Elsevier

Rhizosphere

Volume 20, December 2021, 100430
Rhizosphere

Rhizosphere: A fascinating paleovegetational and paleoclimatic new intermediary in the Quaternary fluvio-lacustrine set-up of the Purna alluvial basin, central India

https://doi.org/10.1016/j.rhisph.2021.100430Get rights and content

Highlights

  • Rhizosphere is reported.

  • Rhizosphere genesis is deciphered.

  • Signs of C3 & C4 have been found.

Abstract

The rhizosphere, a fascinating vegetational and climatic negotiator, has been discovered and being reported from widespread Quaternary fluvio-lacustrine sediments of the Purna alluvial basin, central India. These organo-sedimentary structures representing diversified morphologies i.e., rounded to sub-rounded, spherical to sub-spherical, small to large surfaced, calcretized bodies of 7–20 cm diameter, are confined principally within the constraints of paleosol horizons belonging to the Early Pleistocene period, uncovered at the lower reaches of the Purna river course. These structures, developed in the lower niches/specialities around plant roots, are formed due to the mutual exercises of soil and fungi. Based on morphological criteria and surficial feature demonstrations, four distinctive morphotypes of the same have been categorized i.e., i) concentric, ii) rimmed, iii) concentric disrupted, and iv) nodular or mottled. The initial two sorts are conceived to be formed by fungi associated with living trees, whereas, last two are created by contagious exercise with rotting plant roots. A model portrayed shows their development in open spaces having a close relationship of plant roots belonging to both forests (C3) and grassland (C4) categories with microbial communities underneath the ground. Consequently, the spaces made by plant roots and microbial community are occupied by the calcium carbonate leached out from the encompassing soils during arid to semi-arid climate.

Introduction

A preliminary investigation regarding the rhizospheres, a rounded to sub-rounded, calcretized, organo-sedimentary structures, is being hypothesized for the first time by reporting the same from the Quaternary fluvio-lacustrine sediments of Purna alluvial basin, central India. Initial studies on concretions and nodules of CaCO3, formed in various sedimentary environments, have been endeavored over a century back to facilitate identification and classification of the same (Barrel, 1913; Kindle, 1923), however, over the recent past years, these structures are to a great extent being investigated for paleoclimatic recreations (Srivastava, 2003; Achyuthana et al., 2007; Jha et al., 2020). Klappa (1980), for the first time, exhaustively reviewed the concretion created structures and authored the term ‘rhizolith’ particularly for the cylindrical bodies of the same and further revealed their five different types based on the shape, structure, and appearance, i.e., i) root molds, ii) root casts, iii) root tubules, iv) rhizocretions, and v) root petrifactions. As per Retallack (2001) and Kraus and Hasiotis (2006), there are two unmistakable varieties of rhizoliths i.e., drab holed root mottles and rhizohalos that are likely delivered by the anaerobic disintegration of buried organic matter. Based on the various approaches, Little and Field (2003) put forward these organo-sedimentary structures, addressed chiefly by rhizoliths and rhizospheres, are the participants of regoliths.

Another term ‘megarhizolith’ was designated by McNamara (1995) for a large calcified root framework facilitating columnar features from the Nambung National Park of Australia. Accreditations with regards to the term ‘mega’ for the large columnar structures exposed at the Canary Island have also been made by Alonso-Zarza et al. (2008). Accordingly, they opined that both rhizospheres and megarhizoliths are the common structures that have been noted from various sedimentary successions across the globe, however, overlooked and misinterpreted to date (Genise et al., 2011). Genise et al. (2011) considered rhizospheres as independent structures, however, certain similarities exist with the rhizoliths including their associated structures and advocated their formation by both living and dead plants especially in parched, semi-arid, and sticky environments. The rhizoliths having frequent occurrences in the basin area, are likewise well investigated from many other river settings of the Indian sub-continent and elsewhere and deciphered as a critical intermediary to comprehend climatic and monsoonal prevalences during the Quaternary period (Achyuthana et al., 2007, 2012; Williams et al., 2009; Agrawal et al., 2014; Bhattacharyya et al., 2014). Nonetheless, purposefully, it can not be precluded that the preservation of rhizospheres in the fluvio-lacustrine sediments of the Indian subcontinent, may be even in entire Asia, has yet not been reported even though these alluvial sediments of the continent witness extensive, multidimensional research works.

The basin being scrutinized has been addressed to issues up to specific limitations in the past to understand climate during the Quaternary period based on certain geological identities closely related with the climatic conditions of the region, i.e., Youngest Toba Tuff (YTT, ca 75 ka) (Srivastava and Singh, 2019a, b, 2020, 2021; Srivastava et al., 2020), vertebrate fossil remains (Thakur et al., 2018) and calcretes (Srivastava and Bansod, 2019; Srivastava et al., 2019, 2021). Nonetheless, still there are various issues in our insight from different perspectives including climatic reproduction. Our present focus on the rhizosphere is primarily due to its first report from India that may be extendable to entire Asia. Accordingly, we, hereby, tried to lay out a fundamental endeavor to comprehend the paleovegetation and paleoclimate in the basin area by detailing the rhizospheres. Present investigation works with its identification, morphological categorizations, lithological affiliations, and sidelong profiling.

Section snippets

Study area

The study area of the Purna basin, limited by 200 100 to 210 410 N and 760 00 to 770 550 E, constitutes a total area of 18,514 km2, of which, 6522 km2 is the alluvial tract distributed in the central part, whereas, the rest is covered with low to moderately and at places, highly dissected, basaltic terrain of the Deccan Trap (Kale, 2010). The alluvial store is predominantly areno-argillaceous, however, rudaceous lithounits are likewise perceptible. Stratigraphically, the succession consists of

Studied localities and their lithological set-ups

To explore the lithological set-ups and sedimentological ascribes, total 13 sites have been examined along the Purna river course viz., Kodori (77041′58″ E, 21016′49″ N), Kural (77040′30″ E, 21013′38″ N), Masod (77039′17″ E, 21013′41″ N), Asegaon (77034′40″ E, 21008′38″ N), Kholapur (77030′18″ E, 21057′14″ N), Parad (77016′02″ E, 20051′10″ N), Wadad (77007′39″ E, 20051′50″ N), Kapileshwar (77006′45″ E, 20051′31″ N), Gandhigram (76059′38″ E, 20052′02″ N), Andura (76051′09″ E, 20053′18″ N),

Macromorphology of rhizospheres

The intend to do macromorphology of rhizospheres was led for their detailed field investigations including preservational attributes, reasonable assortment, categorization, detailing of external features, photodocumentation, etc. These structures are represented by light gray to grayish-brown colored, lithified, solid to compact, calcretized bodies of 7–20 cm diameters. In specific cases, it shows a hole or notch of 3–5 cm diameter on the top. Infrequently, abundant, small-sized rhizoliths or

Lithological association, origin and depositional environment

The paleosols, having the rhizospheres, are represented by reddish-yellowish brown, mottled, massive to faintly laminated beds, constituting together a column of 3–5 m thickness in almost entire basin area (Srivastava et al., 2020) and has been assigned as Lower Pleistocene in age (Tiwari et al., 2010). Traditionally, the paleosols, have been widely portrayed as marker horizons because of having preservations of shreds of evidence related to environmental and climatological cycles along with

Conclusions

The rhizospheres in the Purna alluvial basin have been reported for the first time in the Indian subcontinent that are plentifully preserved in the paleosols of the Quaternary time frame. It has been hypothesized that the same is formed in the specialties created by the exercises between living and decaying plant roots and fungi. Later on, these were calcified with the solutions leached out from the host or encompassing rocks under the arid to semi-arid climate in the basin area. Based on the

Submission declaration and verification

We authors, hereby, declare and verify that the work described has not been published or submitted previously to any journal and has been approved by all authors. If the manuscript is accepted, it will not be published elsewhere in the same form either in English or in any other language including electronically without the written consent of the copyright holder.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work is financially supported by Science and Engineering Research Board (SERB), New Delhi, India in the form of a major research project (SB/S4/ES-692/2013) awarded to AKS. Thanks are extended to Dr. Mangla Bansod for her help in the preparation of line diagrams.

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      They proposed that the plains were covered with mixed C3-C4 plants between 80 and 20 ka duration, however, dramatic increase in C4 vegetation around 45 ka has been noticed as revealed by 13C values of C3 fatty acid. Remains of vegetational activity i.e., rhizospheres and rhizoliths have also been reported from the paleosol horizons developed in entire pre-tephra succession at the Kapileshwar locality of the Purna alluvial basin, Central India (Srivastava and Singh, 2019a, b; Singh and Srivastava, 2021). During further course of field work, the authors have found out preservation of rhizospheres and rhizolith, restricted to the silty-clayey paleosols of 3–5 m thickness, constituting lower part of the pre-tephra succession in entire alluvial basin that acts as a marker horizon (Srivastava et al., 2021).

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    Present address: 3A, Yogiraj Nagar, Camp, Amravati-444602, India.

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