Abstract
Selection of appropriate tree species is an important forest management decision that may affect sequestration of carbon (C) in soil. However, information about tree species effects on soil C stocks at the global scale remains unclear. Here, we quantitatively synthesized 850 observations from field studies that were conducted in a common garden or monoculture plantations to assess how tree species type (broadleaf vs. conifer), mycorrhizal association (arbuscular mycorrhizal (AM) vs. ectomycorrhizal (ECM)), and N-fixing ability (N-fixing vs. non-N-fixing), directly and indirectly, affect topsoil (with a median depth of 10 cm) C concentration and stock, and how such effects were influenced by environmental factors such as geographical location and climate. We found that (1) tree species type, mycorrhizal association, and N-fixing ability were all important factors affecting soil C, with lower forest floor C stocks under broadleaved (44%), AM (39%), or N-fixing (28%) trees respectively, but higher mineral soil C concentration (11%, 22%, and 156%) and stock (9%, 10%, and 6%) under broadleaved, AM, and N-fixing trees respectively; (2) tree species type, mycorrhizal association, and N-fixing ability affected forest floor C stock and mineral soil C concentration and stock directly or indirectly through impacting soil properties such as microbial biomass C and nitrogen; (3) tree species effects on mineral soil C concentration and stock were mediated by latitude, MAT, MAP, and forest stand age. These results reveal how tree species and their specific traits influence forest floor C stock and mineral soil C concentration and stock at a global scale. Insights into the underlying mechanisms of tree species effects found in our study would be useful to inform tree species selection in forest management or afforestation aiming to sequester more atmospheric C in soil for mitigation of climate change.
Highlights
In the face of global climate change and elevated atmospheric carbon dioxide (CO2) concentrations, forest soils play an important role in global carbon (C) cycling and are potential terrestrial C sinks (Pan et al, 2011)
We extracted studies from our search that met the following criteria: (1) studies were carried out in forest ecosystems; (2) at least one response variable of C or litter production was reported; (3) tree species were identified by the Latin name; (4) only common garden or monoculture plantations with replicated plots within the same site were included in our database; (5) the means and sample sizes of the selected response variables were available or could be calculated from the related publications
Litter production, forest floor C stock, and mineral soil C concentration and stock all differed significantly according to tree species type, mycorrhizal association, and N-fixing ability (Fig. 3)
Summary
In the face of global climate change and elevated atmospheric carbon dioxide (CO2) concentrations, forest soils play an important role in global carbon (C) cycling and are potential terrestrial C sinks (Pan et al, 2011). A more recent hypothesis has suggested that tree species with foliar litter traits conducive to fast decomposition will lead to more pronounced microbial stabilization and transformation of plant litter C through greater production of microbial residues (Cotrufo et al, 2013), supporting greater mineral soil C stocks. The latter tree species are mainly deciduous and in a temperate climate, some of these are associated with arbuscular mycorrhizae (AM). It remains to be confirmed if one of these hypotheses has general validity or if they are valid within different contexts
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