Plasticity in root system architecture of rice genotypes exhibited under different soil water distributions in soil profile

The root system architecture (RSA) has been reported to be determined by several root traits such as branching, elongation, and growth angle. This study aimed to evaluate the genotypic variation of plasticity in RSA in response to different soil water distributions in a soil profile. IR64 (shallow root system), YTH183 (adapted to rainfed lowland conditions due to high plasticity in root elongation), and Kinandang Patong (KP – deep root system) were grown in PVC root boxes for 34 days under continuously waterlogged conditions and with soil moisture fluctuations (SMF). For SMF, watering was done from the top of the root box (TI-SMF) or from the bottom of the root box (BI-SMF). A water gradient was observed more clearly in BI-SMF than in TI-SMF, while mean soil moisture content in the root box was kept at around 23% (v/v) after first irrigation in both SMF treatments. RSA changed drastically with SMF in all cultivars, all of which tended to shift root distribution to deeper soil layers in response to SMF. Such changes in RSA resulted from different degrees of plasticity exhibited mainly in nodal root and L-type lateral root development. YTH183 showed a greater ability to change its root growth angle and thus its root distribution in the deeper soil layer compared to IR64 and KP under SMF, indicating that YTH183 could help to improve RSA in cultivars adapted to SMF

Waterlogged Conditions Influence the Nitrogen, Phosphorus, Potassium, and Sugar Distribution in Sago Palm (<i>Metroxylon sagu</i> Rottb.) at Seedling Stages

Sago palm (Metroxylon sagu Rottb.) grows in well-drained mineral soil and in peatland with high groundwater levels until complete submersion. However, the published information on nutrient uptake and carbohydrate content in sago palms growing under waterlogging remains unreported. This experiment observed sago palm growth performance under normal soil conditions (non-submerged conditions) as a control plot and extended waterlogged conditions. Several parameters were analyzed: Plant morphological growth traits, nitrogen, phosphorus, potassium, and sugar concentration in the plant organ, including sucrose, glucose, starch, and non-structural carbohydrate. The analysis found that sago palm morphological growth traits were not significantly affected by extended waterlogging. However, waterlogging reduced carbohydrate levels in the upper part of the sago palm, especially the petiole, and increased sugar levels, especially glucose, in roots. Waterlogging also reduced N concentration in roots and leaflets and P in petioles. The K level was independent of waterlogging as the sago palm maintained a sufficient level in all of the plant organs. Long duration waterlogging may reduce the plant’s economic value as the starch level in the trunk decreases, although sago palm can grow while waterlogged

(DS05) Offsets applied to DSDP Site 86-577

Rainfed lowland rice fields are characterized by soil moisture fluctuations (SMF) and the presence of hardpan that impedes deep rooting and thus limits water extraction from deep soil layer during the periods of drought. In this study, we used rootboxes with three layers; shallow layer, artificial hardpan, and deep and wet layer below the hardpan, to evaluate differences in the plasticity of nodal roots elongation through the hardpan and promote root branching below the hardpan in response to SMF among four rice varieties; Sasanishiki, Habataki, Nipponbare, and Kasalath. Experiments were conducted during the summer and autumn seasons. Plasticity was computed as the difference in root traits within each variety between the SMF and continuously well-watered treatments. In both experiments, Habataki consistently tended to exhibit higher root plasticity than the other three varieties by increasing number of nodal roots that penetrated the hardpan during rewatering period in SMF, when the soil moisture increased and penetration resistance decreased. This root plasticity then contributed to greater water use at the deeper soil during the subsequent drought period and overall shoot dry matter production. Habataki had significantly higher δ13C value in roots at deep layer than roots at the shallow and hardpan layers under SMF, which may indicate that these were relatively newly grown roots as a consequence of root plasticity. This study also indicates that CSSLs derived from Sasanishiki and Habataki varieties may be suitable for the analysis of QTLs associated with root plasticity expression in rainfed lowland with hardpan and experiencing SMF

Enhanced Nitrogen Uptake and Photosynthesis of Rice Grown with Deep and Permanent Irrigation Method: Possible Mechanism for Chalky Grain Reduction

Recently, the occurrence of chalky grain caused by high temperature stress at the ripening stage has been a global problem for rice. We previously showed that the deep and permanent irrigation method, which is the combination of the V-furrow direct seeding and deep-flood irrigation methods, reduced chalky grain occurrence. To study the possible physiological mechanisms for reduced chalky grain occurrence by the deep and permanent irrigation method, we conducted field experiments in 2008 and 2009 to examine the effects of the deep-flood treatment on plant nitrogen (N) content, stomatal conductance and photosynthetic rate especially at the ripening stage. Results showed that in the deep-flood treatment that maintained a 20 cm water depth, leaf N content was consistently and significantly higher than the control with only a 10 cm water depth. Except two measured days, the stomatal conductance under the deep-flood treatment was significantly higher than in the control. Furthermore, stomatal conductance and photosynthetic rate in the deep-flood treatment were always significantly higher than in the control in both years. Thus, the deep-flood treatment enhanced N uptake, and consequently photosynthetic activity, resulting in the reduction of chalky grain formation, as previously reported. Accordingly, the effects of deep- flood treatment on grain quality improvement in rice may possibly be attributed to the improvement in source activity

Grain Yield and Gross Return above Fertilizer Cost with Parameters Relating to the Quality of White Rice Cultivated in Rainfed Paddy Fields in Cambodia

This study aims to compare the grain yield, gross return above fertilizer cost (GRAFC: (paddy sales)–(fertilizer cost)), and several parameters relating to the quality of white rice cultivated with different soil-specific nutrient management in 14 provinces where different soil types are distributed. The grain yield tended to increase with increased fertilizer application; however, the relationship between the fertilization rate and the yield was not linear in areas where clay soil dominates. In cases of popular varieties cultivated from the northern to southern province, the amount of fertilizer applied was up to 163 kg ha−1 (sum of N-P2O5-K2O), and the GRAFC and the fertilization rate showed a nonlinear relationship, with a peak of around 120 kg ha−1 fertilization. The nitrogen concentration recognized as a negative factor for the quality of rice tended to increase with an increasing fertilization rate, and the carbohydrate concentration and carbohydrate/protein ratio that are a positive factor for the quality were related negatively with the fertilizer rate. The amylopectin concentration in white rice was positively related with the carbohydrate concentration, which decreased with an increasing fertilization rate. The levels of fertilizer application required to achieve a higher yield, GRAFC, and the maintenance and improvement of parameters relating to grain quality were different