Arundo donax L. (giant reed) is a perennial rhizomatous grass with high drought and salinity tolerance, making it a promising low-input bioenergy crop. However, the understanding of the combined effects of irrigation and nitrogen application in salinized soil on physiological adaptations and biomass allocation is still limited. In this study, we conducted a three-factor orthogonal pot experiment with four levels per factor in 2023 and 2024 as follows: salinity (S0: non-saline, S1: low salinity, S2: moderate salinity, S3: high salinity); irrigation amount (W0: 605, W1: 770, W2: 935, W3: 1100 mm); and nitrogen application (N0: 0, N1: 60, N2: 120, N3: 180 kg/ha). This resulted in 14 irrigation-nitrogen-salinity combined treatments. The results showed the following: (1) Irrigation, nitrogen and salinity significantly affected leaf dimensions, photosynthetic rate, plant height, biomass allocation and dry matter of the total plant (p < 0.05). (2) Significant coupling interactions were observed between salinity and irrigation, as well as between nitrogen and irrigation, affecting leaf morphology, plant height, leaf dry matter and total biomass accumulation; a coupling interaction of salinity and nitrogen was found to affect the leaf area, root, stem and leaf dry weight. (3) The S0N2W2 treatment produced the highest dry biomass, which was 2.2 times higher than for the S3N2W2 treatment. (4) Under moderate-salinity conditions (S2), biomass allocation favored stems and leaves, whereas under high-salinity conditions (S3) biomass allocation shifted towards leaves, followed by stems and roots. A combination of 935 mm irrigation amount and 120 kg/ha nitrogen (N2W2) under S1 and S2 is recommended to optimize biomass production. Our study provides practical irrigation and nitrogen management strategies to enhance A. donax cultivation on marginal saline lands, supporting climate-resilient bio-economy initiatives.

Changes in crop types and long-term monoculture substantially impact soil microbial communities. Exploring these changes and their influencing factors is of great significance for addressing the challenges posed by continuous cropping. Soil surface layer samples from greenhouse tomatoes fields cultivated for 5 (Y5), 9 (Y9), 13 years (Y13), and a surrounding corn field (CK) as a control were analyzed. The Y13 sample showed a significant increase in the relative abundance of Pseudomonadota (43.1%) and a decrease in Actinobacteria (50.3%) compared to the CK sample. Soil bacterial alpha diversity generally declined from the CK to Y13 (0.1–22.2%) sample, with a small peak in Y9 for Chao1 and Observed_species. Significant differences in Chao1 and Observed_ species were observed between the CK and Y13 samples. Beta diversity analysis revealed a pronounced variation in soil bacterial community structure across planting years, with the divergence from the CK sample intensifying over time. In comparison to the Y5 vs. CK samples, Y9 and Y13 exhibited marked differences from the CK across the same and broader metabolic pathways, suggesting a potential convergence of microbial activities over time. The Y9 and Y13 samples showed significantly higher biosynthesis abundance (7.50% and 6.36%, respectively) than the CK. In terms of soil physicochemical indices, the carbon–nitrogen ratio was the primary factor influencing soil bacterial composition. In conclusion, we found that crop alteration and continued planting changed the soil’s bacterial composition and increasing planting years suppressed the soil’s bacterial diversity, leading to a stable bacterial ecology after nine years. Implementing appropriate measures during this critical period is vital for optimal soil utilization.

Agro-photovoltaics (APV) or agrivoltaic systems integrate crop cultivation with solar energy production, offering a promising solution through the dual-use of land. This two-year study (2023 and 2024) examined the effects of an APV system on rice production. The results indicated that APV arrays created spatially variable light environments, with shadow lengths following predictable solar azimuth patterns and cloudy conditions mitigating shading effects through enhanced diffuse light. Compared with CK (non-shadow area), inter-panel plots (BP) maintained 77% photosynthetic efficiency and 85.4% plant height, whereas the areas beneath the panel showed a significant decrease in the relative chlorophyll content (SPAD values), photosynthesis rates, and yield. BP plots preserved a 78% fruiting rate through adaptive stomatal regulation, whereas LP zones (directly under the low eave) exhibited 35% higher intercellular CO₂ because of the limited assimilation in shading. Rice yield losses were correlated with shading intensity, driven by reduced panicles and grain filling. Moreover, the APV system achieved a high land equivalent ratio of 148–149% by combining 65–66% rice yield with 82.5% photovoltaics output. Based on the microenvironment created by the APV system, optimal crop types and fertilisation are essential for enhancing agricultural yields and improving land use efficiency.

Arundo donax L. (giant reed) is a perennial rhizomatous grass with high drought and salinity tolerance, making it a promising low-input bioenergy crop. However, the combined effects of irrigation and nitrogen application in salinized soil on physiological adaptations and biomass allocation are still limited. In this study, we conducted a three-factor orthogonal pot experiment with four levels per factor in 2023 and 2024: salinity (S0: non-saline, S1: low salinity, S2: moderate salinity, S3: high salinity); irrigation amount (W0: 605, W1: 770, W2: 935, W3: 1100 mm); and nitrogen application (N0: 0, N1: 60, N2: 120, N3: 180 kg/ha). This resulted in 14 irrigation-nitrogen-salinity combined treatments. The results showed the following: (1) Irrigation, nitrogen and salinity significantly affected leaf dimensions (length, width, area and leaf elongation rate, specific leaf weight), photosynthetic rate, plant height, biomass allocation and dry matter of total plant (p < 0.05). (2) Significant coupling interactions were observed between salinity and irrigation, as well as between nitrogen and irrigation, affecting leaf width, leaf elongation rate,plant height,leaf dry matter and total biomass accumulation; coupling interaction of salinity and nitrogen were found to have effect on leaf width, leaf area, leaf fresh weight, root, stem and leaf dry weight. (3) The S0N2W2 treatment produced the highest dry biomass (44.76 ± 0.68 g/plant), which was 2.2 times higher than the S3N2W2 treatment (20.13 ± 0.50 g/plant). (4) Under moderate salinity conditions (S2), biomass allocation favoured stems (42.70%, mean values of 2023 and 2024) and leaves (39.53%, mean values of 2023 and 2024), whereas under high salinity conditions (S3) biomass allocation shifted towards leaves, followed by stems and roots. A combination of 935 mm irrigation amount and 120 kg/ha nitrogen (N2W2) in S1 and S2 is recommended to optimise biomass production. Our study provides practical irrigation and nitrogen management strategies to enhance A. donax cultivation on marginal saline lands, supporting climate-resilient bio-economy initiatives.

The rational use of reclaimed water for irrigation is a vital strategy to alleviate water scarcity in arid and semi-arid regions. Assessing its impact on heavy metal behavior in soil–plant systems is crucial for ensuring agricultural safety. This study evaluated the effects of four irrigation water sources—well water (CK, control), river water (R0), a 1:1 mixture of river and reclaimed water (R1), and reclaimed water (R2)—on the distribution of heavy metals (Mn, Zn, Cu) in soil profiles and their accumulation in corn organs across growth stages. Results indicated that soil Mn content increased over time, whereas Zn and Cu levels generally decreased, with the smallest reduction observed in the R2 treatment at deeper soil layers. In corn, Mn and Cu were primarily concentrated in roots and leaves, while Zn accumulated notably in grains. Plant heavy metal content was generally lower under R2 than CK. Risk assessment indicated slight Mn pollution in soil, whereas Zn and Cu remained within safe limits. Health risk indices (THQ) for R1 and R2 were lower than CK. Overall, the mixed water treatment (R1) showed the strongest potential for controlling heavy metal contamination, suggesting that blended reclaimed water can support sustainable irrigation with long-term Mn monitoring recommended.

Soil respiration (Rs) plays a pivotal role in carbon cycling within semi-arid ecosystems. In our millet field experiment, we measured Rs, autotrophic respiration (Ra), heterotrophic respiration (Rh), water consumption (ET), yield (Y), water use efficiency (WUE), and key soil environmental properties to examine the effects of supplemental irrigation and selenium application on Rs dynamics and to clarify the controlling factors. The experiment was conducted from 2023 to 2024 with four treatments and three replicates per treatment each year. These treatments comprised conventional rainfed (CK), supplemental irrigation (SI, 50 mm), rainfed with Se addition (CS, 67.84 g·hm⁻²), and supplemental irrigation with Se addition (SIS). SI increased CO₂ emissions in the millet field, whereas selenium application (CS) suppressed them. Ra was the dominant component of Rs and was 1.03–4.01 times greater than Rh. SI and CS significantly affected cumulative CO₂ emissions through Ra (p < 0.05), whereas their effects on Rh were minor. The CS treatment resulted in the lowest cumulative CO₂ emissions at 4233 and 4009 g·m⁻² in 2023 and 2024, respectively. Diurnal variation patterns of Rs, Ra, and Rh differed across millet growth stages. Both supplemental irrigation and selenium application improved soil water retention, soil enzyme activity, and soil organic matter (SOM), and moderated soil temperature. Classification and Regression Tree (CART) algorithm analysis revealed that Ra was primarily driven by soil temperature, with a feature weight of 86.95% determined by CART based on machine learning, whereas Rh was mainly influenced by soil enzyme activity, with a feature weight of 76.11%. The CS treatment enhanced production while promoting emission mitigation. The combined SIS treatment achieved the highest WUE and maintained a lower Rs than SI. These findings suggest an environmentally sustainable management strategy for millet production in semi-arid regions. However, due to the limited number of parcels in this study, further field-scale validation and additional experimental research involving multiple levels of supplemental irrigation and Se addition are necessary.