Aims Modular theory of plants considers plant roots are relatively independent in resource absorbing and responding to heterogeneous soil environments, particularly resource environments. According to the cost-benefit theory, proliferation, growth and death of individual absorbing roots (modules) depend upon their resource uptake related to the carbon costs of their construction and maintenance, with a certain time-lag. Thus we hypothesized that: 1) a root will die when available nutrients are below a certain low threshold and last for a certain period and 2) new roots will emerge when available nutrients are above a certain high threshold and last for a certain period.
Methods We designed a greenhouse split-root experiment using three plant species: Ailanthus altissima, Callistephus chinensis and Solidago canadensis. The plants were grown individually in pots, and then three fine roots (uptaking roots) per plant were carefully sorted and placed in three plastic vessels of about 70 mL with one root per vessel. Three nutrient levels of 0, 20 and 200 μg N·g^-1soil were applied in the three vessels. These roots were carefully exposed and photographed every four days, and the numbers of lateral roots, the length of 1st order laterals and the root length were evaluated. Repeated-measure ANOVA was used for statistical analysis.
Important findings The numbers of laterals and total root length differed significantly among the three species and under the three N levels. Both lateral numbers and total root length were the least in the 0 μg N·g^-1 treatment for A. altissima, and the highest in the 200 μg N·g^-1 level for S. canadensis. The length of 1st order laterals was less responsive than the other two measures. No fine roots were found dead during the experiment. These results demonstrated that the different species had different growth rates of fine roots under the same N treatments as expected, and indicated that different species may have different N thresholds. Results provided partial support for our hypotheses and hints for future experiments. We suggest that a sufficient examination of the hypotheses may require 1) a longer experiment period, 2) control of other vital resources such as water and other limiting nutrients and 3) consideration of the resource contrast between the treatment patches and the overall level. The relative contrast of C costs between root construction and root maintenance should also be considered.

Aims Population density changes with spatial scales in plant communities. Surprisingly, few previous studies explored this theme, despite the possibility that variation in density with spatial scales should be significant for detecting ecological phenomena and answering ecological problems. In this study, we call variation in density with spatial scales (the local neighborhood density at different spatial scales) as scale density.
Methods O-Ring function can measure the local neighborhood density at different spatial scales. We used it to measure scale densities of Leymus chinensis, Agropyron michnoi and A. michnoi relative to L. chinensis in different restorative successional stages in steppe community in Inner Mongolia.
Important findings Local densities of two populations (L. chinensis and A. michnoi) were both higher in a degraded community than the other two restoration communities, which demonstrated the “stress gradient hypothesis” and further illustrated that the ecological phenomena were induced by facilitation. By comparing the scale densities of L. chinensis and A. michnoi relative to L. chinensis, we found that L. chinensis and A. michnoi were negatively associated as induced by facilitation in a degraded community, and positively associated as induced by competition in the other two restoration communities. Findings illustrate that analyzing the variation in the population density with spatial scales in plant communities is valuable in ecology.

Aims Our objectives were to find the optimal models for different drought stresses by comparing four light response models of photosynthesis in leaves of Periploca sepium growing in sand formed from seashells, investigate the adaptability law of parameters of light response models to drought stresses, and define the adaptability of P. sepium to the shell sand moisture conditions.
Methods We used three-year-old P. sepium grown in shell ridge island of China’s Yellow River Delta as experimental material, set up four moisture conditions simulating those in shell sand, measured light responses of photosynthesis in leaves of P. sepium under different drought stresses using CIRAS-2 portable photosynthesis system, and fitted and analyzed the light response curves by four models: rectangular hyperbola, non-rectangular hyperbola, exponential and modified rectangular hyperbola.
Important findings The sequence of fitting effect of the four light response models was in descending order: modified rectangular hyperbola model > non-rectangular hyperbola model > exponential model > rectangular hyperbola model. This result was related to the latter three models not having extreme values, not fitting the process of light response curve declining after light saturation point (LSP), and not directly and accurately solving maximum net photosynthetic rate (P_nmax) and LSP. Among them, the non-rectangular hyperbola model best fit dark respiration rate (R_d), the rectangular hyperbola model best fit light compensation point (LCP) and modified rectangular hyperbola model best fit P_nmax and LSP. The adaptabilities of the four models to different drought stresses varied. The modified rectangular hyperbola model well fit the curves under all the drought stresses, the rectangular hyperbola model and exponential model suited mild drought stress and the non-rectangular hyperbola model suited severe drought stress. The light response parameters, including apparent quantum yield (AQY), R_d, LCP, P_nmax and LSP, responded to drought stresses differently. AQY, R_d and LCP first increased and then decreased with the aggravation of drought stress, while P_n, P_nmax and LSP decreased gradually. LSP decreased by 5.2%, 16.3% and 34.55% under light stress, moderate stress and severe stress, respectively, in comparison to the control (1556 μmol·m^-2·s^-1). P_nmax decreased by 17.8%, 39.0% and 59.0% compared to the control (22.58 μmol·m^-2·s^-1). Light use capability of P. sepium leaf was strongest and light ecological amplitude (1520 μmol·m^-2·s^-1) was widest under sufficient water condition; photo-saturation and photo-inhibition occurred significantly, light use capability weakened, and photosynthetic capacity was inhibited seriously under severe stress.

Aims Our objective was to determine the effects of nitrogen regulation on photosystem II (PSII) chlorophyll fluorescence of functional leaves in sugar beet (Beta vulgaris) under salt environment.
Methods Using potted sugar beet plants, different salt environments were produced with NaCl; nitrogen was produced with NH₄NO₃.
Important findings Maximal PSII quantum yield (F_v/F_m), and latent PSII quantum yield (F_v/F_o), effective PSII quantum yield (Y(II)), quantum yield of non-regulated energy dissipation (Y(NO)), electron transport rate (ETR) and coefficient of photochemical quenching (q_P) were increased by nitrogen application under mild, moderate and high salt environments, and these parameters increased with increased nitrogen application. The results of rapid light-response curves of chlorophyll fluorescence parameters showed that quantum yield of regulated energy dissipation (Y(NPQ)), ETR and coefficient of nonphotochemical quenching (NPQ) increased with the increase of light intensity under every treatment. By contrast, Y(II), Y(NO) and q_P decreased with increased light intensity. Openness of PSII reaction centers of functional leaves in sugar beet were also improved in range of effective intensity (0-1000 μmol·m^-2·s^-1) by nitrogen application, and PSII was adjusted to dissipate excess photon energy to protect the PSII reaction centers. Application of nitrogen could also increase the content of chlorophyll, carotenoid and ratio of chlorophyll a to chlorophyll b, and the content of chlorophyll and carotenoid were increased with the increase of nitrogen application under every salt environment. These results indicated that PSII activity and light-use efficiency could be improved by nitrogen application, and then the adaptability of sugar beet to salt environment was strengthened.

Aims Optimal spatial scale of hydrological response unit (HRU) is a precondition for eco-hydrological modeling as it is essential to improve accuracy. Our objective was to evaluate the spatial scale of HRU for application of the WASSI-C model.
Methods We determined the best HRU scale for the eco-hydrological model (WASSI-C) through examining the modeling accuracies at different HRU thresholds. This study focused on a large watershed, the upper Zagunao River watershed, situated in the upper reach of the Minjiang River, Yangtze River Basin, China.
Important findings Variation of spatial scales in HRU significantly affected the modeling accuracy. With the increase of the spatial scale of HRU, the accuracy of simulated results first increased then remained relatively unchanged and then decreased, suggesting existence of a threshold around 85 km² in HRU for this model for this watershed. We validated the model using this optimum spatial scale and discussed the potential to improve model output by addressing input parameters such as temperature.

Aims Our objective was to document the effects of different forest management strategies on carbon storage in both vegetation and soil in a Cinnamomum camphora plantation.
Methods We investigated the biomass of trees, shrubs, herb and the litter layer to calculate the carbon storage of vegetation and collected soil samples of 0-60 cm depth to analyze the soil carbon storage in a C. camphora plantation.
Important findings The carbon storage of vegetation was higher in understory removal stands than that of non-removal stands, with an increase of 48.87% and an increment of 0.62 t·hm^-2·a^-1. The soil carbon content was lower when the understory vegetation was removed, with a significant decrease ranging from 4.79% to 34.13%, and a significant decline of 10.16 g·kg^-1and 8.58 g·kg^-1in the 0-10 and 10-20 cm layers, respectively (p < 0.05). Carbon storage in soil was reduced by understory removal treatment in each interval of 0-60 cm depth with a decrease ranging from 1.98% to 43.45% and an especially sharp decline of 15.39 t·hm^-2 and 11.58 t·hm^-2in 0-10 cm (p < 0.01) and 10-20 cm (p < 0.01) layers, respectively. However, the total forest carbon storage in the C. camphora plantation was not significantly reduced by understory removal treatment. Therefore, understory removal contributed to the accumulation of carbon storage in vegetation, but lowered the soil carbon content and storage.

Aims Pinus densata is the natural diploid hybrid of P. tabuliformis and P. yunnanensis, and is one of a few known examples of homoploid hybrid speciation. In order to describe the adaptive and growth characteristics among the three pine species at seedling stage and clarify the role of ecological selection in interspecific isolation between hybrid and parental species, we conducted a common garden comparative analysis of fitness traits at seedling stage in this species complex.
Methods We investigated 14 adaptive and growth characters in seedlings from 25 representative populations of the three pine species in a typical habit of P. tabuliformis. The 14 traits are germination rate, seedling survival in Aug., Sept. and Nov. 2011, winter survival rate of one-year old seedlings, seedling survival rate in Oct. 2012, rates of bud-set in Nov. 2011 and Oct. 2012, the proportion of yellow, green and purple seedlings, seedling height, ground diameter and crown height of seedlings. Patterns of the variation of these characters were analyzed using multi-factor nested analysis of variance and correlated to geographical factors of each population.
Important findings Most of the traits were significantly differentiated among species and among populations at seedling stage, and the large amount of variance were partitioned among species or among populations. Germination rate, the rates of bud-set in two years, and the survival rate in Oct. 2012 of two-year old seedlings were the best indicators of among-species divergence. P. tabuliformis showed the highest values in most of the traits and appeared as more fit in its native habits than the other two pines. P. yunnanensis was at disadvantage in several critical traits, e.g. the survival rates of Aug., Sept., Nov. 2011 and rates of bud-set in two years. Most of one-year old seedlings of P. yunnanensis have not bud-set at the end of Nov. and the proportion of yellow seedlings were highest and its survival rate in Oct. 2012 was zero, which illustrates its low fitness in P. tabuliformis habitat. The hybrid pine, P. densata was intermediate between the parental species in most of traits except indice of the proportion of purple seedlings. The populations from the ancestry hybrid zone in the northeast of P. densata range coped with the test site environment better than the populations from the western range. Our study highlights the role of ecological selection in speciation of this homoploid hybrid pine.

Aims Alhagi sparsifolia is one of the dominant perennial species in the extreme drought region of Taklamakan Desert in northwestern China. Alhagi sparsifolia usually cannot reproduce sexually in natural, non-irrigated environments, where the only way to maintain and extend its populations is to reproduce clonally. In the natural habitats, therefore, clonality and the resultant clonal traits such as clonal integration for water (i.e., water integration) may have played great roles in maintaining populations of A. sparsifolia. So far, however, few studies have been conducted to investigate the water integration pattern between mother and daughter ramets of A. sparsifolia.
Methods We carried out an experiment with four treatments involving the spacer (i.e., the interconnection between adjacent ramets) between mother and daughter ramets. The spacer was: (1) connected, (2) severed, (3) connected and the mother ramet was supplied with 200 L additional water, and (4) severed and the mother ramet was supplied with 200 L additional water. After 15 days of spacer severance, we measured water potential of the mother and daughter ramets and their leaf morphological and growth parameters. In the water supplement treatment, we measured water potential of the mother and daughter ramets immediately before and 24 h after the water supplement. We also measured soil water content at 0 cm (soil surface) to 200 cm soil depth of the mother and daughter ramets before and after water supplement.
Important findings The difference of predawn water potential for both mother and daughter ramets was not significant (p > 0.05) between the spacer connected and spacer severed group, but the midday water potential of both mother and daughter ramets increased significantly after spacer severance (p < 0.01). After water supplement to the mothers, water potential of mothers was significantly increased in both the spacer severance and connection treatments. Water potential of daughter ramets in spacer connection treatment also increased significantly (p < 0.01), but that in spacer severance treatment did not. Leaf relative water content and the increase of height, crown width, branch number and basal diameter of the daughter ramets in spacer connection treatment were significantly higher than that in the spacer severance treatment (p < 0.01). We concluded that water integration exists between mother and daughter ramets of A. sparsifolia and the mother can transfer water to daughter ramets by spacer. This result is important for vegetation restoration and utilization of water resources of this area.

Aims Castanea mollissima and C. dentata are typical chestnut species in Asia and North America, respectively. They play important roles in the ecology and economy in their existing forest ecosystems. Chestnut blight has caused catastrophic losses of C. dentata populations since 1904. It is especially important to understand the differences in chemical ecology characteristics between C. dentata and C. mollissima when scientists try to make use of blight resistance of C. dentata to help the recovery of C. mollissima populations in North America. The objective of this research is to compare the allelopathy effect of C. dentata and C. mollissima by leaf water extract bioassay method.
Methods Using germination rate and vigor as seed germination parameters and radicle, plumule elongation and fresh weight change of seedling as seedling growth parameters, we studied the effect of water extract of C. mollissima leaves on dicotyledons lettuce, radish and cucumber and monocotyledons onion, rice and wheat. We compared the allelopathic intensity of water extract and 11 elution components that were separated by X-5 macroporous resins from water extract of C. dentata and C. mollissima. The strongest allelopathic fraction of C. dentata and C. mollissima was analyzed by liquid chromatograph-mass spectrometer technique and standard substance counterevidence experiment.
Important findings Evidence of inhibition of seed germination and seedling growth of test plants indicated that water extract of C. mollissima leaf has allelopathic properties. Data on inhibition of seed germination and seedling growth in lettuce indicated that the allelopathy of C. mollissima leaves was stronger than C. dentata leaves. The allelochemicals of C. dentata and C. mollissima extracts are in 7:3, 6:4 and 5:5 elution fractions, as documented by the bioassay data. The strongest allelopathy fraction of C. dentata and C. mollissima extract (5:5 elution fraction) contained chlorogenic acid, p-hydroxybenzoic acid, protocatechuic acid, gallic acid, etc. Results suggest that the difference of chemical ecology characteristics between C. dentata and C. mollissima should not be ignored by restoration ecologists.