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Carbon allocation in boreal black spruce forests across regions varying in soil temperature and precipitation

TitleCarbon allocation in boreal black spruce forests across regions varying in soil temperature and precipitation
Publication TypeJournal Article
Year of Publication2008
AuthorsVogel, JG, Bond-Lamberty, BP, Schuur, EAG, Gower, ST, Mack, MC, O’Connell, KEB, Valentine, DW, Ruess, RW
JournalGlobal Change Biology

A common hypothesis for northern ecosystems is that low soil temperatures inhibit plantproductivity. To address this hypothesis, we reviewed how separate components ofecosystem carbon (C) cycling varied along a soil temperature gradient for nine welldrained,relatively productive boreal black spruce (Picea mariana Mill. [B.S.P.]) forests inAlaska, USA, and Saskatchewan and Manitoba, Canada. Annual soil temperature[expressed as soil summed degree days (SDD)] was positively correlated with abovegroundnet primary productivity (ANPP), while negatively correlated with total belowgroundcarbon flux (TBCF). The partitioning of C to ANPP at the expense of rootprocesses represented a nearly 1 : 1 tradeoff across the soil temperature gradient, whichimplied that the amount of C cycling through these black spruce ecosystems wasrelatively insensitive to variation in SDD. Moreover, the rate at which C accumulatedin the ecosystem since the last stand replacing fire was unrelated to SDD, but SDD waspositively correlated to the ratio of spruce-biomass : forest-floor-mass. Thus, plant partitioningof C and the distribution of ecosystem C were apparently affected by soiltemperature, although across regions, precipitation co-varied with soil temperature.These two factors likely correlated with one another because of precipitation’s influenceon soil heat balance, suggesting that a soil temperature–precipitation interaction could beresponsible for the shifts in C allocation. Nonetheless, our results highlight that for thisboreal ecosystem, ANPP and TBCF can be negatively correlated. In tropical andtemperate forests, TBCF and ANPP have been reported as positively correlated, andour results may reflect the unique interactions between soil temperature, forest flooraccumulation, rooting depth, and nutrient availability that characterize the black spruceforest type.

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