Spatial and temporal effects of soil temperature and moisture and the relation to fine root density on root and soil respiration in a mature apple orchard

We identified the role of various soil parameters and root density as drivers of soil respiration (Rs) in an apple orchard, measured during different periods of the year and at a range of distances from trees, in plots with a different history of nutrient supply. Rs was measured in April, May, August and December and studied in relation to soil temperature and moisture, total soil C and N, as well as to fine root density and medium-, and large-sized root density and root N concentration. The study also aimed to partition Rs by applying the root regression technique. Rs ranged from 0.06 in December to 1.49 g CO2 m−2 h−1 in August. Average soil temperature alone explained up to 71% of the annual variability of Rs, while soil water content was negatively correlated to Rs. Fertilization, soil C and N concentration and root N had negligible effects on Rs. Fine root density, but not medium- and large-sized root density, contributed to explaining part of the yearly variability of Rs and proved to be a good predictor in December, when the statistical significance of the regression made it possible to estimate the autotrophic component of Rs as being about 35% of total soil respiration.