Comparison of rhizosphere impacts of wheat (triticum aestivum l.) genotypes differing in phosphorus efficiency on acidic and alkaline soils

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Comparison of Rhizosphere Impacts of
Wheat (Triticum aestivum L.) Genotypes
Differing in Phosphorus Efficiency on
Acidic and Alkaline Soils
Wenke Liu a b , Yanyan Hou a , Xiaoying Zhan a , Guihua Li a &
Shuxiang Zhang aa Ministry of Agriculture Key Laboratory of Plant Nutrition andNutrient Cycling, Institute of Agricultural Resources and RegionalPlanning, Chinese Academy of Agricultural Sciences, Beijing, Chinab Institute of Environment and Sustainable Development inAgriculture, Chinese Academy of Agricultural Sciences, KeyLaboratory for Agro-environment and Climate Change, Ministry ofAgriculture, Beijing, China To cite this article: Wenke Liu, Yanyan Hou, Xiaoying Zhan, Guihua Li & Shuxiang Zhang (2012):
Comparison of Rhizosphere Impacts of Wheat (Triticum aestivum L.) Genotypes Differing in
Phosphorus Efficiency on Acidic and Alkaline Soils, Communications in Soil Science and Plant Analysis,
43:6, 905-911
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Downloaded by [Chinese Academy of Agricultural Sciences] at 00:05 31 March 2012 Communications in Soil Science and Plant Analysis, 43:905–911, 2012Copyright Taylor & Francis Group, LLCISSN: 0010-3624 print / 1532-2416 onlineDOI: 10.1080/00103624.2012.653026 Comparison of Rhizosphere Impacts of Wheat
(Triticum aestivum L.) Genotypes Differing in
Phosphorus Efficiency on Acidic
and Alkaline Soils
WENKE LIU,1,2 YANYAN HOU,1 XIAOYING ZHAN,1GUIHUA LI,1 AND SHUXIANG ZHANG1 1Ministry of Agriculture Key Laboratory of Plant Nutrition and Nutrient Cycling, Institute of Agricultural Resources and Regional Planning, Chinese Academy ofAgricultural Sciences, Beijing, China2Institute of Environment and Sustainable Development in Agriculture, ChineseAcademy of Agricultural Sciences, Key Laboratory for Agro-environment andClimate Change, Ministry of Agriculture, Beijing, China A glasshouse study was conducted to compare the rhizosphere characteristics of twowheat genotypes, Xiaoyan54 (XY54) and Jing411 (J411) on two soils. The resultsshowed that supplying phosphorus (P) increased the biomass and P content of twowheat lines significantly on alkaline soil, but P fertilization altered their biomass and Pcontent on acidic soil only slightly. XY54 decreased rhizosphere pH more significantlythan J411 on Fluvo-aquic soil without P addition, but similar acidity ability was shownwhen P applied. On red soil, two wheat genotypes showed similar rhizosphere pH. Twowheat lines showed similar rhizoshphere phosphatase activity on alkaline soil, whereasXY54 demonstrated greater rhizoshphere phosphatase activity than J411 on acidic soil.
Rhizoshphere phosphatase activities of two wheat lines on acidic soil were greater thanalkaline soil. Therefore, stronger acidity on alkaline soil and greater phosphatase activ-ity on acidic soil are principal rhizosphere mechanisms for XY54 to adapt to low-Psoils. Keywords
Genotype, phosphatase activity, rhizosphere acidity, soil type, wheat Introduction
Low soil phosphorus (P) is a major limitative factor for crop growth and yield in China, Downloaded by [Chinese Academy of Agricultural Sciences] at 00:05 31 March 2012 particularly for calcareous soils and acidic soils. It was estimated that about 51% of arablelands in China are deficient in available P (less than 5 mg kg−1) (State EnvironmentalProtection Administration of China 2007). Phosphorus inactivation and fixation by asso-ciation with the cations of calcium (Ca) in calcareous soil and aluminum (Al) and iron(Fe) in acidic soil were the main reasons for the low bioavailability of soil P (Marschner,Solaiman, and Rengel 2005). In addition, large proportions of soil P was presented in Received 25 May 2010; accepted 17 July 2011.
Address correspondence to ShuXiang Zhang, Ministry of Agriculture Key Laboratory of Plant Nutrition and Nutrient Cycling, Institute of Agricultural Resources and Regional Planning, ChineseAcademy of Agricultural Sciences, 100081, Beijing, China. E-mail: [email protected] forms of organic compounds (mainly phytate, inositol hexaphosphate, etc.) in some soils(Schachtman, Reid, and Ayling 1998), but they were released slowly for being stronglybound to soil particles (Turner et al. 2002). The mineralization rate of organic P dependedon soil phosphatase activity of rhizosphere (Tarafdar and Claassen 1988). In agriculturalproduction, although P fertilizer application could enhance the available P concentrationin soil, the enhancement effect usually disappeared soon for rapid chemical fixation, par-ticularly in calcareous soils and acidic soils. Furthermore, overuse of P fertilizers wouldnot only lead to accumulation of more unavailable P in soil (Lu 2004) but also pose a greatpollution threat to the quality of the surface water in the vicinity of the fields (Chambers,Gawood, and Unwin 2000; Butler and Coale 2005). Therefore, to develop methods toutilize the fixed phosphates and organic P already accumulated in soils is an efficient,sustainable avenue for conservation-orientated agriculture.
Intraspecific variations in P efficiency of many crop species have been well docu- mented (Gahoonia, Nielsen, and Lyshede 1999; Valizadeh, Rengel, and Rate 2002), andsome biochemical mechanisms in P activation and utilization have also been revealed(Marschner, Solaiman, and Rengel 2005). Selecting P-efficient genotypes and introduc-ing them in the areas with low-P soils have received attention, and relevant studies onmechanisms performed by P-efficient genotypes were extensively conducted worldwidein the past decade. Phosphorus-efficient genotypes could increase inorganic P activationand organic P mineralization by biochemical mechanisms, such as rhizosphere acid-ity and improvement of rhizosphere phosphatase activity (Valizadeh, Rengel, and Rate2002). Wheat is a principal crop in China that is widely planted nationwide. Some wheatgenotypes differ in P requirements, and growth capacities had been identified (Valizadeh,Rengel, and Rate 2002; Li, Pang, and Zhang 2003; Qiu et al. 2004). Among them,Xiaoyan54 (XY54) and Jing411 (J411) are typical cultivars with contrasting P efficiency(Li, Tong, and Liu 2004). Our previous study showed that XY54’s large root biomass andstrong acidification ability were the main mechanisms that allowed it to acquire more P onP-deficient calcareous soil (Yan et al. 2010).
There are large areas of calcareous soil and acidic soil distribution in northern and southern China with huge variation in pH levels. However, few comparative studies havebeen conducted to determine the differences in growth responsiveness and rhizosphereimpacts of the cultivars with contrasting P efficiency, including acidity, and phosphataseactivity on alkaline and acidic soils. Furthermore, the effects of P fertilization on P-utilization mechanisms of wheat genotypes differing in P efficiency on alkaline and acidicsoils were rarely investigated and little understood. In the present study, two wheat culti-vars (XY54 and J411) with contrasting P efficiencies were grown in a Fluvo-aquic soil anda red soil to investigate the intraspecific differences in growth, P acquirement, rhizospherepH, and phosphatase activity with or without P supply.
Downloaded by [Chinese Academy of Agricultural Sciences] at 00:05 31 March 2012 Materials and Methods
Soils and Plants
Two soils, one alkaline soil (Fluvo-aquic soil) and one acidic soil (red soil), were usedin the experiment. The alkaline soil was sampled from Fengqiu (E 114.04◦, N 34.03◦) ofHenan Province, and the acidic soil was collected from Qiyang (E 111.85◦, N 26.59◦),Hunan Province. Two soils were air-dried and sieved (<2 mm) for the pot experiment. Thegeneral physical and chemical properties of the soils are listed in Table 1. Two different Rhizosphere Impacts of Wheat Genotypes Physical and chemical properties of the soils tested wheat (Triticum aestivum L.) genotypes, XY54 (P-efficient) and J411 (P-inefficient), wereused in this study and obtained from the Institute of Crop Sciences, Chinese Academy ofAgricultural Sciences (CAAS).
Experimental Design
A three-factorial experiment was designed, including two soils, two P levels, and two wheatgenotypes. Six treatments were included, and each treatment was replicated four times.
Two P rates are 0 and 100 mg P (KH2PO4) per kg soil, and they are denoted by P0 and P1.
In addition, uniform nitrogen [N, in the form of urea, CO(NH2)2, 150 mg N per kg soil]and potassium (K, in the form of potassium sulfate, K2SO4, 100 mg K per kg soil) fertilizerwere applied to two soils as basic fertilizers. The configurations of the Plexiglass rhizoboxare 20 cm × 7 cm × 20 cm (length × height × width). They were separated into threecompartments separated by two-layer 25-µm nylon mesh that did not allow wheat rootsto grow into the outer compartment but did allow nutrients, water, and root exudates topenetrate. Each box was packed with a total of 3 kg air-dried soil. The inner compartmentwas packed with 1.5 kg soil for wheat growth, and another 1.5 kg soil was packed in theouter compartments.
Wheat seeds were surface sterilized with 10% hydrogen peroxide (H2O2) for 20 min and geminated at 25◦C for 24 h. Seeds were sown in the inner compartment of the growthbox, and the wheat seedlings were thinned to 25 plants per pot after 10 days of growth.
The pots were randomly arranged in a glasshouse of the Institute of Crop Sciences, CAAS.
The temperature in the glasshouse ranged from 15◦C to 25◦C, with 8–10 h of light. Plantswere irrigated with distilled water to maintain the soil water content at 80% field watercapacity.
Wheat shoots and roots were harvested 50 days after seedling. The roots were care- fully taken out of the soil. The soil adhered to the roots in the outer compartment wassampled, and rhizosphere soil layers were called R1 to R5 (0–5 mm from root surface,1 mm rhizosphere soil made up a sample). In addition, soil 6 to 20 mm soil from the root Downloaded by [Chinese Academy of Agricultural Sciences] at 00:05 31 March 2012 surface was sampled and called R6. They were incrementally sliced by a sharp knife into1-mm-wide sections. The sampling method was described in Yan et al. (2010). Subsamplesof soil samples (fresh soil) were kept at –20 ◦C for soil phosphatase activity analysis, whilethe remaining soil was air dried for soil pH measurement.
Determination and Data Analysis
The wheat roots and shoots were dried at 65 ◦C for 48 h and weighed. Soil pH was deter-mined using a deionized water solution (1:2.5 w/v, soil/water). The acid phosphataseactivity of soils was examined according to the method of Hoffman as modified by Zhao and Jiang (1986). Shoot and root P concentration was determined colorimetrically by thephosphomolybdate method. The significant differences between treatments were analyzedby the SAS software (6.12; SAS Institute, Cary, N.C.).
Biomass and P Content
Wheat with high P treatment had significantly greater shoot, root, and total dry weight thanlow P treatment on Fluvo-aquic soil for two genotypes (Table 2). The biomass of J411 wassimilar or greater than XY54 on red soil, whereas biomass of XY54 was greater or similarthan J411 on Fluvo-aquic soil. XY54 had greater P content than J411 on Fluvo-aquic soil,but the situation was altered on red soil. On red soil, XY54 absorbed slightly more P thanJ411 at low P supply, but contrary results were shown at high P supply.
Rhizosphere pH
XY54 decreased rhizosphere pH more significantly for R1 to R6 location soils than J411 onthe Fluvo-aquic soil with low P addition, but XY54 showed the similar acidity as J411 athigh P treatment (Table 3). On red soil, all wheat genotypes showed similar rhizospherepH independent of soil location and P level.
Rhizoshphere Phosphatase Activity
On Fluvo-aquic soil, J411 and XY54 showed similar rhizoshphere phosphatase activityirrespectively of soil P level and rhizosphere site (Table 4). On Red soil, rhizospherephosphatase activity of XY54 was greater than J411 independent of soil P level andrhizosphere site. Rhizoshphere phosphatase activity of Fluvo-aquic soil was greater thanred soil at the P < 0.01 level.
Wheat biomass and P content of XY54 and J411on Fluvo-aquic and red soil Downloaded by [Chinese Academy of Agricultural Sciences] at 00:05 31 March 2012 Note. In the same column, the different letters following the averages indicated significantly differences between treatments at the P < 0.05 level.
Rhizosphere Impacts of Wheat Genotypes Rhizosphere pH values of the two wheat genotypes at two P levels Note. In the same column, the different letters following the averages indicated significantly differences between treatments at the P < 0.05 level.
Rhizosphere phosphatase activity of the two wheat genotypes at two P levels on Fluvo-aquic and red soils (mg phenol/kg soil) 123.8efgh 128.3defg 123.8efgh 119.0fgh 116.3h Note. In the same column, the different letters following the averages indicated significantly differences between treatments at the P < 0.05 level.
Discussion
Two wheat genotypes could grow well in both alkaline and acidic soils, which indi-cated that they adapted to acidic and alkaline soils. However, two genotypes differed Downloaded by [Chinese Academy of Agricultural Sciences] at 00:05 31 March 2012 in rhizosphere pH reduction and phosphatase activity enhancement at low-P conditions.
In addition, rhizosphere properties of two wheat genotypes were affected by P fertiliza-tion. On alkaline soil, P-efficient XY54 reduced rhizosphere pH of across a wide soilvolume at low-P conditions compared with the P-inefficient J411. The results indicatedthat XY54 may be more efficient in activating rhizosphere-unavailable inorganic P (e.g.,Ca P) than J411 for alkaline soil. In addition, greater root biomass of XY54 might facilitatesoil P exploitation in low-P soil because morphological modification was a mechanisms toenhance P uptake (He, Liao, and Yan 2003). However, the situation changed when P fer-tilizer was applied into alkaline soil because two genotypes showed similar rhizosphereacidity ability. This suggested that two genotypes may have similar P activation ability through rhizosphere pH reduction on alkaline soil at high soil P levels. On acidic soil, twowheat lines demonstrated no difference in rhizosphere pH reduction at two P levels, whichindicated that two genotypes are unable to utilize inorganic fixed P by the pH reductionpathway. Our previous study showed that XY54’s large root biomass and strong acidifi-cation ability were the main mechanisms contributing to high P uptake under P-deficientconditions on calcareous soil (Yan et al. 2010).
It was well documented that high rhizosphere phosphatase activity could increase the mineralization of organic P (Tarafdar and Claassen 1988). Irrespective of P fertilizationand sampling site, XY54 showed similar rhizoshphere phosphatase activity on alkalinesoil and demonstrated greater rhizoshphere phosphatase activity than J411 on acidic soil.
Furthermore, rhizoshphere phosphatase activity of two wheat lines on alkaline soil wasgreater than on acidic soil. The data suggested that XY54 demonstrated more capacity toutilize organic P in acidic soil by increasing rhizoshphere phosphatase activity pathway.
In addition, the results indicated that soil type and soil P level influenced rhizoshpherephosphatase activity of two wheat lines on acidic soil but not alkaline soil. It is well knownthat soils differ in organic P content and components. Therefore, it is necessary to investi-gate the response of J411 and XY54 to organic P components and levels. Furthermore,phosphatase activity on red soil was much greater than Fluvo-aquic soil for all wheatgenotypes, which hinted that organic P activation by J411 is more effective on acidic soilthan alkaline soil. It is concluded that P supply and soil type modified rhizosphere prop-erties of two wheat genotypes. Stronger acidity on alkaline soil and greater phosphataseactivity on acidic soil are principal rhizosphere mechanisms for XY54 to acquire more Pin low-P soils.
Acknowledgments
This work was supported by the National Basic Research Program of China(2007CB109302 and 2005CB121102) and the Special Fund for Agro-scientific Researchin the Public Interest (201103007).
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