COS 40-5
Climate change and water use partitioning by different plant functional groups in a grassland on the Tibetan Plateau

Tuesday, August 12, 2014: 2:50 PM
Regency Blrm A, Hyatt Regency Hotel
Jia Hu, Montana State University, Bozeman, MT
Kelly A. Hopping, Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO
Joseph K. Bump, School of Forest Resources and Environmental Science, Michigan Technological University, Houghton, MI
Shichang Kang, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China
Julia A. Klein, Department of Ecosystem Science and Sustainability, Colorado State University, Fort Collins, CO
Background/Question/Methods

The Tibetan Plateau (TP) is predicted to experience increases in air temperature, increases in snowfall, and decreases in monsoon rains; however, there is currently a paucity of data that examine the ecological responses to such climate changes.  In this study, we examined the effects of increased air temperature and snowfall on: 1) water use partitioning by different plant functional groups, and 2) ecosystem CO2 fluxes throughout the growing season.  We increased snowfall by adding snow additions to our plots and increased air temperatures using open top fiberglass chambers.  

Results/Conclusions

At the individual plant scale, we used stable hydrogen isotopes (δD) to partition water use between shallow- and deep-rooted species.  Prior to the arrival of summer precipitation (typically mid-July), snowmelt was the main water source in the soils.  During this time, shallow and deep-rooted species partitioned water use by accessing water from shallow and deep soils, respectively.  However, once the monsoon rains arrived, all plants used rainwater from the upper soils as the main water source.  Snow addition did not result in increased snowmelt use throughout the growing season; instead, snowmelt water was pushed down into deeper soils when the rains arrived.  At the larger plot scale, CO2 flux measurements demonstrated that rain was the main driver for net ecosystem productivity (NEP).  NEP rates were low during June and July and reached a maximum during the monsoon season in August.  Warming decreased NEP through a reduction in gross primary productivity (GPP), and snow additions did not mitigate the negative effects of warming by increasing NEP or GPP.  Both the isotope and CO2 flux results suggest that rain drives productivity in the Nam Tso region on the TP.  This also suggests that the effects of warming-induced drought on the TP may not be mitigated by increased snowfall.  Further decreases in summer monsoon rains may affect ecosystem productivity, with large implications for livestock-based livelihoods.