| The response and its mechanism of boreal forest to climate change is a hot topic focused by scientists.Dahurian Larch(Larix gmelinii)is one of the dominant tree species in Eurasian boreal forests with a broad bio-geographic range under divergent habitats,and thus an ideal tree species to study the response of trees to climate change.The climate warming and frequent fire caused by climate change are the two main factors that affect the growth of larch trees.At present,the effects of field warming and fire on the growth of larch and its mechanism are not clear.Climate warming and fire can not only directly affect tree growth by affecting the metabolic rate,but also indirectly affect tree growth by changing the nutrient content of soil,and had spatio-temporal variations in these effects.Photosynthesis and respiration,as the most important metabolic process,are closely related to the trees growth;while the soil microbe,as the participants in the process of soil nutrient transformation and fixation,has an important impact on soil nutrient content.In this study,we constructed a warming experiment by transplanting Dahurian larch(Larix gmelinii)trees from four geographically distant sites(with the increase of latitude,the order is Dailing,Heihe,Songling,Tahe)to a common garden near the warm edge of this species' range in China.Additionally,eight research sites disturbed by fire from 1990 to 2015 in Greater Khingan Mountains were selected.We studied the effects of climate warming and fire on the growth,photosynthesis,respiration and soil microbe of larch tree,in order to explicitly understand the impacts of climate change on trees.The main results were summarized as follows:1.Warming treatment,latitudinal site,measuring time,and their interactions significantly(P<0.05)influenced on the trunk growth of larch trees.The diameter at 10 cm of trunk(D10)and its annual growth increased significantly(P<0.05)under warming treatment for all sites.The response of Dio to warming varied with four sites.The most northern site of Tahe had the largest absolute growth of D10 and the relative growth rate of D10 than other sites.The effect of warming on D10 also was affected by time.The largest absolute growth and the relative growth rate of D10 in the later stage of warming treatment were significantly(P<0.05)higher than those in the earlier stage.2.Warming treatment,latitudinal site,measuring time,and their interactions significantly(P<0.05)influenced on the photosynthetic characteristics and associated factors for larch trees.The maximum net photosynthetic rate(Pmax)increased significantly(P<0.05)under warming treatment for all sites;where,trees at warm sites had the high Pmax and trees at cold sites had the high increase of Pmax.The photosynthetic optimum temperature of trees at Songling and Tahe increased significantly(P<0.05)under warming treatment.Apparent quantum yield(AQY),maximum rate of carboxylation(Vmax),maximum electron transport rate(Jmax),triose phosphate utilization rate(TPU),and mesophyll conductance(gm)all increased significantly(P<0.05)under warming treatment,while the light compensation point(LCP)showed an opposite trend.Pmax was positively correlated with AOY,Vmax,Jmax,TPU and gm,but negatively with LCP(P<0.05).Pmax showed strong acclimation to climate warming.The four sites had the similar short-time acclimation,but different longterm acclimation,which was greater for the trees from the southern sites than the northern sites.The absolute increase of Pmax and relative increase rate of Pmax had significant positive relationships with the absolute growth of D10 and the relative growth rate of D10,respectively.3.The warming significantly decreased the leaf dark respiration(Rd)at 25?(Rd-25)and the temperature sensitivity of Rd(Q10)in trees from all sites,consistent with leaf nitrogen and soluble sugar shifts with warming.The effect of warming treatment on was significantly correlated with the annual mean temperature at the original sites.We also found that the trees near the cold limit of the species range had lower acclimation of Rd and greater response of Q10 to warming than those near the cold limit.These findings suggest that intra-specific differences in the response of Rd to warming can be attributed to variability in leaf nutrient concentration and adaptation of trees to climatic conditions at their sites of origin.4.Warming treatment,latitudinal site,measuring time,and their interactions significantly(P<0.05)influenced on the soil microbial biomass and community.The PLFAs(phospholipid fatty acids)content of total soil microbe and the PLFAs content of each soil microbial group all decreased significantly under warming treatment.Dailing had the highest total soil microbe PLFAs content than other sites in each month,and Tahe had the lowest values accordingly.The total PLFAs content of soil microbe peaked in September and minimized in August across the growing season.The relative abundance of PLFAs of bacteria and arbuscular mycorrhizal fungi increased under warming treatment for all sites(except arbuscular mycorrhizal fungi at Dailing),while relative abundance of PLFAs of fungi and actinomycetes showed an opposite trend.Soil microbe can adapt to the warming environment by changing the amount and composition.The soil microbe showed obvious temporal dynamics during the spring freezing-thawing period.Soil temperature,soil moisture,soil carbon and nitrogen availabilities were the main influence factors affecting soil microbial community during the spring soil freezing-thawing period,but the degree of influence varied with the freezing-thawing stages and microbial groups.5.The intensity of fire,post-fire recovery times and their interaction had significant(P<0.05)effects on soil microbial community.With the increase of fire intensity,the PLFAs content of total soil microbe,the PLFAs content and relative abundance of bacteria,the PLFAs... |
PDF Full Text Request