To efficiently improve the productivity of strawberries under growing environmental change, the photosynthesis, root growth, and nitrogen allocation of strawberries (Fragaria × ananassa Duch. cv. Toyonoka) were investigated in a factorial design of CO₂, temperature, and nitrogen supply. Elevated CO₂ decreased the maximum CO₂ assimilation rate (A_max), maximum CO₂ carboxylation capacity per unit leaf area (V_cmax), and maximum CO₂ carboxylation capacity per unit leaf mass (V_cm-m) by 20%, 24%, and 44%, respectively. Meanwhile, it reduced the SPAD value, maximal fluorescence level in the dark-adapted state (F_m), and maximal photochemical efficiency of PSII (F_v/F_m). Moreover, root branches, root number, root dry weight, and nitrogen-use efficiency were further increased in response to elevated CO₂ under low nitrogen. When elevated CO₂ was applied together with nitrogen nutrients, the V_cm-m and root nitrogen concentration (RNC) declined by 32% and 12%, respectively, but the total root dry weight (TRDW) increased by 88%. If the nitrogen nutrient was individually applied, the TRDW decreased by 16%, while the RNC increased by 21%. When the high temperature was individually applied, the TRDW increased by 104%, but the RNC decreased by 5%. Overall, elevated CO₂ exacerbated photosynthetic down-regulation and significantly affected nitrogen redistribution among strawberry organs, reducing leaf nitrogen concentration and accelerating leaf senescence. However, it could increase seed quantity and improve its quality as well. In other words, under nitrogen-deficient conditions, elevated CO₂ could improve the survival of offspring via the cost of the mother plant’s growth capacity.

Elodea nuttallii is a significant submerged macrophyte utilized in shrimp and crab aquaculture, yet it exhibits low thermotolerance. This study investigated the physiological responses and transcriptomic characteristics of E. nuttallii under high-temperature stress (HTS). The results indicated that HTS significantly reduced the absolute growth rate (AGR) and photosynthetic efficiency of E. nuttallii while concurrently elevating antioxidant enzyme activities, malondialdehyde (MDA) content, and concentrations of osmotic adjustment compounds. Furthermore, the apical segments of E. nuttallii demonstrated greater sensitivity to HTS compared to the middle segments. Under exposure to 35 °C and 40 °C, antioxidant enzyme activities, MDA content, and osmotic adjustment compound levels were significantly higher in the apical segments than in the middle segments. Transcriptomic analysis revealed 7526 differentially expressed genes (DEGs) in the apical segments at 35 °C, a number substantially exceeding that observed in the middle segments. Enrichment analysis of DEGs revealed significant upregulation of key metabolic regulators under HTS, including carbohydrate metabolism genes (HXK, FRK) and phenylpropanoid biosynthesis enzymes (4CL, COMT). This transcriptional reprogramming demonstrates E. nuttallii’s adaptive strategy of modulating carbon allocation and phenolic compound synthesis to mitigate thermal damage. Our findings not only elucidate novel thermotolerance mechanisms in aquatic plants but also provide candidate genetic targets (HXK, 4CL) for molecular breeding of heat-resilient cultivars through transcriptomic screening.