| Nitrogen is one of the important elements in forest ecosystem. Nitrogen is existed mainlyin the state of organic nitrogen in forest ecological system and more than90%of the nitrogenis present in the forest soil. The process that organic nitrogen transform to inorganic nitrogennot only determines the structure and function of the forest ecological system, but also affectsthe nitrogen maintaining and leaching of forest ecosystem. On limestone mountains of Jinansouthern, the soil layer is very thin, and the soil erosion is serious, which resulted the soil isdifficult to form and is easy to lose. Besides, the main vegetation is Platycladus orientalis (L.)Franco plantation with different restoration years on limestone mountains.This research was implemented in three Platycladus orientalis (L.) Franco plantations withdifferent succession phases on limestone mountains. Through the in situ incubation method,we studied the soil nitrogen mineralization ability change and its influencing factors of theartificial forest with different recovery years. In order to explore nitrogen mineralization ofthe Platycladus orientalis (L.) Franco plantation during dry season and wet season onlimestone mountains. We employed an intact soil core in situ incubation technique with PVCtubes, and studied the soil nitrogen mineralization under Platycladus orientalis (L.) Francoplantation for different restoration years (5years,10years,25years) from1November2011to1February2012and31May2012to27August. The results demonstrated that in dryseason, NO3--N content were increased first. Then it decreased and increased in the researchedmonths. However, the NH4+-N content had no obvious regularity. The net nitrogennitrification rates and mineralization rates reached maximum in November and they were0.07±0.04,0.11±0.01,0.15±0.02mg/(kg·d) and0.15±0.04,0.29±0.02,0.33±0.03mg/(kg·d)in three restored forest soil respectively. The soil net nitrogen mineralization rate showedquadratic function relation with soil moisture as well as significantly negative correlation withthe soil pH value (r=-0.452, P=0.018). The net nitrogen mineralization reduced with theincreasing soil moisture. Besides, the soil net nitrogen mineralization rate has positivelycorrelated with the soil organic carbon content, microbial biomass carbon content and C/N ratio, but the correlations were not significant (r=0.076, p=0.707; r=0.374, p=0.055; r=0.337, p=0.086). There was strong nitrogen transform in the soil of Platycladus orientalis(L.) Franco plantation during dry season. The changes of soil condition resulted fromtemperature have significant effects on the soil nitrogen mineralization. In wet season,NO3--N content and NH4+-N content have similar change rule, with little difference. The netnitrogen nitrification rates and mineralization rates reached maximum in June and they were0.351±0.051,0.382±0.028,0.587±0.095mg· kg-1·d-1and0.358±0.060,0.476±0.027,0.613±0.109mg·kg-1·d-1in three restored forest soil respectively. Besides, in wet season anddry season, the typical soil physical and chemical characteristics had certain correlations withsoil nitrogen mineralization ability, and the relations were different in different habitats. Thesoil humidity and net nitrogen mineralization rate also showed a quadratic function relation (r=0.891, p=0.011), however, the soil pH value almost had no influence on the soil netnitrogen mineralization rates, the soil net nitrogen mineralization rate was negativelycorrelated with C/N ratio and soil organic carbon content (r=-0.176, p=0.651; r=-0.326, p=0.392). This indicated that the special habitat of limestone mountain decided the differenceof the soil net nitrogen mineralization rates between the dry season and wet season.Through the study of the soil nitrogen mineralization ability change and its influencingfactors of the artificial forest with different recovery years on limestone mountains. The aimwas to explore soil nitrogen contents changes during the process of vegetation restorationsuccession in limestone mountains, and studied the influences of soil typical characteristicfactors on the soil net nitrogen mineralization rates. Thus which would provide basic data forthe vegetation restoration and nitrogen management of limestone mountains. |
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