Root morphology and cluster root formation by seabuckthorn ( Hippophaë rhamnoides L.) in response to nitrogen, phosphorus and iron deficiency.

Background and aims: The aims were to investigate effects of availability of nitrogen (N), phosphorus (P) and iron (Fe) on root properties of seabuckthorn ( Hippophaë rhamnoides) and to test the hypothesis that seabuckthorn is able to form cluster roots (CRs). Methods: Two sources of seabuckthorn were used: the seabuckthorn cultivar BHi10726 originating from a breeding programme based on H.r. ssp mongolica and carried out in rich agricultural field soil in the black earth (chernozem) region of Russia and the seabuckthorn accession named Pk originating in a natural population of H.r. ssp turkestanica in the mountainous region of northern Pakistan. Three cultivation systems giving different water availabilities were used at two levels each of N, P and Fe. Root morphology of seedlings and clones was characterized and metabolite content in extracts of young and old CRs of Pk was analyzed by proton nuclear magnetic resonance spectroscopy. Results: Availability of N affected growth and distribution of biomass between shoot and root, while P and Fe deficiency modified root system architecture towards more lateral roots. Densely positioned rootlets with a determinate type of growth consistent with the definition of CR were observed under low P and low Fe. Pk formed on average 12 CRs per plant, which was 3 to 4-fold higher compared to BHi10726 also when normalized per root length. Malate and glycine were most abundant of the organic acids and amino acids, respectively, and decreased in old CRs. Conclusions: Seabuckthorn has the ability to form cluster roots especially in Pk and under deficiency of P and Fe. The two sources of seabuckthorn with different histories showed distinctly different root system architectures. The high contents of malate and glycine and their decrease in old CRs may reflect roles in CR metabolism. [ABSTRACT FROM AUTHOR]