A combined rain shelter and free-air CO2 enrichment system to study climate change impacts on plants in the field

1. There is a clear need for field experiments to estimate the effects of global climate change like decreasing precipitation and rising atmospheric CO2 concentration. Adequate methods for controlled manipulations of these environmental parameters under field conditions are scarce, particularly in regard to multi-factor experiments. Here, we describe a new flexible rain shelter system, which can be assembled manually and easily be combined with further experimental treatments in field studies. 2. Frames of tents with a ground area of 12 m x 20 m were assembled on a field site after the sowing of the maize and sorghum crop and after the equipment for free-air CO2 enrichment has been set up. The tents were equipped with transparent tarpaulins, which were installed on the frames only in cases of high amounts of precipitations forecast. In autumn, the entire experimental equipment was removed from the field site. 3. The rain shelter tents were operated in the growing seasons 2008 and 2010 for 9 and 20 days with 54 mmand 176 mmof precipitation excluded, respectively. In the months with rain shelters in operation, pronounced reductions in precipitation were achieved 2008: 39 5%, 2010: 58 6%). The tent frames did not affect temperature or CO2 concentration, but slightly decreased incident photosynthetic active radiation PAR) by 6 6%. In times with tarpaulins installed, PAR decreased by 24 1%. Comparing times without and with tarpaulins installed, the fraction of time in which 1-min mean CO2 concentration was within similar to 20% limits of the setpoint was decreased from 99 7% to 97 8% in 2008 and from 99 0% to 96 7% in 2010, respectively. 4. The rain shelter tents provide a suitable and versatile tool for excluding precipitation from larger areas in the field without relevant disturbances to the soil and aerial environment except a slight decrease in incident radiation, which can be accounted for i. e. in the evaluation of plant growth data. Furthermore, they can be easily combined with further experimental treatments like free- air CO2 enrichment.