Scaling of soil C and N and its relationship to vegetation and soil attributes in a subtropical savanna landscape.
Liu, Feng*,1, Wu, Ben1, Archer, Steve2, Boutton, Thomas1, Bai, E1, Jessup, Kirk1, 1 Texas A&M University, College Station, TX2 University of Arizona, Tucson, AZ
ABSTRACT- Invasion of woody plants into grassland has occurred worldwide. At present, there is no clear consensus as to whether soil carbon (C) and nitrogen (N) pools increase, decrease, or remain unchanged following shifts from grass to woody plant domination. The purpose of this study was to quantify spatial patterns of soil C and N in conjunction with spatial patterns of soil and vegetation parameters on a savanna topo-sequence in Southern Great Plains (Texas) where woody cover is known to have increased over the past 100 years. Variables measured along a 309 m upland-to-lowland catena gradient included soil bulk density, soil particle size distribution, grass biomass, forb biomass, shrub and tree basal diameter, litter and root biomass, soil C and soil N (0-15 cm). Results indicated that vegetation cover was an important determinant of soil C and N; and that soil C and N mass have increased since woody plant invasion. Among the variables examined, litter and root biomass had strongest correlation with soil C and N. Contrary to expectations, soil C and N was not significantly related to tree basal area. Relationships between grass biomass and soil C and N differed in herbaceous vs. woody dominated patches. The scale of the spatial patterns of soil C and N was about 45m based on quadrat variance methods and corresponded approximately to the distance between the centers of dominant woody patches and the adjacent herbaceous patches. Soil C, N, litter, root and grass biomass exhibited similar scaling characteristics and differed from those of shrub and tree basal areas. Spatial scaling of soil C and N was more strongly related to that of litter and root biomass than to the basal area of neighboring trees and shrubs. This suggests increases in near surface soil C and N accompanying woody plant encroachment is related to production and turnover of litter and root biomass. These, in turn, are likely related to local leaf biomass which increases logarithmically with basal area. This knowledge of scaling and correlations will facilitate efforts to extrapolate point estimates of ecosystem properties to landscapes and regions.
Key words: spatial scaling, quadrat variance methods, carbon sequestration, woody invasion
All materials copyright The Ecological Society of America (ESA), and may not be used without written permission.