黄土丘陵区油松人工林与天然林养分分布和生物循环比较

Nutrient distributions and bio-cycle patterns in both natural and artificial Pinus tabulaeformis forests in Hilly Loess Regions

对黄土丘陵区油松人工林和天然林的养分积累与分配以及养分循环特征进行了比较研究,结果表明:(1)油松林各组分养分含量的变化趋势为:针叶>树枝>树皮>树根>树干;地上部分的养分在针叶、树枝、树干和凋落物中呈:Ca>N>K>Mg>P(林型Ⅰ的针叶、枝干和林型Ⅳ的树枝N含量较其它元素含量高),而在土壤层中呈:Ca>K>Mg>N>P;不同林型内各养分含量因林龄的不同而有差异。(2)油松林生态系统中养分总贮量的80.83%～98.81%集中在土壤组分中,乔木层养分量占总贮量的0.76%～5.52%,林下植被层和凋落物层的养分贮量分别占系统总贮量的0.05%～0.17%和0.38%～3.48%。人工油松林的养分贮量随抚育林龄的增加先升后降,30a时养分贮量最大,50a时养分贮量明显降低,其中N素衰减较其它养分快(30龄油松林是50龄油松林的4.23倍)。(3)油松林地上部分养分贮量主要集中在针叶,且随着抚育林龄的增加,针叶不但贮量增加而且占地上各组分总贮量比例也增大,树枝和树干只是绝对贮量增加,但所占地上总贮量的比例下降。(4)油松林地上部分养分的年积累量以30a人工林最高,变化趋势为Ⅱ>Ⅲ>Ⅳ>Ⅰ。各组分养分的年积累量总的变化趋势为:针叶>树枝>根系>树皮>树干,同一组分各养分年积累量与各组分养分贮量变化顺序基本一致,即10年生幼林为N>Ca>K>P>Mg,人工成熟纯林Ca>N>K>P>M,天然林与人工成熟林相似。(5)天然林的吸收量、存留量明显高于人工林。人工林随着抚育林龄的增加,吸收量和归还量增大,存留量和循环系数先增后降。各林地油松利用系数为:Ca>Mg>N>K>P,但同一养分利用率,油松人工林随着林龄的增加而降低,油松天然林与人工成熟林的利用系数和周转期相似。

ePinus tabulaeformis forests as dominant communities in Ziwuling Mountain lying in Hilly Loess Regions, its nutrient distributions and bio-cycle patterns in both natural and artificial Pinus tabulaeformis forests were studied in this paper. The results were shown as follows： （1） Changes in nutrient contents for different components in the same Pinus tabulaeformis forest stood in the order of needles 〉 branches 〉 bark 〉 roots 〉 bole, and aboveground nutrient elements in needles, branches, bark, bole and litterfalls stood in the order of Ca 〉 N 〉 K 〉 Mg 〉 P （ N contents were higher than other nutrient elements in needles,branches and bole for stand Ⅰ and in branches for stand Ⅳ）, but nutrients stored in the soil stood in the order of Ca 〉 K 〉 Mg 〉 N 〉 P. The accumulative amounts of nutrient differed much among various forest stands because of differences in forest-ages. （2） The artificial forest with 30a had the highest nutrient amounts in Pinus tabulaeformis forest ecosystems, and accumulative nutrients in the arbor layer accounted for 0.76 % - 5.52 % of total amounts, while that in the forest floor and litterfalls layers accounted for 0.05% - 0.17% and 0.38% - 3.48%, respectively. The accumulative amounts of nutrient increased first and then decreased with increased forest-ages in artificial Pinus tabulaeformis forest. The nutrient amounts reached maximum when the stand was 30- year, and decreased greatly when it was 50-year. Particularly, N contents decreased faster than other nutrient elements, and the reduction rate of N contents in the 30a Pinus tabulaeformis forest was 4.23 times as much as that in 50a stand. （3） The aboveground nutrients largely stored in the needles for Pinus tabulaeformis forest, and with increased forest-ages, needles not only increased its nutrient amounts, but also enhanced the proportion of total amounts in aboveground components. However, branches and bole only increased their absolute amounts, while decreased their proportions of total aboveground amounts. （4） The artificial Pinus tabulaeformis forest with 30a had the highest annual accumulative amounts of nutrient elements, and different stands stood in the order of Ⅱ〉Ⅲ〉Ⅳ〉Ⅰ. Comparison of annual accumulative nutrient amounts in different components stood in the order of needles 〉 branches 〉 roots 〉 bark 〉 bole. Changes in annual amounts of various nutrients in the same component was similar to that in various components, that is, N 〉 Ca 〉 K 〉 P 〉 Mg in 10a young forests and Ca 〉 N 〉 K 〉 P 〉 M in artificial matured forests. So there is a parallel between natural forests and artificial matured forests. （5） The amounts of nutrient annually taken in from and annually retained in the natural forests were significantly higher than that in artificial Pinus tabulaeformis forest. With increased forest-ages, the amounts of nutrient annually taken in from and annually released to soil were increased in artificial Pinus tabulaeformis forest, but annually retained amounts increased first and then decreased. The nutrient use coefficient in various Pinus tabulaeformis stands stood in the order of Ca 〉 Mg 〉 N 〉 K 〉 P, but use efficiency of the same nutrient element decreased with increased forest-ages. There was no differences in use coefficient and turning over-perlod of nutrients in both natural and artificial matured Pit, us tabulaeformis forest. The cycling coefficients of nutrient elements increased first and then decreased with increased forest-ages.