Experimental warming differentially affects vegetative and reproductive phenology of tundra plants

Abstract

Rapid climate warming is altering Arctic and alpine tundra ecosystem structure and function, including shifts in plant phenology. While the advancement of green up and flowering are well-documented, it remains unclear whether all phenophases, particularly those later in the season, will shift in unison or respond divergently to warming. Here, we present the largest synthesis to our knowledge of experimental warming effects on tundra plant phenology from the International Tundra Experiment. We examine the effect of warming on a suite of season-wide plant phenophases. Results challenge the expectation that all phenophases will advance in unison to warming. Instead, we find that experimental warming caused: (1) larger phenological shifts in reproductive versus vegetative phenophases and (2) advanced reproductive phenophases and green up but delayed leaf senescence which translated to a lengthening of the growing season by approximately 3%. Patterns were consistent across sites, plant species and over time. The advancement of reproductive seasons and lengthening of growing seasons may have significant consequences for trophic interactions and ecosystem function across the tundra.

Towards rainy high Arctic winters: how ice-encasement impacts tundra plant phenology, productivity and reproduction

“…Interestingly, this suggests an interaction effect of icing and warming magnifying the advancement of phenology found under warming alone (Table S4). Advanced phenology patterns due to warming are consistent with results of simulated summer warming at a circumpolar scale (Collins et al, 2021). Similar to Collins et al (2021), we found a larger shift in reproductive than vegetative phenophases, resulting in a shorter period between leaf emergence and seed dispersal.…”

“…Advanced phenology patterns due to warming are consistent with results of simulated summer warming at a circumpolar scale (Collins et al, 2021). Similar to Collins et al (2021), we found a larger shift in reproductive than vegetative phenophases, resulting in a shorter period between leaf emergence and seed dispersal. This pattern was particularly pronounced under the combined icing and warming treatment, indicating a higher energy investment to reproduction, despite the also high investment to vegetative growth under icing.…”

“…Our data from the extremely warm summer of 2020 also indirectly support the notion that warming may enhance the investment in both vegetative and reproductive production, as suggested by a record high number of flowers, including in control plots (Figure S6). However, the nonetheless lower flower production in warming and icing × warming plots compared to control plots possibly reflects the nutrient limitations of the system, under which vegetative growth and advanced flowering phenology are prioritized (Collins et al, 2021;Petraglia et al, 2013).…”

“…Nevertheless, this study has shown that winter rain-on-snow, and associated tundra icing, can have similarly large impacts as summer warming on high Arctic plant communities. On the occasion of the 30-year anniversary of ITEX experiments conducted across the poles, which have provided critical knowledge regarding tundra responses to summer warming (Bjorkman et al, 2018;Collins et al, 2021;Prevéy et al, 2019), we call for the implementation of similar large-scale experiments investigating effects of winter warming, and rain-on-snow events in particular. Such a coordinated effort on long-term effects across communities, plant functional types and species is required to gain a holistic understanding of future changes in the tundra biome and its possible resistance and resilience to both winter and summer warming (Bjorkman et al, 2020).…”

Onset of autumn senescence in High Arctic plants shows similar patterns in natural and experimental snow depth gradients

“…In a meta-analysis of the international tundra experiment (ITEX), there was generally no treatment effect after four years of OTC treatment on the timing of senescence in various species in up to six different arctic and alpine sites (Arft et al 1999). A more recent meta-analysis including studies with up to 20 years of OTC treatment found a mean delay in senescence across 61 species (Collins et al 2021), which could indicate that there is a lag of several years in the response of autumn senescence to warming. A recent review of ITEX found that the timing of senescence is overall not sensitive to temperature increases across time or space when considering multiple species across the Arctic (Prevéy et al 2017).…”