Variation in plant belowground resource allocation across heterogeneous landscapes: implications for post-fire resprouting

Premise: Resource availability affects biomass allocation in ways that could influence plant responses to disturbance such as fire. This is important because fire also varies across landscapes in ways that are correlated to resource availability. We hypothesized that plants growing in landscape microsites with a shortage of nutrients and water allocate more biomass and resources to belowground structures (and thus promote traits that enhance post-fire resprouting ability) than plants in more mesic sites. Methods: We selected sites in three contrasting topographies (3 gullies, 3 midslopes, and 3 ridges) that supported different vegetation types and fire regimes, in Jalisco, Mexico. At each site, we measured soil nutrient and water content and light availability. Then we sampled biomass and root starch allocation in three post-fire resprouting shrubs that grow across a wide range of microenvironmental conditions. Results: The ridges showed the highest values of solar radiation and the lowest of soil N and water content. Overall, we found a significant tendency for higher root-to-shoot (R/S) ratios, greater fine root biomass, and higher root starch content, in individuals growing in ridges or midslopes compared to the values of the plants living in gullies. Conclusions: Plants located in open canopy sites, characterized by a shortage of nutrients and water, tend to allocate more biomass belowground than plants in wet and fertile sites. Thus, plants in wet and fertile forests should be more vulnerable to increased disturbance such as wildfires.