|Deng, Qi - Tennessee State University|
|Aras, Sadiye - Tennessee State University|
|Yu, Chih-li - Tennessee State University|
|Dzantor, E - Tennessee State University|
|Luo, Yiqi - University Of Oklahoma|
|Shen, Weijun - Chinese Academy Of Sciences|
|Hui, Dafeng - Tennessee State University|
Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/17/2017
Publication Date: 7/23/2017
Publication URL: http://handle.nal.usda.gov/10113/5801806
Citation: Deng, Q., Aras, S., Yu, C., Dzantor, E.K., Fay, P.A., Luo, Y., Shen, W., Hui, D. 2017. Effects of precipitation changes on aboveground net primary production and soil respiration in a switchgrass field. Agriculture, Ecosystems and Environment. 248:29-37. https://doi.org/10.1016/j.agee.2017.07.023.
Interpretive Summary: The relationship of crop productivity to rainfall has been recognized as long as there has been agriculture. Understanding what controls the relationship of rainfall to crop productivity takes on new importance as rising concentrations of greenhouse gases in the atmosphere alter the global energy balance and the amount, geographic distribution, and timing of rainfall, with increasing likelihood of rainfall regimes developing more extreme swings in drought and deluge beyond the limits of adaptation of many current crops. Novel crops are being considered for bioenergy production, and one, switchgrass, is a native grass with high drought tolerance. To understand and forecast potentially switchgrass yields and carbon sequestration potential, it’s response to extremes of rainfall need to be determined, but little information is currently available. In this study, field plots of ‘Alamo’ switchgrass were watered to create extreme water abundance, or kept in extreme drought using rainfall exclusion shelters. Two key aspects of yield and carbon sequestration were measured- the amount of plant biomass aboveground, and the rate of loss of carbon dioxide from the soil back to the atmosphere. Plant biomass decreased more with extreme drought than it increased with extreme wet conditions, while soil carbon dioxide loss responded similarly and strongly to drought and wet conditions. Thus extreme rainfall variability shifted switchgrass toward increased carbon loss, but for different reasons- by stimulating CO2 loss with little increase in carbon gain in plant biomass under wet conditions, and by reducing plant biomass during drought. This information can improve efforts to predict switchgrass yield and carbon sequestration in a more variable climate, and identifies rates of carbon loss as an important trait to consider when developing new switchgrass varieties to improve potential carbon sequestration.
Technical Abstract: This study attempted to test whether switchgrass aboveground net primary production (ANPP) responds to precipitation (PPT) changes in a double asymmetry pattern as framed by Knapp et al. (2016), and whether it is held true for other ecosystem processes such as soil respiration (SR). Data were collected from a two-year precipitation manipulation experiment with five treatments: -50%, -33%, +0%, +33%, and +50% of ambient precipitation, in an "Alamo" switchgrass field in Nashville, TN. The +/-33% PPT treatments represent nominal variations in PPT and the +/-50% PPT treatments represent extremes in PPT in the region. Switchgrass ANPP, leaf gas exchange, and soil respiration were determined each growing season. Results showed that the wet (+33%, and +50%) treatments had little effects on ANPP and leaf gas exchange compared to the ambient precipitation treatment, regardless of fertilization or not. The -33% treatment also did not change ANPP and leaf photosynthesis, but significantly decreased transpiration and enhanced water use efficiency (WUE). Only the -50% treatment significantly decreased ANPP and LAI, without changing leaf photosynthesis. SR generally decreased under the drought treatments and increased under the wet treatments, while there was no significant difference between the two drought treatments or between the two wet treatments. Our results demonstrate that switchgrass ANPP responded in a single negative asymmetry model to PPT changes probably due to relative high precipitation in the region. However, even in such mesic ecosystems, SR responded strongly to PPT changes in contrast to ANPP, suggesting that future climate changes may have greater but more complex effects on switchgrass belowground and aboveground processes.