Nitrogen stable isotopes reveal enhanced nitrogen losses and altered plant nitrogen uptake strategies in degraded alpine peatlands

Ten sites along a peatland degradation gradient in Zoige were investigated in July 2022 . The ten sites were classified into four degradation levels, including flooded wetlands (FW), wet meadows (WM), moderately-degraded meadows (DM), and severely-degraded meadows (SM) . We set up three 1 m × 1 m quadrats that were at least 50 m apart from each other at each site, and recorded total plant cover and the relative cover of four functional types (i.e., sedge, grass, non-leguminous and leguminous forb) in each quadrat. Aboveground biomass was harvested and placed in paper bags. Five soil cores of 30 cm depth were collected in each quadrat using an auger of 38 mm in diameter. One core was used to measure belowground biomass, and the remaining cores were used for measuring soil chemical properties, including soil δ¹⁵N (‰) (δ¹⁵N_soil), total nitrogen content (STN, g kg^-1), organic carbon content (SOC, g kg^-1), total phosphorus content (STP, g kg^-1), and pH. Soil cores were separated into three layers, i.e., 0–10 cm, 10–20 cm, and 20–30 cm. Samples for measuring belowground biomass were rinsed with running water before placing in paper bags. Samples for measuring other soil properties were homogenized, with plant debris and rocks removed, and were stored at ambient temperature. Additionally, soil samples for measuring soil water content (SWC, g g^-1) and bulk density (BD, g cm^-3) were collected using 100 cm³ cutting rings.

2022年7月，我们对若尔盖（Zoige）泥炭地退化梯度上的10个样点开展了调查。将这10个样点划分为4个退化等级，分别为淹水湿地（Flooded Wetlands, FW）、湿草甸（Wet Meadows, WM）、中度退化草甸（Moderately-degraded Meadows, DM）以及重度退化草甸（Severely-degraded Meadows, SM）。我们在每个样点设置3个间距不小于50米的1米×1米样方，并记录每个样方内的总植物盖度，以及莎草（Sedge）、禾草（Grass）、非豆科杂类草（Non-leguminous Forb）和豆科杂类草（Leguminous Forb）4种功能型植物的相对盖度。采集地上生物量样品并装入纸袋中。使用直径38毫米的土钻，在每个样方内采集5个深度为30厘米的土芯。其中1个土芯用于测定地下生物量，剩余土芯用于测定土壤化学性质，包括土壤δ¹⁵N（‰，记为δ¹⁵N_soil）、全氮含量（Total Nitrogen, STN，单位：g·kg⁻¹）、有机碳含量（Soil Organic Carbon, SOC，单位：g·kg⁻¹）、全磷含量（Total Phosphorus, STP，单位：g·kg⁻¹）以及pH值。将土芯划分为0–10 cm、10–20 cm以及20–30 cm三个土层。用于测定地下生物量的样品需经流水冲洗后再装入纸袋。用于测定其余土壤性质的样品则经过均质化处理，去除植物残体与石块后，置于室温环境下保存。此外，我们使用100 cm³环刀采集用于测定土壤含水量（Soil Water Content, SWC，单位：g·g⁻¹）和土壤容重（Bulk Density, BD，单位：g·cm⁻³）的土样。