Root and shoot responses of upland New Rice for Africa varieties to fluctuating soil moisture conditions as affected by different levels of nitrogen fertilization

Abstract

Drought cycling and soil re-watering trends due to intermittent rainfall patterns are key stress factors that influence rice growth and yield under upland cultivation conditions. However, upland rice adaptation responses to fluctuating soil moisture conditions remain poorly understood. This study investigated root and shoot responses of upland New Rice for Africa (NERICA) varieties to episodic drought and re-watering during growth. We examined root and shoot growth of NERICA 1 and NERICA 4 compared with those of IR72, an improved lowland variety, and Dular, a traditional drought-tolerant variety, in terms of soil moisture fluctuations with different levels of nitrogen fertilization under field conditions that impeded deep root development.During soil moisture fluctuation, all varieties reduced shoot dry weight compared with well-watered plants, regardless of nitrogen fertilization levels. However, total root length for the three upland varieties was enhanced by soil moisture fluctuations at moderate and high nitrogen fertilization, while that of the lowland variety was reduced. Comparing root development during water fluctuations revealed that NERICA 1 had a greater root system than NERICA 4, which was attributed to lateral root development. Furthermore, we found that NERICA varieties increase lateral root mass during soil desiccation under adequate nitrogen fertilization, while Dular and IR72 reduced their root growth rate during drought and increased it after rewatering. Both root growth patterns developed, from around maximum tillering to heading. The analysis of regression between root elongation and shoot growth with fluctuating soil moisture indicated that an enhanced root system during drought, on adequate nitrogen fertilization, can contribute to shoot growth when sufficient water becomes available, specifically around the maximum tillering to the heading growth stage of rice. K E Y W O R D S drought stress, nitrogen fertilization, re-watering, root development, shoot growth, upland NERICA | 323 MENGE Et al.

The outstanding rooting1 mutation gene maintains shoot growth and grain yield through promoting root development in rice under water deficit field environments

“…For instance, (Suralta et al., 2010) demonstrated that a rice variety with a well‐developed root system exhibited a rapid recovery of photosynthetic ability during specific waterlogged periods following drought, resulting in increased shoot dry matter production. Additionally, according to (Menge et al., 2020), enhanced root development during drought can contribute to shoot growth during subsequent flooded periods, when sufficient water is available. These findings support our hypothesis that the enhanced S‐type LR development in the our1 mutant contributed to shoot growth through increased water uptake ability as a corresponding response to sufficient water availability between drought periods.…”

Do shoot anatomical characteristics allow rice to grow well under water deficit?

“…Rice ( Oryza sativa L.), an essential crop for global food security, requires massive amounts of fresh water for irrigation. Various water‐saving practices have been designed, such as alternate wetting and drying (Bouman & Tuong, 2001; Carrijo et al., 2017; Menge et al., 2020; Mishra & Salokhe, 2010), and controlled soil drying during grain filling (Yang & Zhang, 2006; Yang et al., 2003). However, yield penalties appear unavoidable.…”