Succeeding in breeding super hybrid rice has been considered as a great progress in rice production in China. This on-farm study was conducted with Minirhizotron techniques to identify dynamic root morphological traits and distribution (0–30 cm) under different nitrogen treatments. Five elite super hybrid rice cultivars, Liangyoupeijiu (LYPJ), Yliangyou 1(YLY1), Yliangyou 2(YLY2), Yliangyou 900(YLY900) and Super 1000(S1000), were grown at four N levels: 0 kg ha−1 (N1), 210 kg ha−1 (N2), 300 kg ha−1 (N3) and 390 kg ha−1 (N4) in 2015 and 2016. Results showed these cultivars had greater root traits and higher grain yield under N3. Total root number (TRN) and total root length (TRL) of these cultivars reached maximum at 55 days after transplanting (DAT). The new released cultivars YLY900 and S1000 were featured with an improved root system among these cultivars. The percentage of root number on 10–20 cm soil was over 50% compared with other soil layer. A significant positive correlation was found between grain yield and both TRN and TRL at 10–20 cm soil layer (P < 0.01). Given this situation, the grain yield of super rice cultivars could be further improved by increasing the proportion of roots at 10–20 cm soil layer under suitable nitrogen management.

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Root Morphological Traits and Spatial Distribution under Different Nitrogen Treatments and Their Relationship with Grain Yield in Super Hybrid Rice

Compensatory effect is observed during the process of gradual adaptation of plants to abnormal environmental conditions; nitrogen fertilizer compensation has been extensively studied in rice production in recent years. However, metabolite production of the phenomenon has not been studied clearly. In this study, we used super hybrid early rice as the material and planted it in a barrel. Experiments were performed under two conditions of treatment, namely, CK (normal quantities of nitrogen fertilizer distribution at different growth stages) and T1 (nitrogen deficiency at tillering stage and compensatory application at young panicle differentiation stage). Liquid chromatography–mass spectrometry (LC–MS) was used to analyze metabolomics of rice leaves under conditions of nitrogen deficiency and compensation after the same period of CK treatment. Results showed that there was a significant difference between T1 and CK metabolites. The levels of stress-resistant substances and amino acid substitution product nitrogen deficiency increased under T1 treatment compared to CK, and the metabolites were consumed as the energy source. However, after compensation, the levels of the stress response products returned to normal, lipids were synthesized in large quantities, and fatty acid accumulation had increased.

Analysis of main metabolisms during nitrogen deficiency and compensation in rice

To investigate the effects of the spatial distribution of rice root systems on dissolved CH4 and CH4 emissions and the CH4 transport efficiency of aboveground plant parts in paddy fields. A two-year field and leaf cutting experiment was conducted on seven rice varieties, and we determined the dynamics of CH4 emissions, root system traits and dissolved CH4 concentrations in different soil layers, and the CH4 transport efficiencies of the leaf and stem sheath. CH4 emissions, the root distribution and the distribution of dissolved CH4 concentration showed large discrepancies among the different rice varieties. Correlation analysis and structural equation modeling (SEM) revealed that CH4 emissions had strong negative associations with root morphological traits (root dry weight, root area index and root volume density) and a clear positive correlation with dissolved CH4 concentrations in the 0–20 cm soil layer. In addition, the root system had an indirect negative correlation with CH4 emissions by influencing the dissolved CH4 concentrations. Furthermore, root traits had strongly positive correlations with grain yield. In the aboveground parts, the CH4 transport efficiencies of the leaf (20–70%) and stem sheath (30–80%) presented large differences among the different rice varieties, and CH4 emissions exhibited significant positive correlations with leaf CH4 transport efficiency and leaf dry weight. Our results suggest that varieties with larger and deeper root distributions and lower leaf dry weight can decrease CH4 emissions in paddy fields and maintain higher grain yield.

Hu XiangYu

Papers

Effects of different nitrogen supply patterns on root morphological and physiological characteristics of rice.

Physiological mechanism of nitrogen forms affect aerenchyma formation of rice root under water stress.