Abstract
The soil environment is linked to aboveground management including plant species composition, grazing intensity, levels of soil disturbance, residue management, and the length of time of a living plant is growing. Soil samples were collected under rangeland [native grass, rotational grazing (NGRG); tame grass, heavy grazing (TGRG); and tame grass, rotational grazing (TGHG)] and cropland [conventional till (CT); CT plus manure (CTM); and long term no till (NT)] systems. The rangeland systems were hypothesized to have higher glomalin content [measured as Bradford-reactive soil protein (BRSP)] and water stable aggregation (WSA) than the cropland systems. In addition, within both rangeland and cropland systems, BRSP and WSA were expected to decline with increased disturbance due to grazing or tillage and going from native to introduced plant species. Differences were detected for BRSP with NGRG and CTM having the highest values in range and cropland systems, respectively. However, the CTM system had higher BRSP values than one or both of the tame grass systems while the CT and NT systems had similar values. Correlation analysis showed strong relationships between all of the BRSP values and WSA.
Highlights
The symbiotic relationship between arbuscular mycorrhizal fungi (AMF) and about 90% of all vascular plants provides a direct linkage between above and belowground activities [1,2]
Because most studies have shown that as grazing intensity increases, soil carbon levels and microbial activities decrease [19], it was unexpected that the TGRG site would have lower Bradford-reactive soil protein (BRSP) values than the TGHG system
These studies did indicate that the results were probably dependent upon if the plant species composition was dominated by native or tame grasses which impacts the intensity of the mycorrhizal relationship [1,13] and impacts rooting depth and rhizosphere dynamics [19,20,21]
Summary
The symbiotic relationship between arbuscular mycorrhizal fungi (AMF) and about 90% of all vascular plants provides a direct linkage between above and belowground activities [1,2]. The level of mycorrhizal dependency [1] of the host plant as well as photosynthetic activity may impact glomalin content and water stable aggregation (WSA) [2]. Unlike the Liebig et al [21] study, these authors examined microbial community and soil C dynamics under different grazing treatments and found that the rhizosphere environment was the driver behind changes in soil C [19,20]. These results are worth noting because often soil C levels are related to soil aggregation and glomalin concentrations [2, 22]
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