Interactive effects of irrigation and exponential fertilization on nutritional characteristics in Populus 3 euramericana cv. ‘74/76' cuttings in an open-air nursery in Beijing, China

Nutritional characteristics determine tree stock quality to a considerable extent. Exponential fertilization can induce nutrient reserves within juvenile trees, but its validity on poplar is contingent on interaction with a scientific irrigation regime due to limited water resources under global warming. In the present study, we raised 3200 Populus 9 euramericana cv. ＇74/76＇ cuttings under four irrigation regimes of 0（I0）, 60 %（I60）, 80 %（I80）, and100 %（I100） of field capacity for soil moisture content with or without（control） the employment of nitrogen（N） addition delivered as exponential fertilization at the rate of 8 g N cutting^（-1）（E8） in an open-air nursery in Beijing, China. Both height and diameter increased with the increment of soil moisture ratio or in response to exponential fertilization（EF） without any interactive effects. In general, concentrations of N, phosphorus（P）,and potassium（K） declined with time in stem but foliar N concentration did not change. Under the I100 regime, EF increased foliar N concentration relative to the control but failed to affect N concentration in stem in September, when both N concentration and N content were increased by EF under the I80 regime. Stem-K content and concentration by EF under the I80 regime also increased in September,therefore EF-treated cuttings had a higher ratio of K content in stem to that in whole plant（%ANAR）. Vector diagnosis for nutritional status indicated that EF resulted in dilution of K concentration but induced a steady-state P uptake in leaves under all irrigation regimes. Therefore, EF of N addition could promote N uptake to leaves of P. 9 euramericana cv. ＇74/76＇ cuttings, but it had a null effect on N and P reserves in stem and impaired K reserves.In conclusion, the irrigation regime of 80 % field capacity of soil moisture content was suggested for the culture of juvenile P. 9 euramericana cv. ＇74/76＇ cuttings. As the interactive meaning, EF was also suggested for its excellent promotion on both N and K uptakes.

Foliar C/N stoichiometry in urban forest trees on a global scale

Foliar C/N stoichiometry is an indicator of geochemical cycling in forest ecosystems,but the driving changes for its response to urbanization at the wide scale is not clear.In this study,data on tree-leaf C and N stoichiometry were collected in papers from across 105 tree species from 82 genera and 46 families.The foliar C/N of urban forest trees varied among different climate zones and tree taxonomic variation and tended to be higher in trees of urban forests near the equator and in eastern regions,mainly driven by lowered foliar N concentration.Neither the foliar C concentration nor foliar C/N for trees of urban forests was statistically higher than those of rural forests.For variation by taxonomic classification,C_4 species Amaranthus retroflexus and Chenopodium ambrosoides(Amaranthaceae) had lower foliar C/N than did other species and families.Myrsine guianensis(Primulaceae) and Myconia fallax(Asteraceae) had the highest foliar C/N.Therefore,urbanization has not caused a significant response in forest trees for foliar C/N.The change in foliar N concentration was globally the main force driving of the differences in foliar C/N for most tree species in urban forests.More work is needed on foliar C/N in trees at cities in polar regions and the Southern Hemisphere.

Geographical distribution of Aralia elata characteristics correlated with topography and forest structure in Heilongjiang and Jilin Provinces,Northeast China

The Araliaceae family consists of numerous species of medical plants of significant value as non-wood forest products.To conserve and culture these plants in natural forest stands is an important undertaking which should be implemented according to the relationship between forest structure and understory population.In this study,thirtyfive plots were established in natural A ralia elata stands.Taller individual and denser populations were found in the northern and in the eastern regions,respectively.Both population densities and individual leaf weight increased along longitude.In contrast,their relationship with elevation and DBH were negative.Along with the altitude gradient,both height and root-collar diameter increased but population density declined.Root-collar diameter and population density decreased with latitude and DBH,respectively.Overall,dominant trees unlikely enforced strong disturbance to the development of understory A.elata populations unless concerning some specific topographic factors.