Historical variation in normalized difference vegetation index compared with soil moisture at a taiga forest ecosystem in northeastern Siberia

Abstract

Abstract. The taiga ecosystem in northeastern Siberia, a nitrogen-limited ecosystem on permafrost with a dry climate, changed during the extreme wet event in 2007. We investigated the normalized difference vegetation index (NDVI) as a satellite-derived proxy of needle production and compared it with ecosystem parameters such as soil moisture water equivalent (SWE), foliar C/N ratio, δ13C and δ15N, and ring width index (RWI) at the Spasskaya Pad Experimental Forest Station in Russia for the period from 1999 to 2019. Historical variations in NDVI showed a large difference between typical larch forest (unaffected) and the sites affected by the extreme wet event in 2007 because of high tree mortality at affected sites under extremely high SWE and waterlogging, resulting in a decrease in NDVI. Before 2007, the NDVI in a typical larch forest showed a positive correlation with SWE and a negative correlation with foliar C/N. These results indicate that not only the water availability (high SWE) in the previous summer and current June but also the soil N availability increased needle production. NDVI was also positively correlated with RWI, resulting from similar factors controlling them. However, after the wet event, NDVI was negatively correlated with SWE, while NDVI showed a negative correlation with foliar C/N. These results indicate that after the wet event, high soil moisture availability decreased needle production, which may have resulted from lower N availability. Needle δ15N was positively correlated with NDVI before 2007, but after the wet event, needle δ15N decreased. This result suggests damage to roots and/or changes in soil N dynamics due to extremely high soil moisture.

Arctic Plant Responses to Summer Climates and Flooding Events: A Study of Carbon and Nitrogen‐Related Larch Growth and Ecosystem Parameters in Northeastern Siberia

“…Needle δ 15 N remained relatively stable from 2009 to 2013 across sites, except for site K tree wet , where a downward trend was observed (Figure 3d), which may be associated with wetting events. Excessive SM resulting from flooding or waterlogging events can reduce soil O 2 levels, slowing down microbial activity responsible for SOM decomposition (Kozlowski, 1984; Nguyen et al., 2018; Nogovitcyn et al., 2023). This process leads to a higher C content in the soil, increasing the C/N ratio (Nogovitcyn et al., 2023; Reichel et al., 2018).…”

“…Excessive SM resulting from flooding or waterlogging events can reduce soil O 2 levels, slowing down microbial activity responsible for SOM decomposition (Kozlowski, 1984; Nguyen et al., 2018; Nogovitcyn et al., 2023). This process leads to a higher C content in the soil, increasing the C/N ratio (Nogovitcyn et al., 2023; Reichel et al., 2018). Microbes tend to preferentially use available N for their own growth when the C/N ratio is high, resulting in reduced N availability for plants (Reichel et al., 2018), as observed at site K tree wet .…”