Study on the biological communities and bioweathering of the marble surfaces of the Hall of Prayer for Good Harvests at the Temple of Heaven (Beijing, China)

Abstract

This study investigates the biological communities and bioweathering of the marble surfaces of the Hall of Prayer for Good Harvests at the Temple of Heaven in Beijing. The dominant organisms are aerophytic cyanobacteria, which thrive in calcareous environments, are drought-resistant, slow-growing, and highly resilient. These cyanobacteria exhibit different community compositions depending on the orientation of the marble surface. On east-facing, warm and humid surfaces, the communities are mainly composed of small filamentous cyanobacteria such as Scytonema sp.2 and coccoid cyanobacteria like Gomphosphaeria sp. On west-facing, hot and humid surfaces, the dominant organisms are Scytonema sp.1 (a small filamentous cyanobacterium) and mosses. On north-facing, cold and humid surfaces, the biological communities mainly consist of coccoid cyanobacteria such as Myxosarcina sp. and Gomphosphaeria sp. On south-facing, hot and dry surfaces, the communities are primarily made up of small or large filamentous cyanobacteria, including Scytonema sp.1 and Nostoc sp. The intensity of weathering observed varies by orientation: South > West > East > North. This pattern aligns with the observed “Cloud Chi Heads” weathering features on surfaces facing different directions. The biological communities on the marble surface display a range of colors, with gray-black being the most common, followed by gray-white, black, brown, and dark brown. The gray-black communities are mainly composed of Myxosarcina sp. and Gomphosphaeria sp. These communities also exhibit various morphologies, including membranous, pilose, carpet-like, leathery, shell-like, and powdery layers. The species composition varies across these morphological types. The growth of aerophytic organisms on rock surfaces is controlled by macroscopic hydrodynamics and micro-topographical features. At the macro scale, in areas with low rainfall intensity, biofilms are sparse and biological weathering is weak. In areas with high rainfall, cyanobacteria-rich “ink bands” can form, leading to intense biological weathering. At the micro scale, micro-topographical features regulate local hydrological conditions and determine colonization patterns: rough, uneven surfaces and discrete water films promote spot-like bio-colonies that lead to solution pores and pits; linear decorations or joints with directional water retention drive linear biological growth, forming solution marks and grooves; smooth, dense surfaces with uniform water film coverage support planar microbial growth, ultimately resulting in overall layer separation from weathering. The mechanism of biological weathering involves the secretion of organic acids by aerophytic organisms. These acids dissolve inorganic salts in the rock, providing nutrients while gradually “eroding” the rock, damaging its surface structure, and leading to progressive weathering. Preventing or reducing the growth of aerophytic organisms is key to slowing the biological weathering of the stone relics on the Hall of Prayer for Good Harvests.