Carbon fluxes response of an artificial sand-binding vegetation system to rainfall variation during the growing season in the Tengger Desert

Abstract

Revegetation is considered as an effective approach for desertification control, and artificial sand-binding vegetation exerts a significant contributor to carbon cycling in arid and semiarid regions; however, this is largely determined by the rainfall regime. We measured carbon fluxes (the net ecosystem CO2 exchange (NEE), the gross ecosystem productivity (GEP) and the ecosystem respiration (Reco)) during the growing season of 2014–2016 using the eddy covariance technique and explored the effects of rainfall variables (amount, timing distribution and pulse size) and environmental factors on carbon fluxes at different time scales. The system had NEE values of −117.5 and −98.9 g C m−2 during the growing seasons of 2015 (dry year) and 2016 (wet year), respectively. When the rainfall amount did not differ significantly between spring and autumn, the cumulative GEP was greater in spring than in autumn, whereas the cumulative Reco and NEE showed the opposite pattern. Small (<5 mm) rain events failed to trigger obvious GEP and NEE pulses, whereas ≥ 5 mm or a series of small rain events led to high assimilation but with hysteresis. The magnitude of Reco increased as the rain pulses increased. The Random Forest (RF) algorithm revealed that soil water contents had a great impact on carbon fluxes at different integration periods. A correlation analysis showed that the soil water contents were positively correlated with GEP and Reco and negatively correlated with NEE over different time scales in most cases. These findings suggest that artificial vegetation not only improves habitat restoration but is a significant carbon sink during both dry and wet growing season, which is likely to supplement our knowledge gap to accurately evaluate the current carbon budget in dry land.