Photosynthesis Adaption In Korean Pine To Gap Size And Position Within Populus Davidiana And Betula Platyphylla Forests,China

It is very important to determine the suitable gap area and micro-habitat for the restoration of the temperate climax vegetation broad-leaved Korean pine forests from the secondary forest in the northeast of China.In this study,the young trees of Korean pine(Pinus Koraiensis)(35 years)in the gaps between Populus davidiana and forests in the middle period of Xiaoxing’anling in the temperate zone of northeast China were studied.The photo synthetic response parameters(the maximum net photosynthetic rate(Pmax),light saturation point,light compensation point,transpiration rate,stomatal conductance,etc.),chlorophyll content and its micro-environmental factors(Light intensity,leaf temperature,etc.)of young Korean pine trees at different positions(the center area,transition area and edge area)of gaps in Populus davidiana and Betula platyphylla forests with different gap size(Large gap201 m2、Middle gap-113 m2、Small gap-50 m2)and Understory(12 m2))were measured by using CIRAS-2 photosynthetic apparatus in Xiaoxing’anling,to explore the photosynthetic adaption of young Korean pine trees to the gap size and position within the gap.The results show that:(1)The young Korean pine trees of Populus davidiana forests and Betula platyphylla forests showed obvious photosynthetic adaption with the increase of gap size,the Pmax(2.11～6.12 μmol·m-2·s-1)of young Korean pine trees increased with the increase of gap in the center and transition areas(4.4%～98.7%),and increased in a stepwise way in the edge area(10.7%～51.4%).(2)The young Korean pine trees of Populus davidiana forests and Betula platyphylla forests also show obvious photo synthetic adaption with changes of position in the gaps,the Pmax of young Korean pine trees in various gaps shows a decreased pattern along the microenvironmental gradient of the center,transition and edge areas of the gap(20.3%～95.1%).(3)In the Populus davidiana and Betula platyphylla forests,as the gap increases,the light increases,the light saturation point of the young Korean pine trees increased(2.1%～102.8%)and the light compensation point decreased(7.1%～85.8%),at the same time,the transpiration rate and stomatal conductance increased(1.1%～79.7%and 0.7%～100.6%),but its dark breathing rate and chlorophyll content are reduced(1.6%～79.0%and 1.6%～43.7%);The transpiration rate and stomatal conductance showed a decreasing trend(6.4%～82.4%and 9.1%～91.3%)along the center area,transition area,and edge area in the gap,but the chlorophyll content showed an increasing trend(7.9%～38.2%).(4)The leaf morphology(needle length,needle width,specific leaf area)of Korean pine in the Populus davidiana and Betula platyphylla forests is significantly affected by the gap size and the position within the gap.The needle length and needle width generally increase with the increase of the forest gap,and show a decreasing trend along the center area,transition area,and edge area within the forest gap.While the specific leaf area(SLA)generally decreases with the increase of the gap,and shows an increasing trend along the center area,transition area,and edge area.(5)The maximum net photosynthetic rate of Korean pine in the Populus davidiana and Betula platyphylla forests is highly significantly positively correlated with light transmittance,tree height,diameter at breast height,light saturation point,transpiration rate,and stomatal conductance(P<0.001),and has a significant positive correlation with water use efficiency(P<0.01),and there is a highly significant negative correlation with the light compensation point and the total chlorophyll content(P<0.001).The climax species or the constructive species of the broad-leaved Korean pine forests of temperate zonal climax vegetation in northeast my country have obvious photosynthetic adaption and growth plasticity in the sapling stage,and it has two survival strategies(grow quickly in the gap under strong light conditions;under the canopy to survive under shading and low light conditions).Therefore,the center area of the large gap(200 m2 or gap diameter/surrounding tree height≈1.0)of the secondary Populus davidiana forests and Betula platyphylla forests is the most suitable gap micro-habitat for the growth of young Korean pine trees,therefore,in the practice of restoring broad-leaved Korean pine forests,suitable gaps should be created and gap microhabitats fully utilized to accelerate the restoration process.