Department of Ecology, School of Life Science, Nanjing University, Nanjing 210046, China.
Nanjing Institute of Environmental Science, Ministry of Environmental Protection of the People's Republic of China, Nanjing 210042, China.
Sci Total Environ. 2019 Feb 20;652:671-682. doi: 10.1016/j.scitotenv.2018.10.295. Epub 2018 Oct 22.
Net primary productivity (NPP) and carbon use efficiency (CUE) are common ecological indicators for assessing the terrestrial carbon cycle. However, despite their widespread use, considerable uncertainties exist toward the response patterns of NPP and CUE to climate variability along an aridity gradient, especially for grassland ecosystems. The aridity index (AI) was calculated in this study to specify arid-humid zones across the global grassland ecosystem. The dynamics of grassland NPP, CUE, and their dependence on climate under different AI levels from 2000 to 2013 were investigated. Results showed that the NPP and CUE of grasslands demonstrated a slightly increasing trend with regional increasing precipitation in most AI zones, except for arid regions (AR) from 2000 to 2013. The NPP and CUE of grasslands exhibited a remarkable spatial heterogeneity in different AI zones. High NPP values mainly occurred in the dry and sub-humid (DSH) and humid (HU) regions of Southern Hemisphere with warm and wet climate. High CUE values were mostly found in the HU of the Northern Hemisphere with cold and wet climate. In addition, low NPP and CUE values were observed in most parts of AR and semi-AR (SAR) with hot and dry climate. Overall, the NPP and CUE of grasslands were significantly affected by precipitation at the global scale. Specifically, grassland NPP was positively correlated with the mean annual precipitation (MAP) in SAR and AR, but negatively related with the MAP in the HU region. The positive correlation between NPP and mean annual temperature (MAT) was found only for HU regions. Grassland CUE indicated a positive relation with MAP, but a negative relation was observed with MAT in all AI zones. The correlation coefficients between CUE and MAP decreased from AR to HU regions. This finding indicated that grassland CUE was highly sensitive to precipitation in dry areas, but this relationship weakened in HU ecosystems.
净初级生产力 (NPP) 和碳利用效率 (CUE) 是评估陆地碳循环的常用生态指标。然而，尽管它们被广泛应用，但对于 NPP 和 CUE 对干旱梯度气候变异性的响应模式仍存在相当大的不确定性，特别是对于草原生态系统。本研究中计算了干旱指数 (AI)，以明确全球草原生态系统的干旱-湿润带。研究了 2000 年至 2013 年不同 AI 水平下草原 NPP、CUE 及其对气候的依赖性的动态变化。结果表明，在大多数 AI 区，随着区域降水量的增加，草原的 NPP 和 CUE 呈略微增加趋势，但在 2000 年至 2013 年的干旱区 (AR) 除外。不同 AI 区的草原 NPP 和 CUE 表现出显著的空间异质性。高 NPP 值主要出现在南半球干和半湿润 (DSH) 和湿润 (HU) 地区，气候温暖湿润。高 CUE 值主要出现在北半球 HU 地区，气候寒冷湿润。此外，在大多数 AR 和半干旱 (SAR) 地区，NPP 和 CUE 值较低，气候炎热干燥。总体而言，全球范围内，草原 NPP 和 CUE 受降水影响显著。具体来说，SAR 和 AR 草原 NPP 与年平均降水量 (MAP) 呈正相关，但与 HU 区的 MAP 呈负相关。仅在 HU 区发现 NPP 与年平均气温 (MAT) 呈正相关。草原 CUE 与 MAP 呈正相关，但在所有 AI 区与 MAT 呈负相关。CUE 与 MAP 的相关系数从 AR 区向 HU 区逐渐降低。这表明草原 CUE 对干旱地区的降水高度敏感，但在 HU 生态系统中，这种关系减弱。
