The agreement of Leaf Area Index (LAI) assessments from three indirect methods, i.e. the LAI–2200 Plant Canopy Analyzer, the SS1 SunScan Canopy Analysis System and Digital Hemispherical Photography (DHP) was evaluated for four canopy types, i.e. a short rotation coppice plantation (SRC) with poplar, a Scots pine stand, a Pedunculate oak stand and a maize field. In the SRC and in the maize field, the indirect measurements were compared with direct measurements (litter fall and harvesting). In the low LAI range (0 to 2) the discrepancies of the SS1 were partly explained by the inability to properly account for clumping and the uncertainty of the ellipsoidal leaf angle distribution parameter. The higher values for SS1 in the medium (2 to 6) to high (6 to 8) ranges might be explained by gap fraction saturation for LAI–2200 and DHP above certain values. Wood area index –understood as the woody light-blocking elements from the canopy with respect to diameter growth– accounted for overestimation by all indirect methods when compared to direct methods in the SRC. The inter-comparison of the three indirect methods in the four canopy types showed a general agreement for all methods in the medium LAI range (2 to 6). LAI–2200 and DHP revealed the best agreement among the indirect methods along the entire range of LAI (0 to 8) in all canopy types. SS1 showed some discrepancies with the LAI–2200 and DHP at low (0 to 2) and high ranges of LAI (6 to 8).
Abstract. Global warming may lead to carbon transfers from soils to the atmosphere, yet this positive feedback to the climate system remains highly uncertain, especially in subsoils (Ilyina and Friedlingstein, 2016; Shi et al., 2018). Using natural geothermal soil warming gradients of up to +6.4 ∘C in subarctic grasslands (Sigurdsson et al., 2016), we show that soil organic carbon (SOC) stocks decline strongly and linearly with warming (−2.8 t ha−1 ∘C−1). Comparison of SOC stock changes following medium-term (5 and 10 years) and long-term (>50 years) warming revealed that all SOC stock reduction occurred within the first 5 years of warming, after which continued warming no longer reduced SOC stocks. This rapid equilibration of SOC observed in Andosol suggests a critical role for ecosystem adaptations to warming and could imply short-lived soil carbon–climate feedbacks. Our data further revealed that the soil C loss occurred in all aggregate size fractions and that SOC stock reduction was only visible in topsoil (0–10 cm). SOC stocks in subsoil (10–30 cm), where plant roots were absent, showed apparent conservation after >50 years of warming. The observed depth-dependent warming responses indicate that explicit vertical resolution is a prerequisite for global models to accurately project future SOC stocks for this soil type and should be investigated for soils with other mineralogies.
Abstract. Global warming may lead to carbon transfers from soils to the atmosphere, yet this positive feedback to the cli- mate system remains highly uncertain, especially in subsoils (Ilyina and Friedlingstein, 2016; Shi et al., 2018). Using natural geothermal soil warming gradients of up to +6.4 °C in subarctic grasslands (Sigurdsson et al., 2016), we show that soil organic carbon (SOC) stocks decline strongly and linearly with warming (−2.8 ton ha−1 °C−1). Comparison of SOC stock changes following medium-term (5 and 10 years) and long-term (> 50 years) warming revealed that all SOC loss occurred within the first five years of warming, after which continued warming no longer reduced SOC stocks. This rapid equilibration of SOC observed in Andosol suggests a critical role for ecosystem adaptations to warming and could imply short-lived soil carbon-climate feedbacks. Our data further revealed that the soil C loss occurred in all aggregate size fractions, and that SOC losses only occurred in topsoil (0–10 cm). SOC stocks in subsoil (10–30 cm), where plant roots were absent, remained unaltered, even after > 50 years of warming. The observed depth-dependent warming responses indicate that explicit vertical resolution is a prerequisite for global models to accurately project future SOC stocks for this soil type and should be investigated for soils with other mineralogies.
Quantifying and analysing leaching water is essential to understand water and nutrient cycles and the vertical transport of elements through soils. Zero tension lysimeters (ZTLs) have been widely used to capture the soil solution leaching by gravity. This study designed and evaluated a 3D‐printed ZTL (ZTL3D) with specific characteristics and materials to quantitatively capture dissolved element fluxes. By 3D‐printing the ZTLs, we were able to include specific 3D structures and precise details in the design allowing installation of samplers from the surface rather than trenches, and thus avoiding the need for installation trenches to remain open. The ZTLs3D connect directly with the surface, do not depend on secondary collectors, can be installed at any depth, and samplers are easily retractable when dismantling the field set up. The material used, Nylon 12, was tested for dissolved organic carbon (DOC) release. The ZTL3D design was printed in two different external shapes while characteristics and internal design were identical. The difference in external shape was to study the effects of two contrasting types of installation: a cylindrical sampler for vertical installation (by soil coring from the surface) and a rectangular samplers for horizontal installation (from a pit or a trench wall). We installed them at different depths (2, 30 and 75 cm) in a forest soil and conducted rainfall simulation experiments. A water bucket model (WBM), created to calculate the water drainage fluxes that the ZTLs3D should collect, reproduced very well the variation in soil water content measured by soil moisture sensors installed adjacent to the ZTLs3D at 16, 30, 50 and 75 cm depth. Drainage fluxes simulated by the WBM showed that the vertical installation performed better at collecting water at all depths than the horizontal installation, but overall the ZTLs3D failed to collect the simulated amounts of drainage water. Nonetheless, the ZTLs3D did collect leachate water, enabling their chemical analysis. Combining the concentrations in the water collected by the ZTLs3D with the modelled drainage fluxes does allow estimation of DOC‐ and elemental leaching rates. This article presents the novel design of these two types of ZTLs3D because future improvements may result in better performance, and discusses their (dis)agreement with the modelled WBM fluxes. Highlights New 3D‐printed zero tension lysimeters (ZTLs) to capture element fluxes when installed vertically (cylindrical design) or horizontally (cubic design) were tested. Two external sampler shapes were created to optimise the installation process and both collected drainage water successfully. Vertical installation ZTLs worked better than horizontal types, but neither well‐reflected drainage fluxes simulated by water bucket model (WBM). Combined with WBM, both ZTL types provided a reliable method for quantifying nutrient and organic carbon leaching at different soil depths.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.