Lehrstuhl für Pflanzenökologie der Universität, Universitätsstrasse 30, D-8580, Bayreuth, Germany.
Planta. 1984 Sep;162(3):268-75. doi: 10.1007/BF00397449.
Xylem-tapping mistletoes are known to have normally a higher rate of transpiration and lower water-use efficiency than their hosts. The relationships between water relations, nutrients and growth were investigated for Phoradendron juniperinum growing on Juniperus osteosperma (a non-nitrogen-fixing tree) and for Phoradendron californicum growing on Acacia greggii (a nitrogen-fixing tree). Xylem sap nitrogen contents were approximately 3.5 times higher in the nitrogen-fixing host than in the non-nitrogen-fixing host. The results of the present study show that mistletoe growth rates were sevenfold greater on a nitrogen-fixing host. At the same time, however, the differences in water-use efficiency between mistletoes and their hosts, which were observed on the non-nitrogen-fixing host did not exist when mistletoes were grown on hosts with higher nitrogen contents in their xylem sap. Growth rates and the accumulation of N, P, K, and Ca as well as values for carbon-isotope ratios of mistletoe tissues support the hypothesis that the higher transpiration rates of mistletoes represent a nitrogen-gathering mechanism.
木质部泌蜜型槲寄生的蒸腾速率通常高于其宿主，水分利用效率较低。本研究调查了生长在 Juniperus osteosperma（一种非固氮树）上的 Phoradendron juniperinum 和生长在 Acacia greggii（一种固氮树）上的 Phoradendron californicum 的水分关系、养分和生长之间的关系。固氮宿主的木质部汁液氮含量约是非固氮宿主的 3.5 倍。本研究的结果表明，槲寄生在固氮宿主上的生长速度是在非固氮宿主上的 7 倍。然而，当槲寄生生长在木质部汁液中氮含量较高的宿主上时，在非固氮宿主上观察到的槲寄生与其宿主之间水分利用效率的差异并不存在。槲寄生的生长速率以及 N、P、K 和 Ca 的积累以及碳同位素比值的值支持这样一种假设，即槲寄生较高的蒸腾速率代表一种氮收集机制。
