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Three of the six measurement plots at each location have received experimental N deposition (3?g?-N?m?2?yr?1) since 1994. We measured specific root respiration rates and N concentrations of roots from four size classes ( http://www.selleck.cn/products/gsk-j4-hcl.html depths was used in combination with specific respiration rates to assess the response of whole-root-system respiration. Root N and respiration rate were greater for smaller diameter roots and roots at shallow depths. In addition, root N concentrations were significantly greater under chronic N deposition, particularly for larger diameter roots. Specific respiration rates and root biomass were unchanged for all depths and size classes, thus whole-root-system respiration was not altered by chronic N deposition. Higher root N concentrations in combination with equivalent specific respiration rates under experimental N deposition resulted in a lower ratio of respiration to tissue N. These results indicate that relationships between root respiration rate and N concentration do not hold if N availability is altered significantly. For these forests, http://www.selleckchem.com/products/BEZ235.html use of the ambient respiration to N relationship would over-predict actual root system respiration for the chronic N deposition treatment by 50%. ""Tropical savannas are typically highly productive yet fire-prone ecosystems, and it has been suggested that reducing fire frequency in savannas http://www.selleckchem.com/products/byl719.html could substantially increase the size of the global carbon sink. However, the long-term demographic consequences of modifying fire regimes in savannas are difficult to predict, with the effects of fire on many parameters, such as tree growth rates, poorly understood. Over 10 years, we examined the effects of fire frequency on the growth rates (annual increment of diameter at breast height) of 3075 tagged trees, at 137 locations throughout the mesic savannas of Kakadu, Nitmiluk and Litchfield National Parks, in northern Australia. Frequent fires substantially reduced tree growth rates, with the magnitude of the effect markedly increasing with fire severity. The highest observed frequencies of mild, moderate and severe fires (1.0, 0.8 and 0.4?fires?yr?1, respectively) reduced tree growth by 24%, 40% and 66% respectively, relative to unburnt areas. These reductions in tree growth imply reductions in the net primary productivity of trees by between 0.19?t?C?ha?1?yr?1, in the case of mild fires, and 0.51?t?C?ha?1?yr?1, in the case of severe fires. Such reductions are relatively large, given that net biome productivity (carbon sequestration potential) of these savannas is estimated to be just 1�C2?t?C?ha?1?yr?1.