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Ecosystems

, Volume 18, Issue 3, pp 533–545 | Cite as

The Effect of the Foresummer Drought on Carbon Exchange in Subalpine Meadows

  • Lindsey L. SloatEmail author
  • Amanda N. Henderson
  • Christine Lamanna
  • Brian J. Enquist
Article

Abstract

Climate in subalpine meadows of the Rocky Mountains can be characterized by an early (foresummer) drought that occurs after snowmelt (May) and lasts until the start of the summer monsoon season (July). Climate change models predict an increase in the length and severity of this dry period due to earlier snowmelt dates, rising air temperatures, and shifts in the start and/or intensity of the North American monsoon. However, it is unknown how changes in the severity of this early season dry period will affect ecosystem carbon exchange. To address the importance of early season drought, we combined a watering manipulation with 11 years of ecosystem carbon exchange data across an elevational gradient at the Rocky Mountain Biological Laboratory in Gothic, Colorado. Long-term trends reveal that earlier snowmelt dates lead to a decrease in net ecosystem productivity (NEP), in part because of the positive effect on early growing season drought conditions. Manipulating the strength of the foresummer drought by watering revealed that the timing of growing season precipitation is more important than the total amount for determining cumulative NEP. The strength of the foresummer drought did not significantly impact ecosystem respiration rates, but plants that experienced a strong foresummer drought exhibited more water stress, and lower instantaneous rates of NEP, even during the rainy season. Our results highlight the central role of the foresummer drought in determining rates of carbon exchange throughout the growing season, and the potential for an increasingly negative balance of carbon in subalpine meadows under future climate change.

Keywords

climate change sualpine NEP foresummer drought elevation gradient watering manipulation 

Notes

Acknowledgments

We would like to thank Vanessa Buzzard, Colby Sides, and William Driscoll for help in the field during the summer of 2012. Further, we would like to thank all previous Enquist lab field assistants for collecting data along the elevation gradient including A Kerkhoff, P Gaube, M Wilson Colner, L Crumbacher, J Stegen, R Sleith, R Poore, T Potter, B Chaszar, M Smith, N Prohaska, and B Blonder. LS was supported by NSF funding to BJE and AH was supported by an NSF GFRP fellowship. CAL was supported by an EPA STAR Fellowship during data collection and is currently supported by NSF award EPS-0904155 to Maine EPSCoR at the University of Maine and the Senator George J. Mitchell Center. BJE was supported by funding from an NSF CAREER and an NSF Macrosystems award. In addition, funding from the Aspen Center for Environmental Science helped support BJE. We would also like to thank Amy Iler for comments that significantly strengthened this manuscript and the staff of RMBL including Ian Billick and Jennie Reithel and for helping to facilitate this study. Lastly, Billy Bar allowed us to use his weather station data and observations.

Supplementary material

10021_2015_9845_MOESM1_ESM.docx (20 kb)
Supplementary material 1 (DOCX 20 kb)
10021_2015_9845_MOESM2_ESM.tiff (34.3 mb)
Supplementary Figure 1: Gravimetric soil moisture over the course of the 2012 growing-season. During the watering treatment, currently watered plots were significantly wetter than un-watered or previously watered plots. Asterisks indicate significant differences as determined by ANOVA with p < 0.05. The first measurement period was before the watering treatments began, the second measurement period was the first day of the watering treatments, the last measurement period was after the watering treatments had concluded. (TIFF 35161 kb)
10021_2015_9845_MOESM3_ESM.tiff (34.3 mb)
Supplementary Figure 2: Percent organic soil carbon over the course of the 2012 growing-season. At no measurement point is soil carbon statistically different between treatments, although during the last time period the May and Control groups had more soil carbon than the June and July groups at a nearly significant level (ANOVA, df = 1, F = 3.893, p = 0.064). The first measurement period was before the watering treatments began, the second measurement period was the first day of the watering treatments, the last measurement period was after the watering treatments had concluded. (TIFF 35161 kb)
10021_2015_9845_MOESM4_ESM.tiff (34.3 mb)
Supplementary Figure 3: Daily precipitation for the summer of 2012. The date of first bare ground in 2012 was April 23rd (day of the year 114). Data was recorded from b.barr’s weather station - 38°57’47”, 106°59’36”, elevation 2,917m. Weather station is less than 1 km from the study site. Data download available: http://rmbl.info/rockymountainbiolab/rdc/rdc_perm_down.html. (TIFF 35161 kb)
10021_2015_9845_MOESM5_ESM.tiff (34.3 mb)
Supplementary Figure 4: Boxplot of differences in NPP between watering treatments. NPP is measured as rate of grams of biomass per day. ‘June’ and ‘July’ plots have significantly larger biomass accumulation than ‘May’ and ‘Control’ plots (ANOVA, df = 1, F = 4.77, p = 0.042).(TIFF 35161 kb)
10021_2015_9845_MOESM6_ESM.tiff (34.3 mb)
Supplementary Figure 5: Daytime soil respiration over the course of the 2012 growing-season. Soil respiration is not significantly different between treatments at any time point. (TIFF 35161 kb)
10021_2015_9845_MOESM7_ESM.tiff (34.3 mb)
Supplementary Figure 6: There are no differences in cumulative NEP between watering treatment groups when plots are divided by total biomass (ANOVA, df = 3, F = 0.699, p = 0.554). (TIFF 35161 kb)
10021_2015_9845_MOESM8_ESM.tiff (34.3 mb)
Supplementary Figure 7: Nighttime soil respiration over the course of the 2012 growing-season. There are significant differences in nighttime respiration between treatments at 3 of seven time points. Asterisks indicate significant differences as determined by ANOVA with p < 0.05. (TIFF 35161 kb)
10021_2015_9845_MOESM9_ESM.tiff (34.3 mb)
Supplementary Figure 8: Linear regression of the June Palmer Index and snowmelt date reveal a positive correlation (df = 1 and 257, F = 140, p < 0.001, adj. R 2  = 0.35). Data points are labeled as years for context. (TIFF 35161 kb)
10021_2015_9845_MOESM10_ESM.tiff (34.3 mb)
Supplementary Figure 9A: Antecedent effects of 2012 watering on 2013 NEP during the day. Watering treatment in 2012 did not have a significant effect on NEE in 2013 during the day or night. Black dots indicate measurement times. Lines are smoothed using a Loess function. Shadows are 95% confidence intervals. (TIFF 35161 kb)
10021_2015_9845_MOESM11_ESM.tiff (34.3 mb)
Supplementary Figure 9B: Antecedent effects of 2012 watering on 2013 ecosystem respiration. Watering treatment in 2012 did not have a significant effect on NEE in 2013 during the day or night. Black dots indicate measurement times. Lines are smoothed using a Loess function. Shadows are 95% confidence intervals. (TIFF 35161 kb)

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Copyright information

© Springer Science+Business Media New York 2015

Authors and Affiliations

  • Lindsey L. Sloat
    • 1
    • 2
    Email author
  • Amanda N. Henderson
    • 1
    • 2
  • Christine Lamanna
    • 2
    • 3
  • Brian J. Enquist
    • 1
    • 2
    • 4
  1. 1.Department of Ecology and Evolutionary BiologyThe University of ArizonaTucsonUSA
  2. 2.The Rocky Mountain Biological LaboratoryGothicUSA
  3. 3.World Agroforestry CentreUnited Nations Ave.NairobiKenya
  4. 4.The Santa Fe InstituteSanta FeUSA

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