Rooting depths, lateral root spreads, and belowground/aboveground allometries of plants in water limited ecosystems

Authors: Schenk, HJ, RB Jackson

. 2002. . , doi:10.1046/j.1365-2745.2002.00682.x
In water-limited environments, availability of water and nutrients to plants depends on environmental conditions, sizes and shapes of their root systems, and on root competition. The goal of this study was to predict root system sizes and shapes for different plant growth forms using data on aboveground plant sizes, climate, and soil texture.
A new dataset of >1300 records of root system sizes for individual plants was collected from the literature for deserts, scrublands, grasslands, and savannas with £1000 mm mean annual precipitation (MAP). Root system sizes and shapes for were characterized by maximum rooting depths, maximum lateral root spreads, and their ratios.
Root system sizes differed among growth forms and increased with aboveground size: annuals < perennial forbs = grasses < semi-shrubs < shrubs < trees. Stem succulents were as shallowly rooted as annuals and had lateral root spreads similar to shrubs.
Absolute rooting depths increased with MAP in all growth forms except shrubs and trees, but were not strongly related to potential evapotranspiration (PET). Except in trees, root systems tended to be shallower and wider in dry and hot climates and deeper and narrower in cold and wet climates. Shrubs were more shallowly rooted under climates with summer than winter precipitation regimes.
Root system sizes relative to aboveground sizes increased for all growth forms with decreasing PET, and for herbaceous plants only with decreasing MAP. Thus relative rooting depths tended to increase with aridity, although absolute rooting depths decreased with aridity.
Rooting depths in an independent dataset of 20 test locations were predicted from MAP using regression models for three broad growth forms. The models succeeded in explaining 62% of the observed variance in median maximum rooting depths.
Our results suggest that Walter's two-layer model of soil depth partitioning between woody and herbaceous plants is most appropriate in drier regimes (<500 mm precipitation) and in systems with substantial winter precipitation. The results also highlight many climate change implications, including the distribution of summer and winter precipitation in monsoonal systems that, when altered, may affect the rooting depth of woody but not herbaceous plants.



jecol02.pdf