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Biswas C, Ferdous J, Sarker RR, Islam KR, Jahangir MMR. Forty-two years impact of chemical fertilization on soil phosphorus partition and distribution under rice-based cropping systems. PLoS One 2024; 19:e0305097. [PMID: 38857213 PMCID: PMC11164328 DOI: 10.1371/journal.pone.0305097] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2023] [Accepted: 05/23/2024] [Indexed: 06/12/2024] Open
Abstract
Understanding of soil phosphorus (P) transformation is crucial to minimize its edge-of-field loss associated with ecosystem disservices. A sequential chemical extraction procedure was used to assess the impact (42 years) of organic and chemical fertilizations on soil P partition and distribution under subtropical rice based cropping systems. Experimental treatments were control, N, NP, NK, NS, NZn, NPK, NSZn, NPKSZn, and N+FYM (farmyard manure). Composite soils were collected from 0-5, 20-25 and 40-45 cm depths, extracted, and analyzed for soluble P, NaHCO3-P (inorganic and organic), NaOH-P (inorganic and organic), acid soluble (H2SO4), and residual P fractions. The NPKSZn significantly increased the concentration of soil inorganic P compared to other treatments. When FYM was applied together with N fertilizer, the organic P concentration increased, which was statistically identical to NPKSZn and NPK treatments. While the labile (NaHCO3-Pi, NaOH-Po), residual, and total P concentrations were stratified at 0-5 cm depth, the concentration of NaHCO3-Po, NaOH-Pi, and acidic P fractions increased with soil depth. The soluble, NaHCO3 (Pi and Po), NaOH-Pi and NaOH-Po, acidic, and residual P fractions constituted about 0.4, 6.6, 1.7, 21.3, 37.7, and 8.3%, respectively, of the total P. A higher concentration of the labile P at the surface soil indicated that the impact of chemical fertilization stratified the available P for plant uptake or susceptible to edge-of-field loss. The NPKSZn and N+FYM both had higher NaHCO3-Po and NaOH-Po concentrations within 40-45 cm and 0-25 cm depths, suggesting that N+FYM could promote the transformation of non-labile P into labile P pool, by reducing P fixation by soil and transport them at 20-45 cm depth. It is concluded that long-term fertilization increased the concentration of P pools especially labile P by saturating the soil adsorption sites especially in surface soil.
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Affiliation(s)
- C. Biswas
- Department of Soil Science, Bangladesh Agricultural University, Mymensingh, Bangladesh
| | - J. Ferdous
- Department of Soil Science, Bangladesh Agricultural University, Mymensingh, Bangladesh
| | - R. R. Sarker
- Department of Soil Science, Bangladesh Agricultural University, Mymensingh, Bangladesh
- Soil science Division, Bangladesh Institute of Nuclear Agriculture, Mymensingh, Bangladesh
| | - K. R. Islam
- College of Food, Agricultural and Environmental sciences, The Ohio State University, Columbus, Ohio, United States of America
| | - M. M. R. Jahangir
- Department of Soil Science, Bangladesh Agricultural University, Mymensingh, Bangladesh
- Liebig Centre for Agroecology and Climate Impact Research, Justus Liebig University, Giessen, Germany
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2
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Chaudhary A, Venkatramanan V, Kumar Mishra A, Sharma S. Agronomic and Environmental Determinants of Direct Seeded Rice in South Asia. CIRCULAR ECONOMY AND SUSTAINABILITY 2022; 3:253-290. [PMID: 35573660 PMCID: PMC9075927 DOI: 10.1007/s43615-022-00173-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/25/2021] [Accepted: 04/08/2022] [Indexed: 01/16/2023]
Abstract
Rice (Oryza sativa L.) is the staple food of more than 50% of the world's population. Manual puddled transplanted rice (PTR) system is still the predominant method of rice establishment. However, due to declining water tables, increasing water scarcity, water, labor- and energy-intensive nature of PTR, high labor wages, adverse effects of puddling on soil health and succeeding crops, and high methane emissions, this production system is becoming less profitable. These factors trigger the need for an alternative crop establishment method. The direct-seeded rice (DSR) technique is gaining popularity because of its low input demand compared to PTR. It is done by sowing pre-germinated seeds in puddled soil (wet-DSR), standing water (water seeding), or dry seeding on a prepared seedbed (dry-DSR). DSR requires less water and labor (12-35%), reduces methane emissions (10-90%), improves soil physical properties, involves less drudgery and production cost (US$9-125 per hectare), and gives comparable yields. Upgraded short-duration and high-yielding varieties and efficient nutrient, weed, and resource management techniques encouraged the farmers to switch to DSR culture. However, several constraints are associated with this shift: more weeds, the emergence of weedy rice, herbicide resistance, nitrous oxide emissions, nutrient disorders, primarily N and micro-nutrients, and an increase in soil-borne pathogens lodging etc. These issues can be overcome if proper weed, water, and fertilizer management strategies are adopted. Techniques like stale bed technique, mulching, crop rotation, Sesbania co-culture, seed priming, pre-emergence and post-emergence spray, and a systematic weed monitoring program will help reduce weeds. Chemical to biotechnological methods like herbicide-resistant rice varieties and more competitive allelopathic varieties will be required for sustainable rice production. In addition, strategies like nitrification inhibitors and deep urea placement can be used to reduce N2O emissions. Developing site and soil-specific integrated packages will help in the broader adoption of DSR and reduce the environmental footprint of PTR. The present paper aims to identify the gaps and develop the best-bet agronomic practices and develop an integrated package of technologies for DSR, keeping in mind the advantages and constraints associated with DSR, and suggest some prospects. Eco-friendly, cost-effective DSR package offers sustainable rice production systems with fewer resources and low emissions. Graphical abstract
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Affiliation(s)
- Anjali Chaudhary
- School of Interdisciplinary and Transdisciplinary Studies (SOITS), Indira Gandhi National Open University (IGNOU), New Delhi, 110068 India
| | - V. Venkatramanan
- School of Interdisciplinary and Transdisciplinary Studies (SOITS), Indira Gandhi National Open University (IGNOU), New Delhi, 110068 India
| | - Ajay Kumar Mishra
- International Rice Research Institute South Asia Regional Centre (ISARC), Varanasi, 221106 Uttar Pradesh India
| | - Sheetal Sharma
- International Rice Research Institute South Asia Regional Centre (ISARC), Varanasi, 221106 Uttar Pradesh India
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3
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Kirk GJD, Manwaring HR, Ueda Y, Semwal VK, Wissuwa M. Below-ground plant-soil interactions affecting adaptations of rice to iron toxicity. PLANT, CELL & ENVIRONMENT 2022; 45:705-718. [PMID: 34628670 DOI: 10.1111/pce.14199] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2021] [Revised: 08/11/2021] [Accepted: 08/13/2021] [Indexed: 06/13/2023]
Abstract
Iron toxicity is a major constraint to rice production, particularly in highly weathered soils of inland valleys in sub-Saharan Africa where the rice growing area is rapidly expanding. There is a wide variation in tolerance of iron toxicity in the rice germplasm. However, the introgression of tolerance traits into high-yielding germplasm has been slow owing to the complexity of the tolerance mechanisms and large genotype-by-environment effects. We review current understanding of tolerance mechanisms, particularly those involving below-ground plant-soil interactions. Until now these have been less studied than above-ground mechanisms. We cover processes in the rhizosphere linked to exclusion of toxic ferrous iron by oxidation, and resulting effects on the mobility of nutrient ions. We also cover the molecular physiology of below-ground processes controlling iron retention in roots and root-shoot transport, and also plant iron sensing. We conclude that future breeding programmes should be based on well-characterized molecular markers for iron toxicity tolerance traits. To successfully identify such markers, the complex tolerance response should be broken down into its components based on understanding of tolerance mechanisms, and tailored screening methods should be developed for individual mechanisms.
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Affiliation(s)
- Guy J D Kirk
- School of Water, Energy and Environment, Cranfield University, Cranfield, UK
| | - Hanna R Manwaring
- School of Water, Energy and Environment, Cranfield University, Cranfield, UK
| | - Yoshiaki Ueda
- Crop, Livestock and Environment Division, Japan International Research Center for Agricultural Sciences, Tsukuba, Japan
| | | | - Matthias Wissuwa
- Crop, Livestock and Environment Division, Japan International Research Center for Agricultural Sciences, Tsukuba, Japan
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4
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Wu Z, Wang S, Ji N. Distribution character of localized iron microniche in lake sediment microzone revealed by chemical image. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2019; 26:35704-35716. [PMID: 31701417 DOI: 10.1007/s11356-019-06219-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2018] [Accepted: 08/16/2019] [Indexed: 06/10/2023]
Abstract
DGT (diffusive gradients in thin films) technique and LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry) for heterogeneous distribution of the soluble labile iron (Fe) at submillimeter resolution in lake sediment porewater are reported. The soluble labile Fe species include ion and labile organic complexes. The chemical images in two dimensions (2D) for DGT concentration of Fe (CDGT(Fe)) are investigated for Fe remobilization character. There are 902 CDGT(Fe) values between 1000 and 2000 μg L-1, 463 values between 2000 and 3000 μg L-1, and 112 values over 3000 μg L-1 in all chemical maps. Based on the linear correlation relationships between CDGT (Fe) and total Fe (TFe), total organic carbon (TOC), acid-volatile sulfide (AVS), Eh, concentrations of the soluble reactive phosphorus (P) (SRP), and soluble labile trace metals (Zn, Cu, Pb, and Zn) in a vertical 1D profile of sediment or porewater, Fe release mechanisms are mainly due to the reductive Fe release from iron oxyhydroxides and the decomposition of organic matter in algae biomass and deep sediment layer. It can be used to explain the formation mechanisms of Fe microniches in chemical maps with heterogeneous character to a great extent. CDGT(Fe) peak flux in the center of Fe microniche and the low CDGT (Fe) at the edge of a microniche are due to the formation of the insoluble iron sulfide and the abundant acid-volatile sulfide (AVS) in sediment. The verified co-remobilization of the soluble labile Fe and trace metals or SRP in sediment porewater can be used to predict their simultaneous release from Fe microniches with the large CDGT (Fe) peaks. The different kinds of Fe microniche zones and hot spots from sediment/water interface (SWI) to deep sediment correspond to the formation mechanisms of microniches mentioned above. Moreover, some narrow Fe microniche zones with the large CDGT (Fe) across chemical maps are due to the desorption of Fe(II) from the freshly formed oxide on Myriophyllum verticiilatur roots, which are located at sites of microniche zones.
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Affiliation(s)
- Zhihao Wu
- National Engineering Laboratory for Lake Pollution Control and Ecological Restoration, Chinese Research Academy of Environmental Sciences (CRAES), Beijing, 100012, China
- Yunnan Key Laboratory of Pollution Process and Management of Plateau Lake-Watershed, Kunming, 650034, Yunnan Province, China
| | - Shengrui Wang
- National Engineering Laboratory for Lake Pollution Control and Ecological Restoration, Chinese Research Academy of Environmental Sciences (CRAES), Beijing, 100012, China.
- Yunnan Key Laboratory of Pollution Process and Management of Plateau Lake-Watershed, Kunming, 650034, Yunnan Province, China.
- College of Water Sciences, Beijing Normal University, Beijing, 100875, China.
| | - Ningning Ji
- National Engineering Laboratory for Lake Pollution Control and Ecological Restoration, Chinese Research Academy of Environmental Sciences (CRAES), Beijing, 100012, China
- College of Water Sciences, Beijing Normal University, Beijing, 100875, China
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5
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Xu M, Gao P, Yang Z, Su L, Wu J, Yang G, Zhang X, Ma J, Peng H, Xiao Y. Biochar impacts on phosphorus cycling in rice ecosystem. CHEMOSPHERE 2019; 225:311-319. [PMID: 30884292 DOI: 10.1016/j.chemosphere.2019.03.069] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/07/2019] [Revised: 03/03/2019] [Accepted: 03/11/2019] [Indexed: 06/09/2023]
Abstract
Biochar can affect the phosphorus (P) cycle in the rice ecosystem through various pathways. Pot experiments were conducted to investigate the risk of P contamination and the P supply rate to crops with the application of maize straw-derived biochar (BM) and P fertilizer. The biochar increased 18.3% and 8.45% total phosphorus (TP) concentration in the low-P level and high-P level soils, respectively. The addition of biochar increased the phosphorus activation coefficient (PAC) by 9.00% at low-P levels, while the PAC was reduced by 10.4% at high-P levels. The results suggested that biochar could serve as either a source or a sink for P. The P concentration in the dithionite-citrate-bicarbonate (DCB) extracts on the root surfaces in biochar-treated soils increased by 467.1% and 46.1% in the low-P level and high-P level soils, respectively. It may cause by the acidification of soils near the root and the increase in Fe plaque. The results also showed the addition of biochar increased the DCB-P concentration and subsequently promoted rice growth. The biochar additions enhanced bacterial community richness and diversity, while the P supplementations inhibited bacterial growth. Redundancy analysis (RDA) showed that available nitrogen (AN), Fe-P, Ca-P, P uptake and, DCB extracted Fe (DCB-Fe) were significantly correlated with microbial community composition and explained 46.8%, 37.1%, 38.0%, 37.5% and 36.7% of the total community variability, respectively. This study provided evidence that biochar might affect the P cycle by impacting the microbial community composition and the Fe-reducing processes in the rice ecosystem.
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Affiliation(s)
- Min Xu
- College of Environmental Science, Sichuan Agricultural University, Chengdu, 611130, China
| | - Peng Gao
- Soil and Water Sciences Department, University of Florida, Gainesville, FL, 32611, USA
| | - Zhijun Yang
- College of Environmental Science, Sichuan Agricultural University, Chengdu, 611130, China
| | - Linlin Su
- College of Environmental Science, Sichuan Agricultural University, Chengdu, 611130, China
| | - Jun Wu
- College of Environmental Science, Sichuan Agricultural University, Chengdu, 611130, China.
| | - Gang Yang
- College of Environmental Science, Sichuan Agricultural University, Chengdu, 611130, China
| | - Xiaohong Zhang
- College of Environmental Science, Sichuan Agricultural University, Chengdu, 611130, China
| | - Jing Ma
- College of Water Conservancy and Hydropower Engineering, Sichuan Agricultural University, Yaan, 625014, China
| | - Hong Peng
- College of Environmental Science, Sichuan Agricultural University, Chengdu, 611130, China
| | - Yinlong Xiao
- College of Environmental Science, Sichuan Agricultural University, Chengdu, 611130, China
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6
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Dissanayaka DMSB, Plaxton WC, Lambers H, Siebers M, Marambe B, Wasaki J. Molecular mechanisms underpinning phosphorus-use efficiency in rice. PLANT, CELL & ENVIRONMENT 2018; 41:1483-1496. [PMID: 29520969 DOI: 10.1111/pce.13191] [Citation(s) in RCA: 43] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2017] [Revised: 02/27/2018] [Accepted: 03/03/2018] [Indexed: 05/18/2023]
Abstract
Orthophosphate (H2 PO4- , Pi) is an essential macronutrient integral to energy metabolism as well as a component of membrane lipids, nucleic acids, including ribosomal RNA, and therefore essential for protein synthesis. The Pi concentration in the solution of most soils worldwide is usually far too low for maximum growth of crops, including rice. This has prompted the massive use of inefficient, polluting, and nonrenewable phosphorus (P) fertilizers in agriculture. We urgently need alternative and more sustainable approaches to decrease agriculture's dependence on Pi fertilizers. These include manipulating crops by (a) enhancing the ability of their roots to acquire limiting Pi from the soil (i.e. increased P-acquisition efficiency) and/or (b) increasing the total biomass/yield produced per molecule of Pi acquired from the soil (i.e. increased P-use efficiency). Improved P-use efficiency may be achieved by producing high-yielding plants with lower P concentrations or by improving the remobilization of acquired P within the plant so as to maximize growth and biomass allocation to developing organs. Membrane lipid remodelling coupled with hydrolysis of RNA and smaller P-esters in senescing organs fuels P remobilization in rice, the world's most important cereal crop.
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Affiliation(s)
- D M S B Dissanayaka
- Graduate School of Biosphere Science, Hiroshima University, Kagamiyama 1-7-1, Higashi-, Hiroshima, 739-8521, Japan
- Department of Crop Science, Faculty of Agriculture, University of Peradeniya, Peradeniya, 20400, Sri Lanka
| | - William C Plaxton
- Department of Biology and Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, K7L3N6, Canada
| | - Hans Lambers
- School of Biological Sciences and Institute of Agriculture, The University of Western Australia, 35 Stirling Highway, Crawley (Perth), Western Australia, 6009, Australia
| | - Meike Siebers
- Max-Planck-Institute for Plant Breeding Research, Carl-von-Linné-Weg 10, 50829, Cologne, Germany
| | - Buddhi Marambe
- Department of Crop Science, Faculty of Agriculture, University of Peradeniya, Peradeniya, 20400, Sri Lanka
| | - Jun Wasaki
- Graduate School of Biosphere Science, Hiroshima University, Kagamiyama 1-7-1, Higashi-, Hiroshima, 739-8521, Japan
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7
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Shehata HR, Dumigan C, Watts S, Raizada MN. An endophytic microbe from an unusual volcanic swamp corn seeks and inhabits root hair cells to extract rock phosphate. Sci Rep 2017; 7:13479. [PMID: 29044186 PMCID: PMC5647395 DOI: 10.1038/s41598-017-14080-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2017] [Accepted: 10/05/2017] [Indexed: 12/14/2022] Open
Abstract
In the animal microbiome, localization of microbes to specific cell types is well established, but there are few such examples within the plant microbiome which includes endophytes. Endophytes are non-pathogenic microbes that inhabit plants. Root hairs are single cells, equivalent to the nutrient-absorbing intestinal microvilli of animals, used by plants to increase the root surface area for nutrient extraction from soil including phosphorus (P). There has been significant interest in the microbiome of intestinal microvilli but less is known about the root hair microbiome. Here we describe a bacterial endophyte (3F11) from Zea nicaraguensis, a wild corn discovered in a Nicaraguan swamp above rock-P lava flowing from the San Cristobal volcano. Rock-P is insoluble and a major challenge for plants. Following seed coating and germination on insoluble-P, the endophyte colonized epidermal surfaces, ultimately colonizing root hairs intracellularly. The endophyte promoted root hair growth and secreted acids to solubilize rock-P for uptake by a larger root hair surface. The most interesting observation was that a seed-coated endophyte targeted and colonized a critical cell type, root hair cells, consistent with earlier studies. The endophyte maintained its targeting ability in two evolutionary divergent hosts, suggesting that the host recognition machinery is conserved.
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Affiliation(s)
- Hanan R Shehata
- Department of Plant Agriculture, University of Guelph, Guelph, ON, N1G 2W1, Canada
- Department of Microbiology, School of Pharmacy, Mansoura University, Mansoura, Egypt
| | - Christopher Dumigan
- Department of Plant Agriculture, University of Guelph, Guelph, ON, N1G 2W1, Canada
| | - Sophia Watts
- Department of Plant Agriculture, University of Guelph, Guelph, ON, N1G 2W1, Canada
| | - Manish N Raizada
- Department of Plant Agriculture, University of Guelph, Guelph, ON, N1G 2W1, Canada.
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8
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9
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10
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Cheng H, Wang YS, Fei J, Jiang ZY, Ye ZH. Differences in root aeration, iron plaque formation and waterlogging tolerance in six mangroves along a continues tidal gradient. ECOTOXICOLOGY (LONDON, ENGLAND) 2015; 24:1659-1667. [PMID: 25956983 DOI: 10.1007/s10646-015-1474-0] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 04/28/2015] [Indexed: 06/04/2023]
Abstract
Mangrove is a special coastal forest along tropical and subtropical intertidal shores. However, how mangroves adapt to tidal flooding and the mechanisms involved in mangrove zonation are still poorly understood. In this study, a pot trial with different tide treatments was conducted to investigate the differences in root anatomy, porosity, radial oxygen loss, iron plaque formation and waterlogging tolerance among six mangroves along a continuous tidal gradient. The index of waterlogging tolerance illustrated that Sonneratia apetala possessed the highest index, followed by Aeguceras corniculatum/Kandelia, Rhizophora stylosa, Heritiera littorlis and Thespesia populnea. Waterlogging tolerances of the mangroves were found to be positively correlated with their root porosity, radial oxygen loss and iron plaque formation. Waterlogging-sensitive species such as landward semi-mangroves exhibited small root porosity and ROL, while waterlogging-tolerant species such as seaward pioneer and rhizophoraceous mangroves exhibited extensive porosity, ROL and iron plaque formation. Nevertheless, grater root porosity and iron plaque formation were detected in permanent waterlogged plants when compared to drained plants. In conclusion, The present study proposes a structural adaptive strategy to tidal flooding in mangroves, such that the mangroves with higher root porosity, ROL and iron plaque appeared to exhibit higher waterlogging tolerance and adaptability in anaerobic foreshores.
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Affiliation(s)
- Hao Cheng
- State Key Laboratory of Tropical Oceanography and Daya Bay Marine Biology Research Station, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, 510301, China
| | - You-Shao Wang
- State Key Laboratory of Tropical Oceanography and Daya Bay Marine Biology Research Station, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, 510301, China.
| | - Jiao Fei
- State Key Laboratory of Tropical Oceanography and Daya Bay Marine Biology Research Station, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, 510301, China
| | - Zhao-Yu Jiang
- State Key Laboratory of Tropical Oceanography and Daya Bay Marine Biology Research Station, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, 510301, China
| | - Zhi-Hong Ye
- State Key Laboratory for Bio-control, School of Life Sciences, Sun Yat-sen University, Guangzhou, 510006, China
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11
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Williams PN, Santner J, Larsen M, Lehto N, Oburger E, Wenzel W, Glud RN, Davison W, Zhang H. Localized flux maxima of arsenic, lead, and iron around root apices in flooded lowland rice. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2014; 48:8498-506. [PMID: 24967508 PMCID: PMC4124062 DOI: 10.1021/es501127k] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2014] [Revised: 06/25/2014] [Accepted: 06/26/2014] [Indexed: 05/21/2023]
Abstract
In wetland-adapted plants, such as rice, it is typically root apexes, sites of rapid entry for water/nutrients, where radial oxygen losses (ROLs) are highest. Nutrient/toxic metal uptake therefore largely occurs through oxidized zones and pH microgradients. However, the processes controlling the acquisition of trace elements in rice have been difficult to explore experimentally because of a lack of techniques for simultaneously measuring labile trace elements and O2/pH. Here, we use new diffusive gradients in thin films (DGT)/planar optode sandwich sensors deployed in situ on rice roots to demonstrate a new geochemical niche of greatly enhanced As, Pb, and Fe(II) mobilization into solution immediately adjacent to the root tips characterized by O2 enrichment and low pH. Fe(II) mobilization was congruent to that of the peripheral edge of the aerobic root zone, demonstrating that the Fe(II) mobilization maximum only developed in a narrow O2 range as the oxidation front penetrates the reducing soil. The Fe flux to the DGT resin at the root apexes was 3-fold higher than the anaerobic bulk soil and 27 times greater than the aerobic rooting zone. These results provide new evidence for the importance of coupled diffusion and oxidation of Fe in modulating trace metal solubilization, dispersion, and plant uptake.
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Affiliation(s)
- Paul N. Williams
- Lancaster
Environment Centre, Lancaster University, Lancaster LA1 4YQ, United Kingdom
- Institute
for Global Food Security, Queen’s
University Belfast, Belfast BT9 5HN, United Kingdom
| | - Jakob Santner
- Rhizosphere
Ecology and Biogeochemistry Group, Institute of Soil Science, Department
of Forest and Soil Sciences, University
of Natural Resources and Life Sciences, Konrad-Lorenz-Straße 24, A-3430 Tulln, Austria
| | - Morten Larsen
- Institute
of Biology and Nordic Centre for Earth Evolution (NordCEE), University of Southern Denmark, 5230 Odense M, Denmark
- Greenland
Climate Research Centre, Greenland Institute
of National Resources, Kivioq 2, Post Office Box 570, 3900 Nuuk, Greenland
- Scottish
Marine Institute, Scottish Association for
Marine Science, Oban PA37 1QA, United Kingdom
| | - Niklas
J. Lehto
- Lancaster
Environment Centre, Lancaster University, Lancaster LA1 4YQ, United Kingdom
- Faculty
of Agriculture and Life Sciences, Lincoln
University, Post Office Box 84, Lincoln 7647, New Zealand
| | - Eva Oburger
- Rhizosphere
Ecology and Biogeochemistry Group, Institute of Soil Science, Department
of Forest and Soil Sciences, University
of Natural Resources and Life Sciences, Konrad-Lorenz-Straße 24, A-3430 Tulln, Austria
| | - Walter Wenzel
- Rhizosphere
Ecology and Biogeochemistry Group, Institute of Soil Science, Department
of Forest and Soil Sciences, University
of Natural Resources and Life Sciences, Konrad-Lorenz-Straße 24, A-3430 Tulln, Austria
| | - Ronnie N. Glud
- Institute
of Biology and Nordic Centre for Earth Evolution (NordCEE), University of Southern Denmark, 5230 Odense M, Denmark
- Greenland
Climate Research Centre, Greenland Institute
of National Resources, Kivioq 2, Post Office Box 570, 3900 Nuuk, Greenland
- Scottish
Marine Institute, Scottish Association for
Marine Science, Oban PA37 1QA, United Kingdom
- Arctic
Research Center, Arhus University, 8000 Aarhus C, Denmark
| | - William Davison
- Lancaster
Environment Centre, Lancaster University, Lancaster LA1 4YQ, United Kingdom
| | - Hao Zhang
- Lancaster
Environment Centre, Lancaster University, Lancaster LA1 4YQ, United Kingdom
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Behera B, Singdevsachan S, Mishra R, Dutta S, Thatoi H. Diversity, mechanism and biotechnology of phosphate solubilising microorganism in mangrove—A review. BIOCATALYSIS AND AGRICULTURAL BIOTECHNOLOGY 2014. [DOI: 10.1016/j.bcab.2013.09.008] [Citation(s) in RCA: 117] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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13
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Kirk GJD, Greenway H, Atwell BJ, Ismail AM, Colmer TD. Adaptation of Rice to Flooded Soils. PROGRESS IN BOTANY 2014. [DOI: 10.1007/978-3-642-38797-5_8] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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14
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Jalali M, Matin NH. Soil phosphorus forms and their variations in selected paddy soils of Iran. ENVIRONMENTAL MONITORING AND ASSESSMENT 2013; 185:8557-8565. [PMID: 23616078 DOI: 10.1007/s10661-013-3195-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2012] [Accepted: 04/04/2013] [Indexed: 06/02/2023]
Abstract
Fractionation of soil phosphorus (P) can provide useful information for assessing the risk of soil P as the potential sources of eutrophication in aquatic systems. Little information exists on P forms in paddy soils of Isfahan Province in central Iran, where P fertilizers have been continuously applied for at least 45 years. The objectives of this study were to investigate concentrations and proportions of P forms in paddy soils and correlate the content of P forms with basic soil properties. Soil samples from three paddy sites were obtained, and soil P forms were determined by a modified Hedley fraction method. Results show that the total P concentrations ranged from 288 to 850 mg kg(-1) and were enriched in site 1. In all sites, the rank order of P fractions was HCl-P (CARB-P) > residual-P (RES-P) > NaOH-P (Fe-Al-P) > KCl-P (EXCH-P), indicating that Ca compounds are the main soil components contributing to P retention in these calcareous paddy soils. The EXCH-P represented on average < 1 % of the total P, while the Fe-Al-P ranged 3.3-18 %. The CARB-P showed considerable contribution (63.6-85.6 %) to the total P. The Pearson correlation matrix indicated that Fe-Al-P only was positively correlated with total P, but did not show any significant correlations with other soil geochemical properties. Calcium-bound P fraction was significantly correlated with the clay, silt, cation exchange capacity, and total P.
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Affiliation(s)
- Mohsen Jalali
- Department of Soil Science, College of Agriculture, Bu-Ali Sina University, Hamadan, Iran.
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Morikawa CK, Saigusa M. Recycling coffee grounds and tea leaf wastes to improve the yield and mineral content of grains of paddy rice. JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE 2011; 91:2108-2111. [PMID: 21547921 DOI: 10.1002/jsfa.4444] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2010] [Revised: 03/16/2011] [Accepted: 03/24/2011] [Indexed: 05/30/2023]
Abstract
BACKGROUND Coffee grounds and tea leaf wastes exhibit strong affinity for metals such as Fe and Zn. The objective of this experiment was to evaluate the effect of top-dressing application of Fe- and Zn-enriched coffee grounds and tea leaf wastes at the panicle initiation stage on the mineral content of rice grains and the yield of paddy rice. RESULTS The Fe and Zn contents of brown rice grains increased significantly on application of both coffee and tea waste materials. The concentration of Mn was increased by top-dressing application of coffee waste material only. For Cu, no significant (P < 0.05) differences were found between the control and ferrous sulfate/zinc sulfate treatment. The application of coffee and tea waste materials led to a significant (P < 0.05) increase in the number of grains per panicle, which was reflected in increases in the total number of grains per hill and in grain yield. CONCLUSION The top-dressing application of these materials is an excellent method to recycle coffee grounds and tea wastes from coffee shops. Use of these novel materials would not only reduce the waste going to landfill but would also benefit the mineral nutrition of rice consumers at low cost by increasing Fe and Zn levels of rice grains as well as grain yield.
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Affiliation(s)
- Claudio K Morikawa
- National Agriculture and Food Research Organization, National Institute of Vegetable and Tea Science (NIVTS), Tsu, Mie, Japan.
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Schnepf A, Jones D, Roose T. Modelling Nutrient Uptake by Individual Hyphae of Arbuscular Mycorrhizal Fungi: Temporal and Spatial Scales for an Experimental Design. Bull Math Biol 2011; 73:2175-200. [DOI: 10.1007/s11538-010-9617-1] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2010] [Accepted: 12/09/2010] [Indexed: 11/28/2022]
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Zhou LL, Cao J, Zhang FS, Li L. Rhizosphere acidification of faba bean, soybean and maize. THE SCIENCE OF THE TOTAL ENVIRONMENT 2009; 407:4356-62. [PMID: 19249080 DOI: 10.1016/j.scitotenv.2009.02.006] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
Interspecific facilitation on phosphorus uptake was observed in faba bean/maize intercropping systems in previous studies. The mechanism behind this, however, remained unknown. Under nitrate supply, the difference in rhizosphere acidification potential was studied by directly measuring pH of the solution and by visualizing and quantifying proton efflux of roots between faba bean (Vicia faba L. cv. Lincan No.5), soybean (Glycine max L. cv. Zhonghuang No. 17) and maize (Zea mays L. cv. Zhongdan No.2) in monoculture and intercrop, supplied without or with 0.2 mmol L(-1) P as KH(2)PO(4). The pH of the nutrient solution grown faba bean was lower than initial pH of 6.0 from day 1 to day 22 under P deficiency, whereas the pH of the solution with maize was declined from day 13 after treatment. Growing soybean increased solution pH irrespective of P supply. Under P deficiency, the proton efflux of faba bean both total (315.25 nmol h(-1) plant(-1)) and specific proton efflux (0.47 nmol h(-1) cm(-1)) was greater than that those of soybean (21.80 nmol h(-1) plant(-1) and 0.05 nmol h(-1) cm(-1), respectively). Faba bean had much more ability of rhizosphere acidification than soybean and maize. The result can explain partly why faba bean utilizes sparingly soluble P more effectively than soybean and maize do, and has an important implication in understanding the mechanism behind interspecific facilitation on P uptake by intercropped species.
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Affiliation(s)
- L L Zhou
- College of Resources and Environmental Sciences, China Agricultural University, Key Laboratory of Plant and Soil Interactions, Ministry of Education, Beijing, PR China
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Huguenin-Elie O, Kirk GJD, Frossard E. The effects of water regime on phosphorus responses of rainfed lowland rice cultivars. ANNALS OF BOTANY 2009; 103:211-20. [PMID: 18945744 PMCID: PMC2707314 DOI: 10.1093/aob/mcn199] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/2008] [Revised: 05/27/2008] [Accepted: 08/14/2008] [Indexed: 05/27/2023]
Abstract
BACKGROUND AND AIMS Soil phosphorus (P) solubility declines sharply when a flooded soil drains, and an important component of rice (Oryza sativa) adaptation to rainfed lowland environments is the ability to absorb and utilize P under such conditions. The aim of this study was to test the hypothesis that rice cultivars differ in their P responses between water regimes because P uptake mechanisms differ. METHODS Six lowland rice cultivars (three considered tolerant of low P soils, three sensitive) were grown in a factorial experiment with three water regimes (flooded, moist and flooded-then-moist) and four soil P levels, and growth and P uptake were measured. Small volumes of soil were used to maximize inter-root competition and uptake per unit root surface. The results were compared with the predictions of a model allowing for the effects of water regime on P solubility and diffusion. KEY RESULTS The plants were P stressed but not water stressed in all the water regimes at all P levels except the higher P additions in the flooded soil. The cultivar rankings scarcely differed between the water regimes and P additions. In all the treatments, the soil P concentrations required to explain the measured uptake were several times the concentration of freely available P in the soil. CONCLUSIONS The cultivar rankings were driven more by differences in growth habit than specific P uptake mechanisms, so the hypothesis cannot be corroborated with these data. Evidently all the plants could tap sparingly soluble forms of P by releasing a solubilizing agent or producing a greater root length than measured, or both. However, any cultivar differences in this were not apparent in greater net P uptake, possibly because the restricted rooting volume meant that additional P uptake could not be converted into new root growth to explore new soil volumes.
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Affiliation(s)
- O. Huguenin-Elie
- International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines
| | - G. J. D. Kirk
- International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines
| | - E. Frossard
- Swiss Federal Institute of Technology (ETH Zürich), Institute of Plant Sciences, Eschikon 33, CH-8315 Lindau, Switzerland
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Irshad M, Inoue M, Khattak RA, Yamamoto S, Honna T. Phosphorus and Metal Fractions in Paddy Soils Under Different Fertilizer Management. ACTA ACUST UNITED AC 2008. [DOI: 10.1080/10440040802170863] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Møller CL, Sand-Jensen K. Iron plaques improve the oxygen supply to root meristems of the freshwater plant, Lobelia dortmanna. THE NEW PHYTOLOGIST 2008; 179:848-856. [PMID: 18513220 DOI: 10.1111/j.1469-8137.2008.02506.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
* High radial oxygen loss (ROL) from roots of aquatic plants to reduced sediments is thought to deplete the roots of oxygen and restrict the distribution of those species unable to form a barrier to oxygen loss. Metal precipitates with high iron content (Fe-plaques) frequently form on roots of aquatic plants and could create such a diffusion barrier, thereby diverting a larger proportion of downward oxygen transport to the root meristems. * To investigate whether Fe-plaques form a barrier to oxygen loss, ROL and internal oxygen concentrations were measured along the length of roots of the freshwater plant Lobelia dortmanna using platinum sleeve electrodes and Clark-type microelectrodes. * Measurements showed that ROL was indeed lower from roots with Fe-plaques than roots without plaques and that ROL declined gradually with thicker iron coating on roots. The low ROL was caused by low diffusion coefficients through root walls with Fe-plaques resulting in higher internal oxygen concentrations in the root lacunae. * By diverting a larger proportion of downward oxygen transport to root meristems in L. dortmanna, the presence of Fe-plaques should diminish root anoxia and improve survival in reduced sediments.
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Affiliation(s)
- Claus Lindskov Møller
- Freshwater Biological Laboratory, Biological Institute, University of Copenhagen, Helsingørgade 51, DE-3400 Hillerød, Denmark
| | - Kaj Sand-Jensen
- Freshwater Biological Laboratory, Biological Institute, University of Copenhagen, Helsingørgade 51, DE-3400 Hillerød, Denmark
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ARMSTRONG JEAN, ARMSTRONG WILLIAM. Rice: sulfide-induced barriers to root radial oxygen loss, Fe2+ and water uptake, and lateral root emergence. ANNALS OF BOTANY 2005; 96:625-38. [PMID: 16093271 PMCID: PMC4247030 DOI: 10.1093/aob/mci215] [Citation(s) in RCA: 125] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2005] [Revised: 04/14/2005] [Accepted: 04/28/2005] [Indexed: 05/03/2023]
Abstract
BACKGROUND AND AIMS Akagare and Akiochi are diseases of rice associated with sulfide toxicity. This study investigates the possibility that rice reacts to sulfide by producing impermeable barriers in roots. METHODS Root systems of rice, Oryza sativa cv. Norin 36, were subjected to short-term exposure to 0.174 mm sulfide (5.6 ppm) in stagnant solution. Root growth was monitored; root permeability was investigated in terms of polarographic determinations of oxygen efflux from fine laterals and the apices of adventitious roots, water uptake, anatomy and permeability to Fe2+ using potassium ferricyanide. KEY RESULTS Both types of root responded rapidly to the sulfide with immediate cessation of growth, decreased radial oxygen loss (ROL) to the rhizospheres and reduced water uptake. Profiles of ROL measured from apex to basal regions of adventitious roots indicated that more intense barriers to ROL than normal were formed around the apices. Absorption of Fe2+ appeared to be impeded in sulfide-treated roots. In adventitious roots, deposition of lipid material (suberisation) and thickenings of walls within the superficial cell layers were obvious within a week after lifting the treatment and could prevent the emergence of laterals and commonly result in their upward longitudinal growth within the cortex. Death of laterals sometimes occurred prior to emergence; emergent laterals eventually died. In adventitious roots, blockages formed within the vascular and aeration systems in response to the sulfide. CONCLUSIONS In both adventitious and lateral roots, sulfide-induced cell wall suberization and thickening of the superficial layers were correlated with reduced permeability to O2, water and Fe2+. This study sheds light on some of the symptoms of diseases such as Akiochi. The results correlate with the authors' previous findings on the effects on roots of sulfide and lower organic acids in Phragmites and of acetic acid in rice.
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Affiliation(s)
- JEAN ARMSTRONG
- Department of Biological Sciences, University of Hull, Kingston upon Hull HU6 7RX, UK
| | - WILLIAM ARMSTRONG
- Department of Biological Sciences, University of Hull, Kingston upon Hull HU6 7RX, UK
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Kirk GJD. Rice root properties for internal aeration and efficient nutrient acquisition in submerged soil. THE NEW PHYTOLOGIST 2003; 159:185-194. [PMID: 33873689 DOI: 10.1046/j.1469-8137.2003.00793.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
• The characteristics of Oryza sativa roots required for internal aeration may conflict with those for efficient nutrient acquisition, particularly the surface area available for absorbing nutrients and the extent of oxygenation of the rhizosphere. • A model was developed for calculating the steady-state diffusion of O2 through a primary root and its laterals and the simultaneous consumption of O2 in respiration and loss to the soil. Results for a realistic set of parameter values were compared with available experimental data, and a sensitivity analysis given. • It was seen that a system of coarse, aerenchmymatous, primary roots with gas-impermeable walls conducting O2 to short, fine, gas-permeable laterals (i.e. the basic architecture of current rice genotypes) provided the greatest absorbing surface per unit aerated root mass. • With this architecture and typical rates of root respiration, rates of O2 loss to the soil can be sufficient to, for example, nitrify sufficient NH4 + to NO3 - to allow a plant to absorb half its N as NO3 - , as well as to oxidize toxins such as Fe2+ .
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Affiliation(s)
- Guy J D Kirk
- Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, UK
- National Soil Resources Institute, Cranfield University, Silsoe MK45 4DT, UK
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Armstrong J, Armstrong W. Rice and Phragmites: effects of organic acids on growth, root permeability, and radial oxygen loss to the rhizosphere. AMERICAN JOURNAL OF BOTANY 2001. [PMID: 21669668 DOI: 10.2307/3558443] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Young Phragmites plants were grown in two cocktails of monocarboxylic acids (C(1)-C(5)) at pH 6, where the concentration of each acid was innocuous and the total undissociated (potentially toxic) concentrations were 0.35 mmol/L and 0.42 mmol/L. Rice plants were subjected to 1.5 mmol/L acetic acid at pH 4.5 (undissociated concentration = 1.05 mmol/L). In Phragmites, each cocktail curtailed root growth especially and induced premature shoot senescence. In both species, after 3-5 d of treatment, radial oxygen loss (ROL) from apical regions of adventitious roots, and from Phragmites laterals, was reduced to very low values and associated with cell wall lignification and suberization in the surface cell layers. At later stages of treatment, rice responded to acetic acid in similar ways to Phragmites, with the development of intercellular and callus type occlusions in the gas space system, vascular blockages, and the failure of laterals to emerge. The results are relevant to the supply of oxygen from Phragmites roots to sediments for the phytopurification of waste waters, to the efflux of methane and carbon dioxide from wetlands, and to rice cultivation.
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Affiliation(s)
- J Armstrong
- Department of Biological Sciences, University of Hull, Hull, UK, HU6 7RX
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Ye ZH, Baker AJM, Wong MH, Willis AJ. Copper and nickel uptake, accumulation and tolerance in Typha latifolia with and without iron plaque on the root surface. THE NEW PHYTOLOGIST 1997; 136:481-488. [PMID: 33863014 DOI: 10.1046/j.1469-8137.1997.00758.x] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The effects of iron plaque on the growth of Typha latifolia L. and accumulation of copper and nickel in T. latifolia were investigated under laboratory conditions in nutrient solution cultures. Seedlings with and without iron plaque on their roots were exposed to 0.05 μg ml-1 Cu and 0.10 μg ml-1 Ni solutions for 72 d. The results showed no differences in root and shoot d. wt and leaf elongation when Cu or Ni were added to the solution and in the presence or absence of plaque. However, root length was reduced by Cu and Ni, and the reduction in root length was greater in the presence of plaque. Some Cu and Ni was adsorbed on root surfaces; roots with plaque took up more Cu, but less Ni than those without. The presence of plaque did not alter Cu uptake and translocation but increased Ni uptake and translocation. Most of the Cu and Ni taken up was retained in the roots, suggesting that the root tissue rather than the root surface or plaque is the main barrier for Cu and Ni transport. The results differ from those reported for other species.
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Affiliation(s)
- Z H Ye
- Department of Animal and Plant Sciences, University of Sheffield, Sheffield, S. Yorks, S10 2TN, UK
| | - A J M Baker
- Department of Animal and Plant Sciences, University of Sheffield, Sheffield, S. Yorks, S10 2TN, UK
| | - M H Wong
- Department of Biology, Hong Kong Baptist University, 224 Waterloo Rd, Kowloon Tong, Hong Kong
| | - A J Willis
- Department of Animal and Plant Sciences, University of Sheffield, Sheffield, S. Yorks, S10 2TN, UK
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Kirk GJD, Bajita JB. Root-induced iron oxidation, pH changes and zinc solubilization in the rhizosphere of lowland rice. THE NEW PHYTOLOGIST 1995; 131:129-137. [PMID: 33863159 DOI: 10.1111/j.1469-8137.1995.tb03062.x] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Rice plants (Oryza sathiva L., cv. IR34) were grown with their roots sandwiched between cylinders of an anaerobic low-Zn Mollisol. After periods of root-soil contact of up to 12 d (total plant age c. 28 d) the profiles of different Zn fractions, reduced and oxidized Fe, and pH in the soil near the root plane' were determined. The concentration of easily plant-extractable Zn in the soil (measured by extraction in I M KCl) was negligible, and so it was necessary for the plants to induce changes in the soil to solubilize Zn. After 6 d, there was a substantial accumulation of Zn associated with organic matter and amorphous ferric hydroxide within 4-5 mm of the root plane. Over the next 6 d, the accumulation continued but there was a substantial depletion of the accumulated fractions within 2 mm of the root plane. The zones of accumulation and depletion coincided with zones of Fe(III) accumulation and soil acidification in which the pH decreased from the bulk soil value of 7.3 by over 0.2 pH units; i.e. a two-fold increase in H+ concentration, The acidification was the result of H+ released from the roots to balance excess intake of cations over anions, and H+ generated in the oxidation of Fe(H) by root-released O2 . At the high pH and CO., pressure of the experimental soil (7.3 and c. 0.9 kPa. respectively), soil acidity diffusion is fast and consequently the pH drop at the root surface was small. The rate of Fe oxidation peaked before 6 d, but the acidification and Zn accumulation continued beyond 6 d unabated. It is concluded that Fe oxidation released Zn from highly insoluble fractions, and that this Zn was re-adsorbed on Fe(OH)3 and on organic matter in forms that were acid-soluble and therefore accessible to the plants.
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Affiliation(s)
- G J D Kirk
- International Rice Research Institute, P.O. Box 933, 1099 Manila, Philippines
| | - J B Bajita
- International Rice Research Institute, P.O. Box 933, 1099 Manila, Philippines
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