# Biochar Improved Sugarcane Growth and Physiology under Salinity Stress
## 3 Results
### Effects of Salinity and Biochar Application on Physiological Responses of Sugarcane  
Generally, photosynthetic efficiency (Fv /Fm) and chlorophyll content (SPAD) of sugarcane were significantly affected by salinity and decreased over time (Figure 3). Photosynthetic efficiency (Fv/Fm) decreased from week 8 while the chlorophyll content decreased as soon as the salinity treatment was applied. Biochar application also increased photosynthetic efficiency (Fv/Fm) and chlorophyll content with the highest values recorded at the rate of 10 tons ha\({}^{-1}\) under both non-saline and saline conditions.  
On the final day of salinity treatment, no significant difference in the relative ion leakage was found among three levels of biochar application under non-salinity treatment (Figure 4A). However, the addition of 10 ton ha\({}^{-1}\) resulted in significantly lower relative ion leakages compared with that of 0 and 5 tons ha\({}^{-1}\) in salinity. In addition, the influences of biochar application were clearly seen at 4 weeks after the salinity treatment (Figure 4B). Biochar significantly reduced the relative ion leakages of sugarcane. This was observed under both salinity and non-salinity conditions. An increase in the level of applied biochar led to a larger reduction in the relative ion leakages with the smallest values of this parameter recorded in plants with 10 tons-ha\({}^{-1}\) of biochar (Figure 4B). Salinity stress had a significant effect on relative ion leakage with higher values at salinity treatment. However, applying biochar minimized the impact of salinity stress which was shown by smaller differences in relative ion leakage values between non-salinity and salinity treatments at biochar-applied treatments compared with non-biochar-applied treatments.  
Salinity increased the water saturation deficit in sugarcane leaves (Figure 5). Applying biochar helped reduce the water saturation deficit compared with the control (without biochar). On the final salinity treatment day, an increase in the level of biochar application resulted in a decrease in the water saturation deficit, with the lowest values of this parameter recorded at plants applied with 10 tons-ha\({}^{-1}\) under both saline and non-saline conditions. However, in four weeks after the final salinity treatment day, an increase in biochar from 5 to 10 tons-ha\({}^{-1}\) only helped to decrease the water saturation deficit of plants under saline conditions. The effects of different rates of biochar were not significantly observed in plants in control conditions (non-saline).  
Figure 2: Root volume of sugarcane in response to biochar treatments of 0, 5, and 10 tons ha\({}^{-1}\) under non-saline and saline conditions on the final treatment day (**A**) and 4 weeks after the final treatment day (**B**). Vertical bars represent \(\pm\) SD, \(n=9\). Different letters showed significance among biochar rates under non-salinity (capital letters) and salinity (lowercase letters), respectively, by [PERSON]’s multiple range tests at \(p\leq 0.05\). For salinity treatment, significance levels (\(t\)-test) are demonstrated as follows: ns: non-significant; *: \(p<0.05\).  
Figure 3: The quantum efficiency of photosystem II (Fv/Fm) and chlorophyll content (SPAD) of sugarcane in response to salinity treatments under 0, 5, and 10 tons of biochar hs\({}^{-1}\). Vertical bars represent mean \(\pm\) SD, \(n=12\). PTP: Pre-treating period, TP: Treating period, ATP: After treating period. Significance levels (\(b\)-test): ns: non-significant; \(p<005\), \(n\); \(p<0.01\); \(n\); \(p<0.001\).