Summary: 1. We examined geographic variation in mean individual seed mass (MISM) among 38 populations within and across nine Pedicularis species in the eastern Tibetan Plateau, measuring the effects of one extrinsic factor (elevation) and two intrinsic factors (plant size and mean seed number per fruit). 2. Across all populations, elevation is negatively correlated with MISM; within eight of nine species, this pattern is also observed among populations. This relationship, however, is not significant when controlling for variation in plant size or seeds per fruit. High‐elevation populations produce smaller plants with more seeds per fruit than low‐elevation populations; controlling for these variables eliminates the negative correlation between elevation and MISM. 3. Across all populations, the predicted trade‐off between MISM and seeds per fruit is consistently strong, with or without controlling for the effects of plant size. By contrast, the trade‐off between MISM and total seasonal fecundity can be detected only when controlling for plant size. 4. Independent of plant size, populations that produce small seeds do not support individuals with particularly low reproductive yield (fecundity × MISM). Accordingly, high‐elevation populations exhibit neither lower reproductive yield nor smaller seeds than expected given their lower biomass. 5. Synthesis. In Pedicularis, elevation, plant size and seeds per fruit are all correlated with MISM among populations across species. Elevation is less important, however, than intrinsic factors in determining the MISM of a population; the effect of elevation on MISM disappears when the effects of intrinsic factors are controlled statistically. The observed decline in MISM with increasing elevation is therefore partly mediated by the decline in plant size and partly by an increase in mean seed number per fruit with elevation. Altitudinal variation in MISM across populations or species has been described before, but this is the first study to control for the effect of intrinsic factors simultaneously. This result calls into question the conclusions of studies that have detected geographic variation in MISM without controlling for variation in intrinsic factors.

1 Reproductive biomass (RB) is a key component of plant life history. Because RB is allometric, it remains unclear whether the observed variations of RB in response to land use are driven only by a size dependency effect or if the partitioning of plant biomass may also shift independently of plant size. This question has not been addressed for all the main component species of a given plant community. 2 Here, we report the results of a 3‐year experimental study conducted in Tibetan alpine grasslands. The above‐ground vegetative biomass (VB) and the RB of 32 species were measured during 2 years in control, grazed and fertilized plots. We estimated the allometric slope and intercept for 301 VB–RB bivariates, using type II regression analyses in order to disentangle size‐dependent and size‐independent effects of treatment on RB. 3 Our results indicate significant changes in the VB–RB allometric slope for 26 out of 102 cases in grazed plots, and 16 out of 88 cases in fertilized plots. Moreover, in cases where slopes were not affected by treatment, a significant change in the allometric intercept was found in 50% of the models. For these cases, intercepts – which are indicative of the biomass invested in reproductive parts for a given VB – generally increased in grazed plots and decreased in fertilized plots. 4 Grazing and fertilization triggered a significant decreases or increases in the plant size for species, especially graminoids. However, we found no relationship between changes in allometric coefficients and magnitude of the biomass response. 5 At the interspecific level, the intercept, but not the slope, of the allometric VB–RB relationships was significantly affected by land use. Graminoids and forbs responded similarly to treatment. 6 Synthesis. We conclude that (i) size‐dependent effects did not explain all the changes observed in RB following grazing and fertilization in alpine grasslands, and that (ii) changes in allometric intercept explained most of the size‐independent variations both at the intra‐ and interspecific level. We discuss why size‐independent changes in RB could be important for plant performance in changing environments.

Germination response to fluctuating temperatures is a mechanism by which seeds detect gaps in vegetation canopies and depth of burial in soil, and it is very important for plants. Thus, studies on the effect of fluctuating temperature on germination at the community level are valuable for understanding community structure and biodiversity maintenance. We determined the effects of two alternating temperatures (5/25°C and 10/20°C) and one constant temperature (15°C) on seed germination of 445 species in a grassland community on the eastern Tibet Plateau. Seed mass was determined for each species, and data on habitat, type of life cycle, altitudinal distribution and functional group (graminoids or forbs) were obtained from the literature. Taking all species into account, alternating temperatures increased germination percentages regardless of amplitude. Overall, species growing in disturbed ground showed a significant germination response to temperature fluctuation, but those living in Alpine/subalpine meadow, forest margin /scrub, marshland and dry sunny slope habitats did not. Species distributed only at high elevations (>2000m) did not show a significant germination response to temperature fluctuation, whereas those occurring at both high and low elevations had a significant positive response. Germination of annuals/biennials was significantly promoted by 5/25°C, but not by 10/20°C, whereas germination of perennials was significantly promoted by both 5/25°C and 10/20°C. Small-seeded species were more likely than large-seeded species to respond positively to fluctuating temperatures. Germination of forbs had a positive response to temperature fluctuation, but germination of graminoids did not. Regeneration ability by seeds for about 36% of the species studied in the grassland can be increased by temperature fluctuation. The differential response among species to alternating vs. constant temperatures helps maintain community structure and biodiversity. A positive germination response to temperature fluctuation can partly explain why there are more forbs in degraded meadows.