Water use characteristics of bamboo (South China)
Zusammenfassung der Projektergebnisse
Bamboos are grasses (Poaceae) widespread in tropical and subtropical regions. We aimed at exploring water use patterns of four tropical bamboo species with sap flux measurement techniques and a deuterium tracing method. Our methods studies included a pot experiment with a comparison of thermal dissipation probes, the stem heat balance method and gravimetric readings using potted Bambusa vulgaris culms, an in situ calibration of thermal dissipation probes with the stem heat balance method for four bamboo species (B. vulgaris, Dendrocalamus asper, Gigantochloa atroviolacea and Gigantochloa apus), and deuterium tracing with simultaneous observation of young and old neighboring culms. In our field monitoring water use of the four bamboo species along with three tropical tree species (Gmelina arborea, Shorea leprosula and Hevea brasiliensis) was quantified along with controlling environmental factors, and the importance of the culm/stem water storage was assessed. In the pot experiment, it was confirmed that the stem heat balance method is well suited for bamboos but that thermal dissipation probes need to be calibrated. In situ, species-specific parameters for such calibration formulas were derived. The deuterium tracer method with classical assumptions yielded strong overestimates when compared with the other methods. Water transfer from the labelled culm to neighboring culms was indicated by increased deuterium concentrations in neighboring culms. After including this transfer in the calculation, the deuterium tracing method yielded more plausible results. The water transfer between culms itself is very interesting; it warrants further analyses and deuterium tracing may play an important role therein. During field monitoring we found that some bamboo species reached high maximum sap flux densities. Across bamboo species, maximal sap flux density increased with decreasing culm diameter. In the diurnal course, sap flux densities in bamboos peaked much earlier than radiation and vapor pressure deficit (VPD), and also much earlier than sap flux densities in trees. There was a pronounced hysteresis between sap flux density and VPD in bamboos, which was less pronounced in trees. Three of the four bamboo species showed reduced sap flux densities at high VPD values during the dry period, which was associated with a decrease in soil moisture content. Patterns of sap flow at different heights of the culm indicate water extraction from the culm water storage for transpiration in the morning and refilling of the storage in the afternoon. This is similar to other observations in trees but contrasts with the only other study addressing patterns in culm water storage use in a bamboo species. In relation to daily water use rates, the importance of the culm water storage was lower than expected and is at the lower end of values reported for trees and palms. However, per unit of sapwood volume it was much higher in the bamboos than in the studied trees. In the bamboos, we found an over-proportional increase in the contribution of the storage to water use with decreasing daily water use. Thus, it may help bamboos to maintain a somewhat elevated gas exchange even under conditions otherwise resulting in low transpiration. We conclude that water use patterns of bamboos differ from trees in some respect. Ongoing land use change with an increase of bamboo plantations would call for a better understanding of the water use characteristics of bamboos. In this project, possible approaches were tested and further developed, some insights were acquired and open questions were indicated.
Projektbezogene Publikationen (Auswahl)
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2016. Water use patterns of four tropical bamboo species assessed with sap flux measurements. Frontiers in Plant Science 6, 1202
Mei, T., Fang, D., Röll, A., Niu, F., Hendrayanto, and Hölscher, D.
