| The forest tree leaf nutrient resorption is equally important as plants absorbing nutrients from the inorganic environment, it can keep trees have enough nutrition to live. Our country is the largest area in plantation forestry area countries, Eucalyptus is returning farmland to forest in the southwest area in China, mainly introduced tree species, the area has reached2.6million hm2. The forest nutrient cycling in the nutrient cycle reflect the inherent law, is common and close in the process of plant growth and development and is one of the characteristics of plantation ecosystem nutrient cycling. Eucalyptus grandis plantation leaf nutrient resorption characteristics research can provide the basis of the theory of technology to raise the level of artificial management mode of operation and nutrient management, in order to improve the service function and value of giant eucalyptus plantation. To explain characteristics of Eucalyptus grandis leaf nutrient across a range of ages, the place of this experiment is in the town of Yang Chang of Sichuan Danling and set up six sites with same condition but different ages in artificial forest areas. Using the method of " space instead of time "to1—6years the Eucalyptus grandis to discuss the changes of the leaf nutrient and their resorptions across a range of ages. Through the one year field experiment and laboratory experiments from August of2011to July of2012, the results show that:1) Dynamic of Mature leaf nutrient element content and stoichiometric ratio each yearEach element of1—6age leaves in the overall average size of N>K>Mg>P>Ca, each content is:10.23mg/g,7.13mg/g,2.37mg/g,1.03mg/g,0.93mg/g. Except Ca element content is the highest in the age of2, other elements’ green peaks are in the age of3. Each element content of Eucalyptus grandis leaves in average overall trend as follows:N first up then down along with the age change; P first downward trend then rise; K first down then rise, after4age gradually rise; Ca first increased then decreased,3—6age gradual change little trend; Mg at first up and lowered later.The dynamic stoichiometric ratio is such as:the value of C:P first fall then rise trend along with age change, fell again in6years, the minimum is in3age;4,5age increased, the peak of C:P is in5age,6age fell, the C:P value range1—6age is:442.0-542.3. N:P ratio as follows:1—3age is on the decline, in3age is minimum and then increases,4-6years were similar, but showed a trend of decreasing, the ratio of1and2age is relatively high,1to6age leaf N:P value range is:9.7—12.2. The average of C:N and C:N:P increases with age, C:N in scope of year average is:45.9—57.0, C:N:P in the average range for:45.1—55.7.2) Dynamic of litter leaf nutrient element content1—6age Eucalyptus grandis litter leaf total average of each element in the N>K>Mg> Ca>P, respectively is:5.18mg/g,3.52mg/g,1.98mg/g,0.96mg/g,0.50mg/g. The highest average of N element in litter leaf is in the age of1year, the highest average of P, K of Mg element is in the age of3years, the highest average average Ca element in the age of2years The each element in the average of Eucalyptus grandis leaf content developed trend changes with age as follows:N drop again upward trend; P rise first then fall,6age increased, K at first upward then down; the level of3age is highest, the age of4to6is gradually increased; Ca decline, age of land2is higher,3—6is relatively instar increase low and flat; Mg at first increases then lowered later, the age of6upward intensity fluctuation.3) Each element of transfer rateEach element of the changes along with the age has a certain rule, the method using calculating by unit area is litter different with calculating by the unit mass to years average of transfer rates of N, P, K, the change trend is roughly same, but had a greater influence on the average of the Ca Mg transfer rate in one year is mainly embodied on the change trend and the positive and negative value of part.1—6different age Eucalyptus grandis transfer rate of each element (basis in terms of unit mass), the total average size was N>P>K>Mg> Ca, respectively:48.72%,48.52%,43.81%,48.72%,48.52%.1-6age Eucalyptus grandis transfer rate of each element (basis in terms of unit area), total average size is N> P> K>Mg> Ca, respectively:56.38%,56.14%,49.98%,24.94%,9.13%.Transfer rate of each element in the average (based on unit mass) changes with age is as follows:N transfer rate is gradually rising then falling, P transfer rate first curve type slow and lowered later, K transfer rate change is no regularity, the two peaks appeared in the age of2and5age, Ca transfer rate change regularity, negative in age of1,2,4year, Mg transfer first increase then decrease, negative only in age of1and2year.4) suggestion for plantation management application according to the element transfer rate and stoichiometric ratio in each ageEach age N, P, K, Ca, Mg transfer rate can be calculated by unit mass size:4age litter>5age litter>6age litter>3age litter>2age litter>1age litter,5age litter>4age litter>6age litter>3age litter>1age litter>2age litter,2age litter>5age litter>6age litter>3age litter>1age litter>4age litter,5age litter>3age litter>4age litter>6age litter>2age litter>1age litter,5age litter>4age litter>3age litter>6age litter>2age litter>1age litter.the average of living leaf N content in range is:9.70mg/g—10.78mg/g,<20mg/g, annual average growth in leaf P content range is at0.94mg/g—1.19mg/g, the range of N:P ratio every year is9.7—9.7. Overall1—6age N for restrictive elements (N:P<14), the young period is limited by P more apparently, the middle is limited by N apparently, but restricted by N completely in3age, so recommendations for artificial management fertilizer P to1—6age for improving the external environment to make it grow into a period of stability, in the age of3age exert plenty of K fertilizer in the soil in order to offer that, provide a small amount of Mg for6age appropriate element for its stable live, Also can strengthen the Eucalyptus grandis plantation nutrient cycling mechanism, such as litter leaf nutrient return to use, more efficient and low cost, promote the growth of trees and maintain woodland soil fertility. |
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