Aims The optimal patterns of plant community for water use and nutrient utilization, the responses of soil carbon and nitrogen turnover processes to forest succession, and the mechanisms of soil organic carbon accumulation, are three critical issues in forest ecosystem study. It is difficult to accurately detect these ecological processes with conventional methodologies in the short term, yet the application of ¹³C and ¹⁵N natural abundance technique may yield important information about these processes.Methods This study was conducted in Dinghushan Biosphere Reserve. We investigated the natural isotopic abundance of both ¹³C and ¹⁵N of plant-soil continuum along a successional gradient from Pinus massoniana forest (PF) to coniferous and broad-leaved mixed forest (MF), and monsoon evergreen broad-leaved forest (BF). We also analyzed the correlations of foliar stable carbon isotope ratio (δ¹³C) and stable nitrogen isotope ratio (δ¹⁵N) with foliar elemental contents and the variations of soil δ¹³C and δ¹⁵N along soil profiles at different successional stages.Important findings A significant positive correlation between foliar δ¹³C and foliar C:N was observed. In both litter and soil, the δ¹³C values tended to decrease along the forest succession, with the order as PF > MF > BF. Foliar δ¹⁵N was positively correlated with foliar N content. The δ¹⁵N values of litter and upper soil (0-10 cm) increased with successional status. Both soil δ¹³C and δ¹⁵N values increased with increasing soil depth at all three forests. Our results imply that 1) trade-off between water use efficiency and nitrogen use efficiency did not necessarily exist in subtropical forests of China; 2) the application of isotopic technique could assist understanding of the mechanisms of soil carbon accumulation in subtropical forests, especially in old-grow forests; 3) the ¹⁵N natural abundance of plant-soil continuum could be a potential indicator of soil nitrogen availability and ecosystem nitrogen saturation status.

Aims Plant roots play a critical role in the uptake of nutrients, and nitrogen (N) absorption is considered as the first step and a pivotal process in N metabolism of plants. Our objective was to better understand the absorption of two major inorganic N forms (NH₄⁺ and NO₃^-) in subalpine coniferous forests under global warming Methods Experimental warming using infrared heater was applied to two dominant species in subalpine coniferous forests of Sichuan, China, Picea asperata and Abies fargesiivar. faxoniana. The non-invasive micromeasurement technology was used to investigate the effects of warming on the uptake rates of NH₄⁺ and NO₃^- and the potential interactions between these two ions.Important findings Results showed that the maximal net root uptake of NH₄⁺ and NO₃^-occurred at a distance of 17-18 mm and 17 mm from root tips, respectively for P. asperata. and at a distance of 11 mm and 11.5 mm from root tips respectively for A. fargesiivar. faxoniana. Experimental warming elevated the uptake rates of NH₄⁺ and NO₃^- in both species, but the interactions between NH₄⁺ and NO₃^- differed between the two species. While NO₃^- uptake was inhibited in the presence of NH₄⁺ for both P. asperataand A. fargesiivar. faxoniana, net NH₄⁺ uptake was promoted by NO₃^- supply only in P. asperata roots under experimental warming.

Aims This study aimed to understand the impact of exclosure on interspecific associations of species in a typical temperate grassland. We compared the species associations of dominant and companion species in grassland plots with the six-year exclosure and grazing in Taips County, Nei Mongol.Methods We selected 14 species according to important values in each plot, using variance ratio to analyze the overall association. The χ² test with 2 × 2 contingency table, Ochiai index and spearman rank correlation test were applied to analyze the inter-specific associations of dominant and companion species. We used the niche breadth index to analyze the ability of resource utilization of species and inter-specific competition for grazed plots and ones with exclosure.Important findings The inter-specific associations among 91 species pairs inside the exclosure showed that nine species pairs were significantly positive but 4 pairs were negative based on the χ² test with 2 × 2 contingency table. Ten species pairs had significantly positive correlations and 16 species pairs were negative through the Spearman correlation test. For the plots outside the exclosure, we found 19 species pairs were positively associated but 8 pairs were negative associated using the χ² test, and 12 species pairs were significantly positively correlated but 30 pairs were negatively correlated using the Spearman correlation test. The results indicated that the community inside the exclosure was in a continuous development state while the outside community was degradating. The Ochiai indices of dominant species were high both inside and outside the exclosure but the differences using the χ²test were nonsignificant. It implied that there was some connection among dominant species but their patterns of distribution were relatively independent. The niche breadth for dominant species inside the exclosure was higher than ones outside, which suggested the exclosure has an important role in protecting dominant species.

Aims The mechanism of herbivore foraging effect on plant diversity and ecosystem functions of grasslands is the core issue of grazing ecology research. This study is aimed to examine 1) how species respond to different grazing intensity in grassland, and how plant diversity responds to different grazing intensity within different organization scales and whether there are cascade effects across multiple organization scales? 2) How herbivore foraging affects plant diversity.Methods Based on a six-year grazing experiment in Sonid Right Banner, Xilingol, the study attempted to explain the relationships between plant diversity and herbivore foraging from two perspectives, i.e. plant diversity index and herbivore preference index.Important findings Results showed that there were four modes for desert grassland plant in response to herbivore: grazing-hidden species, grazing-sensitive species, grazing-non inductive species and absolute dominant species. At the community scale, species diversity index decreased with an increased grazing intensity. Compared with no grazing, heavy grazing and moderate grazing treatments decreased community plant diversity, and the same principle is applicable to the functional group diversity. Further analysis found that differences of grazing species diversity within a functional group were mainly caused by shrubs and semi-shrubs. Compared to plots without grazing, the herbivore preference degree on the whole species was lower for moderate grazing plots than heavy grazing ones. The foraging preference order on the plant functional groups was annual and biennial forbs (AB), perennial forbs (PF), shrubs and semi-shrubs (SS) and perennial grasses (PG). The preferred species were mainly distributed in AB and PF. The diversity index of plant and preference index of herbivore were basically significant and negatively correlated (p < 0.05).

Aims Woody materials and clumping effects are key error sources in estimating leaf area index (LAI) by optical methods. However, how to correct the error caused by woody materials has not reached consensus. The aims of this study are (1) to evaluate the accuracy of optical methods for estimating effective LAI (L_e) in a deciduous needle leaf forest stand, and (2) to develop a practical correction scheme to improve the accuracy of optical methods in estimating LAI.Methods L_ewas estimated by two indirect methods (i.e., digital hemispherical photography (DHP) and LAI-2000 plant canopy analyzer method (LAI-2000 method) in an annual maximum leaf area period in a Larix gmelinii plantation. Then, we developed three correction schemes to improve the accuracy of indirect methods in estimating LAI. Meanwhile, two direct methods (i.e., litter collection and allometry methods) were used to estimate LAI. Taking LAI from litter collection as a reference, we evaluated the effectiveness of three correction schemes and tested the influence of zenith angle ranges on the correction results.Important findings With zenith angle ranges of 0-45° (rings 1-3), 0-60° (rings 1-4), 45°-60° (ring 4) and 0-75° (rings 1-5), L_eobtained from DHP underestimated LAI from both litter collection and allometry by 19%-32% and 18%-29%, respectively. L_efrom LAI-2000 method with four zenith angles also underestimated LAI from both litter collection and allometry by 9%-30% and 8%-28%, respectively. Although the contribution of woody materials to LAI was overestimated in correction scheme A, it was effective in correcting L_efrom DHP with zenith angles of 45º-60º (ring 4), and also effective for L_efrom LAI-2000 method with zenith angles of rings both 1-3 and 1-4. Correction scheme B was all effective in correcting L_efrom DHP with four zenith angle ranges. Generally, correction scheme C was more effective than other two schemes in correcting L_efrom both DHP and LAI-2000 method with four zenith angle ranges. These results indicate that the zenith angle range is a key factor for determining the accuracy of optical methods in estimating LAI besides woody materials and clumping effects.

Aims Taxodium ‘Zhongshansha’ had a strong submergence tolerance, but the biological mechanism is not clearly defined. The respiratory metabolism for the tolerance of Taxodium ‘Zhongshansha 118’ ((Taxodium distichum × Taxodium mucronatum) × Taxodium mucronatum) to long-term flooding was investigated through the measuring and analyzing the changes in root starch and soluble sugar as well as the contents of anaerobic respiration enzymes, including lactic dehydrogenase (LDH), ethanol dehydrogenase (ADH) and pyruvate decarboxylase (PDC)), in the ‘Zhongshansha 118’ seedling. The biomass and activities of the seedling roots were also measured and analyzed.Methods 24 1-year Taxodium ‘Zhongshansha 118’ seedlings were randomly and equally divided into four groups and each group experienced one of four different levels of flooding (i.e., no flooding, waterlogging, partial submergence, deep submergence) from August 8 to November 8, 2014.Important findings The results showed that the contents of the anaerobic respiration enzymes in the seedling roots and leaves are increasing with the levels of severity of flooding, which indicated the roots and leaves adapt to long-term flooding by reinforcing their anaerobic respiration and activities of ADH that were higher than LDH for roots and leaves used in alcoholic fermentation mainly. The activities of anaerobic respiration enzymes in leaves were higher than that in roots, while leaves were more sensitive to flooding. The starch and soluble sugar in roots and leaves had similar trend with anaerobic respiration enzymes. However, roots starch was higher than leaves where soluble sugar was lower than roots. The higher content of starch were the important reason of strong submergence tolerance, and we consider the strategy to fit into long-term flooding is patience type. The paper demonstrate Taxodium ‘Zhongshansha 118’ have the physiological and the morphological properties to adapt to long-term flooding, including aerial root and basal part of stem expanded and the outer wall of the root lignified to protect the roots from flooding.

Aims Our objective was to investigate the responses of maize photosynthesis and growth to repeated drought.Methods Maize seedlings were exposed to different soil water deficit for three weeks, then rewatering for one week, and again to different water deficit for three weeks, to examine the effects of repeated drought on photosynthesis and growth.Important findings After the first water deficit treatments, under severe drought, plant height, total leaf area of individual plant, shoot and root biomass declined significantly, also transpiration rate (T_r), stomatal conductance (G_s), intercellular CO₂ concentration (C_i), net photosynthetic rate (P_n), maximum net photosynthetic rate (A_max), but light compensation point and dark respiration rate increased significantly. Under medium drought, plant height, leaf area, and shoot biomass decreased significantly, but root biomass did not vary, hence, the ratio of roots to shoots (R/S) increased. Moreover, plants did not show significant differences in photosynthetic parameters. After rewatering, photosynthesis and growth rate of plants previously exposed to water deficit could recover to the levels of well-watered plants, but plant height and leaf area did not recover to the levels of the control. When maize were subjected to recurrent drought, plants pre-exposed to medium drought showed no significant difference in plant height, biomass, and photosynthetic parameters, but a significant decrease in leaf area, compared to plants only exposed to second medium drought. Plants pre-exposed to severe drought had significantly higher T_r, G_s, C_i, P_n, A_max, and, apparent quantum yield but significantly lower plant height, leaf area, and biomass than plants without previous exposure. These results indicated that the first severe drought significantly reduced photosynthetic capacity and maize growth, rewatering could recover photosynthesis and growth rate to the levels of well-watered plants, but could not eliminate the adverse influence of the first drought on growth. The first medium drought could stimulate the growth of maize root system and significantly increased R/S, which can enhance maize drought resistance to subsequent repeated drought, and maintain the total biomass in the control level; the first severe drought could enhance maize drought resistance to subsequent repeated drought in the aspect of photosynthesis, but could not compensate for the adverse effect of early drought on plant growth. Hence, in practice, drought hardening should be limited in the level of medium drought, and avoiding severe drought.

Aims Root exudates have specialized roles in nutrient cycling and signal transduction between a root system and soil, as well as in plant responses to environmental stresses. They are the key regulators in the rhizosphere communications and can modify the biological and physical interactions between roots and soil organisms. Phytoremediation is an important measure to remove organic pollutants from contaminated soil, and root exudates are considered to be closely related to the mechanisms in the phytoremediation of soils contaminated by organic pollutants．This study was designed to determine the characteristics of root exudates in five Festuca species under the stress of benzo [α] pyrene (BaP) and to identify the effects of BaP on the organic compounds of low molecule weight in root exudates.Methods Five Festuca species, which had been tested to be tolerant to the BaP stress, were used in this study. A soil-cultivating test, with rhizobag technique, was conducted to investigate the effect of BaP concentration on the organic compounds of low molecule weight in root exudates at different growth stages (30-70 days). The BaP concentrations in the contaminated soils were set for 10.25 mg·kg^-1, 20.37 mg·kg^-1, 40.45 mg·kg^-1, 80.24 mg·kg^-1, and 161.74 mg·kg^-1(denoted by T₁, T₂, T₃, T₄ and T₅, respectively).Important findings The presence of vegetation enhanced the dissipation of BaP in soils. This effect was especially marked in treatment with F. arundinacea, followed sequentially by that of F. chelungkiangnica, F. rubra subsp. arctica and F. sinomutica; the dissipation of BaP in treatment with F. stapfiwas lowest during the entire experiment. The contents of soluble sugars, organic acids, and amino acids in root exudates were all increased by the BaP treatments. The contents of soluble sugars in root exudates increased notably at relatively low BaP levels (T₁-T₃) or in earlier stress stages (30-40 days), and declined at relatively high BaP levels (T₄-T₅) or in later stress stages (40-70 days), with highest values always occurring in the T₃ treatments on day 50 of the experiments. In the five Festuca species, oxlic acid, acetic acid, lactic acid and malic acid are the main constituents of organic acids in root exudates, at greater than 97.34% in total in all treatments. However, there are traces of fumaric acid in the root exudates of Festuca species with stronger remediation potentials. When the contents of organic acids in root exudates reached the peak, the stronger the remediation potentials of plants were, the higher the concentrations of BaP would be to induce stress. Nineteen types of common amino acids were found in root exudates of Festuca and the proportion of total amino acids in root exudates remain stable under all the BaP stress treatments, albeit varying contents of the 19 types of amino acids under different BaP concentrations. The contents of all amino acid in root exudates increased with increasing BaP concentrations; especially, the contents of secreted threonine, serine, glycine and alanine increased significantly among the 19 types of amino acids and the differences were significant among all treatments with different BaP concentrations (p< 0.05). However, proline, hydroxyproline, and aspartic acid participated in the stress responses of plants almost in the form of additive or synergistic effects, and their contents in root exudates increased markedly with increasing BaP concentrations in soils; the differences among different treatments were significant (p< 0.05). The more constituents of amino acids there were in stress responses, the stronger the remediation potentials of plants would be. All these illustrate that the characteristics of root exudates in Festuca were closely related to their remediation potential under the BaP stress. The greater the remediation potentials were, the more organic compounds of low molecular weight there were and the more complex those compounds would be. Moreover, they also showed a stronger environment adaptability and physiological plasticity.

Three 1-hm² permanent plots were established in the Yaoluoping National Nature Reserve in Anqing of Anhui Province. All trees with diameter at breast height (DBH) ≥ 2 cm were mapped, tagged with aluminum plates of unique numbers, and identified by species. On the basis of the importance value of the canopy and shrub layer, the three plots in Yaoluoping, Diaoguanjing and Anjiping were classified as Castanea seguinii + Lindera glauca deciduous broad-leaf forest community, Platycarya strobilacea + Lindera glauca deciduous broad-leaf forest community, and Platycarya strobilacea + Lindera chienii deciduous broad-leaf forest community, respectively. The three plots were all dominated by deciduous trees with evergreen trees only found in the Diaoguanjing plot. The Diaoguanjing plot was most abundant in species (81), followed by the Anjiping plot (76) and the Diaoguanjing plot (62). The local plant communites are stable and the vegetation is well restored.

The survival and growth strategies, community structure and functions of microbial decomposers vary with substrate stoichiometry, which profoundly influences substrate decomposition, turnover, and hence the carbon and nutrient cycles of terrestrial ecosystems. It is crucial to understand the relationships among microbial metabolism, community structure and ecosystem processes of terrestrial ecosystems and their responses and feedbacks to global changes. In this review, we first introduced the significance of microbial decomposers in the carbon, nitrogen, and phosphorus cycles of terrestrial ecosystems from perspectives of ecological stoichiometry and metabolic theories. Then we synthesized four potential mechanisms of microbial response and control on substrate stoichiometric variations, i.e., through (1) modifying microbial stoichiometry, (2) shifting microbial community structure, (3) producing extracellular enzymes to acquire limiting resources, and (4) changing microbial carbon, nitrogen, and phosphor use efficiencies. Finally, we proposed three research directions in this field: (1) to comprehensively explore various microbial mechanisms in response to changes in substrate stoichiometry and the relative importance of these mechanisms; (2) to examine influences of global changes on microbial-driven cycles of carbon, nitrogen, and phosphorus; and (3) to explore spatiotemporal changes in the strategies of microbial adaptation to changes in the substrate stoichiometry.

Among the most critical processes in simulating terrestrial ecosystem performance is the regulatory role of stomata in carbon and water cycles. Compared with field measurements, the changes in stomatal slope caused by the biophysical environment provide a simple but effective synthetic framework for studying climate-related carbon and water cycling, due to its sensitivity to CO₂, vapor pressure deficit, and photosynthesis. It is also crucial in understanding the effects of climate change on photosynthesis and water use efficiency. Endeavored by numerous scholastic efforts, stomatal conductance models have been improved based on experimental, semi-experimental, and mechanical processes. However, the underlying biological mechanisms and the dynamics of key parameters in these models remain unexplored, especially regarding the changes in stomatal slope. By improving the understanding of the stomata’s regulatory role, we reduced the uncertainty of stomatal conductance simulation. We then synthesized the recent developments and lessons in optimal stomatal behavior theory to simulate stomatal conductance and included an introduction to widely used stomatal conductance models and parameters, the main factors influencing stomatal slopes, and applications of the mechanical stomatal conductance models in different ecosystems. Based on our literature review, we proposed that future research is needed on the optimal stomatal behavior theory and its applications in simulating stomatal conductance.