Changes in seed germination strategy along the successional gradient from abandoned cropland to climax grassland in a subalpine meadow and some implications for rangeland restoration

Abstract Various plant successional gradients on the Qinghai-Tibetan Plateau are created by overgrazing of rangelands and by abandonment of cultivated land. A key point for restoration of these grasslands is the germinability of seeds that are sown in the field. Thus, information on how germination strategies change during succession will be helpful in restoring the grasslands in different successional stages. We sampled subalpine meadows abandoned from agriculture for 1, 5 and 15 years and an undisturbed (climax) meadow. Seed germination of species of communities in different successional stages and the climax were tested in the laboratory under different conditions. Change in germination strategy from the pioneer stage to climax was analyzed at the community level. Our results indicated that 1) at the community level, germination of species in the pioneer stage of succession (SS) is significantly different with that of those in the later SS; 2) species in the pioneer SS germinated better at 10-25℃ than those in the later (5 and 15 years) stages and in the climax; 3) the optimal temperature range for germination for the 1-year-old and climax communities (15-25℃) is wider than that of the 5- and 15-year-old communities (20-25℃); 4) germination of species in the 5- and 15-year-old communities had a significant positive response to alternating temperature and wet-cold storage but the 1-year-old and climax communities did not; 5) the SS has different effects on the diversity index for a single germination trait (FDrao), depending on the kind of trait, however, the diversity for the suite of seed germination traits (FRic) tends to decrease with progression of succession; 6) both species richness and phylogenetic diversity increase with progression of succession. Thus, the seed germination strategy changed with the progression of succession, and it was correlated with changes in vegetation density and height along the successional gradient. This research can give us some guidelines for grassland restoration by adding seeds.