| During the long-term interactions or evolution with biotic and abiotic environment, plant developed a set of defensive strategies to resist adverse conditions. Two major defensive strategies, physical defense and chemical defense, were usually defined to address this issue. The physical defense strategy is adopted by plants through changing the morphological structure; while the chemical defense strategy refers to physiological and biochemical responses. The current research often focus on a single defense strategy, especially chemical defense, while ignoring the correlation between multiple defense strategies. And many conclusion for plant geographic variation pattern of chemical defense and its environment interpretation often were controversial. The Chinese cork oak(Quercus variabilis Blume) is one of the most widespread tree species in eastern Asia. The species became as an excellent candidate to study the ontogenetic variation of defense along latitudinal grandients at a single species level. In this paper, we discussed the plant defense strategy and contribution of environmental factors from the perspective of biological violations, climate factors, and resource allocation in plants. The paper would, to some extent, contribute to further understand the internal relationship between plant’s traits and environment, and also provide some references for plants’ regional adaptation, selective breeding in germplasm resources, and forest management.(1)Chemical defense characteristics and latitude pattern based on phenols in Quercus variabilis organsWe compared and analyzed the chemical defense characteristics, latitude pattern, ontogenetic and seasonal dynamics based on phenols in Quercus variabilis organs. Results show that: 1) Both mature trees and young trees, Total phenolics and total condensed tannins concentration in leaves was the highest among the different tissues of Quercus variabilis, and significantly higher than other tissues, followed by the roots and twig barks, peeled twigs in the lowest levels. Flavonoids concentration is characterized by twig barks and leaves the highest, followed by the root, peeled twigs in the lowest levels. 2) Both mature trees and juvenile trees, there are consistent trends with latitude for the chemical defense substances, i.e. total phenol, total condensed tannins and flavonoids concentration at different growing periods. The concentration of chemical defensive substances in tissues of cork oak were increased with decrease of latitude, which further indicated that plants in low latitudes have higher chemical defence level. Our findings support the low latitudes/high defense hypothesis that low latitudinal population are better defended. 3) the Chinese cork oak exhibited contrasting chemical defense differences between the two ontogenetic stages, with leaf of juveniles having a higher TP and TCT concentration than mature trees for leaf in the middle of the growing season, with twigs, twig barks and roots of matures having a higher TP and TCT concentration than juvenile trees in the begining and middle of the growing season and non-growing season. 4) The different growing periods bring different degree effects on chemical defensive substances of different organs in Quercus variabilis. In the beginning of the growing season, the leaves and twig barks had significantly higher concentration in total phenolics and condensed tannins. While, at the ending of the growing season, peeled twigs had significantly higher concentration in total phenolics and flavonoids. And in the middle of the growing season, the roots had significantly higher concentration in total phenolics, condensed tannins and flavonoids.(2)Chemical defense characteristics and latitude pattern based on VOCs in Quercus variabilis branches and leavesThe plant volatile organic compounds(VOCs) from branches and leaves of Quercus variabilis were collected and analyzed with TDT-GC/MS. Results shows that: 1) Eight kinds of volatile components, such as esters, alkanes, terpenes, aromatic hydrocarbons, aldehydes and ketones, alcohols, alkenes, as well as other N-containing, S-containing and Cl-containing compound, etc, were detected. And esters and alkanes were the main components of Quercus variabilis, and account for 22.64 % ~ 44.34 % and 22.72 % ~ 44.24 % of the total plant volatile organic compounds content. 2) The comparison of undamaged and mechanically-damaged leaves of Quercus variabilis indicated that they had similar VOCs, while the components and contents of volatile substances changed. Dibutyl phthalate, 4- Hexen- 1- ol acetate, 2,6,10-s trimethyl- Tetradecane, Heptacosane, d- Limonene, 2- ethenyl- 1,1- dimethyl- 3-methylene- Cyclohexane, etc. were the main components(more than 5%). 3) Mechanical damage brings different degree effects on components and relative content of volatile organic compounds of Quercus variabilis branches and leaves. Naphthalene 、 d-Limonene 、4-Hexen-1-ol, acetate、Dibutyl phthalate、Acetic acid, hexyl ester、Benzoic acid, butyl ester、Cyclohexane, 2-ethenyl-1,1-dimethyl-3-methylene-, etc. could be induced and their content increased obviously after mechanical damage. 4) No significant trends across latitudes for VOCs in Quercus variabilis branches and leaves were found. However, the higher content of terpene chemicals, such as d-Limonene(accounts for 24.89% ~ 38.44%), was found in Chengbu Hu’nan. And both under the natural state and mechanical damage, Quercus variabilis branches and leaves in the low latitude contain higher content of Dibutyl phthalate, etc. These substances have certain ecological function and effect on the anti-herbivory. This may be a chemical defense strategy of Quercus variabilis in response to herbivory or against external stress.(3)Physical defense and latitude pattern based on fibers in Quercus variabilis leavesWe compared the physical defensive traits(including cellulose, hemicellulose, lignin and LDMC) in Quercus variabilis leaves among two ontogenetic stages and seven latitudinal bands, and analyzed the relationship between the chemical and physical defence. Results show that: 1) The ontogeny has no significant effects on physical defensive traits. However, latitude significantly influence physical defense with exception of hemicellulose. Meanwhile, no significant trends across latitudes in all physical defense substances, though the concentration of leaf cellulose, hemicellulose present somewhat increasing trend with latitude, while ligin descreasing with latitude. 2) In addition, the trade-offs between chemical and physical defense was found irrespective of ontogenetic variation.( 4) Herbivory characteristics of Quercus variabilis leaves and correlation with meteorological factorsHerbivory is the common characteristics of plant community. To explore the effects of latitude and meteorological factors on herbivory, we investigated the entomic herbivory characteristics of Quercus variabilis leaves a corss different geographical regions, with a 14° latitudinal spanning from 26° N(Chengbu, Hu’nan province) to 40°N(Pinggu, Beijing). The results showed that: 1) Either the mature tree or juvenile tree, leaf herbivory rate and frequency significantly increased toward the equator or at lower latitudes(P < 0.05). 2) According to the insect herbivory structure, the proportion of the non-chewed leaves decreased, while the proportion of the above 25%-chewed leaves increased toward the equator. Namely, it shows strong herbivory at lower latitudes. 3) Except the southest site(Chengbu, Hu’nan province), the proportion of herbivory mainly concentrated between 0.5 ~ 5 % for all other sites. 4) Leaf herbivory rates in the juvenile tree were significantly higher than that in the mature tree(P < 0.05). 5) Multiple regression results revealed significant effects of annual precipitation and minimum temperature of the coldest month on leaf herbivory rate and frequency despite ontogenetic stages, but the maximum temperature of the warmest month significantly affected leaf herbivory frequency in the juvenile tree. Accordingly, we suggest that latitudinal variation in leaf herbivory likely appears to be driven predominantly by variation in extreme temperature and precipitation.(5)The relationship between defense and environmental factorsWe firstly processed all the chemical and physical defensive traits/indexes by data dimension reduction(PCA) and investigated the effect of the meteorological factors, edaphic factors and herbivory on plant defence, and to attempt to identify the dominant drivers of plant defence function. Results shows that: 1) there was a significantly positive correlation between the comprehensive level of defense and leaf herbivory rate in Quercus variabilis, Which shows the cork comprehensive level of defense(PC1) increase with the increase of the leaf herbivory rate. And the comprehensive level of defense correlates positively and significantly with both annual precipitation and minimum temperature of the coldest month, and no obvious relationship with both annual mean temperature and maximum temperature of the warmest month. Redundancy analysis(RDA) among four climatic variables, four soil variables and one biological factors showed that the three totally explained 69.27 % and 61.11 % for defensive traits in mature and juvenile trees, respectively. And annual precipitation, minimum temperature of the coldest month and herbivory can significantly explain geographic variation of defensive traits in both mature and juvenile Quercus variabilis, and can be thought to be relatively important driving factors which influenced the distribution of defensive substances.We found that, in previous study, soil conditions have less effect on the plant defense characteristics, and were concealed by meteorological factors, herbivory or other factors at a regional scale. We compared the chemical defensive traits in five Quercus variabilis provenance seedlings for three organs under the low/optimum P(LP/OP) and low/optimum N(LN/ON). Results show that: 1) Under the environment of low nitrogen(LN), the organs of Quercus variabilis seedlings showed higher chemical defense substances, such as total phenolics, total condensed tannins and flavonoids concentration. Especially under the OPLN, the chemical defense substances concentration reached the highest. Our findings support the growth-differentiation balance hypothesis and carbon:nutrient balance hypothesis. 2) At the same level of nutrition, the higher net photosynthetic rate, total biomass and SPAD were, the less chemical defense substances concentration were, and vice versa. On the whole, the comprehensive level of defense correlates negatively and significantly with net photosynthetic rate, total biomass and SPAD, Namely which indicated significant trade-offs between defence and growth. Our findings support the resource availability hypothesis and protein competition model. 3) Under the different N, P level, the comprehensive level of defense correlates negatively and significantly with latitude of provenance, which shows Quercus variabilis provenance seedlings from the low latitudes has a higher level of chemical defense. Besides, the comprehensive level of defense correlates positively and significantly with both annual precipitation and minimum temperature of the coldest month, and correlates negatively and significantly with maximum temperature of the warmest month, and no obvious relationship with annual mean temperature. This is consistent with the sampling analysis results of natural forest Quercus variabilis, which further indicated that the chemical defensive traits have epigenetics/heritability.In conclusion, we studied Quercus variabilis defensive traits and its relationship with environment factors, and found that: 1) Quercus variabilis in the low latitudes showed higher chemical defense ability, and physical defense traits was not a certain latitudinal variation pattern. There is a trade-off between chemical and physical defense.2) Annual precipitation, minimum temperature of the coldest month and herbivory were main driving factors which influenced the distribution of defensive substances. Our research proves that, according to the change of environmental stress, the plant could change its defensive characteristics/strategies to achieve coordination and balance between growth and defense, and have a best adaptability in various habitats. |
PDF Full Text Request