The ability of the following four organic amendments to ameliorate saline soil in coastal northern China was investigated from April 2010 to October 2012 in a field experiment: green waste compost (GWC), sedge peat (SP), furfural residue (FR), and a mixture of GWC, SP and FR (1∶1∶1 by volume) (GSF). Compared to a non-amended control (CK), the amendments, which were applied at 4.5 kg organic matter m−3, dramatically promoted plant growth; improved soil structure; increased the cation exchange capacity (CEC), organic carbon, and available nutrients; and reduced the salt content, electrical conductivity (EC), and exchangeable sodium percentage (ESP). At the end of the experiment in soil amended with GSF, bulk density, EC, and ESP had decreased by 11, 87, and 71%, respectively, and total porosity and organic carbon had increased by 25 and 96% respectively, relative to the CK. The GSF treatment resulted in a significantly lower Na++K+ content than the other treatments. CEC and the contents of available N, P, and K were significantly higher in the GSF-treated soil than in the CK and were the highest in all treatments. The FR treatment resulted in the lowest pH value and Ca2+ concentration, which decreased by 8% and 39%, respectively, relative to the CK. Overall, the results indicate that a combination of green waste compost, sedge peat and furfural residue (GSF treatment) has substantial potential for ameliorating saline soils in the coastal areas of northern China, and it works better than each amendment alone. Utilization of GWC and FR can be an alternative organic amendment to substitute the nonrenewable SP in saline soil amelioration.

Water use efficiency (WUE) is an important indicator of ecosystem functioning but how ecosystem WUE responds to climate change including precipitation and nitrogen (N) deposition increases is still unknown. To investigate such responses, an experiment with a randomized block design with water (spring snowfall or summer water addition) and nitrogen addition was conducted in a temperate steppe of northern China. We investigated net ecosystem CO2 production (NEP), gross ecosystem production (GEP) and evapotranspiration (ET) to calculate ecosystem WUE (WUEnep = NEP/ET or WUEgep = GEP/ET) under spring snow and summer water addition with or without N addition from 2011 to 2013. The results showed that spring snow addition only had significant effect on ecosystem WUE in 2013 and summer water addition showed positive effect on ecosystem WUE in 2011 and 2013, as their effects on NEP and GEP is stronger than ET. N addition increased ecosystem WUE in 2012 and 2013 both in spring snow addition and summer water addition for its increasing effects on NEP and GEP but no effect on ET. Summer water addition had less but N addition had greater increasing effects on ecosystem WUE as natural precipitation increase indicating that natural precipitation regulates ecosystem WUE responses to water and N addition. Moreover, WUE was tightly related with atmospheric vapor-pressure deficit (VPD), photosynthetic active radiation (PAR), precipitation and soil moisture indicating the regulation of climate drivers on ecosystem WUE. In addition, it also was affected by aboveground net primary production (ANPP). The study suggests that ecosystem WUE responses to water and N addition is determined by the change in carbon process rather than that in water process, which are regulated by climate change in the temperate steppe of northern China.

Photosynthetic characteristics are widely used as indicators of plant responses to global environmental changes such as precipitation change and nitrogen (N) deposition increase. How different plant species respond physiologically to the future precipitation change combined with increasing N availability is largely unclear. A field experiment was conducted to study responses in seasonal and interannual leaf carbon (C) exchange of two dominant plant species, Leymus chinensis and Stipa grandis, to additional water (either as spring snow or as summer water) and N application in a semi-arid temperate steppe of China. Our results showed that spring snow and summer water addition both increased the maximum photosynthetic rate (Amax) of two dominant species. Such effect was likely caused by raised light saturation point, the maximum apparent quantum yield, stomatal conductance, and transpiration rate. The N application combined with spring snow or summer water addition both enhanced Amax of S. grandis in both experimental years, whereas N application only increased Amax of L. chinensis combined with summer water addition. Their responses were attributed to a concurrent increase in leaf N concentration (Nleaf) and decrease in leaf phosphorus (P) concentration (Pleaf), indicating that Nleaf and Pleaf affect photosynthetic characteristics to regulate leaf C exchange. Our results suggest that differentiated responses among different species in photosynthetic characteristics may lead to changes in ecosystem structure and functioning under increasing precipitation and N deposition.