Interacting Effects of CO₂, Temperature, and Nitrogen Supply on Photosynthetic, Root Growth, and Nitrogen Allocation of Strawberry at the Fruiting Stage

To efficiently improve the productivity of strawberries under growing environmental change, the photosynthesis, root growth, and nitrogen allocation of strawberries (<i>Fragaria</i> × <i>ananassa</i> 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.