Effect of simulated precipitation on the ecosystem carbon exchange in a desert steppe

Changes in global precipitation patterns are bound to affect the functions of terrestrial ecosystems. The carbon sink function of grasslands is very sensitive to changes in the soil water content. To study the effects of precipitation on ecosystem carbon exchange in a desert steppe ecosystem, four different precipitation gradients were set up in a desert grassland using a random group design (50% reduced precipitation, natural precipitation, and 50% and 100% increased precipitation), and each precipitation gradient had three replicates. The net ecosystem carbon exchange (NEE), ecosystem respiration (ER), and gross ecosystem productivity (GEP), were measured during the growing season of 2017 using the portable optical LI-6400 and the static chamber method. The results showed that: 1) Soil moisture content and above-ground biomass significantly increased, and soil temperature significantly decreased, in treatments with increasing water availability (P < 0.05). 2) Under 50% water reduction, NEE was the carbon source; whereas under natural precipitation, and 50% and 100% increased precipitation, NEE was a carbon sink (P < 0.05). Furthermore, with an increase in precipitation, ER and GEP increased significantly (P < 0.05). The determination coefficient of GEP and soil water content was greater than that of ER and soil water content. 3) The correlation coefficient between NEE and soil temperature was the largest, so was the correlation coefficient between ER, GEP, and above-ground biomass. The results indicate that water can promote ecosystem carbon exchange in a desert steppe by increasing the above-ground biomass and reducing the soil temperature.