Chin J Plant Ecol ›› 2021, Vol. 45 ›› Issue (5): 444-455.DOI: 10.17521/cjpe.2020.0135

• Research Articles • Previous Articles     Next Articles

Variations of nitrogen and phosphorus limitation along the environmental gradient in alpine grasslands on the Northern Xizang Plateau

ZONG Ning1, SHI Pei-Li1,2,*(), ZHAO Guang-Shuai3, ZHENG Li-Li1,2, NIU Ben1, ZHOU Tian-Cai1,2, HOU Ge1,2   

  1. 1Lhasa Plateau Ecological Research Station, Key Laboratory of Ecosystem Network Observation and Modelling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China
    2University of Chinese Academy of Sciences, Beijing 100049, China
    3Economics and Development Research Center, National Forestry and Grassland Administration, Beijing 100714, China
  • Received:2020-05-08 Accepted:2020-08-10 Online:2021-05-20 Published:2020-11-02
  • Contact: SHI Pei-Li
  • Supported by:
    the National Key R&D Program of China(2017YFA0604802);the National Key R&D Program of China(2016YFC0501803);National Natural Science Foundation of China(31870406);National Natural Science Foundation of China(41703079);the Second Tibetan Plateau Scientific Expedition and Research (STEP) Program(2019QZKK0302)

Abstract:

Aims Understanding the mode of nutrient limitation on ecosystem net primary production is an important issue of modern ecology. Nutrient availability is a key determinant of ecosystem dynamics, but the relationship between soil resource availability and ecosystem nutrient limitation is still unclear.
Methods A series of nitrogen and phosphorus nutrient addition experiments were set up in four types of alpine grasslands (alpine meadow, alpine meadow-steppe, alpine steppe and alpine desert-steppe) along the precipitation gradient on the Northern Xizang, to systematically study the effects of nitrogen and phosphorus addition on different types of alpine grasslands, and to explore the nitrogen and phosphorus limitation models of different alpine grasslands.
Important findings The results showed that: (1) The effects of nitrogen and phosphorus addition on different alpine grasslands varied. Nitrogen addition significantly increased the aboveground biomass of alpine meadows and alpine meadow grasslands, but had no effect on alpine meadows and alpine desert grasslands. The addition of phosphorus alone had no significant effect on the four alpine grasslands, while the addition of nitrogen and phosphorus had a promoting effect on the aboveground biomass of the four alpine grasslands. (2) With the decrease of precipitation, the nitrogen limitation index of the alpine grasslands gradually decreased from 1.18 to 0.52-0.64, and the nutrient limitation mode transitioned from nitrogen limitation to co-limitation by nitrogen and phosphorus; the phosphorus limitation index was negative in the alpine meadow-steppe and alpine steppe, indicating that phosphorus addition alone has side effects on these two grassland types. These results suggest that alpine meadow is mainly limited by nitrogen availability, and phosphorus addition alone has side effects; the alpine meadow-steppe is between the nitrogen limit and the joint nitrogen and phosphorus limitation, and phosphorus addition alone also has side effects; the alpine steppe is limited by both nitrogen and phosphorus availability, and the addition of phosphorus has side effects; the alpine desert-steppe is jointly limited by nitrogen and phosphorus availability. These results show that nutrient limitation mode transits from nitrogen limitation to nitrogen and phosphorus co-limitation with the decrease of precipitation. This study implies that the impacts of increasing nitrogen deposition under future climate change on different types of alpine grasslands may be different. Additionally, the differences in nitrogen and phosphorus limitation mode should also be taken into consideration when nutrient addition is used to restore different types of degraded alpine grasslands.

Key words: control experiment, nitrogen and phosphorus limitation, grassland type, plant functional group