Inter-annual variability in carbon dioxide exchange of an oak/grass savanna and open grassland in California
Inter-annual variability in carbon dioxide exchange of an oak/grass savanna and open grassland in California
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DOI：
10.1016/j.agrformet.2007.07.008
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发表时间：
2007-12-10
影响因子：
6.2
通讯作者：
Hehn, Ted
中科院分区：
文献类型：
--
作者：
Ma, Siyan;Baldocchi, Dennis D.;Hehn, Ted
为了了解生态系统碳循环的动态，在加利福尼亚州的橡树-草稀树草原和邻近的草原上和下面测量了二氧化碳通量。这些测量是在2000年至2006年间使用涡旋协方差技术进行的。稀树草原和邻近草地的年净碳交换分别为-155~-56Gm(-2)年(-1)和-88~141Gm(-2)年(-1)。热带草原、草原和乔木树冠的年际变化与生长季节的长短显著相关。我们将NEE划分为两个单独的术语--初级生产力(GPP)和呼吸(生态系统呼吸，R-ECO)--发现稀树草原和草原的GPP和R-ECO主要取决于草地和树木同时活跃时发生的季节性降雨量，而不是取决于年降雨量。研究还发现，NEE受R-ECO和GPP的制约较大，而R-ECO受GPP的制约较大。GPP每增加100Gcm(-2年)，R-ECO增加79Gcm(-2)年(-1)。此外，多年来分别测量稀树大草原上层和下层的二氧化碳交换，使我们能够以一种新的直接方式将RECO划分为异养和自养呼吸项。R-ECO对GPP的敏感度(DR(ECO)/dGPP)和呼吸项基线都为了解当前气候条件和生态系统演替阶段下生态系统吸收CO2的动态变化提供了有用的工具。(C)2007爱思唯尔B.V保留所有权利。
To understand the dynamics of ecosystem carbon cycling, CO2 fluxes were measured over and under an oak-grass savanna and over a proximate grassland in California. The measurements were made from 2000 to 2006 using the eddy covariance technique. Annual net carbon exchange (NEE) ranged from -155 to -56 gC m(-2) year(-1) and from -88 to 141 gC m(-2) year(-1) at the savanna and nearby grassland, respectively. Inter-annual variability in NEE was significantly related to length of growing season for the savanna, grassland, and tree canopy. We partitioned the NEE into two separate terms-primary productivity (GPP) and respiration (ecosystem respiration, R-eco)-and found that the GPP and R-eco of the savanna and grassland depended primarily on the amount of seasonal precipitation that occurred while grass and tree canopies were simultaneously active rather than depending on annual precipitation. We also found that NEE was greatly constrained by both R-eco and GPP and R-eco was significantly constrained by GPP. R-eco increased by 79 gC m(-2) year(-1) with each 100 gC m(-2) year(-1) increase in GPP. In addition, measuring CO2 exchange separately in the overstory and understory of the savanna over multiple years enabled us to partition Reco into heterotrophic and autotrophic respiration terms in a new and direct way. The sensitivity of R-eco to GPP (dR(eco)/dGPP) and the baseline of respiration terms both provide useful tools for understanding the dynamics of ecosystem CO2 uptake under current conditions of climate and ecosystem succession stage. (c) 2007 Elsevier B.V All rights reserved.