Effect Of Rainfall On Transpiration Of Artemisia Ordosica And Salix Psammophila In The Mu Us Desert

Water is the most limitation for plant growth in arid and semi-arid areas (drylands). Plant physiological responses to water availability depend largely on the intensity and frequency of rain events which is the mainly input source of water for drylands. Plant transpiration is the most portion of evapotranspiration, therefore, knowledge on the responses of xerophytic plants to rain events is important for predicting the response of drylands ecosystem on climate change. Studies focused on plant transpiration in drylands were mostly concentrated in the dynamics of sap flow of plants at different time scales so far. How plants transpiration response to rainfall in different time scales is unclear, the response of different plant functional types to rainfall and plant water-use strategies would vary widely within a given area. Artemisia ordosica and Salix psammophila are excellent plants for fixing sand in the Mu Us Desert. Sap flow of Artemisia ordosica and Salix psammophila, biotic factors and environmental variables were continuously measured during the growing seasons in 2014 and 2015. Aim to study the effect of rainfall events and its seasonal distribution on transpiration of Artemisia ordosica and Salix psammophila.(1) Sap flow of Artemisia ordosica and Salix psammophila respond differently to seasonal distribution of rainfall. The sap flow of Artemisia ordosica was more affected by summer drought in 2015 than the spring drought in 2014. But both the periods of drought in 2014 and 2015 decreased the sap flow of Salix psammophila. Sufficient rainfall after summer drought in 2015 most likely delay the phonological stages of Artemisia ordosica and Salix psammophila which made sap flow keep at a high level and a sensitive state to changes in solar radiation in the post growing season.(2) Sap flow of Artemisia ordosica and Salix psammophila decreased on rainy days, sap flow was significantly positive related to solar radiation and decoupled with precipitation and rainfall duration. After the rainfall event, both the sap flow of Artemisia ordosica and Salix psammophila and its sensitivity to solar radiation increased. The sap flow of Artemisia ordosica and Salix psammophila, was significantly increased by rainfall pulses greater than 20 mm, while was unaffected by small rainfall events (0-5 mm). Variation of sap flow increment rate after rainfall event was primarily impacted by the amount of rainfall and evapotranspiration. The response of sap flow of Salix psammophila to rainfall events was affected by antecedent condition in soil moisture. When antecedent soil moisture was lower, the increase in sap flow by rainfall was greater. The rainfall-induced increase in sap flow of Artemisia ordosica was affected by the phenological period, the response of sap flow to rain event was greater during the beginning of the growing season (May and June) than other periods.(3) The total transpiration for Artemisia ordosica from May to September in 2014 and 2015 were 13.32 mm and 15.70 mm, respectively, at the canopy scale. And those for Salix psammophila were 46.85 mm and 40.92 mm. Precipitation distributed evenly in 2014, transpiration at the canopy scale for Artemisia ordosica and Salix psammophila was affected by meteorological factors and soil water content. While little rainfall dropped within summertime in 2015, transpiration at the canopy scale for Artemisia ordosica and Salix psammophila was more affected by soil water content. During the dry period, Salix psammophila could reduce transpiration through falling leaves.We studied how the seasonal distribution of rainfall and single rainfall events affect the transpiration characteristics of Artemisia ordosica and Salix psammophila. Results indicate that Artemisia ordosica and Salix psammophila responded consistently to single rainfall events, and differently to seasonal distribution of rainfall. The results may provide a scientific support for management and revegetation of ecosystem in the Mu Us Desert in northern China.