Schenk,H.J. and Jackson,R.B.(2002): Rooting depths, lateral root spreads and below-ground/above-ground allometries of plants in water-limited ecosystems. Journal of Ecology, 90, 480-494.


In water-limited environments, the availability of water and nutrients to plants depends on environmental conditions, sizes and shapes of their root systems, and root competition. The goal of this study was to predict root system sizes and shapes for different plant growth forms using data on above-ground plant sizes, climate and soil texture.
2 A new data set 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). Maximum rooting depths, maximum lateral root spreads and their ratios were measured.
3 Root system sizes differed among growth forms and increased with above-ground size: annuals<perennial forbs=grasses<semi-shrubs<shrubs<trees. Stem succulents were as shallowly rooted as annuals but had lateral root spreads similar to shrubs.
4 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.
5 Relative to above-ground plant sizes, root system sizes decreased with increasing PET for all growth forms, but decreased with increasing MAP only for herbaceous plants. Thus relative rooting depths tended to increase with aridity, although absolute rooting depths decreased with aridity.
6 Using an independent data set of 20 test locations, rooting depths were predicted from MAP using regression models for three broad growth forms. The models succeeded in explaining 62% of the observed variance in median rooting depths.
7 Based on the data analysed here, Walter's two-layer model of soil depth partitioning between woody and herbaceous plants appears to be most appropriate in drier regimes (<500 mm MAP) and in systems with substantial winter precipitation.

Key-words: climate; plant growth forms; potential evapotranspiration; precipitation; root systems』

 個々の植物に対する根系の大きさの1300を超える記録からなる新しいデータ・セットが、年平均降水量≦1000 mmの砂漠・低木地・草原・サバンナについての文献から集められた。最大の根の深さ・最大の側根の広がり・その比が測られた。
 ここで解析したデータを基にすれば、木本と草本の植物間で分けるWalterによる土壌深さの2層モデルは、乾燥期(<500 mm 年平均降水量)および実質的な冬期降水の系において、もっとも適切であるように思われる。』

Materials and methods
 Root systems of different growth forms
 Absolute rooting depths and climate
 Below-ground/above-ground allometries and environmental factors
 Ecosystem rooting along a precipitation gradient
 Applicability of water's two-layer model
 Plant traits and rooting depths
Supplementary material
Appendix 1
Appendix 2
Appendix 3