Gesche Blume-Werry

The hidden season: growing season is 50% longer below than above ground along an arctic elevation gradient

There is compelling evidence from experiments and observations that climate warming prolongs the growing season in arctic regions. Until now, the start, peak, and end of the growing season, which are used to model influences of vegetation on biogeochemical cycles, were commonly quantified using above-ground phenological data. Yet, over 80% of the plant biomass in arctic regions can be below ground, and the timing of root growth affects biogeochemical processes by influencing plant water and nutrient uptake, soil carbon input and microbial activity. We measured timing of above- and below-ground production in three plant communities along an arctic elevation gradient over two growing seasons. Below-ground production peaked later in the season and was more temporally uniform than above-ground production. Most importantly, the growing season continued c. 50% longer below than above ground. Our results strongly suggest that traditional above-ground estimates of phenology in arctic regions, including remotely sensed information, are not as complete a representation of whole-plant production intensity or duration, as studies that include root phenology. We therefore argue for explicit consideration of root phenology in studies of carbon and nutrient cycling, in terrestrial biosphere models, and scenarios of how arctic ecosystems will respond to climate warming.

Short-term climate change manipulation effects do not scale up to long-term legacies: Effects of an absent snow cover on boreal forest plants

1. Despite time-lags and nonlinearity in ecological processes, the majority of our knowledge about ecosystem responses to long-term changes in climate originates from relatively short-term experime ...

Burned and Devoured-Introduced Herbivores, Fire, and the Endemic Flora of the High-Elevation Ecosystem on La Palma, Canary Islands

Abstract Novel disturbance regimes (e.g., introduced herbivores and fire) are among the major drivers of degradation in island ecosystems. High-elevation ecosystems (HEEs) on islands might be especially vulnerable to these disturbances due to high endemism. Here, data from an 11-year exclosure experiment in the HEE of La Palma (Canary Islands) are presented where mammalian herbivores have been introduced. We investigate the combined effect of herbivory and fire on total species richness, seedling richness, and seedling establishment on the whole system and a subset of highly endangered species (target species). Total species richness, seedling species richness, and seedling establishment decreased with herbivory. Five out of eight target species were exclusively found inside the exclosures indicating the negative impact of introduced herbivores on endemic high elevation flora. Target species were generally affected more negatively by introduced herbivores and were subject to significantly higher browsing pressure, probably owing to their lack of defense strategies. A natural wildfire that occurred six years before data sampling substantially increased total species richness and seedling richness in both herbivory exclosure and reference conditions. We conclude that species composition of the HEE has been severely altered by the introduction of non-native herbivores, even though fire seems to have a positive effect on this system.

Winter warming effects on tundra shrub performance are species-specific and dependent on spring conditions

Climate change-driven increases in winter temperatures positively affect conditions for shrub growth in arctic tundra by decreasing plant frost damage and stimulation of nutrient availability. Howe ...

Root phenology unresponsive to earlier snowmelt despite advanced above‐ground phenology in two subarctic plant communities

1. Earlier snowmelt at high latitudes advances above-ground plant phenology, thereby affecting water, nutrient and carbon cycles. Despite the key role of fine roots in these ecosystem processes, ph ...

Proportion of fine roots, but not plant biomass allocation below ground, increases with elevation in arctic tundra

Questions: Roots represent a considerable proportion of biomass, primary production and litter input in arctic tundra, and plant allocation of biomass to above- or below-ground tissue in response t ...

Long-term in situ permafrost thaw effects on bacterial communities and potential aerobic respiration.

The decomposition of large stocks of soil organic carbon in thawing permafrost might depend on more than climate change-induced temperature increases: indirect effects of thawing via altered bacterial community structure (BCS) or rooting patterns are largely unexplored. We used a 10-year in situ permafrost thaw experiment and aerobic incubations to investigate alterations in BCS and potential respiration at different depths, and the extent to which they are related with each other and with root density. Active layer and permafrost BCS strongly differed, and the BCS in formerly frozen soils (below the natural thawfront) converged under induced deep thaw to strongly resemble the active layer BCS, possibly as a result of colonization by overlying microorganisms. Overall, respiration rates decreased with depth and soils showed lower potential respiration when subjected to deeper thaw, which we attributed to gradual labile carbon pool depletion. Despite deeper rooting under induced deep thaw, root density measurements did not improve soil chemistry-based models of potential respiration. However, BCS explained an additional unique portion of variation in respiration, particularly when accounting for differences in organic matter content. Our results suggest that by measuring bacterial community composition, we can improve both our understanding and the modeling of the permafrost carbon feedback.