Effects of 8-Year Nitrogen and Phosphorus Treatments on the Ecophysiological Traits of Two Key Species on Tibetan Plateau

Dan Wang; Tianqi Ling; Pengpeng Wang; Panpan Jing; Jiazhi Fan; Hao Wang; Yaoqi Zhang

doi:10.3389/fpls.2018.01290

Effects of 8-Year Nitrogen and Phosphorus Treatments on the Ecophysiological Traits of Two Key Species on Tibetan Plateau

Front Plant Sci. 2018 Sep 11:9:1290. doi: 10.3389/fpls.2018.01290. eCollection 2018.

Authors

Dan Wang¹, Tianqi Ling¹, Pengpeng Wang¹, Panpan Jing¹, Jiazhi Fan¹, Hao Wang¹, Yaoqi Zhang²

Affiliations

¹ International Center for Ecology, Meteorology and Environment, Jiangsu Key Laboratory of Agricultural Meteorology, Nanjing University of Information Science and Technology, Nanjing, China.
² School of Forestry and Wildlife Sciences, Auburn University, Auburn, AL, United States.

Abstract

Understanding how nitrogen (N) and/or phosphorus (P) addition affects plants carbon- and water- related ecophysiological characteristics is essential for predicting the global change impact on the alpine meadow ecosystem structure and function in carbon and water cycling. The Qinghai-Tibetan Plateau (QTP) with the largest alpine meadow in the world is regarded as the third pole in the earth and has been experiencing increased atmospheric N deposition. In this project, we focused on two key species (Elymus dahuricus and Gentiana straminea) of the alpine meadow on the Tibetan Plateau and investigated the variability of photosynthetic and stomatal responses to 8-year N and/or P treatments through field measurements and modeling. We measured photosynthesis- and g_s-response curves to generate parameter estimates from individual leaves with two widely used stomatal models (the BWB model and MED model) for validation of growth and ecosystem models and to elucidate the physiological basis for observed differences in productivity and WUE. We assessed WUE by means of gas exchange measurements (WUE_i) and stable carbon isotope composition (Δ¹³C) to get the intrinsic and integrated estimates of WUE of the two species. P and N+P treatments, but not N, improved the photosynthetic capacity (A_net and V_cmax) for both species. Stomatal functions including instaneous measurements of stomatal conductance, intrinsic water-use efficiency and stomatal slope parameters of the two widely used stomatal models were altered by the addition of P or N+P treatment, but the impact varied across years and species. The inconsistent responses across species suggest that an understanding of photosynthetic, stomatal functions and water-use should be evaluated on species separately. WUE estimated by Δ¹³C values had a positive relationship with A_net and g_s and a negative relationship with WUE_i. Our findings should be useful for understanding the underlying mechanisms of the response of alpine plants growth and alpine meadow ecosystem to global change.

Keywords: integrated water-use efficiency; intrinsic water-use efficiency; photosynthesis; stomatal conductance; stomatal slope parameter.