Determination of acid phosphatase and dehydrogenase activities in the rhizosphere of nodulated legume species native to two contrasting savanna sites in Venezuela

Rhizospheric soils from 13 nodulated legume species were collected at two contrasting savanna sites. Site 1 (S-1) was characterized by 2.6 mug available P g(-1) soil, 2.5% Al saturation and a pH of 5.9. Site 2 (S-2) presented a pH of 4.0, 1.0 mug available P g(-1) soil and 40% Al saturation. For all legume species and at both sites, acid phosphatase (AP) and dehydrogenase (Dh) activities were significantly higher in rhizospheric than in non-rhizospheric soils. Between sites, the highest significant rhizospheric and non-rhizospheric AP and Dh activities were recorded at S-1, indicating a negative effect of S-2 properties on soil enzymatic activity. Among species, the highest significant AP activity was detected in the rhizosphere of Aeschynomene hystrix at S-1 and Galactia jussieuana and Mimosa pudica at S-2. The Dh activity was significantly higher in the rhizosphere of Calopogonium mucunoides at S-1 and Chamaecrista flexuosa and G. jussieuana in S-2. Dh activity was below detectable values in the rhizosphere of Chamaecrista rotundi-folia, C. mucunoides and Phaseolus gracilis at S-2. Glucose amendment (GA) of soils did not enhance AP activity in all rhizospheric and non-rhizospheric S-1 and S-2 soils. In contrast, GA increased the Dh activity in all soils, regardless of the site and legume species. Nevertheless, Dh activity in GA S-2 rhizospheric and non-rhizospheric soils did not reach the values detected in non-amended rhizospheric and non-rhizospheric S-1 soils, respectively. The non-response of AP to glucose amendment can be considered as an indicator of its plant origin.