Elevated CO ₂ induces substantial and persistent declines in forage quality irrespective of warming in mixedgrass prairie

Journal Article · 28 February 2018 · Ecological Applications

DOI: https://doi.org/10.1002/eap.1680 · OSTI ID:1423173

Augustine, David J. ^[1]; Blumenthal, Dana M. ^[1]; Springer, Tim L. ^[2]; LeCain, Daniel R. ^[1]; Gunter, Stacey A. ^[2]; Derner, Justin D. ^[3]

---

1. Rangeland Resources and Systems Research Unit USDA Agricultural Research Service 1701 Centre Avenue Fort Collins Colorado 80525 USA
2. Southern Plains Range Research Station USDA Agricultural Research Service 2000 18th Street Woodward Oklahoma 73801 USA
3. Rangeland Resources and Systems Research Unit USDA Agricultural Research Service 8408 Hildreth Road Cheyenne Wyoming 82009 USA

Abstract Increasing atmospheric [ CO ₂ ] and temperature are expected to affect the productivity, species composition, biogeochemistry, and therefore the quantity and quality of forage available to herbivores in rangeland ecosystems. Both elevated CO ₂ ( eCO ₂ ) and warming affect plant tissue chemistry through multiple direct and indirect pathways, such that the cumulative outcomes of these effects are difficult to predict. Here, we report on a 7‐yr study examining effects of CO ₂ enrichment (to 600 ppm) and infrared warming (+1.5°C day/3°C night) under realistic field conditions on forage quality and quantity in a semiarid, mixedgrass prairie. For the three dominant forage grasses, warming effects on in vitro dry matter digestibility ( IVDMD ) and tissue [N] were detected only in certain years, varied from negative to positive, and were relatively minor. In contrast, eCO ₂ substantially reduced IVDMD (two most abundant grasses) and [N] (all three dominant grass species) in most years, except the two wettest years. Furthermore, eCO ₂ reduced IVDMD and [N] independent of warming effects. Reduced IVDMD with eCO ₂ was related both to reduced [N] and increased acid detergent fiber ( ADF ) content of grass tissues. For the six most abundant forage species (representing 96% of total forage production), combined warming and eCO ₂ increased forage production by 38% and reduced forage [N] by 13% relative to ambient climate. Although the absolute magnitude of the decline in IVDMD and [N] due to combined warming and eCO ₂ may seem small (e.g., from 63.3 to 61.1% IVDMD and 1.25 to 1.04% [N] for Pascopyrum smithii ), such shifts could have substantial consequences for the rate at which ruminants gain weight during the primary growing season in the largest remaining rangeland ecosystem in North America. With forage production increases, declining forage quality could potentially be mitigated by adaptively increasing stocking rates, and through management such as prescribed burning, fertilization at low rates, and legume interseeding to enhance forage quality.

• Sponsoring Organization: USDOE
• Grant/Contract Number: SC0006973
• OSTI ID: 1423173
• Journal Information: Ecological Applications, Journal Name: Ecological Applications Journal Issue: 3 Vol. 28; ISSN 1051-0761
• Publisher: Wiley Blackwell (John Wiley & Sons)Copyright Statement
• Country of Publication: United States
• Language: English