The Influence of Encroaching Woodland On Grassland Soil Enzymatic Activities.

Grass-dominated ecosystems around the world are experiencing woody plant invasion due to human land uses. Vast regions in southern Texas have been transformed from open grasslands to subtropical thorn woodlands during the past 150 yrs.  The assumption is that the soil microbial activity in the remaining grasslands remain unaffected by the nearby woody clusters.  An experiment was designed to test this hypothesis by sampling grasslands and measuring potential soil enzymatic activities.  Samples were taken from Texas Agricultural Experiment Station La Copita Research Area (mean annual precipitation = 715 mm; mean annual temperature = 22.4 °C). Topography consists of nearly level uplands which grade (1-3% slopes) into lower-lying drainage woodlands. This formerly grassland plain is subject to invading woodlands. The woody areas form “clusters” surrounding a single mesquite tree, which over time merge into patches of woodlands. The mesquite is the first species to invade, which then provides support for  other  woody species in its understory. The age of the clusters were determined through measuring basal diameters of the oldest mesquite tree. Soil cores were taken in the grasslands 15 feet away from each cluster canopy edge.  Five enzymes activities were measured: β-1,4 glucosidase (BG), N-acetyl-β-D-glucosaminidase (NAG), acid phosphatase (APH), arylamidase (AM), fluorescein diacetate hydrolysis (FDAH) , phenol oxidase (PO).  Results will be discussed.