Genotypic richness affects inorganic N uptake and N form preference of a clonal plant via altering soil N pools

Similar to species richness, genotypic richness of plants plays a pivotal role in the structure and function of ecosystems. While the contribution of intraspecific variability to ecosystem function has been well-established, the mechanisms underlying the effect of genotypic richness on nitrogen (N) uptake patten remain poorly understood. We established experimental populations consisting of 1, 4, or 8 genotypes of the clonal plant Hydrocotyle verticillata in microcosms and conducted ¹⁵N-labeling to quantify plant N uptake. NH₄⁺-N uptake rate of the populations with 8 genotypes was significantly higher than that of the populations with 1- and 4-genotypes, while genotypic richness did not influence NO₃⁻-N uptake rate. Increasing genotypic richness also enhanced NH₄⁺-N uptake preference and reduced NO₃⁻-N uptake preference. Additionally, increasing genotypic richness facilitated the transformation of the soil nitrogen pool, resulting in a reduction of total soil N content and an increase in soil NH₄⁺-N, thereby causing a shift in population N uptake preference. Our findings highlight the importance of genotypic richness on both N uptake and N form preference of plant populations. Such intraspecific variability in N uptake and N form preference may further influence population dynamics and ecosystem function.