Soil CO2 efflux in boreal pine forests in the current climate and under CO2 enrichment and air warming

Abstract

The aims of the study were to identify factors related to temporal and spatial variation in forest soil CO2 efflux (Fs), compare measurement chambers, and to test effects of a climate change experiment. The study was based on four-year measurements in upland Scots pine forests. Momentary plot averages of Fs ranged from 0.04 to 1.12 gCO2m −2 h −1 and annual estimates for the forested area from1750 to 2050 gCO2m −2. Soil temperature was a dominant predictor of the temporal variation in Fs (R 2 =76-82%). A temperature and degree days model predicted Fs of independent data within 15% on the average but underestimated it during the peak efflux period (July-August), possibly because of seasonal pattern in growth of roots and mycorrhiza. A comparison sub-study indicated that the reliability of the measurement chambers was not related to the principle i.e. non-steady-state through-flow, non-steady-state non-through-flow or steady-state through-flow. Spatial variability of Fs within 400 m 2 plots in four stands was large; coefficients of variation (CV) ranged from 0.10 to 0.80, with growing season averages of 0.22-0.36. A positive spatial autocorrelation was found at short distances (3-8 m). In data from several stands, thickness of the humus layer explained 28% of the variation in Fs, and with the distance to the closest trees it explained 40%. Fs also correlated with root mass of the humus layer. Between-plot differences in Fs were small. In the climate change experiment, CO2 enrichment and air warming consistently, but not always significantly, increased Fs in whole-tree chambers. Their combined effect was additive, with no interaction; i.e. +23-37% (elevated CO2), +27-43% (elevated temperature), and +35-59% (combined treatment), depending on year. Air warming was a significant factor in the 4-year data according to ANOVA. Temperature sensitivity of Fs under the warming, however, decreased in the second year.

Warming Rather Than Increased Precipitation Increases Soil Recalcitrant Organic Carbon in a Semiarid Grassland after 6 Years of Treatments

“…The significant decrease in labile SOC at the 10–20 cm depth with warming was in contrast to a previous study that warming increased soil microbial biomass C and labile organic C in a tallgrass prairie [16]. However, our finding was supported by previous studies in which warming decreased microbial biomass C [22] and soil respiration [3], [4]. The discrepancy between results from our grassland study and the tallgrass prairie study [16] could be due to complexity of ecosystems and various key controlling factors for C cycling in different ecosystems [23].…”

Changes in biocrust cover drive carbon cycle responses to climate change in drylands

“…Warming significantly increased soil CO 2 efflux at both study sites, albeit the effects of this treatment were affected by both RE and biocrust cover in Aranjuez. Our findings agree with results from experiments conducted in a wide variety of environments, which have reported significant increases in soil CO 2 efflux with warming during the first years (typically between 20% and 40%), which are later reduced due to acclimatization processes (Rustad et al ., ; Luo et al ., ; Niinistö et al ., ; but see Lellei‐Kovács et al ., ; de Dato et al ., ). Differences between sites in the magnitude of warming effects with biocrust development may have caused by variations in overall fertility, as soil CO 2 efflux has been found to be influenced not only by moisture and temperature, but also by the amount of available soil organic carbon (Sponseller, ; Moyano et al ., ).…”

Responses of CO2, N2O and CH4 fluxes between atmosphere and forest soil to changes in multiple environmental conditions

“…The effects of diurnal warming on soil respiration or ecosystem carbon exchange were not equal to the separate effects of day and night warming in a temperate steppe (Xia et al, 2009). However, studies of soil CO 2 emission to multiple environmental conditions found that response to temperature was by far the most dominant one (Edwards & Norby, 1998;Lin et al, 2001;Niinist€ o et al, 2004;Zhou et al, 2006). Soil CO 2 emission increased with temperature, largely independent of the changes of other factors.…”