# Growth and Photosynthetic Response of _Capsicum annum_ L. in Biochar Amended Soil
## 3 Results
### LAI and PRI Changes over Time  
The data collected on the investigated pepper plants during the experiment showed that the average highest leaf area per plant was measured in the case of BC2.5 treatment (Figure 4). During the first 6 weeks of the experiment, plant growth was substantial, the time at which plant flowering and fruit production began. Statistically significant differences were observed for the treatments between the third and 10 th week of the study (\(p<0.05\)), while the LAI values between week 6 and 10 did not show significant differences (\(p>0.05\); Figure 4). Through the first part of the study, control treatments showed similar growth compared with other treatments; however, by the end of week 12 the lowest leaf areas were observed in the case of control. Average leaf area measurements showed that BC2.5 and BC5.0 had similarly high values (Figure 4) with no significant differences between them at the end of the experiment (\(p>0.05\)). At the same time, BC0.5 had approximately 12% lower leaf areas than the control. The calculated average LAI at the end of the experiment were the following: 1.58, 1.59, 2.03, and 1.89 for control, BC0.5, BC2.5, and BC5.0, respectively (\(n=8\)). However, during earlier plant development stages, higher biochar amendment (BC5.0) also resulted in the highest LAI (Figure 4). In this study we found that BC2.5 treatment was unique in terms of leaf area per plant as it could continuously grow until W12. It is in consistency with the findings that stem thickness and plant height were also larger in this treatment; consequently the total plant biomass as well. Continuous monitoring of the amount of light transferred to the ground using PAR sensors showed that during the first few weeks of the plant growth, there were no differences between plants, especially when only a few leaves might have provided shadows to the sensors causing changes in the measured PAR values. Therefore, data from the first few weeks are demonstrative information only. However, at later weeks, very distinctive changes were observed (Figure 5), resulting in significant differences between the treatments (\(p<0.05\)) for the PAR and fAPAR values. While this measurement technique only provide insight to the light reaching the ground, the destructive method, where all leaves were measured separately, offers more precise LAI values. Both measurements resulted in similar outcomes, biochar addition to the soils increased the LAI of the pepper plants compared to control. Although transmitted radiation data was collected from 4 partial plant canopies per treatment, the calculated intercepted radiation values were in consistency with destructively measured LAI values for all plants, hence both methods can be used to estimate relative changes in plant response to different treatments. The PRI value, which might reflect the stress response from the plants mainly to drought or nitrogen deficiency [37], showed lower values for both BC2.5 and BC5.0 treatment compared to control during the entire measuring time (from week 4 through 12; Figure 6a). The differences between the treatments and control were significant (\(p<0.001\)), indicating changes in light use efficiency when biochar is used in excess amount. However, the difference between BC2.5 and BC5.0 was not significant (\(p>0.05\)). The relationships between the different treatments' PAR and PRI values were investigated (Figure 6b), and we did not find an effect of increasing amount of PAR on the PRI values. Water related stress in the present study only included high water amount, which could pond on the soil surface. Silt loam soil after compaction can slow water movement through the soil matrix [38], which was visually observable after larger precipitation events in the present study. However, these larger precipitation events (>15 mm d\({}^{-1}\)) occurred only four times during the experiment, while drought conditions could be occurring more often without frequent irrigation [30].