320 ph meter

Soil organic matter (OM) was measured by the procedure of K₂CrO₇-H₂SO₄ humid oxidation, alkali-hydrolysable N (AN) by the alkaline hydrolysis diffusion method [15 ]. Available P (AP) was extracted with NaHCO₃ following the Olsen method [16 ] and determined with spectrophotometer (UV-2450, Shimadzu, Japan) by reacting with (NH₄)₂MoO₄ using ascorbic acid as a reductant in the presence of antimony method of Murphy and Riley [17 ]. Available K (AK) was extracted with NH₄HCO₃ + DTPA (diethylenetriaminepentaacetic acid) and analyzed using an ICP-AE spectrometer. Soil pH was determined using a suspension of the soil sample in water at a ratio of 1 : 2.5 (w/v) with a Mettler Toledo 320 pH meter (Mettler-Toledo Ltd., Switzerland).

All of the leaf samples were oven-dried at 70 °C to a constant weight, and were ground for further analysis. Leaf N concentration was measured with a flow injection analyser (FIAstar 5000, FOSS, Sweden), while leaf P concentration was measured by the molybdenum blue colorimetric method after the leaf samples were digested in an H₂SO₄ + H₂O₂ solution.
Soil samples were air-dried and sieved to remove coarse fragments (<0.5 mm for organic carbon and total N concentration; <0.1 mm for total P concentration; <2 mm for other analyses). Soil pH was determined from a solution containing a 1:2.5 ratio (w/v) of soil to distilled water using a Mettler Toledo 320 pH meter (Mettler-Toledo Instruments Co., Ltd., China). Soil organic carbon concentration was measured by wet oxidation with KCr₂O₇ + H₂SO₄, and titrated with FeSO₄. Total soil N concentration was measured using the Kjeldahl method, and total soil P concentration was determined by acid digestion with an H₂SO₄ + HClO₄ solution. Concentrations were expressed based on oven-dried soil weight. Soil water content was determined by drying soil samples in an oven at 105 °C for at least 72 h.