4种退耕模式细根(草根)分解及N动态

Fine Root and Grass Root Decomposition and N Dynamics in Four Land Use Types of Converting Farmland to Forest

采用原状土芯法对光皮桦与扁穗牛鞭草复合模式(HN)、光皮桦人工林(H)、扁穗牛鞭草(NC)、柳杉人工林(LS)4种退耕模式细根(草根)分解、影响分解的质量指标及N动态进行研究。结果表明:各模式细根(草根)分解速率符合Olson单指数分解模型,年分解常数(k)分别为1.06,0.93,1.32,0.86,分解1年后干质量损失率分别为65.49%,60.55%,73.32%,57.51%。在1年研究期内,各模式细根(草根)分解过程中的C/N与细根分解速率呈极显著负相关(P≤0.01),与N含量无关,其中光皮桦细根分解速率还与C含量有关。分解90天后,各模式细根(草根)木质素含量与分解速率关系分别为,H,LS呈显著负相关(P≤0.05),HN呈较弱负相关(P=0.087),NC不相关(P=0.279)。分解1年后N初始含量最高的HN具有最高的N释放率,N初始含量最低的LS具最低的N释放速率,4种模式N释放速率大小顺序为HN(70.12%)>H(56.49%)>NC(46.67%)>LS(21.76%),N初始含量高是导致此现象的原因。

Decomposition and its influencing factor as well as N dynamics of fine woody root （ 〈 2 mm diameter） and grass root in four vegetation forms of birch （Betula luminifera ）-grass （ Hemarthria compressa ） compound（HN）, birch （ Betula luminifera ） plantation （H）, grass （Hemarthria compressa） （NC） ,cedar （Cryptomeriafortunei） plantation（LS） which were all founded in the process of converting farmland to forest or grass. This study was conducted in Hongya, China with the intact-core technique. The decomposition rate pattern showed a good fit for the Olsoris single-exponential model and the decomposition constant（k） for the four vegetation models were 1.06,0.93,1.32,0.86 a^-1 respectively, with an annual loss in dry weight of 65.49 %, 60.55 %, 73.32 %, 57.51%. C/N of roots was negative significantly correlated with the root decomposition rate for all models during the one year experiment. C concentration of birch was also negative significantly correlated with fine root decomposition rate （P≤0.01 ）. After 90 days lignin concentration relative to initial lignin content of birch and cedar fine roots was negatively correlated with fine root decomposition rate （P≤0.05）. As for birch-grass compound model its lignin concentration of mixed roots showed a poorly correlation with fine roots decomposition rate （ P = 0.087 ）. The rate of N release was strongly influenced by the initial N concentration of the roots. After one year fine root of HN with the highest initial N concentration released the most N and LS with the lowest initial N concentration released the least N.