The photosynthetic niche breadth of several desert shrubs and their potential ecological significance

The combination of niche theories and plant ecophysiology may show a link between macroscopic ecology and microscopic physiology. The experiment simulated three rainfall treatments representing the minimum, average and maximum annual precipitation found in the Shapotou area. The net photosynthesis rate (Pn) of four dominant desert shrubs (Reaumuria soongorica maximum, Salsola passerina Bge., Artemisia ordosica Krasch. and Caragana korshinskii Komar.) that grow in the arid zone in Northwest China was measured, together with the available environmental resources, photosynthetically active radiation (PAR), air temperature (CT) and volumetric soil moisture (SW). Based on these data and means derived from the Levins niche breadth index, this study calculated the photosynthesis - PAR niche breadth (PBi), the photosynthesis - CT niche breadth (TBi) and the photosynthesis - SW niche breadth (WBi) of the four shrubs. The results showed that PAR was not a directly limiting factor on growth and survival of the four shrubs and the values for PBi were consistent either with the PAR response ranges (R. soongorica and S. passerina) or with the values for Pn (A. ordosica and C. korshinskii), although the values for PBi between the four desert shrubs varied. In accordance with the calculated TBi values, the CT tolerance ranges for photosynthesis also varied among the four desert shrubs. The lowest SWs that stopped photosynthesis varied amongst the four shrubs, and the lower the SW was: the wider the response range and the higher the WBi value. The photosynthetic niche breadth and the photosynthetic response ranges of the four shrubs were in agreement with their ecological breadth and geographic distributions. Thus, some micro-mechanisms can be explained using these relationships such as floral evolution, succession and the varietal development processes of the plant communities of R. soongorica - S. passerine and A. ordosica Krasch. - C. korshinskii Komar. It is also possible to account for the physiological changes that occur in each plant by calculating the photosynthetic niche breadth. These results show that this research methodology can be extended to niche theory and promote the practicality of plant physiological ecology as well as provide new ideas for the study of plant ecology.