Large-scale exploration of nitrogen utilization efficiency in Asia region for rice crop: Variation patterns and determinants.

Improving rice nitrogen utilization efficiency (NUtE) is imperative to maximizing future food productivity while minimizing environmental threats, yet knowledge of its variation and the underlying regulatory factors is still lacking. Here, we integrated a dataset with 21,571 data compiled by available data from peer-reviewed literature and a large-scale field survey to address this knowledge gap. The overall results revealed great variations in rice NUtE, which were mainly associated with human activities, climate conditions, and rice variety. Specifically, N supply rate, temperature, and precipitation were the foremost determinants of rice NUtE, and NUtE responses to climatic change differed among rice varieties. Further prediction highlighted the improved rice NUtE with the increasing latitude or longitude. The indica and hybrid rice exhibited higher NUtE in low latitude regions compared to japonica and inbred rice, respectively. Collectively, our results evaluated the primary drivers of rice NUtE variations and predicted the geographic responses of NUtE in different varieties. Linking the global variations in rice NUtE with environmental factors and geographic adaptability provides valuable agronomic and ecological insights into the regulation of rice NUtE.

The sensitivity of photosynthesis to magnesium deficiency differs between rice (Oryza sativa L.) and cucumber (Cucumis sativus L.).

Magnesium is an essential macronutrient for plant photosynthesis, and in response to Mg deficiency, dicots appear more sensitive than monocots. Under Mg deficiency, we investigated the causes of differing photosynthetic sensitivities in a dicot and a monocot species. Rice (Oryza sativa L.) and cucumber (Cucumis sativus L.) were grown in hydroponic culture to explore their physiological responses to Mg deficiency stress. Both Mg-deficient rice and cucumber plants exhibited lower biomass, leaf area, Mg concentration, and chlorophyll content (Chl) compared with Mg-sufficient plants. However, a more marked decline in Chl and carotenoid content (Car) occurred in cucumber. A lower CO2 concentration in chloroplasts (C c) was accompanied by a decrease in the maximum rate of electron transport (J max) and the maximum rate of ribulose 1,5-bisphosphate carboxylation (V cmax), restricting CO2 utilization in Mg-deficient plants. Rice and cucumber photorespiration rate (P r) increased under Mg deficiency. Additionally, for cucumber, Car and non-photochemical quenching (NPQ) were reduced under lower Mg supply. Meanwhile, cucumber Mg deficiency significantly increased the fraction of absorbed light energy dissipated by an additional quenching mechanism (Φf,D). Under Mg deficiency, suppressed photosynthesis was attributed to comprehensive restrictions of mesophyll conductance (g m), J max, and V cmax. Cucumber was more sensitive to Mg deficiency than rice due to lower NPQ, higher rates of electron transport to alternative pathways, and subsequently, photooxidation damage.

Identification of photosynthetic parameters for superior yield of two super hybrid rice varieties: A cross-scale study from leaf to canopy.

Enhancing photosynthetic capacity is widely accepted as critical to advancing crop yield. Therefore, identifying photosynthetic parameters positively related to biomass accumulation in elite cultivars is the major focus of current rice research. In this work, we assessed leaf photosynthetic performance, canopy photosynthesis, and yield attributes of super hybrid rice cultivars Y-liangyou 3218 (YLY3218) and Y-liangyou 5867 (YLY5867) at tillering stage and flowering stage, using inbred super rice cultivars Zhendao11(ZD11) and Nanjing 9108 (NJ9108) as control. A diurnal canopy photosynthesis model was applied to estimate the influence of key environmental factors, canopy attributes, and canopy nitrogen status on daily aboveground biomass increment (AMDAY). Results showed that primarily the light-saturated photosynthetic rate at tillering stage contributed to the advancing yield and biomass of super hybrid rice in comparison to inbred super rice, and the light-saturated photosynthetic rate between them was similar at flowering stage. At tillering stage, the higher CO2 diffusion capacity, together with higher biochemical capacity (i.e., maximum carboxylation rate of Rubisco, maximum electron transport rate (J max), and triose phosphate utilization rate) favored leaf photosynthesis of super hybrid rice. Similarly, AMDAY in super hybrid rice was higher than inbred super rice at tillering stage, and comparable at flowering stage partially due to increased canopy nitrogen concentration (SLNave) of inbred super rice. At tillering stage, model simulation revealed that replacement of J max and g m in inbred super rice by super hybrid rice always had a positive effect on AMDAY, and the averaged AMDAY increment was 5.7% and 3.4%, respectively. Simultaneously, the 20% enhancement of total canopy nitrogen concentration through the improvement of SLNave (TNC-SLNave) resulted in the highest AMDAY across cultivars, with an average increase of 11.2%. In conclusion, the advancing yield performance of YLY3218 and YLY5867 was due to the higher J max and g m at tillering stage, and TCN-SLNave is a promising target for future super rice breeding programs.

Variation in photosynthetic induction between super hybrid rice and inbred super rice.

It is well documented that yield superiority of super hybrid rice is linked with its improved photosynthetic capacity and/or efficiency. In natural environments, the amounts of CO2 assimilated by plants was also impacted by the rapidity of leaf photosynthesis response to fluctuations of light. However, it remains unknow whether the high yield of super hybrid rice was associated with photosynthetic traits under dynamic state. Here, photosynthetic traits under steady-and dynamic state in two super hybrid rice varieties (Ylinagyou 3218 and Yliangyou 5867) with high yield and two inbred super rice varieties (Zhendao 11 and Nanjing 9108) with lower yield. Under steady state, the net photosynthetic rate (A*) in super hybrid rice was 25.3% larger compared with inbred super rice. During photosynthetic induction, there was no obvious association of the rapidity of net photosynthesis rate (A) to sunflecks with rice subpopulations. Stomatal conductance (gs) of super hybrid rice increased slower than that of inbred super rice. The cumulative CO2 fixation (CCF) during photosynthetic induction was 25.2% larger in super hybrid rice than that in inbred super rice. The primary limitation during induction was biochemical limitation rather than stomatal limitation. There was a significantly positive relationship between A* and CCF, while A* was not related with the induction response rate of A. Overall, A* and CCF in super hybrid rice have been improved together, which contributed to its yield superiority, whereas its yield potential still can be improved by increasing induction rate of A under fluctuations of irradiance.

Fe° enhanced acetification of propionate and granulation of sludge in acidogenic reactor.

Acidogenic reactors commonly operated at short hydraulic retention times (HRT) are liable to cause low chemical oxygen demand (COD) removal and acidogenic efficiency especially under fluctuating feed. Granular sludge as an efficient form for anaerobic microbial community to resist shocks in methanogenic reactors has been widely investigated, which however was less focused in acidogenic reactors. Adding Fe(0) in an acidogenic reactor with propionate as the substrate operated at HRT of 2 h was found to enhance the propionate decomposition and sludge granulation in this study. When increasing the organic load and decreasing pH in the feed, the propionate conversion and COD removal in the reactor with Fe(0) were higher than those in the control reactor. The sludge granulation was well developed in this reactor. Fe(0) advanced the growth of homoacetogenic bacteria that consumed the hydrogen produced in acetification of propionate. The propionate-oxidizing bacteria and homoacetogenic bacteria grew together in the sludge to accelerate hydrogen transfer, which was an important reason for the enhanced propionate decomposition and sludge granulation in the acidogenesis.