Time lag effect of vegetation response to seasonal precipitation in the Mara River Basin

Background Mara River Basin is an ecologically fragile area in East Africa,with a pattern of alternating wet and dry seasons shaped by periodic precipitation.Considering the regional biological traits and climatic change,the vegetation’s response to seasonal variation is complicated and frequently characterized by time lags.This study analyzed the variation of the Normalized Difference Vegetation Index(NDVI)and investigated its time lag to precipitation at the monthly scale.NDVI characteristic peaks were proposed from the perspective of seasonal mechanisms and were quantified to assess the lag effect.Results The results showed that the Anomaly Vegetation Index could identify low precipitation in 2006,2009,and 2017.The NDVI showed an increasing trend in 75%of areas of the basin,while showed a decreased significance in 3.5%of areas,mainly in savannas.As to the time lag,the 1-month lag effect dominated most months,and the spatiotemporal disparities were noticeable.Another method considering the alternations of wet and dry seasons found that the time lag was approximately 30 days.Based on the time distribution of NDVI characteristic peaks,the average time lag was 35.5 days and increased with the range of seasons.Conclusions The findings confirmed an increasing trend of NDVI in most regions from 2001 to 2020,while the trends were most obvious in the downstream related to human activities.The results could reflect the time lag of NDVI response to precipitation,and the 1-month lag effect dominated in most months with spatial heterogeneity.Four NDVI characteristic peaks were found to be efficient indicators to assess the seasonal characteristics and had a great potential to quantify vegetation variation.

Comparison of gene expression responses of zebrafish larvae to Vibrio parahaemolyticus infection by static immersion and caudal vein microinjection

infection model for studying inflammation and the innate immune response.We investigated the genes and signaling pathways activated by static immersion and caudal vein microinjection infection using transcriptome profiling and reverse-transcription quantitative PCR(RT-qPCR)to compare the innate immune response in 3 days post-fertilization(dpf)zebrafish larvae infected by Vibrio parahaemolyticus Vp13 strain.The median lethal dose(LD50)values at 96 h following immersion and microinjection were 3.63×107 CFU/mL and 5.76×102 CFU/nL,respectively.An innate immune response was initiated after 2 h of incubation with the respective LD50 for each infection method.Six hundred and two genes in the immersion group and 359 genes in the microinjection group were activated and differentially expressed post-infection.Sixty-three Gene Ontology(GO)terms and four Kyoto Encyclopedia of Genes and Genomes(KEGG)pathways were significantly enriched in the immersion group,compared with only three GO terms and no KEGG pathways in the microinjection group.Two genes,tnfb and ccl20a.3,were significantly up-regulated in both groups.We speculated that immersion infection may affect initial dorsal determination,cytochromes,and fatty acid-binding proteins,as well as inflammation,while microinjection infection may mainly directly affect the immune response.Infection with doses>LD50(1.09×109 CFU/mL and 1.09×103 CFU/nL by immersion and microinjection,respectively)caused more significant up-regulation of il11a,tnfa,tnfb,il1b,ccl34a.4,ccl20a.3,irak3,cxcl18b,and ccl35.1,suggesting that in addition to the classical innate immunity genes tnfa,tnfb,il1b,and il6,the genes il11a,ccl34a.4,ccl20a.3,cxcl18b,and ccl35.1 were also important for defending against Vp13 infection.These findings highlight the genes involved in the responses of zebrafish to Vp13 infection via different routes and doses,and thus provide the basis for further analyses of immune response signaling pathways.