Effects Of Gap On Photosynthetic Plasticity Of Korean Pine Saplings In Quercus Mongolica Forests In Xiaoxing’ An Mountains

Forest tending management is a common way of disturbance in forests,different sizes of gaps will be formed when forest management measures of different intensity are adopted,the growth and development(such as saplings height,breast diameter change,dry matter accumulation and photosynthetic physiological indicators,etc.)of saplings in gaps of different sizes can reflect their adaptability and renewal potential to the microenvironment in the gaps.At the same time,it can also provide theoretical support for optimizing felling management measures,and it is very important to determine the suitable gap area and positions in the gaps for the growth of Korean pine(Pinus Koraiensis)saplings under secondary forests for the restoration the temperate zonal climax vegetation broad-leaved Korean pine forests.In this study,the photosynthetic response parameters(the maximum net photosynthetic rate,light saturation point,light compensation point,transpiration rate,stomatal conductance and water use efficiency,etc.),chlorophyll content and its micro-environmental factors(transmittance,temperature,etc.)of Korean pine sapling(15a)at different positions in gaps(center area,transition area and edge area)in Quercus Mongolica forests with different gap size(Large gap-206m2(clear cutting),Medium gap-117m2(harvesting accumulation ratio 40%),Small gap-52m2(harvesting accumulation ratio 20%),understory(control plot)-13m2(not harvested))were measured by using CIRAS-2 photosynthetic apparatus in Xiaoxing’an Mountains,to explore the effects of gap size and different positions in the gaps on the photosynthetic plasticity of Korean pine saplings.The results showed:(1)The Korean pine sapling showed obvious photosynthetic plasticity in the medium and small forest gaps,their maximum net photosynthetic rate(2.48～6.77 μmol·m-2·s-1)were significantly increased by 20.0%～60.7%in the medium and small forest gaps compared with the understory,and it was significantly higher 9.2%～15.1%in the medium forest gap than that in the small forest gap,but the big forest gap has no significant effect on it.The light saturation point and the light compensation point of Korean pine sapling in both the medium and small forest gaps was higher(9.5%～24.5%)or lower(26.4%～42.4%)than that in forest understory,but only in the medium forest gap the transpiration rate(45.9%～101.8%),stomatal conductance(82.3%～115.5%)and intercellular CO2 concentration(7.1%～15.6%)were higher than those in forest understory,while the chlorophyll content was lower than that in forest understory(7.3%～19.9%)(P<0.05).(2)The Korean pine sapling also had obvious photosynthetic plasticity with the changes of the position within various size forest gaps,their maximum net photosynthetic rate showed decreasing regularity(22.5%to 92.7%)along the position gradient from the center area to edge area of the forest gaps.From the central area to the edge area of each forest gap,the light saturation point was reduced(6.2%to 24.2%)and the light compensation point was increased(18.1%to 31.6%),the transpiration rate(19.1%to 78.1%)and stomatal conductance(36.1%to 96.5%)showed the decreasing trend,while the chlorophyll content showed the increasing trend(5.0%to 25.9%)(P<0.05).(3)The maximum net photosynthetic rate of Korean pine saplings was significantly linear positive correlated with the growth parameters(tree height and diameter at breast height)(P<0.01).There was highly significant linear positive correlation between the maximum net photosynthetic rate and transpiration rate of Korean pine saplings in the large gap(P<0.001),there was highly significant linear positive correlation with the light saturation point in the medium gap(P<0.001),and it was significant linear negative correlation with the light compensation point(P<0.01),there was significant linear positive correlation with water use efficiency in the medium gap(P<0.01),there was significant linear positive correlation with transpiration rate and water use efficiency in the forest understory(P<0.01).(4)When in the center area of the gap,the maximum net photo synthetic rate of Korean pine saplings was highly significant linear positive correlation with the light saturation point(P<0.001),when in the transition area of the gap,there was highly significant linear positive correlation with the light saturation point and transpiration rate(P<0.001),when in the edge area of the gap,there was highly significant linear positive correlation with the light saturation point(P<0.001),there was highly significant linear negative correlation with the light compensation point(P<0.001).Therefore,Korean pine is the constructive species of broad-leaved Korean pine forests with climax vegetation in the temperate zone of Northeast in my country has obvious photosynthetic plasticity in medium gaps in the sapling stage,in the follow-up management practice of restoring broad-leaved Korean pine forests in the secondary forests in northeast,the resource advantages of the central area(group planting or transparent tending around Korean pine)of medium forests gaps(117m2 or gap diameter/tree height at the edge of the gap≈1.0)should speed up the restoration process.