Habitat Characteristics As Determined By Available Nitrogen In Forest Soils Of Temperate Zone

It is well know that nitrogen is the most nutritional element for plant growth and is the most important nutritional element. In forest ecosystem nitrogen is one of the most important environment factor for limited plant growth. It have important effect for forest community succession. Nitrogen can ensure stability of climax community and can keep proportion of tree species. Plant species frequently create a certain type of adaptation to its original "nutrition habitat" during the long process of evolution, of which the apparent preferences for different nitrogen soures(e.g. NH₄⁺—N or NO₃^-—N) might be an improtant aspect.A large number of researches have resulted that "nutrition habitats" associated with forest soils were typically dominated by NH₄⁺ rather than NO3", generally with low levels NO3", far inferior to that of NH₄⁺ in the soils. Low levels of NO₃ in the these soils generally correspond to low rates of net nitrate production, which might be the result of(l)nitrification limitations and(or)inhibitions caused by low pH, low NH₄⁺ availability(autotrophic nitrifiers do not successfully compete for NH₄⁺ with heterotrophic organisms and plants) as well as allelopathic inhibitors in the soil, or(2)the substantial microbial acquisition of nitrate in some of these soils which made gross nirification rates greatly underestimated by net rates.The adaptation of many coniferous species(especially that dominate late successional forest stands)to their primeval NH₄⁺ dominated "nutrition habitats" is so complete, they often have a diminished ability to use non-reduced forms of nitrogen(e.g. NO₃^-). These conifers typically show apparent NH₄⁺ preference, whereas their growth would invariably be reduced because of nitrogen-metabolism disorder when supplied with NO3" as the main nitrogen source.In this paper, we chose different sites in temperate zone forest. We set up three sites ,they are primeval korean pine forest, plantational korean pine forest, secondry forest. We want to find the characteristics of nitrogen nutrition habitat. Used the close-top tude incubations and waterlogged incubation, we study the change of available nitrogen in a year. The study shows that different tree species, different sites and different time have different available nitrogen content range and the change of nitrogen is complex.The main resultes are as follows:1. Before incubations, the season tends of ammoniacal nitrogen change more strongly in A₁ , A₀ layer of primeval korean pine forest than plantational korean pine forest and broad leaved secondary forest, while the nitrate nitrogen content of these three types forest is lower than the ammoniacal nitrogen content of themselves. It apparently shows that the korean pine forest soils are typically dominated by NH₄⁺ rathen than NO₃^-, but ammonical nitrogen has no powerful dominance than nitrate nitrogen in primeval korean pine forest soils.In same site, season trends of ammoniacal nitrogen and nitrate nitrogen have similar trends between korean Pine forest soils and secondary forest soils.2. The results of close-top tude incubations show: six forest types have similar trends ofnet ammonification rates, almost, in early or late June to July and April to September month, there are two higher net ammonification rates. Net ammonification rates appear negative in spring. The net nitrification of six forest types is lower in spring and autumn and higher in summer.The net nitrification rates and net ammonification rates of primeval korean pine forest do not overmatch other forest types. Except some particular sesason, their effect overmatch other forest types.3. The results of waterlogged incubation show: the net ammonification rates of Ai layer in six forest types have similar trends. Primeval korean pine forest and secondary forest in Liangshui emerge higher net ammonification rates.The habitat characteristics of ammoniacal nitrogen and nitrate nitrogen are different because of different forest type, different site and different season. The habitat characteristics variability is complex. We found that the levels of ammoniacal nitrogen and net ammonification rate are not too high, and net nitrification effect is not so foebleness as theory supposition on which is based. Probably the original hypothesis that korean pine forest soils were typically dominated by NH41" is not exit. We need to study further into the problem.Because different sites have different temperature, humidity and different jamming degree, season trends of ammoniacal nitrogen, nitrate nitrogen, net ammonification effect and net nitrification effect are different to the same type vegetation in different sites.In addition, the available nitrogen season trends are similar in either the growing season or the conditon of the close-top tude incubations and waterlogged incubation in different forest type (korean pine forest, secondary forest) of same site. The results show nitrogen nutrition habitats have no significant change in broad-leaved secondary forest soils and late successional stage korean pine forest soil or plantational korean pine forest of same site. Probably, degenerate succession stage forest types stand in unstable state.