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Empirical and model-based estimates of spatial and temporal variations in net primary productivity in semi-arid grasslands of Northern China

机译：中国北方半干旱草原净初级生产力时空变化的基于经验和模型的估计

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摘要

Spatiotemporal variations in net primary productivity (NPP) reflect the dynamics of water and carbon in the biosphere, and are often closely related to temperature and precipitation. We used the ecosystem model known as the Carnegie-Ames-Stanford Approach (CASA) to estimate NPP of semiarid grassland in northern China counties between 2001 and 2013. Model estimates were strongly linearly correlated with observed values from different counties (slope = 0.76 (p < 0.001), intercept = 34.7 (p < 0.01), R2 = 0.67, RMSE = 35 g C·m-2·year-1, bias = -0.11 g C·m-2·year-1). We also quantified inter-annual changes in NPP over the 13-year study period. NPP varied between 141 and 313 g C·m-2·year-1, with a mean of 240 g C·m-2·year-1. NPP increased from west to east each year, and mean precipitation in each county was significantly positively correlated with NPP—annually, and in summer and autumn. Mean precipitation was positively related to NPP in spring, but not significantly so. Annual and summer temperatures were mostly negatively correlated with NPP, but temperature was positively correlated with spring and autumn NPP. Spatial correlation and partial correlation analyses at the pixel scale confirmed precipitation is a major driver of NPP. Temperature was negatively correlated with NPP in 99% of the regions at the annual scale, but after removing the effect of precipitation, temperature was positively correlated with the NPP in 77% of the regions. Our data show that temperature effects on production depend heavily on recent precipitation. Results reported here have significant and far-reaching implications for natural resource management, given the enormous size of these grasslands and the numbers of people dependent on them.
机译：净初级生产力（NPP）的时空变化反映了生物圈中水和碳的动态，并且通常与温度和降水密切相关。我们使用称为卡内基-艾姆斯-斯坦福方法（CASA）的生态系统模型估算了2001年至2013年间中国北方各县半干旱草原的NPP。模型估算值与不同县的观测值高度线性相关（坡度= 0.76（p <0.001），截距= 34.7（p <0.01），R 2 = 0.67，RMSE = 35 g C·m -2 ·year -1 ，偏差= -0.11 g C·m -2 ·year -1 ）。我们还量化了13年研究期内NPP的年际变化。 NPP在141和313 g C·m -2 ·年 -1 之间变化，平均值为240 g C·m -2 · year -1 。 NPP每年从西向东增加，并且每个县的平均降水量与NPP呈正相关（每年一次，在夏季和秋季）。春季平均降水量与NPP呈正相关，但与春季的NPP没有明显关系。全年和夏季温度与NPP呈负相关，但温度与春季和秋季NPP呈正相关。在像素尺度上的空间相关性和偏相关性分析证实了降水是NPP的主要驱动力。在年尺度上，温度与NPP呈负相关，在99％的地区，但除去降水影响后，温度与77％的区域与NPP呈正相关。我们的数据表明温度对生产的影响在很大程度上取决于近期的降水。考虑到这些草原的巨大面积和依赖这些草原的人数，这里报告的结果对自然资源管理具有重大而深远的影响。

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