Leaf and stem traits variation of Stellera chamaejasme Linn. with slope aspect in alpine steppe

Geographic Variation in the Petiole-Lamina Relationship of 325 Eastern Qinghai-Tibetan Woody Species: Analysis in Three Dimensions

The petiole-lamina relationship is central to the functional tradeoff between photosynthetic efficiency and the support/protection cost. Understanding environmental gradients in the relationship and its underlying mechanisms remains a critical challenge for ecologists. We investigated the possible scaling of the petiole-lamina relationships in three dimensions, i.e., petiole length (PL) vs. lamina length (LL), petiole cross sectional area (PCA) vs. lamina area (LA), and petiole mass (PM) vs. lamina mass (LM), for 325 Qinghai-Tibetan woody species, and examined their relation to leaf form, altitude, climate, and vegetation types. Both crossspecies analysis and meta-analysis showed significantly isometric, negatively allometric, and positively allometric scaling of the petiole-lamina relationships in the length, area, and mass dimensions, respectively, reflecting an equal, slower, and faster variation in the petiole than in the lamina in these trait dimensions. Along altitudinal gradients, the effect size of the petiole-lamina relationship decreased in the length and mass dimensions but increased in the area dimension, suggesting the importance of enhancing leaf light-interception and nutrient transport efficiency in the warm zones in petiole development, but enhancing leaf support/protection in the cold zones. The significant additional influences of LA, LM, and LA were observed on the PL-LL, PCA-LA, and PM-LM relationships, respectively, implying that the single-dimension petiole trait is affected simultaneously by multidimensional lamina traits. Relative to simple-leaved species, the presence of petiolule in compound-leaved species can increase both leaf light interception and static gravity loads or dynamic drag forces on the petiole, leading to lower dependence of PL variation on LL variation, but higher biomass allocation to the petiole. Our study highlights the need for multidimension analyses of the petiole-lamina relationships and illustrates the importance of plant functional tradeoffs and the change in the tradeoffs along environmental gradients in determining the relationships.

Shifts and plasticity of plant leaf mass per area and leaf size among slope aspects in a subalpine meadow

The composition of vegetation on a slope frequently changes substantially owing to the different micro-environments of various slope aspects. To understand how the slope aspect affects the vegetation changes, we examined the variations in leaf mass per area (LMA) and leaf size (LS) within and among populations for 66 species from 14 plots with a variety of slope aspects in a subalpine meadow. LMA is a leaf economic trait that is tightly correlated with plant physiological traits, while the LS shows a tight correlation with leaf temperature, indicating the strategy of plants to self-adjust in different thermal and hydraulic conditions. In this study, we compared the two leaf traits between slope aspects and between functional types and explored their correlation with soil variables and heat load. Our results showed that high-LMA, small-leaved species were favored in south-facing slopes, while the reverse was true in north-facing areas. In detail, small dense-leaved graminoids dominated the south slopes, while large thin-leaved forbs dominated the north slopes. Soil moisture and the availability of soil P were the two most important soil factors that related to both LMA and LS, and heat load also contributed substantially. Moreover, we disentangled the relative importance of intraspecific trait variation and species turnover in the trait variation among plots and found that the intraspecific variation contributed 98% and 56% to LMA and LS variation among communities, respectively, implying a large contribution of intraspecific trait plasticity. These results indicate that LMA and LS are two essential leaf traits that affect the adaptation or acclimation of plants underlying the vegetation composition changes in different slope aspects in the subalpine meadow.

Influence of slope aspect on the macro- and micronutrients in Artemisia sacrorum on the Loess Plateau in China

Slope aspect is an important topographic factor for a micro-ecosystem environment that may affect macro- and micronutrients in plants and soil. The south-, northwest-, and north-facing slopes were selected to investigate the influence of slope aspect on the concentrations, storage, and allocation of macro- and micronutrients in Artemisia sacrorum on the Loess Plateau in China. The concentrations of available manganese (Mn) in both rhizosphere and non-rhizosphere soils reached their maximum on the north-facing slope. The concentrations of available iron (Fe) in rhizosphere soil and available copper (Cu) in non-rhizosphere soil reached their maximum on the south-facing slope. Slope aspect significantly affected the total concentrations of potassium (K), calcium (Ca), magnesium (Mg), Cu, and Mn in rhizosphere and non-rhizosphere soils, and all of these elements reached their maximum on the northwest-facing slope. Slope aspect significantly influenced the concentrations of aboveground K, Ca, and Mg, sodium (Na), Mn, and belowground K in A. sacrorum, and the concentrations of aboveground K, Ca, Mg, and Na and belowground Mn, Na, Fe, Ca, and Mg in weed. Most elements in A. sacrorum and the weeds reached their maximum on the south-facing slope. Slope aspect significantly changed the aboveground-to-belowground concentration ratios of K, Ca, and Na in A. sacrorum and weed. Slope aspect significantly affected the storage of macro- and micronutrients in A. sacrorum and weed but not the storage in the plants of the entire plot. Slope aspect predominantly affected the storage allocation of macro- and micronutrients in A. sacrorum but not those in weed. Slope aspect is an important topographic factor that affects the macro- and micronutrients in plants and soil in micro-ecosystem environments.