Effects Of Nitrogen Deposition On Soil Nitrogen Fractions Of Several Forests Stands In Muchuan County

Forest ecosystem is of great significance to the biosphere, the increase of nitrogen deposition can destroy the structure and function of forest ecosystem, thus affecting the nitrogen cycle of the forest. The pollution problem caused by the atmospheric nitrogen deposition has caused attention from the people. The soil nitrogen both is closely related to the growth and development of the organism, and also plays a very important role in the relationship of nitrogen in-carbon-climate. At present, the research on soil nitrogen is relatively weak. This paper mainly studied on the influence of Nitrogen deposition with the soil N components of the four forest, with natural evergreen broad-leaved forest (abbreviation as:natural forest) and its artificial regeneration, Polishing, Metasequoia glyptostroboid.es, Fortunei Cryptomeria forestas the research object, which formed by artificial regeneration of natural evergreen broadleaved forest in Muchuan County,Leshan city, Southern Sichuan Province, China. Four levels of N treatment:control (CK,0 kg N·hm-2·a-1),low-N (LN,50 kg N·hm-2·a-1),medium-N (MN,100 kg N·hm-2·a-1), and high-N (HN,150 kg N·hm-2·a-1) were set in the present study. The main results are as follows. (1) After the simulated nitrogen deposition, the same level of N deposition in Natural forest, Polishing, Metasequoia glyptostroboid.es, Fortunei Cryptomeria, the different soil layer TN, NO3--N, NH4+-N, PON, AON, NFA, NHA all decreased with increasing soil depth, that is,0?10 cm> 10?20 cm> 20?30 cm> 30?40 cm. (2) N deposition increase the soil NO3--N and NH4+-N content of different layer of Natural forest, Polishing, Metasequoia glyptostroboides, Fortunei Cryptomeria, HN is the strongest promoting, Under the LN, MN, HN conduct, different forest N03--N additional ranges; Natural forest is 8.02?40.05%, Polishing is 7.70?41.55%, Metasequoia glyptostroboides is 7.24?41.94%, Fortunei Cryptomeria is 9.98?36.80%; The soil NH4+-N additional ranges:Natural forest is 16.54?54.69%, Polishing is 16.1050.33%, Metasequoia glyptostroboides is 15.67-55.76%, Fortunei Cryptomeria is 14.20?42.07%.The content of NO3--N, NH4+-N was higher with the increasing of deposit level, and N deposition influence the soil available nitrogen has accumulative effect, the longer the time, the gap between control sample available nitrogen content and CK sample will be more and more big. In summary, N deposition influence the availability of N, promoting the nitrogen availability, so promoting the grow of forest.(3) N deposition had no obvious effect on content of TN in the different layer of Natural forest, Polishing, Metasequoia glyptostroboides, Fortunei Cryptomeria.(4) N deposition had no obvious effect on the content of PON in the different layer of Natural forest, Polishing, Metasequoia glyptostroboides, Fortunei Cryptomeria, but in comparison with CK, under the 0?10 cm and 10?20 cm layer, N deposition had an increasing trend on the content of soil PON.(5) N deposition increase the soil AON content of different layer in Natural forest, Polishing, Fortunei Cryptomeria, but had no obvious effect on the soil AON content of Metasequoia glyptostroboides. In summary, LN conduct all had no obvious effect on the four forest, MN conduct all had obvious effect on the soil AON content of Natural forest, Polishing in all layer and 0?10 cm layer of Fortunei Cryptomeria, Metasequoia glyptostroboides; LN and HN conduct of Natural forest increased from 7.76% to 22.04%, MN conduct of Fortunei Cryptomeria and Polishing increased from 6.47% to 13.10%, 8.99% to 20.11%, HN conduct only had obvious effect on the soil AON content of Natural forest. With increasing soil depth, the smaller N deposition effect on the soil AON content.(6) N deposition has no obvious effect on the content of NFA and NHA in the different layer of Natural forest, Polishing, Fortunei Cryptomeria, Metasequoia glyptostroboides. But under the every layer, in comparison with CK, N deposition had an increasing trend on the content of soil NFA and NHA.(7) Because of the addition of N, had effect on different N components, the LN, MN, HN conduct of different forest, the soil TN show the Natural forest is biggest, Fortunei Cryptomeria is lowest; NO3--N, NH4+-N, PON, AON, NFA, NHA of soil all show Natural forest> Polishing> Metasequoia glyptostroboides> Fortunei Cryptomeria, it is explain that Natural forest after artificial regeneration, the content are all obvious decreased.