The greening of the Northern Great Plains and its biogeochemical precursors
The greening of the Northern Great Plains and its biogeochemical precursors
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DOI：
10.1111/gcb.15115
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发表时间：
2020-05-12
影响因子：
11.6
通讯作者：
Finney, Bruce
中科院分区：
文献类型：
--
作者：
Brookshire, E. N. Jack;Stoy, Paul C.;Finney, Bruce
近几十年来，全球大部分陆地表面的植被绿色度都有所增加。预计这一趋势将继续下去，特别是在北方纬度地区，但未来的绿化可能会受到植物碳（C）同化所需的养分供应的限制，以应对CO2富集（eCO（2））。eCO（2）影响叶片化学和功能，但这些影响与气候在植被绿化驱动模式中的相对强度仍不确定。在这里，我们结合联合收割机的绿化卫星测量与植物碳和氮（N）浓度和稳定同位素比（三角洲C-13和三角洲N-15）在北美北方大平原（NGP）的135年的记录，以检查绿化的N约束。我们记录了过去二十年来的显著绿化，净绿化增长比例最高的是干燥和最温暖的地区。与绿化的气候依赖性相反，我们发现叶水平细胞间CO2和内在水分利用效率的空间均匀增加，跟踪大气CO2的上升。尽管绿化的空间变化很大，我们发现在过去的世纪，持续和气候无关的叶面氮下降。平行下降叶片三角洲N-15和C：N比的增加点减少N的可用性作为可能的原因。在我们的研究区域，绿化的同时增加和叶面氮的下降表明，在过去的二十年中，氮的利用效率（NUE）增加。然而，我们的研究结果表明，植物NUE响应可能不足以维持观察到的绿化趋势在NGP草原在未来。
Vegetation greenness has increased across much of the global land surface over recent decades. This trend is projected to continue-particularly in northern latitudes-but future greening may be constrained by nutrient availability needed for plant carbon (C) assimilation in response to CO2 enrichment (eCO(2)). eCO(2) impacts foliar chemistry and function, yet the relative strengths of these effects versus climate in driving patterns of vegetative greening remain uncertain. Here we combine satellite measurements of greening with a 135 year record of plant C and nitrogen (N) concentrations and stable isotope ratios (delta C-13 and delta N-15) in the Northern Great Plains (NGP) of North America to examine N constraints on greening. We document significant greening over the past two decades with the highest proportional increases in net greening occurring in the dries and warmest areas. In contrast to the climate dependency of greening, we find spatially uniform increases in leaf-level intercellular CO2 and intrinsic water use efficiency that track rising atmospheric CO2. Despite large spatial variation in greening, we find sustained and climate-independent declines in foliar N over the last century. Parallel declines in foliar delta N-15 and increases in C:N ratios point to diminished N availability as the likely cause. The simultaneous increase in greening and decline in foliar N across our study area points to increased N use efficiency (NUE) over the last two decades. However, our results suggest that plant NUE responses are likely insufficient to sustain observed greening trends in NGP grasslands in the future.