I affirmed that the dead batteries in last field trip resulted from a wrong way of charging. This time, I was quite sure that the batteries were fully charged.

Antonio, Guang, John and I went to the field at 8:00 am on September, 14, 2016. Guang helped me to measure photosynthesis and stomatal conductance. We measured two variables on the same branch which we selected on August, 26. We succeed in establishing two light responsive curves by using auto-measuring program setting light intensity at 2000, 1500, 1000, 500, 250, 126, 60, 30, 15, 1 umol/m2s. Photosynthesis rate responded to light intensity gradient very well, but stomatal conductance showed less responsive. When I took data from last field trip together, the patterns were divergent. The stomatal conductance on August, 26 was not stable, which may due to the power failure of the system.

   

           Fig. 1 Light-responsive curves of photosynthesis rate

        

        Fig. 2 Light-responsive curves of stomatal conductance

We also measured photosynthesis rate under different temperatures in considering that temperature played an important role in regulating sap flow rate. But when we made the second temperature responsive curve, the batteries ran out. Actually, the temperature responsive curves didn’t seem good, because LICOR 6400 XT can not really control block temperature to higher or lower 3℃ than the ambient temperature.

          

       Fig. 3 Temperature response curves of photosynthesis rate

        

         Fig. 4 Temperature response curves of stomatal conductance

Photosynthesis rate and stomatal conductance varied at morning and afternoon, even under similar temperature and light intensity, with those in the morning were systematically higher than those in the afternoon.

After batteries ran out, we disassembled the machine, and then I downloaded data from datalogger.

Antonio and John helped me measure the tree height and DBH in all three blocks. However, I thought that it was not necessary to measure tree height in each month, because we used a four-meter ruler which was quite heavy and inconvenient to carry through forests. The most important reason was that this simple but crude measurement gave too many errors, as a majority of trees were around four meter, and did not have a significant increase in height in each month. I compared the tree height of previous month, and found that some heights in one or two month later were even lower than their previous values. I would discussed with Adam and Antonio about it.

Then, with the help of Antonio, I reconnected the wires of soil moisture sensors and put them in junction boxes. Some soil moisture sensors in T2 did not work well, which may be due to bad contact with soil, so we watered it and waited for the signals. Fortunately, the sensors started to report reasonable values. Antonio was genius!!!

We had achieved our goals today! 🙂