Nelson Castañeda Ortiz Phosphorus efficiency of Arachis pintoi genotypes and possible mechanisms for tolerance to low soil P supply Phosphorus efficiency of Arachis pintoi genotypes and possible mechanisms for tolerance to low soil P supply Doctoral Dissertation Submitted for the degree of Doctor of Agricultural Science of the Faculty of Agricultural Science Georg-August-University of Göttingen by Nelson Castañeda Ortiz Göttingen, May 2006 D 7 1st examiner: Prof. Dr. N. Claassen 2nd examiner: Prof. Dr. H. Becker Day of oral examination: 13th of July 2006 To my wife Viviane and my sons Daniel and Raphael for their patience, support and encouragement throughout this study Table of contents 1 General introduction……………………………………………………………………... 1 1.1 Review of literature ……………………………………………………………………... 2 1.2 Objectives, hypothesis and outline of the thesis…………………………………………. 10 1.3 Statistical analysis……………………………………………………………………….. 11 2 Screening of promising Arachis pintoi genotypes for phosphorus efficiency in acidic soils of low P availability…………………………………………………………………. 12 2.1 Introduction……………………………………………………………………………… 12 2.2 Material and methods……………………………………………………………………. 14 2.2.1 Field experiment……………………………………………………………………….. 15 2.2.2 Pot experiment…………………………………………………………………………. 17 2.3 Results and Discussion…………………………………………………………………... 21 2.3.1 Field experiment……………………………………………………………………….. 21 2.3.1.1 Shoot biomass production and the influence of the germination……………………. 21 2.3.1.2 Shoot P concentration………………………………………………………………... 26 2.3.1.3 Extractable P-Bray II and pH of the soil samples after harvesting………………….. 27 2.3.2 Pot experiment…………………………………………………………………………. 30 2.3.2.1 Shoot biomass production…………………………………………………………… 30 2.3.2.2 Phosphorus concentration and P use efficiency……………………………………... 32 2.3.2.3 Phosphorus content and the root length-shoot ratio…………………………………. 34 2.3.2.4 Phosphorus uptake per unit of root length and P concentration in the soil solution… 37 2.3.2.5 pH value in soil and soil solution and extractable P of soil samples after harvesting.. 41 2.4 Concluding discussions...….…………………………………………………………….. 42 3 Influence of arbuscular mycorrhizae fungi (AMF) on morphological and physiological plant parameter related to P efficiency of Arachis pintoi genotypes growing in acidic conditions……………………………………………………………... 44 3.1 Introduction……………………………………………………………………………… 44 3.2 Material and methods……………………………………………………………………. 48 3.3 Results and Discussion…………………………………………………………………... 53 3.3.1 Soil analysis………………………………………………………….………………… 53 3.3.2 Root colonisation grade of the arbuscular mycorrhizae fungi (AMF)………………… 54 3.3.3 Shoot biomass production……………………………………………………………... 56 3.3.4 Shoot P concentration and P content…………………………………………………... 60 3.3.5 Phosphorus use efficiency and the acid phosphatase activity in the leaves and roots.... 64 3.3.6 Root length and root length-shoot ratio………………………………………………... 70 3.3.7 The P uptake per unit root length and the P inflow..…………………………………... 75 3.4 Concluding discussions.…………………………………………………………………. 81 4 The development of P efficiency mechanisms with plant age of perennial peanut (Arachis pintoi) genotypes and of one groundnut (Arachis hypogea) genotype………. 83 4.1 Introduction……………………………………………………………………………… 83 4.2 Material and methods……………………………………………………………………. 85 4.3 Results and Discussion…………………………………………………………………... 88 4.3.1 Shoot biomass production and shoot growth rate……...……………..….…………….. 88 4.3.2 Shoot P concentration and P content…………………………………………………... 91 4.3.3 Root length-shoot ratio and P inflow…………………………………………………... 93 4.3.4 Phosphorus concentration and pH in the soil solution and the extractable P in the soil. 96 4.4 Conclusions..…………………………………………………………………………….. 102 5 Root exudation of organic acids and acid phosphatase of two different P efficient Arachis pintoi genotypes and their influence on P acquisition efficiency...…………… 103 5.1 Introduction……………………………………………………………………………… 103 5.2 Material and methods……………………………………………………………………. 105 5.3 Results………………………………………………………………………………….... 110 5.3.1 Dry shoot matter production and shoot growth rate (GRs)…………………………….. 110 5.3.2 Shoot P concentration and P content…………………….…………………………….. 111 5.3.3 Root length shoot ratio and P inflow…………………….…………………………….. 113 5.3.4 Phosphorus concentration and pH in the soil solution and the extractable P in the soil. 115 5.3.5 Colonisation grade in roots of native arbuscular mycorrhizae fungi (AMF)………….. 118 5.3.6 Acid phosphatase activity (APase) and pH on the root surface……………………….. 118 5.3.7 Root exudation of organic acids……………………………………………………….. 119 5.4 General Discussion……………………………………………………………………... 121 6 Summary………………………………………………………………………………….. 131 7 References………………………………………………………………………………… 133 8 Appendix………………………………………………………………………………….. 155 Acknowledgements Curriculum vitae List of abbreviations Ah Arachis hypogea AMF Arbuscular mycorrhizae fungi ANOVA Analysis of variance Ap Arachis pintoi APase Acid phosphatase CAL Calcium acetate lactate extractant solution CIAT International Center for Tropical Agriculture DAE Days after establishment DAS Days after sowing DAT Days after transplanting HPLC High performance liquid chromatography LOD Limit of determination OA Organic acids PAE Phosphorus acquisition efficiency Pi Inorganic phosphorus PNP p-Nitrophenol pNPP p-Nitrophenyl Phosphate Po Organic phosphorus PR Phosphate rock PUE Phosphorus use efficiency PURL Phosphorus uptake per unit root length RL Root length RSR Root length-shoot biomass ratio SAS Statistical analysis system TSP Triple superphosphate 1 Chapter 1 1 General Introduction While in most countries of Western and Central Europe and North America the production of agricultural products per unit area takes place at high level, it is low in other parts of the world, particularly in developing countries of the tropics and subtropics (Vlek et al. 1992; Cakmak 2002). Biotic and abiotic factors are the major causes of the low yields of the most important crops, when they are compared with the best yields obtained with best management practices. Biotic factors (insects, diseases and weeds) are an important source of these losses (less than 20% of the record yields) (Boyer, 1982; Zeigler, 1990; Krieg, 1994), but the abiotic factors (edaphic and climatic) account for the most important losses of yield and are, hence, a great source of agriculture research. Among the edaphic factors, low availability of phosphorus (P) is a major constraint to crop production in the tropics (World Bank, 1994; Batjes, 1997). Von Uexküll and Mutert (1995) estimate that 95% of the acid soils located in tropical areas are deficient in P. The most evident way to improve the availability of P is to add phosphate fertilisers to P- deficient acid soils, either as water soluble P fertiliser or as phosphate rock (Von Uexküll and Mutert, 1995; Sanchez et al., 1997). However, this option in tropical areas is very restricted by the low purchasing power of the small-scale farmers, by the lack of fertiliser availability, and by low fertiliser efficiency due to a high P sorption in acid soils. On the other hand, phosphate resources are limited and not renewable and their unlimited use leads to the environment pollution (soil, ground waters, rivers, etc). Other convenient alternatives are: i) to identify plant species that are efficient in term of P uptake under low P soil availability and to include them in crop rotation in combination with relatively low levels of P inputs, and ii) to improve P- acquisition efficiency by identifying genes responsible for the adaptation of given plants to low- P soils and to transfer them in agricultural crops that present a low P acquisition. Such research strategies are highly promising to an increased food production in the tropics, because growing nutrient-efficient plants will enable to increase the output at a maintained low input. These allow a sustainable agriculture and conserve the environment. However, in order to achieve the maximum use of P in P-limited native soil and strategic P inputs, it is necessary to focus the research on identifying genotypic differences and on understanding the specific mechanisms involved in the acquisition of P from different P sources (Rao et al., 1999b). 2 Chapter 1 1.1 Review of literature Phosphorus availability in tropical soils Poor soils dominate the tropical latitudes, hence most developing countries. The inherent infertility of many tropical soils is a consequence of their formation on geological parent materials that were low in essential mineral elements coupled with the intense rates of weathering they have experienced under warm humid tropical conditions that develop highly acidic solum (Richter and Babbar, 1991). Most of these tropical soils have limited available P (Oxisols, Ultisols and Andisols). Oxisols and Ultisols are constituted by clays, oxides of iron (Fe) and Aluminium (Al) and weatherable minerals in which phosphorus in the form of calcium phosphate is hydrolyzed (Walker and Syers 1976; Van Wambeke, 1991). With weathering the clays lost silica and generated iron and aluminium hydrous oxides onto which phosphates adsorb or precipitate. Strong weathering is also correlated with an increase in the amount of sesquioxides, which exhibit high P-sorption properties (Frossard et al., 1995; Torrent, 1997). Oxisols and Ultisols require great amounts of applied P to attain the required equilibrium solution concentration to support adequate crop growth (Sánchez and Uehara, 1980). On the other hand,