We analyzed leaf traits related to carbon-fixation, nutrient conservation strategies, and decomposability and their relationships with potential N-mineralization and microbial N in soil in 19 species of 5 dominant life forms growing in 40 sites across a regional humidity gradient in northern Patagonia. We hypothesized that (1) the shifting of species and life forms across the humidity gradient is related to a shifting in traits of green and senesced leaves with some overlapping among life forms, and (2) leaf traits associated with litter decomposition are related to the potential dynamics of soil-N across the humidity gradient. LMA in green leaves and P-resorption efficiency decreased with humidity while concentrations of lignin and total phenolics in green and senesced leaves and P concentration in senesced leaves increased with humidity. Soil C and N concentrations were positively correlated to humidity. Increasing soil N concentration was related to increasing rates of absolute (per unit soil mass) potential net N-mineralization and microbial-N flush. Relative (per unit N mass) potential net N-mineralization and microbial-N flush decreased with soil N and were inversely correlated to lignin concentration and C/N ratio in senesced leaves. We found overlapping in N concentration and C/N ratio in green and senesced leaves, P concentration in green leaves, and N resorption among species and life forms across the humidity gradient. We concluded that (1) leaf traits related to carbon fixation and the decomposition pathway significantly varied with humidity and were not overlapped between plant life forms from dry and humid habitats, (2) the largest overlapping among species and plant life forms across the gradient occurred in those leaf traits related to N conservation in the plant, and (3) life forms from humid habitats produce more recalcitrant litter that induce lower rates of relative potential net N mineralization (per unit N) than those of dry habitats.

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Selective sheep grazing in the Patagonian Monte induces the reduction of total and perennial grass cover, species replacement within life forms, and the increase in dominance of long-lived evergreen woody plants with slow growth rates and high concentration of secondary compounds in leaves. We hypothesized that these changes in the canopy structure induced by sheep grazing will affect the mass, chemistry and decomposability of leaf litter and fine roots. We selected two sites in the Patagonian Monte, representative of ungrazed and grazed vegetation states. At each site, we assessed canopy structure (total cover and absolute and relative grass and shrub cover), monthly leaf litterfall, and fine-root biomass and production in the upper soil (15 cm). We also estimated the rates of mass, C, soluble phenolics, lignin and N decay in litterbags containing both leaf litter and fine roots of each site under field conditions during two consecutive years. The ungrazed site exhibited higher total plant cover, absolute and relative grass-and shrub-cover than the grazed one. Leaf litterfall was lower at the grazed site than at the ungrazed site. Fineroot production did not vary between sites. Leaf litter and fine root tissues had higher concentration of secondary compounds at the grazed than at the ungrazed site. However, fine roots showed lower mass and C decay than leaf litter, attributable to the predominant secondary compound (lignin and soluble phenolics, respectively). Leaf litter decomposed slower but released more N during decay at the ungrazed than at the grazed site, probably due to its low concentration of secondary compounds. We concluded that changes in canopy structure induced by grazing disturbance such as those explored in our study could reduce leaf litterfall mass and increase the concentration of secondary compounds of both leaf litter and fine roots leading to slow N release to soil during decay.

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