Aims Forest litter is both a large source of CO₂ released from terrestrial ecosystems to the atmosphere and a critical sink of carbon and nutrients for plant growth. Studying dynamics of forest litter and its response to temperature and precipitation changes can improve our understanding of forest carbon and nutrient cycles and their interactions with projected climate change. Our objective was to examine the stocks and chemical quality of forest litter in natural birch (Betula platyphylla) forests that vary in both annual mean temperature (AMT) and annual mean precipitation (AMP).

Methods During July and August 2008, we measured the standing stocks and concentrations of carbon, nitrogen and phosphorus and organic fractions (extractives, acid soluble fraction (AS) and acid insoluble fraction (AIF)) of three litter layers (L1: slightly decomposed layer, L2: half-decomposed layer and L3: humus layer) in the forest floor of 12 birch forests in Inner Mongolia, China.

Important findings Along the decomposition gradient (i.e., from L1 to L3), nitrogen and phosphorus concentrations increased, AS concentration decreased, AIF concentration increased but extractives did not show significant change. Temperature and precipitation did not have significant effects on carbon fractions but at sites where AMT was higher, carbon stocks in L3 layer were higher, probably because of greater accumulation at higher-temperature sites as a result of higher litter production but similar decomposition rate compared to lower-temperature sites. These findings indicate that the litter layer (particularly the L3 layer) is an important carbon and nutrient pool at the ecosystem scale and future increases in temperature without concurrent increases in precipitation may enhance litter accumulation in these natural birch forests.

Aims Xilin Gol steppe of Inner Mongolia is located in the typical steppe area in China, but some areas have been invaded by desert steppe species such as Stipa gobica, with which S. grandis and S. krylovii mixed to form three types of patches (Stipa grandis, S. krylovii and S. gobica) within the community. It is not known what kinds of relationships exist among the dominant species in the community. Our objective was to investigate how the dominant species in the three patches interact with each other and with other species.

Methods Field data were collected in August during 2007 to 2009 in the three different kinds of Stipa patches. Ten plots were set in each patch type and placed at random within the site, giving a total of 90 plots in three years. The 2 × 2 contingency table, variance ratio (VR) of the overall association, Pearson coefficient and Spearman rank correlation coefficient were used in quantitative analysis of the interspecific associations among the 24 plant species in the three kinds of patches.

Important findings The overall inter-specific association among 24 plant species of the community showed no correlation, indicating that species association was weak. The distribution and formation patterns of patches, which were possibly due to interactions among interference, competition, soil environment and plant function, were verified by analyzing species correlation in the three kinds of Stipa patches. These results provide evidence for the theory of species association. We noted that the nature (positive or negative) or degree of association varied with different kinds of patches. According to their adaptability to the environment and relationships between plants and environment, the 24 species were divided into three ecological species groups.

Aims We previously found that non-leguminous species had a higher photosynthetic rate despite lower leaf N content. Nitrogen is a critical factor limiting plant growth in the desert. Our objectives were to determine if, as hypothesized, non-leguminous species have lower leaf N content, allocate a lower fraction of leaf N to photosynthesis and have higher maximum net photosynthetic rate (P_max) and photosynthetic N-use efficiency (PNUE).

Methods We compared the leguminous species Alhagi sparsifolia and non-leguminous species Karelinia caspica and Tamarix ramosissima in their typical habitat at the southern fringe of China’s Taklamakan Desert.

Important findings As hypothesized, the non-leguminous species had significantly lower leaf N content and allocated a lower fraction of leaf N to photosynthesis. They also were more efficient in photosynthetic N partitioning. The non-leguminous species partitioned a higher fraction of the photosynthetic N to carboxylation and showed higher use efficiency of the photosynthetic N, while the leguminous species partitioned a higher fraction of the photosynthetic N to light-harvesting components. For the non-leguminous species, the higher fraction of leaf N allocated to carboxylation and bioenergetics led to higher P_max and therefore to higher PNUE, water-use efficiency and apparent quantum yield. These physiological advantages of the non-leguminous species and their higher leaf area ratio may contribute to their higher resource capture ability.

Aims Many recent studies indicated that the regional climate of northwest China had changed from a warm-dry to a warm-wet pattern. Therefore, it is important to assess vegetation cover change in this area. Our objective is to evaluate the normalized difference vegetation index (NDVI) record in eastern, middle and western parts of the Qilian Mountains and assess past long-term vegetation cover change with tree-ring chronologies.

Methods Temporal and spatial changes of NDVI, and its relationship with tree-ring width were analyzed using 8 km × 8 km resolution multi-temporal NOAA/AVHRR-NDVI data from 1986-2003 and five ring-width chronologies in the Qilian Mountains. Then, we used liner regression to reconstruct annual NDVI varieties for 1843-2003.

Important findings Vegetation cover in the Qilian Mountains decreased from east to west, and the main growing season lasted from June to August. In addition, during the period 1986-2003, an increasing NDVI-trend was evident in three regions in the Qilian Mountains, indicating that vegetation activity has been rising recently. In the eastern, central and western parts of the Qilian Mountains, values of NDVI during the growing season have increased by 3.28%, 4.82% and 7.75% per year, respectively. We also found a strong relationship between NDVI and the first principal component (PC1) of the five tree-ring width chronologies (r = 0.74, p < 0.01). Growing season NDVI was reconstructed based on correlation analysis. Six periods characterized by high and low values were reflected in the NDVI curve, and the poorest period of plant growth was 1923-1932. Moreover, the amplitude of the fluctuation was larger during 1989-2003, accompanied by an increasing trend since 1991.

Aims It is generally assumed in dendroclimatological studies that the approximate relationship between tree growth and the limiting climatic factors is stable over time. However, observed spatial and temporal instabilities in growth-climate relationships suggest diverse growth responses expected to be triggered by unprecedented climatic changes in the future may greatly complicate dendroclimatic reconstructions of past climate histories. We test the stability of the growth-climate relationship using tree ring-width data of Abies faxoniana in Wolong National Natural Reserve of western Sichuan, China to provide qualitative verification for regional paleoclimatic studies and dynamic vegetation models for carbon uptake.

Methods Standardized dendroecological methods were used to study the effects of climatic variability on radial growth of A. faxoniana, a subalpine conifer that was the dominant and economically most important tree species in this region. Fifty-two increment cores of A. faxoniana were sampled in a pristine forest site at 2 750 m and several statistics were used to identify common patterns of interannual growth variability. A shift in climate facilitated comparison of growth-climate relationships during two distinct periods: 1956-1976 and 1977-2008. Tree radial growth was correlated against monthly total precipitation, sunshine time and mean, minimum, and maximum temperature from the nearby meteorological station.

Important findings Tree radial growth showed time-dependent relationships to interannual climate variation. For 1956-1976, tree growth showed a positive growth response to temperature in late winter to early spring (prior December to current April), whereas high temperature in late spring (May) negatively impacted tree growth. For 1977-2008, tree growth responded more strongly to sunshine time (positive) and winter temperature (negative). In addition, tree growth showed an internally consistent positive response to precipitation in autumn to early winter (prior September to December). An anomalous reduction in growth indices was a noteworthy feature in 1977-2008 and resulted in increasing divergence between the trends in ring width and temperature. In recent decades, the combination of decline in sunshine time and more cloud cover effectively decreased the amount of solar radiation available for photosynthesis and plant growth, and this was the most probable cause for the recent progressive decline in growth.

Aims Garden plants account for the main part of urban green spaces, and their gas exchange is the key ecological process for regulating urban ecosystem function. Our objectives were to determine whether there are significant differences in gas exchange characteristics among different green spaces and plant guilds in Wuhan City, China and to explore how different environmental conditions and species composition affect these gas exchange characteristics.

Methods Photosynthetic capacity (A_max), transpiration rate (T_r) and photosynthetic water use efficiency (PWUE) were measured for 51 garden species in five green spaces in summer, using a portable photosynthesis system (CIRAS-2, PP systems, Amesbury, USA).

Important findings There were significant differences in A_max, T_r and PWUE among green spaces, shrubs and trees and deciduous and evergreen plants. However, the variation among green spaces was mainly related to differences among species and to a minor extent to differences in microclimate. Based on these gas exchange parameters, the species studied can be divided into three groups: low photosynthesis and low water use efficiency species (38 species), high photosynthesis and high transpiration species (10 species) and low water consumption but high water use species (Ormosia henryi, Cinnamomum septentrionale and Michelia bedinieri).

Aims Fine root longevity plays a key role in the processes of root production and mortality and is important to precisely estimate carbon and nutrient cycling in terrestrial ecosystems. However, few studies have simultaneously examined the influence of multiple factors on fine root longevity. Our objectives were to examine: 1) seasonal patterns of fine root length production and mortality in plantation-grown Pinus sylvestris var. mongolica, 2) effects of fine root diameter, order, season of fine root birth, soil depth and mycorrhizal colonization on fine root longevity, and 3) relative strength of the influences of these factors on fine root survivorship.

Methods Minirhizotrons were used to estimate fine root length production, mortality and longevity. In July 2007, three 20 m × 30 m plots were established in a P. sylvestris plantation, and six minirhizotron tubes (90 cm length, 5.5 cm inside diameter) were installed randomly throughout the plot. Video images were collected at approximately four-week intervals during the growing season from 5 May 2008 to 22 October 2009. Video images were digitized via RooTracker software (NC, USA). Kaplan-Meier method in survival analysis was used to estimate mean longevity, median longevity and cumulative survival rate. The effects on root longevity by single factors, including root diameter, order, season of root birth, soil depth and mycorrhizal colonization, were tested by Log-rank test. The relative strength of the influences of these factors on fine root survivorship was examined by Cox proportional hazards regression analysis.

Important findings Fine root length production and mortality exhibited strong seasonal patterns, in which production peaked in spring and summer and mortality peaked in late summer, autumn and winter. Mean and median fine root longevity were (322 ± 10) d and (310 ± 15) d, respectively. Log-rank test indicated that fine-root longevity was significantly affected by root diameter, order, season of birth, soil depth and mycorrhizal colonization. Cox proportional hazards regression suggested that mycorrhizal colonization, root diameter and soil depth significantly influenced fine root survivorship, controlling for other factors (covariates). The risk of fine root mortality decreased 99% with a 1 mm diameter increase, and fine root longevity increased 5% with a 1 cm increase in soil depth. However, the risk of mortality of mycorrhizal roots was 175% higher than for non-mycorrhizal roots. Root order and season of root birth had no significant effects on fine root longevity. Our findings highlight that fine root longevity is influenced by endogenous and exogenous factors simultaneously, and multi-covariate analysis is an efficient way to reveal variation of fine root longevity.

Aims Despite extensive studies on effects of clonal integration in the past three decades, little is known about the effects of clonal integration on the performance of waterlogged clonal plants. Our objective was to test the hypothesis that clonal integration could improve performance of Cynodon dactylon, a stoloniferous clonal herb commonly found in riparian areas of reservoirs, under waterlogging stress.

Methods Relatively young apical ramets of C. dactylon clonal fragments were submerged in water at depths of 0 (control), 5 and 15 cm, and their connections to the relatively old basal ramets of the fragments under normal conditions were either severed (preventing clonal integration) or not (allowing integration). Performances of apical ramets, basal ramets and whole fragments were investigated after one month of treatment. Meanwhile, chlorophyll fluorescence parameters (F_v/F_m, maximum quantum yield of PSII; Yield, effective quantum yield of PSII) were measured.

Important findings Severing the stolon connection significantly decreased the growth of apical ramets under submergence in terms of biomass, total stolon length and number of ramets. Submergence also significantly decreased the growth of apical ramets, but had little effects on basal ramets. Performance of both basal ramets and clonal fragments was enhanced if the basal ramets were connected with the apical ramets subjected to 5 cm depth of submergence. However, stolon severing treatment had little effects on chlorophyll fluorescence parameters of both apical ramets and basal ramets. Results indicate that clonal integration increased performance of waterlogged ramets and the growth of non-waterlogged connected ramets. Clonal integration could help C. dactylon resist submergence stress.

Aims Rhodiola dumulosa (Crassulaceae) is a perennial herbaceous plant. It grows among rocks on mountains at 1 600-3 900 m, and its populations are spatially scattered in their areas of distribution. Our objectives were to study the population genetic diversity and genetic structure of R. dumulosa in northern China and determine relationships between genetic diversity and environmental factors.

Methods We analyzed 776 individuals from 25 natural populations using amplified fragment length polymorphism (AFLP) markers.

Important findings We obtained 398 unambiguous bands from the four pairs of selective primers, 312 bands (78.46%) of which were polymorphic across all individuals. The Nei’s gene diversity was 0.364 9, and the Shannon’s information index was 0.542 2 at the species level. Therefore, there was a high level of genetic diversity within R. dumulosa populations in northern China. The population genetic differentiation index G_st was 0.150 7, and the indirect estimate of gene flow Nm was 2.82, which indicated that genetic differentiation among northern populations was low and gene exchange was frequent. Analysis of molecular variance (AMOVA) revealed that the majority of AFLP variations resided within populations (67.9%). The STRUCTURE and UPGMA cluster analyses showed that the closely related populations are geographically restricted and occur in proximity to each other. This result was confirmed by the Mantel test, which revealed a significant positive correlation (r = 0.512 9, p < 0.001) between geographical distance and genetic distance. In addition, the correlation analysis of population genetic diversity and altitude showed a significant negative relationship (p < 0.05), i.e., population genetic diversity decreased with increasing altitude. However, there was no significant correlation between genetic diversity and slope direction. The software Dfdist was used to detect outliers caused by altitude, but the results were non-significant. All research results showed that geographical distance affected genetic distance significantly.

Aims Oil contamination in marine environments poses a significant threat to marine life, especially phytoplankton. We simulate oil contamination on the natural phytoplankton community and study species changes in the community. Our objectives are to determine influences of oil pollution on the ecology of marine phytoplankton and to provide basic data for the assessment of losses in marine ecosystems caused by oil spills and oil pollution.

Methods In four seasons from November 2008 to July 2009, we collected phytoplankton from Yueqing Bay in China’s Zhejiang Province. We chose eight levels of crude oil water accommodated fraction (WAF) to perform 14-day culture experiments of phytoplankton under different WAF stresses. We measured phytoplankton cell density and identified species every 24 h.

Important findings Diversity (H), evenness (J), species number (S) and species composition of phytoplankton were significantly influenced by crude oil WAF in all four seasons. Values of S and H in crude oil WAF groups were all lower than in control groups, but there were no significant differences in J. The influences of crude oil WAF on dominant species of phytoplankton were different among seasons, concentrations, and species. Under high levels of crude oil WAF (≥ 2.28 mg·L^-1), dominance of Skeletonema costatum increased in the four seasons, while dominance of Nitzschia longissima decreased in all seasons except autumn. Dominance of Prorocentrum minimum first increased and then decreased, while dominance of Pleurosigma sp. and Melosira moniliformis decreased in autumn and winter. Under low levels of crude oil WAF (≤ 1.16 mg·L^-1), dominance of S. costatum decreased in all seasons except autumn, N. longissima increased in spring and summer, and M. moniliformis increased in winter. With the impact of crude oil WAF, species with r-strategy may gradually replace species with k-strategy, thus leading to abnormal succession.

Agro-biodiversity plays an important ecological function. It is essential for global food production, livelihood security and sustainable agricultural development. Agro-biodiversity is a key to the stable, healthy, productive, sustainable field ecosystem and for sustainable management of pests. It has attracted increased attention for the prevention and control of pests based on the principles and methods of systems engineering to regulate the biodiversity in agro-ecosystems. We discuss the ecological functions and mechanism of biodiversity of agro-ecosystems in preventing and controlling pests, utilizing information from multiple disciplines including plant pathology, agricultural ecology, plant nutriology, plant physiology and plant allelopathy.

Aims Castanopsis sclerophylla is a constructive species in the zonal climax community of the subtropics. It is important for regional forest resource protection and sustainable use. With serious acid rain in this region, studies of physiological and ecological responses of C. sclerophylla to acid rain have important theoretical and practical value. My objective was to determine the effects of acid rain stress on photosynthetic and physiological characters of C. sclerophylla.

Methods Three gradients of simulated acid rain treatments were applied to the species: pH = 2.5, 4.0 and 5.6. Tests were done in April, July and October of both 2007 and 2008.

Important findings In the pH 2.5 treatment, the relative chlorophyll content of C. sclerophylla seedlings was lowest during a short time, and there were significant differences between the pH 2.5 and 5.6 treatments (p < 0.05). After a period of time for acid rain treatment processing, the relative chlorophyll content of C. sclerophylla seedlings was highest with pH 4.0, indicating that acid rain of low concentrations would increase the relative chlorophyll content. In April 2007, the net photosynthetic rate (P_n), maximal photochemical efficiency of photosystem II (F_v/F_m) and potential activity of photosystem II (F_v/F₀) were almost unchanged under different acid rain treatments. With the extension of acid rain treatment, P_n, light compensation point (LCP), light saturation point (LSP) and dark respiration rate (R_d) were greatly reduced in the treatments with pH 2.5, and there were significant differences between the treatments with pH 2.5 and pH 5.6 (p < 0.05). The differences of F_v/F_m and F_v/F₀ between pH 2.5 and 5.6 were smaller than before. The changes of stomatal conductance (G_s) and apparent quantum yield (AQY) were not obvious. In the early phase of acid rain treatments, the high concentrations of acid rain stress significantly affected the relative chlorophyll content and photosynthetic physiological parameters, but with the processing of treatment, the effects of acid rain stress on C. sclerophylla seedlings reduced gradually, which showed that the seedlings have some resistance and adaptability to the detrimental environment stresses.