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.

[Responses of soil microbial carbolic metabolism characteristics to home-field advantage of leaf litter decomposition in Liaoheyuan Nature Reserve of northern Hebei Province, China].

Using litter bag method, we studied the responses of soil microbial biomass carbon (MBC), microbial respiration (MR) and microbial metabolic quotient (qCO2) in 0-5 cm, 5-10 cm and 10-20 cm soil layers to home-field advantage of Betula platyphlla and Quercus mongolica leaf litter decomposition in Liaoheyuan Nature Reserve, northern Hebei Province. The results showed that the contents of MBC in Betula platyphila and Quercus mongolica leaf litter treatments in home environment (Bh and Qh treatments) were significant higher than that in B. platyphlla and Q. mongolica leaf litter treatments in non-home environment (Ba and Qa treatments). There was no significant difference in MR between home and non-home environments. Response degree of MBC and MR to home-field advantage of different litter decomposition was inconsistent. The MBC of the different soil layers in Qa treatment fell by 39.6%, 34.9% and 33.5% compared to Qh treatment, respectively, and that in B. platyphlla treatment was decreased by 31.6%, 27.1% and 17.0%, respectively. MR of the different soil layers in Qa treatment accounted for 96.3%, 92.4% and 83.7% of Qh treatment, respectively, while MR in B. platyphila treatment was 99. 4%, 97. 3% and 101.3%, respectively. In contrast to MBC, qCO2 in soil showed a reverse pattern. Our study suggested that rich nutrients in soil enhanced microbial activity and weakened the conflict of nutrient uptake between plants and microorganisms, which led to the result that MBC and qCO2 had an obvious response to home-field advantage of litter decomposition, when litter decomposed in its home environment. There was a weak response between MR and home-field advantage of litter decomposition, because of influence of soil temperature, water content and their interaction. Furthermore, MBC, MR and qCO2 had a higher response degree to home-field advantage of Q. mongolica litter than B. platyphila litter, since lower quality litter exhibited higher home-field advantage of litter decomposition.

[Responses of soil microbial carbon metabolism to the leaf litter composition in Liaohe River Nature Reserve of northern Hebei Province, China].

Using litter bag method, we studied the effects of single and mixed litters from Betula platyphlla, Populus davidiana and Quercus mongolica on soil microbial biomass carbon (MBC), microbial respiration (MR) and microbial metabolic quotient (qCO2) in 0-5, 5-10 and 10-20 cm soil layers. The results showed that the average contents of MBC in 0-20 cm soil layer were 124.84, 325.29, 349.79 and 319.02 mg . kg-1 in the leaf litter removal treatment, Betula platyphlla treatment, Populus davidiana treatment and Quercus mongolica treatment, and the corresponding average rates of MR were 0.66, 1.12, 1.16 and 1.10 µg . g-1 . h-1, respectively. Meanwhile, in 0-20 cm soil layer, the average contents of MBC in the treatments with single leaf litter, mixed litter of two plant species and mixed litter of three plant species were 331. 37, 418. 52 and 529. 34 mg . kg-1, and the corresponding average rates of MR were 1.13, 1.30 and 1.46 µg . g-1 . h-1, respectively. In contrast to the MBC and MR, qCO2 in soil showed a reverse pattern. Our study suggested that characteristics of microbial carbolic metabolism were influenced by litter quality. Namely, the treatment with high litter quality had higher MBC, MR and utilization efficiency of soil carbon, compared with the treatment with low litter quality. Moreover, mixture of different species of leaf litter improved soil microbial activities, increased utilization efficiency on soil carbon and promoted diversity of microbial metabolic pathways, which could then contribute to maintaining and enhancing soil quality of forestland.