Growing season variability in evapotranspiration, ecosystem water use efficiency, and energy partitioning in switchgrass

Abstract

Evapotranspiration (ET), ecosystem water use efficiency (EWUE), and energy partitioning in switchgrass (Panicum virgatum L.) ecosystems are crucial to understand its water and energy balances since switchgrass acreage is expanding for cellulosic biofuels. We measured CO2, H2O, and energy fluxes over a switchgrass field in Chickasha, OK, USA, using eddy covariance method. The objective of this study was to quantify seasonal variations in ET, EWUE, and seasonal distributions of energy partitioning in response to controlling factors. Seasonal (May to mid‐November) cumulative ET (450 mm) was similar to cumulative rainfall (432 mm). During June to September, ET was 1·92 times of rainfall, indicating that the crop experienced severe drought during the mid‐growing season. ET showed clear seasonality with 3–4 mm day−1 during the active growing season (late May and June) to low rates of about 0·5 mm day−1 during the late growing season (November). The ET rate decreased during dry periods. On seasonal scale, more energy was partitioned to sensible heat flux (H) than latent heat (LE) because of drought. Estimation of EWUE by dividing time integrals of gross ecosystem photosynthesis (GEP) by respective H2O fluxes (ET) at monthly time scale provided EWUE from 10·46 (August) to 14·08 g CO2 mm−1 ET (October) with a seasonal average of 12·01 g CO2 mm−1 ET. Seasonal patterns in EWUE were observed with smaller values during drought because of more rapid reduction in carbon assimilation (GEP) than ET. These findings confirm the major role of precipitation in determining water and energy balances in switchgrass. Copyright © 2012 John Wiley & Sons, Ltd.

Differential responses of carbon and water vapor fluxes to climate among evergreen needleleaf forests in the USA

“…3 Seasonal changes (8-day averages) of ecosystem water use efficiency (EWUE GPP and EWUE NEP ) based on gross primary production (GPP) and evapotranspiration (ET) and net ecosystem production (NEP) and ET at ten forest sites, respectively ecosystem level: GPP or ER (which includes both autotrophic and heterotrophic respiration) in response to environmental effects ). In addition, carbon uptake (NEE or GPP) is constrained more than ET by VPD through restriction of stomatal regulation (Kuglitsch et al 2008;Wagle and Kakani 2014). The wavelet analysis showed that NEE and ET deviated from each other at seasonal-to-interannual timescales at all ENFs (Fig.…”

Carbon and water dynamics of a bioenergy crop (Cynara cardunculus L.) under different meteorological conditions in a semi-arid region

“…The slopes of these linear relationships forced to zero are a good representation of the WUE (Wagle and Kakani, 2012) and are very close to the WUE values found as ratio between NEE and ET, cumulated at seasonal scale in the same period. In this case the slopes are not significantly different (ANCOVA P=0.71) even if the correlations are very strong.…”

“…Except for the senescence phase, in accordance with Emmerich (2007) and Wagle and Kakani (2012), daily WUE values along the seasons, show a great variability, ranging between -0.89 and -41.68 gCO2 kgH2O -1 in the WS and between 0.12 and -42.68 gCO2 kgH2O -1 in the DS. This variability is due to the effects of weather and plant physiology on CO2 and ET fluxes.…”

“…The literature is rich of examples relative to ecosystem WUEs, defined in terms of net carbon uptake by the ecosystem per amount of water loss as ET, both obtained by EC measurements [Li et al, 2015 -vineyard;Wagle and Kakani 2012 -switchgrass;Tallec et al, 2013 -winter wheat and maize; Zeri et al, 2013 -biofuel (row crops, Miscanthus, Switchgrass, native prairie); Shurpali et al, 2013 -reed canary grass, a perennial bioenergy crop]. Wagle and Kakani (2012) summarized different metrics for defining the ecosystem WUE at different time scales (from seasonal to instantaneous scale) by EC measurements. This approach can be helpful to gain insight into environmental and eco-physiological mechanisms of carbon and water (Yu et al, 2008).…”

Stress-Tolerant Feedstocks for Sustainable Bioenergy Production on Marginal Land

“…tolerance during establishment [64], possibly because of lower water use efficiency related to lower carbon assimilation during drought [111]. Although when drought was imposed after establishment, Panicum virgatum plants appeared to be drought hardy [64,65]-particularly upland cytotypes [67,68].…”