Comprehensive characterization of an aspen (<i>Populus tremuloides</i>) leaf litter sample that maintained ice nucleation activity for 48 years

Abstract

Abstract. Decaying vegetation was determined to be a potentially important source of atmospheric ice nucleation particles (INPs) in the early 1970s. The bacterium Pseudomonas syringae was the first microorganism with ice nucleation activity (INA) isolated from decaying leaf litter in 1974. However, the ice nucleation characteristics of P. syringae are not compatible with the characteristics of leaf litter-derived INPs since the latter were found to be sub-micron in size, while INA of P. syringae depends on much larger intact bacterial cells. Here we determined the cumulative ice nucleation spectrum and microbial community composition of the historic leaf litter sample 70-S-14 collected in 1970 that conserved INA for 48 years. The majority of the leaf litter-derived INPs were confirmed to be sub-micron in size and to be sensitive to boiling. Culture-independent microbial community analysis only identified Pseudomonas as potential INA. Culture-dependent analysis identified one P. syringae isolate, two isolates of the bacterial species Pantoea ananatis, and one fungal isolate of Mortierella alpina as having INA among 1170 bacterial colonies and 277 fungal isolates, respectively. Both Pa. ananatis and M. alpina are organisms that produce heat-sensitive sub-micron INPs. They are thus both likely sources of the INPs present in sample 70-S-14 and may represent important terrestrial sources of atmospheric INPs, a conclusion that is in line with other recent results obtained in regard to INPs from soil, precipitation, and the atmosphere.

Surfaces of silver birch (<i>Betula pendula</i>) are sources of biological ice nuclei: in vivo and in situ investigations

“…Through strong winds at the ground level, INMs could be aerosolized through abrasive dislodgment and transported further. Another pathway would be that the aqueous INM extracts on the ground form a liquid film and get aerosolized during the mechanical impact of following rain droplets, similar to the bioaerosol generation mechanism suggested by Joung et al 2017, Wang et al (2016) and Kim et al (2020). Thereafter, splashinduced aerosol can be transported further during turbulent wind events and convection.…”

Best practices for precipitation sample storage for offline studies of ice nucleation in marine and coastal environments

“…INPs have been sampled in clouds and precipitation for decades (e.g., Rogers et al, 1998;Vali, 1971Vali, , 1966 to measure abundances, probe their compositions and investigate the extent to which they impact the properties of clouds. There are several caveats to consider when inferring in-cloud INP concentrations or properties from precipitation samples (Petters and Wright, 2015), including sweep-out of additional INPs as the hydrometeor traverses the atmosphere below the cloud (Vali, 1974) and heterogeneous chemistry due to adsorption or absorption of gases (Hegg and Hobbs, 1982;Kulmala et al, 1997;Lim et al, 2010). However, assessing the composition of INPs in precipitation samples is more straightforward than cloud particles.…”

“…Storage protocols vary widely, including total storage time; time between collection and storage; and temperature fluctuations between collection, shipment and storage (if these details are provided at all; see summary Table S1 in the Supplement). Storage temperatures range from −80 • C (Vali et al, 1971) to +4 • C (e.g., Petters and Wright, 2015;Failor et al, 2017;Joyce et al, 2019), yet generally samples are stored between +4 and −20 • C. Reported storage intervals range between hours (Schnell et al, 1977;Christner et al, 2008) to 48 years (Vasebi et al, 2019).…”

“…Schnell (1977) reported significant losses in fog and seawater samples after storage at room temperature for short periods (6-11 h). Several studies have reported on the lability of commercially available dust and biological IN entities in storage above 0 • C or under freezing conditions, including Arizona test dust and Snomax ® (Perkins et al, 2020;Polen et al, 2016;Wex et al, 2015), and similar labilities could affect the INPs of similar composition in precipitation samples (Creamean et al, 2013;Martin et al, 2019). Considering the abundance of precipitation-based INP studies, the lack of bounds on potential impacts of storage on INP concentration measurements represents a critical uncertainty in conclusions derived from data on stored samples.…”

Surfaces of Silver Birch (<i>Betula pendula</i>) are Sources of Biological Ice Nuclei: <i>In-vivo</i> and <i>In-situ</i> Investigations

“…Additionally, decayed leaf litter was found to be a potent source for INPs (Conen et al, 2016;Conen et al, 2017;Schnell and Vali, 1973), some of which may be stable for almost 50 years (Vasebi et al, 2019). Conen et al (2017) found that the emission of these INPs (active at temperatures above -8°C) increases in autumn and it is hypothesized that the vegetation could contribute to local climate.…”