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In arid and semi-arid regions freshwater resources have become scarcer with increasing demands from socio-economic development and population growth. Until recently, water research and management in these has mainly focused on blue water but ignored green water. Here we report on spatial and temporal patterns of both blue and green water flows simulated by the Soil and Water Assessment Tool (SWAT) for the Heihe river basin, the second largest inland river basin in Northwest China. Calibration and validation at two hydrological stations show good performance of the SWAT model in modelling hydrological processes. The total green and blue water flows were 22.09 billion m³ in the 2000s for the Heihe river basin. Blue water flows are larger in upstream sub-basins than in downstream sub-basins mainly due to high precipitation and large areas of glaciers in upstream. Green water flows are distributed more homogeneously among different sub-basins. The green water coefficient was 88.0% in the 2000s for the entire river basin, varying from around 80-90% in up- and mid-stream sub-basins to above 95% in downstream sub-basins. This is much higher than reported green water coefficient in many other river basins. The spatial patterns of green water coefficient were closely linked to dominant land covers (e.g. glaciers in upstream and desert in downstream) and climate conditions (e.g. high precipitation in upstream and low precipitation in downstream). There are no clear consistent historical trends of change in green and blue water flows and green water coefficient at both the river basin and sub-basin levels. This study provides insights into green and blue water endowments for the entire Heihe river basin at sub-basin level. The results are helpful for formulating reasonable water policies to improve water resources management in the inland river basins of China. [ABSTRACT FROM AUTHOR]

We present the measurement and modelling of transpiration from squash ( Cucurbita maxima Duchesne) growing in the field under a tropical maritime climate. Measurements were carried out on Tongatapu (175°12′ W, 21°08′ S), a coral atoll located in the Pacific Ocean. Transpiration was determined from heat-pulse measurements of sap flow in the vine stem using the T-max method. Steady-state porometry was used to monitor stomatal conductance ( g S, mm s−1). The data were used to derive parameters for a functional model of conductance that includes response functions for light, air temperature and vapour pressure deficit of the air, and a novel response function for soil moisture. Leaf area development was monitored through the growing season using a point quadrant approach. The maximum leaf area was about 2.7 m2 per plant and the effective ground area was about 1 m2 for each plant. Transpiration losses were calculated using a 2-layer big-leaf model in combination with modelled stomatal response and measured leaf area. In general, the sap flow measurements were in good agreement with the calculations of plant water use. Peak water use was between 3 and 5 L per plant per day. Daily transpiration measurements from heat-pulse were used to derive a crop factor, K C, for squash in this tropical maritime climate. The derived seasonal pattern of K C was similar to the FAO recommended crop factor for squash. However, the growing season was a little shorter. Measured sap flow also revealed periods of short-term drought and leaf fungal disease that reduced the actual transpiration losses, and there was often a rapid recovery from water stress following rainfall events. [ABSTRACT FROM AUTHOR]

The distribution of genetic diversity in Mycelis muralis , or wall lettuce, was investigated at a European scale using 12 microsatellite markers to infer historical and contemporary forces from genetic patterns. Mycelis muralis has the potential for long-distance seed dispersal by wind, is mainly self-pollinated, and has patchily distributed populations, some of which may show metapopulation dynamics. A total of 359 individuals were sampled from 17 populations located in three regions, designated southern Europe (Spain and France), the Netherlands, and Sweden. At this within-region scale, contemporary evolutionary forces (selfing and metapopulation dynamics) are responsible for high differentiation between populations (0.34