Publications

Jonard, F; Feldman, AF; Gianotti, DJS; Entekhabi, D (2022). Observed water and light limitation across global ecosystems. BIOGEOSCIENCES, 19(23), 5575-5590.

Abstract
With a changing climate, it is becoming increasingly critical tounderstand vegetation responses to limiting environmental factors. Here, weinvestigate the spatial and temporal patterns of light and water limitationon photosynthesis using an observational framework. Our study is unique incharacterizing the nonlinear relationships between photosynthesis and waterand light, acknowledging approximately two regime behaviours (no limitationand varying degrees of limitation). It is also unique in using anobservational framework instead of using model-derived photosynthesisproperties. We combine data from three different satellite sensors, i.e.,sun-induced chlorophyll fluorescence (SIF) from the TROPOspheric Monitoring Instrument (TROPOMI), surface soilmoisture from the Soil Moisture Active Passive (SMAP) microwave radiometer, and vegetation greenness from the ModerateResolution Imaging Spectroradiometer (MODIS). We find bothsingle-regime and two-regime models describe SIF sensitivity to soilmoisture and photosynthetically active radiation (PAR) across the globe. Thedistribution and strength of soil moisture limitation on SIF are mapped inthe water-limited environments, while the distribution and strength of PARlimitations are mapped in the energy-limited environments. A two-regimebehaviour is detected in 73 % of the cases for water limitation onphotosynthesis, while two-regime detection is much lower at 41 % for light limitation on photosynthesis. SIF sensitivity to PAR strongly increasesalong moisture gradients, reflecting mesic vegetation's adaptation to makingrapid usage of incoming light availability on the weekly timescales. Thetransition point detected between the two regimes is connected to soil typeand mean annual precipitation for the SIF-soil moisture relationship and forthe SIF-PAR relationship. These thresholds therefore have an explicitrelation to properties of the landscape, although they may also be relatedto finer details of the vegetation and soil interactions not resolved by thespatial scales here. The simple functions and thresholds are emergentbehaviours capturing the interaction of many processes. The observationalthresholds and strength of coupling can be used as benchmark information forEarth system models, especially those that characterize gross primaryproduction mechanisms and vegetation dynamics.

DOI:
10.5194/bg-19-5575-2022

ISSN:
1726-4189