Aims Sabina przewalskii and Picea crassifolia, widely distributed in the Qilian Mountains, were employed to analyze the response of leaf δ¹³C of subalpine trees to altitude and its mechanism.

Methods Leaf samples were taken at 2 600-3 600 m elevation in October 2007. The δ¹³C was determined using an isotope mass spectrometer, carbon content was estimated with the potassium dichromate method and nitrogen content was measured with the micro-Kjeldahl method. Data were evaluated with one-way analysis of variance and correlation analysis using SPSS version 11.5.

Important findings Foliar δ¹³C in both species was positively related to elevation (p < 0.000 1) and annual mean precipitation, but negatively related to annual temperature (p < 0.000 1). The δ¹³C value of S. przewalskii increased as leaf and soil water content increased, while that of P. crassifolia was not significantly related to soil water content, leaf water content, leaf N content or C/N ratio. Altitude, which can lead to changes of hydrothermal conditions, is the main factor influencing carbon isotope fractionation in these subalpine trees; however, the combined effects of various factors on the mechanism of action maybe more complicated and need further study.

Aims Light, temperature and humidity conditions differ among individual leaves and may influence leaf morphology, anatomy, stomatal conductance, chlorophyll content and distribution and leaf photosynthetic processes. Our objective was to determine the influence of local microenvironment on structure and biophysical characteristics of leaves through research on changes of leaf morphology and biophysical indices along the lateral distribution of leaves within tree crowns and with orientation differences.

Methods We selected five tree species with wide crowns (Sophora japonica, Platanus orientalis, Ginkgo biloba, Ficus microcarpa and F. lacor) and measured leaf photosynthetic pigments (including chlorophyll a, chlorophyll b and carotenoids), leaf mass per area (LMA) and carbon isotope ratio (δ¹³C) along the horizontal distance from the sample point to the tree trunk and with different orientations in each tree species. Pigment content was measured by colorimetry, LMA as the ratio of leaf dry mass to fresh area and δ¹³C with a mass spectrograph.

Important findings Leaf δ¹³C and LMA increased and photosynthetic pigment decreased with horizontal distance from the sample point to the trunk. Leaf δ¹³C and LMA also differed by orientation, with southward leaves having the highest values, followed by westward leaves, and eastward leaves having the lowest values. Photosynthetic pigments had a more complex relation with orientation, although chlorophyll a, chlorophyll b, total chlorophyll content, chlorophyll a to b ratio and carotenoids were the highest in eastward leaves. These results suggest that southward, westward and leaves on the outside of the crown have increased LMA, reduced stomatal aperture and photosynthetic pigment content and, as a result, decreased photosynthesis and increased δ¹³C values in response to stronger irradiance, higher temperature and lower humidity. Therefore, local microenvironmental differences within an individual tree greatly influence leaf morphological and biophysical characteristics.

Aims Fast, efficient breeding of fast-growth and high water use efficiency (WUE) in Populus tomentosa clones is a pressing need for afforestation in arid and semi-arid regions. There is much research on the correlation between stable carbon isotope and WUE in crops and a few trees, but little in different clones of P. tomentosa. Our objective was to explore the application of δ¹³C on selection of clones with high photosynthesis and WUE.

Methods We examined 13 clones of Populus-grafted seedlings in Beijing Forestry University (39°46′ N, 116°19′ E) Nursery in Beijing, China. We studied leaf δ¹³C of the seedlings by MAT-251-MS in two different growth periods (mid-July and September) and gas exchange parameters (net photosynthetic rate (P_n), transpiration rate (T_r), instantaneous water use efficiency (WUE_i), stomatal conductance (G_s) and intercellular CO₂ concentration (C_i)) by LI-6400 portable photosynthesis system between 9:30 and 11:30 a.m. in the same periods.

Important findings Leaf δ¹³C, T_r, WUE_i, G_s and C_i significantly differed between the periods and among clones. Leaf δ¹³C and WUE_i were higher in July than September; however, T_r, G_s and C_i were lower in July than September and P_n showed no significant difference between periods. The main reason for the difference of leaf δ¹³C was seasonal variation. Leaf δ¹³C and WUE_i of the clones were consistent during the same period, i.e, the higher WUE_i appeared in clones of 30, 42, 46, 83, BL2 and BL5 with higher δ¹³C and the lower WUE_i occurred in clones of B331 and TG34 with lower δ¹³C. There was strong positive correlation between δ¹³C and WUE_i (r = 0.739 0 and 0.545 8 in July and September, respectively); therefore, high δ¹³C can be used as an effective indicator of high WUE_i in Populus. Clones with higher WUE_i may have moderate or low G_s and C_i, but not necessarily high P_n.

Aims Plants with high water use efficiency could contribute to an overall lower water-using landscape. Our objective was to analyze differences in water use efficiency among landscaping plants in Beijing, China.

Methods We used stable carbon isotope techniques to investigate δ¹³C values of 75 species belonging to 35 families and 65 genera in spring, summer and autumn in 2006 and analyzed variations in water use efficiency of different plant species and different life forms (evergreen tree, deciduous tree, evergreen shrub, deciduous shrub, forb and liana).

Important findings Leaf δ¹³C values varied between -30.7‰ and -23.4‰ in spring, -31.5‰ and -25.1‰ in summer and -31.4‰ and -23.9‰ in autumn. Differences of δ¹³C values were not significant in deciduous shrub species (p = 0.114), but were significant in evergreen trees (p = 0.005), deciduous trees (p < 0.001), evergreen shrubs (p = 0.022), forbs (p < 0.001) and lianas (p = 0.001). Leaf δ¹³C values were significantly different among seasons, being greater in spring than in summer and autumn (except for evergreen trees). The δ¹³C values for life forms were significantly different in different seasons, with a sequence of trees>shrubs>lianas>forbs, and evergreen plants>deciduous plants. Results showed that variation of leaf δ¹³C is dependent on species and life form, especially life form, and that water use efficiency differed greatly among life forms.

Aims Stable N isotope signature (δ¹⁵N) in both plant and soil is potentially an important parameter to evaluate N cycling in grassland ecosystems. Grazing is a dominant land use in northern China grasslands and might have greatly changed N cycling. Our objective was to determine the¹⁵N signature of leaves and soils in grazed and fenced plots of a typical steppe to investigate how δ¹⁵N values in an ecosystem are affected by grazing.

Methods We collected foliar and soil samples in a nearly 20 years fenced plot and an adjacent freely grazed plot. The foliar samples came from eight dominant species, including three perennial legumes (Caragana microphylla, Astragalus galactites and Melilotoides ruthenica), two grasses (Leymus chinensis and Stipa grandis), two forbs (Heteropappus altaicus and Potentilla acaulis) and a semi-shrub (Kochia prostrata). We also sampled 0-10 and 10-20 cm rhizosphere soils of C. microphylla and K. prostrata. Nitrogen isotope ratios were determined with a Thermal Finnigan MAT Delta^plus XP isotope-ratio mass spectrometer (IRMS).

Important findings Although the δ¹⁵N value of leaves of different plant species varied greatly, the observed pattern of variability is consistent in both grazed and fenced plots, i.e., semi-shrub > forbs and grasses > legumes. Long-term grazing reduced foliar δ¹⁵N values of forbs, semi-shrub and S. grandis significantly while changing little or even increasing that of potential biological N fixers (legumes and L. chinensis). As the only arbuscular mycorrhizae non-infected plant species, K. prostrata is enriched in¹⁵N (with δ¹⁵N values of 4.34‰ ± 0.35‰ and 2.04‰ ± 0.20‰ in fenced and grazed plots, respectively) compared with the depletion of other species. Mycorrhizal association may be considered to play an important role in plant nutrient transfer in those N-limited grassland ecosystems. In contrast to results of previous studies, soil δ¹⁵N values decreased significantly with grazing.

Aims Stable isotopes technique and Keeling Plot relationship offer great promise for partitioning evapotranspiration (ET), which can help us better understand the hydrologic cycle within terrestrial ecosystems. Our objectives are to evaluate the Keeling Plot method in ET partitioning using in situ continuous δ¹⁸O data and find the fractional contribution of crop transpiration to total ET in a winter wheat (Triticum aestivum) field.

Methods Field experiments were conducted at Luancheng Agro-ecology Station, Chinese Academy of Sciences. A hydrogen and oxygen isotopes in situ measurement system based on Tunable Diode Laser Absorption Spectroscopy (TDLAS) was used to obtain the continuous atmospheric vapor δ¹⁸O data. Other measurements were made with the eddy covariance technique, cryogenic vacuum distillation and stable isotope ratio mass spectrometry.

Important findings An analysis on the Keeling Plot relationships based on data from different time intervals in one daytime showed that the Keeling Plot would be better when using the midday time interval data to build Keeling Plot, which inferred that the plant transpiration isotopic steady-state (ISS) can be more easily obtained during midday when plant transpiration flux is generally largest. ISS was not always satisfied in field conditions, especially when mature wheat suffered from water stress. Using isotopic partitioning, we estimated transpiration contributed roughly 94%-99% to the total ET during the field measurement period, which indicated plant transpiration dominated local ET.

With the increase of anthropogenic SO₂ emission, behavior of sulfur isotopes during biogeochemical processes has been the focus of numerous studies. We reviewed the potential contributions of studies using sulfur stable isotope, which include studies on 1) sources of sulfur in atmospheric processes, 2) sulfur dynamics in forest, farmland and aquatic ecosystems, 3) additions of sulfur stable isotope in ecological systems and 4) acid rain research in China. Furthermore, we made suggestions on future research, proper analysis methods and source partitioning models using sulfur stable isotopes.

Aims Unusually low temperatures associated with heavy rain, snow and frost occurred in 19 provinces in southern China in January-February 2008. Our objectives were to evaluate the impact of the cold weather event on mangroves and to compare differences in cold tolerance between exotic and native mangrove species.

Methods In March 2008, we conducted an intensive survey of cold damage in ten mangrove nature reserves along the coastal areas of mainland China. Parameters such as scorch percentage, defoliation percentage and leaf F_v/F_m values (an indicator of leaf physiological health) were determined on selected seedlings and trees of the mangrove species at each site.

Important findings With low latitudes in Hainan, Guangxi and Zhanjiang of Guangdong, low air temperature coupled with the ebb tide at night, which caused serious damage to several mangrove species. However, native mangrove species in Fujian, such as Kandelia obovata, Aegiceras corniculatum, Avicennia marina and transplanted Bruguiera gymnorrhiza, which were adapted to low temperature events in winters, had higher cold resistance. Among all mangrove species surveyed, K. obovata, Aegiceras corniculatum and Avicennia marina were the most cold-resistant, followed by B. gymnorrhiza, B. sexangula and Rhizophora stylosa, which belong to the family Rhizophoraceae. Sonneratia caseolaris was the least cold-resistent mangrove species, having suffered serious damage or even complete loss in some locations. S. apetala introduced from Bangladesh showed much less damage than its counterpart S. caseolaris, indicating higher resistance to low temperature. Furthermore, mangrove seedlings were more sensitive than mature trees. The extreme cold event killed many mangrove seedlings in the nurseries and caused immature flowers and fruits to drop from trees, which would have an adverse effect on mangrove natural reproduction and reforestation projects. Thus, it is essential to consider cold resistance in future mangrove afforestration and restoration projects.

Aims Forest ecosystems were seriously damaged by unusually heavy snow and ice in early 2008 in southern China. Chinese fir (Cunninghamia lanceolata), the main timber tree in southern China, was one of the most severely affected species. Our objective was to investigate and assess types and extent of damage to this tree species in plantation stands in northern Guangdong, analyze relationships among site condition, forest structure and damage, and provide a theoretical basis and technical guidance for protecting existing forest resources and restoring damaged forests.

Methods The study was conducted in Chinese fir plantation in Tianjingshan forest farm of Guangdong, which was damaged by this snow and ice event. Thirteen plots 20 m × 30 m (or 15 m × 30 m) were placed in typical damaged areas in August 2008. Site factors such as altitude, aspect, slope position and slope steepness were recorded, and forest structure factors such as trunk diameter at breast height (DBH), tree height, crown size, lowest height of living branches, trunk taper (diameter/height) and stand density were measured.

Important findings Over 80% of the Chinese fir trees at 500-900 m elevation were damaged. There were three types of damage: crown broken (65.09%), uprooted (18.37%) and trunk bent (3.20%). The crown broken category was divided into five grades corresponding to extent of damage: top broken, crown fracture from the top to the central part, crown fracture from the top to the lower part with serious injury, entire crown broken, trunk broken off near the base or tree death after trunk broken. Plantation density was very important for the resistance of Chinese fir to the snow and ice storms, because trees were more severely broken where stand density was > 3 500 per hm² or < 1 500 per hm². DBH was a sensitive index of the type and extent of damage. Stunted trees tended to show mild damage. Trunk taper was an important factor for Chinese fir in the prevention and mitigation of snow and ice damage.

Aims During mid-January and mid-February 2008, an unexpected severe ice storm occurred over southern China that caused heavy damage to forests. Our objectives were to examine the effect of this storm on subtropical planted forests and to quantify biomass and carbon losses.

Methods We evaluated damage to the forest ecosystem at Qianyanzhou Ecological Station in subtropical China. Twenty-one plots of 10 m × 10 m dimensions were investigated in the affected slash pine (Pinus elliottii) plantation. The relationship between damaged area and terrain factors was analyzed using Digital Elevation Model data.

Important findings Of the five major plantations at the ecological station, damages occurred mainly in the slash pine plantation. The area of severely damaged forest with most fallen trees was 7.72 hm², accounting for 6.12% of the total forest area. The aboveground carbon loss in the severely damaged area ranged from 655 to 5 230 g·m^-2, with a mean value of 1 462 g·m^-2. Continuous low-temperature and strong rainfall, particularly when accompanied by strong winds on February 1, 2008, were the direct causes of the damage. Analysis shows that elevation is a good indicator for ice storm damage in the hilly area even though the elevation range was small (60-140 m), because elevation is tightly linked to local terrain factors and weather conditions. Forest growing on the top of a hill was vulnerable to the ice storm due to the barren soil and strong wind. We found that trees planted on the sunny slopes tended to form unbalanced crowns; this might be the reason that severe damage occurred mainly on sunny slopes. The vulnerability of slash pine to the ice storm is believed related to crown types, timber quality, root distribution, leaf characteristics and resin tapping.

Aims The forest ecosystem of north Guangdong Province, China was severely damaged by a freezing rain and ice storm in early 2008. Our aim is to assess tree damage and factors that influence it in a subtropical montane evergreen broadleaved forest.

Methods A 2-hm² plot was set up in the storm-damaged montane evergreen broadleaved forest in Chebaling National Nature Reserve. The plot was divided into 50 subplots, each 400 m², for sampling and measurement of plants and environmental factors. Damages to individual trees were recorded by visual estimation and then translated into a 0-6 scale of damage class. We compared the severity of damage for 12 dominant and co-dominant species. We also assessed variations in tree abundance in different diameter at breast height (DBH) classes and topographic regimes.

Important findings Significant variations in tree damage existed among species, DBH classes and topographic positions. Species of Theaceae and Lauraceae were more resistant to storm damage than species of other families. Most damaged were species of Fagaceae, such as Castanopsis fargesii and the dominant C. carlesii, which was more severely damaged than most co-dominant species. The proportion of damaged trees increased with DBH, with > 70% of the undamaged individuals being concentrated in the smallest DBH class (1-5 cm). χ² test indicated that topographic factors, i.e., slope inclination, aspect and position, had significant effects on the severity of tree damage. Trees on the upslope position were more susceptible to damage than those on the downslope or midslope positions, which might be due to increased cooling by wind on the upper slope. For slope aspects, semi-sunny slopes generally had a significantly higher proportion of damaged trees than semi-shady slopes. For slope inclination, the highest proportion of severely damaged trees was on slope classes of 15°-25°, 25°-35° and 35°-45°. Findings have significant implications for conservation of subtropical evergreen broadleaved forest, protection of forests from possible future damage by ice storms and forest management.

Aims Our objective was to investigate ice and snow damage to Pinus taiwanensis, which is widely grown in plantations in Jiulongshan Nature Reserve, Zhejiang Province, China. Findings will assist sustainable management of plantations exposed to such natural events.

Methods We investigated 6 000 m² plots representative of the geographic distribution of Pinus taiwanensis and features of the affected area. Differences of resistance to ice and snow damage were analyzed in relation to tree height, diameter at breast height (DBH), crown width and other tree characteristics. We also analyzed damage by altitude.

Important findings Pinus taiwanensis was severely damaged by ice and snow. Many individuals with different damage types, except stem bending, were found in the plots, but crown breakage was most common. Resistance to ice and snow damage depended on tree size. Trees with greater DBH and height were susceptible to limb and crown breakage, while ones with smaller DBH and height were susceptible to stem breakage and uprooting. Moreover, most trees killed were saplings with smaller DBH and shorter height. There were large differences of damage types among trees with different crown widths. Those with larger crown width had more serious damage, such as stem breakage and uprooting. Taper, crown relative height and degree of crown heterogeneity greatly influenced resistance to ice and snow damage. Pinus taiwanensis was seriously damaged in higher altitudes, with stem breakage and uprooted trees distributed mainly at 950-1 000 m.

Aims Few studies have examined snow damage on ecosystem composition and function in ecologically fragile areas, and most studies were qualitative. Therefore, quantitative study on this topic has important theoretical and practical significance.

Methods We used quadrat and transect methods to investigate snow-damaged forest in Jiuhua Mountain, China and analyzed damage to Phyllostachys pubescens in different locations and with different biological characteristics.

Important findings Preliminary analysis revealed that the extent of damage on P. pubescens was related to its location: shaded slope > sunny slope and high latitude > low latitude. The damage to P. pubescens was positively correlated to its importance value in the community, that is, pure forest > mixed forest. The average diameter at breast height (DBH) of damaged P. pubescens was (9.8 ± 1.3) cm, and most damage occurred in the juvenile stage. Individuals within 4 m from roads were damaged significantly more than individuals further away (p < 0.05). We proposed principles for forest management and forestation after snow damage.