Photosynthetic, physiological, and morphological characteristics of Haloxylon ammodendron assimilation twigs in Minqin Oasis

Haloxylon ammodendron is a dominant species in arid zones and plays an important role in regional ecosystem stability. In order to more fully understand the photosynthetic, physiological, and morphological characteristics of H. ammodendron and to determine how they adapt to environmental factors, we employed comparative analytical methods to study these traits at the end of May and the end of July in Minqin Oasis. Our results showed that the change trends for assimilation twigs were bimodal on a daily scale for net photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs) in May and July. The Pn reduction was mainly due to stomatal limitation factors in May; the Pn reduction was caused by non-stomatal limitation factors in July. Morphological characteristics, including area (LA), fresh weight (FW), dry weight (DW), water content (LWC), dry matter content (LDMC), and specific leaf area (SLA) increased by 79%, 94%, 99%, 33%, 14%, and 3%, respectively, in July more than in May. Area was the most representative morphological character of the assimilation twigs. The environmental impact factors of H. ammodendron were mainly photosynthetically active (PAR), air relative humidity (RH), and soil water content (SWC) in May. Other factors of importance were atmospheric temperature (Ta) and SWC in July.