关键词: 天山北坡, DNDC模型, 施肥阈值, 净初级生产力, 蒙特卡洛分析

Abstract:

In the context of climate change and increasing human activities， a series of ecological problems have emerged in arid and semi-arid regions as one of the important and very vulnerable components of the terrestrial ecosystem. Exploring the impact of climate change and human activities on the net primary productivity （NPP） is of great significance for the rational use of natural resources and the sustainable development of agriculture and animal husbandry. Nitrogen fertilization is a way to promote increased NPP and appropriate fertilization can improve the NPP of grassland. To further explore the potential use of N fertilization， this study investigated four grassland types， alpine meadow （AM）， mid-mountain forest meadow （MMFM）， low mountain dry grassland （LMDG） and plain desert grassland （PDG）， distributed along the altitude gradient on the northern slope of Tianshan Mountains， and employed a denitrification-decomposition model to analyze the NPP responses of the typical grassland ecosystem in this region to the application of different nitrogen fertilizers， and reveal the nitrogen fertilizer threshold and the optimal fertilization strategy. It was found that： 1） Appropriate nitrogen addition led to an increase in NPP of all types of grassland ecosystems， but there was a threshold value for the response of grassland NPP to fertilizer application， and different types of grassland NPP had different threshold values. There was no unified optimal fertilization method applicable to the four types of grassland. LMDG grassland ecosystem is the most sensitive to nitrogen application. 2） The maximum NPP in PDG grassland was achieved by applying 100 kg·ha^-1 nitrate twice a year， and the maximum NPP was 68.72 g C·m^-2·yr^-1. The maximum NPP fertilization strategy in LMDG grassland is 260 kg·ha^-1 of urea applied twice a year， and the maximum NPP value is 263.28 g C·m^-2·yr^-1. The maximum NPP of MMFM was achieved by applying 80 kg·ha^-1 of urea once a year， and the maximum NPP is 171.22 g C·m^-2·yr^-1. In AM grassland， anhydrous ammonia reached the maximum value of NPP （114.62 g C·m^-2·yr^-1） with the minimum amount of fertilizer （60 kg·ha^-1） and was the best nitrogen fertilizer in this grassland type. 3） The result of Monte Carlo uncertainty analysis shows that PDG and LMDG is more sensitive to fertilization time， and the effect of fluctuation in fertilizer application rate variation on LMDG and MMFM is more obvious.

Key words: northern slope of Tianshan Mountain, DNDC model, nitrogen fertilizer threshold, net primary productivity, Monte Carlo analysis