## 5 Conclusions  
In summary, this study demonstrated that the nutrient cycling status and microbial community composition changed in response to different biochar applications and rates in the sandy soil. The TC content increased with the biochar application rate increase. MWD also significantly increased with the addition of biochar and may increase C sequestration. The chemically recalcitrant portion of biochar served as a substrate for microbial activity and growth, as reflected in 2019. The addition of biochar altered the microbial community composition by shifting the bacteria from a gram-negative dominated bacterial community to a more gram-positive dominated community and decreasing microbial community stress. These changes promoted microbial community growth as reflected in the elevated total FAMEs and gram-positive bacteria biomarkers detected. Biochar application decreased soil C and P cycling enzyme activities, while the N and S cycling enzymes increased. Furthermore, soil TN, and to a lesser extent, soil moisture and TC, correlated with soil enzymatic activities. The observed changes in biological properties, specifically microbial communities and enzymatic activities, highlight biochar's potential to alter soil biology and, consequently, soil ecosystem functions. Adopting a higher-resolution molecular-based technique such as metagenomic DNA or RNA analyses to study the impact of pinewood biochar on microbial communities is needed for characterizing microbial assemblages at the family, genera, and species levels, which will be useful for understanding microbial community structure and functionality in biochar-amended sandy soils.  
**Supplementary Materials:** The following are available online at [[https://www.mdpi.com/2076-341](https://www.mdpi.com/2076-341)]([https://www.mdpi.com/2076-341](https://www.mdpi.com/2076-341)) 7/11/4/1473/s1. Table S1. Physical and chemical parameters with and without biochar addition. Numbers in bracket represent standard error of the means (\(n=6\)). TC: total carbon; TN: total nitrogen; POXC: active carbon; MWD: mean weight diameter. Inc: incorporated; Sur: surface. The letter indicates statistical significance differences based on the LSD Fisher test with a \(p\)-value < 0.05. Based on [PERSON] et al. [33].  
**Author Contributions:** Conceptualization, T.G. and J.P.F.; methodology, T.G.; software, J.P.F.; validation, T.G.; formal analysis, T.G. and J.P.F.; investigation, T.G. and J.P.F.; resources, T.G., J.P.F., M.F., S.L., B.C. and M.P.; data curation, T.G. and J.P.F.; writing--original draft preparation, J.P.F.; writing--review and editing, T.G. and J.P.F.; visualization, J.P.F.; supervision, T.G.; project administration, T.G.; funding acquisition, T.G. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The authors confirm that the data supporting the findings of this study are available within the article and its supplementary materials.  
**Conflicts of Interest:** The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.