Effects of soil fauna on leaf litter decomposition under different land uses in eastern coast of China

Soil fauna decompose litter, whereas land use changes may significantly alter the composition and structure of soil fauna assemblages. However, little is known of the effects of land-use on the contribution of soil fauna to litter decomposition. We studied the impacts of soil fauna on the decomposition of litter from poplar trees under three different land uses （i.e. poplar-crop integrated system, poplar plantation, and cropland）, from December 2013 to December 2014, in a coastal area of Northern Jiangsu Province. We collected litter samples in litterbags with three mesh sizes （5, 1 and 0. 01 mm, respectively） to quantify the contribution of various soil fauna to the decomposition of poplar leaf litter. Litter decomposition rates differed significantly by land use and were highest in the cropland, intermediate in the poplar-crop integrated system, and lowest in the poplar plantation. Soil fauna in the poplar-crop integrated system was characterized by the highest numbers of taxa and individuals, and highest Margalef＇s diversity, which suggested that agro-forestry ecosystems may support a greater quantity, distribution, and biodiversity of soil fauna than can single-species agriculture or plantation forestry. The individuals and groups of soil fauna in the macro-mesh litterbags were higher than in the meso-mesh litterbags underthe same land use types. The average contribution rate of meso- and micro-fauna to litter decomposition was 18.46%, which was higher than the contribution rate of macro-fauna （3.31%）. The percentage of remaining litter mass was inversely related to the density of the soil fauna （P 〈 0.05） in poplar plantations; however, was unrelated in the poplar-crop integrated system and cropland. This may have been the result of anthropogenic interference in poplar-crop integrated systems and croplands. Our study suggested that when land-use change alters vegetation types, it can affect species composition and the structure of soil fauna assemblages, which, in turn, affects litter decomposition.

Characteristics of carbon storage in Shanghai's urban forest

Urban forest has undergone rapid development in China over the last three decades because of the acceleration of urbanization.Urban forest thus plays an increasingly important role in carbon sequestration at a regional and national scale.As one of the most urbanized cities in China,Shanghai showed an increase of forest coverage from 3% in the 1990s to 13% in 2009.Based on CITY-green model and the second soil survey of Shanghai,the forest biomass carbon(FBC) was estimated to be 0.48 Tg in the urban area and,forest soil organic carbon(SOC)(0-100 cm soil depth) is 2.48 Tg in the urban and suburban areas,respectively.These values are relatively within the median and lower level compared with other Chinese megacities,with the FBC of 0.02 Tg in Harbin to 47.29 Tg in Chongqing and the forest SOC of 1.74 Tg in Nanjing to 418.67 Tg in Chongqing.For the different land-use types in Shanghai,the SOC density ranges from 13.8(tidal field) to 38.6 t ha-1(agricultural land).On average,the forest SOC density(31.5 t ha-1) in Shanghai is lower than that in agricultural lands(38.6 t ha-1) and higher than that in lawns(26.5 t ha-1) and gardens(21.3 t ha-1).In Shanghai,the SOC density in newly established urban parks is generally lower than that in older parks.In the northern and southeastern suburban areas(e.g.,Baoshan,Yangpu,and Nanhui districts),greenspace SOC density is higher than that in the central commercial areas(Hongkou,Putuo,Changning,and Zhabei districts) and in newly developed district(Pudong District).Uncertainties still exist in the estimation of urban forest carbon in Shanghai,as well as in other Chinese cities.Thus,future research directions are also discussed in this paper.