Fast-growing Acer rubrum differs from slow-growing Quercus alba in leaf, xylem and hydraulic trait coordination responses to simulated acid rain

Does fertilization explain the extraordinary hydraulic behaviour of apple trees?

Fertilization of woody plants plays a central role in agriculture and forestry, but little is known about how plant water relations are thereby affected. Here we investigated the impact of fertilization on tree hydraulics, and xylem and pit anatomy in the high-yield apple cultivars Golden and Red Delicious. In fertilized trees of Golden Delicious, specific hydraulic conductivity of branch xylem, hydraulic conductance of the root system, and maximum stomatal conductance increased considerably. In Red Delicious, differences between fertilized and control trees were less pronounced. In both cultivars, xylem embolism resistance of fertilized trees was significantly lower and stomatal closure occurred at lower water potentials. Furthermore, water potential at turgor loss point and osmotic potential at full saturation were higher and cell wall elasticity was lower in fertilized plants, suggesting reduced drought tolerance of leaves. Anatomical differences were observed regarding conduit diameters, cell wall reinforcement, pit membrane thickness, pit chamber depth, and stomatal pore length, with more pronounced differences in Golden Delicious. The findings reveal altered hydraulic behaviour in both apple cultivars upon fertilization. The increased vulnerability to hydraulic failure might pose a considerable risk for apple productivity under a changing climate, which should be considered for future cultivation and management practices.

Effect of simulated acid rain on CO2, CH4 and N2O fluxes and rice productivity in a subtropical Chinese paddy field

The need of more food production, an increase in acidic deposition and the large capacity of paddy to emit greenhouse gases all coincide in several areas of China. Studying the effects of acid rain on the emission of greenhouse gases and the productivity of rice paddies are thus important, because these effects are currently unknown. We conducted a field experiment for two rice croppings (early and late paddies independent experiment) to determine the effects of simulated acid rain (control, normal rain, and treatments with rain at pH of 4.5, 3.5 and 2.5) on the fluxes of CO₂, CH₄ and N₂O and on rice productivity in subtropical China. Total CO₂ fluxes at pHs of 4.5, 3.5 and 2.5 were 10.3, 9.7 and 3.2% lower in the early paddy and 28.3, 14.8 and 6.8% lower in the late paddy, respectively, than the control. These differences from the control were significant for pH 3.5 and 4.5. Total CH₄ fluxes at pHs of 4.5, 3.5 and 2.5 were 50.4, 32.9 and 25.2% lower in the early paddy, respectively, than the control. pH had no significant effect on CH₄ flux in the late paddy or for total (early + late) emissions. N₂O flux was significantly higher at pH 2.5 than 3.5 and 4.5 but did not differ significantly from the flux in the control. Global-warming potentials (GWPs) were lower than the control at pH 3.5 and 4.5 but not 2.5, whereas rice yield was not appreciably affected by pH. Acid rain (between 3.5 and 4.5) may thus significantly affect greenhouse gases emissions by altering soil properties such as pH and nutrient pools, whereas highly acidic rain (pH 2.5) could increase GWPs (but not significantly), probably partially due to an increase in the production of plant litter.