Divergent Responses of the Diazotrophic Microbiome to Elevated CO2 in Two Rice Cultivars

Abstract

The species-specific responses of plant growth to elevated atmospheric CO2 concentration (eCO2) could lead to N limitation and potentially influence the sustainability of ecosystem. Questions remain unanswered with regards to the response of soil N2-fixing community to eCO2 when developing high-yielding agroecosystem to dampen the future rate of increase in CO2 levels and associated climate warming. This study demonstrates the divergent eCO2 influences on the paddy diazotrophic community between weak- and strong-responsive rice cultivars. In response to eCO2, the diazotrophic abundance increased more for the strong-responsive cultivar treatments than for the weak-responsive ones. Only the strong-responsive cultivars decreased the alpha diversity and separated the composition of diazotrophic communities in response to eCO2. The topological indices of the ecological networks further highlighted the different co-occurrence patterns of the diazotrophic microbiome in rice cultivars under eCO2. Strong-responsive cultivars destabilized the diazotrophic community by complicating and centralizing the co-occurrence network as well as by shifting the hub species from Bradyrhizobium to Dechloromonas in response to eCO2. On the contrary, the network pattern of the weak-responsive cultivars was simplified and decentralized in response to eCO2, with the hub species shifting from Halorhodospira under aCO2 to Sideroxydans under eCO2. Collectively, the above information indicates that the strong-responsive cultivars could potentially undermine the belowground ecosystem from the diazotrophs perspective in response to eCO2. This information highlights that more attention should be paid to the stability of the belowground ecosystem when developing agricultural strategies to adapt prospective climatic scenarios by growing high-yielding crop cultivars under eCO2.

Effects of Elevated CO2 on Tomato (Lycopersicon esculentum Mill.) Growth and Rhizosphere Soil Microbial Community Structure and Functionality

“…N cycling was also stimulated by eCO 2 , especially in terms of the increased absolute abundance of nifH. Our result was consistent with the findings of studies conducted in other soil ecosystems, such as rice ecosystems [81] but differed from the findings of one study, which reported no effect of eCO 2 on N fixation [82]. The higher absolute abundance of nifH under eCO 2 fumigation indicated high demand for N and high metabolic activity.…”

Elevated Atmospheric CO2 and Nitrogen Fertilization Affect the Abundance and Community Structure of Rice Root-Associated Nitrogen-Fixing Bacteria

“…The experimental FACE platform was located in Zongcun Village (119 • 42 0 E, 32 • 35 5 N), Yangzhou City, Jiangsu Province (Figure 1; Yu et al, 2018). The long-term experimental platform with a rice-wheat rotation crop system started in 2004.…”

“…The long-term experimental platform with a rice-wheat rotation crop system started in 2004. From 2010, the rice-wheat rotation system was changed to a rice-fallow system (Yu et al, 2018). The region has a north subtropical monsoon climate with a mean annual temperature of 16 • C and a mean annual precipitation of 900-1,000 mm.…”

“…The reactions were performed on a CFX Connect Optical Real-Time Detection System (Bio-Rad Laboratories, Hercules, CA, United States) in volumes of 20 µL and containing 1 µL extracted DNA (approximately 50 ng), 10 µL 2 × SYBR Premix Ex Taq (Takara Biotech, Dalian, China), and 500 nM primers PolF (Poly et al, 2001) and AQER (Wartiainen et al, 2008). The parameters were those previously described in the literature (Yu et al, 2018). Briefly, the amplifications were performed with an initial denaturation step at 95 • C for 30 s, followed by 36 cycles of denaturation at 95 • C for 30 s, annealing at 57 • C for 45 s and extension at 72 • C for 45 s. The specificity of the amplification products was confirmed by melting curve analysis, and the expected sizes (340 bp) of the amplified fragments were checked in a 1.5% agarose gel stained with ethidium bromide.…”

“…eCO 2 can increase the N demand for plants, which is beneficial for N 2 fixation (Luo et al, 2004). A previous study showed that soil diazotrophic abundance significantly increased in two difference rice cultivars to satisfy the increased N demand under eCO 2 in paddy fields (Yu et al, 2018). This may be due to an increase in the organic acid content of the root system released into the soil by eCO 2 (Bhattacharyya et al, 2013), thus providing carbon source and energy to N 2fixing bacteria.…”