Water sources of evergreen and deciduous species depend upon season, ecosystem type and snowpack depth in arctic tundra near Toolik Lake, Alaska
Abstract
Arctic ecosystems are experiencing rapid increases in surface air temperatures, which are altering the hydrological cycle and its components. In the absence of increased precipitation, these changes will result in surface drying. Recent increases in the frequency and magnitude of tundra fires provide evidence that this change is already occurring. As temperature rises, active layers deepen and soils dry, plant-water relations will become an increasingly important component of the functioning of Arctic ecosystems (previously viewed as water-abundant). Arctic ecosystems are covered by snow for approximately 9 months and yet little is known about the importance of snowmelt as a water source for arctic plants. In this study, we examined seasonal variation in the water sources of two evergreen and two deciduous species in two ecosystems (tussock and dry heath tundra) in response to long-term experimental increases in snow depth. We analyzed δ18O and δD in xylem water and Δ18O, Δ13C and N concentration in leaf tissue reveal differences in water sources and in leaf gas exchange physiology. Our hypotheses were as follows: 1. Plants will use increasingly enriched water as the growing season progresses and the snowmelt water pool is diluted by rain, transpired and evaporatively enriched (increasing xylem water δ18O and δD); 2. Plants growing in tussock tundra will use more snowmelt water than plants growing in dry heath tundra (lower xylem water δ18O and δD), because snowmelt water will drain quickly from the porous soils of the dry heath; 3. Evergreen species will use more snowmelt water than deciduous species in both ecosystems because they initiate gas exchange earlier after snowmelt (lower xylem water δ18O and δD); 5. Plants in tussock tundra will be less water use-efficient than those in dry heath tundra and the difference will be greater for evergreen than deciduous species (greater leaf Δ13C); 6. Experimental snow additions will lead to lower water-use-efficiency in tussock tundra (greater leaf Δ13C), but no change in the dry heath; 7. Experimental snow additions will lead to warmer soils and greater N availability in tussock tundra. These changes will lead to greater rates of stomatal conductance, higher leaf N concentrations and greater rates of leaf-level photosynthesis (small change in leaf Δ13C per unit decrease in leaf Δ18O). Our findings indicate that snowmelt water may ameliorate the progressive drying of tundra during the summer; however, this is primarily confined to tussock as opposed to dry tundra. Identifying the importance of snowmelt as a source of water for arctic plants will improve our ability to predict changes in plant species composition and ecosystem function in a warmer and drier arctic.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMGC43B0978E
- Keywords:
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- 0475 BIOGEOSCIENCES / Permafrost;
- cryosphere;
- and high-latitude processes;
- 0476 BIOGEOSCIENCES / Plant ecology;
- 0718 CRYOSPHERE / Tundra