The role of biochar in improving the survival, growth and physiological traits of Arizona cypress seedlings, in a semi-arid mountainous region

Biochar, a porous carbon-rich substance, is considered a soil amendment with the ability to preserve food and water and increase drought tolerance in plants. The present study aimed to investigate the effects of biochar (derived from hornbeam wood and produced at a pyrolysis temperature of 450 °C) on the survival, growth, and physiological traits of Arizona cypress (Cupressus arizonica Green) seedlings under rainfed and irrigation conditions in a mountainous degraded forest (Do-Ab in Savadkouh region, north of Iran).

The experiment was conducted as a completely randomized design for five months during the dry months of spring and summer. The treatment combinations included: 1) control soil-irrigation, 2) control soil-rainfed, 3) soil treated with biochar-irrigation, and 4) soil treated with biochar-rainfed. Two-way analysis of variance (AOVA) was used to determine the significant effect of the treatments, and a paired t-test was used to compare the means.

The results showed that, regardless of the effect of soil treatment, irrigated seedlings had greater survival (90%) compared to rainfed seedlings (56%). However, under rainfed conditions, the survival rate in the biochar treatment was 75%, almost twice that of the control soil. In both rainfed and irrigation conditions, the seedlings grown with biochar had larger sizes than those in the control soil. Regardless of the effect of soil treatment, the rates of photosynthesis and transpiration decreased under rainfed conditions. Similar to the irrigation treatment, the biochar treatment caused an increase in gas exchanges (20-60%) compared to those in the control soil. Mesophyll conductance, relative water content, and photosynthetic pigments were higher in the irrigation treatment than in the rainfed condition.

To restore the degraded forests of the semi-arid mountainous regions of northern Iran with Arizona cypress seedlings, it is recommended that in the early years, the seedlings be managed by irrigation without applying biochar. However, under rainfed conditions, it is recommended to use biochar to enhance seedling survival and growth.