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The carbon fertilization effect over a century of anthropogenic CO2 emissions: higher intracellular CO2 and more drought resistance among invasive and native grass species contrasts with increased water use efficiency for woody plants in the US Southwest

Drake, Brandon L., Hanson, David T., Lowrey, Timothy K., Sharp, Zachary D.
Global change biology 2017 v.23 no.2 pp. 782-792
Bromus, C3 plants, Pinus edulis, Pinus longaeva, Poa, acclimation, carbon, carbon dioxide, data collection, drought, drought tolerance, dry environmental conditions, free air carbon dioxide enrichment, grasses, greenhouse gas emissions, indigenous species, invasive species, photosynthesis, plant growth, reproduction, stomatal conductance, trees, water shortages, water use efficiency, wet environmental conditions, woody plants, New Mexico
From 1890 to 2015, anthropogenic carbon dioxide emissions have increased atmospheric CO₂ concentrations from 270 to 400 mol mol⁻¹. The effect of increased carbon emissions on plant growth and reproduction has been the subject of study of free‐air CO₂ enrichment (FACE) experiments. These experiments have found (i) an increase in internal CO₂ partial pressure (cᵢ) alongside acclimation of photosynthetic capacity, (ii) variable decreases in stomatal conductance, and (iii) that increases in yield do not increase commensurate with CO₂ concentrations. Our data set, which includes a 115‐year‐long selection of grasses collected in New Mexico since 1892, is consistent with an increased cᵢ as a response to historical CO₂ increase in the atmosphere, with invasive species showing the largest increase. Comparison with Palmer Drought Sensitivity Index (PDSI) for New Mexico indicates a moderate correlation with Δ¹³C (r² = 0.32, P < 0.01) before 1950, with no correlation (r² = 0.00, P = 0.91) after 1950. These results indicate that increased cᵢ may have conferred some drought resistance to these grasses through increased availability of CO₂ in the event of reduced stomatal conductance in response to short‐term water shortage. Comparison with C₃ trees from arid environments (Pinus longaeva and Pinus edulis in the US Southwest) as well as from wetter environments (Bromus and Poa grasses in New Mexico) suggests differing responses based on environment; arid environments in New Mexico see increased intrinsic water use efficiency (WUE) in response to historic elevated CO₂ while wetter environments see increased cᵢ. This study suggests that (i) the observed increases in cᵢ in FACE experiments are consistent with historical CO₂ increases and (ii) the CO₂ increase influences plant sensitivity to water shortage, through either increased WUE or cᵢ in arid and wet environments, respectively.