Effects of enriched CO2, temperature, and irrigation on soil properties in greenhouse apple tree cultivation

The significant contributions of anthropogenic activity to global warming are evidenced by the increasing average atmospheric temperatures and CO2 concentration. To date, data on the impact of global warming on crops, particularly field-scale fruit growth and the soil environment, remain lacking. Therefore, we conducted a 4-year monitoring experiment on semi-closed apple tree populations cultivated under the present or near-future climate to assess the effects of atmospheric temperature and CO2 concentrations on soil moisture, temperature, and inorganic ion concentration. Apple saplings were grown in three independent environment-controlled greenhouses, namely greenhouses A (GH_A; control), B (GH_B; high-temperature), and C (GH_C; high-temperature and high CO2), representing climate modification experiments. The pH increased by 0.02, 0.20, and 0.12/year for GH_A, GH_B, and GH_C, respectively. In particular, GH_B (standard irrigation plot; STD) showed a significant pH increase of 0.25/year. The EC increased by 0.014 mS/cm/year for GH_A, decreased by -0.010 mS/cm/year for GH_B, and increased by 0.006 mS/cm/year for GH_C, showing no clear overall increasing or decreasing trend. The NO3 concentration increased by 1.2 mg/L/year for GH_A, decreased by 10.2 mg/L/year for GH_B and decreased by 0.7 mg/L/year for GH_C. The apparent activation energy (Ea) ranged from 85.3 to 214.4 (kJ/mol NH4+) and, regardless of watering treatment, GH_A > GH_B > GH_C. The values in STD plots were 1.4 to 1.7 times those in abundant irrigation plots. Using GH_A (STD) as a standard, the soil temperature dependence of the nitrification rate did not change overall at high or low air temperatures with increasing watering (Ea = 150.5 kJ/mol) or heating (Ea = 154.1 kJ/mol). The soil temperature dependence of the nitrification rate did not vary under heating and increased watering (Ea = 89.5 kJ/mol) or under heating, increased watering, and increased CO2 (Ea = 85.3 kJ/mol). This study provides novel insights into determining the environmental impacts of apple tree community soils under near-future climatic conditions.