Tropical Grasslands (2007) Volume 41, 292–300

An in vitro evaluation of some drought-tolerant native range plants in terms of ruminal microbial nitrogen, microbial biomass and their fermentation characteristics utilising a gas-production technique

M.R. AL-MASRI

Department of Agriculture, Atomic Energy Commission, Damascus, Syria

Abstract

Native drought-tolerant perennial range shrubs (Alhagi camelorum, Salsola vermiculata, Peganum harmala) and herbaceous range plants (Poa sinaica, Erodium cicutarium, Schismus arabicus) grown naturally on the south-eastern semi-desert of Syria and harvested in the early bloom stage or at seeding were evaluated in terms of microbial nitrogen (MN) and biomass (MBM) production after incubation with or without polyethylene glycol (PEG, 6000) at a ratio of 2:1 PEG:substrate for 96 h. Fermentation kinetics were assessed using an in vitro incubation technique with rumen fluid. The relationships between in vitro gas production (GP), MN and MBM were studied. MN and MBM production varied between species. The response of the range plants to PEG treatment in terms of increased gas production varied between species and with time of incubation, the greatest response occurring between 6 and 24 h incubation. Plants harvested at early bloom produced more gas per unit weight than those harvested at seeding. Initial gas production (a) was highest for E. cicutarium, whereas gas production during incubation (b) and potential gas production (a + b) were high for P. sinaica and E. cicutarium but low for A. camelorum, S. vermiculata and P. harmala. The amount of MN produced from 100 mg substrate was dependent on species and amounted to 0.02–0.54 mg without PEG and 0.17–0.79 mg with PEG. Corresponding values for MBM were 1.62–6.25 mg without PEG and 0.35–9.10 mg with PEG. Microbial nitrogen and MBM production were negatively correlated with GP.

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