Interactions between biochar, arbuscular mycorrhizal fungi and photosynthetic processes in potato (Solanum tuberosum L.)

Pyrolyzed biomass, generating biochar for use as soil amendment, is recognized as a promising strategy for carbon sequestration. Current understanding of the interactions between biochar, arbuscular mycorrhizal (AM), and plant photosynthesis, in terms of biochemical processes and CO2 uptake, is fragmentary. The aim of this study was to investigate the effects on photosynthesis in potato including maximum rate of carboxylation by Rubisco (Vcmax), maximum rate of electron transport rate for RuBP-regeneration (Jmax), mesophyll conductance (gm) and other plant traits. Four types of biochar (wheat or miscanthus straw pellets pyrolyzed at temperatures of either 550 °C or 700 °C) were amended into low phosphorus soil. Potato plants were inoculated with the AM fungus Rhizophagus irregularis (M+) or not (M-). The results showed that four types of biochar generally decreased nitrogen and phosphorus content of potato, especially the biochars pyrolyzed at high temperature. This negative effect of biochar on nutrient content was alleviated by AM. It was found that Vcmax was limited by low plant nitrogen content as well as leaf area and phosphorus content. Plant phosphorus content also limited Jmax, which was mutually constrained by Vcmax of leaves. Low gm was an additional limiting factor for photosynthesis. The gm was positively correlated to nitrogen content, which influenced the leaf anatomical structure by alteration of leaf mass per area. In conclusion, the influence of interactions between quality of biochar and AM symbiosis on photosynthesis of potato seems to relate to effects on plant nutrient content and leaf structures. Accordingly, a model for the dependence of Vcmax on nitrogen and phosphorus content and their interactive effect exhibited a high correlation coefficient. As potato plants form AM symbiosis under natural field conditions, the extent and interaction with the quality of amended biochar can be a determining factor for plant nutrient content, growth and yield.