Leaf spectral responses of Poa crymophila to nitrogen deposition and climate change on Qinghai-Tibetan Plateau

Abstract

Temperature and nitrogen (N) are limited factors on the Qinghai-Tibetan Plateau (QTP). Climate change and increasing N deposition on the QTP have posed threats to the sustainability of alpine ecosystems. To examine plant spectral responses to N deposition and climate change, we measured leaf spectral reflectance of Poa crymophila, a common forage species grown in alpine meadow (AM) and alpine steppe (AS) on the eastern QTP under four N addition treatments (CK, 8, 40, 72 kg N ha −1 yr −1). We used natural climate gradients from colder and drier AS to warmer and wetter AM to simulate the climate change on the QTP. Results showed that both N deposition and climate change had significant effects on entire visible and near-infrared regions (p < 0.05), but the interactive effects were insignificant (p> 0.05). Enhanced visible absorption, increased near-infrared reflection, a red shift for red edge and a blue shift for green peak were observed with increasing N addition levels. The modified red edge simple ratio index and photochemical reflective index increased gradually in response to N addition (p < 0.05). These responses indicated that N deposition may make leaf wider and thicker, increase leaf chlorophyll content and photochemical efficiency, and enhance photosynthetic capacity. Climate warming and wetting had opposite effects from N deposition on leaf reflectance of Poa crymophila. These observations showed the potential to monitor the status of Poa crymophila under future climate change and N deposition with leaf spectral measurements.