Source of inorganic N affects the cost of growth in a legume tree species (Virgilia divaricata) from the Mediterrean-type Fynbos ecosystem

Aims In Mediterranean-type ecosystem, the Cape Fynbos, legumes may be able to switch between soil N and atmospheric N 2 sources during growth to adjust the carbon costs of N acquisition. This study investigated the utilization of different inorganic N sources by Virgilia divaricata, a native legume from the Mediterranean-type ecosystem of the Cape Floristic Region.Methods Plants were cultivated in sterile quartz sand, supplied with 25% strength Long Ashton nutrient solution, modified to contain 500 μM Phosphate. At the phosphate level (500 μM), plants were treated with 500 μM NH 4 NO 3 (treatment named N), or grown in N-free nutrient solution and inoculated with effective Burkholderia sp. (Bact.) or treated with combined N sources (500 μM NH 4 NO 3) and inoculated with effective Burkholderia sp. (N+Bact.).Important findings The application of NH 4 NO 3 to the legumes resulted in a greater increase in plant dry matter. Carbon construction costs were higher in plants that were supplied with mineral and symbiotic N sources. Maximum photosynthetic rates per leaf area was maintained, irrespective of the N sources. Although the plant roots were nodulated, the plant dependence on N 2 fixation decreased with addition of N. Roots and nodules of the plants solely reliant on N 2 fixation showed an increase in glutamine content. These results show that V. divaricata is highly adapted for growth at the forest margin. Fynbos and possibly anthropic soils by utilizing both atmospheric and soil N sources.     

Soil nutrient status of KwaZulu–Natal savanna and grassland biomes causes variation in cytokinin functional groups and their levels in above-ground and underground parts of three legumes

Cytokinins (CKs) are involved in several developmental stages in the life-cycle of plants. The CK content in plants and their respective organs are susceptible to changes under different environmental conditions. In the current study, we profiled the CK content in the above and underground organs of three legumes (Lessertia frutescens, Mucuna pruriens and Pisum sativum) grown in soils collected from four locations (Ashburton, Bergville, Hluhluwe and Izingolweni) in KwaZulu-Natal province, South Africa. The quantified CK contents in the three legumes were categorized on the basis of their side chains (isoprenoid, aromatic and furfural) and modifications (e.g. free bases and glucosides). Legume and soil types as well as their interaction significantly influenced the concentrations of CKs. Lessertia frutescens, Mucuna pruriens and Pisum sativum had CK content that ranged from 124–653, 170–670 and 69–595 pmol/g DW, respectively. Substantial quantity (> 600 pmol/g DW) of CK were observed in plants grown in Bergville (above-ground part of Lessertia frutescens) and Izingolweni (underground part of Mucuna pruriens) soils. A total of 28 CK derivatives observed in the legumes comprised of isoprenoid (22), aromatic (5) and furfural (1) side-chain CKs. However, the 16 CK derivatives in Mucuna pruriens were isoprenoid-type based on the side-chain. Generally, a higher ratio of cis-zeatin (cZ) relative to the trans-zeatin (tZ) was evident in the above-ground part of Lessertia frutescens and Pisum sativum for the four soil treatments. In terms of functional and physiological importance of the CKs, the free bases (active form) and ribosides (translocation form) were the most abundant CK in Lessertia frutescens and Pisum sativum. However, N-glucoside, a deactivation/detoxicification product was the most dominant CK in Mucuna pruriens from Hluhluwe and Izingolweni soils. The total CKs in the underground parts of the legumes had a positive significant correlation with the total phosphorus and nitrogen content in the plant as well as the soil nitrogen. Overall, the CK profiles of the legumes were strongly influenced by the soil types.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12298-021-01021-2.     

Symbionts in Mucuna pruriens stimulate plant performance through nitrogen fixation and improved phosphorus acquisition

刺毛黎豆共生体通过固氮和提高磷吸收来提高植株的生长表现 南非主要以热带稀树草原和草原生态系统为主，这些生态系统具有酸性和营养缺乏的属性，特别是磷和氮素的缺乏。刺毛黎豆(Mucuna pruriens)是在大多数非洲国家广泛存在的一种本土豆科植物，该 植物可以抵御这些不利的土壤条件。豆科植物在世界上许多国家具有药用价值，也被用于土壤施肥。尽管已有文献记载了在营养胁迫生态系统中刺毛黎豆的生长和建植，但尚未对其在磷缺乏条件下的共生互作、氮源偏好和与生长相关的碳成本进行研究。在本研究中，我们确定了微生物共生体对磷缺乏条件下的刺毛黎豆氮营养和生长相关的碳成本的影响。我们从4个不同的地理位置采集微生物接种土壤，然后将种子在这些天然土壤中发芽，在根瘤发育的早期，将幼苗转移到无菌石英砂中，并提供不同磷 浓度的营养培养基。16S RNA序列结果显示，在不考虑磷浓度的情况下，Burkholderia sp., Paenibacillus sp.和Bacillus 均有分枝。尽管磷缺乏导致总生物量/生长下降，但根系生物量、根瘤数量和碳成本增加。低磷供给的幼树丛枝菌根真菌根系定殖率最高。刺毛黎豆中，大气中的氮与磷水平呈正相关关系，幼树对大气氮素和土壤氮素具有双重依赖，低磷植株对土壤氮素的依赖程度增加。因此，在磷缺乏的情况下，刺毛黎豆表现出不同的形态和微生物共生关系。