Microbial community composition explains soil respiration responses to changing carbon inputs along anAndes‐to‐Amazon elevation gradient

Abstract

1. The Andes are predicted to warm by 3–5 °C this century with the potential to alter the processes regulating carbon (C) cycling in these tropical forest soils. This rapid warming is expected to stimulate soil microbial respiration and change plant species distributions, thereby affecting the quantity and quality of C inputs to the soil and influencing the quantity of soil-derived CO2 released to the atmosphere.2. We studied tropical lowland, premontane and montane forest soils taken from along a 3200-m elevation gradient located in south-east Andean Peru. We determined how soil microbial communities and abiotic soil properties differed with elevation. We then examined how these differences in microbial composition and soil abiotic properties affected soil C-cycling processes, by amending soils with C substrates varying in complexity and measuring soil heterotrophic respiration (RH).3. Our results show that there were consistent patterns of change in soil biotic and abiotic properties with elevation. Microbial biomass and the abundance of fungi relative to bacteria increased significantly with elevation, and these differences in microbial community composition were strongly correlated with greater soil C content and C:N (nitrogen) ratios. We also found that RH increased with added C substrate quality and quantity and was positively related to microbial biomass and fungal abundance.4. Statistical modelling revealed that RH responses to changing C inputs were best predicted by soil pH and microbial community composition, with the abundance of fungi relative to bacteria, and abundance of gram-positive relative to gram-negative bacteria explaining much of the model variance.5. Synthesis. Our results show that the relative abundance of microbial functional groups is an important determinant of RH responses to changing C inputs along an extensive tropical elevation gradient in Andean Peru. Although we do not make an experimental test of the effects of climate change on soil, these results challenge the assumption that different soil microbial communities will be ‘functionally equivalent’ as climate change progresses, and they emphasize the need for better ecological metrics of soil microbial communities to help predict C cycle responses to climate change in tropical biomes.

Nutrient limitations to bacterial and fungal growth during cellulose decomposition in tropical forest soils

“…2b and 3b-d). This result supported our second hypothesis and, when examined alongside evidence for fungal dominance of the microbial community at higher elevation (Traunspurger et al 2017;Whitaker et al 2014), provided a degree of indirect support for our first hypothesis of a more N-constrained fungal-dominated community at higher elevation. This hypothesis was also indirectly supported by a previous study of enzymatic stoichiometry in the same sites, which showed an increase in the ratio of N-to Pdegrading soil enzyme activities with increased elevation (Nottingham et al 2015b).…”

“…Further descriptions of soil properties (Quesada et al 2010;Whitaker et al 2014;Zimmermann et al 2009), climate (Rapp and Silman 2012) and aboveground productivity and floristic composition (Asner et al 2013;Feeley et al 2011;Girardin et al 2010) for these sites are reported elsewhere.…”

“…The plots were situated next to long-term 1 ha permanent sampling plots (Nottingham et al 2015a). Because soil biological and physicochemical properties within the 1 ha plots have relatively minor variation compared to among the 1 ha plots (Whitaker et al 2014), our experimental plots accurately represented variability in soil characteristics at each site and provided ecologically meaningful comparisons between sites. The collars were placed in the soil at least 2 weeks prior to the experiment.…”

Spatial variability of soil microbial biomass and its relationships with edaphic, vegetational and climatic factors in the Three-River Headwaters region on Qinghai-Tibetan Plateau

“…We found negative correlation between soil microbial biomass and elevation in the study region, which was not in line with some previous studies that reported a positive relationship between soil microbial biomass and elevation below 3000 m in elevation (Huang et al, 2014;Pabst et al, 2013;Wardle, 1992;Whitaker et al, 2014). Our result was supported by the recent finding that soil microbial biomass phosphorus decreases with elevation above 3500 m on the eastern slope of Gongga Mountain, China (Sun et al, 2013a) and was helpful in refining the current understanding of soil microbial biomass distributions.…”

Building Predictive Models for Diverse Microbial Communities in Soil

“…It is not yet clear how emergent microbial properties and responses vary with state factor gradients. There have been some studies of microbial trait parameters across environmental gradients [German et al, 2012;Whitaker et al, 2014], but more studies with additional environmental drivers are needed to scale up to the global level. Additional gridded data products on state factor variables at the global scale represent another key need for scaling up these models.…”