Plant Soil (2013) 372:319–337 DOI 10.1007/s11104-013-1741-x
REGULAR ARTICLE
Modelling root plasticity and response of narrow-leafed lupin to heterogeneous phosphorus supply Ying L. Chen & Vanessa M. Dunbabin & Johannes A. Postma & Art J. Diggle & Kadambot H. M. Siddique & Zed Rengel
Received: 4 January 2013 / Accepted: 23 April 2013 / Published online: 8 May 2013 # Springer Science+Business Media Dordrecht 2013
Abstract Background & Aims Searching for root traits underpinning efficient nutrient acquisition has received increased attention in modern breeding programs aimed at improved crop productivity. Root models provide an opportunity to investigate root-soil interactions through representing the relationships between rooting traits and the non-uniform supply of soil resources. This study used simulation modelling to predict and identify phenotypic plasticity, root growth responses and phosphorus (P) use efficiency of contrasting Lupinus angustifolius genotypes to localised soil P in a glasshouse. Methods Two L. angustifolius genotypes with contrasting root systems were grown in cylindrical columns
containing uniform soil with three P treatments (nil and 20 mg P kg−1 either top-dressed or banded) in the glasshouse. Computer simulations were carried out with root architecture model ROOTMAP which was parameterized with root architectural data from an earlier published hydroponic phenotyping study. Results The experimental and simulated results showed that plants supplied with banded P had the largest root system and the greatest P-uptake efficiency. The P addition significantly stimulated root branching in the topsoil, whereas plants with nil P had relatively deeper roots. Genotype-dependent root growth plasticity in response to P supply was shown, with the greatest response to banded P.
Responsible Editor: Michael Denis Cramer. Electronic supplementary material The online version of this article (doi:10.1007/s11104-013-1741-x) contains supplementary material, which is available to authorized users. Y. L. Chen (*) : Z. Rengel (*) School of Earth and Environment (M087), The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia e-mail:
[email protected] e-mail:
[email protected] Y. L. Chen : K. H. M. Siddique : Z. Rengel The UWA Institute of Agriculture (M082), The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia
V. M. Dunbabin Tasmanian Institute of Agriculture, The University of Tasmania, Private Bag 54, Hobart, Tas. 7000, Australia J. A. Postma IBG-2: Plant Sciences, Forschungszentrum Jülich, 52425 Jülich, Germany A. J. Diggle The Department of Agriculture and Food, Western Australia, Locked Bag 4, Bentley, WA 6983, Australia
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Conclusions Both experimental and simulation outcomes demonstrated that 1) root hairs and root proliferation increased plant P acquisition and were more beneficial in the localised P fertilisation scenario, 2) placing P deeper in the soil might be a more effective fertilisation method with greater P uptake than top dressing, and 3) the combination of P foraging strategies (including root architecture, root hairs and root growth plasticity) is important for efficient P acquisition from a localised source of fertiliser P. Keywords Lupinus angustifolius . Narrow-leafed lupin . Phosphorus efficiency . Localised P . Root modelling . Root plasticity . Root system architecture . ROOTMAP
Introduction Narrow-leafed lupin (Lupinus angustifolius L.) is a recently domesticated crop that has become an important component of sustainable farming systems in the Mediterranean climatic region (Palta et al. 2004; Berger et al. 2012). It is the predominant grain legume crop in southern Australia due to its general phenological adaptation to Mediterranean-type environments (e.g. Buirchell 2008). A large germplasm pool of wild L. angustifolius from diverse climatic and geographic locations has been established, containing a significant proportion of the world’s genetic resource for this species (Clements and Cowling 1991). This resource provides a broad genetic basis for developing improved L. angustifolius varieties. We observed large genotypic variation in root architectural traits in a core collection selected from this germplasm pool using our novel semi-hydroponic phenotyping system (Chen et al. 2011a, b, 2012). Given the variability in the genome for root architecture, plastic responses and foraging strategies, there is an opportunity to improved crop productivity by selecting for root traits which are beneficial for nutrient and water uptake in the Mediterranean-type environments (de Dorlodot et al. 2007; Lynch 2007; Ao et al. 2010; Lynch and Brown 2012). Root system architecture plays a vital role in the exploration of soil zones and acquisition of soil nutrients such as P (Lynch 1995; Li et al. 2007; Gregory et al. 2009; Hammond et al. 2009; Lynch and Brown 2012). Heterogeneous distribution of P in soil and the presence of enriched-P patches (localised sites where
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P concentration is relatively high) often occurs largely due to the localised placement of P in practical fertilisation. Root plasticity is important in acquiring heterogeneous resources in soil. Numerous studies show that roots proliferate in a nutrient-enriched patch in response to a heterogeneous nutrient (e.g. Drew and Saker 1978; de Jager and Posno 1979; Jackson and Caldwell 1989; Gross et al. 1993; Snapp et al. 1995; Hodge 2004). Selection for root architectural traits linked to resource acquisition efficiency has the potential in improving crop performance and productivity (Lynch and Brown 2012). However, the complexity of the heterogeneous soil environment, coupled with complex root architecture and plastic root growth responses, present a challenge to accurate phenotyping (de Dorlodot et al. 2007). Significant advances have been made in root architecture and functional-structural plant modelling in recent decades. However, parameterising complex root and plant models can be a challenge (Dupuy et al. 2010). Furthermore, the capacity of these models to represent phenotypic plasticity in response to the environment has not been fully tested (Tardieu and Tuberosa 2010). Root architecture models, such as ROOTMAP (Dunbabin et al. 2002), provide an opportunity to investigate the complexity of the soil-root environment by representing heterogeneous and dynamic interactions between roots and soil (Pagès et al. 2004; de Dorlodot et al. 2007; Lynch and Brown 2012). ROOTMAP is a 3-dimensional (3D) model of root architecture and growth and resource capture (Diggle 1988; Dunbabin et al. 2002). It was modified to enable the simulation of plant growth responses to soil water and nutrient dynamics (N and P), and the interaction of plant roots and soil water and nutrients with soil barriers (Dunbabin et al. 2011). Root growth is driven by the feedback between plant demand for belowground resources (N, P and water), and the capacity for individual root segments to supply those resources. Using this approach the model can represent whole root system responses to resource supply, as well as localised nutrient uptake and root proliferation responses to localised nutrient patches (Dunbabin et al. 2002). Local nutrient uptake is calculated using the Baldwin et al. (1973) model and Michaelis-Menten kinetics (Dunbabin et al. 2002), and the phosphate routine models−the reactivity of the labile phosphate solid–liquid phases across 3D space at each time-step (Dunbabin et al. 2006). The ROOTMAP model was recently parameterised to represent the root architecture and root growth of
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four contrasting wild genotypes of narrow-leafed lupin (Chen et al. 2011b, 2012). The aim of this study was to investigate whether, given an accurate parameterisation of root architecture from a hydroponic screening trial, the ROOTMAP model could predict P uptake and root growth responses of the lupin genotypes in soil. This study also compared differences in model results to a subsequent glasshouse trial designed to: 1) investigate the interaction between the distribution of P in a local coarse-textured soil suitable for lupin and root growth and P uptake of wild genotypes of narrow-leafed lupin; 2) examine the interaction between lupin root architecture and P acquisition from soil, and 3) determine P efficiency between genotypes with contrasting root architecture in two agronomically important fertiliser P applications (top-dressed and banded P).
Materials and methods Glasshouse experiment Plant, soil and column materials The experiment was set up in a completely randomised block design consisting of two genotypes and three P treatments. There were three replications in each treatment. Two genotypes of narrow-leafed lupin (Lupinus angustifolius L.), one with large root system (DArT#085) and the other with average-sized root system (DArT#071), were chosen among 111 wild Fig. 1 Placement of P in cylindrical columns (100 mm diameter, 600 mm height): nil P (a); top-dressed P (b); banded P (c; an even layer covering the whole cross section of the column); narrow-band P (d, side view; e, top view; 10 mm×40 mm band, offset from the centre line; included in model simulations only). A PVC tube (12 mm diameter) was placed in each column with outlet holes for watering to reduce nutrient displacement into lower parts of the columns (because less water needed to be applied to the soil surface)
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genotypes screened for root traits in a semi-hydroponic phenotyping system (Chen et al. 2011b, 2012). A local coarse-textured soil suitable for lupin was used in this experiment (dried and sieved, < 2 mm). Basal soil properties were: pH 6.7 (H2O) and 6.0 (CaCl2), conductivity 0.031 dS m−1, P buffering index 12.2, organic carbon 2 g kg−1 and nutrients (in mg kg−1): N (nitrate 1, ammonium 1), K (Colwell) 27, S 12, P (Colwell) 3, and reactive Fe 120. Three P treatments were applied to the soil columns as top dressed P, banded P and nil P (see below). Cylindrical PVC columns (100 mm internal diameter, 600 mm deep) were cut vertically into halves and then secured together with waterproof tape and braced by two stainless steel brackets. Columns were lined with open-end transparent polyethylene sleeves. PVC cap with holes was fit over the lower end of the tubing and was attached with waterproof tape. A narrow PVC tube (12 mm external diameter, capped on the lower end) was placed inside each column as illustrated in Fig. 1a– c; the narrow tube was perforated below the top 10 cm of soil to supply water to the subsoil. This enabled water to be applied throughout the column, reducing the risk of nutrient leaching during watering of the columns. Placement of P The P-amended soil was prepared by mixing 200 g of soil in a soil tumbler with 0.575 g of ground Ca(H2PO4)2 ·H2O (
