Publications

We introduce and review Brassica crop improvement via trigenomic bridges. Six economically important Brassica species share three major genomes (A, B, and C), which are arranged in diploid (AA, BB, and CC) and allotetraploid (AABB, AACC, and BBCC) species in the classical triangle of U. Trigenomic bridges are Brassica interspecific hybrid plants that contain the three genomes in various combinations, either triploid (ABC), unbalanced tetraploid (e.g., AABC), pentaploid (e.g., AABCC) or hexaploid (AABBCC). Through trigenomic bridges, Brassica breeders can access all the genetic resources in the triangle of U for genetic improvement of existing species and development of new agricultural species. Each of the three Brassica genomes occurs in several species, where they are distinguished as subgenomes with a tag to identify the species of origin. For example, the A subgenome in B. juncea (2n = AABB) is denoted as Aj and the A subgenome in B. napus (2n = AACC) as An. Trigenomic bridges have been used to increase genetic diversity in allopolyploid Brassica crop species, such as a new-type B. napus with subgenomes from B. rapa (Ar) and B. carinata (Cc). Recently, trigenomic bridges from several sources have been crossed together as the ‘founders’ of a potentially new allohexaploid Brassica species (AABBCC). During meiosis in a trigenomic bridge, crossovers are expected to form between homologous chromosomes of related subgenomes (for example Ar and An), but cross-overs may also occur between non-homologous chromosomes (for example between A and C genome chromosomes). Irregular meiosis is a common feature of new polyploids, and any new allotetraploid or allohexaploid Brassica genotypes derived from a trigenomic bridge must achieve meiotic stability through a process of diploidisation. New sequencing technologies, at the genomic and epigenomic level, may reveal the genetic and molecular basis of diploidization, and accelerate selection of stable allotetraploids or allohexaploids. Armed with new genetic resources from trigenomic bridges, Brassica breeders will be able to improve yield and broaden adaptation of Brassica crops to meet human demands for food and biofuel, particularly in the face of abiotic constraints caused by climate change.

Irrigation is a common practice in agriculture to increase crop yield. However, the impacts of irrigation on microbial-mediated processes that influence soil carbon (C) pools and crop yield remains largely unknown. Therefore, we conducted a 2-year field experiment to investigate the effects of low (I1, 80% field capacity, 80%FC), medium (I2, 90%FC), and high (I3, 100%FC) irrigation upper limits on rhizosphere soil bacterial community, soil organic carbon (SOC) content, and wheat yield. The results showed that as the irrigation upper limit increased, the α-diversity of the bacterial community decreased. The bacterial community structure significantly differed across various irrigation upper limits. As the irrigation upper limit increased from low (80%FC) to medium (90%FC) or high (100%FC), the abundance of copiotrophic taxa (Proteobacteria, Actinobacteria, Bacteroidetes) decreased, and oligotrophic taxa (Acidobacteria) increased, enhancing the decomposition of persistent C pools. In the second year of the irrigation experiment, the I2 and I3 treatments significantly decreased microbial biomass carbon (MBC), SOC content (by 4.62–7.30%), and the microbial quotient (MQ) compared to I1. Wheat straw biomass and grain yield also decreased as the irrigation upper limit increased from 80%FC to 100%FC, with key bacterial taxa (Proteobacteria, Actinobacteria, and Chloroflexi) and functional processes (glycan biosynthesis and metabolism; folding, sorting, and degradation; translation; transport, and catabolism) playing key roles in wheat grain formation. Our findings indicate that adjusting irrigation levels affects the rhizosphere soil bacterial communities, and that the lowest upper limit of irrigation application (80%FC) is associated with maximum crop yield and microbial diversity.

In the Yangtze River Valley in China, 300 kg N/ha is normally applied to cotton crops in three splits: pre-plant application (PPA, 30%), first bloom application (FBA, 40%) and peak bloom application (PBA, 30%).However, low plant fertilizer N recovery (FNR) (30-35%) was accompanied with the negative effects on the environment.Two-year field trial has proven the feasibility of obtaining the same cotton yield by allocating more N for later application (PBA) with lower N rate.A pot experiment was carried out to testify if there was any improvement in N absorption and FNR in cotton (Gossypium hirsutum L. cv Huazamian H318) plants by fixing 40% of 225 kg 15 N/ha for FBA.The results showed that both total N and fertilizer 15 N accumulation in cotton plants responded positively to N split ratio resulting in a (curve) meeting point at 80 DAE (days after emergence).The total N and fertilizer 15 N amount (mg/plant) increased from 1526 and 1194 to 2143 and 1924, respectively, as the ratio of N allocated to PBA increased from 20% (N42) to 60% (N06).Cotton plants absorbed N the most during flowering, but N06 had the highest 15 N uptake rate (mg/plant/d) (33) during boll setting, which was almost the same as that during flowering; whereas N42 dropped drastically to 5

Additional file 9: Supplementary Table 8. SNP variation identified in 11 rice land race accessions used in this study.

Plants are exposed to various biotic and environmental stresses under a natural environment that trigger the reactive oxygen species (ROS). These ROS are produced during plant metabolism in different cellular compartments (mitochondria, chloroplast, peroxisomes, plasma membrane NADPH oxidases, etc.) and have a dual function. Higher production and accumulation of ROS lead to oxidative stress, causing injury to cell organelles and vital biomolecules. However, in normal growth conditions, ROS act as signaling molecules and regulate several processes related to plant growth and development, including cell division, germination, reproductive development, and hormonal regulation. The role of ROS in stress-related responses has been well established. Among different ROS, the hydrogen peroxide (H2O2), hydroxyl ions (OH¨), superoxide anions (O2 ¨), and singlet oxygen (1O2) are more important. These ROS are produced at specific cellular compartments and vary in their reactivity. H2O2 is relatively stable ROS and acts as a strong signaling molecule during biotic and abiotic stresses. In this chapter, the production and metabolism of different ROS, their toxicity, and a scavenging mechanism in plants have been discussed. The role of ROS in the regulation of plant growth and development and effect of abiotic stress on ROS production has also been described.

Straw return is an important agricultural practice with the potential to impact soil carbon (C) and nitrogen (N) cycling. Extracellular enzyme activity (EEA) is crucial for soil organic matter degradation. However, it remains unclear how soil EEA respond to straw return or whether these responses can predict changes in soil C and N cycling induced by straw return. By synthesizing 135 field studies worldwide, we showed that straw return significantly increased the activities of C-acquisition ( C-acq ), N-acquisition ( N-acq ), phosphorus-acquisition ( P-acq ), and oxidative-decomposition ( OX ) enzymes by 26.5 %, 20.3 %, 17.8 %, and 9.1 %, respectively. Notably, we found a significant positive relationship between the logarithmic response ratios (ln R ) of the activities of OX and C-acq and soil C, suggesting that changes in combined EEA might serve as indicators of soil C storage under straw return. Interestingly, the changes in EEA due to straw return were unrelated to increases in soil total N (TN). Moreover, the positive effects of straw return on the activities of C-acq and P-acq negatively correlated with the amount of straw applied. Some abiotic factors, such as soil pH and soil C:N ratio, influenced the straw return-induced changes in soil C and N. These findings highlight the importance of considering key abiotic factors in understanding the microbial mediation of soil C and N cycling under straw return. Overall, by analyzing the changes in EEAs, we can gain in-depth mechanistic understandings of how soil carbon and nitrogen transform and cycle, which is crucial for elucidating soil C and N dynamics. • Meta-analysis to identify powerful predictors of straw return on combined extracellular enzyme activities. • Straw return significantly enhanced extracellular enzyme activities. • No relationship between combined extracellular enzyme activities and soil total nitrogen due to straw return.