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Soil water content strongly affects permafrost dynamics by changing the soil thermal properties. However, the movement of liquid water, which plays an important role in the heat transport of temperate soils, has been under-represented in boreal studies. Two different heat transport models with and without convective heat transport were compared to measurements of soil temperatures in four boreal sites with different stand ages and drainage classes. Overall, soil temperatures during the growing season tended to be over-estimated by 2-4°C when movement of liquid water and water vapor was not represented in the model. The role of heat transport in water has broad implications for site responses to warming and suggests reduced vulnerability of permafrost to thaw at drier sites. This result is consistent with field observations of faster thaw in response to warming in wet sites compared to drier sites over the past 30 years in Canadian boreal forests. These results highlight that representation of water flow in heat transport models is important to simulate future soil thermal or permafrost dynamics under a changing climate.

A major obstacle to selecting the most appropriate crops and closing the yield gap in many areas of the world is a lack of site-specific soil information. Accurate information on soil properties is critical for identifying soil limitations and the management practices needed to improve crop yields. However, acquiring accurate soil information is often difficult due to the high spatial and temporal variability of soil properties at fine scales and the cost and inaccessibility of laboratory-based soil analyses. With recent advancements in predictive soil mapping, there is a growing expectation that soil map predictions can provide much of the information needed to inform soil management. Yet, it is unclear how accurate current soil map predictions are at scales relevant to management. The main objective of this study was to address this issue by evaluating the site-specific accuracy of regional-to-global soil maps, using Ghana as a test case. Four web-based soil maps of Ghana were evaluated using a dataset of 6514 soil profile descriptions collected on smallholder farms using the LandPKS mobile application. Results from this study revealed that publicly available soil maps in Ghana lack the needed accuracy (i.e., correct identification of soil limitations) to reliably inform soil management decisions at the 1–2 ha scale common to smallholders. Standard measures of map accuracy for soil texture class and rock fragment class predictions showed that all soil maps had similar performance in estimating the correct property class. Overall soil texture class accuracies ranged from 8 %–14 % but could be as high as 38 %–64 % after accounting for uncertainty in the evaluation dataset. Soil rock fragment class accuracies ranged from 26 %–29 %. However, despite these similar overall accuracies, there were substantial differences in soil property predictions among the four maps, highlighting that soil map errors are not uniform between maps. To better understand the functional implications of these soil property differences, we used a modified version of the FAO Global Agro-Ecological Zone (GAEZ) soil suitability modeling framework to derive soil suitability ratings for each soil data source. Using a low-input, rain-fed, maize production scenario, we evaluated the functional accuracy of map-based soil property estimates. This analysis showed that soil map data significantly overestimated crop suitability for over 65 % of study sites, potentially leading to ineffective agronomic investments by farmers, including cash-constrained smallholders. [ABSTRACT FROM AUTHOR]

Black spruce (Picea mariana (Mill.) B.S.P.) forest stands range from well drained to poorly drained, typically contain large amounts of soil organic carbon (SOC), and are often underlain by permafrost. To better understand the role of soil drainage class in carbon dioxide ([CO.sub.2]) exchange and decomposition, we measured soil respiration and net [CO.sub.2] fluxes, litter decomposition and litterfall rates, and SOC stocks above permafrost in three Alaska black spruce forest stands characterized as well drained (WD), moderately drained (MD), and poorly drained (PD). Soil respiration and net [CO.sub.2] fluxes were not significantly different among sites, although the relation between soil respiration rate and temperature varied with site ([Q.sub.10]: WD > MD > PD). Annual estimated soil respiration, litter decomposition, and groundcover photosynthesis were greatest at PD. These results suggest that soil temperature and moisture conditions in shallow organic horizon soils at PD were more favorable for decomposition compared with the better drained sites. SOC stocks, however, increase from WD to MD to PD such that surface decomposition and C storage are diametric. Greater groundcover vegetation productivity, protection of deep SOC by permafrost and anoxic conditions, and differences in fire return interval and (or) severity at PD counteract the relatively high near-surface decomposition rates, resulting in high net C accumulation. Resume: Les peuplements d'epinette noire (Picea mariana (Mill.) B.S.P.) sont etablis sur des stations variant de bien a mal drainee, dont le sol contient typiquement une grande quantite de carbone organique et qui reposent souvent sur une couche de pergelisol. Pour mieux comprendre le role de la classe de drainage sur les echanges de dioxyde de carbone ([CO.sub.2]) et sur la decomposition, nous avons mesure les flux de respiration du sol et de [CO.sub.2] net, les taux de decomposition et de deposition de la litiere, et les stocks de carbone organique du sol (COS) au-dessus de la couche de pergelisol dans trois peuplements d'epinette noire de l'Alaska correspondant a des stations bien (BD), relativement (RD) et mal drainees (MD). Les flux de respiration du sol et de [CO.sub.2] net n'etaient pas significativement differents entre les stations, bien que la relation entre le taux de respiration du sol et la temperature variat d'une station a l'autre (Q10: BD > RD > MD). La respiration estimee du sol, la decomposition de la litiere et la photosynthese du couvert vegetal au sol avaient des valeurs annuelles plus elevees sur la station MD. Ces resultats indiquent que la temperature du sol et l'humidite des horizons organiques minces du sol de la station MD sont plus favorables a la decomposition comparativement aux stations mieux drainees. Cependant, les stocks de COS augmentaient en passant de la station BD a la station RD et de la station RD a la station MD, de sorte que la decomposition de la litiere et l'entreposage du C sont diametralement opposes. Une plus grande productivite du couvert vegetal au sol, une protection du COS en profondeur par le pergelisol et par les conditions anoxiques, ainsi que des differences dans l'intervalle entre les feux ou la severite des feux sur la station MD contrebalancent le taux relativement eleve de decomposition pres de la surface, ce qui produit une forte accumulation nette de C. [Traduit par la Redaction], Introduction Boreal soils contain a major portion of the world's soil organic carbon (C), and the distribution of boreal soil C is spatially heterogeneous across the landscape (Billings 1987; Trumbore [...]