Evaluation Of Germplasm Resources Of The Upper Reaches Of Minjiang River Pinus Radiata Plantation And Soil Biological Fertility

Many previous studies have been widely emphasized the introduction and selection of species with high resistibility during vegetation restoration and rebuilding in dry valley. Few attentions have paid to soil bio-fertility,which greatly limited the effects of restoration and rebuilding practice.Therefore,the evaluation of germplasm resource of P.radiata plantation in the upper reach of Minjiang River were studied in combined with soil characters and the urgent needs of ecological constitution,and through the varieties of seedlings resistibility between P.radiata and P.tabulaeformis,the evaluation of the soil bio-fertility and community relationships of Pinus radiata plantations was studied also. The results were expected to provide effective theory for vegetation restoration and rebuilding,low-effect forest modification,and community succession in the upper reach of Mingjiang River and other regions,and provide scientific data for germplasm resource management of introduced P.radiata plantation.Ten plantations with different forest age were selected under the same environmental conditions in Maoxian.Wenchuan and Lixian in the upper reach of Minjiang River,20 m×20 m sampling plots in each plantation were selected for soil microbial and soil enzyme research.21 typical fresh leaf samples were collected to community relationships research by SSR molecular method.2-year-old seedlings of P.radiata and P.tabulaeformis from Aba institute of forestry research were used for drought stress experiment in the greenhouse in Sichuan Agricultural University. The results as follows:(1) The results from SSR molecular method to 21 sampling material indicated that three groups could be formed by the limited genetic similarity coefficient GS0.8041.The 1^st Group included the P.radiata from 17 geomorphic resources,including material 1-6, 10-19 and 21,which introduced from the USA,Australian,Mexico and New Zealand,11 samplings were introduced from New Zealand.The 2^nd Group included the P.radiata from three geomorphic resources,including material 7-9,which introduce from New Zealand. The 3^rd Group included only one P.radiata(material 20) from New Zealand.Groupâ… could be divided into three sub-groups(â… ₁,â… ₂,â… ₃) by the limited genetic similarity coefficient GS0.8247.Groupâ… ₁,groupâ… ₂ and groupâ… ₃ included the samples 1-6,the samples 13-19 and the sample 21,respectively.Samples 1-4 could be looked as the same gene type and sample 15 and 17 could also be looked as the same gene type.The results suggested that SSR molecular method could effectively reveal the relationships among the introduced P.radiata plantations in the upper Minjiang River,which also indicated that P. radiata communities could be beneficial to gene flow and population reproduction due to high genetic diversity.However,the plantations were not called the same name although which with the same gene type,which was not facility to the evaluation,conservation and exploration of P.radiata germplasm resource. (2) Soil water content decreased with the increase of drought stress time in planting both P.radiata and P.tabulaeformis seedlings in the greenhouse experiment,showing more rapid in the early period.After 24d treatment,soil water content was 6.45%,water loss rate was 66.55%,daily loss rate 2.77%in planting P.radiata seedlings.After 48d treatment,the seedling died,soil water content was 4.48%,water loss rate 76.76%,daily loss rate 1.60%.After 24d treatment,soil water content was 4.72%,water loss rate was 79.79%,daily loss rate 3.32%in planting P.tabulaeformis seedlings.After 56d treatment, the seedling died,soil water content was 3.21%,water loss rate 82.26%,daily loss rate 1.47%.The results suggested that the seedlings of P.radiata had lower drought resistibility compared to that in P.tabulaeformis seedlings.The seedling of both species reduced the transpiration rate by increasing the depth of horn,pellicle and hypoderm and decreasing stomata conductance during the whole drought stress period.Needle horn,pellicle,and hypoderm and organize density of P.radiata increased to 16.33%,72.23%,80.16%and 88.02%,while 53.06%,74.91%,and 73.85% for P.tabulaeformis,respectively.The depth of green collapsed organism and stomata conductance of P.radiata needles were decreased to 34.55%and 45.11%,while 39.51 and 32.62%for P.tabulaeformis,respectively.Although both species showed high adaptation by analyzed needle anatomies character,their adaptive types were different,their adaptive degrees of drought were different.(3) The relative water content,water saturation deficient,water conservation ability of seedling needles were different between species.The relative water content of needles was significantly decreased as drought stress proceeded,but water saturation deficient increased.Water conservation ability decreased more rapidly in the early period of drought stress,but increased after 24d for P.radiata seedlings with 94.84%ascend ratio,14.75% for P.tabulaeformis.The results indicated that both species could resist to drought by decreasing relative water content,although water saturation deficient,water conservation ability of seedling needles were higher for P.radiata than that for P.tabulaeformis.(4) Drought stress had significant effects on PMP,MDA,Pro,WSS,Chla,Chlb and Chlab of seedlings.The relative conductance increased with increasing drought stress, 58.43%for P.radiata and 54.14%for P.tabulaeformis after 56d drought treatment.The content of MDA decreased in the early period of drought treatment,and then increased in the later period.The content of Pro,WSS and ABA increased with the increasing drought stress.The results indicated that the mechanism of drought stress of the both species seedlings were similar.(5) Ten plantations with different forest age were selected in the upper reach of Minjiang River,and the soil organic matter content was studied:the maximum number was inâ… andâ…¡sampling plots and the minimum number inâ…¨sampling plots,the soil organic matter content was exhibited obvious seasonal varieties with highest in autumn,then spring and winter,lowest in summer also.The results suggested that the soil organic matter content was increased with the increase of plantation time.(6) Microbe number increased with the increase of plantation time with the maximum number(4.96×10⁶·g^-1) inâ…¡sampling plots and minimum(1.33×10⁶·g^-1) number inâ…§sampling plots,showed the order as:â…¡(1992 plantation,coverage 10%)＞Ⅰ(1992 plantation,coverage 20%)＞Ⅲ(1998 plantation,coverage 70%)＞Ⅶ(2003 plantation, coverage 25%)＞Ⅳ(1998 plantation,coverage 15%)＞Ⅴ(1999 plantation,coverage 15%)＞Ⅸ(2004 plantation,coverage 10%)＞Ⅹ(2005 plantation,coverage 2%)＞Ⅵ(2002 plantation,coverage 30%)＞Ⅷ(2003 plantation,coverage 5%).This suggested that the soil microbe number and bio-fertility were increased with the increase of plantation time. However,some specific plantations especially for new plantation were not similarity with the orderliness which indicated that the factors which affecting ecological characteristics of soil were complex.(7) The ratio of microbial community in the total as the order:bacteria(54.81～75.13%)＞actinomycetes(24.87～46.38%)＞azotobacteria(3.03～5.06%)＞fungus(0.03～0.14%) with maximum in autumn,then in spring and winter,minimum in summer.The seasonal dynamics of soil enzyme activity in the sampling plots were different,and the general tendency was highest in autumn.Invertase and catalase activity were highest inâ… andâ…¡sampling plots,â…©were lowest;urea activity was highest inâ…£plantation,and lowest inâ…§plantation;phosphatase activity was highest inâ… plantation,the lowest inâ…¨plantation.The topper soil was higher in the four plantations than that in lower soil.The results suggested that soil enzyme activity increased with the increase of plantation time, which be beneficial to the improvement of soil quality.Bacteria were correlated positively with actinomycetes(0.818),azotobacteria(0.812), catalase(0.806) and invertase(0.691).Actinomycetes were positively correlated with azotobacteria(0.843),catalase(0.637) and invertase(0.798).Catalase was correlated positively with invertase(0.681).The results suggested the significant positive relationships between microbe number and soil enzymes.(8) PCA statistics in soil organic matter,soil microbe number and soil enzyme indicated that:the first components are soil organic matter,invertase,urea,catalase, bacteria and actinomycetes,which accounted for 44.96%of total information,the characteristics value was 4.047;the second components were bacteria,azotobacteria, fungus and actinomycetes,which accounted for 27.74%of total information,the characteristics value was 2.497;the third components were phosphatase and invetase, which accounted for 17.33%of total information,the characteristics value was 1.560.The accumulated contribution rate of the total of three components was 90.04%,suggesting that the parameters could be indicators in evaluating soil bio-fertility.As the result of it,the order of synthetic evaluation in soil bio-fertility for sampling plots were:â…¡plantation＞ â… plantation＞Ⅲplantation＞Ⅳplantation＞Ⅵplantation＞Ⅶplantation＞Ⅴplantation＞Ⅹplantation＞Ⅸplantation＞Ⅷplantation.The results suggested that introduced P.radiata plantation could be beneficial to the improvement of soil quality in the upper reach of Minjiang River since soil organic matter,microbe number and enzyme increased with the increase of plantation time.