关键词: 半干旱区, 叶片氮分配, 光合氮利用效率, 最大净光合速率, 油蒿, 赖草

Abstract: Abstract Aims Studying the adaptation mechanisms of species in the context of climate change has been a concern in plant ecology. Investigating the effect of leaf nitrogen allocation of desert species on the photosynthetic capacity of plants help with understanding their adaptive capacity under changing climate. Methods This study selected two common desert species, Artemisia ordosica and Leymus secalinus, in Yanchi, Northwest China. The effects of the parameters of leaf nitrogen allocation on the maximum net photosynthetic rate (Amax) of the two species were analyzed using in-situ measurements of photosynthetic light- and CO2-response curves, leaf traits, and enviromental variables from May to October 2021. Important findings The results showed that the mean leaf nitrogen content per unit mass (Nmass) was about 0.02 g·g-1 for both species. The mean values of Amax and the distribution proportion of leaf nitrogen in photosynthetic system (Pp) for Artemisia ordosica were 22.44 μmol CO2·m-2·s-1 and 42.9%, respectively. The mean values of Amax and Pp of Leymus secalinus were 11.99 μmol CO2·m-2·s-1 and 27.5%, respectively, which were lower than those of Artemisia ordosica. During the water deficit period in middle growing season, Amax and Pp decreased for Artemisia ordosica and remaind relatively unchanged for Leymus secalinus. Compared with Leymus secalinus, Amax of Artemisia ordosica was more affected by leaf nitrogen distribution. The main controlling factor of Amax were Pp and leaf nitrogen distribution in carboxylation system (Pc) in Artemisia ordosica and Leymus secalinus, respectively. In the middle growing season with low soil moisture, the Nmass decreased for both species, photosynthetic nitrogen use efficiency (PNUE) decreased in Artemisia ordosica due to its greater sensitivity of the nitrogen distribution ratio to soil moisture and more nitrogen invesment in non-photosynthetic organisms and thus higher stress resistance, and remained relatively stable in Leymus secalinus. The Amax in Artemisia ordosica was greater than Leymus secalinus during the observation period due to its relatively high Pp. The diferences between two desert species in varitions in leaf nitrogen allocation and leaf photosynthetic capacity indicates that the research area might be dominated by shrub species Artemisia ordosica under changing climate.

Key words: semi-arid zone, leaf nitrogen allocation, photosynthetic nitrogen use efficiency, maximum net photosynthetic rate, Artemisia ordosica, Leymus secalinus