Assessing the interplay between canopy energy balance and photosynthesis with cellulose δ18O: large-scale patterns and independent ground-truthing
There are few whole-canopy or ecosystem scale assessments of the interplay between canopy temperature and photosynthesis across both spatial and temporal scales. The stable oxygen isotope ratio (δ18O) of plant cellulose can be used to resolve a photosynthesis-weighted estimate of canopy temperature, but the method requires independent confirmation. We compare isotope-resolved canopy temperatures derived from multi-year homogenization of tree cellulose δ18O to canopy-air temperatures weighted by gross primary productivity (GPP) at multiple sites, ranging from warm temperate to boreal and subalpine forests. We also perform a sensitivity analysis for isotope-resolved canopy temperatures that showed errors in plant source water δ18O lead to the largest errors in canopy temperature estimation. The relationship between isotope-resolved canopy temperatures and GPP-weighted air temperatures was highly significant across sites (p < 0.0001, R2 = 0.82), thus offering confirmation of the isotope approach. The previously observed temperature invariance from temperate to boreal biomes was confirmed, but the greater elevation of canopy temperature above air temperature in the boreal forest was not. Based on the current analysis, we conclude that canopy temperatures in the boreal forest are as warm as those in temperate systems because day-time-growing-season air temperatures are similarly warm.
KeywordsStable oxygen isotope Energy balance Canopy temperature Leaf temperature Gross primary production δ18O
BRH would like to acknowledge the intellectually stimulating and unfailingly supportive environment provided by Jim Ehleringer during those young and formative years, despite the ongoing and fruitless quest to locate Baby Jesus. BRH and XS were supported by the National Science Foundation under award number IOS-0950998. The National Center for Atmospheric Research (NCAR) is sponsored by NSF.
Author contribution statement
BRH and XS conceived and designed the data collection and modeling approach. BRH, XS, MLG, KC, PB, JWM, JC, AN, DH, SW, TM, DB, EE, AD and SPB collected and analyzed data. BRH and XS wrote the manuscript; other authors provided editorial advice.
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