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

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 gs-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 (WUEi) 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 (Anet and Vcmax) 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 Anet and gs and a negative relationship with WUEi. Our findings should be useful for understanding the underlying mechanisms of the response of alpine plants growth and alpine meadow ecosystem to global change.

Diurnal and Seasonal Variations in the Photosynthetic Characteristics and the Gas Exchange Simulations of Two Rice Cultivars Grown at Ambient and Elevated CO2

“…A net -C i curves were fit to the FvCB models (Equations 1, 2) to solve the photosynthetic parameters including maximum ribulose 1⋅5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylation rate (V cmax , μmol m –2 s –1 ), potential light saturated electron transport rate (J max , μmol m –2 s –1 ), and leaf dark respiration (R d , μmol m –2 s –1 ), respectively. A net -C i curves were then fit to the BWB (Equation 3) and Medlyn (Equation 4) models to solve the parameters of m and g 1 ( Wolz et al, 2017 ; Wang D. et al, 2018 ).…”

Warming Treatment Methodology Affected the Response of Plant Ecophysiological Traits to Temperature Increases: A Quantitive Meta-Analysis

“…Predictions of response to global warming may be derived from experimental and observational studies (Tilman, 1989; Wang et al, 2008, 2018; Knapp et al, 2012). While both types of study are common, relatively few authors have investigated whether they produce similar predictions or reflect reality (Dunne et al, 2004; Knapp et al, 2018).…”

“…Many manipulative experiments controlling physical and environmental factors have been conducted around the world to investigate the potential effects of global change on plants and terrestrial ecosystems (Sage and Kubien, 2007; Rustad, 2008; Wang et al, 2018). However, the methodology used in these experiments was different in their research settings, treatment intensities and durations and targeted species.…”

Plant Evolution History Overwhelms Current Environment Gradients in Affecting Leaf Chlorophyll Across the Tibetan Plateau

“…The symbiont of rhizobium costs a lot of resources and energy (Zahran, 1999 ). Besides, more N needs to be invested in resisting the stress of coldness, high radiation, and drought (Wang et al, 2018 ). These indicate that legume tends to increase investment in belowground resources and abiotic stress resistance, which may reduce aboveground allocation and further decrease leaf Chl.…”