| Nowadays,the frequency and intensity of extreme weather events such as low temperature and drought have been increasing,which posting a great challege for the persistence of terrestrial orgnisms.The distribution pattern of modern vegetation is the result of long-term adaptation of vegetation to climate and environment.Therefore,it is an important basis and prerequisite to understand and predict the adaptability and survival potential of plant population in the context of global climate change.At the large geographical scale,the tolerance to low temperature has been considered as the main factor to determine the northward-or upward-shift of terrestrial plants.In the present study,from the perspective of plant temperature tolerance,my main focus was to elucidate latitudinal pattern of thermal tolerance and explore adaptive mechanism of widely distributed species.The results would not only fill knowledge gaps related to latitudinal range limits,but also provide theoretical basis for understanding environmental driven mechanism of plant distribution,which has important academic and practical significance in global climate change research.The Chinese cork oak(Quercus variabilis Blume)is a widely distributed woody species in East Asia,with its distribution regions spanning several chimate zones,such as temperate zone,warm temperate zone,north subtropical zone,mid-subtropical zone and south subtropical zone,and become an ideal candidate for investigating the response of plants to environmental changes(e.g.,temperature).In this paper,by intergrating with the common gardon experiment and the greenhouse nutrient control experiment,thermal tolerance of the oak from different latitudinal origins,based on the comprehensive analysis of soil and meteorological factors,were studied.The main findings are as follows:? Relationship between thermal tolerance and growth environment of Q.variabilis seedlings(1)In the reciprocal common gardon experiment,the thermal tolerance was not significantly effected by provenances and the growing sites,but the heat tolerance of the northern provenance leaves was generally higher than those of the southern provenances in two sites,and increased with increasing latitude in southern sites.Cold tolerance and thermal span were positively correlated with the principal component 1 of climate variables(climate PC1)but negatively correlated with the principal component 1 of soil variables(soil PC1)in northern site;however,thermal parameters had no correlation with climate and soil variables.(2)In the southern site,thermal parameters(cold?heat and span)were significantly affected by seasonal transition.Cold tolerance of five provenances increased with latitude increasing,but heat tolerance and thermal span had no trend.In autumn,thermal span were negatively correlated with climate PC2(Mainly contains max air temperature of the warmest month and Mean air temperature of the warmest quarter),but cold tolerance were positively correlated with climate PC1 and soil PC1.NSCs(Soluble sugar,starch,NSC and the ratio of sugar to starch)of leaf in summer were significantly higher than that in autumn.NSC had no significant correlation with latitude,but the ratio of sugar to starch declined with increasing latitude,starch inversed.Leaf nutrient content and utilization efficiency of oak had no trend with latitude,and the ratio of N to P of five provenances in summer was significantly higher than that in autumn.The results of RDA showed that cold tolerance of seedling leaves was positively correlated with phosphorus use efficiency,soluble sugar and the ratio of soluble sugar and starch but negatively correlated with NSC and starch.Heat tolerance had a negative correlation with soluble sugar and the ratio of soluble sugar and starch.In autumn,cold tolerance was positively correlated with N,P and NSC,and negatively correlated with nitrogen use efficiency.? Effects of nitrogen and phosphorus addition on leaf thermal tolerance in different provenances of Q variabilis(1)Nutrient absorption and utilization efficiency varied between oak origins,but with no obviously geographical trends.Specially,PG(Pinggu,Beijing)had higher nitrogen use efficiency(NUE)and phosphorus use efficiency(PUE),whereas,NX(Neixiang,Henan)had lower PUE under all treatments.In addition,CB(Chengbu,Hunan)had the highest PUE under phosphorus addition.(2)Compared to the combined limitation treatments,nutrient addition increased the cold tolerance of PG and LC(Lincheng,Hebei),and to some extent,increased the heat tolerance of three middle provenances which are LC,NX and ZG(Zigui,Hubei).However,the thermal span was opposite to the cold tolerance,as nutrient addition decreased the thermal span of PG and LC,but increased that of NX.(3)The leaf cold tolerance was significantly positive with soluble sugar concentration,while the heat tolerance negatively and positively correlated with leaf phosphorus and ratio of nitrogen to phosphorus,respectively.Furthermore,no significant correlation was found between leaf thermal span with leaf chemical substances.? The trends in growth and substance allocation in Q variabilis seedlings from five provenances in southern siteIn the southern grown site,(1)for 1-yr seedling,pooled non-structural carbohydrates concentrations(NSCs)increased with increasing latitude and this trend was dominated by leaf NSCs,especially by leaf sugar concentrations.Leaf sugar and root starch increased but root sugar decreased with the increase of latitude,and no obvious geographical trends were found in shoot NSCs.For 2-yr seedling,to whole seedling,there was no significant correlation between NSC and latitude,but sugar concentration and the ratio of sugar to starch was negatively correlated with latitude.To different organ,shoot NSC decreased with increasing latitude,starch increased but the ratio of sugar and starch declined with the increase of latitude in root and leaf.(2)On the other hand,the nitrogen concentration in various tissues of 1-yr seedling,along with leaf P,increased with an increase of latitude,but inverse for the ratio of N to P.The nutrient use efficiency(NUE,expressed as C:N and C:P)in tissues all exhibited a weakly decreasing trend with latitude with an exception of leaf NUE.However,there was no significant correlation between nitrogen and phosphorus in different organs of 2-yr seedling.For nitrogen and phosphorus utilization efficiency,only stem decreased with increasing latitude,root and leaf had no trend.(3)The relative growth rate decreased significantly with increasing latitude for both age seedlings.To sum up,our results showed that,(1)Thermal tolerance of oaks among 5 provenances to some extent was related to original site and heat tolerance in northern provenance were higher than in southern sites.(2)Nutrient use efficiency varying in provenances was contributed by the original habitats and consequently developed some local adaptation strategies,which complicated the response of thermal tolerance to nutrient addition.(3)The strategy of substance allocation for oak seedling among different origins had variationhad,but the relative growth rate decreased with increasing latitude. |
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