Plant-Soil interactions in temperate grasslands

Abstract

We present a conceptual model in which plant-soil interactions in grasslands are characterized by the extent to which water is limiting. Plant-soil interactions in dry grasslands, those dominated by water limitation ('belowground-dominance'), are fundamentally different from plant-soil interactions in subhumid grasslands, where resource limitations vary in time and space among water, nitrogen, and light ('indeterminate dominance'). In the belowgrounddominance grasslands, the strong limitation of soil water leads to complete (though uneven) occupation of the soil by roots, but insufficient resources to support continuous aboveground plant cover. Discontinuous aboveground plant cover leads to strong biological and physical forces that result in the accumulation of soil materials beneath individual plants in resource islands. The degree of accumulation in these resource islands is strongly influenced by p!ant functional type (lifespan, growth form, root:shoot ratio, photosynthetic pathway), with the largest resource islands accumulating under perennial bunch grasses. Resource islands develop over decadal time scales, but may be reduced to the level of bare ground following death of an individual plant in as little as 3 years. These resource islands may have a great deal of significance as an index of recovery from disturbance, an indicator of ecosystem stability or harbinger of desertification, or may be significant because of possible feedbacks to plant establishment. In the grasslands in which the dominant resource limiting plant community dynamics is indeterminate, plant cover is relatively continuous, and thus the major force in plant-soil interactions is related to the feedbacks among plant biomass production, litter quality and nutrient availability. With increasing precipitation, the over-riding importance of water as a limiting factor diminishes, and four other factors become important in determining plant community and ecosystem dynamics: soil nitrogen, herbivory, fire, and light. Thus, several different strategies for competing for resources are present in this portion of the gradient. These strategies are represented by different plant traits, for example root:shoot allocation, height and photosynthetic pathway type (C3 vs. C4) and nitrogen fixation, each of which has a different influence on litter quality and thus nutrient availability. Recent work has indicated 122 that there are strong feedbacks between plant community structure, diversity, and soil attributes including nitrogen availability and carbon storage. Across both types of grasslands, there is strong evidence that human forces that alter plant community structure, such as invasions by nonnative annual plants or changes in grazing or fire regime, alters the pattern, quantity, and quality of soil organic matter in grassland ecosystems. The reverse influence of soils on plant communities is also strong; in tum, alterations of soil nutrient supply in grasslands can have major influences on plant species composition, plant diversity, and primary p...

Across-scale patterning of plant-soil–water interactions surrounding tree islands in Southern Everglades landscapes

“…Once established in the marsh, woody plants are believed to generate below-canopy resource islands through autogenic nutrient and peat redistribution mechanisms (Burke et al 1998;Wetzel et al 2005). Rietkerk et al (2004) described one such mechanism occurring in temperate peatlands, where mass flow of groundwater nutrients, especially nitrogen (N), move towards areas with higher vascular plant biomass due to differential transpiration rates.…”

Different plant traits affect two pathways of riparian nitrogen removal in a restored freshwater wetland

“…Lower C:N ratios make plant inputs of higher quality (Burke et al 1998) so roots are more easily decomposed by microbes, providing needed carbon to denitrifiers.…”

Management of Canadian prairie region grazed grasslands: Soil C sequestration, livestock productivity and profitability

“…The aboveground net primary productivity (ANPP) of the grasslands of North America is strongly influenced by the amount and distribution of annual precipitation (Sala et al 1988). Where available moisture is less limiting, changes in nutrient supply can have major influences on grassland primary productivity, plant species composition, litter quality, N availability and SOC sequestration (Wedin and Tilman 1996;Burke et al 1998;Schuman et al 1999;Franzlubbers et al 2000;Schnabel et al 2001;Weinhold et al 2001). In intensively managed pastures of the humid regions of North America, Franzlubbers et al (2000) concluded that appropriate grazing strategies can produce C gains up to 1000 kg C ha -1 yr -1 .…”

“…Tame pastures of crested wheatgrass (CWG) (Agrpyron cristatum) with and without alfalfa (Medicago sativa) were compared at various levels of fertility inputs, stocking density and season length. As the overriding constraint of water limitation diminishes with increasing annual precipitation, herbivory and soil nitrogen, in addition to fire and light, gain in importance in determining grassland plant community and ecosystem dynamics (Burke et al 1998). The drier prairie regions (Moist Mixed and Mixed Grassland) were considered too dry to experience benefits from N fertilization (FERT), seeded pastures of grass/legume grazed continuously (GLGC) or rotationally (GLGR), or complementary grazing (CG) practices.…”

“…Sixty to ninety percent of the net primary productivity in grasslands occurs belowground and standing biomass pools can be relatively small in these systems compared to C stored in root biomass Schuman et al 1999). The ratio of BNP:ANP (belowground net production:aboveground net production) varies from over 8:1 in warm-arid grassland regions to about 1.2:1 on most moist prairie sites (Burke et al 1998;Reeder et al 2001). Root residue C inputs were calculated using derived BNP:ANP ratios (Table 3).…”