Shifts in bryophyte carbon isotope ratio across an elevation × soil age matrix on Mauna Loa Hawaii: do bryophytes behave like vascular plants?

摘要

The carbon isotope ratio (δ¹³C) of vascular plant leaf tissue is determined by isotope discrimination, primarily mediated by stomatal and mesophyll diffusion resistances and by photosynthetic rate. These effects lead to predictable trends in leaf δ¹³C across natural gradients of elevation, irradiance and nutrient supply. Less is known about shifts in δ¹³C for bryophytes at landscape scale, as bryophytes lack stomata in the dominant gametophyte phase, and thus lack active control over CO2 diffusion. Twelve bryophyte species were sampled across a matrix of elevation and soil ages on Mauna Loa, Hawaii Island. We tested hypotheses based on previous findings for vascular plants, which tend to have less negative δ¹³C at higher elevations or irradiances, and for leaves with higher leaf mass per area (LMA). Across the matrix, bryophytes spanned the range of δ¹³C values typical of C3 vascular plants. Bryophytes were remarkably similar to vascular plants in exhibiting less negative δ¹³C with increasing elevation, and with lower overstory cover; additionally δ¹³C was related to bryophyte canopy projected mass per area, a trait analogous to LMA in vascular plants, also correlated negatively with overstory cover. The similarity of responses of δ¹³C in bryophytes and vascular plants to environmental factors, despite differing morphologies and diffusion pathways, points to a strong direct role of photosynthetic rate in determining δ¹³C variation at the landscape scale.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-010-1903-y) contains supplementary material, which is available to authorized users.