Document: SCH-3-32-37

Determinants of rooting depth in water-limited ecosystems of the temperate zone.

SCHENK, H.J.* and R.B.JACKSON

Duke University, Durham, NC, USA ¹

Abstract:
Amount and timing of precipitation and potential evapotranspiration are major factors in determining which plant life-forms dominate water-limited ecosystems. Global arid and semi-arid ecosystems of the temperate zone dominated by succulents, shrubs, dwarf-shrubs, or grasses were the subject of this study. Plant life-forms often differ in rooting depth, and results from modeling studies suggest that climatic change may alter life-form spectra in water-limited ecosystems by altering soil water dynamics and thus favoring more deeply or more shallowly rooted plants. Alternatively, climate may primarily affect life-form specific traits above ground, and changes in rooting characteristics may largely be an indirect consequence of vegetation change. The relative importance of abiotic vs. biotic factors for determining rooting depth was analyzed for ~100 root profiles, together with data on site hydrology, soil characteristics, presence of life forms, deciduous vs. evergreen habit, and photosynthetic type of the dominant life forms. General linear models of rooting depth as a function of abiotic and biotic factors explained ~50% of the variation observed in the data, with site hydrology explaining ~17% and life form explaining ~24%. In a discriminant analysis, where rooting depth was treated as one of several environmentally controlled factors determining life-form dominance, inclusion of rooting depth improved predictions by only ~10% overall, but greatly improved ability to predict dwarf-shrub dominance. The results suggest that differences in rooting depth are only one of several factors driving changes in life form dominance, such as the widespread encroachment of woody plants into grasslands.

Keywords: roots water balance arid semi-arid ecosystems life-forms

This abstract is being presented at: 8:45 AM in session:
Oral Session #45: Water Relations in Shrubs and Annuals.