Soil respiration and mass balance estimation of fine root production in Fitzroya cupressoides forests of southern Chile

Abstract

Citation: Urrutia-Jalabert, R., Y. Malhi, and A. Lara. 2017. Soil respiration and mass balance estimation of fine root production in Fitzroya cupressoides forests of southern Chile. Ecosphere 8(4):e01640. 10.1002/ecs2.1640Abstract. The soil carbon dynamics of southern hemisphere temperate rainforests have rarely been studied. Here, we report for the first time soil CO 2 effluxes and their partitioning for medium-age and old-growth Fitzroya cupressoides forests growing under contrasting environmental conditions in the Coastal Range and Andean Cordillera of southern Chile. Fitzroya is a high biomass and one of the longest lived species in the world. We characterized soil respiration patterns over almost 2 yr. Annual soil respiration was slightly higher in younger forests from the Coastal Range compared with Andean forests during the first studied year (6.37-6.66 vs. 5.06-6.14 Mg CÁha À1 Áyr À1 ), and significantly higher during the second year mainly due to a warmer and drier summer (8. ). Therefore, warmer and drier conditions, likely to become more common in this region under future climate change, were associated with significantly higher respiration in the shallow soils of the coast, but not in the Andes. A higher proportion of autotrophic respiration was found in the Coastal Range forest probably due to a much higher fine root biomass in this site. However, fine root productivity, an important contributor of belowground carbon fluxes, was a little lower (not significantly) in the coastal site (0.81 AE 0.60 vs. 1.50 AE 0.42 Mg CÁha ), indicating a longer root residence time in forests from this area. Soil CO 2 effluxes from these forests and their root productivity are at the lower end of values recorded for other mature and old-growth temperate wet forests worldwide. The intrinsic longevity and the particularly poor soils and rainy conditions where these forests grow may influence these facts. Interannual climate variability appears to be especially important for soil respiration in the Coastal Range due to the more Mediterranean climate influence and shallow, poor water retention soils in this area.

Warming and Drought Weaken the Carbon Sink Capacity of an Endangered Paleoendemic Temperate Rainforest in South America

“…Annual soil respiration measured in our study was higher compared to previous monthly measurements using the manual closed chamber method in Fitzroya forests in 15 points systematically distributed in two 0.6 ha plots located around the tower (637–864 g C m −2 year −1 for years 2011–2012 and 2012–2013, respectively; Urrutia‐Jalabert et al., 2017) although the main drivers (soil temperature and water content) are consistent in both studies. The main difference could be due to the different methods used, since in the previous study, measurements were done using a manual environmental gas analyzer with a closed static chamber once a month (values were interpolated between measurements).…”

“…Tree‐ring carbon isotopes showed that despite this declining growth, leaf‐level intrinsic water use efficiency of this forest has increased with rising CO 2 concentrations in the atmosphere, likely due to a decrease in stomatal conductance (Urrutia‐Jalabert, Malhi, Barichivich, et al., 2015). At the ecosystem level, soil respiration in the area was found to increase substantially with warm and dry conditions during summer, reinforcing the idea that the carbon sink of Fitzroya rainforest ecosystems in the Coastal Range can be negatively affected by current and projected climate trends (Urrutia‐Jalabert et al., 2017).…”

“…The main difference could be due to the different methods used, since in the previous study measurements were done using a manual environmental gas analyzer with a closed static chamber once a month (values were interpolated between measurements). The high fine root biomass reported for the Fitzroya forests surrounding the area of the tower and a higher proportion of autotrophic respiration, compared with heterotrophic respiration in this site ( Urrutia-Jalabert et al, 2017 ), may explain the high difference observed between areas with tree cover and small forest gaps.…”

“…It has indeed been reported that the low water retention capacity of the soils in this site has been critical for the negative radial growth trend of the forest since the 1970s, which has not been seen in many sites of the Andean Cordillera ( Urrutia-Jalabert et al, 2015c , Lara et al, 2020 ). Moreover, low soil water content was also reported to drive high soil respiration in this site ( Urrutia-Jalabert et al, 2017 ).…”

Representing Grasslands Using Dynamic Prognostic Phenology Based on Biological Growth Stages: 1. Implementation in the Simple Biosphere Model (SiB4)

“…For grasslands, we hypothesize that aboveground biomass mortality occurs primarily at the end of the growing season as litterfall (see next section); thus, for the canopy pools E cp = 0.95. In contrast, root mortality depends solely on turnover given that root turnover is still poorly constrained due to the complexity of factors that influence root mortality, the heterogeneity in root life spans, and difficulties in measurement techniques (Urrutia‐Jalabert et al, ; Riley et al, ; Smithwick et al, ). Since root production, respiration, mortality, and turnover all interact, SiB4 uses root respiration efficiencies ( E rp ) ranging from 0.45 to 0.6.…”