Yu Zhanyuan

Soil Inorganic Nitrogen and Microbial Biomass Carbon and Nitrogen Under Pine Plantations in Zhanggutai Sandy Soil

The dynamics of soil inorganic nitrogen (NH4+-N and NO3--N) and microbial biomass carbon (C-mic) and nitrogen (N-mic) under 30-year-old fenced Pinus sylvestris L. var. mongolica, Litvin (SF), unfenced P. sylvestris L. var. mongolica Litvin (SUF), and unfenced Pinus densiflora Siebold et Zucc. (DUF) plantations in the Zhanggutai sandy soil of China were studied during Apr. to Oct. 2004 by the in situ closed-top core incubation method. All mentioned C and N indices in each stand type fluctuated over time. The ranges of inorganic N, C-mic, and N-mic contents in the three stand types were 0.7-2.6, 40.0-128.9, and 5.4-15.2 mu g g(-1), respectively. The average contents of soil NH4+-N and C-mic under the three 30-year-old pine plantations were not different. However, soil NO3--N and total inorganic N contents decreased in the order of SUF >= SF >= DUF, the N-mic content was in the order of SF = SUF > DUF, and the C-mic:N-mic ratio was3 in the order of SUF = DUF > SF. Seasonal variations were observed in soil inorganic N, microbial biomass, and plant growth. These seasonal variations had certain correlations with microbe and plant N use in the soil, and their competition for NH4+-N was mostly regulated by soil N availability. The influence of tree species on inorganic N and N-mic were mainly because of differences in litter quality. Lack of grazing decreased the C-mic:N-mic ratio owing to decreased carbon output and increased the ability of soil to supply N. The soil N supply under the P. sylvestris var. mongolica plantation was lower than under the P. densiflora plantation.

Soil animals and nitrogen mineralization under sand-fixation plantations in Zhanggutai region, China

The effects of soil animals on soil nitrogen (N) mineralization and its availability were studied by investigating soil animal groups and their amounts of macro-faunas sorted by hand, and middle and microfaunas distinguished with Tullgren and Baermann methods under three Pinus sylvestris var. mongolica Litv. plantations in Zhanggutai sandy land, China. In addition, soil N mineralization rate was also measured with PVC closed-top tube in situ incubation method. The soil animals collected during growing season belonged to 13 orders, 5 groups, 4 phyla, whose average density was 86 249.17 individuals·m−2. There were significant differences in soil animal species, densities, diversities and evenness among three plantations. Permanent grazing resulted in decrease of soil animal species and diversity. The average ammonification, nitrification and mineralization rates were 0.48 g·m−2·a−1, 3.68 g·m−2·a−1 and 4.16 g·m−2·a−1, respectively. The ammonification rate in near-mature forest was higher than that in middle-age forests, while the order of nitrification and net mineralization rates was: middle-age forest without grazing < middle-age forest with grazing < near-mature forest with grazing (P<0.05). Soil N mineralization rate increased with soil animal amounts, but no significant relationship with diversity. The contribution of soil animals to N mineralization was different for different ecosystems due to influences of complex factors including grazing, soil characteristics, the quality and amount of litter on N mineralization.

Effects of adding water on seasonal variation of soil nitrogen availability under sandy grasslands in semi-arid region

Water is usally thought of a limiting factor for the restoration of semi-arid ecosystem. In the growing season of 2006, a study was conducted to determine the effects of modeling precipitation on seasonal patterns in concentrations of soil-available nitrogen and to describe the seasonal patterns in soil nitrogen availability and seasonal variation in the rates of net nitrogen mineralization of topsoil at Daqinggou ecological station in Keerqin sand lands, Inner Mongolia Autonomous Region, China. Manipulation of water (80 mm) was designed to be added to experiment plots of sandy grasslands in dry season. Water addition (W) treatment and control (CK) treatment were separately taken in six replications and randomly assigned in 12 plots (4 m×4 m for each) with 2-m buffers betweens. Results showed that the content of soil inorganic nitrogen and net nitrogen mineralization rate were not affected by adding water in sandy grassland of Keerqin sand lands. Net nitrogen mineralization rates ranged from 0.5 μg·μg−1·month−1 to 4 μg−1g−1·month−1. The highest values of soil inorganic nitrogen and net nitrogen mineralization occurred on October 15 in control plots. The seasonal changes of soil inorganic nitrogen contents exhibited “V” shape pattern that was related to seasonal patterns of soil ammonium-N (ascending trend) and nitrate-N transformation (descending trend).

Understory Flora and Community Physiognomy of Planted Forests in the Degraded Purple Soil Ecosystem, South China

The flora and community physiognomy of degraded plantation ecosystems on purple soil were investigated in Ninghua County of Fujian Province, China to understand the relationship between plant diversity and ecosystem processe. Four different restoration communities (labeled as ecological restoration treatment I, II, III and IV) were selected by space-time replacement method according to the erosion intensity in degraded purple soil ecosystem. The results showed that there were totally 86 plant species belonging to 78 genera and 43 families in the degraded purple soil ecosystem. Of the 15 types of distribution area in spermatophyte genus, 12 types were found in the purple soil ecosystem. Along restoration gradient from low to high, plant growth type and life form spectra became abundant more and more, and the spermatophyte genera for each distribution area type and genera numbers for different foliage characters increased as well. It is concluded that the plant flora and physiognomy in ecological restoration process become more complex and diverse, indicating that the forest ecosystem on purple soil tends to be more stable.