Study reveals seasonal peak photosynthesis hindered by late canopy development in northern ecosystems

The dynamic change mechanism of the seasonal peak rate of photosynthesis, also known as GPPmax (Maximum Gross Primary Productivity), has become a hot topic in carbon cycle research. In the Northern Hemisphere, the GPPmax of vegetation is closely related to the year-on-year variation of the ecosystem carbon sink function.

Climate conditions and canopy structure are equally important factors affecting the size and occurrence time of the GPPmax of vegetation. The compatibility of their seasonal peak timings directly determines whether GPPmax is able to reach its maximum potential.

Therefore, in order to more accurately understand the carbon sequestration potential of vegetation in the Northern Hemisphere, it is necessary to understand how the canopy structure of vegetation in the Northern Hemisphere adjusts to changes in environmental conditions, thereby affecting the occurrence time of GPPmax, in times of rapid climate change.

The research group led by Academician Piao Shilong from Peking University College of Urban and Environmental Sciences conducted quantitative analysis on the GPPmax time and normalized difference vegetation index (NDVI, which characterizes the canopy structure of vegetation) of vegetation in the Northern Hemisphere from the past 20 years, and compared the differences in seasonal peak timings and variation mechanisms. Their research was based on multisource remote sensing and flux observation data, combined with machine learning methods.

The study found that compared with the GPPmax time of vegetation, the seasonal peak time of vegetation canopy structure lagged by an average of 8 days, mainly due to climate and nutrient limitations. Over the past 20 years, the increase in atmospheric CO₂ concentration has led to an earlier GPPmax time of vegetation. However, the peak time of vegetation canopy structure remained relatively stable, limited by climate and nutrient conditions. As a result, the mismatch in peak timing between the two is increasing.

The paper is published in the journal Nature Plants.

The study proved that the current ecosystem model does not accurately reflect the spatial-temporal dynamics between GPPmax time of vegetation and peak time of canopy structure. Therefore, related mechanisms have to be enhanced. This study provides a new perspective for understanding the dynamic mechanism of vegetation growth seasons in the Northern Hemisphere.