Comparative response to nitrogen deficiency of a tropical and temperate grass in the interrelation between photosynthesis, growth, and the accumulation of non-structural carbohydrate.

Abstract

A tropical grass, Panicum maximum var. trichoglume and a temperate grass, Lolium perenne, were grown in controlled environment rooms at near optimum temperatures of 25 and 18 deg C, respectively. After an initial period of growth on full nitrogen nutrient solution, a proportion of the plants of both species were transferred to 'nil' N nutrient solution. A sequence of destructive harvests was taken as the plants became increasingly N deficient, and calculations were made of relative growth rate (RW), relative leaf area growth rate (RA) and net assimilation rate per unit leaf area (EA). On a similarly treated group of plants, net photosynthetic rate (PN) and dark respiration rate of attached leaves were measured.Organic and nitrate N were estimated on the photosynthesis-tested leaves, and on comparable leaves from the growth analysis plants at each harvest. Percentage total non-structural carbohydrate (%TNC) was estimated for P. maximum only.P. maximum maintained a higher RW and PN than L. perenne at comparable percent leaf N. With increasing N stress, EA of both species declined to a similar relative extent, but RA of P. maximum decreased much less than that of L. perenne. This difference in response to N between the species in the balance of assimilate input and consumption in new growth may in part explain why, under N deficiency, published studies indicate that % TNC reach higher levels in L. perenne and other temperate grasses than in tropical grasses such as P. maximum. (Abstract retrieved from CAB Abstracts by CABI’s permission)