Mycorrhizal symbiosis induces plant carbon reallocation differently in C3 and C4 Panicum grasses

Aims Although arbuscular mycorrhizal symbiosis is common in many plants with either C-3 or C-4 photosynthesis, it remains poorly understood whether photosynthesis type has any significant impact on carbon (C) fluxes in mycorrhizal plants. Thus, we compared mycorrhizal and non-mycorrhizal (NM) plants belonging to Panicum bisulcatum (C-3) to its congeneric P. maximum (C-4). Methods Plants were or were not exposed to arbuscular mycorrhiza (AM) fungal inoculation and/or phosphorus (P) fertilization. Plants' C budgets were assembled based on (CO2)-C-13 pulse-chase labelling and sequential harvesting. Results Mycorrhizal plants allocated on average 3.9% more recently fixed C belowground than did their NM counterparts. At low P, mycorrhizal C-3-Panicum plants allocated less C to aboveground respiration as compared to their respective NM controls. In contrast, mycorrhizal C-4-Panicum increased the rates of photosynthesis and allocated more C to aboveground respiration than the respective NM controls. At high P, the differences were less prominent. Conclusions We demonstrated consistent differences in aboveground C allocation due to AM symbiosis formation in congeneric C-3 and C-4 grasses. Both grasses benefited from AM symbiosis in terms of improved P uptake (at least at low P). These results advocate a holistic (whole-plant) perspective in studying C fluxes in mycorrhizal plants.