Short communicationEco-physiological adaptability in mixtures of Robinia pseudoacacia and Fraxinus velutina and coastal eco-engineering

Mixed-species plantations have potential advantages than monocultures. In this paper, the eco-physiological adaptability of single seedlings of nitrogen (N)-fixing Robinia pseudoacacia and non-N-fixing Fraxinus velutina were compared with mixed-species with the proportion of 1:1 under salt stress by pot experiments. The results showed that relative growth rate (RGR) and the maximum net photosynthetic rate decreased with the increase of soil salinity, while relative conductivity of leaves increased. R. pseudoacacia and F. velutina showed higher RGR in mixtures than in their monocultures, respectively. The relative conductivity of R. pseudoacacia in mixtures was similar to in monocultures while it was lower for F. velutina in mixtures than in monocultures. The activities of urease and phosphatase, hydrolysis nitrogen and available phosphorus in rhizosphere were affected significantly in salinity treatments, but total nitrogen and phosphorus did not. Compared to monocultures, F. velutina in mixtures increased urease activity and hydrolysis nitrogen in rhizosphere soil, and R. pseudoacacia increased phosphatase activity, available phosphorus and total phosphorus in rhizosphere soil. Therefore, there was a reciprocal benefit on the use of N and P in rhizosphere soil between them in mixtures, which was an important mechanism for more productivity in the mixture of R. pseudoacacia and F. velutina and an efficient method for coastal eco-engineering on large scale.