Sensitivity of Functional Traits to Environmental factors in a Karst Plant Community

In this study, the plant communities at five succession stages (herbage, herbage-shrub, shrub, tree-shrub, and tree) in the Zhenning Karst Plateau area of Guizhou were examined. The changes of plant functional characteristics in different succession stages were analyzed, as was the relationship between functional traits and environmental factors. The main results include the following. (1) During the succes-sion process, plant height, leaf dry matter mass, leaf area, leaf nitrogen content, and leaf phosphorus content gradually increased, whereas leaf thickness and specific leaf area decreased, and leaf C:P ratio and leaf N:P ratios did not change significantly. (2) Soil organic matter, soil total nitrogen, soil total phosphorus, soil C:N, soil C:P, and soil C:K increased at first and then decreased, reaching a peak at the tree-shrub stage. Soil total potassium fluctuated and soil bulk density gradually decreased and reached the lowest value at the tree-shrub stage. (3) Redundancy analysis (RDA) showed that the plant community shifted from a nutri-ent-poor soil environment to a nutrient-rich environment. Soil total phosphorus, soil C:K, soil organic mat-ter, soil C:N, and soil bulk density were the key environmental factors affecting the change of functional traits. (4) Structural equation modeling suggests that that specific leaf area and leaf nitrogen content had more sensitive responses to soil nutrient resources and environmental factors, respectively.

Consistent Grime’s CSR Strategy of Daisy Fleabane Erigeron annuus (L.) Pers. despite Its High Morphological Variability—A Case Study from Zagreb and Medvednica Mt., Croatia

Alongside the direct destruction of natural habitats and changes in land use, invasive species are considered one of the greatest threats to global biodiversity. Daisy fleabane Erigeron annuus (L.) Pers. is among the most widespread invasive plants in Croatia. Invasions of E. annuus may be aided by morphological variability, which this study investigates. The variability of life traits (stem height, fresh and dry leaf mass, length, width and leaf area, specific leaf area, and leaf dry matter content) was examined among 18 locations throughout Zagreb and Medvednica Mt. Overall, 87 plant specimens and 435 leaves were measured and analysed using univariate and multivariate statistics. Viable populations were recorded in diverse habitat types, mostly with marked human impact. We determined Grime’s CR plant life strategies for all, except for two localities with C/CR plant strategies. Two populations with a more pronounced competitive strategy had high leaf dry matter content, with smaller leaves and medium height stems. Significant differences between the localities were found, with the specific leaf area (SLA) and plant height being the most diverse. Despite its high morphological variability, daisy fleabane had a consistent CSR strategy, which likely enables its widespread invasions across variable habitats.

Mercury accumulation in leaves of different plant types – the significance of tissue age and specific leaf area

Mercury, Hg, is one of the most problematic metals from an environmental perspective. To assess the problems caused by Hg in the environment, it is crucial to understand the processes of Hg biogeochemistry, but the exchange of Hg between the atmosphere and vegetation is not sufficiently well characterized. We explored the mercury concentration, [Hg], in foliage from a diverse set of plant types, locations and sampling periods to study whether there is a continuous accumulation of Hg in leaves and needles over time. Measurements of [Hg] were made for deciduous and conifer trees in Gothenburg, Sweden (botanical garden and city area), as well as for evergreen trees in Rwanda. In addition, data for wheat from an ozone experiment conducted at Östad, Sweden, were included. Conifer data were quantitatively compared with literature data. In every case where older foliage was directly compared with younger, [Hg] was higher in older tissue. Covering the range from the current year up to 4-year-old needles in the literature data, there was no sign of Hg saturation in conifer needles with age. Thus, over timescales of approximately 1 month to several years, the Hg uptake in foliage from the atmosphere always dominated over Hg evasion. Rwandan broadleaved trees had generally older leaves due to lack of seasonal abscission and higher [Hg] than Swedish broadleaved trees. The significance of atmospheric Hg uptake in plants was shown in a wheat experiment where charcoal-filtrated air led to significantly lower leaf [Hg]. To search for general patterns, the accumulation rates of Hg in the diverse set of tree species in the Gothenburg area were related to the specific leaf area (SLA). Leaf-area-based [Hg] was negatively and non-linearly correlated with SLA, while mass-based [Hg] had a somewhat weaker positive relationship with SLA. An elaborated understanding of the relationship behind [Hg] and SLA may have the potential to support large-scale modelling of Hg uptake by vegetation and Hg circulation.

Rooting Volume Impacts Growth, Coverage and Thermal Tolerance of Green Façade Climbing Plants

Green façades can provide cooling benefits through the shading of walls, evapotranspiration, and insulation. These benefits depend on good plant coverage and tolerance of heat stress. This requires sufficient rooting volume for plant growth and an adequate supply of moisture. On high-rise buildings, plants can be constrained by small rooting volumes due to engineering weight limits and cost. We assessed effects of rooting volume (21, 42, and 63 L) on the growth and coverage of Akebia quinata and Pandorea pandorana and leaf stress (chlorophyll fluorescence) in response to increasing air temperatures. We showed that 42 and 63 L rooting volumes significantly increased early plant growth and the percentage wall coverage for both species. Specific leaf area was significantly greater when grown in 63 L compared with 21 L. Shoot/root ratio did not change with rooting volumes. Regardless of rooting volume, higher air temperatures on west-facing aspects led to afternoon leaf stress. In practice, for each cubic meter of rooting volume, 21 m2 (P. pandorana) and 10 m2 (A. quinata) canopy coverage can be expected within six months.

Feasibility in Estimating the Dry Leaf Mass and Specific Leaf Area of 50 Bamboo Species Based on Nondestructive Measurements

Specific leaf area (SLA) is a good predictor of aboveground net primary productivity. However, the SLA of bamboo species is generally estimated on the basis of destructive measurements rather than the cost-effective and recyclable nondestructive measurements using easily accessible leaf traits such as leaf length (L) and width (W). Considering the strong empirical relationships between leaf area (LA) and leaf structural parameters of bamboo species that were developed by previous studies, this study explores the feasibility of estimating the leaf dry mass (LDM) and SLA of 50 bamboo species using L and W. The results show that the Montgomery equation and its similar forms precisely estimated LA of the 50 bamboo species at both leaf scale (R2 > 0.96 and MAE% < 4.67%) and the canopy scale (R2 > 0.99 and RMSE < 0.09); the LDM of the 50 bamboo species could also be estimated using L and W at both leaf scale (R2 > 0.52 and MAE% < 26.35%) and the canopy scale (R2 > 0.99 and RMSE < 0.003), and the estimated mean SLA of each of the 50 bamboo species had good agreement with the measured values (R2 > 0.99 and RMSE < 1.88) because of the precisely estimated mean LA and mean LDM at the canopy scale, indicating the feasibility of estimating SLA of the 50 bamboo species at the canopy scale based on nondestructive measurements. However, the empirical relationships used for mean SLA estimations are not suitable for SLA estimations at the leaf scale because of the uncertainties in the estimated LDM at the leaf scale.

Root Growth Dynamics and Structure in Seedlings of Four Shade Tolerant Mediterranean Species Grown under Moderate and Low Light

Specific functional traits such as shade tolerance or leaf habits can enhance root growth dynamics and structure of planted seedlings in the understory of planted forests. We assessed how low and moderate light levels (17 and 33% of full sunlight, mimicking after-thinning stocking) affect the root growth dynamics and structure of four late successional trees, three deciduous (Acer monspessulanum L., Quercus pyrenaica Willd and Sorbus torminalis (L.) Crantz) and one evergreen (Quercus ilex L.) species. Rooting depth, dynamics and structure were mainly explained by species functional differences. Roots of deciduous trees elongated faster and deeper and were larger than the roots of the evergreen Q. ilex. Among deciduous trees, S. torminalis had the lowest root growth. Specific leaf area and nutrient concentration were positively related to root growth, highlighting the importance of traits related to the plant economic spectrum, as determinants of species root growth differences. Moderate light level slightly enhanced root growth and decreased the specific leaf area (SLA). Species differences in water potential under drought were positively related to rooting depth, evidencing the importance of its role in overcoming drought stress during seedling establishment. These findings can guide the selection of late successional, shade tolerant tree species for underplanting thinned Mediterranean plantations and provide insights into their ecology.