Controls of Soil Spatial Variability in a Dry Tropical Forest

We examined the roles of lithology, topography, vegetation and fire in generating local-scale (<1 km²) soil spatial variability in a seasonally dry tropical forest (SDTF) in southern India. For this, we mapped soil (available nutrients, Al, total C, pH, moisture and texture in the top 10cm), rock outcrops, topography, all native woody plants ≥1 cm diameter at breast height (DBH), and spatial variation in fire frequency (times burnt during the 17 years preceding soil sampling) in a permanent 50-ha plot. Unlike classic catenas, lower elevation soils had lesser moisture, plant-available Ca, Cu, Mn, Mg, Zn, B, clay and total C. The distribution of plant-available Ca, Cu, Mn and Mg appeared to largely be determined by the whole-rock chemical composition differences between amphibolites and hornblende-biotite gneisses. Amphibolites were associated with summit positions, while gneisses dominated lower elevations, an observation that concurs with other studies in the region which suggest that hillslope-scale topography has been shaped by differential weathering of lithologies. Neither NO₃⁻-N nor NH₄⁺-N was explained by the basal area of trees belonging to Fabaceae, a family associated with N-fixing species, and no long-term effects of fire on soil parameters were detected. Local-scale lithological variation is an important first-order control over soil variability at the hillslope scale in this SDTF, by both direct influence on nutrient stocks and indirect influence via control of local relief.     

Woody plant diversity in relation to environmental factors in a seasonally dry tropical forest landscape

Questions

Water availability is known to be a first‐order driver of plant diversity; yet water also affects fire regimes and soil fertility, which, in turn, affect plant diversity. We examined how precipitation, fire and soil properties jointly determine woody plant diversity. Specifically, we asked how woody plant diversity varies along a sharp precipitation gradient (about 600–1,800 mm mean annual precipitation [MAP ]within a ~45‐km distance) exhibiting considerable variation in long‐term fire burn frequency and soil fertility, in a southern Indian seasonally dry tropical forest (SDTF ) landscape.

Location

Mudumalai, Western Ghats, India.

Methods

Woody plants ≥1‐cm DBH were enumerated in 19 1‐ha permanent plots spanning a range of tropical vegetation types from dry thorn forest, through dry and moist deciduous forest to semi‐evergreen forest. Burn frequencies were derived from annual fire maps. Six measures of surface soil properties – total exchangeable bases (Ca + Mg + K), organic carbon (OC ), total N, pH , plant available P and micronutrients (Fe + Cu + Zn + Mn) were used in the analyses. Five measures of diversity – species richness, Shannon diversity, the rarefied/extrapolated versions of these two measures, and Fisher's α – were modelled as functions of MAP , annual fire burn frequency and the principal components of soil properties.

Results

Most soil nutrients and OC increased with MAP , except in the wettest sites. Woody productivity increased with MAP , while fire frequency was highest at intermediate values of MAP . Woody plant diversity increased with MAP but decreased with increasing fire frequency, resulting in two local diversity maxima along the MAP gradient – in the semi‐evergreen and dry thorn forest – separated by a low‐diversity central region in dry deciduous forest where fire frequency was highest. Soil variables were, on the whole, less strongly correlated with diversity than MAP .

Conclusions

Although woody plant diversity in this landscape, representative of regional SDTF s, is primarily limited by water availability, our study emphasizes the role of fire as a potentially important second‐order driver that acts to reduce diversity in this landscape.

     

Studies on spice principles as antioxidants in the inhibition of lipid peroxidation of rat liver microsomes

Polyunsaturated fatty acids (PUFA) are vulnerable to peroxidative attack. Protecting PUFA from peroxidation is essential to utilize their beneficial effects in health and in preventing disease. The antioxidants vitamin E, t-butylhydroxy toluene (BHT) and t-butylhydroxy anisole (BHA) inhibited ascorbate/Fe²⁺-induced lipid peroxidation in rat liver microsomes. In addition, a number of spice principles, for example, curcumin (5–50 µM) from turmeric, eugenol (25–150 µM) from cloves and capsaicin (25–150 µM) from red chillies inhibited lipid peroxidation in a dose-dependent manner. Zingerone from ginger inhibited lipid peroxidation at high concentrations (> 150 µM) whereas linalool (coriander), piperine (black pepper) and cuminaldehyde (cumin) had only marginal inhibitory effects even at high concentrations (600 µM). The inhibition of lipid peroxidation by curcumin and eugenol was reversed by adding high concentrations of Fe²⁺.     

Isolation and characterization of a <Emphasis Type="Italic">Glutamate decarboxylase</Emphasis> (GAD) gene and their differential expression in response to abiotic stresses from <Emphasis Type="Italic">Panax ginseng</Emphasis> C. A. Meyer

Glutamate decarboxylase (GAD) catalyzes the conversion of l-glutamate to γ-aminobutyric acid (GABA). A full-length cDNA encoding GAD (designated as PgGAD) was isolated and characterized from the root of Panax ginseng C. A. Meyer. The length cDNA of PgGAD was 1881 bp and contained a 1491 bp open reading frame (ORF) encoding a glutamate decarboxylase protein of 496 amino acids, possessing a Ser-X-X-Lys active site, which belongs to the GAD group. The deduced amino acid sequence of the PgGAD was classified in the plant GAD family and has 76–85% high similarity with other plants as like petunia, Arabidopsis, tomato. Secondary structure of PgGAD was predicted by using SOPMA software program. Southern blot analysis of genomic DNA suggests that, there is more than one copy of the PgGAD gene. The organ specific gene expression pattern also studied in P. ginseng seedlings, in which the stem showed elevated expression than root, leaf, bud and rhizomes. Along with this, we also confirmed the gene expression of PgGAD under various abiotic stresses like temperature stress, osmotic stress, anoxia, oxidative stress, and mechanical damage. Temporal analysis of gene expression except exposure of oxidative stress revealed an enhanced expression after each stresses. The enzyme activity of PgGAD was stimulated to 2-fold under cold stress.