Aims To describe the biodiversity patterns of plants along an altitudinal gradient on the Qinghai-Tibetan Plateau and to clarify the bias in plant specimen records at high altitude.
Methods We conducted a large-scale investigation of vegetation at a wide range of altitudes, focusing on a high-altitudinal range (3?200–5?200 m) at different locations on the Qinghai-Tibetan Plateau. We then compared the altitudinal distribution of plant species obtained from our field investigation with that in plant specimen records from published sources and an online database.
Important findings Our data provide evidence that altitude plays a large role in regulating species composition on the Qinghai-Tibetan Plateau. We could not, however, detect a clear relationship between altitude and species richness, although a weak monotonically increasing trend of richness was detected with increasing altitude. According to specimen records, most species have been sampled at a wide range of altitudes, and the average range of 145 species is>2?000 m. Despite this wide range, more than half of the species we observed were at higher altitudes than the specimen records indicate. High-altitude areas have probably been so poorly sampled that only a small fraction of the resident species has been recorded. This study clearly shows the regional bias of specimen records in the Qinghai-Tibetan Plateau.

Aims Our objectives were (i) to elucidate the phylogeography of chloroplast DNA (cpDNA) in Potentilla fruticosa in relation to Quaternary climate change and postglacial colonization, (ii) to infer historical population range expansion using mismatch distribution analyses and (iii) to locate the refugia of this alpine species on the Qinghai-Tibetan plateau during glacial–interglacial periods.
Methods Potentilla fruticosa is a widespread species distributed on the Qinghai-Tibetan Plateau. We sampled leaves of P. fruticosa from 10 locations along a route of ~1?300 km from the northeastern plateau (Haibei, Qinghai) to the southern plateau (Dangxiong, Tibet). We examined the cpDNA of 15 haplotypes for 87 individuals from the 10 populations based on the sequence data from ~1?000 base pairs of the trnS–trnG and rpl20–rps12. Phylogenetic relationship of haplotypes was analyzed using the Phylip software package and the program TCS. The diversity of populations indices was obtained using the program ARLEQUIN.
Important findings With the limited samples, we found that (i) higher nucleotide diversity often occurs in high-altitude populations, (ii) the ancestral haplotypes distribute in the populations with higher nucleotide diversity than recent haplotypes, (iii) the expansion time of population in the high altitudes was estimated to be approximately at 52–25 ka BP (1000 years Before Present, where “Present” is AD 1950) and that in the low altitudes to be ~5.1–2.5 ka BP and (iv) the source location of P. fruticosa is at the high altitudes, which might provide refugia for the species during the interglacial warm periods. The species expanded from the high-elevated locations on the Tanggula Mountains during the Holocene.

Aims Bryophytes play an important role in primary production in harsh alpine environment. As other alpine plants, the alpine bryophytes are often exposed to stronger UV radiation than lowland plants. Plants growing under high UV radiation may differ from those from low UV regimes in their physiological response to UV radiation. We were to (i) test the hypothesis and to address whether and/or how alpine bryophytes differ in photosynthetic photochemical characteristics in response to UV light and (ii) understand the potential effects of UV radiation on photosynthetic photochemical process in alpine bryophytes.
Methods We examined the maximum quantum efficiency of photosystem II (PSII) photochemistry (F v /F m) for two alpine bryophyte species, Distichium inclinatum and Encalypta alpine, from a Kobresia humilis meadow and a Kobresia tibetica wetland, respectively, in Haibei, Qinghai (37°29′N, 101°12′E, altitude 3?250 m), and for a lowland bryophyte, Polytrichum juniperinum, under different spectrum of UV light. Biological spectral weighting function (BSWF) was obtained to evaluate the effect of UV light on the physiological response in these species.
Important findings1)?The maximum quantum efficiency of photosystem II photochemistry (F v /F m) declined linearly with the increase of radiation dose in wavelengths from 250 to 420 nm. The effect of UV radiation on F v /F m decreased with higher rate from 250 to 320 nm and from 400 to 420 nm than in UVA range. 2)?The three species from different ecosystems contrasting in altitudes showed similar pattern of UV effectiveness. In comparison with other species reported so far, the moss BSWF was among those with the most modest decrease trend with spectrum effect of UV light 50 times higher at 250 than at 420 nm. 3)?Under the scenario of 16% reduction of stratospheric ozone, the integrated effectiveness from 290 to 345 nm increased only 5%, suggesting that the photochemical activity of the bryophyte PSII is likely to insensitive to O 3 depletion.

Aims Theories based on resource additions indicate that plant species richness is mainly determined by the number of limiting resources. However, the individual effects of various limiting resources on species richness and aboveground net primary productivity (ANPP) are less well understood. Here, we analyzed potential linkages between additions of limiting resources, species loss and ANPP increase and further explored the underlying mechanisms.
Methods Resources (N, P, K and water) were added in a completely randomized block design to alpine meadow plots in the Qinghai-Tibetan Plateau. Plant aboveground biomass, species composition, mean plant height and light availability were measured in each plot. Regression and analysis of variance were used to analyze the responses of these measures to the different resource-addition treatments.
Important findings Species richness decreased with increasing number of added limiting resources, suggesting that plant diversity was apparently determined by the number of limiting resources. Nitrogen was the most important limiting resource affecting species richness, whereas P and K alone had negligible effects. The largest reduction in species richness occurred when all three elements were added in combination. Water played a different role compared with the other limiting resources. Species richness increased when water was added to the treatments with N and P or with N, P and K. The decreases in species richness after resource additions were paralleled by increases in ANPP and decreases in light penetration into the plant canopy, suggesting that increased light competition was responsible for the negative effects of resource additions on plant species richness.

Aims Rising concentrations of atmospheric carbon dioxide ([CO₂]) may influence forest successional development and species composition of understory plant communities by altering biomass production of plant species of functional groups. Here, we describe how elevated [CO₂] (eCO₂) affects aboveground biomass within the understory community of a temperate deciduous forest at the Oak Ridge National Laboratory sweetgum (Liquidambar styraciflua) free-air carbon dioxide enrichment (FACE) facility in eastern Tennessee, USA. We asked if (i) CO₂ enrichment affected total understory biomass and (ii) whether total biomass responses could be explained by changes in understory species composition or changes in relative abundance of functional groups through time.
Materials and Methods The FACE experiment started in 1998 with three rings receiving ambient [CO₂] (aCO₂) and two rings receiving eCO₂. From 2001 to 2003, we estimated species-specific, woody versus herbaceous and total aboveground biomass by harvesting four 1 × 0.5-m subplots within the established understory plant community in each FACE plot. In 2008, we estimated herbaceous biomass as previously but used allometric relationships to estimate woody biomass across two 5 × 5-m quadrats in each FACE plot.
Important findings Across years, aboveground biomass of the understory community was on average 25% greater in eCO₂ than in aCO₂ plots. We could not detect differences in plant species composition between aCO₂ and eCO₂ treatments. However, we did observe shifts in the relative abundance of plant functional groups, which reflect important structural changes in the understory community. In 2001–03, little of the understory biomass was in woody species; herbaceous species made up 94% of the total understory biomass across [CO₂] treatments. Through time, woody species increased in importance, mostly in eCO₂, and in 2008, the contribution of herbaceous species to total understory biomass was 61% in aCO₂ and only 33% in eCO₂ treatments. Our results suggest that rising atmospheric [CO₂] could accelerate successional development and have longer term impact on forest dynamics.

Aims and Methods The relationship between genetic diversity and species diversity and the underlying mechanisms are of both fundamental and applied interest. We used amplified fragment length polymorphism (AFLP) and vegetation records to investigate the association between genetic diversity of Plantago lanceolata and plant species diversity using 15 grassland communities in central Germany. We used correlation and partial correlation analyses to examine whether relationships between genetic and species diversity were direct or mediated by environmental differences between habitats.
Important findings Both within- and between-population genetic diversity of P. lanceolata were significantly positively correlated with plant species diversity within and between sites. Simple and partial correlations revealed that the positive correlations indirectly resulted from the effects of abiotic habitat characteristics on plant species diversity and, via abundance, on genetic diversity of P. lanceolata. Thus, they did not reflect a direct causal relationship between plant species diversity and genetic diversity of P. lanceolata, as would have been expected based on the hypothesis of a positive relationship between plant species diversity and niche diversity.

Aims In this study, we examined the extent to which between-species leaf size variation relates to variation in the intensity of leaf production in herbaceous angiosperms. Leaf size variation has been most commonly interpreted in terms of biomechanical constraints (e.g. affected by plant size limitations) or in terms of direct adaptation associated with leaf size effects in optimizing important physiological functions of individual leaves along environmental gradients (e.g. involving temperature and moisture). An additional interpretation is explored here, where adaptation may be more directly associated with the number of leaves produced and where relatively small leaf size then results as a trade-off of high 'leafing intensity'—i.e. number of leaves produced per unit plant body size.
Methods The relationships between mean individual leaf mass, number of leaves and plant body size were examined for 127 species of herbaceous angiosperms collected from natural populations in southern Ontario, Canada.
Important findings In all, 88% of the variation in mean individual leaf mass across species, spanning four orders of magnitude, is accounted for by a negative isometric (proportional) trade-off relationship with leafing intensity. These results parallel those reported in recent studies of woody species. Because each leaf is normally associated with an axillary bud or meristem, having a high leafing intensity is equivalent to having a greater number of meristems per unit body size—i.e. a larger 'bud bank'. According to the 'leafing intensity premium' hypothesis, because an axillary meristem represents the potential to produce either a new shoot or a reproductive structure, high leafing intensity should confer greater architectural and/or reproductive plasticity (with relatively small leaf size required as a trade-off). This greater plasticity, we suggest, should be especially important for smaller species since they are likely to suffer greater suppression of growth and reproduction from competition within multi-species vegetation. Accordingly, we tested and found support for the prediction that smaller species have not just smaller leaves generally but also higher leafing intensities, thus conferring larger bud banks, i.e. more meristems per unit plant body size.

Aims Plants in their natural habitats frequently cope with a multitude of abiotic stresses, such as high light intensity, extreme temperatures and water deficit, which often co-occur during periods of drought, especially in semi-arid and arid regions. Exposure of plants to stressful environmental conditions usually induce overproduction of reactive oxygen species (ROS) that, as highly toxic derivatives of O 2, can assault all cell macromolecules, leading to the disruption of cellular homeostasis and, consequently, the uncoupling of major metabolic processes, the photosynthesis and photorespiration. In order to minimize ROS-mediated cellular damage, plants have evolved highly efficient antioxidative defense systems that include both enzymatic and non-enzymatic components. Since abiotic stress can also operate as a strong evolutionary force that shapes adaptations in natural plant populations, the aim of this study was to examine the seasonal variation patterns of two distinct antioxidative systems, ROS-scavenging enzymes and anthocyanin pigments, in the leaf tissue of a steppe plant, Iris pumila, as expressed under contrasting light conditions that the species regularly experiences in the wild.
Methods We selected two natural populations of I.pumila inhabiting the alternative radiation environments in the Deliblato Sands, a sun-exposed dune site and a woodland understory. The specific activity of three antioxidative enzymes, superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) and the content of total anthocyanins were examined in leaves of I.pumila plants collected from each of the 31 Iris clones (17 in the exposed population and 14 in the shaded population) once during each of the three seasons, spring, summer and autumn in 2004. Specifically, a fully expanded leaf was cut from each clonal plant between 15:00 and 16:00 h, immediately frozen in liquid nitrogen and stored at ?70°C until preparation.
Important findings Generally, all three antioxidative enzymes were up-regulated in summer-harvested leaves compared to their spring or autumn counterparts, as was observed for the concentration of foliar anthocyanins, indicating that strengthening of antioxidant systems was the key mechanism for long-term acclimatization of I.pumila plants to stressful environmental conditions within their natural ecological niches. When plants from contrasting radiation environments were compared, SOD and CAT activities appeared to be greater in shade-exposed than in sun-exposed leaves. Conversely, POD activity and the content of foliar anthocyanins were notably higher in foliage experiencing full sunlight relative to those developed under vegetation canopy, suggesting the synergistic function of these two molecules in protecting leaf cells against photoinhibitory and photooxidative effects of strong light.