In the Southern High Plains, dairies are expanding to take advantage of favorable climatic conditions. Currently, corn (Zea mays L.) and forage sorghum [Sorghum bicolor (L.) Moench] are the two major crops grown in th...In the Southern High Plains, dairies are expanding to take advantage of favorable climatic conditions. Currently, corn (Zea mays L.) and forage sorghum [Sorghum bicolor (L.) Moench] are the two major crops grown in the region to meet silage demands for the expanding dairy industry, but they have relatively large water requirements of about 840 and 690 mm, respectively, to achieve desirable results. With rising energy costs and declining water levels in the underlying Ogallala Aquifer, crops that use less water, like finger millet (Eleusine coracana (L.) Gaertn) could become alternate forage crops for dairies to corn or forage silage. In this study, we evaluated the adaptability of five finger millet accessions to the Southern High Plains and compared nutritional quality of their forage to that of corn and sorghum. Results indicated that finger millet can be grown in the Southern High Plains. Comparison of nutrient composition has shown that the quality of finger millet is relatively higher than that of corn and sorghum in terms of calcium, potassium, and phosphorus levels in their forage. However, potential forage yield of most commonly grown corn and sorghum in the region is higher than that of finger millet. Therefore, finger millet may provide a unique opportunity to improve the dairy-fed silage quality by mixing it with corn or sorghum silage while meeting the growing regional forage demand. Further field research is needed to measure its water requirements in the Southern High Plains.展开更多
Carbon and water fluxes of savannas and grasslands have large seasonal dynamics and inter-annual variation. In this study, we selected five savanna and grassland sites, each of them having 10+ years (11−21 years) of e...Carbon and water fluxes of savannas and grasslands have large seasonal dynamics and inter-annual variation. In this study, we selected five savanna and grassland sites, each of them having 10+ years (11−21 years) of eddy covariance (EC) data, and a total of 85 site-years at these five sites which offers a unique opportunity for data analyses and model evaluation. We ran a long-term simulation (2000−2021) of the vegetation photosynthesis model (VPM, v3.0) and vegetation transpiration model (VTM, v2.0) to investigate the seasonal dynamics, interannual variation, and decadal trends of modeled gross primary production (GPPVPM) and transpiration (TVTM) at these sites. The seasonal dynamics of daily GPPVPM and TVTM track well with the seasonal dynamics of EC-based GPP (GPPEC, R2: 0.76−0.93) and evapotranspiration (ETEC, R2: 0.69−0.92). The inter-annual variation of annual GPPVPM tracked well that of annual GPPEC, with the linear regression slopes for GPPEC versus GPPVPM-EC ranging from 0.89 to 1.11. The simulation results of GPPVPM and TVTM using two different climate data sets (in situ climate data and European Center for Medium-Range Weather Forecasts Reanalysis v5 data set (ERA5)) were similar, suggesting that ERA5 data can be used for VPM/VTM simulations at large spatial scales. From 2000 to 2021, annual GPPVPM and TVTM had no significant inter-annual trends at one savanna and three grassland sites but increased significantly at one savanna site. The results demonstrate the potential of using VPM (v3.0) and VTM (v2.0) to predict the seasonal dynamics and inter-annual variation of GPP and T in savannas and grasslands.展开更多
Introduction:Understanding the differences in carbon and water vapor fluxes of spatially distributed evergreen needleleaf forests(ENFs)is crucial for accurately estimating regional or global carbon and water budgets a...Introduction:Understanding the differences in carbon and water vapor fluxes of spatially distributed evergreen needleleaf forests(ENFs)is crucial for accurately estimating regional or global carbon and water budgets and when predicting the responses of ENFs to current and future climate.Methods:We compared the fluxes of ten AmeriFlux ENF sites to investigate cross-site variability in net ecosystem exchange of carbon(NEE),gross primary production(GPP),and evapotranspiration(ET).We used wavelet cross-correlation analysis to examine responses of NEE and ET to common climatic drivers over multiple timescales and also determined optimum values of air temperature(T_(a))and vapor pressure deficit(VPD)for NEE and ET.Results:We found larger differences in the NEE spectra than in the ET spectra across sites,demonstrating that spatial(site-to-site)variability was larger for NEE than for ET.The NEE and ET were decoupled differently across ENF sites because the wavelet cospectra between ET and climate variables were similar at all sites,while the wavelet cospectra between NEE and climate variables were higher(i.e.,closer coupling between NEE and climatic drivers)in semi-arid and Mediterranean sites than in other sites.Ecosystem water use efficiency(EWUE)based on annual GPP/ET ranged from 1.3±0.18 to 4.08±0.62 g C mm^(−1)ET,while EWUE based on annual net ecosystem production(NEP)/ET ranged from 0.06±0.04 to 1.02±0.16 g C mm^(−1)ET)among ENFs.Responses of NEE and ET to T_(a)varied across climatic zones.In particular,for ENF sites in semi-arid and Mediterranean climates,the maximum NEE and ET occurred at lower ranges of T_(a)than in sites with warm and humid summers.The optimum T_(a)and VPD values were higher for ET than for NEE,and ET was less sensitive to high values of T_(a)and VPD.Conclusions:Large spatial variability in carbon and water vapor fluxes among ENFs and large variations in responses of NEE and ET to major climate variables among climatic zones necessitate sub-plant functional type parameterization based on climatic zones to better represent climate sensitivity of ENFs and to reduce uncertainty in model predictions.展开更多
文摘In the Southern High Plains, dairies are expanding to take advantage of favorable climatic conditions. Currently, corn (Zea mays L.) and forage sorghum [Sorghum bicolor (L.) Moench] are the two major crops grown in the region to meet silage demands for the expanding dairy industry, but they have relatively large water requirements of about 840 and 690 mm, respectively, to achieve desirable results. With rising energy costs and declining water levels in the underlying Ogallala Aquifer, crops that use less water, like finger millet (Eleusine coracana (L.) Gaertn) could become alternate forage crops for dairies to corn or forage silage. In this study, we evaluated the adaptability of five finger millet accessions to the Southern High Plains and compared nutritional quality of their forage to that of corn and sorghum. Results indicated that finger millet can be grown in the Southern High Plains. Comparison of nutrient composition has shown that the quality of finger millet is relatively higher than that of corn and sorghum in terms of calcium, potassium, and phosphorus levels in their forage. However, potential forage yield of most commonly grown corn and sorghum in the region is higher than that of finger millet. Therefore, finger millet may provide a unique opportunity to improve the dairy-fed silage quality by mixing it with corn or sorghum silage while meeting the growing regional forage demand. Further field research is needed to measure its water requirements in the Southern High Plains.
基金supported by research grant from the US National Science Foundation (OIA-1946093)supported in part by the US Department of Energy’s Office of Science. Data for these AmeriFlux sites can be downloaded from FLUXNET2015 website.
文摘Carbon and water fluxes of savannas and grasslands have large seasonal dynamics and inter-annual variation. In this study, we selected five savanna and grassland sites, each of them having 10+ years (11−21 years) of eddy covariance (EC) data, and a total of 85 site-years at these five sites which offers a unique opportunity for data analyses and model evaluation. We ran a long-term simulation (2000−2021) of the vegetation photosynthesis model (VPM, v3.0) and vegetation transpiration model (VTM, v2.0) to investigate the seasonal dynamics, interannual variation, and decadal trends of modeled gross primary production (GPPVPM) and transpiration (TVTM) at these sites. The seasonal dynamics of daily GPPVPM and TVTM track well with the seasonal dynamics of EC-based GPP (GPPEC, R2: 0.76−0.93) and evapotranspiration (ETEC, R2: 0.69−0.92). The inter-annual variation of annual GPPVPM tracked well that of annual GPPEC, with the linear regression slopes for GPPEC versus GPPVPM-EC ranging from 0.89 to 1.11. The simulation results of GPPVPM and TVTM using two different climate data sets (in situ climate data and European Center for Medium-Range Weather Forecasts Reanalysis v5 data set (ERA5)) were similar, suggesting that ERA5 data can be used for VPM/VTM simulations at large spatial scales. From 2000 to 2021, annual GPPVPM and TVTM had no significant inter-annual trends at one savanna and three grassland sites but increased significantly at one savanna site. The results demonstrate the potential of using VPM (v3.0) and VTM (v2.0) to predict the seasonal dynamics and inter-annual variation of GPP and T in savannas and grasslands.
基金supported in part by grants from the Agriculture and Food Research Initiative of the USDA National Institute of Food and Agriculture(NIFA,Grant No.2013-69002 to P.Wagle,X.Xiao,and P.Gowda,and Grant No.2013-67003-20652 to B.Law)the National Science Foundation EPSCoR(IIA-1301789 to X.Xiao)+8 种基金supported by US Department of Energy(Grant No.65076)to B.Lawsupported by the North American Carbon Program/USDA CREES NRI(2004-35111-15057,2008-35101-19076)Science Foundation Arizona(CAA 0-203-08)to T.Kolbsupported by grants from US Department of Energy[the National Institute for Climate Change Research(NICCR)and Terrestrial Carbon Processes Program(TCP)]the National Science Foundation Environmental Biology(Grant 0918565)supported by an agreement among the University of Washington,the Pacific Northwest Research Station,and the Gifford Pinchot National Forestsupported by DOE BER-TES awards number 7090112 and 11-DE-SC-0006700USDA NIFA CAP 560 Award 2011-68002-30185USDA Forest Service Eastern Forest Environmental Threat Assessment Center Grant 08-JV-11330147-038。
文摘Introduction:Understanding the differences in carbon and water vapor fluxes of spatially distributed evergreen needleleaf forests(ENFs)is crucial for accurately estimating regional or global carbon and water budgets and when predicting the responses of ENFs to current and future climate.Methods:We compared the fluxes of ten AmeriFlux ENF sites to investigate cross-site variability in net ecosystem exchange of carbon(NEE),gross primary production(GPP),and evapotranspiration(ET).We used wavelet cross-correlation analysis to examine responses of NEE and ET to common climatic drivers over multiple timescales and also determined optimum values of air temperature(T_(a))and vapor pressure deficit(VPD)for NEE and ET.Results:We found larger differences in the NEE spectra than in the ET spectra across sites,demonstrating that spatial(site-to-site)variability was larger for NEE than for ET.The NEE and ET were decoupled differently across ENF sites because the wavelet cospectra between ET and climate variables were similar at all sites,while the wavelet cospectra between NEE and climate variables were higher(i.e.,closer coupling between NEE and climatic drivers)in semi-arid and Mediterranean sites than in other sites.Ecosystem water use efficiency(EWUE)based on annual GPP/ET ranged from 1.3±0.18 to 4.08±0.62 g C mm^(−1)ET,while EWUE based on annual net ecosystem production(NEP)/ET ranged from 0.06±0.04 to 1.02±0.16 g C mm^(−1)ET)among ENFs.Responses of NEE and ET to T_(a)varied across climatic zones.In particular,for ENF sites in semi-arid and Mediterranean climates,the maximum NEE and ET occurred at lower ranges of T_(a)than in sites with warm and humid summers.The optimum T_(a)and VPD values were higher for ET than for NEE,and ET was less sensitive to high values of T_(a)and VPD.Conclusions:Large spatial variability in carbon and water vapor fluxes among ENFs and large variations in responses of NEE and ET to major climate variables among climatic zones necessitate sub-plant functional type parameterization based on climatic zones to better represent climate sensitivity of ENFs and to reduce uncertainty in model predictions.
