ABSTRACT
The significance of interplant transfers of carbon and nutrients have been explored in the review articles of Amaranthus and Perry (1994), Read (1998), and Rayner (1998). Amaranthus and Perry (1989) showed that when Douglas fir was planted into partially cleared sites (containing remnant ectomycorrhizal plant hosts) the survival of the planted trees was around 90%. Where trees were planted into totally cleared areas (no remnant ectomycorrhizal plant hosts) plated tree survival after 2 years was only 50%. They attributed the reduction in survival to the lack of a viable, communal ectomycorrhizal network into which the new trees could connect. They suggested that this network provided greater stability of the system, allowing carbon and nutrient exchange to take place among connected plants, and especially allowing new recruits to be able to access a larger pool of nutrients and carbon than they would be able to on their own. This synergistic activity among surviving mature plants and recruits into the ecosystem would
allow both greater ecosystem stability and greater continuity of the species composition of the ecosystem following disturbance. It has only been recently, however, that the direct net transfer of carbon or nutrients has actually been demonstrated in the field rather than in laboratory or greenhouse conditions. To that end, Simard et al. (1997a,b,c) were able to show transfer of carbon from paper birch (Betula papyrifera) to Douglas fir (Pseudotsuga menziesii) in both partial and deep shade (Fig. 3.30). They showed that the amount of carbon transferred
between plants could form a significant proportion of the carbon contained in the shoots (13% for P. menziesii and 45% for B. papyrifera), which they suggest could considerably supplement photosythetically derived carbon in the plant. Indeed, Wu et al. (2002) have shown that some 24% of 14C label occurring in the underground parts of pine seedlings was allocated to the extraradical hyphal component of their ectomycorrhizal association. Also, the trenching experiments of Simard et al. (1997a) show the importance of maintaining an intact community of mycorrhizae in the forest for seedling trees to connect to. In their trenched plots, Douglas fir seedlings planted into a birch-dominated community had approximately half the diversity of mycorrhizal fungi associated with their roots than counterparts planted into untrenched plots in the same forest. The increased mycorrhizal diversity in untrenched plots significantly increased the photosynthetic capacity of the Douglas fir seedlings compared to that of seedlings in trenched plots, although no significant increase in biomass was evident.
