Changes in chemical element composition of Betula pendula litter during decomposition in a laboratory experiment simulating leaching and salinization

Abstract

The aim of the study was to estimate changes in chemical composition of the white birch litter during decomposition in a laboratory experiment simulating leaching and salinization. Location and time of the study. Fresh litter of Betula pendula leaves were collected in the forest-steppe zone of Priobskoe plateau (40 km to the east of Novosibirsk, Russia) in October 2016. The incubation experiment was carried out in the laboratory of Agrochemistry of the Institute of Soil Science and Agrochemistry of the Siberian Branch of the Russian Academy of Sciences (Novosibirsk, Russia) during 105 days (24.05.2017–06.09.2017) at 24˚С). Methodology. Distilled water (50 ml) or the same volume of NaCl, Na2SO4, FeCl3, Fe2(SO4)3 solutions with concentrations of 0.3, 0.5, 0.7 and 1% were added to 2 g of air-dried birch litter (leaves). The litter was placed into 100 ml plastic cups. The salt concentration in solutions was chosen according to the soil salinity gradation, i.e. 0.3% as weak (0.2–0.4%), 0,5% as medium (0.4–0.6%), 0,7% as strong (0.6–0.8%), and 1% as solonchak (Classification…, 1977). After 24 hours surplus water or salt solutions were decanted and filtered, and the birch litter was air-dried. After that 5 ml soil-water suspension (soil:distilled water 1: 2.5 m/v) was added into half of the cups with litter, whereas another half of cups with litter received 5 ml of distilled water. The variant with litter and no water was also included, designated as “dry birch litter”. The cups with litter were closed up and incubated during 105 days in the thermostat (+24 °С) with periodic ventilation. After incubation the litter was air-dried and weighed. The litter mass loss after decomposition was calculated as a difference between a sample mass at the beginning and at the end of the experiment and expressed as percentage. Concentrations of Na, Fe, K, Ca, Mg, Zn, Cu, Ni were determined by atomic-absorption spectrophotometry (AAnalyst 400, Perkin Elmer Inc., USA) in water samples, 0,3–1% salt solutions and birch litter. The total number of cups with litter in the experiment was 150. The term «under leaching» refers to the decrease in chemical element concentration in the litter after incubation with water. The term «under salinization» refers to the increase of Na or Fe concentrations in the litter after incubation with salt solutions. The litter mass loss presented as air-dry mass, concentration of chemical elements in the litter and ash content are expressed on the oven- dry mass basis. Results. Under leaching the concentration of chemical elements was increased in water extracts (especially К, Са, Mg) and decreased in birch litter in the row: Na (3.6 times) –>К (2.4 times) –> Ni (1.9 times) –> Mg (1.4 times) –> Zn and Cu (1.3 times). In comparison with water, the interaction between litter and Na and Fe salt solutions (concentrations 0.3–1%) led to intensive leaching and, correspondingly, to the 1.3 times lower litter К content, as well as 1.2–1.5 times and 1.5-2.2 times lower Са and Mg content, respectively. The highest concentration of Са, Mg, Zn, Cu, Ni was detected in FeCl3 solutions at the start of the experiment. The maximal mass and ash content losses were detected in the dry birch litter. On average, leaching was found to decrease 1.4 times mass loss and ash content in the litter. The minimal mass and ash content losses under salinization were found after litter incubation with FeCl3 (0.3–1%) solutions. The difference in mass loss between variants litter-water and litter-soil water suspension was not detected, although litter ash content after addition of soil water suspension was 1.1–1.3 times higher. Conclusions. The interaction birch litter with water and Na and Fe salt solutions (0,3-1%) led to modification of elemental chemical composition of plant litter as a result of leaching of chemical elements (especially К, Са, Mg) from litter and increased concentrations of Na, Fe and some other elements (depending on the salt used). It led to the decrease in plant litter decomposition rate, which under the natural conditions in the south of West Siberia can take place as a result of temporary overwetting of the forest litter (for instance, in autumn or spring) as well as in areas occupied by saline soils.