Strong disturbance and environment stress have significant influence on species diversity (SD) and functional diversity (FD) in plant community. However, the changes in SD, FD and their relationships over time remain controversial. Previous studies showed that the SD-FD relationship along disturbance gradients can represent positive correlation, negative correlation and/or sigmoid curve, respectively. Our aim here is to explore the temporal dynamics patterns of SD and FD in a community experienced disturbance. Particularly, we explored how specific disturbance factor and/or disturbance intensity affect the SD-FD relationship over time.

The experiment was conducted in the alpine Kobresia humilis meadow at Haibei Research Station of the Chinese Academy of Sciences with clipping (unclipping, stubbled 3 cm and 1 cm) and fertilizing (12.75 g·m^-2·a^-1 urea + 3.06 g·m^-2·a^-1 ammonium phosphate) treatments from 2007 to 2013. GLMRMANOVA regression analysis and ANCOVA were used for analyzing the effects of different treatment factors and their interaction on SD, FD, the patterns of temporal dynamics of SD and FD and their relationship over time.

SD and FD significantly increase with increasing clipping intensity. In contrast, fertilization decreased SD and increased feebly FD. During the experiment period, SD declined with time while FD increased. The SD-FD relationship was positively correlated in unclipped and moderate clipped plots, but was not correlated in heavy clipped plots. The slope of SD(x)-FD(y) relationship declined with the increase in clipping intensity. In contrast, fertilization did not change the shape and slope of the SD(x)-FD(y) relationship. The effects of the interaction of clipping and fertilization on SD and FD were not significant, and the slope changes along clipping gradients were identical in fertilized and unfertilized plots. These results suggest that clipping disturbance may induce trait divergence rather than trait convergence in this meadow community, while the strong interspecific competition resulted from fertilizing may not significantly intensify the trait divergence. These findings were inconsistent with the predictions of plant community assembly theory. Compared with fertilizing disturbance, clipping disturbance should play a more important role in shaping the SD-FD relationship.

Herb layer plays an important role in maintaining ecosystem functioning of forests. The aims of this study were to determine the pattern of species diversity in early post-fire regeneration of the herb layer in mixed Yunnan pine forests and to identify the effects of topography, fire severity, pre-fire vegetation and herb species life-history feature on post-fire regeneration.

We conducted field investigations of post-fire regeneration by randomly setting 47 transects of 10 m × 100 m in a burned forest stand in Qinfeng Township, Lufeng County, Yunnan Province, from September to October, 2013. The Two-Way Indicator Species Analysis (TWINSPAN) was used to classify the herb community types from the 47 transects, and species richness and two indexes of β-diversity were used to analyze herb species diversity and compositional change within sampling transects. Generalized linear model and hierarchical variation partitioning were applied to estimate factors affecting the pattern of herb species diversity of the post-fire communities.

Four herb community types were identified for the 47 transects, which are differentiated by topographic features and fire severities. The species richness in the herb layer of early post-fire regeneration was primarily affected by elevation, topography, fire severity and the pre-fire forest canopy. Specifically, the species richness decreased with increasing elevation, and was positively correlated with biomass of the standing trees and steepness of site slope and negatively correlated with slope position. However, the species richness of herbs was not correlated with fire severity significantly. The within community β-diversity of the post-fire herb layer had a positive correlation with both basal area of pre-fire canopy trees and fire severity. Moreover, the β-diversity was lower at higher elevations. The results also highlighted the differences between annual and perennial species in their distribution patterns.

Understanding the effects of plant size on the trade-off between twigs and leaves is important for revealing strategies of plants forming different canopy structure, making full use of space resources, and enhancing their photosynthetic efficiency and competitiveness with adjusting plant configuration. Our objective was to study how twig and leaf traits of Zygophyllum xanthoxylum depended on size in the northern slope of Qilian Mountains, China.

The study was conducted in a desert grassland on the northern slope of the Qilian Mountains, Gansu Province, China. A transect was laid out horizontally along latitudinal direction, and three sample plots were set up along the transect at the interval of 50 m. Community traits were investigated by using double diagonal method, and all individuals of Z. xanthoxylum were used for measurement of the height, canopy, single leaf area, leaf numbers, twig length, cross-sectional area of twig, and bifurcation angle. Total of 90 plants were divided into different size classes based on the volume: d (the cube root of plant volume) ≤ 60 cm, 60 cm < d ≤ 120 cm, and d > 120 cm. Twig and leaf traits were log-transformed, and the standardized major axis (SMA) estimation method was used to examine the allometric relationships of twig length with leaf area or leaf number.

With the increase of plant size, the height, individual leaf area, twig length, and twig cross-sectional area of Z. xanthoxylum increased gradually (p < 0.01), while the bifurcation angle and leaf number decreased gradually (p < 0.01). An isometric or allometric relationship was found between twig length and leaf area in all plant size, whereas an allometric relationship was found between twig length and leaf number. The allometric slope between twig and leaf area was significantly decreased with the increase of plant size, the y-intercepts between twig and leaf number was significantly decreased too. To improve the efficiency of resource utilization, small individuals of Z. xanthoxylum tend to have a large number of leaves on short twigs, and large individuals have relatively few leaves on thick and long twigs. The increase of leaf area and the decrease of leaf number influenced the resource allocation pattern of twigs.

This study was conducted to determine the effects of air temperature and relative humidity on the equilibrium moisture content (EMC) and time-lag of forest dead fine fuels by taking Larix gmelinii leaves, Betula platyphylla leaves and mixture of L. gmelinii and B. platyphylla leaves as examples.

Measurements were made on moisture content of fuels under different air temperature and humidity conditions (a total of 20 temperature by relative humidity combinations). Equations describing the dynamics of moisture content of fine-grain fuels in three types of forests were developed and the EMC and time-lag were estimated. The moisture-time mode, EMC-temperature and EMC-relative humidity models, time-lag-temperature and time-lag-relative humidity models for fine-grain fuels were also established.

Data were fit by four EMC models. The Van Wanger model gave the best fit with small errors (both mean absolute error (MAE) and root mean square error (RMAE) within 0.01); the performance of Nelson model was worst. Further analysis revealed that both air temperature and relative humidity significantly affected EMC and time-lag. Air temperature was negatively correlated with EMC and time-lag, whereas relative humidity was positively correlated with EMC and time-lag. Using the time-lag-relative humidity model overestimated the time-lag. There are some uncertainties and limitations remaining in the current analysis, and further research is needed on both desorption and absorption processes of fine fuels, with broader range of fuel types and more influencing factors.

Essential resources for plant growth are usually patchily distributed. During the process of propagation, interconnected ramet pairs of stoloniferous plant buffalograss (Buchloe dactyloides) may therefore experience contrasting resource supply such as light. Under heterogeneous light supply, anatomical structure of newly developed leaves is regulated by the light condition of mature leaves. However, little is known about whether leaf anatomical structure of clonal ramets is affected by the light environment of interconnected ramets in clonal plants under heterogeneous light supply.

Two light levels were set, with high light (natural sunlight) and low light (shade, 10% natural sunlight). Interconnected ramet pairs of buffalograss were exposed to homogeneous or heterogeneous light conditions.

Unshaded EDR benefit from their connection to shaded YDR, while unshaded YDR experience marked cost due to its connection to shaded EDR. The plastic decrease of shaded ramets under heterogeneous light may be associated with its reduced survival cost, and elevated survival rate under shading.

The study of embolism vulnerability to drought has become a hot and key topic under global climate change. The objective of the study was: 1) to identify the relationship between xylem structure and embolism vulnerability; 2) to define the differences in resistance of embolism in xylem structure of each species; and 3) to establish drought tolerance indexes in xylem structure of six species.

Drought tolerance trees of Robinia pseudoacacia, Hippophae rhamnoides, Ulmus pumila, Corylus heterophylla, Salix matsudana, Acer truncatum were studied. Cochard Cavitron centrifuge was used to establish embolism vulnerability curves and to calculate xylem vulnerability value. Staining and silicone injection techniques were used to to measure xylem structure of drought tolerance trees including vessel diameter, conduit wall span, number of vessels per unit area, contact faction, vessel length and wood density.

The results showed: 1) xylem embolism vulnerability of the six species ranked as Robinia pseudoacacia > Ulmus pumila > Hippophae rhamnoides > Salix matsudana > Acer truncatum > Corylus heterophylla; 2) the vulnerability curves is “r” shape for Robinia pseudoacacia, Hippophae rhamnoides, Ulmus pumila and is “s” shape for Corylus heterophylla, Salix matsudana, Acer truncatum, respectively; 3) the xylem vulnerability values is significantly different in trees of “r” shape and “s” shape (p < 0.01). Furthermore, linear analysis showed that the different effects between the xylem structure of the species was closely related to the vulnerability in the following order: the maximum effect was from wood density (t = 0.702), the medium effect was from vessel diameter (t = 0.532), and the minimum effect was from vessel length (t = 0.01).