Roots are a key component of plant-soil feedbacks. However, little is known about the impacts of varying root stage distributions on the strength and direction of feedbacks, resource cycling, or projections of plant growth. A plant’s fraction of biomass in later stage roots and resource uptake efficiency are typically inversely related, with overall growth enhanced by maintaining high-uptake capable early stage roots. There are trade-offs in root demography, with rapid senescence of early stage roots, but circumstances can skew stage distributions towards later stage roots. Root turnover and production may control root distribution, but direct examination of hypotheses for this control is experimentally intractable. We apply a spatial stage-based matrix population model using varying resource acquisition, survivorship, transportation capacity, and maintenance costs for different root stages to analyze stage distribution across a plant’s life. A simulated perennial plant expands into a 2-dimensional soil environment. We include growth and ageing feedbacks to integrate the acquisition of resources by roots and carbon from photosynthesis. A key objective is to project the impacts on individual plant growth of changing root stage distribution and determine conditions for which stage distribution dynamics tend towards a steady state, cycle, or fluctuate in a non-periodic manner.
Results/Conclusions
A parameter space search involving all model parameters which affect growth, transport, uptake and allocation assumptions, produced approximately 100 million simulated results. The outcomes indicated that the highest plant total growth – sum of root and leaf biomass – is associated with a root demography skewed towards early stages. This result arises from a growth allocation strategy favoring new root and leaf growth rather than root maintenance leading to a near complete turnover of roots every season. A regression tree analysis provides interpretation of the relative impact of different components of below ground processes on overall plant growth. Root and leaf photosynthetic conversion rates were the strongest predictors of plant growth followed by the growth allocation strategy. Spatial analysis of root stage distribution indicates how changing spatial arrangement of root stages impacts growth. The component analysis includes: the relationship between root stage and acquisition, survivorship, maintenance cost, transportation capacity, root/shoot allocation pattern, and photosynthetic conversion constants for roots and shoots. These results were used to analyze the relative impact of 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 leaf ratio).