Soil nitrogen mineralization explains seasonal uncertainty of gross primary production estimation for a deciduous broadleaf forest by a light use efficiency model

Nitrogen is an essential nutrient for plant growth and plays a critical role in photosynthesis and gross primary productivity (GPP). The light use efficiency (LUE) models are perhaps the most classical and widely used to estimate GPP. However, large uncertainties remain in seasonal GPP estimation, partly due to neglecting the effect of nitrogen on ecosystem GPP. Here, we firstly evaluate the error source of LUE model at 89 FLUXNET sites worldwide and found that the large seasonal errors in model estimates were primarily attributable to model structure, particularly the omission of soil nitrogen constraints. We then examined the relationships between soil nitrogen content and tower GPP over the seasonal scale for deciduous broadleaf forests. We found soil nitrogen mineralization, a process for determining soil available nitrogen, closely matched and exhibited strong correlation with observed GPP at daily scale (R 2 = 0.66, p < 0.01), monthly scale (R 2 = 0.74, p < 0.01) and seasonal scales (R 2 = 0.67, p < 0.01). We further found that incorporating soil nitrogen into the estimation of GPP can improve the explained variance of GPP up to 18%. Our results demonstrated that the significant positive impact of soil nitrogen mineralization on GPP cannot be ignored in terrestrial ecosystem GPP estimation by LUE models. Our finding highlights the potential of soil nitrogen mineralization in the estimation of GPP by LUE models for deciduous broadleaf forests.