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.

Drought potentially affects carbon balance and growth of trees, but little is known to what extent soil plays a role in the trade-off between carbon gain and growth investment. In the present study, we analyzed leaf non-structural carbohydrates (NSC) as an indicator of the balance of photosynthetic carbon gain and carbon use, as well as growth of European beech (Fagus sylvatica L.) saplings, which were grown on two different soil types (calcareous and acidic) in model ecosystems and subjected to a severe summer drought. Our results showed that drought led in general to increased total NSC concentrations and to decreased growth rate, and drought reduced shoot and stem growth of plants in acidic soil rather than in calcareous soil. This result indicated that soil type modulated the carbon trade-off between net leaf carbon gain and carbon investment to growth. In drought-stressed trees, leaf starch concentration and growth correlated negatively whereas soluble sugar:starch ratio and growth correlated positively, which may contribute to a better understanding of growth regulation under drought conditions. Our results emphasize the role of soil in determining the trade-off between the balance of carbon gain and carbon use on the leaf level and growth under stress (e.g. drought).

Population structure and regeneration dynamics of Quercus variabilis along latitudinal and longitudinal gradients.Ecosphere 8(4):e01737. 10.1002/ecs2.1737Abstract. The upcoming climatic variability is expected to influence the population dynamics of tree species, but few empirical studies have been performed over broad geographical scales, which may be more convincing to address tree range shift under climate change. In the present study, the population structure and regeneration dynamics of Quercus variabilis were investigated along latitudinal and longitudinal gradients over its full range in China. The size structure, density, mortality rate (b), conversion rate (CR), initial recruitment (y 0 ), and survival from birth to the highest class of regeneration (survival rate [SR]) were analyzed. The results showed the following: (1) The population structure of Q. variabilis exhibited an inverse-J shape throughout the latitudinal gradient, and the relative seedling density was significantly higher in the middle populations than in the north and the south. In addition, the y 0 and SR exhibited the highest values in the middle, but no significant differences in the density and total basal area of adults were found across latitudes. (2) Along the longitudinal gradient, an inverse-J-type population structure was present in the west populations, but was not observed in the east due to the scarcity of individuals in regenerated populations. The total basal area and density of adults were similar across longitudes, but both the seedling density and the relative seedling density, along with the y 0 and SR, were higher in the middle than in the east and the west. The b of adults was lower in the middle-longitude populations than in the west and the east. (3) Climate (annual average temperature) was identified as the primary factor affecting regeneration. In addition, local factors, including the soil and stand conditions, were also found to play a significant role in determining the regeneration dynamics. Based on these results, we speculate that populations of Q. variabilis at the range edges would decline in the context of climate change, particularly in the south and the east.