchangeable pools may not be sufficient to support more than a single 65-year forest rotation, but acid-extractable pools are sufficient to support many rotations of net-ecosystem losses. We examine elemental ratios, soil clay and carbon contents, and pool depth trends to identify the likely origin of the HCl-extractable pool. No single candidate compound class emerges, as very strongly supported by the data, as being the major constituent of the HCl-extractable fraction. A combination of microbial biomass, fine grain, potentially shielded, easily weatherable minerals, and non-structural clay interlayer bound potassium may explain the size and distribution of the acid-extractable base cation pool. Sequential extraction techniques and isotope-exchange measurements should be further developed and, if possible, complemented with spectroscopic techniques to illuminate the identity of and flux rates through these important, and commonly overlooked, nutrient pools.
Highlights
1.1 Importance of soil base cation pools for sustainable land useIn an attempt to decrease net CO2 emissions and to meet the increasing demand for woody biomass products and energy, some forest policies encourage the intensification of biomass extraction from forest ecosystems (Royo et al, 2012; Lauri et al, 2014; Kazagic et al, 2016)
Our mass-balance estimates indicate that stem-only harvesting would moderately deplete and whole-tree harvesting would markedly deplete exchangeable cation pools, such that current 0.1 M BaCl2-exchangeable pools of base cations are insufficient to support more than a single forest rotation under whole-tree harvesting of the Kindla forest
A large fraction of these salt-extractable base cation pools were found in the organic rich horizons, especially the humus layer
Summary
In an attempt to decrease net CO2 emissions and to meet the increasing demand for woody biomass products and energy, some forest policies encourage the intensification of biomass extraction from forest ecosystems (Royo et al, 2012; Lauri et al, 2014; Kazagic et al, 2016). These practices may severely impact soil fertility because biomass extraction removes the nutrients elements in the biomass, especially in forest ecosystems where nutrient availability may be low (Feller, 2005; Kreutzweiser et al, 2008; Thiffault et al, 2011; Achat et al, 2015). The pressures on plant-available base cations result from increased harvest intensity and from continued atmospheric nitrogen and sulfur deposition (Iwald et al, 2013; McGivney et al, 2019), and elevated atmospheric concentrations of CO2 (Duval et al, 2012; Terrer et al, 2016)
Sign-in/Register to view highlights & summary 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.
