Vertical Vegetation Structure Below Ground: Scaling from Root

Vertical Vegetation Structure Below Ground: Scaling from Root to Globe 359Table 2. Important variables to be considered in the development of models used forpredicting belowground structure of vegetation at the scale of plant communities to globalbiomes. Predictions for individual plants or plant populations may require considerationof additional variables,such as species-specific root system architecture. Depending on thespatial and temporal scale of the model,not all of these variables will have to be modeledexplicitly, and/or additional variables may have to be included. See text for further discussionsof all variables listedGeneral categories Specific variables Potential effects on rootsMechanical soil 1. Vertical distribution 1. With increasing soil strength rootproperties of soil strength growth declines,and roots areincreasingly likely to preferentiallygrow in soil macropores2. Vertical distribution 2. Affects the relationship between soilof soil texture,water potential and soil waterincluding rockscontent and thereby root growth3. Vertical distribution 3. Affects presence and abundanceof soil structure of macropores which can affectpatterns of root growth andinfiltrationChemical soil 1. Vertical distribution 1. Affects soil water holding capacityproperties of organic matter and fertility. Roots typicallyproliferate in soil that is rich inorganic matter2. Vertical distribution 2. Roots proliferate in soil volumesof plant-available with high contents of plant-availablenutrientsnitrogen and phosphorus3. Vertical distribution 3. Toxins may negatively affectof toxins,especially root growthaluminum concentrationsSoil water balance1. Inputs: precipitation,1. Affect infiltration depth,run-on,groundwater vertical distribution of soil watercontents, and thereby root growth2. Outputs: runoff and 2. Affect vertical distribution of soilevapotranspiration water contents and thereby rootgrowth3. Vertical distribution 3. Affects water flow rates,rootof hydraulicwater uptake,and potentiallyconductivityhydrotropic root growth4. Dynamic vertical 4. Affects vertical distribution of rootdistribution of soil growth,including due towater resultinghydrotropismfrom 1—3