# Biochar-Improved Growth and Physiology of _Eltretia asperula_ under Water-Deficit Condition
## 4 Discussion  
Drought stress affects the growth, phenology, water and nutrient relations, photosynthesis, assimilate-partitioning, and respiration in plants, which results in the production of smaller organs [27]. These phenomena are controlled by physiological factors, such as plant hydraulic status, phytohormones, osmotic adjustment, and reactive oxygen species signaling [28; 29]. In our study, water stress significantly decreased the growth and photosynthetic efficiency of _Ehretia asperula_, as demonstrated by the analysis of parameters such as plant height, number of leaves, dry biomasses of root, shoot, and leaves; \(\rm F_{v}/F_{m}\), chlorophyll content, and leaf relative water content.  
Biochar not only improves the soil structure, fertility, and ion transfer ability but also increased the activity of microbes and nutrient holding and exchange capacity of the soil. Therefore, biochar addition is proposed as an effective management to improve crop performance [21], as supported by the results we obtained from the experiments on _Ehretia asperula_ plants, for which all biochar treatments clearly improved the growth characteristics such as plant height; number of leaves; and dry biomasses of root, shoot and leaves. These results agree with previous data obtained by several researchers who reported that the application of biochar increased the plant height and leaf area of okra [30] and maize [31] under drought-stress conditions. In addition, [PERSON] et al. [32] reported that the application of biochar increased the biomass of field-grown wheat under semiarid Mediterranean conditions. Moreover, [PERSON] et al. [33] also found that the application of biochar in silt clay soil increased the growth of tomato plants when compared with the control.  
On the other hand, several studies have reported that biochar addition improved photosynthesis in plants under drought-stress conditions [18; 34; 35]. Biochar increased photosynthesis and water-use efficiency of okra under drought stress when compared with the control [30]. In addition, biochar increased the water-use efficiency of _Chenopodium quinao_ wild under drought stress [36] and increased the water-use efficiency of maize in sandy soil [37]. Therefore, in our study, WB treatments inversely increased the SPAD values, photosynthetic efficiency (\(\rm F_{v}/F_{m}\)), and leaf relative water content of _Ehretia asperula_ significantly. These results agree with previous results obtained by [PERSON] et al. [31], who reported that biochar application increased the leaf relative water content, transpiration rate, and osmotic potential of drought-stressed maize when compared with the control. In addition, [PERSON] et al. [38] also showed that the application of biochar significantly improved physiological characteristics such as chlorophyll content, stomatal conductance, photosynthetic rate, water-use efficiency, and leaf relative water content as well as increased the stomatal density of tomato leaves under drought stress conditions.  
Biochar improves the physical and biological properties of soils and increases the water-holding capacity of soil under drought stress conditions [39]. In our study, the application of WB significantly increased soil moisture under WSC. On the other hand, WB application enhanced the drought tolerance of _Ehretia asperula_ plants by lowering the wilting point. These results agree with previous results obtained by [PERSON] et al. [38] and [PERSON] et al. [40], who found that biochar application greatly increased the water-holding capacity of soil and, consequently, enhanced plant physiological characteristics such as chlorophyll content, stomatal conductance, photosynthetic rate, and leaf relative water content. In addition, [PERSON] et al. [41] also demonstrated that biochar application in sandy soil significantly increased tomato seedling resistance to wilting.