Germination responses to temperature and soil moisture in three species of the subfamily Caragana and their implications toward restoration in Loess-gully Region, China

The leguminous Caragana species are important components of vegetation in the semi-arid Loess-gully region, China. These shrub species are important for maintaining the dynamics and function of the ecosystem in the region. They are potential plant resources for restoration of degraded ecosystems. The germination responses to temperatures in two indigenous and one exotic Caragana species were studied under controlled conditions in the laboratory. Treatments were nine temperature regimes (constant temperatures of 5, 10, 15, 20, 25, and 30°C and three alternating day/night temperature regimes of 10/5, 25/15, and 30/20°C). Germination response to temperature was different for the three species. For C. intermedia, the temperature range for germination was 5 to 30 °C and germination rate was quick. Percentage germination was low at all temperature regimes for C. licentiana. Germination was inhibited at 30°C for C. opulens and at 5°C for C. licentiana. The average incubation period needed for seeds to germinate was longer for C. licentiana than for the others. Alternating day/night temperature had no significant effect on germination in the three species. Hard-coat seeds existed at different percentages in this plant subfamily. Rate of hard-coat seeds was 5.14 percent for C. licentiana and 0.79 percent for C. intermedia, but C. opulens had no hard-coat seeds. Germination responses to temperature in the three species are related to their ecological distribution and habitat. The different germination patterns in the species imply different life cycles. The germination strategies for C. licentiana and C. opulens mean that these two endemic species include potential value as good candidates for restoration of degraded land in the semi-arid Loess-gully region, China.