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

Abstract

Summary 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, phenological responses to earlier snowmelt have never been assessed below‐ground. We experimentally advanced snowmelt in two contrasting plant community types (heath and meadow) in northern Sweden and measured above‐ and below‐ground phenology (leaf‐out, flowering and fine root growth). We expected earlier snowmelt to advance both above‐ and below‐ground phenology, and shrub‐dominated heath to be more responsive than meadow. Snow melted on average 9 days earlier in the manipulated plots than in controls, and soil temperatures were on average 0·9 °C higher during the snowmelt period of 3 weeks. This resulted in small advances in above‐ground phenology, but contrary to our expectations, root phenology was unresponsive, with root growth generally starting before leaf‐out. These responses to the snowmelt treatment were similar in both plant community types, despite strong differences in dominating plant functional types and root properties, such as root length and turnover. The lack of a response in root phenology, despite warmer soil temperatures and above‐ground phenological advances, adds evidence that above‐ground plant responses might not be directly translated to below‐ground plant responses, and that our understanding of factors driving below‐ground phenology is still limited, although of major importance for water, nutrient and carbon cycling.

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

“…Earlier canopy green‐up in the Northern Hemisphere has been observed as a consequence of snow removal in previous experimental manipulation studies (e.g. Blume‐Werry, Jansson, & Milbau, ; Rosa et al., ; Wipf, ) as well as a result of decreasing snowpack and higher spring temperatures in natural observations (Menzel & Fabian, ; Penuelas & Filella, ). Our result suggests that higher spring soil temperatures specifically drive this advanced green‐up rather than the earlier snowmelt, since the fleece treatment did not advance snowmelt timing.…”

“…Shrub phenology is tightly linked to the extent to which shrubs are vulnerable to spring frost events (Inouye, ; Wheeler et al., ; Wheeler, Hoye, Schmidt, Svenning, & Forchhammer, ), whereby species with later phenology seem to exhibit higher frost sensitivity compared to species with earlier phenology (CaraDonna & Bain, ). The deciduous B. nana which naturally has a later bud break and growth onset than the evergreens V. vitis‐idaea and E. nigrum (Blume‐Werry et al., ; Wipf, ) showed highest frost damage overall. We expected leaf frost damage in shrubs to be generally lower with winter warming due to less severe autumn‐to‐late winter frost (Palacio et al., ; Saarinen & Lundell, ), which could have been counteracted by the increased number of FTCs in the spring warming treatment.…”

Uncertainty of Vegetation Green-Up Date Estimated from Vegetation Indices Due to Snowmelt at Northern Middle and High Latitudes

“…This identification mainly includes three steps: First, we smoothed the NDSI time series by using the 3-points median filter and performed linear fitting using the continuous consecutive 4 points. The use of 4 points (8-day temporal frequency for each point) is because snowmelt usually lasts 2-4 weeks [31,32]; Second, a preliminary period of snowmelt was determined to be the one with the lowest negative slope. The 4 points of this period can be expressed as Pi, Pi+1, Pi+2, and Pi+3; Third, we refined the preliminary period of snowmelt by further investigating edge points (i.e., Pi-1 and Pi at the left edge; Pi+3 and Pi+4 at the right edge).…”

N : P stoichiometry and habitat effects on Mediterranean savanna seasonal root dynamics

“…In most ecosystems, root biomass changes substantially throughout the year, although understanding drivers of this phenology is limited, especially when using quantitative metrics (Radville et al, 2016). In many cases, root growth is desynchronized from production of shoots (Blume-Werry et al, 2017;Mccormack et al, 2017;Steinaker and Wilson, 2008) and linkages between root function and root dynamics are often poorly understood. As a major function of roots is nutrient uptake, supplying resources which are often limiting, nutrient availability may play an important role in regulating the timing and magnitude of root production.…”