Biology Department, Rhode Island College, Providence, Rhode Island, United States of America.
NORCE Norwegian Research Centre, Bjerknes Centre for Climate Research, Bergen, Norway.
PLoS One. 2019 Feb 4;14(2):e0210470. doi: 10.1371/journal.pone.0210470. eCollection 2019.
Dryland ecosystems cover nearly 45% of the Earth's land area and account for large proportions of terrestrial net primary production 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. exposure of standing dead leaf litter to solar radiation prior to litter drop that would chemically change litter and enhance biotic decay of fallen litter. 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 high 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 mass loss over the course of the year-long study, while high N-containing mesquite litter exhibited potential mass loss. 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 precipitation and N played a critical role in litter mass loss. In contrast, photopriming had no detected effects on mass loss over the course of our year-long study. These results underpin the importance of biotic-driven decomposition, even in the presence of photopriming, for understanding litter decomposition and biogeochemical cycles in drylands.
旱地生态系统覆盖了地球陆地面积的近 45%，占陆地净初级生产力和碳库的很大比例。然而，由于其明显干燥且往往炎热的气候条件，以及潜在独特的物理分解驱动因素，预测这些广阔生态系统中植物凋落物分解的速率具有挑战性。在这项研究中，我们阐明了光引发作用的作用，即在凋落物落下之前，将立枯的落叶凋落物暴露于太阳辐射下，这会使凋落物发生化学变化并增强落下凋落物的生物降解。我们将凋落物基质暴露于三种不同的紫外线辐射处理中，模拟新墨西哥州南部三个月的紫外线辐射暴露：无光照、UVA+UVB+可见光和 UVA+可见光。有三种凋落物类型：牧豆树叶片（Prosopis glandulosa，含氮量高）、滤纸（纯纤维素）和椴木（Tilia spp.，高木质素含量）。我们在一个大规模降水管理实验中现场部署了光引发的凋落物：降水减少约 50%、降水增加约 150%和环境对照。我们的结果表明，凋落物基质，特别是氮含量，对旱地整体分解很重要，因为在为期一年的研究过程中，滤纸和椴木都没有表现出可测量的质量损失，而高氮含量的牧豆树凋落物则表现出潜在的质量损失。我们没有观察到光引发对随后微生物分解的影响。我们确实观察到降水对牧豆树的影响，在环境和降水增加处理中，分解速度比干旱处理更快。总体而言，我们发现降水和氮在凋落物质量损失中起着关键作用。相比之下，在我们为期一年的研究过程中，光引发对质量损失没有检测到影响。这些结果支持了生物驱动分解的重要性，即使存在光引发作用，对于理解旱地凋落物分解和生物地球化学循环也很重要。
