Effects of grazing regimes on plant traits and soil nutrients in an alpine steppe, Northern Tibetan Plateau

Abstract

Understanding the impact of grazing intensity on grassland production and soil fertility is of fundamental importance for grassland conservation and management. We thus compared three types of alpine steppe management by studying vegetation traits and soil properties in response to three levels of grazing pressure: permanent grazing (M1), seasonal grazing (M2), and grazing exclusion (M3) in the alpine steppe in Xainza County, Tibetan Plateau. The results showed that community biomass allocation did not support the isometric hypothesis under different grassland management types. Plants in M1 had less aboveground biomass but more belowground biomass in the top soil layer than those in M2 and M3, which was largely due to that root/shoot ratios of dominant plants in M1 were far greater than those in M2 and M3. The interramet distance and the tiller size of the dominant clonal plants were greater in M3 than in M1 and M2, while the resprouting from rhizome buds did not differ significantly among the three greezing regimes. Both soil bulk density and soil available nitrogen in M3 were greater than in M1 at the 15-30 cm soil depth (P = 0.05). Soil organic carbon and soil total nitrogen were greater in M3 than in M1 and M2 (P = 0.05). We conclude that the isometric hypothesis is not supported in this study and fencing is a helpful grassland management in terms of plant growth and soil nutrient retention in alpine steppe. The extreme cold, scarce precipitation and short growing period may be the causation of the unique plant and soil responses to different management regimes.

Figure 1. The experiment sites in alpine steppe, northern Tibetan Plateau.

Figure 2. The vegetation composition diagram is in the study area.

The Vegetation coverage of the alpine steppe was about 20%, which are dominated by Stipa purpurea and Carex moorcrofii (panel A) and the accompanying species are Stellera chamaejasme Linn., Leontopodium alpinum, Oxytropis microphylla (panel B) and so on.

Figure 3. Relationships between AGB and BGB under grazing (M1), seasonal grazing (M2), and grazing exclusion (M3) regimes.

Figure 4. Biomass fractions (% of total biomass) in herbaceous plants in M1, M2 and M3 of Tibetan Plateau.

Figure 5. The morphological characteristics of C. moocroftii in the different grassland management types.

A, represent plant height, B, number of rhizome buds, C, interramet distance, and D tiller number.