Characteristics of net ecosystem carbon dioxide exchange (NEE) from August to October of Alpine meadow on the Tibetan Plateau, China

Abstract

The Alpine meadow is one of the vegetation types widely distributed on the Tibetan Plateau in China with an area of about 1.2 million square kilometers. The Damxung rangeland station, located in the hinterland of the Tibetan Plateau, is covered with an typical vegetation. The continuous carbon flux data (from August to middle October, 2003) measured with the open-path eddy covariance system was used to analyze the diurnal variation pattern of net ecosystem carbon dioxide exchange (NEE) and its relationship with the environmental factors, such as photosynthetically active radiation (PAR), precipitation, and temperature. Results showed that NEE presented obvious diurnal variation pattern with single-peak of diurnal maximum carbon assimilation at 11: 00-12: 00 (local time) with an average of -0.268 mg CO₂ºm^-2ºs^-1, i.e., -6.08 μmol CO₂ºm^-2ºs^-1. During the daytime, NEE fitted fairly well with PAR in a rectangular hyperbola function with the apparent quantum yield (0.020 3 μmol CO₂ μmol^-1 PAR) and maximum ecosystem assimilation (9.741 1 μmol CO₂ºm^-2ºs^-1). During the night-time, NEE showed a good exponential relation with the soil temperature at 5 cm depth.