Abies sibirica Ledeb. fine root respiration in the bilberry-sphagnum pine forest in the middle taiga

A recent interest in the study of physiological and biochemical processes in the underground organs of woody plants is due, first of all, to the assessment of their contribution to the carbon balance of forest ecosystems. Root respiration provides a significant part of the total СО₂ emission from the soil surface. Abies sibirica Ledeb. has a branched, but not deep, root system and prefers a certain soil fertility and moisture. This tree species does not grow on the permafrost grounds unlike Picea obovata Ledeb. and Pinus sylvestris L. Numerous literature sources describe various methods for measuring CO₂ in fine roots, from laboratory measurements to calculating the proportion of root respiration in the total СО₂ emission from soil. Our study is based on the original data on the respiration of non-cut roots of A. sibirica in the litter with the minimal damage of the object and environment. The aim of this research is to characterize the seasonal and daily dynamics of fine root respiration rate in A. sibirica in the bilberry-sphagnum pine forest in the middle taiga for two growing seasons. Measurements were performed from May to October in 2016 and 2018 during the vegetation periods in the bilberry-sphagnum pine forest in the middle taiga (N 62°17' E 50°40') of the 5th class of bonitet, stand composition was 9Po1Bp+Ps+As, tree age was 106-200 years, with soil as peaty-podzolic-gleyic, sandy loam, underlied by loams (Histic Albic Retisol). Weather conditions, litter temperature and moisture are presented in Table 1. Respiration of fine mycorrhizal roots (less than 2 mm in diameter) was measured in mature trees by infrared gas analyzer “Li 6400” (Li-Cor, USA) and soil camera during different times of the day in a stream of atmospheric air. Statistical data processing was performed using Microsoft Excel 2003, and STATISTICA 10. Average values of fir fine root respiration differed significantly in 2016 and 2018 and were 0.79±0.01 mg СО₂ g⁴h⁴ and 0.58±0.01 mg СО₂ g⁴h⁴ (Student’s t-test). In 2016, respiration rate was higher in August and lower in September (See Table 2 and Table 3). In August, an increase in respiration rate was found only at noon and in the afternoon. In July, respiration rate was higher during morning and evening hours. In September, respiration rate was low during all day compared to other months. The lowest values of root СО₂ emission were found in September. In 2018, respiration was high in July and low in August-September. The lowest values of СО₂ emission were found in the beginning of June. July increase and September decrease in respiration rate occurred evenly in each measurement interval during the day. Thus, in July, we found higher daily fine roots’ СО₂ emission compared to other months. In 2016, the daily dynamics demonstrated an increase in root respiration during summer afternoons and its decrease during autumn afternoons followed by an evening increase in respiration. In 2018, summer root respiration increased in the noon and then decreased sharply in the afternoon and evening. The opposite trend was observed in September. We found a positive correlation of fir fine root respiration rate and temperature (See Table 4). The direction of moisture influence on root respiration was different. Fine root respiration rate was correlated positively with camera moisture and negatively with soil moisture. In 2018, the dependence was much stronger than in 2016. Therefore, A. sibirica fine root respiration was different during two years of observation in the bilberry-sphagnum spruce forest and correlated positively with the litter temperature, and negatively with the litter moisture. The seasonal dynamics showed an increased СО₂ emission in July and August. The daily dynamics of the respiration rate was different during different vegetation periods, but, in general, the respiration rate was lower during the afternoon hours. The paper contains 4 Tables and 43 References.

Keywords

Authors

References