Non-linear and contrasting responses of abundant, intermediate and rare prokaryotic phylotypes to environmental gradients in forests of East China

Forest ecosystems are facing challenges from the effects of global climate change, greatly threatening their ecosystem function. Soil prokaryotic community, consisted of a few abundant prokaryotes and a large number of rare prokaryotes, are proven to be critical in soil nutrient cycling. However, how they respond to environmental gradients, and whether these responses are non-linear is unknown. To address this issue, we collected 28 soil samples from forest ecosystems in Eastern China and examined their prokaryotic community using 16S rRNA amplicon sequencing. Totally, 120 abundant phylotypes were identified, which occupied only 0.06 % of the total ASV number but 27.14 % of the total sequence reads across all samples. Regression analysis and random forest analysis revealed that abundant phylotype significantly contributed to soil nutrient availability. The richness of abundant and intermediate phylotypes increased with the increasing pH before the threshold, while it decreased after the threshold. However, it is note worthing that the richness of rare phylotypes consistently increased with increasing pH before and after threshold. When examining the mean annual temperature threshold, the richness of abundant, intermediate and rare phylotypes all sharply decreased after the threshold, with higher thresholds for abundant phylotype (18.51 °C) and intermediate (18.47 °C) than rare phylotype (16.70 °C). TITAN analysis revealed that soil pH and aridity thresholds of abundant prokaryotic community were narrower than intermediate and rare prokaryotic communities, indicating the more sensitive responses of abundant phylotype along pH and aridity gradients. Overall, our findings confirmed the crucial roles of abundant phylotype in forest soil nutrient cycling, and highlighted the non-linear and contrasting responses of abundant, intermediate, and rare phylotypes to environmental gradients, which can be used for building effective strategies to maintain soil nutrient cycling with the ongoing global climate change.