Vegetative biomass production under different inorganic nitrogen forms of the USDA rice (Oryza sativa L.) diversity panel 1

We characterized early vegetative biomass production in response to inorganic nitrogen source, ammonium (NH4+) or nitrate (NO3–), in 390 accessions from the USDA Rice Diversity Panel 1, which contains broad genetic diversity from the global germplasm. We grew these accessions under NO3– versus NH4+ nutrition, and under different concentrations of NH4+ as sole nitrogen sources in a greenhouse with day/night temperatures approximately 28°/24°C under natural sunlight in Davis, California (38°32'20.2"N 121°46'52.5"W) in 2018-2019. This dataset contains dry biomass (g) at three weeks after transplanting. We used the biomass data as inputs for Genome-Wide Association Analyses, with the genotype data publicly available from http://ricediversity.org/.

Methods
We evaluated growth of rice seedlings under NO3– versus NH4+ nutrition, and under different concentrations of NH4+ as sole nitrogen sources. We germinated seeds on a rolled germination paper soaked with 1 mM CaSO4 and placed the rolls in a controlled environment chamber at 28°/20°C light/dark, under 450 μmol⋅s−1⋅m−2 photosynthetic photon flux density at plant height during the 12 hr light period.

At 7 d post germination, when seedlings had one true leaf, we transferred seedlings into 20 dm3 opaque, aerated hydroponic polyethylene containers, each filled with 16 dm3 of nutrient solution. Each tub contained 48 seedlings of different genotypes. The nutrient solution was composed of 1 mM K2HPO4, 1 mM KH2PO4, 2 mM CaCl2, 2 mM MgSO4, and 0.06 g L−1 Fe-NaDTPA, and micronutrients according to a modified Hoagland solution (Epstein & Bloom, 2005). Nitrogen treatments included 3 concentrations of (NH4)2SO4 (0.3, 3, and 10 mM) and a single concentration of KNO3 (3 mM). We adjusted the solution pH with H2SO4 to 5.95 and replaced the solution every few days when pH dropped below 5.30. We arranged the containers in a randomized block design with 4 biological plant replicates of each genotype.

We repeated the experiment twice in a greenhouse with day/night temperatures approximately 28°/24°C under natural sunlight in Davis, California (38°32'20.2"N 121°46'52.5"W): the first replicate examined accessions ID# 0001 – 0220 (last 4 digits of the USDA Genetic Stocks Oryza; GSOR ID) on December 10, 2018 – January 3, 2019 and accessions ID#0220 – 2020 on January 10 – February 3, 2019); the second replicate examined accessions ID#0001 – 0220 on March 14 – April 7, 2019 and accessions ID#0220 – 2020 on April 12 – May 4, 2019). We harvested shoot and root separately at three weeks after transplanting, dried them at 65°C and then weighed them with Sartorius BL120S balance (Sartorius AG, Göttingen, Germany).