Paddy Soil Development Research Articles

Divergent accumulation of microbial and plant necromass along paddy soil development in a millennium scale

Plant inputs and their subsequent microbial transformations drive the formation and accumulation of soil organic carbon (SOC). Rice paddy is more conducive to SOC accumulation than uplands, primarily because of predominant anaerobic conditions. However, the role of microbes and plants in the buildup of SOC under prolonged rice cultivation has not been well explored in the literature. In a millennium-scale paddy soil chronosequence, we used amino sugars (AS) and lignin phenols (LN) as tracers to investigate microbial and plant-derived necromass changes and evaluated their contributions to SOC accumulation with increasing rice cultivation duration. Across the 1000-year rice cultivation process, AS and LN contents increased with SOC accumulation. Soil pH and salinity are considered to play vital roles in regulating the retention of AS and LN. In contrast to the control of soil enzyme activity on LN accrual (e.g., peroxidase), the microbial biomass and fungi-to-bacteria ratio greatly affected AS accumulation in paddy soil. The components of AS and LN also changed with time, exhibiting a significant accumulation of galactosamine and cinnamyl phenol units in the late stage. Long-term rice cultivation is more conducive to the accumulation of bacterial residues. AS demonstrated a greater contribution to SOC than LN compounds within 100 years, whereas the contribution of LN ultimately exceeded AS in the late stage. Concurrently, we found a higher degree of oxidative lignin degradation in younger soils and reduced degradation with increasing duration of rice paddy cultivation. The accumulation of microbial necromass is more than plant necromass in the early stage, and it is the opposite in the late stage. Our results are critical to understand the formation and sequestration processes of SOC in paddy soils.

An examination of the role of biochar and biochar water-extractable substances on the sorption of ionizable herbicides in rice paddy soils

The application of biochar as a soil amendment can increase concentrations of soil organic matter, especially water-extractable organic substances. Due to their mobility and reactivity, more studies are needed to address the potential impact of biochar water-extractable substances (BWES) on the sorption of herbicides in agricultural soils that are periodically flooded. Two paddy soils (100 and 700 years of paddy soil development), unamended or amended with raw (BC) or washed biochar (BCW), were used to test the influence of BWES on the sorption behavior of the herbicides azimsulfuron (AZ) and penoxsulam (PE). The adsorption of AZ to biochar was much stronger than that to the soils, and it was adsorbed to a much larger extent to BC than to BCW. The depletion of polar groups in the BWES from the washed biochar reduced AZ adsorption but had no effect on PE adsorption. The adsorption of AZ increased when the younger soil (P100) was amended with BC and decreased when it was amended with BCW. In P700, which has lower dissolved organic carbon (DOC) content than P100, the adsorption of AZ increased regardless of whether biochar was raw or washed. The adsorption of PE slightly decreased when P100 was amended with BC or BCW and slightly increased when P700 was amended with BC or BCW. In order to evaluate compositional differences in the biochar and BWES before and after the washing treatment, we performed solid-state 13C NMR spectroscopy of BC and BCW, and high resolution mass spectrometry of BWES. Our observations stress the importance of proper consideration of soil and biochar properties before their incorporation into paddy soils, since biochar may reduce or increase the mobility of AZ and PE depending on soil properties and time of application.

Impact of prolonged rice cultivation on coupling relationship among C, Fe, and Fe-reducing bacteria over a 1000-year paddy soil chronosequence

Long-term soil chronosequences are valuable model systems for investigating pedogenesis and investigating the process of element coupling. Here, we assessed the coupling relationships among C, Fe, and Fe-reducing bacteria (Anaeromyxobacter, Geobacter, and Shewanella) in a paddy soil chronosequence of approximately 50 to 1000 years. Soils of the chronosequence originated from tidal marsh under nearly identical landscape and climate conditions. During 1000 years of rice cultivation, soil organic carbon (SOC) contents in surface horizons (0–20 cm) increased from 10.4 to 21.8 g kg−1. In contrast, total Fe contents declined from 59.6 to 45.1 g kg−1 during the initial 50 years of paddy rice cultivation and then further decreased at a low rate of 0.004 g kg−1 soil year−1 (equivalent to 10 kg ha−1 soil year−1). Organically complexed Fe oxides (Fep) increased from 219 to 642 mg g−1 with increasing time of pedogenesis, but free total Fe oxides (Fed) and amorphous Fe oxides (Feo) declined at early stage of soil development, followed by a slow accumulation at later stages of the chronosequence. Gene copy numbers of Anaeromyxobacter and Geobacter increased from 4.6 × 105 and 3.6 × 106 copies g−1 to 3.8 × 107 and 3.6 × 107 copies g−1 dry soil with continuous paddy rice cultivation, while concurrently Shewanella gene abundance decreased gradually from 4.5 × 105 to 9.3 × 104 copies g−1 dry soil. Using structural equation modeling (SEM), different coupling relationships were observed among C, Fe, and Fe-reducing bacteria for the first 300 years of paddy chronosequence and thereafter. Overall, all Fe-reducing bacteria did not show consistent variation. With the stable microbial community and iron oxide fractions, the microbially mediated dissimilatory coupling relationship between C and Fe becomes simple during 1000 years of paddy soil development.

Tracing organic carbon and microbial community structure in mineralogically different soils exposed to redox fluctuations

Submerged rice cultivation is characterized by redox fluctuations and results in the formation of paddy soils, often accompanied by soil organic carbon (SOC) accumulation. The impact of redox fluctuations and the underlying soil type on the fate of organic carbon (OC) in paddy soils are unknown. Hence, we mimicked paddy soil development in the laboratory by exposing two soil types with contrasting mineral assemblages (Alisol and Andosol) to eight anoxic–oxic cycles over 1 year. Soils regularly received 13C-labeled rice straw. As control we used a second set of samples without straw addition as well as samples under static oxic conditions with and without straw. Headspaces were analyzed for carbon dioxide and methane as well as their δ13C signatures, whereas soil solutions were analyzed for redox potential, pH, dissolved iron, and dissolved organic carbon (DOC and DO13C). At the end of the experiment, when eight redox cycles were completed, mineral-associated organic matter (MOM) was isolated by density fractionation and characterized for δ13C, non-cellulosic carbohydrates, and lignin-derived phenols. Moreover, changes in the soil’s microbial community structure were measured. For both soil types, headspace data confirmed less respiration in straw-amended soils with redox fluctuation than in those under static oxic conditions. The δ13C data revealed that, irrespective of soil type, straw carbon allocation into MOM was larger in soils with redox fluctuation than in those with static oxic conditions. A net increase in MOM after the one-year incubation, however, was only observed in the respective Andosol, probably due to abundant reactive minerals capable of OC uptake. In the Alisol, straw OC most likely exchanged initial MOM. A potential for lignin accumulation in the MOM of soils incubated with straw and redox fluctuation was observed for both soil types. Lignin and carbohydrates suggest a plant origin of MOM formed under redox fluctuation. The initially similar bacterial community composition of the Alisol and Andosol changed differently under redox fluctuation. The stronger change in the Alisol indicates less protective microbial habitats. In summary, the overall turnover of straw OC in soils under redox fluctuation seems to be independent of soil type, while net accumulation of SOC as well as the evolution of the bacterial community structure may in part depend on soil type, suggesting an impact of the soil’s mineral composition.

T4-type viruses: Important impacts on shaping bacterial community along a chronosequence of 2000-year old paddy soils

There is increasing evidence to suggest that viruses may influence the succession of individual populations of microorganisms, biogeochemical cycles and, ultimately, microbial community structure. However, it is still not well understood if T4-type viruses can affect the bacterial communities of terrestrial ecosystems. Here, we report an investigation of the impact of T4-type phage and bottom-up (environmental factors) controls on bacterial community structures along a 2000-year paddy soil chronosequence. T4-type myoviral and bacterial communities were evaluated by clone sequencing and high-throughput sequencing of the gene encoding the major capsid protein (g23) and 16S ribosomal DNA, respectively. Long-term (centurial/millennial) anthropogenic managements of paddy soils resulted in an accumulation of nutrients and soil acidification. Significant shifts in soil bacterial and phage communities were detected during the development of paddy soils at millennial time scales. The Mantel test and variation partitioning analysis (VPA) suggested that the profile of bacterial community composition was strongly affected by both T4-type phage and environmental variables. Network analysis between phage and bacterial taxa indicated that six bacterial families were implicated as potential hosts of T4-type phages. These results suggest that phage lysis is important in shaping bacterial communities in the soil environment.

Effects of human activities on pedogenesis and iron dynamics in paddy soils developed on Quaternary red clays

A paddy soil chronosequence consisting of four profiles derived from Quaternary red clay (QRC) in Southern China with cultivation history from 0 to 300 years was studied to understand the underlying mechanisms and processes controlling the centennial scale Fe evolution during anthropedogenesis. We evaluated the chronosequencial changes in depth distribution of Fe oxides and Fe isotopic compositions. Results showed that paddy soil development on QRC over a centennial time scale caused increasing profile differentiation of Fe oxides and measurable Fe isotope fractionation. Total Fe and oxide bound Fe as well as the maximum Fe illuviation depth decreased as paddy soils age, leading to significant differences in morphological properties between paddy and non-paddy soils with the same parent material. Selective extractions showed that the weakly-bound, oxide-bound and silicate bound Fe corresponded to 4–18%, 49–81%, and 11–40% of the total Fe, respectively, and these proportions varied with both time and depth due to the redox-related Fe transformation and redistribution. δ56Fe values in the studied paddy soil chronosequence ranged from 0.05‰ to 0.26‰ and exhibited a strong negative correlation with the logarithm of total Fe concentrations, suggesting mass-dependent Fe isotope fractionation occurred as a result of the preferential removal of lighter Fe isotopes during Fe leaching loss under the predominant reducing conditions. However, the Fe isotopic ratio of a specific paddy soil horizon was a result of a complex interaction of different processes, which were summarized and interpreted in our proposed conceptual model of Fe evolution in terraced paddy soils. Further investigations of Fe isotope signatures in the soil-plant-water system with a combination of laboratory simulation and prediction of Fe isotope fractionation under different pedogenic processes are needed to evaluate the relative contribution of multiple processes to Fe isotope fractionation during anthropedogenesis of paddy soils.

Phases and rates of iron and magnetism changes during paddy soil development on calcareous marine sediment and acid Quaternary red-clay

Dynamic changes in Fe oxides and magnetic properties during natural pedogenesis are well documented, but variations and controls of Fe and magnetism changes during anthropedogenesis of paddy soils strongly affected by human activities remain poorly understood. We investigated temporal changes in different Fe pools and magnetic parameters in soil profiles from two contrasting paddy soil chronosequences developed on calcareous marine sediment and acid Quaternary red clay in Southern China to understand the directions, phases and rates of Fe and magnetism evolution in Anthrosols. Results showed that paddy soil evolution under the influence of artificial submergence and drainage caused changes in soil moisture regimes and redox conditions with both time and depth that controlled Fe transport and redistribution, leading to increasing profile differentiation of Fe oxides, rapid decrease of magnetic parameters, and formation of diagnostic horizons and features, irrespective of the different parent materials. However, the initial parent material characteristics (pH, Fe content and composition, weathering degree and landscape positions) exerted a strong influence on the rates and trajectories of Fe oxides evolution as well as the phases and rates of magnetism changes. This influence diminished with time as prolonged rice cultivation drove paddy soil evolving to common pedogenic features.

Bacterial succession along a long-term chronosequence of paddy soil in the Yangtze River Delta, China

Conversion of tidal wetlands into paddy soils is an ancient and prevalent agricultural practice to meet increasing demand of food in the Yangtze River Delta of China, a coastal region where paddy soils originated. However, the impacts of tidal wetland reclamation and continuous rice cultivation at long time scales on soil bacterial communities remains poorly understood. In this study, we investigated temporal dynamics of bacterial communities using 16S rRNA gene pyrosequencing to delineate the patterns and drivers of soil bacterial succession along a long-term (2000 years) chronosequence of paddy field since reclamation from tidal wetlands. The results exhibited orderly changes in soil physicochemical characteristics and bacterial community composition with increasing rice cultivation time, indicating the occurrence of paddy soil development and bacterial succession since reclamation from tidal wetlands. Soil bacterial diversity significantly increased after reclamation of tidal wetlands. Succession of bacterial community composition was primarily linked with significant decrease in the relative abundances of Gammaproteobacteria and Planctomycetes and increase in those of Alphaproteobacteria and Firmicutes. Further analysis showed that long-term rice cultivation led to the enrichment of certain populations such as Rhodospirillaceae (within the class Alphaproteobacteria) and Clostridiaceae (within the phylum Firmicutes), which are potentially beneficial to higher rice yields. Canonical correspondence analysis indicated that at the time scale of millennia, the shift of bacterial community structure was mainly driven by the changes of soil physicochemical properties, especially cation exchange capacity and pH during paddy soil development. Overall, we demonstrate an orderly shift of soil bacterial communities towards higher productivity along with a 2000-year development of paddy soils after the tidal wetland reclamation, which was primarily associated with soil physicochemical alterations with time, and suggest that such chronosequence of paddy soils can serve as a test bed to delineate the relationship between microbial community and soil functions, particularly crop productivity.

Accelerated soil formation due to paddy management on marshlands (Zhejiang Province, China)

Inundation of paddy soils for submerged rice production strongly impacts soil formation. Here we used chronosequences with up to 2000years of cultivation history to compare soil formation in non-inundated (non-paddy) cropping systems with the formation of soils used for paddy rice production. This approach allowed us to identify the influence of agricultural management at different stages of pedogenesis.Soil samples were taken from two chronosequences derived from uniform parent material in the coastal region of the Zhejiang Province (P.R. China). One chronosequence consisted of paddy soils of different ages (50–2000years), characterized by a yearly cropping sequence of rice cultivation under flooded conditions alternated with a non-inundated crop. The adjacent non-inundated (non-paddy) chronosequence was exclusively used for non-inundated crop production for 50–700years. Lipid biomarkers revealed origin and homogeneity of the original coastal sediments and enabled the reconstruction of a consistent land use history for both chronosequences.The chronological development of soil properties and horizons suggested that the formation of paddy soils can be subdivided into three phases. The initial phase of paddy soil development takes only a few decades and is dominated by desalinization and formation of a compacted plow pan, leading from Fluvisols to Anthraquic Cambisols. During the next centuries (second phase), the differentiation between paddy and non-paddy management becomes increasingly obvious in terms of accelerated carbonate losses and constantly increasing organic carbon concentrations in paddy topsoils. In the third stage of paddy soil development (≥700years), a (trans-)formation and redistribution of oxides is accompanied by clearly visible hydromorphic patterns in paddy subsoils, thus promoting further development from Cambisols to Hydragric Anthrosols. To account for the underlying processes we suggest modifying the depth and mottling criteria for the definitions of anthraquic and hydragric soil horizons in the classification of the World Reference Base for Soil Resources. The non-paddy chronosequence was characterized by a low degree of soil development in which decalcification-related processes dominated throughout 700years of soil formation. Hence, soil formation under paddy management was accelerated relative to that under dryland cropping, even though the 2000-year-old paddy soils lacked evidence of an advanced stage of silicate weathering, formation of pedogenic clay minerals, or clay migration.

Pedogenic Transformation of Phosphorus during Paddy Soil Development on Calcareous and Acid Parent Materials

Soil Sci. Soc. Am. J. 77:2078–2088 doi:10.2136/sssaj2013.01.0033 Received 23 Jan. 2013. *Corresponding author: (glzhang@issas.ac.cn). © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. Pedogenic Transformation of Phosphorus during Paddy Soil Development on Calcareous and Acid Parent Materials Pedology

Management-induced organic carbon accumulation in paddy soils: The role of organo-mineral associations

Iron (Fe) oxides strongly interact with organic matter in soil and play an important role in the stabilization of organic matter. These processes are often influenced by soil cultivation, including tillage, crop rotation and irrigation. We assessed the effect of Fe oxides on organic carbon (OC) accumulation during the development of soils used for paddy rice production in comparison to non-irrigated cropping systems. Soil samples were taken from two chronosequences derived from uniform parent material in the Zhejiang Province (PR China). Bulk soils and soil fractions were analyzed for OC concentrations, soil mineralogy and soil organic matter (SOM) composition was determined by solid-state 13C NMR spectroscopy. Paddy soils were characterized by increasing OC concentrations, from 18mgg−1 to 30mgg−1, during 2000years of rice cultivation, but OC concentrations of non-paddy soils were low in all age classes (11mgg−1). SOM composition revealed from Solid-state 13C NMR spectroscopy did not change during pedogenesis in either chronosequence. Selective enrichment of lignin-derived compounds, caused by long-term paddy rice management, could not be confirmed by the present study. The management of paddy soils creates an environment of Fe oxide formation which was different to those in non-paddy soils. Paddy soils are dominated by poorly crystalline Fe oxides (Feo) and significantly lower content of crystalline Fe oxides (Fed−Feo). This was in contrast to non-paddy soils, which are characterized by high proportions of crystalline Fe oxides. The paddy-specific Fe oxide composition was effective after only 50years of soil development and the proportion Fe oxides did not alter during further pedogenesis. This chronosequence study revealed that the potential for OC accumulation was higher in paddy versus non-paddy soils and was already reached at earliest stages of paddy soil development. Changes in paddy soil management associated with redox cycle changes will not only affect Fe oxide composition of paddy soils but most probably also OC storage potential.

Accumulation of nitrogen and microbial residues during 2000 years of rice paddy and non-paddy soil development in the Yangtze River Delta, China

Lowland rice paddy soils may accumulate significant amounts of organic matter. Our aim was to investigate the role of prolonged paddy management on the nitrogen (N) status of the soils, and to elucidate the contribution of bacteria and fungi to long-term N accumulation processes. For this purpose, we sampled a chronosequence of 0–2000 years of rice cropping with adjacent non-paddy systems in the Bay of Hangzhou, China. The samples were analyzed for bulk density, total, mineral and microbial N (Nmic), and amino sugars as markers for microbial residues. The results showed that during the first 100 years of land embankment, both paddy and non-paddy soils accumulated N at a rate of up to 61 and 77 kg ha−1 per annum, reaching steady-state conditions after 110–172 years, respectively. Final N stocks in paddy fields exceeded those of the non-paddies by a factor of 1.3. The contribution of amino sugars to total N increased to a maximum of 34 g N kg−1 N in both land-use systems, highlighting a significant accumulation of N in microbial residues of the surface soils. Correspondingly, the ratio of Nmic to microbial residue-N decreased to a constant value. In the paddy subsoils, we found that bacterial residues particularly contributed to the pool of microbial residue-N. Nevertheless, the absolute contents of amino sugars in paddy subsoils decreased during the last 1700 years of the chronosequence. We conclude that under paddy cultivation, soil microorganisms may accumulate parts of this N in their residues despite low overall N availability. However, this N accumulation is limited to initial stages of paddy soil development and restricted to the surface horizons, thus challenging its sustainability with future land-use changes.

Ancient paddy soils from the Neolithic age in China’s Yangtze River Delta

Identifying prehistoric irrigated rice fields and characterizing the beginning of paddy soil development are important for a better understanding of human development and agricultural history. In 2003, paddy soils and irrigated rice fields buried at a depth of 100-130 cm were excavated at Chuo-dun-shan in the Yangtze River Delta, close to Suzhou, China. The fields of sizes between 1.4 and 16 m(2) were surrounded with ridges that were connected to ditches/ponds via outlets to control the water level within the fields. Many carbonized and partly carbonized rice grains with an age of 3,903 B.C. (measured (14)C age 5,129+/-45 a BP) were recovered. The surface layers of these buried paddy fields showed a high content of soil organic matter and a considerable high density of rice opals. The latter were identified to derive from Oryza spp. Solid-state (13)C nuclear magnetic resonance spectroscopy revealed aromatic carbon (C) as the predominant organic C form in the fossil surface layer. This is expected, if the major source represents burnt rice and straw. In summary, our data are in agreement with new evidences indicating that in China, paddy soils and irrigated rice cultivation were initiated and developed more than 6,000 years ago.