Theory 58/Carbon cycle/Onset phase
Uptake Begins on a Light Threshold
The claim
The growing-season carbon sink begins above a threshold in the ratio of light to temperature limitation, so an early warm spring without light adds little uptake.
01Mechanism
Photosynthesis requires both; the ratio determines when the canopy becomes a net sink.
02Prediction
Sink onset should track the ratio.
03Refutation
Onset tracking temperature would remove light.