Precipitation and temperature regulate the carbon allocation process in alpine wetlands: quantitative simulation

Abstract

The quantitative study for the allocation of photosynthetically fixed carbon to plant tissues, soil, and respiratory losses is essential for understanding the key process of carbon (C) cycle. In this study, the measured C flux data was used to validate a process-based denitrification-decomposition (DNDC) model, and the C budget components were simulated and quantitatively separated in the Qinghai-Tibet Plateau alpine wetland ecosystem. The field observation and 50-year climate data in this site were used as input to simulate soil environment change, plant growth, and C allocation for DNDC. The local parameterization, optimization, calibration, and evaluation of the process-based DNDC model were conducted to improve the simulation accuracy of the model and to separate the C budget components of the Zoige alpine wetland ecosystem on the basis of measured C flux data. The results show that the modeled and measured values have good consistency on multiple time scales, and the system shows obvious C sink (− 169.16 g C m−2 yr−1). The plant net primary productivity (NPP) accounted for 53% of gross primary productivity (GPP); the plant autotrophic respiration (Ra) accounts for 61% of ecosystem respiration (Re); and the soil heterotrophic respiration (Rh) accounts for 51% of soil respiration (Rs). Vegetation has the strongest photosynthesis and net C sequestration capacity during the peak growth stage, while the system appears as a C source in the senescence stage. Moreover, Ra dominated during the first four periods of plant growth, while Rh was dominant in the plant senescence stage. There was a negative correlation between environmental factors and NEE and a significant positive relationship with other C budget variables (P < 0.001). Precipitation and temperature regulate the C budgets and C distribution. When soil temperature and monthly precipitation exceeded 7 °C and 18 mm mon−1, the ecosystem switched from C source to C sink. The optimized DNDC model can capture the dynamics of C budget in Zoige alpine wetland, and there are large differences in the function of C source and sink, C allocation, and relative contribution during different plant growth stages. Our work will provide support to predict the changes in C cycle components at regional scales in future climate change scenarios and to formulate measures to mitigate greenhouse effects.