Simulated warming enhances the responses of microbial N transformations to reactive N input in a Tibetan alpine meadow

Climate warming promotes deterministic assembly of arbuscular mycorrhizal fungal communities

“…Low temperature is a primary factor limiting microbial activities in the alpine ecosystems (Koch et al, 2007; Zhang et al, 2020), and warming can enhance the rates of soil N and P cycling processes such as mineralization and nitrification, by promoting the activity or shifting community composition of soil microbes (Bai et al, 2013; Salazar et al, 2020). At the same study site, warming has been demonstrated to simulate microbial growth and promote N mineralization and nitrification (Zhang et al, 2020), thereby increasing soil N availability, particularly in the form of NO 3 − (Table 1). Meanwhile, higher P availability was detected under warming conditions (Table 1), which may result from positive effects of warming on both microbial P mineralization and P solubilization (Barrett et al, 2014).…”

“…The native vegetation is dominated by Kobresia graminifolia , Elymus nutans, and Thermopsis lanceolata (Yan et al, 2020). Soil in this region is classified as Cambisol (FAO taxonomy), with soil total C at 98.2 g C kg −1 , soil total N at 6.9 g N kg −1 , and a pH value of 6.0 (Zhang et al, 2020). The experimental site has been fenced off since 2014 to exclude the disturbance from livestock or any other large animals.…”

“…The distance between blocks was 5 m. Because there was no electricity in the field, the warming treatment was achieved with hexagonal open‐top chambers (OTCs) constructed from six transparent poly methyl methacrylate (PMMA) isosceles trapezoidal plates (0.59 m wide at the top, 0.75 m wide at the bottom, and 0.52 m tall). Four OTCs were installed into each plot, which led to an average increase of daily air temperature by 1.54 ± 0.07°C (mean ± SE) throughout the growing season at 15 cm above the ground (see Zhang et al, 2020). In PR plots, PMMA shelters were placed 1 m high above soil surface to intercept 30% of rainfall.…”

“…The rainwater collected from each PR plot was uniformly added to the closest PI plot during the growing season. N input (12 g N m −2 year −1 ) was delivered as urea application twice a year, one (6 g N m −2 year −1 ) each at the beginning (middle May) and middle (late June) of the growing season (Zhang et al, 2020). Soil moisture and atmospheric temperature were continuously recorded by sensors in two of the four blocks from May to September (growing season) every year.…”

“…In cold environments, warming may enhance AMF colonization of roots directly through stimulating hyphal growth or indirectly by increasing plant photosynthesis (Cotton et al, 2015) and subsequent C allocation belowground for AMF (Heinemeyer & Fitter, 2004). Also, warming often stimulates microbial growth and enhances soil mineralization, nitrification, and thus nitrogen (N) availability (Rustad et al, 2001; Zhang et al, 2020). High N availability in soil can in return reduce plant dependence on AMF for N uptake, and thus decrease AMF biomass and alter AMF community composition in favor of the species with less extensive extraradical hyphal networks (Qiu et al, 2021; Treseder et al, 2018).…”