Effects of forest cover types and environmental factors on soil respiration dynamics in a coastal sand dune of subtropical China

Trees on sand dunes are more sensitive to environmental changes because sandy soils have extremely low water holding capacity and nutrient availability. We investigated the dynamics of soil respiration (R-s) for secondary natural Litsea forest and plantations of casuarina, pine, acacia and eucalyptus. Results show that significant diurnal variations of R-s occurred in autumn for the eucalyptus species and in summer for the pine species, with higher mean soil respiration at night. However, significant seasonal variations of R-s were found in all five forest stands. R-s changed exponentially with soil temperatures at the 10-cm depth; the models explain 43.3-77.0% of R-s variations. Positive relationships between seasonal R-s and soil moisture varied with stands. The correlations were significant only in the secondary forest, and the eucalyptus and pine plantations. The temperature sensitivity parameter (Q(10) value) of R-s ranged from 1.64 in casuarina plantation to 2.32 the in secondary forest; annual R-s was highest in the secondary forest and lowest in the pine plantation. The results indicate that soil temperatures and moisture are the primary environmental controls of soil respiration and mainly act through a direct influence on roots and microbial activity. Differences in root biomass, quality of litter, and soil properties (pH, total N, available P, and exchangeable Mg) were also significant factors.