Document Type : Research Paper
Authors
Abstract
Rangelands are one of the important natural ecosystems in our country that were deteriorated during recent decades because of many causes especially earlier and intensive grazing. Grazing management need to determine beginning of grazing season and intensity in rangelands. It is very important to know much about physiological and phenological status of rangeland species. Total nonstructural carbohydrates (TNC) and their changes during seasonal growth is one of the important physiological parameter in perennial plants. Also these reserves are primary source of energy in respiration, growth and survival of perennial plants during their quiescence and growth season and regrowth after grazing or cutting. In this research seasonal changes of TNC reserves in three perennial and desirable grass species(Bromus tomentellus, Festuca ovina, Dactylis glomerata) were studied in Polor summer rangelands(altitude, 2600m; annual precipitation, 535mm; with cold mountain climatic) at the north of Tehran province. Samples were collected in ten stages of plants phenology stages with three replications from above and underground matter (canopy and roots). Samples were oven dried at 70◦C during 48 houres. TNC concentration were measured by phenol-solpheric method (mg per gr dry matter). Data of all attributes were analyzed in the frame of rondomized compeletly block design by using Minitab software, and ANOVA one and two ways. Seasonal changes of TNC reserves in any of studied species and also their root and canopy were shown in annual curves. The results indicated that all species have distinct seasonal changes and they had the lowest TNC reserves at early spring and end of the seasonal growth and then increased. The results showed significant differences in TNC reserves between phenology Stages in root and canopy during seasonal growth (P= 0.05 & 0.01) and all species had higher amount of TNC reserves in root than canopy (P=0.01). The rate of TNC restoration was different between studied species. These differences were related to phenology and seasonal growth along. So in this area Dactylis glomerata is more sensitive to grazing and Bromus tomentellus conversely is more resistant to grazing. At the end we concluded that critical period for all species in relate of their TNC reserves is from starting growth in early spring till early May and at the end of seasonal growth, mid August. Beginning of grazing season from late may until early August is recommended for this area.
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