**4. Conclusions**

Study results supported the hypothesis that wheat straw biochar could be used to decrease soil Cd and Pb bioavailability, decrease Cd and Pb uptake and translocation by rice, and improve a contaminated soil's overall bio-physicochemical characteristics. Biochar improved soil moisture content, increased soil pH, SOM, and reduced Cd and Pb bioavailability. Furthermore, biochar transformed bioavailable Cd and Pb to residual (i.e., unavailable) phases. In turn, biochar helped reduce the BCF and TF within rice, and reduced grain Cd and Pb concentrations to near or below China's national safety concentrations. Other positive responses were observed with respect to greater soil enzymatic activity and microbial community structure, although some positive changes were more evident over shorter (versus longer) time periods following biochar application. Future research should focus on atomic-level mechanisms (e.g., synchrotron-based studies) by which biochar sorbs and stabilizes long-term, in-situ heavy metals over longer time periods and in different soil types.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2076-3298/7/7/53/s1, Figure S1: the schematic diagram fo the acceptor cell title, Figure S2: The effect of long- and short-term, increasing biochar application rates [0(C0), 10 (C1), 20 (C2) and 40 (C3) t ha<sup>−</sup>1] on water-soluble Cd and Pb with in-situ different time (A: Cd long-term; B: Cd short-term; C: Pb long-term; D: Pb short-term), Table S1: Basic paddy soil (0 to 15 cm depth) and biochar (g kg<sup>−</sup>1) properties, Table S2: Bioconcentration (BCF) and translocation (TF) factors associated with biochar amend soil (biochar rates = 0(C0), 10 (C1), 20 (C2) and 40 (C3) t ha<sup>−</sup>1).

**Author Contributions:** Conceptualization, L.C., L.L. and J.Y.; writing—original draft preparation, L.C. and R.B.; formal analysis, L.C., G.Q. and Y.L.; investigation, Y.L.; resources, L.C. and H.W.; review and editing, J.A.I. and L.C.; visualization, H.W.; supervision, L.L. and J.Y.; funding acquisition, L.C. and J.Y. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study received funding from the National Natural Science Foundation of China: 41501339, National Natural Science Foundation of China: 21677119, Jiangsu Province Science Foundation for Youths: BK20140468 and from the QingLan Project.

**Conflicts of Interest:** The authors declare no conflict of interest.
