Pathways of biogenically excreted organic matter into soil aggregates

Guhra, Tom; Stolze, Katharina; Totsche, Kai Uwe

doi:10.1016/j.soilbio.2021.108483

Cited by 91 publications

(52 citation statements)

References 258 publications

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“…The composition of exudates can also change with drought (Gargallo‐Garriga et al ., 2018) and specific compounds in root exudates have been associated with complex and diverse roles, e.g. changing the quantity of osmolytes that maintain cell turgor under water stress, developing the soil structure (Ahmed et al ., 2014; Baumert et al ., 2018; Guhra et al ., 2022) and enabling microbial recruitment or selection (van Dam & Bouwmeester, 2016), which may ensure survival during periodic stresses (Huang et al ., 2019). Such changes in the metabolite composition of root exudates under drought could contribute to the increased belowground C allocation we measured here, presenting an intriguing avenue for further research.…”

Section: Discussionmentioning

confidence: 99%

Carbon allocation to root exudates is maintained in mature temperate tree species under drought

et al. 2022

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Carbon (C) exuded via roots is proposed to increase under drought and facilitate important ecosystem functions. However, it is unknown how exudate quantities relate to the total C budget of a drought-stressed tree, that is, how much of net-C assimilation is allocated to exudation at the tree level.We calculated the proportion of daily C assimilation allocated to root exudation during early summer by collecting root exudates from mature Fagus sylvatica and Picea abies exposed to experimental drought, and combining above-and belowground C fluxes with leaf, stem and fine-root surface area.Exudation from individual roots increased exponentially with decreasing soil moisture, with the highest increase at the wilting point. Despite c. 50% reduced C assimilation under drought, exudation from fine-root systems was maintained and trees exuded 1.0% (F. sylvatica) to 2.5% (P. abies) of net C into the rhizosphere, increasing the proportion of C allocation to exudates two-to three-fold. Water-limited P. abies released two-thirds of its exudate C into the surface soil, whereas in droughted F. sylvatica it was only one-third.Across the entire root system, droughted trees maintained exudation similar to controls, suggesting drought-imposed belowground C investment, which could be beneficial for ecosystem resilience.

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Section: Discussionmentioning

confidence: 99%

Carbon allocation to root exudates is maintained in mature temperate tree species under drought

et al. 2022

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“…The interactions between POM and the mineral matrix are highly relevant for the persistence of OM (Witzgall et al, 2021). Biogenically processed OM can modify the surface of soil particles, affecting the formation of aggregates (Guhra et al, 2022). The short‐term turnover of OC induced by fresh input of OM was shown to be related to a range of microbial and root mechanisms (Jilling et al, 2021; Liang et al, 2018) whereas these processes have not been related so far with structural re‐arrangement of soil aggregates.…”

Section: Introductionmentioning

confidence: 99%

Explicit spatial modeling at the pore scale unravels the interplay of soil organic carbon storage and structure dynamics

Zech

Schweizer

Bucka

et al. 2022

Global Change Biology

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The structure of soil aggregates plays an important role for the turnover of particulate organic matter (POM) and vice versa. Analytical approaches usually do not disentangle the continuous re-organization of soil aggregates, caught between disintegration and assemblage. This led to a lack of understanding of the mechanistic relationship between aggregation and organic matter dynamics in soils. In this study, we took advantage of a process-based mechanistic model that describes the interaction between the dynamic (re-)arrangement of soil aggregates, based on dynamic image analysis data of wet-sieved aggregates, to analyze the turnover of POM, and simultaneous soil surface interactions in a spatially and temporally explicit way. Our novel modeling approach enabled us to unravel the temporal development of aggregate sizes, organic carbon (OC) turnover of POM, and surface coverage as affected by soil texture, POM input, and POM decomposition rate comparing a low and high clay soil (18% and 33% clay content). Our results reveal the importance of the dynamic re-arrangement of soil structure on POM-related turnover of OC in soils. Firstly, aggregation was largely determined by the POM input fostering aggregates through additional gluing joints outweighing soil texture at lower decomposition rate, whereas at higher decomposition rate, soil texture had a higher influence leading to larger aggregates in the high clay soil.Secondly, the POM storage increased with clay content, showing that surface interactions may delay the turnover of OC into CO 2 . Thirdly, we observed a structural priming effect in which the increased input of POM induced increased structural re-arrangement stimulating the mineralization of old POM. This work highlights that the dynamic re-arrangement of soil aggregates has important implications for OC turnover and is driven by underlying surface interactions where temporary gluing spots stabilize larger aggregates.

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“…They are considered to be the main binding agents that glue together single particles of primary and secondary minerals to form SMAs and their precursorsthe composite building units, − at the same time, being occluded within soil macroaggregates >250 μm (hereafter “occluded colloids”). Colloidal forms, such as free or occluded colloids, are likely responsive to changes in land-use and/or management, redox potential, and hydraulic conditions, which can either promote aggregation of soil particles or induce disintegration of soil aggregates, thereby changing the form of colloids. However, little is known to which extent the composition and stability of colloid-associated OM changes with the colloidal form.…”

Section: Introductionmentioning

confidence: 99%

Implications of Free and Occluded Fine Colloids for Organic Matter Preservation in Arable Soils

Tang

Siebers

Leinweber

et al. 2022

Environ. Sci. Technol.

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Colloidal organo−mineral associations contribute to soil organic matter (OM) preservation and mainly occur in two forms: (i) as water-dispersible colloids that are potentially mobile (free colloids) and (ii) as building units of soil microaggregates that are occluded inside them (occluded colloids). However, the way in which these two colloidal forms differ in terms of textural characteristics and chemical composition, together with the nature of their associated OM, remains unknown. To fill these knowledge gaps, free and occluded fine colloids <220 nm were isolated from arable soils with comparable organic carbon (C org ) but different clay contents. Free colloids were dispersed in water suspensions during wet-sieving, while occluded colloids were released from water-stable aggregates by sonication. The asymmetric flow fieldflow fractionation analysis on the free and occluded colloids suggested that most of the 0.6−220 nm fine colloidal C org was present in size fractions that showed high abundances of Si, Al, and Fe. The pyrolysis-field ionization mass spectrometry revealed that the free colloids were relatively rich in less decomposed plant-derived OM (i.e., lipids, suberin, and free fatty acids), whereas the occluded colloids generally contained more decomposed and microbial-derived OM (i.e., carbohydrates and amides). In addition, a higher thermal stability of OM in occluded colloids pointed to a higher resistance to further degradation and mineralization of OM in occluded colloids than that in free colloids. This study provides new insights into the characteristics of subsized fractions of fine colloidal organo−mineral associations in soils and explores the impacts of free versus occluded colloidal forms on the composition and stability of colloid-associated OM.

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Pathways of biogenically excreted organic matter into soil aggregates

Cited by 91 publications

References 258 publications

Carbon allocation to root exudates is maintained in mature temperate tree species under drought

Carbon allocation to root exudates is maintained in mature temperate tree species under drought

Explicit spatial modeling at the pore scale unravels the interplay of soil organic carbon storage and structure dynamics

Implications of Free and Occluded Fine Colloids for Organic Matter Preservation in Arable Soils

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