Understanding the yield attributes of the popular rice (Oryza sativa L.) hybrids can provide useful information for developing new hybrid rice varieties. Field experiments were conducted at two subtropical sites (Hengyang and Xingyi) in two years (2021 and 2022) to compare grain yield and yield attributes of three currently popular hybrid rice varieties (Jingliangyouhuazhan, Jingliangyou 534, and Longliangyouhuazhan) with three representative super hybrid rice varieties (Y-liangyou 1, Y-liangyou 2, and Y-liangyou 900). No significant differences in grain yield were observed between the group of popular hybrids and the group of super hybrids at Hengyang and Xingyi in 2021 or at Xingyi in 2022, but at Hengyang in 2022, the group of popular hybrids produced a 15% higher grain yield. The grain yield at Hengyang in 2022 was lower than that at Hengyang and Xingyi in 2021 and at Xingyi in 2022. At Hengyang in 2022, the group of popular hybrids had 9–15% higher panicles per m², spikelet filling percentage, and harvest index but similar spikelets per panicle and total biomass production and 12% lower grain weight compared to the group of super hybrids. Correlation plot analysis showed that grain yield was significantly related to panicles per m² but not other yield attributes across six varieties at Hengyang in 2022. These results indicated that the currently popular hybrid rice varieties had higher yield performance than the representative super hybrid rice varieties under the condition of relatively lower productivity, and the key factor for this higher yield performance in the popular hybrids was the higher panicles per m². This finding highlights that more attention should focus on the yield performance under medium- and low-productivity conditions in hybrid rice breeding programs, and an effective breeding strategy is to select the varieties with high panicle numbers.

The availability of commercially available portable photosynthesis systems has facilitated widespread photosynthetic research. Our study aimed to evaluate the reliability of a recently developed inexpensive portable photosynthesis system, Yaxin-1105, in measuring gas exchange in rice (Oryza sativa L.) leaves. Gas exchange parameters, including net photosynthetic rate (A_net), stomatal conductance (g_s), intercellular CO₂ concentration (C_i), and transpiration rate (E), were measured on 88 rice leaves across seven rice cultivars and three growth stages (panicle initiation, heading, and early ripening), using both Yaxin-1105 and LI-6400XT. There were significant difference between each gas exchange parameter at each growth stage measured by Yaxin-1105 and LI-6400XT, except C_i at the heading stage. Mean A_net, g_s, and E measured by Yaxin-1105 were 26–66% lower than those measured by LI-6400XT at panicle initiation, heading, and early ripening stages. Mean C_i measured by Yaxin-1105 was 13–22% higher than that measured by LI-6400XT at panicle initiation and early ripening stages. The coefficients of determination between each gas exchange parameter measured by Yaxin-1105 and by LI-6400XT at panicle initiation, heading, and early ripening stages ranged from only 0.0007 to 0.1889. These results indicate that the Yaxin-1105 is not a reliable tool for measuring gas exchange in rice leaves.

Mechanical transplanting often causes root damage to rice seedlings, but its yield impacts in double-cropping systems remain unclear. A two-year field experiment was conducted in early- and late-season rice under three root damage treatments: no damage (CK), mild root damage (T1, seedling roots pruned to 2 cm), and severe root damage (T2, seedling roots pruned to 1 cm). Results showed that T2 reduced early-season rice yield by 8% but had no significant effect on late-season rice, while T1 did not affect yield in either season. In early-season rice, the yield loss was associated with reduced pre-heading biomass (BM_Pre) and total biomass (both 13% lower than CK), primarily due to decreases of 5–32% in SPAD, leaf area index, specific leaf weight, pre-heading crop growth rate, and leaf area duration, with no post-heading compensation. In contrast, late-season rice sustained yield despite a 9% reduction in BM_Pre (attributed to similar leaf trait reductions of 4–26%) by enhancing post-heading biomass (16% increase), driven by a 17% increase in post-heading crop growth rate and an 11% decrease in the rate of leaf area decline. Partial least squares path modeling confirmed that biomass dynamics, rather than yield components, constituted the primary pathway linking root damage to yield. These results demonstrate that the impact of root damage is season-dependent, highlighting the need for root protection in early-season rice and the exploitation of compensatory capacity in late-season rice to optimize mechanical transplanting practices.

Cadmium (Cd) contamination in paddy soils represents a major risk to global food security and human health because Cd can readily enter the food chain through rice consumption. Therefore, clarification of the key processes and mechanisms by which agronomic practices regulate Cd accumulation in rice is essential. Based on integrated two-year pot and field experiments, we showed that different nitrogen fertilizer formulations, including nitrate-N (N), ammonium-N (A), and urea (U), had distinct effects on Cd accumulation and grain yield in rice. The N treatment reduced Cd concentrations in brown rice by 25.29% to 70% in the pot experiment and by 4.25% to 89.97% in the field experiment but decreased grain yield by 5% to 25%. By contrast, the A treatment increased Cd concentrations in brown rice by 17.86% to 58.62%, while maintaining or slightly increasing grain yield (−3% to +5%), and the U treatment showed intermediate responses. These responses were mainly associated with nitrogen-induced shifts in rhizosphere chemistry, especially changes in soil Cd availability linked to pH and exchangeable H⁺, although unmeasured redox-related processes may have also contributed under flooded conditions. Further analyses of internal Cd distribution and translocation, together with exploratory random forest modeling, suggested that Cd transport efficiency at key stem internodes and Cd redistribution from the panicle to the grain were important regulatory nodes associated with Cd concentrations in brown rice. These regulatory nodes were markedly affected by fertilizer formulation. Overall, our results describe a continuous pathway from rhizosphere Cd availability to internal transport and partitioning, through which nitrogen fertilizer formulations regulate Cd accumulation in rice. This study aimed to clarify how different nitrogen fertilizer formulations regulate the trade-off between grain yield and Cd accumulation in rice, based on the hypothesis that these formulations differentially modify rhizosphere chemistry and Cd bioavailability, that specific stem nodes contribute to control of grain Cd accumulation, and that the main regulatory processes differ between pot and field systems. This study provides s a scientific basis for developing practical nitrogen-management strategies to support safe rice production in Cd-contaminated paddy fields.

The simultaneous challenges of cadmium (Cd) contamination and mineral nutrient imbalance in paddy systems necessitate the development of effective agronomic strategies. This study systematically investigated the coordinated effects of different nitrogen fertilizer forms on the accumulation and translocation of Cd and mineral elements in rice. A hydroponic experiment was conducted using four N sources, including urea (U), nitrate-N (N), ammonium-N (AN), and a mixed ammonium-nitrate source (NN), which were applied at two concentrations (2.9 and 5.8 mM L⁻¹). We evaluated Cd accumulation, mineral element uptake, and translocation in rice seedlings under Cd stress. The results indicated that both the form and level of nitrogen markedly affected Cd accumulation. The AN treatment exhibited a strong Cd-reduction effect, especially at the higher nitrogen level, where it significantly reduced Cd concentration in roots and shoots by 68.75% and 26.81%, respectively. In contrast, the N treatment increased Cd accumulation in roots. Nitrogen fertilization also differentially influenced the accumulation of mineral elements, resulting in notable alterations in root Ca, Mg, Cu, and Zn concentrations, while shoot mineral concentrations remained relatively stable. Correlation and random forest analyses revealed a highly significant positive correlation between root Cd concentration and Mg and Cu concentrations, a significant negative correlation with Zn concentration, and a synergistic relationship between the translocation of Cd and that of Ca, Mg, and Cu. Analysis of ion channel tolerance rates further indicated that the AN treatment suppressed Cd uptake by reducing the permeability of root trace element channels to Cd. These findings demonstrate that nitrogen forms modulate Cd accumulation and partitioning by regulating competitive ion uptake and coordinated translocation. In particular, the AN treatment shows promising potential for reducing Cd accumulation while maintaining mineral nutrient balance, thereby providing a theoretical foundation for precise nitrogen management in Cd-contaminated paddy fields.