Heterogeneity of soil and plant N and C associated with individual plants and openings in North American shortgrass steppe

Abstract

Small-scale spatial heterogeneity of soil organic matter (SOM) associated with patterns of plant cover can strongly influence population and ecosystem dynamics in dry regions but is not well characterized for semiarid grasslands. We evaluated differences in plant and soil N and C between soil from under individual grass plants and from small openings in shortgrass steppe. In samples from 0 to 5 cm depth, root biomass, root N, total and mineralizable soil N, total and respirable organic C, C:N ratio, fraction of organic C respired, and ratio of respiration to N mineralization were significantly greater for soil under plants than soil from openings. These differences, which were consistent for two sites with contrasting soil textures, indicate strong differentiation of surface soil at the scale of individual plants, with relative enrichment of soil under plants in total and active SOM. Between-microsite differences were substantial relative to previously reported differences associated with landscape position and grazing intensity in shortgrass steppe. We conclude that microscale heterogeneity in shortgrass steppe deserves attention in investigation of controls on ecosystem and population processes and when sampling to estimate properties at plot or site scales.

Effect of the canopy of Retama sphaerocarpa on its understorey in a semiarid environment

“…In addition, the amount of decomposed organic matter per kg of soil was also higher in IS soils (Moro et al 1997). Though differences in microbial activity between understorey soils and gaps in arid and semiarid areas are the norm (Hook et al 1991;Gallardo & Schlesinger 1992), differences in microbial activity at different microsites below the shrub canopies have not been described. Less favourable conditions for microbial activity in the middle of the canopy may result from higher concentration of toxic substances leached from the litter layer, which is thicker in the centre, or from the canopy.…”

“…Organic matter, N and other soil chemical variables are often higher under tree and shrub canopies than in gaps in semiarid and arid zones such as African savannahs (Bernhard-Reversat 1982), Chilean matorral (Gutiérrez et al 1993) and North American grasslands and deserts (García-Moya & McKell 1970;Charley & West 1975;Barth & Klemmedson 1978;Virginia & Jarell 1983;Hook et al 1991;Halvorson et al 1994), showing that understorey soil characteristics are strongly influenced by the overstorey plants.…”

“…Complex interactions between perennial and annual species are common in these vegetation systems Functional Ecology 1997 11, [425][426][427][428][429][430][431] where growth of annual plants may be facilitated by a higher soil fertility (García-Moya & McKell 1970;Hook, Burke & Lauenroth 1991;Gutiérrez et al 1993), availability of water (Dawson 1993;Joffre & Rambal 1993) or microclimate amelioration (Valiente-Banuet & Ezcurra 1991) caused by perennial species. Light deprivation and mechanical and chemical effects of litter (Facelli & Pickett 1991b) can also reduce understorey growth.…”

Plant Colonizers Shape Early N-dynamics in Gopher-mounds

“…Most work on plant species effects on N cycling has focused on species in well-established stands (Epstein et al, 1998;Hook et al, 1991;Hungate et al, 1996;Wedin and Tilman, 1990), and the role of pioneer species has been less studied. Because nutrients are frequently susceptible to loss after disturbance, attributes of plant colonizers may play a critical role in the N dynamics of disturbed ecosystems.…”

Revising the fundamentals of ecological knowledge: the biota–environment interaction

“…There is a tight correlation between the root-mycorrhiza systems of dominant trees and under-canopy vegetation, which facilitates mutually beneficial sharing of both inorganic and organic nutrients among the dominant tree and the smaller under-canopy plants (Lerat et al, 2002). Dominant plants create and maintain the chemical composition of soil and dictate its spatial organization (Hook et al, 1991;Rhoades, 1997;Døckersmith et al, 1999). Spatial distribution of the smallest heterotrophs, bacteria and mycorrhizal fungi, was also shown to be autocorrelated around individual trees (Pennanen et al, 1999).…”