N and P resorption in a pioneer shrub (Artemisia halodendron) inhabiting severely desertified lands of Northern China

Nutrient resorption is an important conservation mechanism for plants to overcome nutrient limitation in the less fertile area of desertified land. In the semi-arid Horqin Sandy Land of Northern China, the shrub Artemisia halodendron usually colonizes into the bare ground of severely desertified land as a pioneer species. It is, therefore, expected that A. halodendron will be less dependent on current nutrient uptake through efficient and proficient resorption of nutrients. In this study, we found that averaged nitrogen (N) and phosphorus (P) concentrations in senesced leaves significantly varied from 12.3 and 1.2 mg/g in the shifting sand dune to 15.9 and 1.9 mg/g in the fixed sand dune, respectively, suggesting that foliar N and P resorption of A. halodendron were more proficient in the shifting sand dune. In particular, positive relationships between nutrient concentrations in senesced leaves and soil nutrient availability indicate that A. halodendron in infertile habitats is more likely to manage with a low level of nutrients in senesced leaves, giving this species an advantage in infertile soil. Moreover, foliar N- and P-resorption efficiencies and proficiencies showed limited inter-annual variability although annual precipitation varied greatly among 2007-2009. However, N and P resorption of A. halodendron were not more efficient and proficient than those previously reported for other shrubs, indicating that the pioneer shrub in sand dune environments does not rely more heavily than other plants on the process of resorption to conserve nutrients. Incomplete resorption of nutrients in A. halodendron suggests that senesced-leaf fall would return litter with high quality to the soil, and thereby would indirectly improve soil nutrient availability. The restoration of desertified land, therefore, may be accelerated after A. halodendron pioneers into shifting sand dunes.