Marshall John D, Ehleringer James R
Department of Biology, University of Utah, 84112, Salt Lake City, UT, USA.
Oecologia. 1990 Sep;84(2):244-248. doi: 10.1007/BF00318279.
Carbon isotope ratios, photosynthesis, and transpiration were measured on a xylem-tapping mistletoe (Phoradendron juniperinum) and its host (Juniperus osteosperma) in southern Utah, USA. For host tissues, the carbon isotope ratios agreed with theoretical values predicted from gas exchange observations. However, for mistletoe tissues, carbon isotope ratios deviated significantly from values predicted by gas exchange observations. This apparent discrepancy in mistletoe carbon isotope ratios can be resolved if one assumes that organic carbon dissolved in host xylem water was assimilated by the parasite. The mistletoes' high transpiration rates and low photosynthetic rates contributed to their heavy dependence on host xylem carbon. Two lines of evidence suggest that 62±2% of the carbon in the Utah mistletoe is derivated from the host and not from mistletoe autotrophic activities. Whereas xylem-tapping mistletoes have previously been characterized as wholly autotrophic parasites, we suggest that they may instead derive significant amounts of carbon from their hosts.
在美国犹他州南部，对一种吸汁槲寄生（杜松槲寄生）及其寄主（刺柏）的碳同位素比率、光合作用和蒸腾作用进行了测量。对于寄主组织，碳同位素比率与根据气体交换观测预测的理论值相符。然而，对于槲寄生组织，碳同位素比率与气体交换观测预测的值有显著偏差。如果假设溶解在寄主木质部水中的有机碳被寄生植物同化，那么槲寄生碳同位素比率中的这种明显差异就可以得到解释。槲寄生的高蒸腾速率和低光合速率导致它们严重依赖寄主木质部碳。有两条证据表明，犹他州槲寄生中62±2%的碳来自寄主，而非来自槲寄生的自养活动。虽然吸汁槲寄生以前被描述为完全自养的寄生植物，但我们认为它们可能反而从寄主那里获取大量碳。
