Abstract Solar radiation is an important factor influencing dryland decomposition. Research suggests that, in the presence of water, previously irradiated plant litter experiences greater microbial decay than litter which was not exposed to radiation. The mechanism of this photopriming of microbial decomposition is unclear. We tested the hypothesis that solar radiation would (a) increase dissolved organic carbon (DOC) from litter subsequently extracted with water, and (b) produce DOC that stimulates more microbial activity than unexposed litter. Samples of dried senesced grass litter from three species, Bromus diandrus , Avena fatua , and Hordeum murinum , were exposed to radiation in indoor and outdoor experiments. Treated litter was soaked in water and the extract was analyzed to determine the DOC concentration and bioavailability. Radiation exposure produced more DOC in both experiments (40% greater outdoors and 21% greater indoors with visible radiation compared to blocked; 20% greater outdoors and 51% greater indoors with UV and visible compared to visible alone), suggesting that solar radiation enhances grass litter solubility. During a microbial incubation of extracted DOC, mean CO 2 production increased by 24%, and increased significantly for indoor samples. However, radiation reduced CO 2 production by ∼23% when DOC concentration is taken into account, indicating that photodegradation produces recalcitrant compounds. Photodegradation still stimulated the microbial activity overall by increasing the total available DOC. These results suggest that litter carbon is made more soluble by radiation and is mobilized by water, allowing for increased microbial decomposition. This mechanistic insight could improve carbon cycle models that include photopriming.
Romich et al. (Wed,) studied this question.