Data from: Drivers of foliar 15N trends in southern China over the last century

Foliar stable nitrogen (N) isotopes (δ15N) generally reflect N availability to plants and have been used to infer about changes thereof. However, previous studies of temporal trends in foliar δ15N have ignored the influence of confounding factors, leading to uncertainties on its indication to N availability. In this study, we measured foliar δ15N of 1,811 herbarium specimens from 12 plant species collected in southern China forests from 1920 to 2010. We explored how changes in atmospheric CO2, N deposition and global warming have affected foliar δ15N and N concentrations ([N]) and identified whether N availability decreased in southern China. Across all species, foliar δ15N significantly decreased by 0.82‰ over the study period. However, foliar [N] did not decrease significantly, implying N homeostasis in forest trees in the region. The spatiotemporal patterns of foliar δ15N were explained by mean annual temperature (MAT), atmospheric CO2 (PCO2), atmospheric N deposition, and foliar [N]. The spatiotemporal trends of foliar [N] were explained by MAT, temperature seasonality, PCO2, and N deposition. N deposition within the rates from 5.3 – 12.6 kg N ha-1 yr-1 substantially contributed to the temporal decline in foliar δ15N. The decline in foliar δ15N was not accompanied by changes in foliar [N] and therefore does not necessarily reflect a decline in N availability. This is important to understand changes in N availability, which is essential to validate and parameterize biogeochemical cycles of N.植物叶片稳定氮（N）同位素（δ¹⁵N）通常可反映植物可利用氮素水平，既往研究常借此推断氮素有效性的动态变化。然而，过往针对叶片δ¹⁵N时间变化趋势的研究往往忽略了混杂因素的影响，导致其在指示氮素有效性时存在不确定性。本研究测定了1920年至2010年间采自中国南方森林的12种植物共1811份标本馆标本的叶片δ¹⁵N值，探讨了大气CO₂、氮沉降及全球变暖如何影响叶片δ¹⁵N与氮浓度（[N]），并解析了中国南方地区的氮素有效性是否出现下降。整体而言，所有受试物种的叶片δ¹⁵N在研究时段内显著下降了0.82‰；但叶片氮浓度未出现显著下降，暗示该区域林木存在氮稳态特征。叶片δ¹⁵N的时空分布格局可由年平均气温（MAT）、大气CO₂分压（PCO₂）、大气氮沉降及叶片氮浓度予以解释，而叶片氮浓度的时空变化趋势则受年平均气温、气温季节变率、大气CO₂分压及氮沉降共同调控。当氮沉降速率介于5.3~12.6 kg N·ha⁻¹·yr⁻¹区间时，其对叶片δ¹⁵N的时间下降趋势具有显著贡献。叶片δ¹⁵N的下降并未伴随叶片氮浓度的同步变化，因此其未必指示氮素有效性的降低。这一发现对于理解氮素有效性的动态变化至关重要，而氮素生物地球化学循环的验证与参数化亦依赖于此类研究。

搜集汇总

背景与挑战

背景概述

该数据集包含1920年至2010年间中国南方森林12种植物物种的1811个标本的叶片稳定氮同位素（δ15N）和氮浓度数据。研究发现，叶片δ15N在过去一个世纪中显著下降，但叶片氮浓度未显著下降，这主要由大气CO2、氮沉降和全球变暖等因素驱动，表明δ15N下降不一定反映氮可用性的降低，对理解氮生物地球化学循环至关重要。