Effect of slope position on leaf and fine root C, N and P stoichiometry and rhizosphere soil properties in Tectona grandis plantations

Abstract

Little is known about C –N – P stoichiometries and content in teak (Tectona grandis) plantations in South China, which are mostly sited on hilly areas with lateritic soil, and the effect of slope position on the accumulation of these elements in trees and rhizosphere soils. Here we analyzed the C, N, P content and stoichiometry in leaves, fine roots and rhizosphere soils of trees on the upper and lower slopes of a 12-year-old teak plantation. The Kraft classification system of tree status was used to sample dominant, subdominant and mean trees at each slope position. The results showed that the C, N and P contents in leaves were higher than in fine roots and rhizosphere soils. The lowest C/N, C/P and N/P ratios were found in rhizosphere soils, and the C/N and C/P ratios in fine roots were higher than in leaves. Nutrient accumulation in leaves, fine roots and rhizosphere soils were significantly influenced by slope position and tree class with their interaction mainly showing a greater effect on rhizosphere soils. Leaf C content and C/N ratio, fine root C and P contents, and C/N and C/P ratios all increased distinctly with declining slope position. The contents of organic matter (SOM), ammonium (NH₄ ⁺–N), nitrate-nitrogen (NO₃ ⁻–N) and available potassium (AK) in rhizosphere soils were mainly enriched on upper slopes, but exchange calcium (ECa), available phosphorus (AP), and pH were relatively lower. Variations in the C, N and P stoichiometries in trees were mainly attributed to the differences in rhizosphere soil properties. N and P contents showed significant positive linear relationships between leaf and rhizosphere soil, and C content negative linear correlation among leaves, fine roots and rhizosphere soils. Chemical properties of rhizosphere soils, particularly C/N and NH₄ ⁺–N, had significant effects on the leaf nutrients in trees on the upper slope. Correspondingly, rhizosphere soil properties mainly influenced fine root nutrients on the lower slope, and soil AK was the major influencing factor. Overall, these results offer new insights for the sustainability and management of teak plantations in hilly areas.

Keywords

Tectona grandis / Stoichiometric ratio / Rhizosphere soil / Dominant trees / Nutrient accumulation