Aims Stipa breviflora, which is a dominant species of desert steppe in the arid region of China, would be seriously affected by changes of precipitation and atmospheric CO₂ concentration. Our objective is to determine the interactive effects of changing precipitation and elevated CO₂ concentration on photosynthetic parameters of S. breviflora, in order to evaluate the effects of future climate change on the desert steppe.

Methods Open top chambers (OTCs) were used to simulate the elevated CO₂ concentration (control, 450, and 550 µmol·mol^-1) and changing precipitation (-30%, -15%, 0, +15% and +30%, based on the average monthly precipitation during 1978-2007). The photosynthetic parameters of S. breviflora were measured by a LI-6400 portable photosynthesis system.

Important findings The responses of photosynthetic parameters of S. breviflora to changes of CO₂ concentration and precipitation were significant, and interactive effects were observed. With increased CO₂, leaf net photosynthetic rate (P_n) of S. breviflora increased, and photosynthetic acclimation occurred during August. Stomatal conductance (G_s) and transpiration rate (T_r) decreased, and the increase of P_n was more than T_r. As a result, its water use efficiency (WUE) increased. With increased precipitation, P_n, G_s and T_r increased, and the increase of P_n was less than T_r, resulting in a decrease in WUE. Under higher CO₂ and 15% increase in precipitation, P_n, G_s and T_r of S. breviflora increased greatly, the increase of P_n was close to T_r, and consequently WUE did not change significantly.

Aims As one of the main components of terrestrial ecosystems, halophytes play a key role in maintaining arid zone ecosystem balance. Remote sensing has potential for monitoring halophytes in large areas. However, few studies on the spectral properties of halophytes are available. The spectral features of halophytes on the ground provide an important basis for remote sensing applications.

Methods This study used the FieldSpec Pro FR portable spectroscope to record ground reflectance of halophytes, using typical halophytes in the salinization-desert zone of a delta oasis in Weigan-Kuqa River as an example. We first analyzed the data noise characteristic of the spectrum. The noise was removed using the Percentile Filter method. We employed differential spectrum technology to reduce the influence of environmental background. Second, we extracted parameters of spectral absorption features for typical halophytes: Halostachys caspica, Halocnemum strobilaceum, Alhagi sparsifolia, Nitrarria sibirica, Tamarix ramosissima, Karelinia caspia and Phragmites australis. Third, we processed spectral reflectance curves of halophytes using a normalization method.

Important findings The wave troughs/wave length positions of euhalophyte, secretohalophyte and pseudohalophy are very similar, indicating that halophytes have similar absorption band characteristics. Elimination of the elements of noises and deflections caused by different scanning conditions such as soil background improved the recognition accuracy of halophytes. We ultimately identified nine optimal spectral bands, i.e., 510, 550, 690, 730, 950, 1150, 1210, 1290 and 1310 nm, that appeared to contain majority of the salinization-desert zone information of the multispectral signatures. The nine bands can be used to differentiate salinization-desert zone halophytes types. The results not only provide a scientific basis for hyperspectral remote sensing image processing, but also supply references for the identification and classification of halophytes using remote sensing technology.

Aims Shallow groundwater table is the main cause of salinization in the northern Ningxia Plain of China. The uptake of groundwater by halophytes can lower the groundwater table and reduce the demand for irrigation. Our objective was to investigate the potential water sources (different soil profile and groundwater) of four shrubs, i.e., twenty-year-old Tamarix ramosissima and three-year-old T. ramosissima, Lycium barbarum and Atriplex canescens.

Method Stable¹⁸O and D isotope compositions (δ¹⁸O and δD) of different potential water sources and xylem water were analyzed before and after irrigation. The IsoSource mode was used to calculate the probable contribution of different water sources to the total plant water uptake. The photosynthetic gas exchange parameters, contents of salt and water and pH in 0-200 cm soil profile were also determined.

Important findings Soil water δ ¹⁸O and δD in different depths differed consistently. The soil water δ ¹⁸O and δD values decreased with depth. More negative soil water δ ¹⁸O and δD values were recorded after irrigation. There were significant effects of evaporation and irrigation on soil water δ ¹⁸O and δD values. δ ¹⁸O and δD values of twenty-year-old T. ramosissima were lower than that of the three-year-old shrubs. Before irrigation, the three-year-old T. ramosissima, L. barbarum and A. canescens mainly tapped water in the upper soil layer (70.1%, 52.3% and 48.9%); highest groundwater uptake rate (21.5%) was observed for twenty-year-old T. ramosissima. After irrigation, higher water uptake rates from 80-140 cm soil profile were recorded for three-year-old T. ramosissima (59.5%) and L. barbarum (58.8%). Highest groundwater uptake rate was found for twenty-year-old T. ramosissima (18.3%). Before irrigation, the net photosynthetic rate, stomatal conductance and transpiration rate of twenty-year-old T. ramosissima were higher than those of other shrubs. Highest net photosynthetic rate were observed for three-year-old A. canescens after irrigation. Irrigation had significant effects on net photosynthetic rate and stomatal conductance of three-year-old T. ramosissima and L. barbarum. The intrinsic water use efficiency of three-year-old A. canescens was higher than other shrubs. These results suggested that different shrubs have different water use strategies, which is presumably related to species and age of shrubs. Young T. ramosissima mainly extracted soil water from upper un-saturated profile based on its strong tolerance to drought, and it switched its water use to middle soil profile after irrigation. Mature T. ramosissima turned out to bephreatophytic with growth being heavily dependent on groundwater and deep soil water and unresponsive to irrigation.

Aims Forest fire is a major disturbance factor for forest ecosystems and an important pathway of decreasing vegetation- and soil-carbon storage. Scientifically and effectively measuring carbonaceous gases emission from forest fire is important in understanding the significance of forest fire in carbon balance and climate change. However, carbon emissions from forest fire remain unclear. Our objective was to estimate carbon emissions from forest fires from 1965 to 2010 in Daxing’an Mountains of Heilongjiang Province, China.

Methods We used a geographic information system (GIS) based modeling approach to generate emission estimates using a two-step procedure. First, we calculated total carbon released from forest fires in Daxing’an Mountains for selected years between 1965 and 2010 by merging and analyzing several measurement parameters. Second, we calculated amounts of four carbonaceous gases released during the burns, carbon dioxide (CO₂), carbon monoxide (CO), methane (CH₄), and nonmethane hydrocarbon (NMHC), using several different experimentally derived emission factors. The origin of each of the inputs used in our models is based on a combination of analysis of forest fire statistics, forest resources inventory, field research and laboratory experiments.

Important findings Direct total carbon emissions from forest fires in Daxing’an Mountains during 1965-2010 are about 2.93 × 10⁷t, and mean annual carbon emissions are about 6.38 × 10 ⁵t per year, accounting for 5.64% of the direct total carbon emissions from forest fires in China. Carbon atmospheric emissions of CO₂, CO, CH₄ and NMHC from forest fires were 1.02 × 10⁸t, 9.41 × 10 ⁶t, 5.41 × 10 ⁵t and 2.11 × 10 ⁵t, respectively, and mean annual emissions of CO₂, CO, CH₄, and NMHC from forest fires were 2.22 × 10⁶t, 2.05 × 10 ⁵t, 1.18 × 10 ⁴t and 4.59 × 10 ³t, respectively, accounting for 5.46%, 7.56%, 10.54% and 4.06% of the amounts of four carbonaceous gases released from forest fires in China, respectively. Our results indicate that combustion efficiency of coniferous broad-leaved mixed forests is lower than other forest types, and burned area of coniferous broad-leaved mixed forests accounts for 21.23% of total burned area, but carbon emissions accounts for 7.81% of total carbon emissions.

Aims Fine root carbon storage is an important part of forest ecosystem carbon pools. Our objective was to determine the effects of thinning on fine root biomass and carbon storage in a Picea asperata plantation in Western Sichuan Province, China.

Methods We sampled fine roots of a 50 year-old P. asperata plantation thinned by different treatments in August 2010. We excavated soil blocks of 20 cm × 20 cm × 20 cm to sample intact fine root branches of at least the first five branch orders, dissected the intact root branches by order and measured the biomass and carbon storage of each order.

Important findings Fine root biomass and carbon storage significantly increased with root order (p < 0.05). The first order roots had the smallest biomass and carbon storage, and the fifth order roots had the largest. Compared with the control, thinning the plantation had significant effects on fine roots biomass and carbon storage (p < 0.05), while the effects of fine roots biomass per plant varied. Thinning treatments of 10% and 20% were not significantly different from the control (p > 0.05). Thinning significantly affected the distribution of fine root biomass in the five root orders. As the thinning intensity increased, the ratio of biomass distribution in the first and second fine order increased. The first order had the largest increase. The ratio of biomass distribution in orders 3 to 5 decreased, and order 5 had the largest decrease. The 50% thinning significantly reduced the fine root biomass ratio in the lower soil layer (20-40 cm), but there was no significant difference compared with 20% and 30% (p > 0.05).

Aims Our objective is to consider a water uptake model of crop roots under non-uniform water potential. This is based on principles of water conservation in soil-plant system and water potential’s driving force on water transport.

Methods We introduced two expressions of non-uniform soil water potential, linear and exponential functions, and compared the analytical solutions under non-uniform and uniform water potentials. This model is used to analyze the effect of ratio of radial resistance and axial resistance on plant water uptake and to determine the optimal root length within a reasonable range of this ratio.

Important findings In certain circumstances, the water uptake model for plant roots with non-uniform water potential can be simplified to a uniform water potential model, and the optimal root length is close to the actual value after the Poseuille formula is changed to fit plant vessels.

Aims Differences of photosynthesis and chlorophyll fluorescence characteristics between flat young leaves (young leaves) and fully grown leaves (mature leaves) of cotton were compared to study the adaptation mechanisms of photoinhibition and photoprotection on young leaves under strong sunlight.

Methods We measured gas-exchange and chlorophyll fluorescence of young and mature leaves of cotton under field conditions and obtained rapid light curves with a Dual-PAM100 using an internal program.

Important findings There were significant differences between young and mature leaves in photosynthesis and fluorescence characteristics. Young leaves had lower chlorophyll content (Chl) and stomatal conductance (G_s), which accounted for lower net photosynthetic rate (P_n), which in turn resulted in lower actual photochemical efficiency (Φ_PSII) and photochemical quenching (q_P) in photosystem II (PSII). Below 1800 μmol·m^-2·s^-1, the higher cyclic electron flow (CEF) that was useful for composing ATP is one of the reasons for higher photosynthetic capacity in mature leaves. Lower light saturation point (LSP) was more susceptible to photoinhibition in young leaves under the same light; however, the magnitude of diurnal variation of its maximum photochemical efficiency of PSII (F_v/F_m) was significantly less than that of mature leaves. We suggest that photoprotective mechanisms, including direct quenching of reactive oxygen species by abundant carotenoids, photorespiration (P_r), non-photochemical quenching (NPQ) and the cyclic electron flow around PSI (PSI-CEF), can effectively dissipate the excess energy in young leaves to avoid photoinhibition under high irradiance.

Aims Our objective was to reveal the mechanism of the effects of mechanical damage of leaves on emission of C₆-C₁₀ aldehydes and the variation of PSII in Cinnamomum camphora leaves.

Methods We analyzed the composition and content of the C₆-C₁₀ aldehydes in seedlings of damaged C. camphora by the dynamic headspace air-circulation method and thermal desorption system/gas chromatography/mass spectrum (TDS-GC-MS), measured the activity of lipoxygenases (LOX) in leaves after mechanical damage, and investigated the effects of mechanical damage of leaves on chlorophyll a fluorescence parameters.

Important findings Results showed that the emissions of hexanal, heptanal, octanal, nonanal and decanal were increased by 2.47, 0.99, 1.34, 0.91 and 28.38 (p < 0.01) times, respectively, and four kinds of C₆-C₁₀ aldehydes were induced: (E)-2-hexenal, (E, E)-2,4-hexadienal, (E)-2-octenal and (E)-2-nonenal. The activity of LOX was increased by 1.2 times. The absorption flux per PSII reaction center and trapping flux were significantly decreased by 12.8% (p < 0.05) and 11.1% (p < 0.01), respectively. The density of the active reaction centers per cross section, quantum yield of electron transport, electron transport chain further than primary quinone acceptor of PSII (Q_A ^-) and the performance of PSII activity were increased by 23.3%, 24.4%, 22.6% and 82.7% (p < 0.01), respectively. The species and emissions of C₆-C₁₀ aldehydes, activity of LOX and chlorophyll fluorescence parameters nearly recovered after 24 h. This suggested that the damage caused by mechanically damaged stress is more prominent at the donor side of PSII. The activity of LOX was increased, and as a result the emission of C₆-C₁₀ aldehydes increased. In response to high salt stress, C. camphora seedlings improve the quantity of the active reaction centers.

Aims Floral diversification in animal-pollinated species was widely believed to be driven by pollinator-mediated natural selection in response to the geographical mosaic of pollinators. Our objective was to explore the evolutionary response of staminal lever mechanism in Salvia to variation in pollinator assemblage in a spatial context.

Methods We employed three species (four populations) and conducted comparative studies on pollinator-flower interactions in different populations through investigating pollinator assemblage and measuring floral traits and body size of pollinators.

Important findings Floral traits investigated, including corolla length, staminal lever length and other structural traits, exhibited distinct differences among populations. These corresponded with variations in composition of pollinators and the main pollinator and its body size in each population. The two types of pollination modes in each population were ventral pollination and dorsal pollination, which was the effective one. The main pollinator’s body length was significantly positively correlated with staminal lever length and negatively correlated with corolla length in spatial context. Both corolla entrance height and stigma height were related to variation in body thickness of the main pollinator among populations. In conclusion, the vulnerability of lever-like stamens and other relevant floral traits to the geographical mosaic of pollinators implies the key role that the staminal lever plays in pollination, and its high evolutionary plasticity might have contributed to adaptive radiation of species in Salvia.

Aims The valuable ornamental plant Canna indica is widely distributed in city gardens and on roadsides in China. Our objective was to study the stress responses of C. indica to cadmium (Cd) and its accumulation of Cd.

Methods With pot culture experiments, C. indica was cultured with different Cd concentrations. Morphological, ecological, physiological indexes were observed during the growth of C. indica. The distribution of Cd in C. indica plants was determined after harvest.

Important findings The Cd treatment of <1 mg·kg^-1had no obvious effect on growth of C. indica; however, Cd concentration of >5 mg·kg ^-1 inhibited growth. The flowering period was prolonged with <5 mg·kg ^-1Cd concentration. With increasing Cd concentration, root activity, chlorophyll and water content all decreased, soluble sugar content initially increased and then decreased, and free proline content and permeability of cell membrane increased gradually. The distribution of Cd in C. indica was root > shoot. With increasing Cd concentration of the medium, Cd concentration in shoots and roots increased; however, the accumulator and translocation factors decreased gradually. The maximum accumulation of Cd in C. indica was 5.89 mg·plant ^-1with the treatment of 20 mg·kg^-1. It is concluded that C. indica is suitable for landscaping use when the Cd concentration in soil is <1 mg·kg ^-1.

Aims Skeletonema costatum and Scrippsiella trochoidea are two algal species that can cause red tides together. Interspecific competition is thought to be a factor in development of algal blooms. Our objective is to study the effect of nitrogen and phosphorus on interspecific competition between Skeletonema costatum and Scrippsiella trochoidea.

Methods The experiments were carried out in mono-culture and co-culture. The nitrogen (nitrate) and phosphorus (phosphate) concentrations were 32, 32; 128, 32; 512, 32; 512, 8; 512, 2 μmol·L^-1, respectively.

Important findings With increased concentration of nitrogen and phosphorus, the time of Skeletonema costatum as the dominant species was prolonged. Compared with mono-culture, the maximum densities of two species were inhibited in co-culture, and the degree of inhibition increased with higher concentration of nitrogen and phosphorus. The maximum density of Skeletonema costatum was more inhibited than that of Scrippsiella trochoidea. When the concentration of nitrogen and phosphorus was highest, the inhibitory starting point (t_p) of the two species was highest, and with the decline of nutrients, the t_p also decreased. Under various nutritional conditions, competitive inhibition parameters of Scrippsiella trochoidea to Skeletonema costatum (β) were higher than α. Scrippsiella trochoidea out-competed Skeletonema costatum when nitrogen was 512 μmol·L^-1 and phosphorus was 2 μmol·L ^-1. In other nutritional conditions, competition resulted in unstable coexistence of the species.