High Nitrogen Levels Alleviate Yield Loss of Super Hybrid Rice Caused by High Temperatures During the Flowering Stage

Abstract

The effect of high temperatures on rice production has attracted considerable research attention. It is not clear, however, whether nitrogen (N) management can be used to alleviate the damaging effects of high temperatures on flowering in rice. In this study, we compared the yields of five elite super hybrid rice varieties and examined their heat tolerance under four N treatments in two seasons with contrasting temperatures at flowering: 2015 (normal temperature) and 2016 (high temperature). The average daily temperature during the flowering stage in 2016 was 31.1°C, which was 4.5°C higher than that in 2015. There was a significant positive correlation between grain yield and N level (R ² = 0.42, P < 0.01). However, mean grain yield of the five rice varieties in 2015 was 10.5% higher than that in 2016. High N levels reduced yield losses in plants exposed to high temperature in 2016. The mean seed-set percentage in 2016 was 13.0% lower than that in 2015 at higher N levels, but spikelets per panicle increased by 7.6% at higher N levels compared with lower N levels. Higher N levels reduced the number of degenerated spikelets under high temperatures. Spikelets per panicle and N treatment level were positively correlated at high temperatures (R ² = 0.32, P < 0.05). These results confirmed that increasing N application could alleviate yield losses caused by high temperatures in super hybrid rice during the flowering stage.

Keywords: climate change; grain yield; heat stress; high temperature; nitrogen; super hybrid rice.

FIGURE 1

Heat tolerance of tested cultivars under growth chamber conditions. Different lowercase letters indicate significant differences at P < 0.05 between the control (normal temperature) and heat treatment (high temperature).

FIGURE 2

(A) Seasonal mean temperature from June to September of 2001–2016. The dotted line is the average seasonal mean temperature; (B) Daily mean temperature and solar radiation from transplanting to maturity in 2015 and 2016. The red arrows indicate the flowering stage at Jingzhou in 2015 and 2016; (C) Average daily mean temperature during the flowering stage in 2015 and 2016; (D) Duration of temperatures >35°C during the flowering stage in 2016.

FIGURE 3

Grain yield (A), grain filling (B), and spikelets per panicle (C) of five super hybrid rice cultivars grown under different N treatments in Jingzhou, Hubei Province, China, in 2015 and 2016. Data are the means of three replicates and the vertical bars represent the standard error. Different lowercase letters indicate significant differences (P < 0.05). The four N treatments were 0 kg ha^-1 (N1), 210 kg ha^-1 (N2), 300 kg ha^-1 (N3), and 390 kg ha^-1 (N4).

FIGURE 4

Grain yield of five super hybrid rice cultivars under different N treatments in 2015 and 2016 (A), and average grain yields with grain yield production increase from using N (ΔG) (B). The four N treatments were 0 kg ha^-1 (N1), 210 kg ha^-1 (N2), 300 kg ha^-1 (N3), and 390 kg ha^-1 (N4).

FIGURE 5

Correlation between grain yield (A), grain filling (B), spikelet per panicle (C), and N treatments in 2015 and 2016. The four N treatments were 0 kg ha^-1 (N1), 210 kg ha^-1 (N2), 300 kg ha^-1 (N3), and 390 kg ha^-1 (N4).