Department of Microbiology and Plant Biology, Center for Spatial Analysis, University of Oklahoma, Norman, OK, USA.
Department of Microbiology and Plant Biology, Center for Spatial Analysis, University of Oklahoma, Norman, OK, USA.
Sci Total Environ. 2018 Dec 10;644:1511-1524. doi: 10.1016/j.scitotenv.2018.07.010. Epub 2018 Jul 23.
Winter wheat (Triticum aestivum L.) and tallgrass prairie are common land cover types in the Southern Plains of the United States. During the last century, agricultural expansion into native grasslands was extensive, particularly managed pasture or winter wheat. In this study, we measured carbon dioxide (CO) and water vapor (HO) fluxes from winter wheat and tallgrass prairie sites in Central Oklahoma using the eddy covariance in 2015 and 2016. The objective of this study was to contrast CO and HO fluxes between these two ecosystems to provide insights on the impacts of conversion of tallgrass prairie to winter wheat on carbon and water budgets. Daily net ecosystem CO exchange (NEE) reached seasonal peaks of -9.4 and -8.8 g C m in 2015 and -6.2 and -7.5 g C m in 2016 at winter wheat and tall grass prairie sites, respectively. Both sites were net sink of carbon during their growing seasons. At the annual scale, the winter wheat site was a net source of carbon (56 ± 13 and 33 ± 9 g C m year in 2015 and 2016, respectively). In contrast, the tallgrass prairie site was a net sink of carbon (-128 ± 69 and -119 ± 53 g C m year in 2015 and 2016, respectively). Daily ET reached seasonal maximums of 6.0 and 5.3 mm day in 2015, and 7.2 and 8.2 mm day in 2016 at the winter wheat and tallgrass prairie sites, respectively. Although ecosystem water use efficiency (EWUE) was higher in winter wheat than in tallgrass prairie at the seasonal scale, summer fallow contributed higher water loss from the wheat site per unit of carbon fixed, resulting into lower EWUE at the annual scale. Results indicate that the differences in magnitudes and patterns of fluxes between the two ecosystems can influence carbon and water budgets.
冬小麦（Triticum aestivum L.）和高草草原是美国南部平原常见的土地覆盖类型。在上个世纪，农业向原生草原的扩张非常广泛，特别是管理牧场或冬小麦。在这项研究中，我们使用涡度相关法于 2015 年和 2016 年测量了俄克拉荷马州中部冬小麦和高草草原站点的二氧化碳（CO）和水汽（HO）通量。本研究的目的是对比这两个生态系统的 CO 和 HO 通量，以了解将高草草原转化为冬小麦对碳和水预算的影响。2015 年和 2016 年，冬小麦和高草草原站点的日净生态系统 CO 交换（NEE）分别达到季节性峰值-9.4 和-8.8 g C m，-6.2 和-7.5 g C m。两个站点在生长季节均为碳汇。在年度尺度上，冬小麦站点是碳的净源（2015 年和 2016 年分别为 56±13 和 33±9 g C m 年）。相比之下，高草草原站点是碳的净汇（2015 年和 2016 年分别为-128±69 和-119±53 g C m 年）。日蒸腾量在 2015 年达到 6.0 和 5.3 mm day 的季节性最大值，在 2016 年达到 7.2 和 8.2 mm day 的季节性最大值，分别在冬小麦和高草草原站点。尽管在季节性尺度上，冬小麦的生态系统水分利用效率（EWUE）高于高草草原，但小麦田的夏季休耕会导致每固定单位碳的水分损失更高，从而导致年度尺度上的 EWUE 更低。结果表明，两个生态系统之间通量的幅度和模式的差异会影响碳和水预算。
