J Plant Ecol ›› 2020, Vol. 13 ›› Issue (2): 247-255.DOI: 10.1093/jpe/rtaa007

• Research Articles • Previous Articles    

The relative controls of temperature and soil moisture on the start of carbon flux phenology and net ecosystem production in two alpine meadows on the Qinghai-Tibetan Plateau

Xi Chai1, Peili Shi1,2, *, Minghua Song1, Ning Zong1, Yongtao He1,2, Yingnian Li3, Xianzhou Zhang1,2 and Yanjiao Liu4   

  1. 1 Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Science, 11A, Datun Road, Chaoyang District, Beijing 100101, China, 2 College of Resources and Environment, University of Chinese Academy of Sciences, No. 80 Zhongguancun East Road, Haidian District, Beijing 100190, China, 3 Northwest Institute of Plateau Biology, Chinese Academy of Sciences, No. 23 Xinning road, Xining, Qinghai Province 810008, China, 4 Beijing Zhongnong Futong Horticulture Co., Ltd., No. 17 Qinghua East Road, Haidian District, Beijing 100083, China

    *Corresponding author. E-mail: shipl@igsnrr.ac.cn
  • Received:2019-08-27 Revised:2020-01-21 Accepted:2020-02-10 Online:2020-02-13 Published:2020-04-01

Abstract:

Aims

Variations in vegetation spring phenology are widely attributed to temperature in temperate and cold regions. However, temperature effect on phenology remains elusive in cold and arid/semiarid ecosystems because soil water condition also plays an important role in mediating phenology.

Methods

We used growing degree day (GDD) model and growing season index (GSI) model, coupling minimum temperature (Tmin) with soil moisture (SM) to explore the influence of heat requirement and hydroclimatic interaction on the start of carbon uptake period (SCUP) and net ecosystem productivity (NEP) in two alpine meadows with different precipitation regimes on the Qinghai-Tibet Plateau (QTP). One is the water-limited alpine steppe-meadow, and the other is the temperature-limited alpine shrub-meadow.

Important Findings

We observed two clear patterns linking GDD and GSI to SCUP: SCUP was similarly sensitive to variations in preseason GDD and GSI in the humid alpine shrub-meadow, while SCUP was more sensitive to the variability in preseason GSI than GDD in the semiarid alpine steppe-meadow. The divergent patterns indicated a balance of the limiting climatic factors between temperature and water availability. In the humid meadow, higher temperature sensitivity of SCUP could maximize thermal benefit without drought stress, as evidenced by the stronger linear correlation coefficient (R2) and Akaike’s information criterion (AIC) between observed SCUPs and those of simulated by GDD model. However, greater water sensitivity of SCUP could maximize the benefit of water in semiarid steppe-meadow, which is indicated by the stronger R2 and AIC between observed SCUPs and those of simulated by GSI model. Additionally, although SCUPs were determined by GDD in the alpine shrub-meadow ecosystem, NEP was both controlled by accumulative GSI in two alpine meadows. Our study highlights the impacts of hydroclimatic interaction on spring carbon flux phenology and vegetation productivity in the humid and semiarid alpine ecosystems. The results also suggest that water, together with temperature should be included in the models of phenology and carbon budget for alpine ecosystems in semiarid regions. These findings have important implications for improving vegetation phenology models, thus advancing our understanding of the interplay between vegetation phenology, productivity and climate change in future.

Key words: growing degree day, growing season index, the start of carbon uptake period, net ecosystem production, alpine meadows, Qinghai-Tibet Plateau

摘要:

在温带和寒冷地区,春季植被物候的变化普遍受温度影响。然而,在寒冷地区的干旱/半干旱生态系统中,温度对物候的影响仍难以捉摸,因为土壤水分状况有调节物候的重要作用。利用生长度日(growing degree day, GDD)和生长季节指数(growing season index, GSI)模型,对最低温度(minimum daily temperature, Tmin)与土壤水分(daily soil moisture, SM)进行耦合,探索热量需求和水文气候交互作用对青藏高原(QTP)两个不同降水状况的高寒草甸生态系统碳吸收期开始日期(start of carbon uptake period, SCUP)和净生态系统初级生产力(net ecosystem productivity, NEP)的影响。其中,一种是水分限制的高寒草原草甸生态系统,另一种是温度限制的高寒灌丛草甸生态系统。GDD模型和GSI模型与SCUP明显相关联:在湿润的高寒灌丛草甸生态系统中,SCUP对生长季前GDD和GSI的变化同样敏感;而在半干旱高寒草原草甸生态系统中,与GDD相比,SCUP对生长季前GSI的变化更敏感。这些不同模式表明,限制SCUP的气候因子由温度和水分有效性的平衡来决定。在湿润的高寒草甸生态系统中,在不受干旱胁迫的情况下,较高的SCUP温度敏感性可以最大化热效益,正如观察到的SCUPs与GDD模型模拟具有较高的线性相关系数(R2)和AIC。而在半干旱的草原化草甸中,较高的SCUP水分敏感性可以最大化水分效益,正如观测到的SCUPs与GSI模型模拟具有较高的R2和AIC。此外,虽然在高寒灌丛草甸生态系统中SCUPs由GDD决定,但两个高寒草甸生态系统NEP均受累积GSI控制。本研究重点强调湿润和半干旱高寒草甸生态系统水文气候交互作用对春季碳通量物候和植被生产力的影响;揭示半干旱地区高寒草甸生态系统物候和碳平衡模型中应该包括温度和水分条件。这些结果对改善植被物候模型具有重要意义,从而加深我们对将来植被物候、生产力和气候变化相互作用的理解。

关键词: 生长度日模型, 生长季节指数,  碳吸收期启始日期,  净生态系统生产力,  高山草甸,  青藏高原