Invasive species are modifying invaded ecosystems, changing their species composition, diversity and stability, and affecting overall ecosystem functioning. A recent survey in Israel found that multiple planted populations of mesquite (P. juliflora) became invasive and currently invade 690 km2 of the Dead Sea area, Negev desert, Jordan Valley and the Arava Valley. In the Jordan, the extent of area invaded by Prosopis is ~3 times the area in Israel ( >1800 km2), with numerous populations of P. juliflora invading the region around the Dead Sea, mainly in humid habitats with continuous water flow (e.g. river banks and irrigated land). Despite increasing presence and high risk of further spreading, the impact of mesquite encroachment on ecosystem N and C cycles in invaded areas of Israel and Jordan are currently unknown. We studied an established Prosopis population in the Khatsason stream mouth on the western coast of the Dead Sea. We have compared soil emissions of nitrous and nitric oxides (N2O and NO) and carbon dioxide (CO2) during a rewetting event from soil under the canopy of P. juliflora with those from soil under the canopy of the native Red Thorn acacia (Vachellia gerrardii) and to the bare soils far from trees.
Results/Conclusions
We have found that overall dynamics of soil trace gases emissions during the rewetting were same under canopies of both, invasive and native species. Each trace gas, however, had different post-rewetting emission pattern, CO2 emission reached maximum immediately after the rewetting (~15 min), soil N2O flux peaked ~1 hour after and soil NO emissions increased during the measurement period of ~ 5 hours without sign of decrease. The magnitudes of emissions, however, were strikingly different under canopies of the two species. After the rewetting, soils under native V. gerrardii emitted ~25 times more N2O (peak of ~ 90 µg N m-2 min-1) and ~4 times more NO and CO2 (peaks of ~6 µg N m-2 min-1 and 20 × 103 µg C m-2 min-1, respectively). Our results pointing on a potentially slowing-down of the N and C cycles under the canopy of the invasive mesquite. This is surprising because mesquite invading an ecosystem dominated by similar, at list morphologically, N-fixing acacia. Biogeochemical drivers of the observed post-rewetting emissions, however, requiring further research.
