 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.plant-soil.com 456 DOI: 10.1002/jpln.201100336 J. Plant Nutr. Soil Sci. 2012, 175, 456–465 Shoot cadmium concentration of soil-grown plants as related to their root properties Christos Stritsis 1 *, Bernd Steingrobe 1 , and Norbert Claassen 1 1 Department of Crop Sciences, Plant Nutrition, Georg August University of Göttingen, Carl-Sprengel-Weg 1, 37075 Göttingen, Germany Abstract Cadmium (Cd) is toxic to plants, animals, and humans. However, different plant species growing on the same soil may have very different shoot Cd concentrations depending on properties such as size of the root system, Cd net influx, shoot-growth rate, Cd translocation from root to shoot, and the ability to affect Cd availability in the soil. To investigate possible reasons for different shoot Cd concentrations maize, sunflower, flax, and spinach were grown on an acid sandy soil (pH CaCl 2  4.5, and C org 2.8%) in a growth chamber with Cd additions as Cd(NO 3 ) 2 of none, 14, and 40 lmol (kg soil) –1 resulting in Cd soil-solution concentrations of 0.04, 0.68, and 2.5 lM. Only the high Cd addition caused a significant growth reduction of flax and spinach. The shoot Cd concentration was up to 30 times higher in spinach than in maize; the other species were intermediate. Of the plant properties studied only the variation of the Cd net influx explained the differences in shoot Cd concentrations. This was due to a decreased (maize, sunflower) or in- creased (flax) Cd concentration in soil solution or more effective uptake kinetics (spinach). Key words: cadmium mobilization / maize / sunflower / flax / spinach Accepted March 21, 2012 1 Introduction The study of cadmium (Cd) uptake by plants has become necessary because of its potential risk for human health through the food chain. To assess the risk it is necessary to know the plant Cd concentration and to which extent it is influenced by soil properties (Cd content, pH, clay content, humic substances, or water content) and plant properties (root system size, uptake, translocation from root to shoot, plant age, or parts of the plant). The Cd uptake by plants depends on Cd availability in soil and on Cd acquisition which differs among species and among genotypes of the same species. Therefore, Cd accumulation and Cd concentration in the shoot of plants varies greatly (Simmons et al., 2003; Wang, 2002). These studies have also been used to find tolerant plants that can grow on Cd-contaminated soils with large amounts of Cd (higher than 200 mg Cd kg –1 ), usually not present in natural environments. In addition, the studies mainly focused on phy- siological aspects such as differences in leaf surface area and modification in transpiration rate under high Cd stress without considering chemical changes in the rhizosphere. For a synoptic review of these points see di Toppi and Gabbrielli (1999). To our knowledge, only few studies have been carried out to identify relationships between soil properties such as Cd in the soil liquid and solid phase, and plant properties that are related to plant Cd accumulation such as size of the root system, shoot growth rate, or Cd mobilization in the rhizo- sphere. Padeken (1998) growing 13 different plant species on a Cd- contaminated soil found that they varied widely in their shoot Cd concentrations (from 0.62 mg kg –1 in maize to 6.22 mg kg –1 in spinach). The high shoot Cd concentration of spinach was not related to a large root system, on the contrary its root-to-shoot ratio was only one fifth of that of maize. The high shoot Cd concentration of spinach was related to a high Cd uptake per unit of root. The Cd shoot concentration may also be related to the growth rate. A high shoot growth rate may cause a low shoot Cd concentration because of a dilu- tion effect. Furthermore, in contrast to essential heavy metals, e.g., Mn or Zn, for nonessential heavy metals such as Cd a large part of the total Cd absorbed may be retained in the root and only a smaller portion may be transferred to the shoot (Egle, 2002; Grant et al., 1998; Guo et al., 1995; Keller , 2000; Padeken, 1998). A difference in retention of Cd in the roots may be a reason for different Cd concentrations in shoots. Hence, the shoot Cd concentration X S is determined by sev- eral plant properties which act simultaneously; their functional interrelationship is shown in Eq. 1. This equation was devel- oped making the simplification that X S does not change much over time (Nye and Tinker , 1977). The equation shows that X S depends on root surface area (RA) per unit of shoot dry weight (SDW), the relative shoot growth rate RGR S , the total Cd net influx (I nt ), and the proportion of absorbed Cd that is translocated from the root to the shoot (q). X S  RA SDW  1 RGR S  I nt  q: (1) * Correspondence: Dr. Christos Stritsis; e-mail: cstrits@gwdg.de