Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/2005
Publication Date: 3/1/2006
Citation: Potthoff, M., Steenwerth, K.L., Jackson, L.E., Drenovsky, R.E., Scow, K.M., Joergensen, R.G. 2006. Soil microbial community composition as affected by restoration practices in california grassland. Soil Biology and Biochemistry. Interpretive Summary: The restoration of degraded soils, native plants, and the associated ecosystem services is of increasing importance as undisturbed land grows increasingly scarce due to its conversion to urban and agricultural uses. This study also contributes to understanding the impacts of agricultural practices on soil microbial communities. In a grassland restoration project in California, where native perennial bunchgrasses were introduced into non-native annual grassland after a period of intensive tillage, weeding, and herbicide use to reduce the annual seed bank, microbial community composition was investigated. Soil microbial communities and fungal biomass decreased in response to agricultural practices employed during restoration. Contrary to other studies investigating the effect of plant species or community composition on soil microbial communities, the microbial community compostion of the restored perennial grassland was similar to the exotic annual grassland. This suggests that soil microbial communities can recover from the soil degradation caused by the use of agricultural practices during restoration.
Technical Abstract: Agricultural practices strongly impact soil microbes, as reflected by indices related to biomass, community compostion. In a grassland restoration project in California, where native perennial bunchgrasses were introduced into non-native annual grassland after a period of intensive tillage, weeding, and herbicide use to reduce the annual seed bank, microbial community composition was investigated. Three treatments were compared: annual grassland, bare soil fallow, and restored perennial grassland. Soil profiles down to 80 cm in depth were investigated in four separate layers (0 to 15cm, 15 to 30cm, 30 to 60cm, and 60 to 80cm) using both PLFA and ergosterol as biomarkers in addition to microbial biomass C by fumigation extraction. PLFA fingerprinting showed much stronger differences between restored perennial grassland and annual grassland. The presence or absence of plants over several years clearly distinguished microbial communities. Microbial communities in lower soil layers were little affected by management practices. Regardless of treatment, soil depth caused a strong gradient of changing habitat conditions, which was reflected in Canonical Correspondence Analysis of PLFA. Fungal organisms were associated with the presence of plants and/or litter since the total amount and the relative proportion of fungal markers were reduced in the tilled bare fallow and in lower layers of the grassland treatments. Total PLFA and soil microbial biomass were highly correlated, and fungal PLFA biomarkers showed strong correlations to ergosterol content. In conclusion, microbial communities are resilient to the grassland restoration process, but do not reflect the change in plant species composition that occurred after planting native bunchgrasses.