Surprising relationships between soil pH and microbial biomass and activity in a northern hardwood forest

Abstract

Soil microbes mediate major biogeochemical processes in forest ecosystems. Soil pH is considered a "master variable" controlling these processes and many biogeochemical processes in turn in uence pH. Long-term measurements of soil pH, microbial biomass carbon (C) and nitrogen (N) content, microbial respiration, potential net N mineralization and nitri cation rates, denitri cation potential, and soil nitrate (NO 3 -) and ammonium (NH + 4 ) concentrations have occurred since 1994 at the Hubbard Brook Experimental Forest (HBEF), a northern hardwood forest in New Hampshire, USA.Naturally acidic soils at the HBEF have been further acidi ed by anthropogenic acid deposition. Soils in a HBEF watershed have been experimentally treated with calcium silicate to ameliorate acid deposition. While we expected to observe strong positive relationships between soil pH and microbial biomass/activity, weak and/or curvilinear relationships between microbial biomass and activity and soil pH were evident, with peaks at unexpectedly low values (~ 4.5) and values decreased at higher pH values, especially in the calcium-treated soils. It is likely that complexities in plant: microbial interactions inhibit and/or mask microbial response to changes in pH in these acidic soils. These resultsraise fundamental questions about pH as a controller of microbial processes and how ecosystems recover in response to decreases in acid deposition.

Effects of Past Sulfur Deposition on the Soil Microbial Biomass at Spruce Forest Sites

“…We found the same pattern in total and dissolved soil contents, which were also highest at Dav. This indicates for the mineral topsoil that microbial C, N, and S are positively related to soil content but negatively to pH, as shown in recent studies [27,53]. As the MBS contents are considered to be the most active S pool in S-turnover in soil, higher MBS contents indicate a greater S availability for higher plants [26].…”

“…However, unexpected effects of pH changes on microbial biomass and activity in forest soils were also observed in northern hardwood forest plots, and underlying microbial processes are not completely understood [53]. Liming of acidified soils during recovery from pollution has a strong influence on the pH-dependence of microbial activity and therefore crucially impacts S mineralization processes.…”

Aridity threshold for alpine soil nitrogen isotope signature and ecosystem nitrogen cycling

“…In agreement with this, the random forest result showed that among multiple factors, soil N‐cycling traits (e.g., TN, BA, MBN, and denitrifying genes) significantly explained soil δ 15 N changes in wetter sites, which provides robust evidence that 15 N enrichment under relative drought conditions may largely result from strong soil N losses through microbe‐driven N transformations under high N availability conditions. Additionally, this microbe‐driven mechanism of soil 15 N enrichment is further supported by the pronounced contribution of soil pH to soil δ 15 N. As a key factor shaping microbial structure and function, soil pH strongly affects soil N‐cycling microbial communities (Ontman et al., 2023; Rousk et al., 2010; Scarlett et al., 2021). Our results showed that pH was the most pronounced driver of soil δ 15 N in wetter sites, with dramatically different pH values under different aridity conditions (Figure S5), indirectly highlighting the contribution of microbe‐driven N cycling to soil δ 15 N. Overall, these findings show that in wetter regions, soil 15 N closely tracked with soil N dynamics, suggesting that soil 15 N isotopes can accurately reflect soil N cycling and N availability in low aridity environments (Figure 5).…”

“…In agreement with this, the random forest result showed that among multiple factors, soil N-cycling traits (e.g., TN, BA, MBN, and denitrifying genes) significantly explained soil δ 15 N changes in wetter sites, which provides robust evidence that 15 N enrichment under relative drought conditions may largely result from strong soil N losses through microbe-driven N transformations under high N availability conditions. Additionally, this microbe-driven mechanism of soil 15 N enrichment is further supported by the pronounced contribution of soil pH to soil δ 15 N. As a key factor shaping microbial structure and function, soil pH strongly affects soil N-cycling microbial communities (Ontman et al, 2023;Rousk et al, 2010;Scarlett et al, 2021). Our with increasing aridity.…”

Physical and chemical soil quality and litter stock in agroforestry systems in the Eastern Amazon

“…The practice of burning plant residues and the use of mineral fertilizers may have contributed to the increase in soil acidity over time, as these practices reduce soil pH and favor the release of hydrogen ions (H+) and aluminum (Al + 3) (Chaves et al 2020). This continuous acidi cation process may be intensi ed due to base losses by leaching, dissolution reactions of CO 2 in the soil solution, dissociation of H + ions from organic and inorganic radicals by microbial activity(Ontman et al 2023).…”