Effects of light on the emissions of biogenic isoprene and monoterpenes: A review

Light constitutes one of the most important environmental factors for plant growth and development. Besides its regulatory roles in plant growth and productivity, light also affects synthesis and emission of biogenic volatile organic compounds (BVOCs). The influences of light dependence and combined factors (e.g., canopy and leaf development stages with light) on the emissions of biogenic isoprene (ISO) and monoterpenes (MTs) are reviewed, and their emission mechanisms with different light intensities and quality are summarized. The results show that in the range between zero to the saturation points of ISO and MTs, their emission rates increase with an increment of photosynthetically active radiation, and then remain unchanged or fluctuated. After the light-off action, the emission rates of ISO and MTs rapidly drop to near zero, and there is a low-intensity re-emission phenomenon with the peak appeared within 10–20 min. ISO concentration is the highest at the height of the strong ISO-emitting species inside the canopy. Changes of ISO concentration are consistent with its emission rate, peaking at 12:00–14:00. MTs are emitted and accumulated at night, leading to a lag in the canopy concentration. MTs peak concentrations mostly occur near the ground (0–2 m) in the morning of the next day. The ISO emission rates of mature leaves are 90–130% higher than those of young leaves and senescent leaves. MTs are mainly synthesized during the bud stage when the leaf age is 1–30 days. The highest and lowest emission rates of MTs are in the bud stage and mature leaves, respectively. This review provides references for reducing the uncertainty of BVOC emission factors and for optimizing regional BVOC emission models.