Plant Light Stress Tolerance across the New Mexico Elevation Gradient: Scaling from Leaf to Tower

Excess light is a major abiotic component of plant stress especially when combined with sustained periods of drought. Arid and semi-arid ecosystems are regularly exposed to sustained high light, low water conditions. A network of nine Eddy Covariance towers oriented along an elevation gradient in central New Mexico has been utilized to assess differences in light use efficiency and light stress response across six distinct biomes, all of which are subjected to a semi-arid climate regulated by a seasonal monsoon. Leaf level measurements of effective quantum yield (ΦPSII ) and non-photochemical quenching (NPQ) parameters were taken at five of these biomes pre and post monsoon using branch mounted and hand held pulse amplitude modulated (PAM) fluorometers. Diurnal samples of leaf tissue were snap frozen to be analyzed for xanthophyll de-epoxidation state via high pressure liquid chromatography. We analyzed these leaf level parameters in the context of tower based and satellite derived measurements of NDVI, PRI and eddy covariance measures of ecosystem function including net ecosystem exchange and light use efficiency. This multi-biome, multi-scale approach aims to investigate not only leaf level photochemical response to excess light, but also how these responses are perceived by remote sensing platforms at flux tower and low earth orbit scales. We hypothesize that plant photochemical status with respect to light use efficiency and excess light mitigation strategies fluctuates as a function of elevation and the seasonal monsoon. We expect to see the highest regulatory capacity at low elevation, low precipitation sites. The NDVI and PRI signal from the tower level will track changes in ecosystem function with respect to NEE and be explained by differences in the ability of biome specific plant functional types to deal with excess light. The tower footprint, parameterized by plant functional type constituents, will be scaled to the landscape level by analysis of MODIS products.