Examining biomass allocation in tree seedlings along a tropical elevational gradient in the Andes

Background/Question/Methods

As climate change intensifies, understanding the effects of temperature, and other climatic variables on plant biomass allocation is extremely important as these changes will influence rates of carbon sequestration, and storage. Changes in biomass allocation can affect individual plant fitness as well as rates and patterns of ecosystem carbon cycling. In tropical forests, which play a major role in the global carbon cycle and hence in regulating climate change, several studies have examined the influence of climate on aboveground, but virtually nothing is known about the allocation to belowground compartments. In general, net primary productivity, and aboveground standing biomass decreases with elevation/temperature in tropical montane forests.  It is often assumed that the same holds true for belowground allocation but this assumption remains largely untested.

To investigate how belowground carbon allocation differs between species and in response to climate, we looked at how the root to shoot ratio in seedlings of three pairs of congeners (Clusia spp., Weinmannia spp., and Symplocos spp.) varies in relation to climate along an elevational gradient in the Southeastern slopes of the Peruvian Andes.  Specifically, we harvested 340 seedlings from a 700m elevational range (2700-3400 m.a.s.l.) and measured the dry biomass in different tissues.  For each seedling we also collected environmental data on elevation, topography, and light exposure.

Results/Conclusions

We found no differences in the mean root to shoot ratios across species or genera. The root:shoot did not change significantly with elevation. Within species, variation in root:shoot was high at any given elevation suggesting that other environmental variables may be more important than temperature in driving patterns of biomass allocation. Intra-specific variation was lowest around 3000 m.a.s.l., corresponding to the cloud immersion zone of this montane forest which is consistent with results of studies examining patterns of productivity along this same elevational gradient. This may suggest that cloud immersion is acting as a strong environmental filter.  The finding of this study will help to improve our predictions of how carbon sequestration in tropical montane forests will be influenced by future climate change.