Differential seasonal effects of ephemeral legumes in response to moisture-nitrogen coupling in the deserts of northwestern China

Abstract

Desert ecosystems are ecosystems limited by both nitrogen and moisture, while legumes, as an important source of nitrogen in desert ecosystems, are extremely sensitive to respond to moisture and nitrogen changes. In order to reveal the growth and physiological metabolic processes of desert legumes in response to moisture and nitrogen changes. In this study, two dominant ephemeral legumes, Trigonella arcuata C. A. Mey. and Astragalus arpilobus Kar. & Kir. were selected from the Gurbantunggut Desert through a controlled experiment in greenhouse pots: four moisture treatment levels were established: W1(soil moisture content of 5 %), W2(soil moisture content of 7 %), W3( 9 % soil moisture content), W4(11 % soil moisture content) and three N treatment levels: N1(0 mmol/L 15NH4 15NO3), N2(18 mmol/L 15NH4 15NO3), N3(72 mmol/L 15NH4 15NO3), and we conducted a 15N tracking experiment for the pot treatments throughout the growing season. The results showed that: (1) moisture and nitrogen treatments had similar patterns on above-ground and below-ground as well as total fresh weight, plant height and basal diameter, Chla, Chlb and Chla+b of the two legumes, all of which were greatest in the W3N3 treatment and smallest in the W4N1 treatment, but the growth characteristics and chlorophyll parameters had cumulative differences over the growing season. (2) When subjected to severe moisture and nitrogen stresses, the 2 plants would increase the physiological levels of stress tolerance in vivo to enhance cellular resistance, with the osmoregulatory substance content being the most sensitive in response to moisture, and the cell membrane and antioxidant enzyme systems being the most sensitive in response to nitrogen stress. (3) The adaptive characteristics of physiological metabolic processes in plants to seasonal changes, in which growth characteristics, cell membrane and antioxidant enzyme content accumulation showed: rapid growth period maximum biomass period. In general, drought can hinder nitrogen uptake and transport, while sufficient moisture can accelerate the nutrient metabolism process of plants, and there is a nutrient dilution effect once the moisture is in excess, but in the nitrogen starvation state, the moisture factor has almost no effect on plants, therefore, the moisture-nitrogen coupling effect is more reflective of the physiological response characteristics of the plants when they encountered the adversity stress, and the degree of accumulation is different in different growing seasons, and the plants in the The differences in different growing seasons reflect the changes in photosynthetic intensity and energy demand.