Moisture rivals temperature in limiting photosynthesis by trees establishing beyond their cold-edge range limit under ambient and warmed conditions

• Published in: The New phytologist 2015-09, Vol.207 (4), p.1005-1014
• Main Authors: Moyes, Andrew B., Germino, Matthew J., Kueppers, Lara M.
• Format: Article
• Language: English
• Subjects: abiotic stress; alpine treeline; Assimilation; Climate change; Cold Temperature; Colorado; Data lines; Drying; Forest soils; Gases - metabolism; Growing season; Humidity; Low temperature; Microclimate; Microclimates; Mountains; photoinhibition; Photosynthesis; Photosystem II Protein Complex - metabolism; Pine trees; Pinus - physiology; Pinus flexilis; Plant species; Provenance; Response functions; Seasons; Seedlings; Seedlings - physiology; Soil - chemistry; Soil heating; Soil moisture; Soil temperature regimes; Soil water; source limitation; species distribution; Temperature measurement; Timberlines; Time Factors; Treeline; Trees; Trees - physiology; water potential
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/nph.13422

Climate change is altering plant species distributions globally, and warming is expected to promote uphill shifts in mountain trees. However, at many cold-edge range limits, such as alpine treelines in the western United States, tree establishment may be colimited by low temperature and low moisture, making recruitment patterns with warming difficult to predict. We measured response functions linking carbon (C) assimilation and temperature- and moisture-related microclimatic factors for limber pine (Pinus flexilis) seedlings growing in a heating × watering experiment within and above the alpine treeline. We then extrapolated these response functions using observed microclimate conditions to estimate the net effects of warming and associated soil drying on C assimilation across an entire growing season. Moisture and temperature limitations were each estimated to reduce potential growing season C gain from a theoretical upper limit by 15–30% (c. 50% combined). Warming above current treeline conditions provided relatively little benefit to modeled net assimilation, whereas assimilation was sensitive to either wetter or drier conditions. Summer precipitation may be at least as important as temperature in constraining C gain by establishing subalpine trees at and above current alpine treelines as seasonally dry subalpine and alpine ecosystems continue to warm.