In this paper, the influence of drought hardening on the growth, development, resistance physiology, leaf microstructure and stomatal behavior of potato seedlings under drought stress was studied, and the mechanism of drought hardening improvement of potato seedling drought resistance was elucidated.  We found that drought stress had several adverse effects on potato seedlings, yet drought hardening alleviated the decrease in relative water content (RWC), net photosynthetic rate (P_n) and chlorophyll content and inhibited the increase in relative electric conductivity and malondialdehyde (MDA) content.  Compared with contrast seedlings, drought-hardened seedlings also had enhanced root vigor, increased antioxidant enzyme activity and higher levels of abscisic acid (ABA), proline (Pro), soluble sugars and polyamines (PAs) under drought stress.  In addition, the stomatal density of potato seedling leaves increased significantly, while the leaf area, stomatal size and stomatal aperture decreased with drought hardening treatment.  These changes led to reduced leaf transpiration rate (T_r) and improved water utilization efficiency (WUE).  The changes in leaf microstructure also had a positive effect on the drought resistance of the drought-hardened potato seedlings. So it can be concluded that through increasing the content of some endogenous hormones, osmotic regulatory substances and the activities of antioxidant enzymes, the resistance physiology of drought-hardened potato seedlings was enhanced. 

We investigated the correlation between leaf/soil minerals and fruit quality in apple trees grown in orchards, with the ultimate goal of improving the latter. Leaf mineral nutrients; soil nutrients in the 0–20, 20–40, and 40–60 cm layers; and fruit quality traits in 32 apple orchards in China were monitored for 2 years. Significant factors associated with fruit quality were identified via correlation analysis. An analysis of leaf data revealed that leaf nitrogen (N) and leaf magnesium (Mg) levels were extremely high in 75 and 89% of the orchards, respectively. In the Bohai Gulf region, 94% of the orchards showed significantly higher values than the standard. The soil pH values of the orchards in eastern China like eastern Shandong or Liaoning were lower than 7.0, while the pH values in the Loess Plateau of northwestern China like Shaanxi were much higher than 7. Soil alkali-hydrolyzable N levels in 47% of the orchards were lower than the optimal level of 70 mg kg–1. Generally, the soil alkali-hydrolyzable N levels of orchards in the Bohai Gulf region were significantly higher than those in the Loess Plateau region. The available P levels in the orchards of the Bohai Gulf region were up to three times higher than those of the Loess Plateau region. However, although the available potassium (K) in most orchards was sufficient (51.39–309.94 mg kg–1), leaf K content in 73% of the orchards was low, possibly due to fruit bagging or fruit overload. Approximately 63% of the orchards in Shandong and 29% of the orchards in Shannxi showed leaf Fe deficiencies. In the Loess Plateau, most orchards showed high leaf Ca levels, a strong correlation was observed between leaf and soil phosphorus/potassium (P/K) content and fruit organic acid content. The amounts of fruit soluble sugar or fructose were positively correlated with soil calcium/potassium (Ca/K) levels and leaf calcium/boron (Ca/B) levels in most orchards. The excessive leaf N levels caused by the extensive application of N fertilizers had a negative effect on fruit quality in most apple orchards in China. P, K, Ca, and B were key minerals associated with fruit quality.

Salt stress contains osmotic and ionic stress, while iso-osmotic polyethylene glycol (PEG) has only osmotic stress. This study aimed to compare the different effects on the activity of H+-ATPase, proton pump and Na+/H+ antiport in Malus seedlings between osmotic and ionic stress. Species of salt tolerant Malus zumi, middle salt tolerant Malus xiaojinensis and salt sensitive Malus baccata were used as experimental materials. Malus seedlings were treated with NaCl and iso-osmotic PEG stress. The activity of H+-ATPase, proton pump and Na+/H+ antiport of plasmolemma and tonoplast in Malus seedlings were obviously increased under salt stress, and those in salt-tolerant species increased more. Under the same NaCl concentration, the activity of H+- ATPase, proton pump and Na+/H+ antiport of plasmolemma and tonoplast in salt-tolerant species were all obviously higher than those in salt-sensitive one. Higher Na+/H+ antiport activity of plasmolemma and tonoplast in salt-tolerant species could help to extrude and compartmentalize sodium in roots under salt stress. The ascent rate of activity of H+-ATPase, proton pump and Na+/ H+ antiport in Malus seedlings under the three salt concentration stress was all obviously higher than that under the iso-osmotic PEG stress. It indicated that the sodium ion effect had more stimulation on the activity of H+-ATPase, proton pump and Na+/H+ antiport in salt-tolerant species, and salt-tolerant species has higher capability of sodium extrusion and compartmentalization in roots and is therefore more salt tolerant.