Clonal integration benefits an invader in heterogeneous environments with reciprocal patchiness of resources, but not its native congener.

Many of the world's most invasive plants are clonal, and clonal functional traits are suggested to contribute to their invasiveness. Clonal integration is one of the most important clonal functional traits, but it is still unclear whether clonal integration can benefit invasive alien clonal plants more than native ones in heterogeneous environments with reciprocal patchiness of resources and whether invasive plants show a higher capacity of division of labor than native ones in such environments. We grew connected (allowing clonal integration) and disconnected (preventing clonal integration) ramet pairs of an invasive plant Wedelia trilobata and its occurring native congener W. chinensis in the environment consisting of reciprocal patches of light and soil nutrients (i.e., a high-light but low-nutrient patch and a low-light but high-nutrient patch). Clonal integration greatly promoted the growth of the invasive species, but had no significant effect on the native one. Both invasive and native species showed division of labor in terms of morphology, biomass allocation, and/or photosynthetic physiology, but the capacity of labor division did not differ between the invasive and the native species. We conclude that in heterogeneous environments consisting of reciprocal patches of resources, which are common in nature, clonal integration can confer invasive plants a competitive advantage over natives, but this difference is not related to their capacity of labor division. This study highlights the importance of clonal integration for plants in heterogeneous environments and suggests that clonal integration can contribute to the invasion success of alien clonal plants.

Contrasting Leaf Trait Responses of Conifer and Broadleaved Seedlings to Altered Resource Availability Are Linked to Resource Strategies.

(1) Understanding tree seedling responses to water, nutrient, and light availability is crucial to precisely predict potential shifts in composition and structure of forest communities under future climatic conditions. (2) We exposed seedlings of widespread Central European tree species with contrasting leaf habit, deciduous broadleaves (DB) and evergreen conifers (EC), to factorial combinations of manipulated precipitation (100% and 50% of ambient), shade (40% and 60% of full sunlight), and nutrient availability (low and high NPK), and measured specific leaf area, C/N ratio, soluble sugars, starch and non-structural carbohydrate concentration, and δ13C of the leaves. (3) We found contrasting effects of water and nutrient availability on foliar traits of the two species groups: EC exhibited higher tolerance to low resource availability but also less plasticity in foliar traits, which is congruent with a "slow" resource strategy. In contrast, foliage of DB reacted particularly to altered nutrient availability, corresponding to a "fast" resource strategy with high foliar plasticity and rapid adjustments to resource fluctuations, commonly adopted by species with high growth rates. (4) We conclude that DB will respond to environmental change with foliar acclimation, while EC will either tolerate, to some extent, or shift their distribution range in response to environmental change.

The Concentration of Non-structural Carbohydrates, N, and P in Quercus variabilis Does Not Decline Toward Its Northernmost Distribution Range Along a 1500 km Transect in China.

Understanding the mechanisms that determine plant distribution range is crucial for predicting climate-driven range shifts. Compared to altitudinal gradients, less attention has been paid to the mechanisms that determine latitudinal range limit. To test whether intrinsic resource limitation contributes to latitudinal range limits of woody species, we investigated the latitudinal variation in non-structural carbohydrates (NSC; i.e., total soluble sugar plus starch) and nutrients (nitrogen and phosphorus) in mature and juvenile Chinese cork oak (Quercus variabilis Blume) along a 1500 km north-south transect in China. During the growing season and dormant season, leaves, branches, and fine roots were collected from both mature and juvenile oaks in seven sites along the transect. Tissue concentration of NSCs, N, and P did not decrease with increasing latitude irrespective of sampling season and ontogenetic stage. Furthermore, higher levels of NSCs and N in tissues of juveniles relative to mature trees were found during the dormant season. Partial correlation analysis also revealed that during the dormant season, soluble sugar, NSC, the ratio of soluble sugar to starch, and tissue nitrogen concentration were correlated positively with latitude but negatively with precipitation and mean temperature of dormant season. Our results suggest that carbon or nutrient availability may not be the driving factors of the latitudinal range limit of the studied species. Further studies should be carried out at the community or ecosystem level with multiple species to additionally test the roles of factors such as regeneration, competition, and disturbance in determining a species' northern distribution limit.

Elevation alters carbon and nutrient concentrations and stoichiometry in Quercus aquifolioides in southwestern China.

Elevation is a complex environmental factor altering temperature, light, moisture and soil nutrient availability, and thus may affect plant growth and physiology. Such effects of elevation may also depend on seasons. Along an elevational gradient of the Balang Mountain, southwestern China, we sampled soil and 2-year old leaves, 2-year old shoots, stem sapwood and fine roots (diameter<5mm) of Quercus aquifolioides at 2843, 2978, 3159, 3327, 3441 and 3589m a.s.l. in both summer and winter. In summer, the concentrations of tissue non-structural carbohydrates (NSC) did not decrease with increasing elevation, suggesting that the carbon supply is sufficient for plant growth at high altitude in the growing season. The concentration of NSC in fine roots decreased with elevation in winter, and the mean concentration of NSC across tissues in a whole plant showed no significant difference between the two sampling seasons, suggesting that the direction of NSC reallocation among plant tissues changed with season. During the growing season, NSC transferred from leaves to other tissues, and in winter NSC stored in roots transferred from roots to aboveground tissues. Available soil N increased with elevation, but total N concentrations in plant tissues did not show any clear elevational pattern. Both available soil P and total P concentrations in all plant tissues decreased with increasing elevation. Thus, tissue N:P ratio increased with elevation, suggesting that P may become a limiting element for plant growth at high elevation. The present study suggests that the upper limit of Q. aquifolioides on Balang Mountain may be co-determined by winter root NSC storage and P availability. Our results contribute to better understanding of the mechanisms for plants' upper limit formation.

[Effects of simulated warming and functional group removal on survival and growth of Abies faxoniana seedlings]. / 模拟增温和功能群去除对岷江冷杉幼苗存活和生长的影响.

Warming and herbaceous functional group removal experiment was conducted in subalpine meadow to examine the effects of herbaceous species on Abies faxoniana seedlings by analyzing its physiological responses. The survival rate and non-structural carbohydrate content were significantly increased, but the growth and root/shoot of A. faxoniana were decreased. Seedling survival was significantly positively correlated with non-structural carbohydrate content, especially with soluble sugar. Under the treatment without warming, herbaceous species inhibited the survival of A. faxoniana, increased height growth and aboveground biomass. Grasses and forbs decreased the root length and belowground biomass of A. faxoniana. In the warming treatment, forbs increased the survival of A. faxoniana, sedges decreased root length and belowground biomass of A. faxoniana, and grasses and forbs decreased height growth and aboveground biomass of A. faxoniana. Simulated warming increased the survival of A. faxoniana seedlings, but also made it face stronger competition from herbaceous and thus inhibited its growth.

Clonal integration increases tolerance of a phalanx clonal plant to defoliation.

Defoliation by herbivores commonly imposes negative effects on plants, and physiological integration (resource sharing) can enhance the ability of guerilla clonal plants to tolerate stresses. Here we examined whether physiological integration can increase the ability of phalanx clonal plants to withstand defoliation. On a high mountain grassland in southwestern China, we subjected the phalanx clonal plant Iris delavayi within 10cm×10cm plots to three levels of defoliation intensity, i.e., control (no defoliation), moderate (50% shoot removal to simulate moderate herbivory) and heavy defoliation (100% shoot removal to simulate heavy herbivory), and kept rhizomes at the plot edges connected (allowing physiological integration) or disconnected (preventing integration) with intact ramets outside the plots. Defoliation significantly reduced leaf biomass, root biomass and ramet number of I. delavayi. Clonal integration did not affect the growth of I. delavayi under control, but significantly increased total biomass, rhizome and root biomass under heavy defoliation, and leaf biomass and ramet number under moderate defoliation. We conclude that clonal integration associated with resource reallocation plays an important role in maintaining the productivity of the alpine and subalpine grassland ecosystems in SW China where clonal plants are a dominant component of the grasslands and are commonly extensively managed with moderate grazing intensity. Our results also help to better understand the adaption and tolerance of phalanx clonal plants subjected to long-term grazing in the high mountain environment.

Defense pattern of Chinese cork oak across latitudinal gradients: influences of ontogeny, herbivory, climate and soil nutrients.

Knowledge of latitudinal patterns in plant defense and herbivory is crucial for understanding the mechanisms that govern ecosystem functioning and for predicting their responses to climate change. Using a widely distributed species in East Asia, Quercus variabilis, we aim to reveal defense patterns of trees with respect to ontogeny along latitudinal gradients. Six leaf chemical (total phenolics and total condensed tannin concentrations) and physical (cellulose, hemicellulose, lignin and dry mass concentration) defensive traits as well as leaf herbivory (% leaf area loss) were investigated in natural Chinese cork oak (Q. variabilis) forests across two ontogenetic stages (juvenile and mature trees) along a ~14°-latitudinal gradient. Our results showed that juveniles had higher herbivory values and a higher concentration of leaf chemical defense substances compared with mature trees across the latitudinal gradient. In addition, chemical defense and herbivory in both ontogenetic stages decreased with increasing latitude, which supports the latitudinal herbivory-defense hypothesis and optimal defense theory. The identified trade-offs between chemical and physical defense were primarily determined by environmental variation associated with the latitudinal gradient, with the climatic factors (annual precipitation, minimum temperature of the coldest month) largely contributing to the latitudinal defense pattern in both juvenile and mature oak trees.

[Eco-physiological response of Quercus variabilis seedlings to increased atmospheric CO2 and N supply].

The effect of CO2 enhancement, nitrogen deposition and their interaction on the northern boundary (Zhuanghe in Liaoning Province) of Quercus variabilis seedlings was studied by controlling the CO2 concentration (700 micromol x mol(-1); 400 micromol x mol(-1)) and nitrogen level (non nitrogen fertilizer: CK; nitrogen fertilizer: 120 kg N x hm(-2)). The results showed that under elevated CO2 the Q. variabilis seedlings' leaf morphology, photosynthetic pigments and leaf nitrogen content tended to decrease, and the dark respiration rate decreased 63. 3% and soluble sugar increased 2.6%. Nitrogen deposition significantly promoted the Q. variabilis seedlings' leaf morphology and photosynthetic pigments, leading to increased leaf nitrogen content, decreased potassium content, and 26.7% of increase in nitrogen to potassium ratio. CO2 and N interaction played a significant role on promoting the Q. variabilis seedlings' leaf morphology and photosynthetic. The maximum net photosynthetic and light saturation point were 1.4 and 2.6 times of the control, while dark respiration and light compensation point decreased 65.9% and 50.0%, respectively. Elevated CO2 and nitrogen deposition had a positive effect on Q. variabilis seedlings to some degree, which might result in the movement of distribution boundary of Q. variabilis to north.

Responses of nutrients and mobile carbohydrates in Quercus variabilis seedlings to environmental variations using in situ and ex situ experiments.

Forest tree species distributed across a wide range of geographical areas are subjected to differential climatic and edaphic conditions and long-term selection, leading to genotypes with morphological and physiological adaptation to the local environment. To test the ability of species to cope with changing environmental conditions, we studied the ecophysiological features of Quercus variabilis using seedlings grown in geographically widely isolated populations (Exp. I, in situ) and in a common garden (Exp. II, ex situ) using seedlings originating from those populations. We found that Q. variabilis plants grown in different locations along a south-north gradient had different levels of nutrients (N, P, K) and carbon-physiological performance (photosynthesis, non-structural carbohydrates, such as soluble sugars and starch), and that these physiological differences were not correlated with local soil properties. These geographic variations of plant physiology disappeared when plants from different locations were grown in the same environment. Our results indicate that the physiological performance of Q. variabilis plants is mainly determined by the climatic variations across latitude rather than by their soils or by genetic differentiation. The adaptive ability of Q. variabilis found in the present study suggests that this species has the potential to cope, at least to some extent, with changing environmental conditions.

[Effects of habitat change on nutrient contents in Quercus variabilis seedlings].

Quercus variabilis seedlings were collected from the habitats at different latitudes, and transplanted on the same experimental sites installed in the central part and southern and northern boundaries of China, where Q. variabilis has a natural distribution, aimed to study the effects of habitat change on the nutrient contents in the seedlings in their vigorous growth period. With habitat change, the various organs nitrogen (N) content and the stem phosphorous (P) content of the transplanted seedlings changed significantly, but the organs potassium (K) content and the leaf- and root P content had less change. In the experimental sites, the organ N content of the transplanted seedlings had significant positive correlation with the latitudes where the seedlings grew, the stem- and root P contents decreased with the increasing latitude, while the leaf N:P ratio had less change. The organ N and P contents of the transplanted seedlings growing in northern boundary decreased significantly, and the effect of the latitudes was more obvious. The leaf N:P ratio of all the seedlings transplanted from different altitudes increased to different degrees. It was concluded that the nutrient contents in different organs of Q. variabilis seedlings varied with latitude, and the seedlings had different responses to habitat change.

Spatial heterogeneity in light supply affects intraspecific competition of a stoloniferous clonal plant.

Spatial heterogeneity in light supply is common in nature. Many studies have examined the effects of heterogeneous light supply on growth, morphology, physiology and biomass allocation of clonal plants, but few have tested those effects on intraspecific competition. In a greenhouse experiment, we grew one (no competition) or nine ramets (with intraspecific competition) of a stoloniferous clonal plant, Duchesnea indica, in three homogeneous light conditions (high, medium and low light intensity) and two heterogeneous ones differing in patch size (large and small patch treatments). The total light in the two heterogeneous treatments was the same as that in the homogeneous medium light treatment. Both decreasing light intensity and intraspecific competition significantly decreased the growth (biomass, number of ramets and total stolon length) of D. indica. As compared with the homogeneous medium light treatment, the large patch treatment significantly increased the growth of D. indica without intraspecific competition. However, the growth of D. indica with competition did not differ among the homogeneous medium light, the large and the small patch treatments. Consequently, light heterogeneity significantly increased intraspecific competition intensity, as measured by the decreased log response ratio. These results suggest that spatial heterogeneity in light supply can alter intraspecific interactions of clonal plants.