Plasticity in the growth habit prolongs survival at no physiological cost in a monocarpic perennial at high altitudes

Background and Aims Monocarpic plants are those that flower, produce seeds and then die. Although most monocarpic plants are annual or biennial, some of them are perennial. However, relatively little is known regarding the biology of monocarpic perennials. Pyrenean saxifrage (Saxifraga longifolia) is a monocarpic perennial that is well adapted to high-mountain ecosystems. Here, we evaluated altitudinal changes in clonality in various populations growing in their natural habitat with particular emphasis on the physiological costs of clonal growth. Methods We assessed the percentage of clonal plants in nine populations growing in their natural habitat, as well as the plant stress response of clonal and non-clonal plants, in terms of photoprotection and accumulation of stress-related phytohormones, in a 3-year study at Las Blancas (2100 m a.s.l.). We also evaluated the influence of plant size on the activation of defensive responses to biotic and abiotic stresses. Key Results We found that 12 % of Pyrenean saxifrage plants growing at the highest altitudes (2100 m a.s.l.) produced lateral rosettes which survived the flowering of the main rosette and shared the same axonomorphic root, thus escaping monocarpic senescence. This clonal growth did not worsen the physiological performance of plants growing at this altitude. Furthermore, increased plant size did not negatively affect the physiology of plants, despite adjustments in endogenous stress-related phytohormones. In contrast, maturity led to rapid physiological deterioration of the rosette, which was associated with monocarpic senescence. Conclusions This study shows that the evolution of clonality has allowed Pyrenean saxifrage to survive harsh environmental conditions and it provides evidence that harsh environments push plant species to their limits in terms of life form and longevity.

Approach of monocarpic senescence control by nitrogen manipulation in mungbean and cowpea

Pods start growing almost at the same time and mature simultaneously in soybean (Glycine max (L.) Merrill) plants. But mungbean (Vigna radiata L. Wilczek) and cowpea (Vigna sinensis Endl.) perform unsynchronized pod maturity. To overcome unsynchronized pod maturity the nitrogen redistribution aspects of mungbean and cowpea were investigated based on the linkage of soybean. Pot experiment was conducted using a nodulating mungbean variety (cv. XANH NINH THUAN) in 2015 and cowpea variety (cv. IT98K-205-8) in 2016 in the vinyl house at Saga University in Japan. During the experiment, nutrient solution was applied by changing nitrogen concentrations to 5, 25 and 100 ppm (control). Mungbean plants provided with low concentration of 5 and 25 ppm of nitrogen supply was not capable to produce continuous pods. Cowpea plants supplied with low concentration of nitrogen was also unable to produce successful pods continuously. Insufficient nitrogen hampered the continuation of pod setting in both the cases, might be due to, all the vegetative stored nitrogen had been utilized for seed development during the vegetative phase before pod setting. In case of 100 ppm nitrogen supply, for both mungbean and cowpea, no senescence and nitrogen remobilization occurred. However, researches showed that soybean typically undergoes the remobilization evidence, i.e., monocarpic senescence, in 100 ppm of nitrogen supply. J.Bangladesh Agril. Univ. 16(3): 386–395, December 2018