Long‐term soil warming alters fine root dynamics and morphology, and their ectomycorrhizal fungal community in a temperate forest soil

Abstract

Climate warming is predicted to affect temperate forests severely, but the response of fine roots, key to plant nutrition, water uptake, soil carbon, and nutrient cycling is unclear. Understanding how fine roots will respond to increasing temperature is a prerequisite for predicting the functioning of forests in a warmer climate. We studied the response of fine roots and their ectomycorrhizal (EcM) fungal and root‐associated bacterial communities to soil warming by 4°C in a mixed spruce‐beech forest in the Austrian Limestone Alps after 8 and 14 years of soil warming, respectively. Fine root biomass (FRB) and fine root production were 17% and 128% higher in the warmed plots, respectively, after 14 years. The increase in FRB (13%) was not significant after 8 years of treatment, whereas specific root length, specific root area, and root tip density were significantly higher in warmed plots at both sampling occasions. Soil warming did not affect EcM exploration types and diversity, but changed their community composition, with an increase in the relative abundance of Cenoccocum at 0–10 cm soil depth, a drought‐stress‐tolerant genus, and an increase in short‐ and long‐distance exploration types like Sebacina and Boletus at 10–20 cm soil depth. Warming increased the root‐associated bacterial diversity but did not affect their community composition. Soil warming did not affect nutrient concentrations of fine roots, though we found indications of limited soil phosphorus (P) and potassium (K) availability. Our findings suggest that, in the studied ecosystem, global warming could persistently increase soil carbon inputs due to accelerated fine root growth and turnover, and could simultaneously alter fine root morphology and EcM fungal community composition toward improved nutrient foraging.

Long-term soil warming decreases microbial phosphorus utilization by increasing abiotic phosphorus sorption and phosphorus losses

“…Moreover, colloid-associated P contributes up to 91% of total subsurface P fluxes in forest soils 27 . At our site, warming increased fine root production (+128%) more than fine root biomass (+17%), which implies a fast root turnover in warmed soil 24 . When roots die, their previous volume expansion can be preserved via the formation of macropores that might further generate effective and long-lasting preferential flow paths in soils, especially in undisturbed forests 25 , 26 .…”

“…Greater biomass production indicates higher plant P uptake, which removes P from soil and allocates this to the plant compartment, in turn reducing the total soil P pools. Kwatcho Kengdo et al 24 , who studied fine root production, morphology, and element contents at the same site, reported a 128% increase in fine root production and a 17% increase in fine root biomass, but unaltered fine root P contents in the warming treatment compared to the control treatment. These results imply a higher P demand of the trees for fine root production, but they do not account for potentially greater plant P immobilization in aboveground tissues 17 .…”

“…Asterisks show the significance level of warming effects based on the results of mixed-effects models ( * p < .05; ** p < .01; *** p < .001). The results of plant P uptake are derived from Kengdo et al, 2022 24 from the same site in 2019. …”

Soil moisture and temperature dynamics in juvenile and mature forest as a result of tree growth, hydrometeorological forcings, and drought

“…Related to these studies, it could be that the meteorological drought in 2018 (SPI‐1.7. UKCEH, 2022) and persistent higher topsoil temperature in the juvenile plantation (Figure 8a) could be driving root growth (Joslin et al, 2000; Kwatcho Kengdo et al, 2022; Salazar et al, 2020). Similarly, mycorrhizal network growth pulses may play an important role in forest ecosystem resilience (Simard et al, 2012).…”

Effects of High Temperature-Triggered Transcriptomics on the Physiological Adaptability of Cenococcum geophilum, an Ectomycorrhizal Fungus

“…The study showed that the increase of soil carbon input caused by temperature warming changed the composition of the soil fungal community, the relative abundance of Cenococcum geophilum Fr. ( C. geophilum ) increased at 0–10 cm soil depth, and the relative abundance of Sebacina and Boletus increased at 10–20 cm soil depth [ 15 ]. Temperature also changed the colonization and growth of ECMF mycelia.…”