Water use strategies of different aged moso bamboo culms under summer drought

Abstract

Moso bamboo (Phyllostachys edulis (Carriere) J. Houzeau) is distributed widely over the subtropical regions of China, but it encounters a chronic summer reduced rainfall and elevated temperatures induced by subtropical high pressure. In some flash droughts characterized by rapid development speed and high intensity, the newly sprouted culms have much higher mortality than established culms, even though they have the advantage of resource integration. To determine the impact of flash drought on the water use of culms of different ages and the potential relation to differential mortality, we conducted a manipulated throughfall exclusion experiment in the field to simulate a summer flash drought. Under the manipulated summer drought, we found that newly sprouted culms still had higher sap flux densities than the established culms. However, their normalized daily water use had a similar positive response to meteorological factors (radiation and vapor pressure deficit) and soil moisture. Under the summer drought, the established culms significantly decreased water use and relied more on nighttime sap flow. In contrast, the continuously higher water use rates of the newly sprouted culms under drought stress may be attributed to the additional support from the rhizomes via physiological integration. The results indicated that the established and newly sprouted adopted drought-avoidance and drought-tolerance strategies, respectively. However, this drought-tolerance strategy might hurt the hydraulic system of the newly sprouted culms and even lead to hydraulic failure. Our findings provide some initial insight into the integrated responses of moso bamboo to summer drought. Further study on the network integration of bamboo culms will provide more insight into the natural response to drought and corresponding management.