Gross primary productivity (GPP), along with its spatial and temporal variations, is a critical component of the global carbon cycle. Maximum daily GPP (GPPmax) is an important indicator of vegetation's physiological capacity and a primary determinant of ecosystem-level GPP. However, the spatial and temporal dynamics of GPPmax and the underlying climatic controls remain poorly understood. This study synthesized GPPmax data from 859 site-years of eddy covariance observations across 103 flux tower sites in the Northern Hemisphere. We examined spatial patterns, interannual variability, and climatic drivers of GPPmax. GPPmax ranged from 0.87 g C m-2 d-1 to 16.87 g C m-2 d-1, with a mean of 9.07 +/- 3.15 g C m-2 d-1. Temperate ecosystems exhibited the highest GPPmax, with a mean value of 11.06 +/- 2.32 g C m-2 d-1, whereas arid zones showed the lowest, averaging 6.14 +/- 3.24 g C m-2 d-1. Forest ecosystems showed significantly higher GPPmax than other vegetation types. GPPmax increased with latitude up to 50 degrees N, then declined. Climatic factors, including radiation, temperature, and water availability, explained 46 % of the spatial variability. Interannual variability in GPPmax ranged from 0.37 % to 56.14 %, with the highest variability in arid zones. Radiation, temperature, and water availability were the dominant climatic drivers at 41 %, 30 %, and 29 % of sites, respectively. These findings provide new insights into the climatic controls and variability of ecosystem photosynthetic capacity, which can improve GPP estimates and contribute to more accurate carbon modeling and enhance predictions of vegetation responses to climate change.