ABSTRACT
Forests play an important role in terrestrial carbon cycles. The mechanism underlying carbon balance in temperate deciduous broad-leaved forests is not clear. In this study, net ecosystem exchange (NEE) and environmental factors, including air temperature (Ta), soil temperature (Ts), photosynthetically active radiation (PAR), vapor pressure deficit (VPD), soil water content (SWC) and precipitation (P) were continually measured using eddy covariance techniques in 2019 in a deciduous broad-leaved forest in Songshan, Beijing. We analyzed the characteristics of NEE and its response to environmental factors. The results showed that, at diurnal scale, the monthly averaged NEE exhibited a "U" shape curve (i.e., being a carbon sink over daytime while being a carbon source during nighttime) over the growing season. During the non-growing season, NEE was positive (i.e., carbon source) at diurnal scale. At the seasonal scale, NEE exhibited a unimodal curve. The annual cumulative NEE was -111 g C·m-2·a-1. Annual ecosystem respiration was 555 g C·m-2·a-1, while gross ecosystem productivity was 666 g C·m-2·a-1. Carbon sequestration peaked in June, while emission peaked in November. PAR was the dominant factor affecting daytime NEE (NEEd). VPD was the main factor that indirectly affected daytime NEEd, with an optimal VPD value that maximizes daytime NEE around 1-1.5 kPa. Soil temperature was the main factor affecting nighttime NEE (NEEn). SWC was a limiting factor for NEEn. Too high or too low SWC would inhibit NEEn, with an optimal SWC value of 0.28 m3·m-3.
Subject(s)
Carbon , Ecosystem , Beijing , Carbon Dioxide/analysis , China , ForestsABSTRACT
A microRNA (miRNA) is a single-stranded, small and non-coding RNA molecule that contains 20-25 nucleotides. More than 2000 miRNAs have been identified in human genes since the first miRNA was discovered in Caenorhabditis elegans in the early 1990s. miRNAs play a crucial role in various biological processes by regulating gene expression through post-transcriptional mechanisms. The alterations of their levels are associated with various diseases, such as glucometabolic disorder and lipid metabolism disorder. In recent years, miRNAs have been proved to be involved in regulating the functions of pancreatic ß-cells, insulin resistance and other biological behaviors related to glucometabolic disorder and the pathogenesis of diabetes mellitus (DM). This review summarized specific miRNAs, including miRNA-375 (miR-375), miRNA-155 (miR-155), miRNA-21 (miR-21), miRNA-33 (miR-33), the let-7 family and some other miRNAs related to glucometabolic regulation, introduced the obstacles and challenges in miRNA therapy, and discussed the prospect of new treatment methods for glucometabolic disorder.
