Ambient ultraviolet radiation in the Arctic reduces root biomass and alters microbial community composition but has no effects on microbial biomass

Abstract

We assessed the effects of ambient solar ultraviolet (UV) radiation on below-ground parameters in an arctic heath in north-eastern Greenland. We hypothesized that the current UV fluxes would reduce root biomass and mycorrhizal colonization and that these changes would lead to lower soil microbial biomass and altered microbial community composition. These hypotheses were tested on cored soil samples from a UV reduction experiment with three filter treatments (Mylar, 60% UV-B reduction; Lexan, up to 90% UV-B reduction 1 UV-A reduction; UV transparent Teflon, filter control) and an open control treatment in two study sites after 3 years' manipulation. Reduction of both UV-A and UV-B radiation caused over 30% increase in the root biomass of Vaccinium uliginosum, which was the dominant plant species. UV reduction had contrasting effects on ericoid mycorrhizal colonization of V. uliginosum roots in the two sites, while it had no clear effects on fungal (ergosterol) or microbial biomass (measured both with fumigation-extraction and quantitative lipid biomarker analysis) in soil. However, principal component analysis of lipid biomarkers (phospholipid and glycolipid fatty acid profiles) showed that microbial community composition was altered by UV reduction. Although the UV responses were slight considering the large dose difference between the treatments (from near-ambient to up to 90% UV-B reduction), we cannot rule out the possibility that the recovery of ozone layer would change the below-ground functioning of arctic ecosystems.

Phragmites australisroot secreted phytotoxin undergoes photo-degradation to execute severe phytotoxicity

“…All these results suggest that the increased UV-B radiation can influence overall dynamics of a root secreted GA that might indirectly influence invasiveness of a noxious weed P. australis. Effects of UV-B on root secretion have previously been documented [11][12][13][14][15] show that UV-B incidences may regulate the root secretion effluxes. To the best of our knowledge no study has reported the effects of UV-B radiation to augmented root derived allelopathy in plants.…”

“…UV-B incidence modifies root secretion efflux thus affecting the total dissolved oxygen carbon (DOC) content in the rhizosphere. 11,23 Although most of these studies are species specific, it reveals a trend that UV-B radiations could change the litter or secretion chemistry in plants, leading to changes in rhizospheric microbial abundance. Interestingly, UV radiation has been recognized as a significant cause of photochemical transformation of dissolved organic matter (DOM) in surface waters.…”

“…12 Additionally, upon exposure to UV light, leachates from Phragmites leaves inhibited microbial growth as compared to an untreated control. 13 Although the possibility of alterations in the quality and quantity of root exudates has been raised in connection with studies that reported UV-B-induced changes in soil microbial communities, 10,11,14 we have no knowledge of controlled testing of the effects of increased UV-B radiation on root exudation or rhizospheric processes in any other plant system other than rice. 15 Most of the studies pertaining to the effect of UV light on plant growth ranges from wild plant species are limited to African savanna, 16 arctic ecosystems, 17 salt marshes 18,19 and Mediterranean ecosystems.…”

“…However, recently some studies have reported UV-B-induced alterations in the composition soil microbial community. [9][10][11] Such studies stressed the importance of studying the effect of UV radiation on plant roots that form the interface between the plant and the soil and associated rhizospheric processes. It has also been reported that UV radiation can indirectly affect below ground processes via photodegradation of the leachates from foliar litter.…”

The role of abiotic factors modulating the plant-microbe-soil interactions: toward sustainable agriculture. A review

“…The domain Archaea is also resistant to UV-B (Thummes et al, 2007), and there is a general trend of increased species diversity in environments with higher levels of UV-B exposure (Robson et al, 2005). The gram-negative bacterial community in Arctic soils experiences particular environmental stresses and nutrient limitations (Rinnan et al, 2005). Avery et al (2003) conducted a study of the response of the rhizosphere microbial communities associated with populations of Deschampsia antarctica (a native vascular plant from Antarctica), which were exposed to UV-B, and found that radiation not only modified the overall growth of the plant but also the production of secondary metabolites.…”