Short-term effects of biochar on grapevine fine root dynamics and arbuscular mycorrhizae production

Application of biochar to the soil is globally recognised as a means to improve soil structure and fertility, increase carbon sequestration, enhance crop production and mitigate climate change. However, although the fine root system is fundamental for plant growth, crop productivity, carbon and nutrient cycling, little is known about the effect of biochar on plant fine roots. This study, conducted in a Montepulciano (Vitis vinifera L.) vineyard, was aimed at investigating the impact of biochar application (at the rate of 10 t ha−1) on soil chemical and physical properties, fine root dynamics and arbuscular mycorrhizal fungi (AMF) production during a one-year sampling period. To this aim, seasonal variation of fine root mass, length and diameter was measured by the sequential coring technique, whereas fine root annual production was calculated by minimum-maximum procedure and turnover rate of live roots by maximum standing biomass. For AMF annual production, in-growth mesh bags were used to measure glomalin as quantitative indicator of mycorrhizae presence. Results showed that biochar significantly increased organic carbon (20.7%), available ammonium (84.4%), and available water content of the soil (11.8%), while it also promoted the formation of the large fraction of macro aggregates (ø > 2 mm; 3.1% control; 5.5% treated). Cation exchange capacity, pH, total nitrogen content, and total and available phosphorus content remained unaffected. Immediately after biochar soil amendment, while fine root length remained unchanged, a significant increase in fine root biomass was measured resulting in a higher mean annual biomass (8.56 g m−2 control; 13.34 g m−2 treated), annual production (8.71 g m−2 control; 12.7 g m−2 treated) and lifespan (as evidenced by a lower turnover rate; 1.02 yr−1 control; 0.95 yr−1 treated). Moreover, the increase of fine root biomass resulted to be associated with radial growth since mean fine root diameter was significantly higher in biochar-treated plants (0.56 mm) than in control plants (0.46 mm). Biochar had no significant effect on the annual production of AMF. The results of the present study show that the improvements of soil chemical and physical features due to biochar application have an immediate effect on fine root dynamics and morphology. Furthermore, the increase of fine root biomass is mainly due to radial growth and occurs during the water shortage period, supporting fruit setting and ripening in grapevine plants.