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Extreme climatic events (ECEs), such as hurricanes, significantly affect biogeochemical processes and their intensity is predicted to increase. We documented the immediate and short-term consequences of the impact of Hurricane Jova on such processes in primary undisturbed tropical dry forest at the Estación de Biología Chamela. Data from our long-term study in five contiguous small watersheds were used to provide perspective to the hurricane effects. Carbon (C), nitrogen (N) and phosphorus (P) concentrations and fluxes were measured in runoff, litterfall and surface litter prior to and after the impact of the hurricane. Dissolved organic P (DOP) and C (DOC) concentrations in runoff in October 2011 (hurricane landfall), were 96% and 33% greater than the mean concentrations of previous months (July–September 2011). Nutrient fluxes were 10 (DOC), 3 (DON) and 15 (DOP) times greater than the mean fluxes of previous months. N and P concentrations in litterfall collected a few days after the hurricane were not different from pre-disturbance values, but P concentrations were much greater a few months after disturbance. Nutrient fluxes from vegetation to soil due to Jova represented 42% (N) and 30% (P) of the mean annual N and P litterfall fluxes in the period 2010–2012. Surface litter P concentrations, but not N, were very high at the end of the dry season following Jova. In addition, N and P stocks at this time were about 40% higher than the mean stocks in May of the other years of study. Both, litterfall and surface litter P returned to average values about a year after the hurricane. Litterfall P use efficiency, but not N, decreased after hurricane impact. Mean residence time of organic matter and N were similar and did not respond to hurricane disturbance, whereas P residence time was lower and decreased after the hurricane. Overall, our results indicate that hurricane Jova can be identified as an ECE. The return to pre-disturbance values within a year after the event suggests a high degree of short-term biogeochemical resilience in this forest. Variables related to N were resistant (no change) to the impact of Jova and to rainfall variability, but those related to P were highly responsive, quickly recovering to pre-disturbance and long-term dynamics. The P response to the hurricane and its relevance in the ecosystem are discussed in terms of long-term forest productivity and resilience under a scenario of increasing extreme hydrometeorological events. [ABSTRACT FROM AUTHOR]

Trees are dependent on the activity of soil microorganisms, including mutualistic ectomycorrhizal (ECM) fungi and soil-dwelling bacteria, for access to phosphorus (P). While P is a key limiting nutrient in temperate and other forest ecosystems, our understanding of the contributions of ECM fungi to plant P nutrition and cycling are unclear. Further complicating our understanding of these processes are the combined effects of fungal species and future climate scenarios and soil nutrient availability. In this study we characterised how the ECM fungi Pisolithus albus and Pisolithus microcarpus influenced the amount of plant-available P in soils and plant P content of Eucalyptus grandis. We explored how these fungi influence P cycling by studying their relative P-solubilising and P-mineralising abilities and examining their impact on P cycling gene abundance in the soil bacterial community. These were investigated under different levels of nitrogen addition and atmospheric CO 2 to understand how these processes may be impacted by future anthropogenic and climactic change. While inoculation with either P. albus or P. microcarpus resulted in an increase in plant-available P in soil, the amount of plant-available P mobilised was species-specific. This observation was supported by differences in the in vitro P-mobilising abilities of the two fungi. P. albus and P. microcarpus also favoured bacterial communities characterised by a greater abundance of glucose dehydrogenase gene copies for inorganic P solubilisation, complementing the strengths of the ECM fungi in organic P mineralisation and suggesting a distinction in the roles of ECM fungi and bacteria in P cycling. Furthermore, both nitrogen and CO 2 levels impacted these P cycling outcomes, often in a species-specific manner. Our findings expand the current understanding of P cycling between forest trees, ECM fungi and soil bacteria, and have important implications for estimations of future anthropogenic impacts on forest ecosystems. • Pisolithus increases soil available phosphorus for host in species-dependent manner. • Soil bacteria complement role of ectomycorrhizal fungi in phosphorus mobilisation. • Soil nitrogen and CO 2 levels affect phosphorus cycling in ectomycorrhizal symbiosis. [ABSTRACT FROM AUTHOR]

Metabolites in soil play an important role in regulating plant-microbe interactions and, thereby, plant performance. Biotic factors such as root exudation and microbial activity or abiotic factors such as the concentration of atmospheric carbon dioxide (CO 2) can drive both quantitative and qualitative changes in soil metabolite profiles. While the impact of these factors, either in isolation or in combination, are underexplored in soil systems due to technical challenges, recent technological advances have enabled these hurdles to be overcome. Given the key role that mutualistic ectomycorrhizal (ECM) fungi play in forest soils through their symbiotic interaction with trees, and the foreseen changes in forest dynamics with climate change, we investigated the effect of the Eucalyptus grandis - Pisolithus albus (plant host-fungus) association on soil metabolite profiles under ambient and elevated CO 2 conditions (aCO 2 and eCO 2). We found that significant metabolite enrichment predominately occurred in the rhizosphere where a strong effect by ECM fungus was also observed. Specific ECM fungus-induced metabolites were enriched concurrently with an increased host plant root:shoot ratio, suggesting that the influence of ECM fungus on rhizosphere metabolite profiles may impact plant growth. Strikingly, however, we found no observable differences in soil metabolite profiles between the aCO 2 and eCO 2 conditions, which may be due to nutrient limitation given the low level of nutrients found in typical eucalyptus forest soils. Overall, our findings increase our understanding of soil metabolic processes at the symbiotic plant-microbe interface under current and future atmospheric CO 2 scenarios. • Ectomycorrhizal (ECM) fungi substantially modify soil metabolic profiles. • ECM fungi-mediated metabolite changes intensify with proximity to host roots. • Certain ECM fungi-induced soil metabolites are positively corelated to host growth. • Elevated CO 2 modifies plant C:N content but does not affect metabolites in soil. [ABSTRACT FROM AUTHOR]

Increased soil carbon (C) gains projected to occur with elevated CO 2 (eCO 2) might be negated by higher C losses via soil organic matter (SOM) decomposition. The impact of eCO 2 on soil C is usually measured as a change in total soil C which inevitably confounds C gains and losses occurring simultaneously. Furthermore, the impacts of eCO 2 on C gains and losses may differ for contrasting soil organic substrates due to their distinctive physicochemical and microbiological characteristics. Projecting the impacts of eCO 2 on soil C greatly depends on quantifying its individual effects on C gains and losses, which is rarely done in field settings. We used a novel combination of litter bag and isotopic approaches to study temporal C dynamics in two organic substrates: root litter and mineral soil C (SOM-C) to assess C dynamics in a mature Eucalyptus woodland under CO 2 enrichment (EucFACE). We aimed to isotopically separate different C pools for both substrates: a new C pool (C new, plant-derived C from the study site) and a pre-existent, old C pool (C old, present in the original substrates). We also performed comprehensive microbial community analyses to investigate relationships between microbial community structure and individual C pools. We found higher root litter mass losses and slightly greater SOM-C C old losses with eCO 2 during summer months. Gains of C new were not affected by eCO 2 , except for SOM-C during summer, which is linked with the observed C old losses from SOM-C. Moreover, fungal abundance in root litter increased with eCO 2 but decreased in SOM-C. Temporal changes rather than eCO 2 -induced changes in microbial communities were related to C dynamics. Taken together our results suggest that eCO 2 did not lead to significant C new gains but instead lead to moderate enhancement of C new and C old losses, suggesting limited capacity for increased C sequestration of this mature woodland. Image 1 • We quantified the simultaneous impact of elevated CO 2 on soil C gains and losses. • Elevated CO 2 elicits substrate-dependent and seasonal increases in C losses. • Higher C losses were paired with seasonal increases in plant-derived C gains. • Impacts of elevated CO 2 on the microbial community are substrate-dependent. • Temporal shifts in microbial communities were linked with altered C dynamics. [ABSTRACT FROM AUTHOR]