[Absorption and allocation characteristics of K+, Ca2+, Na+ and Cl- in different organs of Broussonetia papyrifera seedlings under NaCl stress].

One-year-old Broussonetia papyrifera seedlings were subjected to 0.4, 1, 2, 3, and 4 g x kg(-1) of soil NaCl stress, and their biomass accumulation, leaf plasma membrane permeability, and the absorption, allocation and translocation of K+, Ca2+, Na+, and Cl-, as well as the symptoms of salt injury, were studied and investigated. The leaf plasma membrane permeability increased with the increase of soil NaCl concentration and of the duration of soil NaCl stress, and the seedling's root/shoot ratio also increased with increasing soil NaCl concentration. When the soil NaCl concentration exceeded 3 g x kg(-1), leaf plasma membrane permeability and seedling' s biomass accumulation were affected significantly. The Na+ and Cl- concentrations in different organs of seedlings increased with increasing soil NaCl concentration while the K+ and Ca2+ concentrations were in adverse, and the ion contents in leaves were always much higher than those in other organs, illustrating that soil NaCl stress affected the K+ and Ca2+ absorbing capability of roots, and inhibited the selective translocation of K+ and Ca2+ to aboveground parts. As a result, the K+ and Ca2+ concentrations in leaves and stems decreased. The study showed that B. papyrifera could effectively resist the injury of osmotic stress from soil salt via absorbing and accumulating Na+ and Cl-, but excessive accumulation of Na+ and Cl- could induce salt toxicity. As a non-halophyte species with relatively strong salt resistance, the aboveground parts of B. papyrifera did not have significant salt-exclusion effect.

[Effects of urbanization on soil nitrogen supply in Pinus elliottii plantations].

With the Pinus elliottii plantations along an urban-rural gradient in Nanchang City as test objectives, and by using ion-exchange resin (IER) bag, this paper studied the seasonal dynamics of soil available nitrogen in the plantations, and analyzed the effects of urbanization on soil nitrogen supply. The results showed that the soil nitrogen supply in the plantations had an obvious seasonal fluctuation. Soil NH4+ -N concentration was significantly higher in autumn and winter than in spring and summer, while soil NO3- -N concentration, mineral N concentration, and relative nitrification rate were in adverse (P < 0.05). The seasonal dynamics of soil available nitrogen was basically consistent with the growth rhythm of P. elliottii. The soil nitrogen availability and relative nitrification ratio along the gradient differed greatly, being significantly higher in urban than in rural area (P < 0.05). Urbanization accelerated soil N mineralization and nitrification, enhanced soil nitrogen supply capacity, and increased soil NO3- -N content. It was suggested that in the construction of urban forest, the plants with high N demand, especially with high NO3- -N absorption capacity, should be introduced to mitigate the soil available N loss and its induced environmental pollution.