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 (R-s) 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. R-s 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 R-s by applying the root regression technique. R-s 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 R-s, while soil water content was negatively correlated to R-s. Fertilization, soil C and N concentration and root N had negligible effects on R-s. Fine root density, but not medium- and large-sized root density, contributed to explaining part of the yearly variability of R-s 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 R-s as being about 35% of total soil respiration.