Variability in soybean yield responses to elevated atmospheric CO2: Insights from non-structural carbohydrate remobilisation during seed filling.

The increasing atmospheric CO2 concentration (e[CO2]) has mixed effects on soybean most varieties' yield. This study elucidated the effect of e[CO2] on soybean yield and the underlying mechanisms related to photosynthetic capacity, non-structural carbohydrate (NSC) accumulation, and remobilisation. Four soybean cultivars were cultivated in open-top chambers at two CO2 levels. Photosynthesis rates were determined from R2 to R6. Plants were sampled at R5 and R8 to determine carbohydrate concentrations. There were significant variations in yield responses among the soybean cultivars under e[CO2], from no change in DS1 to a 22% increase in SN14. DS1 and SN14 had the smallest and largest increase, respectively, in daily carbon assimilation capacity. Under e[CO2], DS1, MF5, and XHJ had an increase in Ci, at which point the transition from Rubisco-limited to ribulose-1,5-bisphosphate regeneration-limited photosynthesis occurred, in contrast with SN14. Thus, the cultivars might have distinct mechanisms that enhance photosynthesis under e[CO2] conditions. A positive correlation was between daily carbon assimilation response to e[CO2] and soybean yield, emphasising the importance of enhanced photosynthate accumulation before the R5 stage in determining yield response to e[CO2]. E[CO2] significantly influenced NSC accumulation in vegetative organs at R5, with variation among cultivars. There was enhanced NSC remobilisation during seed filling, indicating cultivar-specific responses to the remobilisation of sucrose and soluble sugars, excluding sucrose and starch. A positive correlation was between leaf and stem NSC remobilisation and yield response to e[CO2], emphasising the role of genetic differences in carbohydrate remobilisation mechanisms in determining soybean yield variation under elevated CO2 levels.

Co-elevation of atmospheric [CO2] and temperature alters photosynthetic capacity and instantaneous water use efficiency in rice cultivars in a cold-temperate region.

Crop photosynthetic capacity in response to climate change likely constrains crop productivity and adaptability to changing environments, which requests the investigation on the dynamics of photosynthetic parameters over growth season among varieties, especially in cold-temperate regions. Three Japonica rice cultivars i.e., Shoubaimao (SH), Hejiang 19 (HJ); Longjing 31, (LJ). were planted under the control, e[CO2] (700 µmol mol-1), warming (2°C above the air temperature) and the co-elevation of [CO2] and temperature in open-top chambers (OTC). The objective of this study is to examine the rice photosynthetic parameters, water use efficiency (WUE) and yield formation in responses to the co-elevation of [CO2] and temperature which is the main predicted features of future climate. e[CO2] significantly increased An of SH, HJ and LJ by 37%, 39% and 23% in comparison to 34%, 34% and 27% under elevated [CO2] plus warming, respectively. However, An had a weak response to warming for three cultivars. [CO2] and temperature co-elevation significantly decreased the stomatal conductance, resulting in a significant increase of the WUE. e[CO2] significantly increased Vc, max , Jmax and Jmax /Vc, max . e[CO2] significantly increased grain yield and grain number of all cultivars. The positive effect of co-elevation of [CO2] and temperature on grain yield was less than e[CO2]. Warming is likely to partially offset the increased photosynthetic rate caused by e[CO2]. The [CO2] and temperature co-elevation may be favorable to rice crop with increasing the photosynthetic ability of rice crop and improving water use efficiency. The present study provided evidence that the rice genotypic difference in photosynthetic potential under [CO2] and temperature co-elevation. Therefore, it is crucial to explore a broader range of phenotypes and cultivars to be applied to climate change response research, advancing the knowledge that climate change impacts rice crop under the cold-temperate climate region.

Soil microbial metabolism on carbon and nitrogen transformation links the crop-residue contribution to soil organic carbon.

The beneficial effect of crop residue amendment on soil organic carbon (SOC) stock and stability depends on the functional response of soil microbial communities. Here we synchronized microbial metagenomic analysis, nuclear magnetic resonance and plant-15N labeling technologies to gain understanding of how microbial metabolic processes affect SOC accumulation in responses to differences in N supply from residues. Residue amendment brought increases in the assemblage of genes involved in C-degradation profiles from labile to recalcitrant C compounds as well as N mineralization. The N mineralization genes were correlated with the C and N accumulation in the particulate and mineral-associated C pools, and plant-derived aliphatic forms of SOC. Thus, the combined C and N metabolic potential of the microbial community transforms residue into persistent organic compounds, thereby increasing C and N sequestration in stable SOC pools. This study emphasizes potential microbially mediated mechanisms by which residue N affects C sequestration in soils.

Plant phosphorus acquisition links to phosphorus transformation in the rhizospheres of soybean and rice grown under CO2 and temperature co-elevation.

Climate change is likely to influence the reservoir of soil phosphorus (P) as plants adaptably respond to climate change in the perspective of P acquisition capability via root proliferation and mediating biochemical properties in the rhizosphere to access various soil P fractions. It is particularly important in cropping soils where P fertilizer plus soil P is required to synchronize crop P demand for the production sustainability under climate change. However, few studies have examined the effect of CO2 and temperature co-elevation on plant P acquisition, P fractions and relevant functional genes in the rhizosphere of different crops. Thus, the present study investigated the effect of elevated CO2 and warming on P uptake of soybean and rice grown in Mollisols, and soil P fractions and relevant biochemical properties and microbial functions in the rhizosphere with or without P application. Open-top chambers were used to achieve elevated CO2 of 700 ppm combined with warming (+ 2 °C above ambient temperature). CO2 and temperature co-elevation increased P uptake in soybean by 23% and 28% under the no-P and P application treatments, respectively; and in rice, by 34% and 13%, respectively. CO2 and temperature co-elevation depleted organic P in the rhizosphere of soybean, but increased in the rhizosphere of rice. The phosphatase activity negatively correlated with organic P in the highland soil while positively in the paddy soil. The P mineralization likely occurs in soybean-grown soils under climate change, while the P immobilization in paddy soils. CO2 and temperature co-elevation increased the copy numbers of P functional genes including phoD, phoC, pstS and phnX, in soils with P application. These results indicate that the P application would be requested to satisfy the increased P demand in soybean under climate change, but not in rice in paddy soils where soil P availability is sufficient. Therefore, elevated CO2 and temperature facilitated the crop P uptake via biochemical and microbial pathways, and P functional genes played an essential role in the conversion of P.

Elevated CO2 Increases Nitrogen Fixation at the Reproductive Phase Contributing to Various Yield Responses of Soybean Cultivars.

Nitrogen deficiency limits crop performance under elevated CO2 (eCO2), depending on the ability of plant N uptake. However, the dynamics and redistribution of N2 fixation, and fertilizer and soil N use in legumes under eCO2 have been little studied. Such an investigation is essential to improve the adaptability of legumes to climate change. We took advantage of genotype-specific responses of soybean to increased CO2 to test which N-uptake phenotypes are most strongly related to enhanced yield. Eight soybean cultivars were grown in open-top chambers with either 390 ppm (aCO2) or 550 ppm CO2 (eCO2). The plants were supplied with 100 mg N kg-1 soil as 15N-labeled calcium nitrate, and harvested at the initial seed-filling (R5) and full-mature (R8) stages. Increased yield in response to eCO2 correlated highly (r = 0.95) with an increase in symbiotically fixed N during the R5 to R8 stage. In contrast, eCO2 only led to small increases in the uptake of fertilizer-derived and soil-derived N during R5 to R8, and these increases did not correlate with enhanced yield. Elevated CO2 also decreased the proportion of seed N redistributed from shoot to seeds, and this decrease strongly correlated with increased yield. Moreover, the total N uptake was associated with increases in fixed-N per nodule in response to eCO2, but not with changes in nodule biomass, nodule density, or root length.

Microbial association with the dynamics of particulate organic carbon in response to the amendment of elevated CO2-derived wheat residue into a Mollisol.

As the chemical quality of crop residue is likely to be affected by elevated CO2 (eCO2), residue amendments may influence soil organic carbon (SOC) sequestration. However, in Mollisols, the dynamics of the SOC fractions in response to amendment with wheat residue produced under eCO2 and the corresponding microbial community composition remain unknown. Such investigation is essential to residue management, which affects the soil quality and productivity of future farming systems. To narrow this knowledge gap, 13C-labeled shoot and root residue derived from ambient CO2 (aCO2) or eCO2 were amended into Mollisols and incubated for 200days. The soil was sampled during the incubation period to determine the residue-C retained in the three SOC fractions, i.e., coarse intra-aggregate particulate organic C (coarse iPOC), fine iPOC and mineral-associated organic C (MOC). The soil bacterial community was assessed using a MiSeq sequencing instrument. The results showed that the increase in SOC concentrations attributable to the application of the wheat residue primarily occurred in the coarse iPOC fraction. Compared with the aCO2-derived shoot residue, the amendment of eCO2-derived shoot residue resulted in greater SOC concentrations, whereas no significant differences (P>0.05) were observed between the aCO2- and eCO2-derived roots. Principal coordinates analysis (PCoA) showed that the residue amendment significantly (P≤0.05) altered the bacterial community composition compared with the non-residue amendment. Additionally, the bacterial community in the aCO2-derived shoot treatment differed from those in the other residue treatments until day 200 of the incubation period. The eCO2-derived shoot treatment significantly increased (P≤0.05) the relative abundances of the genera Acidobacteriaceae_(Subgroup_1)_uncultured, Bryobacter, Candidatus_Solibacter, Gemmatimonas and Nitrosomonadaceae_uncultured, whereas the opposite trend was observed in Nonomuraea, Actinomadura, Streptomyces and Arthrobacter (P≤0.05). These results imply that the response of the microbial community to the eCO2-derived shoot treatment is associated with its contribution to the POC fractions.

[Genetic diversity of psbA of cyanophage from paddy floodwater in northeast China].

Objective: To provide scientific data for studying the ecology of cyanophage, we studied the genetic diversity of psbA of cyanophage from paddy floodwater in northeast China and its phylogenetic positions. Methods: Membrane separation and concentration of cyanophage, PCR-cloning-sequencing were applied to study the diversity of psbA of cyanophage from paddy floodwater in northeast China. Results: In total 17 psbA sequences of cyanophage were obtained. Novel cyanophages were found by phylogenetic analysis. Compared to those of Japanese paddy floodwater, marine and lakes, psbA gene assemblage of paddy floodwater in northeast China was significantly different. Conclusion: This is the first report to study genetic diversity of cyanophage from paddy floodwater in northeast China with a molecular marker of psbA by PCR-cloning-sequencing. The novel psbA assembly of cyanophage was found in paddy floodwater in northeast China.

[Responses of black soil's microbial respiration and community functional diversity to temperature].

Black soil samples were collected from Lishu (43 degrees 20' N, 124 degrees 28' E), Dehui (44 degrees 12' N, 125 degrees 33' E), Hailun (47 degrees 26' N, 126 degrees 38' E), and Bei' an (48 degrees 17' N, 127 degrees 15' E), and an incubation test was conducted to study their microbial respiration and Biolog metabolic functional diversity at 4 degrees C, 15 degrees C, and 28 degrees C. The soil microbial respiration rate was in the order of Bei' an > Hailun > Dehui > Lishu, irrespective of incubation temperature, but the sensitivity of the respiration to the temperature, i. e., Q10 value, differed. The average value of the Q10 for the soils from Lishu, Dehui, Hailun, and Bei'an was 2.72, 3.26, 3.21, and 3.74 in the range of 4 degrees C-15 degrees C, and was 3.29, 2.36, 2.11, and 1.79 in the range of 15 degrees C to 28 degrees C, respectively. The metabolic quotient (qCO2) also differed with incubation temperature, which was in the order of Lishu > Dehui > Bei' an > Hailun at 28 degrees C and of Bei' an > Dehui > Hailun > Lishu at 15 degrees C, but no significant difference was observed at 4 degrees C. Biolog test showed that the substrate richness and metabolic Shannon diversity index of microbial community were higher for the soils from Hailun and Bei' an at 4 degrees C, but higher for those from Lishu and Dehui at 15 degrees C and 28 degrees C. Principal component analysis with Biolog data suggested that the metabolic function of soil microbial community was similar between Bei' an and Hailun, and between Dehui and Lishu. In sum, the responses of black soil's microbial respiration and community functional diversity to temperature varied with latitude, i. e., more sensitive to low temperature in high latitude region, but more sensitive to high temperature in low latitude region.

[Effects of different land management practices on black soil microbial biomass C and enzyme activities].

In a long-term experimental plot at the Hailun Agricultural Ecology Station of Chinese Academy of Sciences in Heilongjiang Province, Northeast China, the effects of three land management practices including natural restoration, fallowing and cropping on black soil microbial biomass C and enzyme activities at the depths of 0-10, 20-30 and 40-50 cm were investigated. The results showed that at 0-10 cm, soil microbial biomass C and soil urease, phosphatase, catalase and invertase activities were in the sequence of natural restoration > cropping > fallowing, while at 20-30 cm and 40-50 cm, they had less significant differences as those at 0-10 cm. Under natural restoration and cropping, soil microbial biomass C and soil urease, phosphatase and catalase activities decreased with increasing soil depth, while under fallowing, they were higher at 20-30 cm. Correlation analysis showed that there existed significant positive correlations between soil total C and total N, soil total C and microbial biomass C, and soil microbial biomass C and test enzyme activities. The indices soil microbial biomass C and soil enzyme activities showed that black soil under long-term natural restoration had better soil quality.

[Identification of agricultural resource & environment determination of the principle grain production area in China].

The 15 principle grain production areas and 16 non-principle grain production areas were determined on the basis of systematic identification and comprehensive analysis on agricultural resources and environment in the 31 provinces and regions of China, and the fundamental method for solving the problems on the deterioration of agricultural resources and environment has been put forward, which is to carry out macro-regulation of agriculture under the frame of WTO on the basis of developing the soft wares for agricultural macro regulation of the principle and non principle grain production areas.