Nutrient resorption responses of female and male Populus cathayana to drought and shade stress.

Nutrient resorption can increase nutrient use and play important roles in terrestrial plant nutrient cycles. Although several studies have reported individual responses of plant nutrient resorption to drought or shade stress, the interaction of drought and shade remains unclear, especially for dioecious plants. This study explored whether nutrient resorption is correlated to growth characteristics (such as biomass and root/shoot ratio [R/S ratio]) and leaf economics (such as leaf thickness, leaf mass per area [LMA] and leaf vein density [LVD]) in female and male Populus cathayana across different conditions. We found that drought stress significantly increased nitrogen (N) resorption efficiency (NRE) in both sexes, but shade and interactive stress decreased NRE in P. cathayana females. Under drought stress, nutrient resorption was sexually dimorphic such that P. cathayana males have higher NRE than females. Furthermore, NRE and phosphorous (P) resorption efficiency (PRE) were positively related to R/S ratio, leaf thickness, LMA, and LVD in both sexes across different treatments. Our study is the first to present how nutrient resorption is related to biomass accumulation and allocation, and leaf economics, suggesting that nutrient uptake may be modulated by R/S ratio and leaf economics, which is important for understanding the conservation mechanism of plant nutrients.

Nitrogen level induces sex-specific cadmium phloem remobilization and cell wall segregation in Populus cathayana.

Nitrogen (N) fertilization can improve the phytoremediation of contaminated soils. However, limited information is available on the effects and mechanisms of N availability on Cadmium (Cd) phytoextraction by dioecious plants. This study employed female and male Populus cathayana to examine sex-specific long-distance transport and cell wall Cd sequestration. Females had a greater ability to transport Cd from roots to shoots and accumulated more Cd in leaves, but had less Cd bound to the cell wall and S-containing ligands than males, irrespective of N availability. N availability affected the sex-specific ability to transport Cd and chelate it within cell walls and with S-containing ligands. Low N promoted phloem-mediated upward and downward Cd transport and total Cd accumulation in both sexes, and such effects on phloem-mediated downward Cd transport were greater than those on upward Cd transport in males. However, low-N concentration-induced Cd phloem transport was more significant in females than males. In females, low N reduced Cd accumulation in leaves via increased phloem-mediated Cd downward transport, and this Cd was subsequently sequestered in the bark and root cell walls. In contrast, for males, high N promoted xylem-mediated Cd transport to shoots and Cd sequestration in the bark but reduced phloem-mediated Cd downward transport and subsequent sequestration in root cell walls. Sex-specific genes related to root Cd transport and translocation from roots to shoots were also affected by N supply in roots. These results suggested that N availability reduced the sex-based difference in total Cd accumulation, translocation and Cd detoxification, and males showed stronger Cd tolerance than females at both N availabilities.

How anammox process resists the multi-antibiotic stress: Resistance gene accumulation and microbial community evolution.

The effects of multiple antibiotics on the anaerobic ammonia oxidation (anammox) process were investigated. The resistance of the anammox system to high-concentration antibiotics was also demonstrated through gradual acclimation experiments. Inhibition of the anammox process (R1) occurred when the concentrations of erythromycin (ERY), sulfamethoxazole (SMX) and tetracycline (TC) were 0.1, 5.0 and 0.1 mg L-1, respectively. The nitrogen removal efficiency (NRE) of R1 was reduced from 97.2% to 60.7% within 12 days and then recovered to 88.9 ± 9.5% when the nitrogen loading declined from 4.52 ± 0.69 to 2.11 ± 0.58 kg N m-3 d-1. Even when the concentrations of ERY, SMX and TC were as high as 1.0, 15.0 and 1.0 mg L-1, respectively, R1 maintained stable operation. The increases in the abundance of antibiotic resistance genes (ARGs) and in extracellular polymeric substances (EPS) content showed that the anammox process alleviated stress from multiple antibiotics mainly by producing ARGs and secreting EPS. The molecular docking simulation results illustrated the potential binding sites between ammonium transporter and different antibiotics. The upregulation of functional gene expression and the stable abundance of Candidatus Kuenenia in R1 compared with that in the control suggested that the R1 reactor generally maintained more stable long-term operation. This work provides a new understanding of the application of the anammox process to treat wastewater containing multiple antibiotics.