PNNL

Abstract

Dryland ecosystems cover nearly 45% of the Earth’s land area and account for large proportions of global annual productivity and carbon pools. However, predicting rates of plant litter decomposition in these vast ecosystems has proven challenging due to their distinctly dry and often hot climate regimes, and potentially unique physical drivers of decomposition. In this study, we elucidated the role of photopriming, i.e. potential for enhancement of microbial decay due to exposure of standing leaf litter to solar radiation prior to litterfall. We exposed litter substrates to three different UV radiation treatments simulating three-months of UV radiation exposure in southern New Mexico: no light, UVA+UVB+visible, and UVA+Visible. There were three litter types: mesquite leaflets (Prosopis glandulosa, litter with nitrogen (N) concentration), filter paper (pure cellulose), and basswood (Tilia spp, high lignin concentration). We deployed the photoprimed litter in the field within a large scale precipitation manipulation experiment: ~50% precipitation reduction, ~150% precipitation addition, and ambient control. Our results revealed the importance of litter substrate, particularly N content, for overall decomposition in drylands, as neither filter paper nor basswood exhibited measurable decomposition over the course of the year-long study, while high N-containing mesquite litter decayed exponentially. We saw no effect of photopriming on subsequent microbial decay. We did observe a precipitation effect on mesquite where the rate of decay was more rapid in ambient and precipitation addition treatments than in the drought treatment. Overall, we found that N plays a critical role in the overall dryland litter decay regardless of the effects of photopriming, and more importantly that precipitation overshadows the effects of photopriming. This result underpins the importance of biotic-driven decomposition, even in the presences of photopriming, for understanding litter decomposition and biogeochemical cycles in drylands.