Complexity, climate change and soil carbon: A systems approach to microbial temperature response

Abstract

A proliferation of data gathered to predict a critically important, urgent and social-policy related question often leads to debate and divergent model results. This classic feature of complex systems is currently being evidenced in assessing a potentially serious feedback response of soil respiration with increased temperatures due to global climate change.Here we apply soft systems modelling (SSM) for a detailed analysis of the ''soft'' aspects of the topic. Supported by a literature review, we conclude that that varied perspectives on the system's dynamics and its web of controlling factors have led to seemingly conflicting results. We present a simplified hierarchy organizing the comprehensive universe of interacting controls across scales. This model is implemented as a relational database, including relationships between factors such as nesting and feedbacks. We conclude that although this model is currently limited to pairwise interactions, it provides a useful tool to assess potential interactions and factors of interest.

What is recalcitrant soil organic matter?

“…More recently it has been posited that recalcitrance mainly accounts for protection on shorter time scales [46] and that it may be necessary to distinguish between 'primary recalcitrance of plant litter and rhizodeposits as a function of their indigenous molecular characteristics, and the secondary recalcitrance of microbial products, humic polymers and charred materials'. [26] Besides revealing the struggle to find an adequate denominator for an enigmatic phenomenon, the non-numerical character of this latter definition also illustrates the strong contrast between the 'hard' formalisms (known algorithms) of physical chemistry and related science disciplines [17] and the 'soft' semantic category of recalcitrance, which lacks specifity and cannot easily be expressed using numerical categories.…”

“…[7,16] Laboratory incubations tend to show a strong temperature response of recalcitrant organic matter, whereas field studies show either a minor temperature response or one that quickly re-equilibrates at a low level. [17] Part of the problem may be that a large variety of mechanistically independent interpretations of the terms 'recalcitrance' and 'inherent stability' can be encountered in the literature (Table 1). Some authors, for example, understand recalcitrance as a material property [15,[18][19][20][21] based on molecular structure (Table 1, item I1); another approach (Table 1, item I2) considers 'old' organic compounds that have achieved long mean residence time as recalcitrant [14,16,22] and a third view defines recalcitrant organic matter operationally as such that is decomposed during the later stages of an incubation experiment [23,24] (Table 1, item III1).…”

“…It recently has been suggested that contradictory evidence may result, in part, from a large ambiguity and a lack of conceptual rigidity within the complex problem space of organic matter decomposition. [17] It appears therefore that continuing the practice of classifying organic matter as recalcitrant may adversely affect progress in many areas, including the temperature sensitivity of decomposition, carbon-cycle climate feedbacks, carbon turnover models and agricultural soil management. For example, it has been suggested to sequester atmospheric CO 2 in soils by increasing the proportion of recalcitrant aliphatic compounds in soil organic matter.…”

Analyzing spatiotemporal variability of heterotrophic soil respiration at the field scale using orthogonal functions

“…Bond-Lamberty and Thomson, 2010). The reasons for this are rooted in the numerous interactions between environmental factors and CO 2 efflux, in combination with the different scales on which they vary in space and time (Briones, 2009;Davidson and Janssens, 2006;Mahecha et al, 2010;Wixon and Balser, 2009). Point measurements of soil CO 2 efflux have repeatedly been reported to exhibit a poor spatial dependence and strong variability at short distances (i.e.…”

Using environmental variables and soil processes to forecast denitrification potential and nitrous oxide fluxes in coastal plain wetlands across different land uses

“…Controlling factors operate at different spatial (from organisms to ecosystems) and temporal (from hourly to interannual) scales [ Brumme et al , 1999; Groffman et al , 1987; Philippot et al , 2011; Wixon and Balser , 2009]. Proximal factors (e.g., availability of O 2 , C, and NO 3 − ) operate at the organismal and microsite scale, while increasingly distal factors (e.g., water table depth, NF rates, soil type, and land use) affect DNF rates and N 2 O flux at the field and landscape scale [ Groffman , 1991; Groffman et al , 1987].…”