Accumulation and spatial homogeneity of nutrients within termite (Odontotermes yunnanensis) mounds in the Xishuangbanna region, SW China

Abstract

Fungus-growing termites play a prominent role in nutrient cycling in tropical ecosystems by building numerous mounds with differing properties compared to adjacent soils. However, far less is known about the nutrient variability within the mounds and the nutrient stocks in whole mounds. Here, we investigated the spatial distribution of nutrients and their related nutrient stocks within active mounds (built by Odontotermes yunnanensis), abandoned mounds, and adjacent soils in Xishuangbanna, southwestern China. Detailed sampling was conducted in the vertical section of an active mound, an abandoned mound, and an adjacent soil, and soils were also sampled along the central vertical line from the surface to a 1.60 m layer in four active mounds, four abandoned mounds, and four adjacent soils. The samples were collected along their central vertical line at depths of 0, 10, 30, 50, 70, 90, 120, and 160 cm. We found that, compared to the corresponding values in adjacent soils, the nutrient stocks (except for NH4+, exchangeable Na and exchangeable Mg) of organic carbon, total N, exchangeable K, exchangeable Ca, hydrolysable N, available P, and NO3− were increased, on average, by 47.8%, 25.3%, 31.6%, 545.3%, 42.8%, 49.9%, and 620.8%, respectively, in the active mounds. In the abandoned mounds, the nutrient stocks of organic carbon, total N, exchangeable K, hydrolysable N, available P, and NO3− were higher, on average, by 43.5%, 22.4%, 23.3%, 43.7%, 50.4%, and 48.0%, whereas the nutrient stocks of exchangeable Na, exchangeable Ca, exchangeable Mg, and NH4+ were lower by 17.0%, 67.5%, 76.4%, and 44.4%, respectively. High spatial homogeneity and weak or no spatial dependence of nutrient distributions (except for available P and exchangeable cations) were found in the active mounds, whereas high heterogeneity and moderate or strong spatial dependence of nutrient distributions were observed in the abandoned mounds and adjacent soils. The results indicated that the accumulation and spatial distribution of the studied nutrients within termite mounds were not only related to termite activities but were also affected by environmental factors, such as erosion and leaching, and invasion by plants. Our study demonstrates that termite mounds are “hot spots” of nutrients and provides evidence supporting conjectures about the homogeneity of physicochemical properties within mound structures.