State Key Laboratory of Earth Surface Processes and Resource Ecology, Faculty of Geographical Science, Beijing Normal University, Beijing 100875, China.
State Key Laboratory of Earth Surface Processes and Resource Ecology, Faculty of Geographical Science, Beijing Normal University, Beijing 100875, China.
Sci Total Environ. 2022 Mar 1;810:152227. doi: 10.1016/j.scitotenv.2021.152227. Epub 2021 Dec 8.
While the organic carbon stored in soil is a sizeable proportion of the total carbon stored in terrestrial ecosystems, it is also a considerable source of greenhouse gas emissions. In this study, we examined how the carbon pool had changed in an area of temperate grassland in Inner Mongolia, China, over a period of 14 years. A field experiment was set up in 2003 and was treated with 6 nitrogen (N) treatments:0, 2, 4, 8, 16, and 32 g·N·m·yr as dry urea (CO(NH)). We collected soil samples in 2017, and divided them into three size aggregates: silt-clay fraction, microaggregate, and small macroaggregate. We determined various soil extracellular enzyme activities of these three categories, namely β-glucosidase (BG), N-acetyl-β-D-glucosaminidase (NAG), acid phosphatase (AP), peroxidase (PER), and phenol oxidase (POX). We found that the soil enzyme activities increased under N additions. In addition, the BG activity was higher, but the PER activity was lower, in the small macroaggregates than the silt-clay fraction. Furthermore, we found that the soil extracellular enzyme activities and soil physico-chemical properties in the small macroaggregates were not correlated. Rather, we found that some of the soil extracellular enzyme activities were negatively correlated with the pH value, microbial biomass carbon (MBC), total organic carbon (TOC), and positively correlated with the inorganic nitrogen content (IN), in the microaggregates and the silt-clay fraction. A key discovery was that the N additions had no effect on the 0-10 cm soil layer (fractions <2000 um) organic carbon pool or the distribution of different-sized aggregates, probably because they were regulated through the changes of plant, soil, and microbial interactions. The results will contribute to improve our understanding of how N additions affect TOC and different aggregate size classes in soil, and will support better predictions of how N deposition might contribute to future climate change.
尽管土壤中储存的有机碳是陆地生态系统中总碳储存量的相当大一部分，但它也是温室气体排放的重要来源。在本研究中，我们调查了中国内蒙古温带草原地区的碳库在 14 年间发生了怎样的变化。2003 年设立了一个野外实验，用 6 种氮（N）处理进行处理：0、2、4、8、16 和 32 g·N·m·yr-1 作为干尿素（CO(NH)）。我们于 2017 年采集了土壤样本，并将其分为三个大小的团聚体：粉粒-粘粒级、微团聚体和小宏团聚体。我们测定了这三种分类的各种土壤细胞外酶活性，即β-葡萄糖苷酶（BG）、N-乙酰-β-D-氨基葡萄糖苷酶（NAG）、酸性磷酸酶（AP）、过氧化物酶（PER）和多酚氧化酶（POX）。我们发现氮添加会增加土壤酶活性。此外，小宏团聚体中的 BG 活性较高，但 PER 活性较低。此外，我们发现小宏团聚体中的土壤细胞外酶活性与土壤理化性质不相关。相反，我们发现一些土壤细胞外酶活性与微团聚体和粉粒-粘粒级中的 pH 值、微生物生物量碳（MBC）、总有机碳（TOC）呈负相关，而与无机氮含量（IN）呈正相关。一个关键发现是，氮添加对 0-10 cm 土壤层（<2000 µm 级）有机碳库或不同大小团聚体的分布没有影响，这可能是因为它们通过植物、土壤和微生物相互作用的变化得到了调节。研究结果将有助于提高我们对氮添加如何影响土壤总有机碳和不同团聚体大小的理解，并支持对氮沉降如何影响未来气候变化的更好预测。
