Concentrations and seasonal dynamics of dissolved organic carbon in forest floors of two plantations （Castanopsis kawakamii and Cunninghamia lanceolata） in subtropical China

The concentrations and seasonal dynamics of DOC in forest floors of monoculture plantations of Castanopsis kawakamii and Chinese fir （Cunninghamia lanceolata） were assessed in Sanming, Fujian, China （26°11′30″N, 117°26′00″E）. Forest floor samples were taken in January, April, July and October in 2002 and divided into undecomposed material （horizon Oi）, partially decomposed organic material （horizon Oe）, and fully decomposed organic material （horizon Oa）. Upon collection. DOC concentrations of samples were analyzed by a High Temperature TOC. The results showed that the annual average DOC concentration of Chinese fir （1341.7 mg·kg^-1） in the forest floor was higher than that of Castanopsis kawakamii （ 1178.9 mg·kg^-1）. Difference in DOC concentrations was observed among three horizons of the forest floor. DOC concentration of forest floor in the two forests was the highest in horizon Oe. Seasonal trends of DOC concentrations in different horizons of forest floors were similar and the maximal value occurred in autumn （or winter）. The concentration and temporal change of DOC in studied forests were probably related to the variation in moisture, temperature, biological activity and quantity of organic matter in the forest floor.

Carbon Return and Dynamics of Litterfall in Natural Forest and Monoculture Plantation of Castanopsis kawakamii in Subtropical China

The amount of carbon returned through litterfall and its seasonal pattern were studied in a natural forest of Castanopsis kawakamii (NF) and adjacent monoculture plantations of C. kawakamii (CK) and Chinese fir (Cunninghamia lanceolata) (CF) in Sanming, Fujian Province, China. Mean annual carbon return through total litterfall over 3 years (from 1999 to 2001) was 5.097 t穐m2 in the NF, 4.337 t穐m2 in the CK and 2.502 t穐m2 in the CF respectively. Of the total carbon return in the three forests, leaf contribution accounted for 58.96%, 68.53% and 56.12% and twig 24.41%, 22.34% and 26.18%, respectively. The seasonal patterns of carbon return from total litterfall and leaf-litter were quite similar among the three forests. A peak of carbon input from litterfall in the NF and the CK occurred in spring except for the highest annual C return through branch litter of the NF in summer, while the CF showed the maximum C return in summer. The results of this study demonstrate that the natural forest has a greater C return through litterfall than monoculture plantations, which is beneficial to the increase of soil organic matter storage and the maintenance of soil fertility.

Forest gaps regulate seed germination rate and radicle growth of an endangered plant species in a subtropical natural forest

The survival rate of Castanopsis kawakamii from seed to seedling is relatively low,leading to difficulties in the regeneration of its natural forests.Forest gaps play a vital role in plant regeneration and biodiversity maintenance in forest ecosystems.Unfortunately,our understanding of the effects of gap size and within-gap position on the seed germination and radicle growth of C.kawakamii is still limited.In particular,our knowledge on the relationship between gap size and environmental factors and their influence on seed germination and radicle growth is incomplete.In the present study,we studied the influences of forest gaps and within-gap position on seed regeneration on the germination and radicle growth of an endangered species C.kawakamii in a subtropical natural forest in China.We selected three large gaps(LG,gap size above 200 m^(2)),three medium gaps(MG,gap size 50-100 m^(2)),three small gaps(SG,gap size 30-50 m^(2)),and non-gap(NG),and planted the seeds of C.kawakamii in five positions within each gap.The results showed that(1)the influence of forest gaps on seed germination rate was,from highest to lowest,medium gaps(51%),non-gap(47%),small gaps(40%)and large gaps(17%),and the seed germination rate was the highest in all positions in medium gaps,with the exception of the east position.(2)Radicle length in forest gaps was,from highest to lowest,medium gaps,small gaps,large gaps and non-gap,and it was the highest in the east,south,west and north positions of medium gaps.(3)Canopy openness(gap size)and air temperature were the main factors influencing seed germination and radicle growth of C.kawakamii.We concluded that medium-sized gaps were the most suitable for seed germination and radicle growth of C.kawakamii,and they promote the regeneration of this endangered species in the investigated natural forest.