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It has become increasingly important to quantify carbon and water fluxes due to their roles in global warming and climate change, particularly for the agroecosystems. However, the dynamics of carbon and water fluxes have not been clearly recognized in rotation croplands with complex and changeable climate. Here, the variations of net ecosystem productivity (NEP), evapotranspiration (ET) and the water use efficiency (WUE, defined as NEP/ET), and their responses to the environmental factors were investigated in a wheat-maize rotation cropland across the Huaibei Plain of China over 2013–2015. The total average NEP, ET and average WUE respectively were 489.1 gC m-2, 315.8 kgH 2 O m-2, 4.4 gC kg-1H 2 O for wheat and 192.5 gC m-2, 249.0 kgH 2 O m-2, 3.6 gC kg-1H 2 O for maize, implying that wheat season sequestered more CO 2 than maize season. Spring drought and summer flood affected WUE of wheat and maize, respectively. Daily wheat WUE seemed to be more sensitive to changes in photosynthetically active radiation (PAR), vapor pressure deficit (VPD), soil water content (SWC) and canopy conductance (G c). PAR was the dominant factor controlling diurnal dynamics of NEP and ET, while the opposite effect of VPD on NEP was recognized. NEP increasing with PAR was limited by high VPD, which obviously when VPD exceeded 2 kPa during the maize season. Maize NEP was limited with VPD under high solar radiation (> 500 μmol m-2 s-1). WUEs of wheat and maize were negatively related to SWC and G c , and the sensitivity of WUE response to SWC and G c increased with the increase of PAR or VPD range. Sub-diurnal NEP against PAR, VPD or temperature showed clockwise hysteresis but ET against PAR or windspeed showed counter-clockwise hysteresis, and these hystereses were mainly caused by the interplay between evaporative demand and moisture supply, photosynthesis and carbon allocation of the agroecosystems. [Display omitted] • The wheat season sequestered more CO2 than the maize season. • Spring drought and summer flood affected WUE of wheat and maize, respectively. • Wheat WUE seemed to be more sensitive to changes in environmental factors. • PAR was the dominant factor controlling diurnal dynamics of NEP and ET. [ABSTRACT FROM AUTHOR]

Future changes in reference evapotranspiration (ET0) are of increasing importance in assessing the potential impacts on hydrology and water resources systems of more pronounced climate change. This study assesses the applicability of the Statistical Downscaling Model (SDSM) in projecting ET0, and investigates the seasonal and spatial patterns of future ET0 based on general circulation models (GCMs) across the Haihe River Basin. The results indicate that SDSM can downscale ET0 well in term of different basin-averaged measures for the HadCM3 and CGCM3 GCMs. HadCM3 has a much superior capability in capturing inter-annual variability compared to CGCM3 and thus is chosen as the sole model to assess the changes in future ET0. There are three homogeneous sub-regions of the Haihe River Basin: Northwest, Northeast and Southeast. Change points are detected at around 2050 and 2080 under the A2 and B2 scenarios, respectively. The Northwest is revealed to have a slight to strong increase in ET0, while the Northeast and the Southeast tend to experience a pattern change from decrease to increase in ET0. EDITOR M.C. Acreman ASSOCIATE EDITOR J. Thompson [ABSTRACT FROM AUTHOR]

Although soil moisture (SM) is an important constraint factor of evapotranspiration (ET), the majority of the satellite-driven ET models do not include SM observations, especially the SM at different depths, since its spatial and temporal distribution is difficult to obtain. Based on monthly three-layer SM data at a 0.25° spatial resolution determined from multi-sources, we updated the original Priestley Taylor–Jet Propulsion Laboratory (PT-JPL) algorithm to the Priestley Taylor–Soil Moisture Evapotranspiration (PT-SM ET) algorithm by incorporating SM control into soil evaporation (Es) and canopy transpiration (T). Both algorithms were evaluated using 17 eddy covariance towers across different biomes of China. The PT-SM ET model shows increased R2, NSE and reduced RMSE, Bias, with more improvements occurring in water-limited regions. SM incorporation into T enhanced ET estimates by increasing R2 and NSE by 4% and 18%, respectively, and RMSE and Bias were respectively reduced by 34% and 7 mm. Moreover, we applied the two ET algorithms to the whole of China and found larger increases in T and Es in the central, northeastern, and southern regions of China when using the PT-SM algorithm compared with the original algorithm. Additionally, the estimated mean annual ET increased from the northwest to the southeast. The SM constraint resulted in higher transpiration estimate and lower evaporation estimate. Es was greatest in the northwest arid region, interception was a large fraction in some rainforests, and T was dominant in most other regions. Further improvements in the estimation of ET components at high spatial and temporal resolution are likely to lead to a better understanding of the water movement through the soil–plant–atmosphere continuum. [ABSTRACT FROM AUTHOR]

Evidence that the pan evaporation or reference evapotranspiration (ET0) as the indicator of atmospheric evaporation capability have decreased along with the continuous increase in temperature over the past decades (coined as 'evaporation paradox') has been reported worldwide. Here, we provide a nationwide investigation of spatiotemporal change of ET0 using meteorological data from 602 stations with the updated data (1961-2011). In addition, we explore the trigger mechanism by quantitative assessment on the contribution of climatic factors to ET0 change based on a differential equation method. In despite of different shift points regionally, our results suggest that the ET0 generally present decadal variations rather than monotonic response to climate change reported in previous studies. The significant decrease in net radiation dominate the decrease in ET0 before early 1990s in southern regions, while observed near-surface wind speed is the primary contributor to the variations of ET0 for the rest regions during the same periods. The enhancements of atmospheric evaporation capability after early 1990s are driven primarily by recent relative humidity limitation in China. From a continental scale view, as highly correlating with to Pacific Decadal Oscillation, the shift behaviors of ET0 is likely an episodic phenomenon of the ocean-atmosphere interaction in earth. [ABSTRACT FROM AUTHOR]

Abstract Phosphorus (P) is an indispensable resource for plant growth, and under the background with P consumption increase in crop system, the agriculture and crop production may be affected through the changes of phosphorus use efficiency (PUE) due to the human interference and climate change. Therefore, it is of great importance to investigate the responses of PUE to human interference and climate change from the perspectives of historical simulation and future projection. In this study, the changes of PUE from 2001 to 2015 in the middle and lower reaches of the Yangtze River (MLRYR) of China were evaluated by means of empirical PUE-model based on the substance flow analysis (SFA) method. Their responses to future human interference and climate scenarios during 2016–2030 were investigated by driving PUE-model with three neural networks (BP, GA-BP and PSO-BP) as well as the multiple downscaling climatic data (HadGEM2-ES, BCC-CSM1.1 (m) and GFDL-ESM2M) with the help of a statistical downscaling method (SDSM). The results showed that the PUE values of the three crops (rice, wheat and maize) were 53.61%, 36.22%, and 32.56%, respectively, during the period from 2001 to 2015 and 54.11%, 38.92% and 32.78%, respectively, during the period from 2016 to 2030. Consequently, the PUE showed an increasing trend from history to future. However, the overall PUE level was not high, with a value of not more than 60%, and notably for wheat and maize, the PUE was less than 40%. Meanwhile, the precipitation affected the leaching of P because increasing in precipitation may result in a relatively high increase in the probability of low-PUE. Moreover, great potential exists for enhancing the PUE in this region, and measures to improve PUE management practices have been proposed, such as, raising the crop yield, keeping the arable area and balancing the fertilization, etc. The present study provides a beneficial reference to comprehensively understand the impacts of human interference and climate change on the PUE and further improves regional sustainable strategies for future P resource management. Highlights • Evaluating the responses of PUE to human interference and climate change from historical simulation and future projections. • Predicting the future PUE by driving PUE-model with the multiple neural networks and GCMs. • Besides the rice, the PUE values of wheat and maize were less than 40% during 2001–2030. [ABSTRACT FROM AUTHOR]