Diurnal changes in nitrogen and potassium absorption rates of plants grown in a greenhouse

Abstract

In order to increase the efficiency of nutrient utilization in solution culture systems, it is indispensable to understand how plants absorb nutrients. A series of experiments were conducted using hydroponic culture system in the first to third experiments and soil culture system in the fourth experiment in a greenhouse in Okinawa, Japan. In the first experiment, changes in NO 3 -N absorption were measured every three hours during a 24-hour period on 40 days after transplanting (DAT) in cucumber. In the second experiment, daytime and nighttime NO 3 -N absorption were measured from 45 to 48 DAT in five crops including cucumber. In the third experiment, NO 3 -N, NH 4 -N, and K absorption in daytime, nighttime and shaded conditions were determined from 30 to 34 DAT in bitter gourd, a substitute crop for cucumber, and water spinach. In the fourth experiment, daytime and nighttime (NH 4 ) 2 SO 4 -15 N absorption rates were measured from 9 to 12 DAT in cucumber. The results showed that daily NO 3 -N absorption in cucumber peaked twice, just before midday and again just after the nightfall. The corresponding fluctuation pattern was observed in all other tested crops, with 20-41% of the total absorption occurring at night. Absorption rate of 15N in cucumber cultivated in soil also increased in daytime and decreased at night, with the nighttime rate accounting for 39-40% of the daily total absorption. The average nighttime NO 3 -N, NH 4 -N, and K absorption percentages of the daily total before shading the plant were 34-35%, 49-51%, and 33-49%, respectively. During the shaded period, these nutrient absorption rates dramatically decreased, except for NH 4 -N which was not affected by shading. Across all experiments, 20-51% of total absorption took place at night, the majority of which may concentrate around the early nighttime. Furthermore, the absorption rates may be influenced by photosynthetic products.

Nutrient uptake and assimilation under varying day and night root zone temperatures in lowland rice

“…Similarly, Okuyama et al. () found higher uptake rates of during the day than during the night for rice. Matt et al.…”

“…In both soil culture and hydroponic experiments, Okuyama et al. () found that plants took up to 40% of the total N during the night regardless of cultivation systems, while Terabayashi et al. () reported that N and K uptake during the night ranged from 30–40% of the daily uptake, depending on season and temperature.…”

On the modeling paradigm of plant root nutrient acquisition

“…For the diurnal cycle reported in Okuyama et al (2015;Fig. 2a), cucumber nitrate uptake showed two peaks, one in the light and one in the dark.…”

“…We identified 14 experiments (Table S1) that measured the diurnal cycle of plant root nutrient acquisition in crops. For example, Pan et al (1987) studied nitrate, potassium, and phosphate uptake by seedlings of five corn genotypes, and Okuyama et al (2015) observed nitrogen and potassium absorption by cucumber, komatsuna, tomato, and water spinach. Most experiments, except Okuyama et al (2015), collected measurements using artificial light conditions and nutrient solutions without soil, and we found no measurements of diurnal plant root acquisition of phosphate in soil.…”

“…For example, Pan et al (1987) studied nitrate, potassium, and phosphate uptake by seedlings of five corn genotypes, and Okuyama et al (2015) observed nitrogen and potassium absorption by cucumber, komatsuna, tomato, and water spinach. Most experiments, except Okuyama et al (2015), collected measurements using artificial light conditions and nutrient solutions without soil, and we found no measurements of diurnal plant root acquisition of phosphate in soil. For natural ecosystems, we only found one observational study (Schimel et al 1989) that measured nighttime and daytime cumulative ammonium and nitrate uptake by plants and microbes in a grassland ecosystem.…”