While increased efforts to understand the impact of climate change on ecosystem processes has elevated the importance of accurately estimating ecosystem carbon allocation, belowground carbon estimates remain uncertain. Optimal Partitioning Theory and fixed proportion allocation are often incorporated into models to estimate biomass partitioning to root systems. While some experiments do support these types of allocation models, scaling them to the landscape level is challenging because complex topographic variation may drive spatial and temporal patterns of resource availability. We examined patterns of variation in soil inorganic nitrogen, organic matter, rock content, volumetric water content and above- and belowground carbon partitioning across a topographically diverse first-order catchment (Shale Hills CZO). In order to test both fixed proportion and optimal partitioning at the site, we compared leaf area with absorptive root surface area (RSA) and leaf litter production with simulated absorptive root production at each slope position and across an elevation gradient.
Both Optimal Partitioning Theory and fixed proportion allocation were moderately supported by the data. Fractional allocation analysis revealed no significant relationship between partitioning and elevation or slope position, so in general a simple scaling exponent or fixed ratio may be acceptable. However, while soil properties and aboveground growth patterns showed strong relationships with both elevation and slope position, root distribution varied widely across the catchment and followed a less clear pattern. Only soil depth correlated with increased RSA. While belowground patterns did not support optimal partitioning, aboveground patterns did indicate an increase in tree height in increased light competition, despite smaller variations in leaf production.
Orr, Alexandra (2016): TOPOGRAPHIC CONTROLS ON ROOT PARTITIONING PATTERNS IN A TEMPERATE FOREST . Master of Science, Ecology, The Pennsylvania State University, p. 36.