Alfalfa (Medicago sativa L.) is a nutritious forage plant in dryland regions with strong drought tolerance and broad adaptability. To understand the architectural characters and physiological functions of the root systems in response to different drought stress and rehydration, two experiments were conducted in a glasshouse. Experiment 1 used three alfalfa cultivars and four soil moisture treatments in a split-plot design with four replicates to investigate the response of root systems of different alfalfa cultivars to drought stress and subsequent rehydration. Experiment 2 used one alfalfa cultivar and four soil moisture treatments in a randomized complete block (RCB) design with three replicates to measure reactive oxidant species and antioxidant defense systems of alfalfa root. The soil moisture treatments included (1) 75–80% of the water-holding capacity (CK); (2) 60–65% of the water-holding capacity and subsequent rehydration to 75–80% of the water-holding capacity; (3) 45–50% of the water-holding capacity and subsequent rehydration to 60–65% and 75–80% of the water-holding capacity; and (4) 30–35% of the water-holding capacity and subsequent rehydration to 45–50%, 60–65% and 75–80% of the water-holding capacity. Our results demonstrated that plants had higher root biomasses (mean = 0.77 g), fractal dimensions (1.47), fractal abundances (3.84), and branching ratios (0.39) under severe water deficit and rehydration than under less stressful soil moisture conditions. Plant root systems tended to exhibit herringbone branching (Topological Index = 0.63) when soil moisture was at 60–65% water-holding capacity with the soil being then rehydrated, whereas they tended to have a smaller lateral root length, root surface area, root volume, and branching ratio and larger root diameter under more favorable soil moisture conditions for less stressful soil moisture treatments. Severe water stress and subsequent considerably improved superoxide (O₂⁻) generation rate, the content of hydrogen peroxide (H₂O₂) and Malondialdehyde (MDA), and non-enzyme antioxidant glutathione (GSH), and reduced the content of ascorbate (AsA) and activity of catalase (CAT), ascorbate peroxidase (APX), and glutathione peroxidase (GPX). It is concluded that Medicago sativa L. cv Zhaodong (ZD) and cv Aohan (AH) exhibited higher drought resistances than cv Golden empress (GE) using topological and fractal analyses. This could be a key contributor to altering optimum soil moisture conditions and screening alfalfa cultivars based on root system architecture and antioxidant defense systems. The molecular functions warrant further investigation which could help explain the observed root phenotypes after drought conditions and rehydration.

Forty-seven lucerne varieties/lines were examined to quantify their morphological, production characteristics, and nutritive values in southeastern Australia. The experiment was established in 2015 with a randomized complete block design and four replications. The morphological and production characteristics were measured from January to October 2017, and nutritive values were measured in February 2017. The results showed that the cultivars differed significantly (P < 0.01) in morphological, production characteristics, and nutritive values. Total herbage yield was highest for Haymaster 7 (14,186 kg/ha) and lowest for Qingshui (5927 kg/ha). Plant height was highest for Cropper 9.5 (31.4 cm) and lowest for Qingshui (14.5 cm). SF 714QL had the greatest branch number (44.7 branches/15 cm row segment). AV1001 had longest leaf (2.3 cm) and greatest leaf area (16.68 cm²/10 leaves) whereas Force 10 and SARDI 10 SERIES 2 had widest leaves (1.3 cm). AV1005 had the highest leaf-to-stem ratio (5.64). Crude protein (CP) content was highest for SARDI 10 SERIES 2 (15.1%) and lowest for SF 714QL (8.0%). AV12 was highest in crude fat (4.5%). Neutral detergent fiber (NDF) content was lowest in Stamina 5 (33.5%). Acid detergent fiber (ADF) content was lowest in Gannong 4 (29.3%). Relative feed value (RFV) was highest in Force 11 (193.0%). Calcium (Ca) content was highest for Titan 5 (1.8%). Phosphorous content was highest for AV1 and Gannong 6 (0.1%). Overall, Cropper 9.5, SARDI 10 SERIES 2, Haymaster 9, Titan 9, SF 714QL, Kaituna, Haymaster 7, AV1001, AV1002, and WL925HQ performed well based on their comprehensive scores. Graphical Abstract Abbreviations: CP - crude protein; CF - crude fat; NDF - neutral detergent fiber; ADF - acid detergent fiber; Ca - calcium; P - phosphorus; RFV - relative feed value.

A field grazing experiment was conducted in Jingtai County, Gansu Province, China, from 2003 to 2010. The grazing intensity treatments included light grazing (LG, 0.45 sheep unit/ha), moderate grazing (MG, 0.75 sheep unit/ha), heavy grazing (HG, 1.50 sheep unit/ha), and no grazing (NG). Soil physical, chemical, and biological properties were measured. The results showed that, with increasing grazing intensities, the concentrations of total nitrogen, available nitrogen, organic matter, available phosphorus, available potassium, urease, catalase, and alkaline phosphatase in the soil decreased significantly with LG being mostly the greatest (P < 0.05). Soil bulk density for HG and NG was greater than that for LG and MG (P < 0.05). The concentrations of copper, manganese, and zinc were lower than their critical levels for plant growth, whereas iron was greater than its critical level. Correlation and principal component analyses revealed that soil trace elements were the secondary principal component compared with the primary elements, i.e., soil moisture, bulk density, etc.

Alfalfa (Medicago sativa L.) is a perennial leguminous plant, with a strong tap root system that plays an important role in alfalfa’s adaptation to drought stress. However, a better understanding of root functional traits and how these root traits are related to whole plant responses in order to improve pasture productivity under water deficit. Two greenhouse experiments were conducted: Experiment 1 used three alfalfa cultivars and four levels of soil water content treatments to investigate herbage productivity, growth point density, residual shoot weight, and root weight. Experiment 2 assessed relationships among root-sourced abscisic acid (ABA), root system architecture and plant biomass in response to water deficit. The results demonstrated that root system was used as a useful tool to improve tolerant and adaptation when alfalfa copied with lower levels of soil water content. On average, maintaining 60–65% soil water-holding capacity alfalfa had the highest herbage accumulation (6.7 g DM pot-1), growing point density (46.5 pot-1), and residual shoot biomass (1.8 g DM pot-1). At the level of water stress, Medicago sativa L. cv Zhaodong (ZD) and cv Aohan (AH) tended to exhibit a herringbone branching pattern with less root tips, root forks, altitude, and magnitude than cv Golden empress (GE). Principal component analysis and structural equation modeling revealed that root-sourced ABA positively regulated the altitude and magnitude of root system architecture, root tips and root forks, and was closely associated with plant root biomass and herbage biomass. It was concluded that these findings can contribute to developing optimum irrigation strategies and help alfalfa breeders in the development of new cultivars with improved drought tolerance based on root system architecture, plant hormone, and plant growth.

Pasture degradation caused by overgrazing and inappropriate fertiliser management is a major production and environmental threat in Qinghai-Tibet Plateau. Previous research has focused on the effects of mixed nitrogen (N) and phosphorus (P) fertiliser and reduced grazing pressure on the plant community of the grassland; however, the role of P and how it interacts with various defoliation (the process of the complete or partial removal of the above-ground parts of plants by grazing or cutting) intensities on the plant and soil of the grassland ecosystem have not been quantified. A field experiment was conducted to quantify how P application in combination of defoliation pressure could impact the dynamic change of the plant and soil in a native alpine grassland ecosystem of the Qinghai-Tibet Plateau, China, from May 2012 to September 2014. A split-plot design with 4 replicates and repeated measures was used to determine the growth and composition of plant community and soil physical and chemical properties under various levels of P fertiliser and defoliation intensity. The results showed that applying 20 kg P/ha increased the herbage yield of Melissitus ruthenica by 68% and total pasture yield by 25%. Close defoliation favoured the growth and plant frequency of the shorter species, whereas lax defoliation favoured that of the taller plant species. Medium P rate and cutting to 3 cm above ground gave an overall best outcome in pasture yield, quality and frequency and soil moisture and nutrient concentration. Application of P fertiliser with a moderate defoliation pressure to promote legume growth and N fixation has the potential to achieve multiple benefits in increasing pasture and livestock production and improving environmental sustainability in the alpine pasture of Qinghai-Tibet Plateau, a fragile and P-deficient ecosystem zone in China and its western neighbouring countries.