Temperature variations and distribution of living cells within tree stems: implications for stem respiration modeling and scale-up

Abstract

Few studies have examined variation in respiration rates within trees, and even fewer studies have focused on variation caused by within-stem temperature differences. In this study, stem temperatures at 40 positions in the stem of one 30-year-old Norway spruce (Picea abies (L.) Karst.) were measured during 40 days between July 1994 and June 1995. The temperature data were used to simulate variations in respiration rate within the stem. The simulations assumed that the temperature-respiration relationship was constant (Q10 = 2) for all days and all stem positions. Total respiration for the whole stem was calculated by interpolating the temperature between the thermocouples and integrating the respiration rates in three dimensions. Total respiration rate of the stem was then compared to respiration rate scaled up from horizontal planes at the thermocouple heights (40, 140, 240 and 340 cm) on a surface area and on a sapwood volume basis. Simulations were made for three distributions of living cells in the stems: one with a constant 5% fraction of living cells, disregarding depth into the stem; one with a living cell fraction decreasing linearly with depth into the stem; and one with an exponentially decreasing fraction of living cells. Mean temperature variation within the stem was 3.7 degrees C, and was more than 10 degrees C for 8% of the time. The maximum measured temperature difference was 21.5 degrees C. The corresponding mean variation in respiration was 35% and was more than 50% for 24% of the time. Scaling up respiration rates from different heights between 40 and 240 cm to the whole stem produced an error of 2 to 58% for the whole year. For a single sunny day, the error was between 2 and 72%. Thus, within-stem variations in temperature may significantly affect the accuracy of scaling respiration data obtained from small samples to whole trees. A careful choice of chamber position and basis for scaling is necessary to minimize errors from variation in temperature.

Spatial and seasonal variations in stem respiration of beech trees (Fagus sylvatica)

“…Considering R M15 and Q 10 values at breast height and for the upper stem location, the differences in temperature would explain at most 68.5% of the spatial variation in measured respiration rates during the non growing period. Stockfors [45] showed that failure to consider temperature differences within the stem could produce errors representing about 58% of total annual stem respiration.…”

“…(2) The distribution of living cells within the stem can affect maintenance respiration rates [45,46]. (3) The transport and storage of carbohydrates in the stem and in the branches can cause variations in respiration rates as it was shown by Malkina et al [29] and Lavigne [18].…”

“…Very few models dealing with carbon budgets for an entire ecosystem, take into account spatial variations in stem respiration and few attempts have been made to test the impact of such variations on calculations of net carbon uptake at stand level [45]. More information is also needed to be able to choose the best unit to scale up stem or branch respiration to stand level, because this unit can have a large impact on the final results.…”

“…Sprugel et al [43] suggested that sapwood volume was a better calculation base, because respiration rates per unit volume are rather constant within coniferous species. Knowledge of the distribution of living cells in the stem would make it possible to choose the best unit (surface or volume) for expressing stem maintenance respiration, and it would minimize errors when scaling up local measurements to stand level [45].…”

Energy balance storage terms and big-leaf evapotranspiration in a mixed deciduous forest

“…The different pattern of S v observed in this research can be explained by the fact that the measured re-emitted long-wave radiation by the canopy is besides the contribution of stems and branches mainly due to the thermal behaviour of the leaves, which explains why the lag in time is not observed. Stockfors [35] mentions that there is a larger temperature amplitude in the upper parts of the stem, and thus also the branches, compared to the lower, more shaded parts of the stems. So, assuming that only the temperature of the upper part of the biomass was represented by the measured surface temperature, and the temperature of the lower stems equalled air temperature, taking a lag of two hours [30] into account, S v was recalculated ( figure 4).…”