Patterns of nitrogen-fixing tree abundance in forests across Asia and America

Symbiotic nitrogen (N)‐fixing trees can provide large quantities of new N to ecosystems, but only if they are sufficiently abundant. The overall abundance and latitudinal abundance distributions of N‐fixing trees are well characterised in the Americas, but less well outside the Americas. Here, we characterised the abundance of N‐fixing trees in a network of forest plots spanning five continents, ~5,000 tree species and ~4 million trees. The majority of the plots (86%) were in America or Asia. In addition, we examined whether the observed pattern of abundance of N‐fixing trees was correlated with mean annual temperature and precipitation. Outside the tropics, N‐fixing trees were consistently rare in the forest plots we examined. Within the tropics, N‐fixing trees were abundant in American but not Asian forest plots (~7% versus ~1% of basal area and stems). This disparity was not explained by mean annual temperature or precipitation. Our finding of low N‐fixing tree abundance in the Asi...共生固氮树木（Symbiotic nitrogen (N)-fixing trees）可为生态系统输入大量新增氮素，但前提是其种群丰度足够高。目前学界已对美洲地区共生固氮树木的总体丰度及其纬度丰度分布特征开展了充分表征，但在美洲以外区域的相关研究仍较为匮乏。 本研究基于覆盖五大洲、涵盖约5000种树木与近400万株个体的森林样地网络，对共生固氮树木的丰度进行了系统表征。其中86%的样地分布于美洲或亚洲。此外，我们还分析了观测到的共生固氮树木丰度格局与年平均气温、年降水量的相关性。 在热带以外区域，本次调查的森林样地中共生固氮树木始终处于低丰度状态。在热带区域内，美洲森林样地中的共生固氮树木丰度显著高于亚洲样地（分别约占胸高断面积与植株总数的7%与1%），而这种丰度差异无法通过年平均气温或年降水量予以解释。我们在亚洲区域观测到的共生固氮树木低丰度这一结果……