Abstract:

This research investigated the physiological and ecological adaptive mechanisms of Agropyron mongolicum to nitrogen （N） addition. Soluble sugar， starch， carbon （C）， N and phosphorus （P） contents in roots and leaves of A. mongolicum were determined at different levels of nitrogen addition （0， 0.8， 1.6， 2.4 and 4.0 g N·m^-2·yr^-1）. The effects of N addition on the non-structural carbohydrate （NSCs） content and the C∶N∶P stoichiometry in leaves and roots of A. mongolicum were analyzed. The results showed that adding the appropriate amount of N （2.4 g N·m^-2·yr^-1） favoured the accumulation of NSCs and C， N and P contents in the leaves and roots of A. mongolicum， and the responses of different organs were significantly different （P<0.05）. Leaf NSCs content was significantly positively correlated with leaf N， soluble sugar， starch content， C∶P and N∶P； And significantly negatively correlated with leaf P content and C∶N （P<0.05）. Root NSCs content was significantly positively correlated with root C， N content， C∶P， N∶P， soluble sugar and starch content （P<0.05）. Leaf and root N∶P were the main factors affecting the accumulation of soluble sugar； The N content of roots and P content of leaves collectively affected starch synthesis； Leaf P content， root N content and root N∶P were collectively the major factors affecting the accumulation of NSCs in A. mongolicum. In summary， appropriate N addition relieved N limitation， while the addition of large amounts of N produced an imbalance between N and P and exacerbated P limitation. Therefore， optimization of nitrogen fertilizer application and appropriate phosphorus addition should be considered in the establishment and management of artificial A. mongolicum grasslands and in the restoration of degraded grasslandsunder future climate change scenarios.

Key words: leaf, root, non-structural carbohydrates, stoichiometry, nutrient strategy