A plant’s resource uptake efficiency and fraction of biomass in later stage roots – older, thicker, higher branch order – are typically inverse. Overall growth is enhanced by maintaining high-uptake-capable early stage roots – younger, finer, lower branch order – while minimizing allocation to later stage roots. There are trade-offs in life histories with rapid senescence for early stage roots, but circumstances can skew root age distributions towards later stage roots. Root turnover and production are two processes through which plants control root stage distribution. Direct examination of alternative hypotheses for determinants of root distribution is experimentally intractable. The availability of a theoretical model to analyze how root stage distribution affects growth can enhance our capability to project whole-plant growth.
We apply a stage-based matrix population model using varying resource acquisition, survivorship, and maintenance costs for different root stages to analyze root stage distribution across a plant’s life. We include feedbacks between roots and shoots to incorporate the influx of nutrients from roots and carbon from shoots to simulate growth. An objective is to project the impacts on plant growth of changing root stage structure and determine conditions for which stage distribution dynamics tends towards a steady state, cycle, or fluctuate in non-periodic manner.
Results/Conclusions
A parameter space search involving all model parameters which affect growth, transport, uptake and allocation assumptions, produced approximately 28 million simulated results. Results indicated that highest plant total growth – sum of root and shoot biomass – is associated with a root demography heavily skewed towards early stages. A regression tree analysis provides interpretation of the relative impact of different components of below ground processes on overall plant growth. The components investigated include: the relationship between root stage and acquisition, survivorship, maintenance cost, allocation pattern, and photosynthetic conversion constants for root and shoot. These results were used to analyze the relative impact of these different processes on three components of plant response: overall resource uptake, ratio of root biomass in the first and last stages, and overall plant structure (root to shoot ratio).