Continuous in-situ water stable isotopes show the effect of species identity on water use after precipitation events

The need to understand species identity and interaction effects on their water use strategies becomes more urgent considering the eco- and hydrological impacts of climate change. Especially the characteristic timescales and pathways of water movement potentially provide important information on drought resilience of different forest ecosystems. This study investigated the temporal and spatial distribution of precipitation and their effect on the water uptake dynamics of different forest types. Isotope labelling experiments of throughfall and stemflow using continuous in-situ isotope measurements were used in a mixed forest with European beech (Fagus sylvatica, n=18) and Norway spruce (Picea abies, n=18). Our central hypothesis is that species identity and water competition between tree species are major drivers for ecohydrological flux dynamics. The analyses of the labelled irrigation during a drought revealed an immediate increase in water use and resulting fast use of recent irrigated water in F. sylvatica. P. abies saved water over a longer period increasing water use only slowly. The conifer species consequently showed negative competition effects during drought when co-existing with F. sylvatica contrary to the broadleaf species. Consequently, species identity is determining the plant reaction after a precipitation event especially during drought but interspecific interaction can influence the water use uptake species dependent.