Indicators of nitrogen conservation in Austrocedrus chilensis forests along a moisture gradient in Argentina

Plant nitrogen conservation which may affect, for instance, rates of litter decomposition, soil N mineralization and N availability is thought to vary along gradients of soil fertility. Since Austrocedrus chilensis is adapted to a wide moisture gradient, we hypothesed that different intensities of N conservation would be found depending on site characteristics. We studied four sites along a moisture gradient in the Andean-Patagonian Region of Argentina, representative of the three A. chilensis forest-types (marginal, compact and mixed forests), and measured the following indicators of N conservation: (i) carbon, nitrogen and C/N ratio in young, mature and senescent leaves, total soil litter and soil; (ii) lignin concentration and lignin/N ratio in senescent leaves and total litter, and (iii) potential soil N mineralization during a 16-week incubation. A. chilensis showed a strong capacity to conserve N: (i) low N concentration in both young and mature leaves (10 and 6.5 g kg(-1), respectively); (ii) high N resorption proficiency (5.1 g N kg(-1) in senescent leaves) and N use efficiency (200), and (iii) high values of C/N, lignin and lignin/N in senescent leaves (107, 250 g kg(-1) and 50, respectively), and total litter (36, 420 g kg(-1) and 33, respectively). Some indicators (resorption proficiency, C/N in senescent leaves and lignin/N in total litter) were independent of site characteristics, while others (N and C/N in green leaves and lignin in litter) showed significant differences, suggesting a higher capacity to conserve N in the intermediate sites of the gradient (compact forests). Contrary to expectations, the marginal forest (drier, less fertile soils) showed the lowest values of Lignin in litter, the highest N concentrations in green leaves and the highest rates of potential N mineralization. (C) 1998 Elsevier Science B.V. All rights reserved.