Soil type determines how root and rhizosphere traits relate to phosphorus acquisition in field-grown maize genotypes

Aims Phosphorus (P) is frequently limiting crop production in agroecosystems. Large progress was achieved in understanding root traits associated with P acquisition efficiency (PAE, i.e. P uptake achieved under low P conditions). Most former studies were performed in controlled environments, and avoided the complexity of soil-root interactions. This may lead to an oversimplification of the root-soil relations. The aim of the present study was, therefore, to identify the dominant root and rhizosphere-related traits determining PAE, in contrasting soil conditions in the field. Methods Twenty-three maize hybrids were grown at two contrasting P levels of a long-term P-fertilizer trial in two adjacent soil types: alkaline and neutral. Bulk soil, rhizosphere and root parameters were studied in relation to plant P acquisition. Results Soil type had robust effect on PAE. Hybrids’ performance in one soil type was not related to that in the other soil type. In the neutral soil, roots exhibited higher specific root length, higher root/shoot ratio but lower PAE. Best performing hybrids in the neutral soil were characterized by top soil exploration, i.e., greater root surface and topsoil foraging. In contrast, in the alkaline soil, PAE and foraging traits were not correlated, P availability in the rhizosphere was greater than the bulk soil and phosphatase activity was higher, suggesting a ‘mining strategy’ in that case (i.e. traits that facilitate elevated P availability). Conclusions These results indicate the key role of environmental factors for roots traits determining high PAE. The study highlights the need to consider soil properties when breeding for high PAE, as various soil types are likely to require different crop ideotypes.