Jie Liu

The increasing CO₂ concentration ([CO₂]) in the atmosphere decreases mineral nutrients concentration in crops, whereas it increases water use efficiency (WUE). Partial root-zone irrigation (PRI) could not only increase WUE but also improve plant nutrient status. Yet the effect of PRI combined with elevated CO₂ concentration (e[CO₂]) on the element stoichiometry of tomato leaves remains unknown. This study sought to investigate the responses of leaf mineral nutrients status and element stoichiometric ratios in tomatoes to PRI combined with e[CO₂]. Tomato plants (cv. Ailsa Craig) were grown in pots in climate-controlled growth chambers with ambient [CO₂] (a[CO₂], 400ppm) and elevated [CO₂] (e[CO₂], 800ppm), respectively. Three irrigation regimes, i.e., full irrigation (FI), deficit irrigation (DI) and PRI, were applied to tomato plants at the flowering stage. The results showed that plants grown under DI and PRI had a similar biomass, enhanced root growth including greater root to shoot ratio, root length, surface area, volume and specific length, and an improved WUE in comparison with FI under e[CO₂]. Additionally, under e[CO₂], PRI showed an increase in leaf [C](+1.5%) and [N] (+9.3%), no decrease in leaf [K], [Ca], [Mg], [S] and [¹⁵N], but a decrease in leaf C/N (−6.6%) as compared with FI. Conclusively, PRI had the ability to improve leaf N concentration, maintain most leaf mineral nutrient concentrations, and optimize or maintain leaf element stoichiometric ratios under e[CO₂]. Therefore, PRI would be a practicable mode of irrigation for optimizing WUE and nutrient status in tomato leaves in a future freshwater-limited and higher-CO₂ environment.

Increasing CO2 concentration ([CO2]) in atmosphere decreases mineral nutrients concentration in crops whereas increasing water use efficiency (WUE) especially in drought conditions. Partial root-zone irrigation (PRI) could stimulate soil nutrient mineralization and improve crop nutrient status. Yet the effect of PRI combined with elevated CO2 concentration (e[CO2]) on the element stoichiometry of tomato leaves remains unknown. This study was to investigate the responses of leaf mineral nutrients status and element stoichiometric ratio in tomato grown at PRI exposed to e[CO2]. Tomato plants (cv. Ailsa Craig) were grown in pots in climate-controlled growth chambers with ambient [CO2] (a[CO2], 400ppm) and elevated [CO2] (e[CO2] 800ppm), respectively. Three irrigation regimes (IR) i.e. full irrigation (FI), deficit irrigation (DI) and partial root-zone irrigation (PRI) were applied to tomato plants at flowering stage. The result showed that plants exposed to both reduced irrigations had a similar biomass, an enhanced root growth including greater root to shoot ratio (R/S), root length (RL), surface area (RS), volume (RV) and specific length (RSL), and an improved WUE under e[CO2]. Compared to a[CO2], e[CO2] growth environment resulted in a similar leaf [C], [K] and [Mg], leaf C/K and C/Mg, increased leaf [Ca], [S] and leaf C/N, C/P and N/P, but decreased leaf [N], [P], leaf C/Ca, C/S and N/K at PRI. Additionally, under e[CO2], PRI showed an increase in leaf [C], [N] and [S], no decrease in leaf [K], Ca], [Mg], [S] and [15N], but a decrease in leaf C/N and C/S as compared with FI. Conclusively, PRI had the ability to alleviate the negative effects on mineral nutrient concentrations and maintain or improve most leaf element stoichiometric ratios under e[CO2]. Therefore PRI would be a practicable irrigation for optimizing WUE and nutrient status in tomato leaves in a future freshwater-limited and higher CO2 environment.

The effects of inoculating plant growth promoting rhizobacteria (PGPR) and soil water deficits on crop growth and physiology remain largely unknown. Here, the responses of leaf gas exchange, growth, and water use efficiency (WUE) of tomato plants to Bacillus pumilus (B.p.) inoculation under four irrigation strategies (I1-I4) were investigated in a greenhouse. Results showed that soil water deficits, especially at I4 (20%, v/v), significantly decreased leaf stomatal conductance (g_s), transpiration rate (T_r), and photosynthetic rate (A_n), and the decrease of g_s and T_r were more pronounced than A_n. Reduced irrigation regimes significantly lowered dry matter and plant water use both in the non-B.p. control and the B.p. plants, while reduced irrigation significantly increased plant WUE, and B.p. inoculation had little effect on this parameter. Synergistic effects of PGPR and deficit irrigation on leaf gas exchange, leaf abscisic acid content, and stomatal density were found in this study, and specifically, B.p. treated plants at I4 possessed the highest WUE at stomatal and leaf scales, suggesting that B.p. inoculation could optimize water use and partly alleviate the negative effects of soil water deficit. These findings provide useful information for effective irrigation management and the application of PGPR in agriculture in the future.

Global climate change will modify plants in terms of growth and physiology. To better understand the consequences of this effect, the responses of the leaf water relations and nitrogen (N) use efficiency of barley and tomato plants to elevated CO₂ (e[CO₂], 800 ppm) combined with progressive drought stress at two levels of N supply (N1, 0.5 g N pot⁻¹ and N2, 1.0 g N pot⁻¹) were studied. The plants were grown in two separate phytotrons at ambient CO₂ (a[CO₂], 400 ppm) and e[CO₂], respectively. The leaf physiological parameters as well as carbon (C) and N concentrations were determined; plant growth, water and N use efficiencies were evaluated. The results showed that e[CO₂] increased photosynthesis and water use efficiency (WUE) while decreased specific leaf area (SLA) in both species, whereas N supply level differentially influenced WUE in barley and tomato plants. The abscisic acid (ABA)-induced stomatal closure during progressive soil drying varied between the two species where the stomatal conductance (g_s) of barley plants was more sensitive to leaf ABA than tomato plants, though CO₂ environment did not affect the response in both species. Compared to a[CO₂], e[CO₂] reduced plant transpiration rate (T_plant) in barley but not in tomato. e[CO₂] increased the leaf C:N ratio ([C:N]_leaf) in plants by enhancing leaf C concentration ([C]_leaf) in barley and by dilution of leaf N concentration ([N]_leaf) in tomato, respectively, but N2 substantially decreased [C:N]_leaf, and thus, N treatment was the dominant factor controlling [C:N]_leaf. Collectively, appropriate N supply may modulate the acclimation of plants to e[CO₂] and soil water deficits. This study provides some novel insights into N management of different plant species for adapting to future drier and CO₂-enriched environment.

The objective of this study was to explore the effects of plant growth-promoting rhizobacteria (PGPR), strain Bacillus licheniformis, with softwood biochar amendment on potato growth and water use efficiency (WUE) under a deficit irrigation (DI) regime. A pot experiment was conducted in a greenhouse. The results showed that PGPR improved leaf gas exchange rates, including photosynthesis rate, stomatal conductance and transpiration rate at early seedling stage, while tended to depress these parameters gradually until final harvest. The effects of biochar on plant leaf physiology, plant growth and WUE were not evident. Plants were more affected by DI than PGPR inoculation and biochar amendment. DI significantly decreased leaf gas exchange rates after exposure to water treatment for around three weeks, and the negative effect was eliminated at final harvest. At final harvest, DI significantly decreased leaf area, specific leaf area, dry mass of leaf and stem, total dry mass, dry mass increment and plant water use. The synergistical effect of PGPR strain Bacillus licheniformis and DI on plant growth and WUE were not observed in our study. WUE was solely improved by DI, indicating that, compared to PGPR inoculation, DI was a more effective measure to enhance plant WUE.

Faced with the scarcity of water resource and irrational fertilizer use, it is highly important to supply plants with water and fertilizer at desiderated stages to improve yield with high water use efficiency (WUE). A pot experiment was conducted to investigate the effects of growth stage-specific water deficiency and potassium (K) fertilization on tomato yield and WUE. The entire growing season of tomato was divided into 5 stages: vegetative growth stage (VG), flowering and fruit setting stage (FS), early fruit growth stage (FG), fruit development stage (FD) and fruit maturity stage (FM). Three soil moisture (W) and three K fertilization levels were set up. W levels included W1, W2 and W3, indicating that soil water was maintained at 60–70% field capacity, 70–80% field capacity, and 80–90% field capacity, respectively. K levels included K1, K2 and K3, indicating that 0 g K₂O per kg soil, 0.46 g K₂O per kg soil and 0.92 g K₂O per kg soil was applied. All combinations of the three W and three K levels were solely imposed at each of the five growth stages, for other four stages, plants were watered to 80–90% field capacity without K fertilizer (W3K1). The permanent W3K1 over the entire growth stage was taken as control (CK). The results showed that W deficiency imposed at all stages significantly affected tomato yield (P<0.01), except for VG stage in which W deficiency did not cause yield loss. K fertilization level during FS or FM stage had a significant effect on yield (P<0.01). A significant interaction effect of W and K on yield was only observed during FM stage. For WUE, significant effect of W deficiency at FS, FD and FM stages were observed, and a significant effect of K levels at FS, FD and FM stages was observed. Specifically, K fertilization was necessary during specific growth stage of tomato (i.e. FS and FM). During FS stage, even if a sufficient water supply seems necessary, a deficit irrigation with K fertilization could be applied as K fertilization could alleviate the negative effect of soil water deficit, however, excess of K fertilization during FM stage should be avoided to maintain tomato yield and WUE.

Inadequate fertilization may result in water pollution and nutrient leaching, especially in paddy fi elds. It is expected that the combination of organic and inorganic fertilizers reduces water pollution in addition to crop yield improvement. In this study, combined fertilization with organic and inorganic fertilizers was tested under controlled irrigation conditions. With the addition of organic fertilizer, the pH of paddy soil could be maintained in a rather neutral environment, and the soil organic matter concentration could increase – especially under a controlled irrigation regime. Hydrolyzed nitrogen was noticed in the fertilized plots with an increasing trend compared to unfertilized plots. However, available phosphorus concentration decreased in all treatments after rice harvest. During the drainage process, the ammonium nitrogen was the main form of nitrogen loss. Organic fertilizer application signifi cantly improved productive panicles and thus increased paddy yield. We concluded that with the combination of organic-inorganic fertilizer application and controlled irrigation, the pollutants can be removed to some extent and the rice yield can be increased signifi cantly, which is favorable for environmental protection and yield promotion.