Elemental stoichiometry reflects the interaction between plants, soil, and microorganisms, and links biogeochemical patterns with physiological limitations. The stoichiometry of elements in farmland soil is an important part of the function of the agroecosystem. Soil nitrogen (N), phosphorus (P), and potassium (K) are the main macronutrients in terrestrial ecosystems, which are closely related to biogeochemical cycles. Studying the temporal and spatial variability of soil nutrients in tropical farmland is of great significance for exploring the variation of soil nutrients and promoting the sustainable development of tropical agriculture. In this study, soil samples in the farmland of Hainan Island were collected at three different stages for exploring temporal and spatial variations of N, P, and K stoichiometry. Results showed that soil concentrations of available N, P, and K changed markedly with the temporal and spatial variability. The highest available N, P, and K concentrations appeared at the stage of 2016–2020 with values of 110.40 mg/kg, 51.91 mg/kg, and 82.76 mg/kg, respectively, while their lowest values were observed in 2010–2015 with 66.34 mg/kg, 11.27 mg/kg, and 45.77 mg/kg, respectively. The available nitrogen content in the three time periods first increased and then decreased with the increase of available potassium content, an opposite trend was observed between available nitrogen and phosphorus. The content of N increased in Haikou, Lingao, Ding’an, and P increased in Wengchang, and Lingshui and K increased in Danzhou and Wanning as time increased.

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Glomalin-related soil protein (GRSP), as an important component of soil organic carbon (SOC) pool, is a glycoprotein produced by the hyphae of arbuscular mycorrhizal fungi (AMF), which play a vital role in carbon and nutrient cycling in forest ecosystem. Here we investigated the spatial distribution of GRSP in plant community of the dominated species not associated with AMF based on a typical coniferous and broad-leaved temperate forest in Mt. Changbai, Northeastern China. Spatial distribution of GRSP including easily extractable GRSP (EEG) and total GRSP (TG) is represented by Moran’s I on different soil depth among seven soil layers of 0-5 cm, 5-10 cm, 10-20 cm, 20-30 cm, 30-50 cm, 50-70 cm and 70-100 cm. The concentrations of EEG and TG decreased with the increase of soil depth according to a logarithmic function. The Moran’s I coefficient of GRSP was negative in all soil layers except TG in 20-30 cm and 50-70 cm soil layers. When EEG and TG were considered, the Moran’s I coefficient was positive in majority of soil layers within the separation distance of less than 4 m but in soil layers of 10-20 cm and 20-30 cm for EEG and in 30-50 cm for TG. The largest Moran’s I coefficient including EEG and TG was observed in the soil layer of 5-10 cm. The spatial distribution of GRSP was discrete in typical coniferous and broad-leaved temperate forest, and was affected by mycorrhizal colonization rate, soil organic carbon and total nitrogen.   ********* In press - Online First. Article has been peer reviewed, accepted for publication and published online without pagination. It will receive pagination when the issue will be ready for publishing as a complete number (Volume 47, Issue 4, 2019). The article is searchable and citable by Digital Object Identifier (DOI). DOI link will become active after the article will be included in the complete issue. *********