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

Abstract

Although arbuscular mycorrhizal symbiosis is common in many plants with either C3 or C4 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 (C3) to its congeneric P. maximum (C4). Plants were or were not exposed to arbuscular mycorrhiza (AM) fungal inoculation and/or phosphorus (P) fertilization. Plants’ C budgets were assembled based on 13CO2 pulse-chase labelling and sequential harvesting. Mycorrhizal plants allocated on average 3.9% more recently fixed C belowground than did their NM counterparts. At low P, mycorrhizal C3-Panicum plants allocated less C to aboveground respiration as compared to their respective NM controls. In contrast, mycorrhizal C4-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. We demonstrated consistent differences in aboveground C allocation due to AM symbiosis formation in congeneric C3 and C4 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.