Liu Shizhong

Seasonal dynamics of soil CO2 effluxes with responses to environmental factors in lower subtropical forests of China

Seasonal metrics and environmental responses to forestry soil surface CO2 emission effluxes among three types of lower subtropical forests were consistently monitored over two years with static chamber-gas chromatograph techniques among three types of lower subtropical forests. Results showed that annual CO2 effluxes (S+L) reached 3942.20, 3422.36 and 2163.02 CO2 g·m−2·a−1, respectively in the monsoon evergreen broadleaf forest, mixed broadleaf-coniferous forest and coniferous forest. All the three types of forests revealed the same characteristics of seasonal changes with the CO2 effluxes peaking throughout June to August. During this peaking period, the effluxes were 35.9%, 38.1% and 40.2% of the total annual effluxes, respectively. The CO2 emission process responding to the environmental factors displayed significantly different patterns in forestry soils of the three types of forests. The coniferous forest (CF) was more sensitive to temperature than the other two types. The Q10 values were higher, along with greater seasonal variations of the CO2 efflux, indicating that the structurally unique forestry ecosystem has disadvantage against interferences. All the three types of forestry CO2 effluxes showed significant correlation with the soil temperature (Ts), soil water content (Ms) and air pressure (Pa). However, stepwise regression analysis indicated no significant correlation between air pressure and the soil CO2 efflux. With an empirical model to measure soil temperature and water content in 5 cm beneath the soil surface, the CO2 effluxes accounting for 75.7%, 77.8% and 86.5% of the efflux variability respectively in soils of BF, MF and PF were calculated. This model can be better used to evaluate the CO2 emission of soils under water stress and arid or semi-arid conditions.

Evidences and implications of vegetation damage from ceramic industrial emission on a rural site in the Pearl River Delta of China

Community structure characteristics and vegetation damage degree were investigated and analyzed in a forest around village, which had been long term exposed to ambient atmospheric pollution stress, to study the influence of airborne pollutant emissions from the concentrated ceramic industries on vegetation. Field survey was carried out in a semi-natural secondary forest on hilly land, Nanhai District of Guangdong Province, for the tree layer in ten quadrates with the total area of 10×(10 m×10 m), and for shrub and herb layers in eight subquadrates with the total area of 4×(5 m×5 m). Results showed that exotic Eucalyptus exserta and Eucalyptus urophylla were dominated over the community, followed by native tree species, Schefflera octophylla and Bambusa gibba, with the importance value (Iv) of 26.75, 17.08, 16.27 and 11.50, respectively. Among all tree species, Eucalyptus exserta and Pinus massoniana were most severely damaged with nearly 100% damaged rate. Bambusa gibba and Dalbergia balansae were injured with damaged rate of 85.1%–68.3%, however, Eucalyptus urophylla, Celtis sinensis, Helicia cochinchinensis, Cinnamomum burmanni and Vitex negundo revealed moderate injuries (45%–57.5%). Most of other indigenous species including Schefflera octophylla, Viburnum odoratissimum, Desmos chinensis, etc. showed less injured symptoms under the pollution stress. Compared with species in tree layer, damages of undergrowths were largely less. These results suggested that attention and concern should be paid on those introduced Eucalyptus species which had ever been widely used for forest restoration in degraded hilly lands of south China since 1970–1980s, due to their fast growing aspect. The results also demonstrated the potentials and perspectives by developing native species as target plants for restoration of degraded area at similar polluted location, which may provide scientific base for scientists to study and understand the functional aspects of native species and process-based interactions with pollution stress.