Department of Ecology, Evolution and Environmental Biology, Columbia University, New York, NY, USA.
Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ, USA.
Glob Chang Biol. 2017 Nov;23(11):4777-4787. doi: 10.1111/gcb.13716. Epub 2017 May 26.
Symbiotic nitrogen (N)-fixing trees can drive N and carbon cycling and thus are critical components of future climate projections. Despite detailed understanding of how climate influences N-fixation enzyme activity and physiology, comparatively little is known about how climate influences N-fixing tree abundance. Here, we used forest inventory data from the USA and Mexico (>125,000 plots) along with climate data to address two questions: (1) How does the abundance distribution of N-fixing trees (rhizobial, actinorhizal, and both types together) vary with mean annual temperature (MAT) and precipitation (MAP)? (2) How will changing climate shift the abundance distribution of N-fixing trees? We found that rhizobial N-fixing trees were nearly absent below 15°C MAT, but above 15°C MAT, they increased in abundance as temperature rose. We found no evidence for a hump-shaped response to temperature throughout the range of our data. Rhizobial trees were more abundant in dry than in wet ecosystems. By contrast, actinorhizal trees peaked in abundance at 5-10°C MAT and were least abundant in areas with intermediate precipitation. Next, we used a climate-envelope approach to project how N-fixing tree relative abundance might change in the future. The climate-envelope projection showed that rhizobial N-fixing trees will likely become more abundant in many areas by 2080, particularly in the southern USA and western Mexico, due primarily to rising temperatures. Projections for actinorhizal N-fixing trees were more nuanced due to their nonmonotonic dependence on temperature and precipitation. Overall, the dominant trend is that warming will increase N-fixing tree abundance in much of the USA and Mexico, with large increases up to 40° North latitude. The quantitative link we provide between climate and N-fixing tree abundance can help improve the representation of symbiotic N fixation in Earth System Models.
共生固氮（N）树种可以驱动 N 和碳循环，因此是未来气候预测的关键组成部分。尽管对气候如何影响固氮酶活性和生理学有详细的了解，但相对而言，对气候如何影响固氮树种丰度知之甚少。在这里，我们使用了来自美国和墨西哥的森林清查数据（超过 125,000 个地块）以及气候数据来回答两个问题：（1）共生固氮树（根瘤菌、放线菌和两种类型的组合）的丰度分布如何随年均温度（MAT）和降水量（MAP）变化？（2）气候变化将如何改变共生固氮树种的丰度分布？我们发现，根瘤菌固氮树种在 MAT 低于 15°C 时几乎不存在，但在 MAT 高于 15°C 时，随着温度升高，它们的丰度增加。我们在整个数据范围内没有发现对温度呈驼峰形响应的证据。根瘤菌树种在干燥的生态系统中比在湿润的生态系统中更丰富。相比之下，放线菌树种在 MAT 为 5-10°C 时丰度最高，在降水中等的地区丰度最低。接下来，我们使用气候范围方法来预测未来固氮树种相对丰度可能发生的变化。气候范围预测显示，由于气温上升，到 2080 年，根瘤菌固氮树种在许多地区可能会变得更加丰富，特别是在美国南部和墨西哥西部。放线菌固氮树种的预测则更为微妙，因为它们对温度和降水的依赖是非单调的。总的来说，主要趋势是，由于变暖，固氮树种的丰度将在美国和墨西哥的大部分地区增加，在北纬 40°附近增加幅度最大。我们提供的气候与固氮树种丰度之间的定量联系可以帮助提高地球系统模型中共生固氮的代表性。
