Effects of elevated ozone, warming, and their interactions on the stem lodging resistance of rice under fully open-field conditions

Abstract

Global climate change has two notable characteristics: rising ground-level ozone (O₃) concentrations and air temperatures. The goal of this study was to thoroughly examine the interactive effects of these two environmental factors on the rice stem’s lodging resistance. The O₃-temperature-free air enrichment (O₃-T-FACE) facility was used to cultivate a high-yield and high-quality japonica rice (Oryza sativa L.), Nanjing 9108. The experiment involved two levels of O₃ exposure (A-O₃, ambient O₃ concentration; E-O₃, 1.5 times ambient O₃ concentration) and two temperature treatments (CK, ambient temperature; WT, all time warming treatment (CK + 1.6 ℃)) in a field experiment. The study examined the impacts of warming and elevated O₃ concentration on the rice stem’s lodging resistance characteristics. The findings indicated a decreasing trend in the stem height, tiller number, and panicle weight per stem of rice under E-O₃. E-O₃ resulted in a substantial reduction in the pushing resistance of rice at harvest as 32 % and 18 % in intact plants and single stems, respectively. Almost all of the determined parameters for the basal internode traits, including breaking resistance, bending moment, culm wall thickness, cross-sectional area, and dry weight per unit length, were decreased under E-O₃. The changes in the aforementioned parameters caused by E-O₃ became less significant or even slightly increased under warming conditions. WT had no discernible influence on the quantity of tillers, however, it significantly decreased the stem height (-12 %) and single panicle weight (-22 %) of rice. The in situ pushing resistance as well as the basal internode breaking resistance was significantly increased (over 20 %) by WT, resulting in a significant decrease in the basal internodes lodging index (-40 %). This was primarily demonstrated by the shortening of the internode length, and the significant increases in the dry weight per unit length, cross-sectional area, and culm wall thickness of the basal internodes under the warming conditions. The results suggested that the rice stem’s lodging resistance was substantially decreased by E-O₃, whereas WT partially mitigated the O₃-induced negative effects. This can be ascribed to the plant’s relatively low gravity center and the reduced load imposed on the basal internodes, as evidenced by significant decreases in the stem height (basal internodes length) and panicle weight per stem under WT.