Parker
Thomas C.
Parker
Thomas C.
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PreprintShort term changes in moisture content drive strong changes in Normalized Difference Vegetation Index and gross primary productivity in four Arctic moss communities( 2018-04) May, Jeremy L. ; Parker, Thomas C. ; Unger, Steven ; Oberbauer, Steven F.Climate change is currently altering temperature and precipitation totals and timing in Arctic regions. Moss communities constitute much of the understory in Arctic vegetation, and as poikilohydric plants moss are highly sensitive to timing and duration of moisture levels. Here we investigate the role of moisture content on NDVI, red and near-infrared reflectance, and gross primary productivity (GPP) of two sphagnum and two pleurocarpus moss community types during two separate drying experiments. For both experiments, blocks of moss were collected near Imnavait Creek, Alaska, saturated to full water capacity, and then allowed to air dry before being re-saturated. Drying of blocks was conducted in a translucent outdoor tent during the first experiment and under indoor climate-controlled conditions during the second. Community NDVI (experiment 1 and 2), and GPP (experiment 2) were measured at regular intervals during the dry-down and after rewetting. In both experiments, moss NDVI sharply declined between 80% and 70% moisture content for sphagnum moss communities (NDVI change = -0.17 to -0.2), but less so for pleurocarpus moss communities (NDVI change = -0.06 to -0.12). Changes in NDVI were largely the result of increases in reflectance in red wavelengths. Peak GPP for all community types in the second experiment (1.31 to 2.08 μmol m-2 s-1) occurred at 80% moisture content and declined significantly as moisture content decreased. Rates of GPP continued to decline below 80% moisture content until near zero as moss reached a steady weight (air dry) over a period of 84 hours, while NDVI values declined slowly between 70% hydration and fully air dry. Re-saturation caused NDVI to increase in both sphagnum (NDVI change = +0.18 to +0.23) and pleurocarpus (NDVI change = +0.10 to +0.17) communities. Only sphagnum communities showed GPP resuming (0.824 μmol m-2 s-1) after 24 hours. The strong changes in NDVI and mismatch of moss NDVI values and GPP with moisture content fluctuations indicate that using NDVI as a proxy for productivity in Arctic vegetation communities may be problematic and underscores the need for quantification of moss community coverage, composition, and moisture content.
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ArticleSlowed biogeochemical cycling in sub-arctic birch forest linked to reduced mycorrhizal growth and community change after a defoliation event(Springer, 2016-08-25) Parker, Thomas C. ; Sadowsky, Jesse ; Dunleavy, Haley ; Subke, Jens-Arne ; Frey, Serita D. ; Wookey, Philip A.Sub-arctic birch forests (Betula pubescens Ehrh. ssp. czerepanovii) periodically suffer large-scale defoliation events caused by the caterpillars of the geometrid moths Epirrita autumnata and Operophtera brumata. Despite their obvious influence on ecosystem primary productivity, little is known about how the associated reduction in belowground C allocation affects soil processes. We quantified the soil response following a natural defoliation event in sub-arctic Sweden by measuring soil respiration, nitrogen availability and ectomycorrhizal fungi (EMF) hyphal production and root tip community composition. There was a reduction in soil respiration and an accumulation of soil inorganic N in defoliated plots, symptomatic of a slowdown of soil processes. This coincided with a reduction of EMF hyphal production and a shift in the EMF community to lower autotrophic C-demanding lineages (for example, /russula-lactarius). We show that microbial and nutrient cycling processes shift to a slower, less C-demanding state in response to canopy defoliation. We speculate that, amongst other factors, a reduction in the potential of EMF biomass to immobilise excess mineral nitrogen resulted in its build-up in the soil. These defoliation events are becoming more geographically widespread with climate warming, and could result in a fundamental shift in sub-arctic ecosystem processes and properties. EMF fungi may be important in mediating the response of soil cycles to defoliation and their role merits further investigation.
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ArticleEcotypic differences in the phenology of the tundra species Eriophorum vaginatum reflect sites of origin(John Wiley & Sons, 2017-10-19) Parker, Thomas C. ; Tang, Jianwu ; Clark, Mahalia B. ; Moody, Michael L. ; Fetcher, NedEriophorum vaginatum is a tussock-forming sedge that contributes significantly to the structure and primary productivity of moist acidic tussock tundra. Locally adapted populations (ecotypes) have been identified across the geographical distribution of E. vaginatum; however, little is known about how their growth and phenology differ over the course of a growing season. The growing season is short in the Arctic and therefore exerts a strong selection pressure on tundra species. This raises the hypothesis that the phenology of arctic species may be poorly adapted if the timing and length of the growing season change. Mature E. vaginatum tussocks from across a latitudinal gradient (65–70°N) were transplanted into a common garden at a central location (Toolik Lake, 68°38′N, 149°36′W) where half were warmed using open-top chambers. Over two growing seasons (2015 and 2016), leaf length was measured weekly to track growth rates, timing of senescence, and biomass accumulation. Growth rates were similar across ecotypes and between years and were not affected by warming. However, southern populations accumulated significantly more biomass, largely because they started to senesce later. In 2016, peak biomass and senescence of most populations occurred later than in 2015, probably induced by colder weather at the beginning of the growing season in 2016, which caused a delayed start to growth. The finish was delayed as well. Differences in phenology between populations were largely retained between years, suggesting that the amount of time that these ecotypes grow has been selected by the length of the growing seasons at their respective home sites. As potential growing seasons lengthen, E. vaginatum may be unable to respond appropriately as a result of genetic control and may have reduced fitness in the rapidly warming Arctic tundra.
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ArticleIntraspecific variation in phenology offers resilience to climate change for Eriophorum vaginatum(Canadian Science Publishing, 2021-05-19) Parker, Thomas C. ; Unger, Steven L. ; Moody, Michael L. ; Tang, Jianwu ; Fetcher, NedThe phenology of Arctic plants is an important determinant of the pattern of carbon uptake and may be highly sensitive to continued rapid climate change. Eriophorum vaginatum L. (Cyperaceae) has a disproportionate influence over ecosystem processes in moist acidic tundra, but it is unclear whether its growth and phenology will remain competitive in the future. We investigated whether northern tundra ecotypes of E. vaginatum could extend their growing season in response to direct warming and transplanting into southern ecosystems. At the same time, we examined whether southern ecotypes could adjust their growth patterns in order to thrive further north, should they disperse quickly enough. Detailed phenology measurements across three reciprocal transplant gardens over a 2-year period showed that some northern ecotypes were capable of growing for longer when conditions were favourable, but their biomass and growing season length was still shorter than those of the southern ecotype. Southern ecotypes retained large leaf length when transplanted north and mirrored the growing season length better than the others, mainly owing to immediate green-up after snowmelt. All ecotypes retained the same senescence timing, regardless of environment, indicating a strong genetic control. Eriophorum vaginatum may remain competitive in a warming world if southern ecotypes can migrate north.