Zn content in stinging nettle (Urtica dioica L.) as affected by soil characteristics: spatial distribution and statistics

Abstract Understanding metal plant availability as influenced by soil conditions is of key importance for phytoremediation research and for quantification of environmental risk assessment in polluted areas. Urtica dioica L. was chosen as study object as it is omnipresent in the temperate climate region and in the area under study in particular. The study area stretched over 630 km2 in Flanders, Belgium. Soil and plant samples were collected at 1 km intervals. Plant Zn content correlated significantly with all soil parameters yet exhibited no significant correlation with the total Zn content in the soil. Organic matter, clay and CEC appeared to surpress Zn-availability at levels surpassing resp. 3% OM, 10% clay and 15 cmol kg CEC. Reversedly, increasing sand content resulted in higher bioavailability. Soil pH had a less pronounced effect in the interval under study (4.0-8.0). These findings were also encountered in the geostatistical representation of the data. Correspondence analysis performed on discretized Zncontent categories versus soil textures classes revealed that high availability was encountered in sandy soil types, low availability in clayey soil types and intermediate availability in loamy soil types. When comparing total digestion and four distinct single extractions aimed at estimating bioavailability, extractions based on salt solutions resulted in the best correlation with plant-Zn, whereas extractions based on synthetic chelates correlated significantly with total soil content of Zn but not the plant-uptake of this element. This would suggest that extraction methods based on synthetic chelates may be too aggressive to estimate actual bioavailability.