Fungal endophytes from yellowstone CO2 hot springs enhance plant growth due to elevated CO2

Background/Question/Methods

Many C3 plants show enhanced growth when exposed to elevated levels of CO₂. However, this enhancement is often diminished when exposed to long-term elevated CO₂ as a result of down-regulatory acclimation. Dozens of fungal endophytes have been isolated from indigenous plants surviving in very high CO₂ conditions (> 2,000 ppm) near the Mammoth Hot Springs at Yellowstone National Park, Wyoming. These fungal endophytes confer tolerance to toxic CO₂ levels in host plants as a mechanism of habitat adapted symbiosis (HAS). In this study we tested if selected strains of the fungal endophytes from the CO₂ springs will 1) confer improved CO₂ fertilization effects in non-indigenous host plants under moderately elevated CO₂ (800 ppm), and 2) exhibit little or no down-regulation of the CO₂ fertilization effect on the growth of these host plants under moderately elevated CO₂. Two endophytes out of 29 strains were analyzed to determine if they contributed to high CO₂ adaptation by plants.  The endophytes were chosen based on growth characteristics in axenic culture. Xylariales sp.(XS) had a high growth rate in elevated CO₂ and Polyscytalum  pustulans (PP) had a slow growth rate under the same conditions.

Results/Conclusions

Seeds and seedlings of Phytolacca americana (pokeweed) were inoculated with XS and PP endophytes and grown under ambient (400 ppm) and elevated (800 ppm) CO₂ levels in transparent chambers in a greenhouse. Plants symbiotic with XS (XS-S) had more pronounced and lasting growth benefits (e.g., increased biomass and increased leaf chlorophyll content) compared to plants that were inoculated with PP (PP-S) or non-symbiotic (NS) control plants in elevated CO₂ conditions. At elevated CO₂ levels, the XS-S, PP-S and NS plants consumed less water per plant over the entire growth period and produced greater root biomass than their counterparts grown at ambient CO₂. No clear difference was found in total water use between endophyte treatments. Our results 1) highlight the functional importance of fungal endophytes for plants’ adaptation to high CO₂ environments and 2) illustrate potential applications of this symbiotic relationship to capitalize on the benefits of increasing atmospheric CO₂ for crop production in the context of climate change.