Leaf Population Dynamic Of Main Plant Species From Deciduous Broad-Leaved Forest In Xianlin,Nanijng

Leaves are the most basic organs of energy acquiring and the place of respiration and transpiration. According to module theory, leaves can be taken as a module. For a plant species, all the leaves of an individual can be recognized as a population, which can also be called leaf population. Thus, leaf population dynamic includes leaf expansion, leaf abscission and other vital processes. A series of factors such as different species or habitat heterogeneity, may affect the trade-off between leaves’ morphological structure and function, thus shaping the basic behavior and function of plants. Moreover, this trade-off leads to different leaf population dynamic among different plant species. Therefore, the research of leaf population dynamic can reflect the life history strategy of each species to a great extent. So far, many considerable studies of leaf population dynamic had already been made in tropical rainforests and temperate deciduous broad-leaved forests. However, compared with the above studies, the counterparts are much fewer in subtropical areas, most of which are concentrated in mid-subtropics. There have been few studies on the leaf population dynamic of deciduous broad-leaved forests in north subtropics. So we selected 24 representative tree species including 13 simple leaf plants and 11 compound leaf plants from deciduous broad-leaved forest, which was located in XianLin, Nanjing, Jiangsu Province. In terms of leaf area, they can also be divided into 9 mesophyllous species, 5 notophyllous and 10 microphyllous ones. Long-term continuous field observation of leave emergence, leave expansion and leave abscission was made from March to December in 2013, and their leaf population dynamics were analyzed on the basis of leaf areas (mesophyllous, notophyllous and microphyllous), leaf form respectively. The main contents covered leaf number dynamic, leaf area dynamic, and leaf life span of these species. The aim is to reveal the characteristics of leaf expansion, leaf abscission and leaf lifespan of woody species from deciduous broad-leaved forest, and to discuss the maintenance mechanism of the forest in north subtropics. The main results were as follows:(1) Based on field observation of leaf phenology in 2014, the beginning of leaf emergence was in March or April. The earliest tree species was Sageretia thea and Rhamnus globosa, leafing in mid-March (Julian day= 13 d), while the latest tree species were Cassia alata, leafing in early April (Julian day= 38 d). According to the duration time of leaf emergence,24 species can be divided into flushing emergence (5 species), intermediate emergence (10 species) and succeeding emergence (9 species). Among them,66.7 percentage of succeeding emergence species are compound leaf species. Therefore, most compound leaf species in this area are mainly of succeeding emergence type.The correlation analysis of the leaf emergence phenology parameter, the leaf trait, the number of leaves and the relative growth rates of leaf emergence showed that there was an extremely significant negative correlation between LMA (leaf dry mass per area) and the beginning time of leaf emergence (P<0.01), and LMA had a significant negative correlation with leaf area and the ending time of leaf emergence (P<0.05). There was an extremely significant positive correlation between leaf area and the beginning time of leaf emergence (P<0.01). The number of leaves had an extremely significant positive correlation with the ending time of leaf emergence and durations of leaf emergence (P<0.01). There was an extremely significant negative correlation between the number of leaves and relative growth rates of leaf emergence (P<0.01). The relative growth rates of leaf emergence had an extremely significant negative correlation with the ending time and the durations of leaf emergence (P<0.01). All these suggested that the species with a smaller leaf area and a larger LMA had an earlier beginning time of leaf emergence and the species with a smaller relative growth rates of leaf emergence and large number of leaves had a longer duration time of leaf emergence.The beginning time of leaf emergence of simple leaf species was earlier than compound leaf species, and the difference was significant (P<0.05). The ending time of leaf emergence of simple leaf species was earlier than compound leaf species, and the difference was significant (P<0.05). The leaf area of simple leaf species was earlier than compound leaf species, and the difference was extremely significant (P<0.01).(2) In this research, the beginning time of leaf expansion of 24 deciduous broad-leaved plants was in March or April in 2014. The earliest tree species to leaf was Sageretia thea which began to expand in mid-March (Julian day= 19 d), while the latest tree species were Dalbergia hupeana which began to expand in early April (Julian day= 42 d). Quercus glandulifera var. brevipetiolata had the maximum relative growth rate of leaf expansion which was 0.33, and Cassia alata had the minimum relative growth rate of leaf expansion which was 0.063. Furthermore, the former was 5 times of the later. The relative growth rate of leaf expansion of flushing emergence species was larger than the counterpart of intermediate emergence species and succeeding emergence species. The former had an extremely significant correlation with the latter two ones in terms of the relative growth rate of leaf expansion (P<0.01).The correlation analysis of the leaf expansion phenology parameter, the leaf trait, the number of leaves and the relative growth rates of leaf expansion showed that LMA had an extremely significant negative correlation with the beginning time, the peaking time and the ending time of leaf expansion (P<0.01), and a significant negative correlation with the leaf area (P<0.05). The leaf area had an extremely significant positive correlation with the beginning time of leaf expansion (P<0.01), and a significant positive correlation with the peaking time of leaf expansion (P<0.05). Among simple leaf species, the leaf area had a significant negative correlation with the duration time of leaf expansion (P<0.05), while a significant positive correlation with the relative growth rate of leaf expansion (P<0.05). The relative growth rate of leaf expansion had an extremely negative correlation with the ending time and the duration time of leaf expansion (P<0.01). All these suggested that the species with smaller leaf area and larger LMA have an earlier beginning time of leaf expansion and the species with a smaller leaf area and smaller relative growth rate of leaf expansion have a longer duration time of leaf expansion.The beginning time of leaf expansion of simple leaf species was earlier than compound leaf species, but there was no significant difference between simple leaf species and compound leaf species (P>0.05). The peaking time of leaf expansion of simple leaf species was earlier than compound leaf species, and the difference was significant (P<0.05). The ending time of leaf expansion of simple leaf species was earlier than compound leaf species, and the difference was extremely significant (P<0.01). The duration time of leaf expansion of simple leaf species was earlier than compound leaf species, and the difference was significant (P<0.05).(3) In this research, there was much different of the beginning time of leaf abscission among the 24 deciduous broad-leaved plants from June to November in 2014. The earliest tree species was Pterocarya stenoptera which began to fall in mid-June (Julian day= 105 d), while the latest tree species was Quercus glandulifera var. brevipetiolata which began to fall in late November (Julian day= 270 d). The leaf fall pattern of 24 deciduous broad-leaved plants can be divided into unimodal, bimodal and multimodal types.10 species (Pterocarya stenoptera, Dalbergia hupeana, Quercus glandulifera var. brevipetiolata, Pterocarya stenoptera etc.) were unimodal type; however their peaks of leaf fall were in different seasons.9 species (Diospyros rhombifolia, Liquidambar formosana, Rhamnus globosa etc.) were bimodal type; The other 5 species (Broussonetia papyrifera, Vitex negundo var. cannabifolia, Cassia alata etc.) were multimodal type, and their peaks of leaf fall were also in different seasons. The flushing emergence species also showed the flushing abscission. There were a relative correlation between the leaf emergence type and the leaf abscission type. The flushing emergence species showed a unimodal abscission type while the intermediate emergence species showed a multimodal abscission type.The correlation analysis of the leaf abscission phenology parameter, the leaf trait, the number of leaves and the relative growth rates of leaf abscission showed that the beginning time of leaf abscission had a significant negative correlation with the ending time of leaf abscission (P<0.05), while an extremely significant positive correlation with the peaking time and the duration time of leaf abscission (P<0.01). The number of leaves had a significant positive correlation with the ending time of leaf abscission (P<0.05), while an extremely significant positive correlation with the duration time of leaf abscission (P<0.01). The relative growth rate of leaf abscission had a significant positive correlation with the beginning time of leaf abscission (P<0.05), while an extremely significant negative correlation with the ending time and duration time of leaf abscission (P<0.01) and a significant negative correlation with the number of leaves (P<0.05). All these suggested that the species with an earlier beginning of leaf abscission have an earlier ending time of leaf abscission and a shorter duration time of leaf abscission. And also suggested that the species with a large number of leaves have a smaller relative growth rate of leaf abscission, a later ending time of leaf abscission and a longer duration time of leaf abscission.The beginning time of leaf abscission of simple leaf species was earlier than compound leaf species, and the difference was significant (P<0.05). The ending time of leaf expansion of simple leaf species was earlier than compound leaf species, and the difference was significant (P<0.05). There was no significant difference of the duration time and the relative growth rate of leaf abscission between simple leaf species and compound leaf species.(4) The average leaf lifespan of the 24 deciduous broad-leaved plants was 218 days. The longest species is Sageretia thea with 266 days, while the shortest species is Pterocarya stenoptera with 100 days.The correlation analysis of the leaf lifespan, the leaf emergence phenology parameter, the leaf abscission phenology parameter and the leaf trait, showed that the leaf lifespan had a significant negative correlation with the leaf area (P<0.05), while a significant positive correlation with the number of leaves (P<0.05). The leaf lifespan also had an extremely significant positive correlation with the beginning time, the peaking time and the ending time of leaf abscission (P<0.01). All these suggested that the species with a smaller leaf area have a longer leaf lifespan and the species with an earlier beginning time and ending time of leaf abscission have a shorter leaf lifespan.