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Title: Carbon dioxide and water vapour exchange in a tropical dry forest as influenced by the North American Monsoon System (NAMS)

Author
item PEREZ-RUIZ, E.R. - Technical Institute Of Mexico
item GARATUZA-PAYAN, J - Technical Institute Of Mexico
item WATT, C. - University Of Mexico
item RODRIGUEZ, J.C. - University Of Mexico
item YEPEZ, E.A. - Technical Institute Of Mexico
item Scott, Russell - Russ

Submitted to: Journal of Arid Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/23/2009
Publication Date: 5/1/2010
Citation: Perez-Ruiz, E., Garatuza-Payan, J., Watt, C., Rodriguez, J., Yepez, E., Scott, R.L. 2010. Carbon dioxide and water vapour exchange in a tropical dry forest as influenced by the North American Monsoon System (NAMS). Journal of Arid Environments. 74: 556-563.

Interpretive Summary: The North American Monsoon (NAM) dominates summer climate and is responsible for providing the majority of rainfall over a large portion western North America. Knowing how ecosystems respond to this input of rainfall is critical to understanding how surface vegetation response may affect monsoon intensity. To better understand the effects and relationship between precipitation, carbon sequestration and evaporation, we made measurements of these exchanges over a tropical dry forest in the northwest Mexico in 2006. Three markedly defined periods were found during the six-month study period: 1. a pre-rainy season period, where carbon and water exchange was close to zero, 2.a monsoon period characterized by relatively large evaporation losses and large carbon uptake, and 3) a post-rainy season where the ecosystem returned to dormancy. More mechanistic information about biological and environmental variables controlling these exchanges is still needed to predict how seasonally dry ecosystems would respond to climate change.

Technical Abstract: To better understand the effects and relationship between precipitation, net ecosystem carbon dioxide (NEE) and water vapor exchange (ET), we report a study conducted in the tropical dry forest (TDF) in the northwest of Mexico. Ecosystem gas exchange was measured using the eddy correlation technique during the presence of North American Monsoon System (NAMS) in 2006. Patterns in NEE and ET were different in wet and dry periods. Three markedly defined periods were found during the six-month study period. A pre-monsoon period, where gas exchange was close to zero. A monsoon period, divided in two stages: 1) early monsoon: a strong increase in the respiratory rate marked by a peak of positive values, with a maximum of 22 g CO2 m-2 day-1, and, 2) late monsoon: an assimilation period occurred in the peak of the monsoon period, with sustained values around -20 g CO2 m-2 day-1. The final was a postmonsoon period, where ecosystems returned to dormancy. NEE and ET trends in the TDF were similar to other seasonally dry ecosystems influenced by the NAMS. During the study period the TDF of Northwest Mexico acted as a sink capturing 374 g CO2/m2 with an ecosystem water use efficiency (-NEE/ET) comparable to other ecosystems in the region. Mechanistic information about biological and environmental variables controlling gas exchange dynamics is still necessary to predict how seasonally dry ecosystems would respond to climate change.