Abstract:We compared the effect of grazing on biomass allocation of 27 species of plants in alpine meadows of the Qinghai-Tibetan Plateau, to address the following questions: (1) Does grazing significantly affect biomass allocation of these species? (2）If so, what are the general patterns of response? (3) Does this effect differ among species and functional groups within same community? (4) Does grazing affect the biomass allocation of the plant community?
From June to September in 2006, we sampled 25-30 individuals (above-ground parts) of each species from ten random plots of each of two treatments-long-term grazing and grazing exclusion for 7 years. When sampling, we considered the fruiting phenology of each species. We divided species into four functional groups——legumes, unpalatable forbs, palatable forbs and graminoids. Each individual was dissected into reproductive organs，stems, and leaves, dried to constant weight for 48h at 80℃, and weighed with a Sartorius Balance (10-4g). Individual biomass (IB) was calculated as the sum of these biomass components. We then calculated reproductive allocation (RA) = reproductive organ biomass / IB, stem allocation (SA) = stem biomass / IB, and leaf allocation (LA) = leaf biomass / IB. We used independent-samples t-tests to test the difference of IB (RA, SA and LA) between two grazing treatments for each species. We also determined above-ground biomass and biomass allocation for both grazed and grazing exclusion treatments.
The result showed as following. i) Grazing significantly affected individual biomass and biomass allocation of the study species. ii) Generally, grazing decreased average individual biomass while increasing reproductive allocation for most species. Average leaf allocation tended to decrease in response to grazing for most species. iii) The effect of grazing on biomass and biomass allocation differed among species and functional groups. Reproduction allocation tended to increase for palatable forbs, legumes and graminoids, and to decrease for unpalatable forbs. Stem allocation tended to increase for graminoids and decrease for forbs and legumes. Leaf allocation tended to increase for unpalatable forbs and decrease for palatable forbs, legumes and graminoids. iv) At the community level, reproductive allocation and leaf allocation increase because of grazing, and stem allocation decreased.